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Anatomy_Gray. In the clinic Scoliosis is an abnormal lateral curvature of the vertebral column (Fig. 2.27). A true scoliosis involves not only the curvature (rightor left-sided) but also a rotational element of one vertebra upon another. The commonest types of scoliosis are those for which we have little understanding about how or why they occur and are termed idiopathic scoliosis. It is thought that there is some initial axial rotation of the vertebrae, which then alters the locations of the mechanical compressive and distractive forces applied through the vertebral growth plates, leading to changes in speed of bone growth and ultimately changes to spinal curvature. These are never present at birth and tend to occur in either the infantile, juvenile, or adolescent age groups. The vertebral bodies and posterior elements (pedicles and laminae) are normal in these patients.


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Anatomy_Gray. When a scoliosis is present from birth (congenital scoliosis) it is usually associated with other developmental abnormalities. In these patients, there is a strong association with other abnormalities of the chest wall, genitourinary tract, and heart disease. This group of patients needs careful evaluation by many specialists. A rare but important group of scoliosis is that in which the muscle is abnormal. Muscular dystrophy is the commonest example. The abnormal muscle does not retain the normal alignment of the vertebral column, and curvature develops as a result. A muscle biopsy is needed to make the diagnosis. Other disorders that can produce scoliosis include bone tumors, spinal cord tumors, and localized disc protrusions. In the clinic


Anatomy_Gray

Anatomy_Gray. Other disorders that can produce scoliosis include bone tumors, spinal cord tumors, and localized disc protrusions. In the clinic Kyphosis is abnormal curvature of the vertebral column in the thoracic region, producing a “hunchback” deformity. This condition occurs in certain disease states, the most dramatic of which is usually secondary to tuberculosis infection of a thoracic vertebral body, where the kyphosis becomes angulated at the site of the lesion. This produces the gibbus deformity, a deformity that was prevalent before the use of antituberculous medication (Fig. 2.28). In the clinic Lordosis is abnormal curvature of the vertebral column in the lumbar region, producing a swayback deformity. In the clinic


Anatomy_Gray

Anatomy_Gray. In the clinic Lordosis is abnormal curvature of the vertebral column in the lumbar region, producing a swayback deformity. In the clinic There are usually seven cervical vertebrae, although in certain diseases these may be fused. Fusion of cervical vertebrae (Fig. 2.29A) can be associated with other abnormalities, for example Klippel-Feil syndrome, in which there is fusion of vertebrae CI and CII or CV and CVI, and may be associated with a high-riding abnormalities. Variations in the number of thoracic vertebrae also are well described.


Anatomy_Gray

Anatomy_Gray. Variations in the number of thoracic vertebrae also are well described. One of the commonest abnormalities in the lumbar vertebrae is a partial fusion of vertebra LV with the sacrum (sacralization of the lumbar vertebra). Partial separation of vertebra SI from the sacrum (lumbarization of first sacral vertebra) may also occur (Fig. 2.29B). The LV vertebra can usually be identified by the iliolumbar ligament, which is a band of connective tissue that runs from the tip of the transverse process of LV to the iliac crest bilaterally (Fig. 2.29C). A hemivertebra occurs when a vertebra develops only on one side (Fig. 2.29B). In the clinic The vertebrae and cancer


Anatomy_Gray

Anatomy_Gray. A hemivertebra occurs when a vertebra develops only on one side (Fig. 2.29B). In the clinic The vertebrae and cancer The vertebrae are common sites for metastatic disease (secondary spread of cancer cells). When cancer cells grow within the vertebral bodies and the posterior elements, they interrupt normal bone cell turnover, leading to either bone destruction or formation and destroying the mechanical properties of the bone. A minor injury may therefore lead to vertebral collapse (Fig. 2.30A). Cancer cells have a much higher glucose metabolism compared with normal adjacent bone cells. These metastatic cancer cells can therefore be detected by administering radioisotope-labeled glucose to a patient and then tracing where the labeled glucose has been metabolized (Fig. 2.30B). Importantly, vertebrae that contain extensive metastatic disease may extrude fragments of tumor into the vertebral canal, compressing nerves and the spinal cord. In the clinic


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Anatomy_Gray. In the clinic Osteoporosis is a pathophysiologic condition in which bone quality is normal but the quantity of bone is deficient. It is a metabolic bone disorder that commonly occurs in women in their 50s and 60s and in men in their 70s. Many factors influence the development of osteoporosis, including genetic predetermination, level of activity and nutritional status, and, in particular, estrogen levels in women. Typical complications of osteoporosis include “crush” vertebral body fractures, distal fractures of the radius, and hip fractures. With increasing age and poor-quality bone, patients are more susceptible to fracture. Healing tends to be impaired in these elderly patients, who consequently require long hospital stays and prolonged rehabilitation.


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Anatomy_Gray. Patients likely to develop osteoporosis can be identified by dual-photon X-ray absorptiometry (DXA) scanning. Low-dose X-rays are passed through the bone, and by counting the number of photons detected and knowing the dose given, the number of X-rays absorbed by the bone can be calculated. The amount of X-ray absorption can be directly correlated with the bone mass, and this can be used to predict whether a patient is at risk for osteoporotic fractures. In the clinic Back pain is an extremely common disorder. It can be related to mechanical problems or to disc protrusion impinging on a nerve. In cases involving discs, it may be necessary to operate and remove the disc that is pressing on the nerve.


Anatomy_Gray

Anatomy_Gray. Not infrequently, patients complain of pain and no immediate cause is found; the pain is therefore attributed to mechanical discomfort, which may be caused by degenerative disease. One of the treatments is to pass a needle into the facet joint and inject it with local anesthetic and corticosteroid. In the clinic Herniation of intervertebral discs


Anatomy_Gray

Anatomy_Gray. In the clinic Herniation of intervertebral discs The discs between the vertebrae are made up of a central portion (the nucleus pulposus) and a complex series of fibrous rings (anulus fibrosus). A tear can occur within the anulus fibrosus through which the material of the nucleus pulposus can track. After a period of time, this material may track into the vertebral canal or into the intervertebral foramen to impinge on neural structures (Fig. 2.34). This is a common cause of back pain. A disc may protrude posteriorly to directly impinge on the cord or the roots of the lumbar nerves, depending on the level, or may protrude posterolaterally adjacent to the pedicle and impinge on the descending root. In cervical regions of the vertebral column, cervical disc protrusions often become ossified and are termed disc osteophyte bars. In the clinic


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Anatomy_Gray. In cervical regions of the vertebral column, cervical disc protrusions often become ossified and are termed disc osteophyte bars. In the clinic Some diseases have a predilection for synovial joints rather than symphyses. A typical example is rheumatoid arthritis, which primarily affects synovial joints and synovial bursae, resulting in destruction of the joint and its lining. Symphyses are usually preserved. In the clinic The ligamenta flava are important structures associated with the vertebral canal (Fig. 2.39). In degenerative conditions of the vertebral column, the ligamenta flava may hypertrophy. This is often associated with hypertrophy and arthritic change of the zygapophysial joints. In combination, zygapophysial joint hypertrophy, ligamenta flava hypertrophy, and a mild disc protrusion can reduce the dimensions of the vertebral canal, producing the syndrome of spinal stenosis. In the clinic


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Anatomy_Gray. In the clinic Vertebral fractures can occur anywhere along the vertebral column. In most instances, the fracture will heal under appropriate circumstances. At the time of injury, it is not the fracture itself but related damage to the contents of the vertebral canal and the surrounding tissues that determines the severity of the patient’s condition. Vertebral column stability is divided into three arbitrary clinical “columns”: the anterior column consists of the vertebral bodies and the anterior longitudinal ligament; the middle column comprises the vertebral body and the posterior longitudinal ligament; and the posterior column is made up of the ligamenta flava, interspinous ligaments, supraspinous ligaments, and the ligamentum nuchae in the cervical vertebral column.


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Anatomy_Gray. Destruction of one of the clinical columns is usually a stable injury requiring little more than rest and appropriate analgesia. Disruption of two columns is highly likely to be unstable and requires fixation and immobilization. A three-column spinal injury usually results in a significant neurological event and requires fixation to prevent further extension of the neurological defect and to create vertebral column stability. At the craniocervical junction, a complex series of ligaments create stability. If the traumatic incident disrupts craniocervical stability, the chances of a significant spinal cord injury are extremely high. The consequences are quadriplegia. In addition, respiratory function may be compromised by paralysis of the phrenic nerve (which arises from spinal nerves C3 to C5), and severe hypotension (low blood pressure) may result from central disruption of the sympathetic part of the autonomic division of the nervous system.


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Anatomy_Gray. Mid and lower cervical vertebral column disruption may produce a range of complex neurological problems involving the upper and lower limbs, although below the level of C5, respiratory function is unlikely to be compromised. Lumbar vertebral column injuries are rare. When they occur, they usually involve significant force. Knowing that a significant force is required to fracture a vertebra, one must assess the abdominal organs and the rest of the axial skeleton for further fractures and visceral rupture. Vertebral injuries may also involve the soft tissues and supporting structures between the vertebrae. Typical examples of this are the unifacetal and bifacetal cervical vertebral dislocations that occur in hyperflexion injuries. The pars interarticularis is a clinical term to describe the specific region of a vertebra between the superior and inferior facet (zygapophysial) joints (Fig. 2.40A). This region is susceptible to trauma, especially in athletes.


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Anatomy_Gray. If a fracture occurs around the pars interarticularis, the vertebral body may slip anteriorly and compress the vertebral canal. The most common sites for pars interarticularis fractures are the LIV and LV levels (Fig. 2.40B,C). (Clinicians often refer to parts of the back in shorthand terms that are not strictly anatomical; for example, facet joints and apophyseal joints are terms used instead of zygapophysial joints, and spinal column is used instead of vertebral column.) It is possible for a vertebra to slip anteriorly upon its inferior counterpart without a pars interarticularis fracture. Usually this is related to abnormal anatomy of the facet joints, facet joint degenerative change. This disorder is termed spondylolisthesis. In the clinic Surgical procedures on the back


Anatomy_Gray

Anatomy_Gray. In the clinic Surgical procedures on the back A prolapsed intervertebral disc may impinge upon the meningeal (thecal) sac, cord, and most commonly the nerve root, producing symptoms attributable to that level. In some instances the disc protrusion will undergo a degree of involution that may allow symptoms to resolve without intervention. In some instances pain, loss of function, and failure to resolve may require surgery to remove the disc protrusion.


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Anatomy_Gray. It is of the utmost importance that the level of the disc protrusion is identified before surgery. This may require MRI scanning and on-table fluoroscopy to prevent operating on the wrong level. A midline approach to the right or to the left of the spinous processes will depend upon the most prominent site of the disc bulge. In some instances removal of the lamina will increase the potential space and may relieve symptoms. Some surgeons perform a small fenestration (windowing) within the ligamentum flavum. This provides access to the canal. The meningeal sac and its contents are gently retracted, exposing the nerve root and the offending disc. The disc is dissected free, removing its effect on the nerve root and the canal.


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Anatomy_Gray. Spinal fusion is performed when it is necessary to fuse one vertebra with the corresponding superior or inferior vertebra, and in some instances multilevel fusion may be necessary. Indications are varied, though they include stabilization after fracture, stabilization related to tumor infiltration, and stabilization when mechanical pain is produced either from the disc or from the posterior elements. There are a number of surgical methods in which a fusion can be performed, through either a posterior approach and fusing the posterior elements, an anterior approach by removal of the disc and either disc replacement or anterior fusion, or in some instances a 360° fusion where the posterior elements and the vertebral bodies are fused (Fig. 2.41A,B). In the clinic


Anatomy_Gray

Anatomy_Gray. In the clinic Weakness in the trapezius, caused by an interruption of the accessory nerve [XI], may appear as drooping of the shoulder, inability to raise the arm above the head because of impaired rotation of the scapula, or weakness in attempting to raise the shoulder (i.e., shrug the shoulder against resistance). A weakness in, or an inability to use, the latissimus dorsi, resulting from an injury to the thoracodorsal nerve, diminishes the capacity to pull the body upward while climbing or doing a pull-up. An injury to the dorsal scapular nerve, which innervates the rhomboids, may result in a lateral shift in the position of the scapula on the affected side (i.e., the normal position of the scapula is lost because of the affected muscle’s inability to prevent antagonistic muscles from pulling the scapula laterally). In the clinic


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Anatomy_Gray. In the clinic The intervertebral discs are poorly vascularized; however, infection within the bloodstream can spread to the discs from the terminal branches of the spinal arteries within the vertebral body endplates, which lie immediately adjacent to the discs (Fig. 2.57). Common sources of infection include the lungs and urinary tract. In the clinic Fractures of the atlas and axis


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Anatomy_Gray. In the clinic Fractures of the atlas and axis Fractures of vertebra CI (the atlas) and vertebra CII (the axis) can potentially lead to the worst types of spinal cord injury including death and paralysis due to injury of the brainstem, which contains the cardiac and respiratory centers. The atlas is a closed ring with no vertebral body. Axial-loading injuries, such as hitting the head while diving into shallow water or hitting the head on the roof of a car in a motor vehicle accident, can cause a “burst” type of fracture, where the ring breaks at more than one site (Fig. 2.58). The British neurosurgeon, Geoffrey Jefferson, first described this fracture pattern in 1920, so these types of fractures are often called Jefferson fractures.


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Anatomy_Gray. Fractures of the axis usually occur due to severe hyperextension and flexion, which can result in fracture of the tip of the dens, base of the dens, or through the body of the atlas. In judicial hangings, there is hyperextension and distraction injury causing fracture through the atlas pedicles and spondylolisthesis of C2 on C3. This type of fracture is often called a hangman’s fracture. In many cases of upper neck injuries, even in the absence of fractures to the atlas or axis, there may be injury to the atlanto-axial ligaments, which can render the neck unstable and pose severe risk to the brainstem and upper spinal cord. In the clinic


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Anatomy_Gray. In the clinic An injury to the spinal cord in the cervical portion of the vertebral column can lead to varying degrees of impairment of sensory and motor function (paralysis) in all 4 limbs, termed quadriplegia or tetraplegia. An injury in upper levels of the cervical vertebral column can result in death because of loss of innervation to the diaphragm. An injury to the spinal cord below the level of TI can lead to varying degrees of impairment in motor and sensory function (paralysis) in the lower limbs, termed paraplegia. In the clinic A lumbar tap (puncture) is carried out to obtain a sample of CSF for examination. In addition, passage of a needle or conduit into the subarachnoid space (CSF space) is used to inject antibiotics, chemotherapeutic agents, and anesthetics.


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Anatomy_Gray. The lumbar region is an ideal site to access the subarachnoid space because the spinal cord terminates around the level of the disc between vertebrae LI and LII in the adult. The subarachnoid space extends to the region of the lower border of the SII vertebra. There is therefore a large CSF-filled space containing lumbar and sacral nerve roots but no spinal cord. Depending on the clinician’s preference, the patient is placed in the lateral or prone position. A needle is passed in the midline in between the spinous processes into the extradural space. Further advancement punctures the dura and arachnoid mater to enter the subarachnoid space. Most needles push the roots away from the tip without causing the patient any symptoms. Once the needle is in the subarachnoid space, fluid can be aspirated. In some situations, it is important to measure CSF pressure.


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Anatomy_Gray. Local anesthetics can be injected into the extradural space or the subarachnoid space to anesthetize the sacral and lumbar nerve roots. Such anesthesia is useful for operations on the pelvis and the legs, which can then be carried out without the need for general anesthesia. When procedures are carried out, the patient must be in the erect position and not lying on his or her side or in the head-down position. If a patient lies on his or her side, the anesthesia is likely to be unilateral. If the patient is placed in the head-down position, the anesthetic can pass cranially and potentially depress respiration.


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Anatomy_Gray. In some instances, anesthesiologists choose to carry out extradural anesthesia. A needle is placed through the skin, supraspinous ligament, interspinous ligament, and ligamenta flava into the areolar tissue and fat around the dura mater. Anesthetic agent is introduced and diffuses around the vertebral canal to anesthetize the exiting nerve roots and diffuse into the subarachnoid space. In the clinic Herpes zoster is the virus that produces chickenpox in children. In some patients the virus remains dormant in the cells of the spinal ganglia. Under certain circumstances, the virus becomes activated and travels along the neuronal bundles to the areas supplied by that nerve (the dermatome). A rash ensues, which is characteristically exquisitely painful. Importantly, this typical dermatomal distribution is characteristic of this disorder. In the clinic


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Anatomy_Gray. In the clinic Back pain is an extremely common condition affecting almost all individuals at some stage during their life. It is of key clinical importance to identify whether the back pain relates to the vertebral column and its attachments or relates to other structures.


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Anatomy_Gray. The failure to consider other potential structures that may produce back pain can lead to significant mortality and morbidity. Pain may refer to the back from a number of organs situated in the retroperitoneum. Pancreatic pain in particular refers to the back and may be associated with pancreatic cancer and pancreatitis. Renal pain, which may be produced by stones in the renal collecting system or renal tumors, also typically refers to the back. More often than not this is usually unilateral; however, it can produce central posterior back pain. Enlarged lymph nodes in the preand para-aortic region may produce central posterior back pain and may be a sign of solid tumor malignancy, infection, or Hodgkin’s lymphoma. An enlarging abdominal aorta (abdominal aortic aneurysm) may cause back pain as it enlarges without rupture. Therefore it is critical to think of this structure as a potential cause of back pain, because treatment will be lifesaving. Moreover, a ruptured abdominal aortic


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Anatomy_Gray. pain as it enlarges without rupture. Therefore it is critical to think of this structure as a potential cause of back pain, because treatment will be lifesaving. Moreover, a ruptured abdominal aortic aneurysm may also cause acute back pain in the first instance.


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Anatomy_Gray. In all patients back pain requires careful assessment not only of the vertebral column but also of the chest and abdomen in order not to miss other important anatomical structures that may produce signs and symptoms radiating to the back. A 50-year-old man was brought to the emergency department with severe lower back pain that had started several days ago. In the past 24 hours he has had two episodes of fecal incontinence and inability to pass urine and now reports numbness and weakness in both his legs. The attending physician performed a physical examination and found that the man had reduced strength during knee extension and when dorsiflexing his feet and toes. He also had reduced reflexes in his knees and ankles, numbness in the perineal (saddle) region, as well as reduced anal sphincter tone.


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Anatomy_Gray. The patient’s symptoms and physical examination findings raised serious concern for compression of multiple lumbar and sacral nerve roots in the spine, affecting both motor and sensory pathways. His reduced power in extending his knees and reduced knee reflexes was suggestive of compression of the L4 nerve roots. His reduced ability to dorsiflex his feet and toes was suggestive of compression of the L5 nerve roots. His reduced ankle reflexes was suggestive of compression of the S1 and S2 nerve roots, and his perineal numbness was suggestive of compression of the S3, S4, and S5 nerve roots. A diagnosis of cauda equina syndrome was made, and the patient was transferred for an urgent MRI scan, which confirmed the presence of a severely herniating L2-3 disc compressing the cauda equina, giving rise to the cauda equina syndrome (Fig. 2.70). The patient underwent surgical decompression of the cauda equina and made a full recovery.


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Anatomy_Gray. The collection of lumbar and sacral nerve roots beyond the conus medullaris has a horsetail-like appearance, from which it derives its name “cauda equina.” Compression of the cauda equina may be caused by a herniating disc (as in this case), fracture fragments following traumatic injury, tumor, abscess, or severe degenerative stenosis of the central canal. Cauda equina syndrome is classed as a surgical emergency to prevent permanent and irreversible damage to the compressed nerve roots. A 45-year-old man was involved in a serious car accident. On examination he had a severe injury to the cervical region of his vertebral column with damage to the spinal cord. In fact, his breathing became erratic and stopped.


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Anatomy_Gray. If the cervical spinal cord injury is above the level of C5, breathing is likely to stop. The phrenic nerve takes origin from C3, C4, and C5 and supplies the diaphragm. Breathing may not cease immediately if the lesion is just below C5, but does so as the cord becomes edematous and damage progresses superiorly. In addition, some respiratory and ventilatory exchange may occur by using neck muscles plus the sternocleidomastoid and trapezius muscles, which are innervated by the accessory nerve [XI]. The patient was unable to sense or move his upper and lower limbs. The patient has paralysis of the upper and lower limbs and is therefore quadriplegic. If breathing is unaffected, the lesion is below the level of C5 or at the level of C5. The nerve supply to the upper limbs is via the brachial plexus, which begins at the C5 level. The site of the spinal cord injury is at or above the C5 level.


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Anatomy_Gray. It is important to remember that although the cord has been transected in the cervical region, the cord below this level is intact. Reflex activity may therefore occur below the injury, but communication with the brain is lost. A 25-year-old woman complained of increasing lumbar back pain. Over the ensuing weeks she was noted to have an enlarging lump in the right groin, which was mildly tender to touch. On direct questioning, the patient also complained of a productive cough with sputum containing mucus and blood, and she had a mild temperature. The chest radiograph revealed a cavitating apical lung mass, which explains the pulmonary history.


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Anatomy_Gray. The chest radiograph revealed a cavitating apical lung mass, which explains the pulmonary history. Given the age of the patient a primary lung cancer is unlikely. The hemoptysis (coughing up blood in the sputum) and the rest of the history suggest the patient has a lung infection. Given the chest radiographic findings of a cavity in the apex of the lung, a diagnosis of tuberculosis (TB) was made. This was confirmed by bronchoscopy and aspiration of pus, which was cultured.


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Anatomy_Gray. During the patient’s pulmonary infection, the tuberculous bacillus had spread via the blood to vertebra LI. The bone destruction began in the cancellous bone of the vertebral body close to the intervertebral discs. This disease progressed and eroded into the intervertebral disc, which became infected. The disc was destroyed, and the infected disc material extruded around the disc anteriorly and passed into the psoas muscle sheath. This is not an uncommon finding for a tuberculous infection of the lumbar portion of the vertebral column. As the infection progressed, the pus spread within the psoas muscle sheath beneath the inguinal ligament to produce a hard mass in the groin. This is a typical finding for a psoas abscess. Fortunately for the patient, there was no evidence of any damage within the vertebral canal.


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Anatomy_Gray. Fortunately for the patient, there was no evidence of any damage within the vertebral canal. The patient underwent a radiologically guided drainage of the psoas abscess and was treated for over 6 months with a long-term antibiotic regimen. She made an excellent recovery with no further symptoms, although the cavities within the lungs remain. It healed with sclerosis. A 72-year-old fit and healthy man was brought to the emergency department with severe back pain beginning at the level of the shoulder blades and extending to the midlumbar region. The pain was of relatively acute onset and was continuous. The patient was able to walk to the gurney as he entered the ambulance; however, at the emergency department the patient complained of inability to use both legs.


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Anatomy_Gray. The attending physician examined the back thoroughly and found no significant abnormality. He noted that there was reduced sensation in both legs, and there was virtually no power in extensor or flexor groups. The patient was tachycardic, which was believed to be due to pain, and the blood pressure obtained in the ambulance measured 120/80 mm Hg. It was noted that the patient’s current blood pressure was 80/40 mm Hg; however, the patient did not complain of typical clinical symptoms of hypotension. On first inspection, it is difficult to “add up” these clinical symptoms and signs. In essence we have a progressive paraplegia associated with severe back pain and an anomaly in blood pressure measurements, which are not compatible with the clinical state of the patient. It was deduced that the blood pressure measurements were obtained in different arms, and both were reassessed.


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Anatomy_Gray. It was deduced that the blood pressure measurements were obtained in different arms, and both were reassessed. The blood pressure measurements were true. In the right arm the blood pressure measured 120/80 mm Hg and in the left arm the blood pressure measured 80/40 mm Hg. This would imply a deficiency of blood to the left arm. The patient was transferred from the emergency department to the CT scanner, and a scan was performed that included the chest, abdomen, and pelvis.


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Anatomy_Gray. The CT scan demonstrated a dissecting thoracic aortic aneurysm. Aortic dissection occurs when the tunica intima and part of the tunica media of the wall of the aorta become separated from the remainder of the tunica media and the tunica adventitia of the aorta wall. This produces a false lumen. Blood passes not only in the true aortic lumen but also through a small hole into the wall of the aorta and into the false lumen. It often reenters the true aortic lumen inferiorly. This produces two channels through which blood may flow. The process of the aortic dissection produces considerable pain for the patient and is usually of rapid onset. Typically the pain is felt between the shoulder blades and radiating into the back, and although the pain is not from the back musculature or the vertebral column, careful consideration of structures other than the back should always be sought.


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Anatomy_Gray. The difference in the blood pressure between the two arms indicates the level at which the dissection has begun. The “point of entry” is proximal to the left subclavian artery. At this level a small flap has been created, which limits the blood flow to the left upper limb, giving the low blood pressure recording. The brachiocephalic trunk has not been affected by the aortic dissection, and hence blood flow remains appropriate to the right upper limb. The paraplegia was caused by ischemia to the spinal cord.


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Anatomy_Gray. The paraplegia was caused by ischemia to the spinal cord. The blood supply to the spinal cord is from a single anterior spinal artery and two posterior spinal arteries. These arteries are fed via segmental spinal arteries at every vertebral level. There are a number of reinforcing arteries (segmental medullary arteries) along the length of the spinal cord—the largest of which is the artery of Adamkiewicz. This artery of Adamkiewicz, a segmental medullary artery, typically arises from the lower thoracic or upper lumbar region, and unfortunately during this patient’s aortic dissection, the origin of this vessel was disrupted. This produces acute spinal cord ischemia and has produced the paraplegia in the patient. Unfortunately, the dissection extended, the aorta ruptured, and the patient succumbed.


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Anatomy_Gray. Unfortunately, the dissection extended, the aorta ruptured, and the patient succumbed. A 55-year-old woman came to her physician with sensory alteration in the right gluteal (buttock) region and in the intergluteal (natal) cleft. Examination also demonstrated low-grade weakness of the muscles of the foot and subtle weakness of the extensor hallucis longus, extensor digitorum longus, and fibularis tertius on the right. The patient also complained of some mild pain symptoms posteriorly in the right gluteal region. A lesion was postulated in the left sacrum.


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Anatomy_Gray. A lesion was postulated in the left sacrum. Pain in the right sacro-iliac region could easily be attributed to the sacro-iliac joint, which is often very sensitive to pain. The weakness of the intrinsic muscles of the foot and the extensor hallucis longus, extensor digitorum longus, and fibularis tertius muscles raises the possibility of an abnormality affecting the nerves exiting the sacrum and possibly the lumbosacral junction. The altered sensation around the gluteal region toward the anus would also support these anatomical localizing features. An X-ray was obtained of the pelvis.


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Anatomy_Gray. An X-ray was obtained of the pelvis. The X-ray appeared on first inspection unremarkable. However, the patient underwent further investigation, including CT and MRI, which demonstrated a large destructive lesion involving the whole of the left sacrum extending into the anterior sacral foramina at the S1, S2, and S3 levels. Interestingly, plain radiographs of the sacrum may often appear normal on first inspection, and further imaging should always be sought in patients with a suspected sacral abnormality. The lesion was expansile and lytic. Most bony metastases are typically nonexpansile. They may well erode the bone, producing lytic type of lesions, or may become very sclerotic (prostate metastases and breast metastases). From time to time we see a mixed pattern of lytic and sclerotic.


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Anatomy_Gray. There are a number of uncommon instances in which certain metastases are expansile and lytic. These typically occur in renal metastases and may be seen in multiple myeloma. The anatomical importance of these specific tumors is that they often expand and impinge upon other structures. The expansile nature of this patient’s tumor within the sacrum was the cause for compression of the sacral nerve roots, producing her symptoms. The patient underwent a course of radiotherapy, had the renal tumor excised, and is currently undergoing a course of chemoimmunotherapy. 122.e1 122.e2 Conceptual Overview • Relationship to Other Regions Fig. 2.20, cont’d Fig. 2.20, cont’d In the clinic—cont’d Fig. 2.55, cont’d Fig. 2.68, cont’d Fig. 2.69, cont’d


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Anatomy_Gray. 122.e1 122.e2 Conceptual Overview • Relationship to Other Regions Fig. 2.20, cont’d Fig. 2.20, cont’d In the clinic—cont’d Fig. 2.55, cont’d Fig. 2.68, cont’d Fig. 2.69, cont’d The thorax is an irregularly shaped cylinder with a narrow opening (superior thoracic aperture) superiorly and a relatively large opening (inferior thoracic aperture) inferiorly (Fig. 3.1). The superior thoracic aperture is open, allowing continuity with the neck; the inferior thoracic aperture is closed by the diaphragm. The musculoskeletal wall of the thorax is flexible and consists of segmentally arranged vertebrae, ribs, and muscles and the sternum. The thoracic cavity enclosed by the thoracic wall and the diaphragm is subdivided into three major compartments: a left and a right pleural cavity, each surrounding a lung, and the mediastinum.


Anatomy_Gray

Anatomy_Gray. The thoracic cavity enclosed by the thoracic wall and the diaphragm is subdivided into three major compartments: a left and a right pleural cavity, each surrounding a lung, and the mediastinum. The mediastinum is a thick, flexible soft tissue partition oriented longitudinally in a median sagittal position. It contains the heart, esophagus, trachea, major nerves, and major systemic blood vessels. The pleural cavities are completely separated from each other by the mediastinum. Therefore abnormal events in one pleural cavity do not necessarily affect the other cavity. This also means that the mediastinum can be entered surgically without opening the pleural cavities.


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Anatomy_Gray. Another important feature of the pleural cavities is that they extend above the level of rib I. The apex of each lung actually extends into the root of the neck. As a consequence, abnormal events in the root of the neck can involve the adjacent pleura and lung, and events in the adjacent pleura and lung can involve the root of the neck. One of the most important functions of the thorax is breathing. The thorax not only contains the lungs but also provides the machinery necessary—the diaphragm, thoracic wall, and ribs—for effectively moving air into and out of the lungs. Up and down movements of the diaphragm and changes in the lateral and anterior dimensions of the thoracic wall, caused by movements of the ribs, alter the volume of the thoracic cavity and are key elements in breathing. Protection of vital organs


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Anatomy_Gray. Protection of vital organs The thorax houses and protects the heart, lungs, and great vessels. Because of the upward domed shape of the diaphragm, the thoracic wall also offers protection to some important abdominal viscera. Much of the liver lies under the right dome of the diaphragm, and the stomach and spleen lie under the left. The posterior aspects of the superior poles of the kidneys lie on the diaphragm and are anterior to rib XII, on the right, and to ribs XI and XII, on the left. The mediastinum acts as a conduit for structures that pass completely through the thorax from one body region to another and for structures that connect organs in the thorax to other body regions. The esophagus, vagus nerves, and thoracic duct pass through the mediastinum as they course between the abdomen and neck. The phrenic nerves, which originate in the neck, also pass through the mediastinum to penetrate and supply the diaphragm.


Anatomy_Gray

Anatomy_Gray. The phrenic nerves, which originate in the neck, also pass through the mediastinum to penetrate and supply the diaphragm. Other structures such as the trachea, thoracic aorta, and superior vena cava course within the mediastinum en route to and from major visceral organs in the thorax. The thoracic wall consists of skeletal elements and muscles (Fig. 3.1): Posteriorly, it is made up of twelve thoracic vertebrae and their intervening intervertebral discs; Laterally, the wall is formed by ribs (twelve on each side) and three layers of flat muscles, which span the intercostal spaces between adjacent ribs, move the ribs, and provide support for the intercostal spaces; Anteriorly, the wall is made up of the sternum, which consists of the manubrium of sternum, body of sternum, and xiphoid process.


Anatomy_Gray

Anatomy_Gray. Anteriorly, the wall is made up of the sternum, which consists of the manubrium of sternum, body of sternum, and xiphoid process. The manubrium of sternum, angled posteriorly on the body of sternum at the manubriosternal joint, forms the sternal angle, which is a major surface landmark used by clinicians in performing physical examinations of the thorax. The anterior (distal) end of each rib is composed of costal cartilage, which contributes to the mobility and elasticity of the wall. All ribs articulate with thoracic vertebrae posteriorly. Most ribs (from rib II to IX) have three articulations with the vertebral column. The head of each rib articulates with the body of its own vertebra and with the body of the vertebra above (Fig. 3.2). As these ribs curve posteriorly, each also articulates with the transverse process of its vertebra. Anteriorly, the costal cartilages of ribs I to VII articulate with the sternum.


Anatomy_Gray

Anatomy_Gray. Anteriorly, the costal cartilages of ribs I to VII articulate with the sternum. The costal cartilages of ribs VIII to X articulate with the inferior margins of the costal cartilages above them. Ribs XI and XII are called floating ribs because they do not articulate with other ribs, costal cartilages, or the sternum. Their costal cartilages are small, only covering their tips. The skeletal framework of the thoracic wall provides extensive attachment sites for muscles of the neck, abdomen, back, and upper limbs. A number of these muscles attach to ribs and function as accessory respiratory muscles; some of them also stabilize the position of the first and last ribs. Completely surrounded by skeletal elements, the superior thoracic aperture consists of the body of vertebra TI posteriorly, the medial margin of rib I on each side, and the manubrium anteriorly.


Anatomy_Gray

Anatomy_Gray. Completely surrounded by skeletal elements, the superior thoracic aperture consists of the body of vertebra TI posteriorly, the medial margin of rib I on each side, and the manubrium anteriorly. The superior margin of the manubrium is in approximately the same horizontal plane as the intervertebral disc between vertebrae TII and TIII. The first ribs slope inferiorly from their posterior articulation with vertebra TI to their anterior attachment to the manubrium. Consequently, the plane of the superior thoracic aperture is at an oblique angle, facing somewhat anteriorly. At the superior thoracic aperture, the superior aspects of the pleural cavities, which surround the lungs, lie on either side of the entrance to the mediastinum (Fig. 3.3).


Anatomy_Gray

Anatomy_Gray. At the superior thoracic aperture, the superior aspects of the pleural cavities, which surround the lungs, lie on either side of the entrance to the mediastinum (Fig. 3.3). Structures that pass between the upper limb and thorax pass over rib I and the superior part of the pleural cavity as they enter and leave the mediastinum. Structures that pass between the neck and head and the thorax pass more vertically through the superior thoracic aperture. The inferior thoracic aperture is large and expandable. Bone, cartilage, and ligaments form its margin (Fig. 3.4A). The inferior thoracic aperture is closed by the diaphragm, and structures passing between the abdomen and thorax pierce or pass posteriorly to the diaphragm.


Anatomy_Gray

Anatomy_Gray. The inferior thoracic aperture is closed by the diaphragm, and structures passing between the abdomen and thorax pierce or pass posteriorly to the diaphragm. Skeletal elements of the inferior thoracic aperture are: the body of vertebra TXII posteriorly, rib XII and the distal end of rib XI posterolaterally, the distal cartilaginous ends of ribs VII to X, which unite to form the costal margin anterolaterally, and the xiphoid process anteriorly. The joint between the costal margin and sternum lies roughly in the same horizontal plane as the intervertebral disc between vertebrae TIX and TX. In other words, the posterior margin of the inferior thoracic aperture is inferior to the anterior margin. When viewed anteriorly, the inferior thoracic aperture is tilted superiorly. The musculotendinous diaphragm seals the inferior thoracic aperture (Fig. 3.4B).


Anatomy_Gray

Anatomy_Gray. When viewed anteriorly, the inferior thoracic aperture is tilted superiorly. The musculotendinous diaphragm seals the inferior thoracic aperture (Fig. 3.4B). Generally, muscle fibers of the diaphragm arise radially, from the margins of the inferior thoracic aperture, and converge into a large central tendon. Because of the oblique angle of the inferior thoracic aperture, the posterior attachment of the diaphragm is inferior to the anterior attachment. The diaphragm is not flat; rather, it “balloons” superiorly, on both the right and left sides, to form domes. The right dome is higher than the left, reaching as far as rib V. As the diaphragm contracts, the height of the domes decreases and the volume of the thorax increases. The esophagus and inferior vena cava penetrate the diaphragm; the aorta passes posterior to the diaphragm.


Anatomy_Gray

Anatomy_Gray. The esophagus and inferior vena cava penetrate the diaphragm; the aorta passes posterior to the diaphragm. The mediastinum is a thick midline partition that extends from the sternum anteriorly to the thoracic vertebrae posteriorly, and from the superior thoracic aperture to the inferior thoracic aperture. A horizontal plane passing through the sternal angle and the intervertebral disc between vertebrae TIV and TV separates the mediastinum into superior and inferior parts (Fig. 3.5). The inferior part is further subdivided by the pericardium, which encloses the pericardial cavity surrounding the heart. The pericardium and heart constitute the middle mediastinum. The anterior mediastinum lies between the sternum and the pericardium; the posterior mediastinum lies between the pericardium and thoracic vertebrae. The two pleural cavities are situated on either side of the mediastinum (Fig. 3.6). Each pleural cavity is completely lined by a mesothelial membrane called the pleura.


Anatomy_Gray

Anatomy_Gray. The two pleural cavities are situated on either side of the mediastinum (Fig. 3.6). Each pleural cavity is completely lined by a mesothelial membrane called the pleura. During development, the lungs grow out of the mediastinum, becoming surrounded by the pleural cavities. As a result, the outer surface of each organ is covered by pleura. Each lung remains attached to the mediastinum by a root formed by the airway, pulmonary blood vessels, lymphatic tissues, and nerves. The pleura lining the walls of the cavity is the parietal pleura, whereas that reflected from the mediastinum at the roots and onto the surfaces of the lungs is the visceral pleura. Only a potential space normally exists between the visceral pleura covering lung and the parietal pleura lining the wall of the thoracic cavity.


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Anatomy_Gray. The lung does not completely fill the potential space of the pleural cavity, resulting in recesses, which do not contain lung and are important for accommodating changes in lung volume during breathing. The costodiaphragmatic recess, which is the largest and clinically most important recess, lies inferiorly between the thoracic wall and diaphragm. The superior thoracic aperture opens directly into the root of the neck (Fig. 3.7). The superior aspect of each pleural cavity extends approximately 2 to 3 cm above rib I and the costal cartilage into the neck. Between these pleural extensions, major visceral structures pass between the neck and superior mediastinum. In the midline, the trachea lies immediately anterior to the esophagus. Major blood vessels and nerves pass in and out of the thorax at the superior thoracic aperture anteriorly and laterally to these structures.


Anatomy_Gray

Anatomy_Gray. An axillary inlet, or gateway to the upper limb, lies on each side of the superior thoracic aperture. These two axillary inlets and the superior thoracic aperture communicate superiorly with the root of the neck (Fig. 3.7). Each axillary inlet is formed by: the superior margin of the scapula posteriorly, the clavicle anteriorly, and the lateral margin of rib I medially. The apex of each triangular inlet is directed laterally and is formed by the medial margin of the coracoid process, which extends anteriorly from the superior margin of the scapula. The base of the axillary inlet’s triangular opening is the lateral margin of rib I. Large blood vessels passing between the axillary inlet and superior thoracic aperture do so by passing over rib I. Proximal parts of the brachial plexus also pass between the neck and upper limb by passing through the axillary inlet.


Anatomy_Gray

Anatomy_Gray. Proximal parts of the brachial plexus also pass between the neck and upper limb by passing through the axillary inlet. The diaphragm separates the thorax from the abdomen. Structures that pass between the thorax and abdomen either penetrate the diaphragm or pass posteriorly to it (Fig. 3.8): The inferior vena cava pierces the central tendon of the diaphragm to enter the right side of the mediastinum near vertebral level TVIII. The esophagus penetrates the muscular part of the diaphragm to leave the mediastinum and enter the abdomen just to the left of the midline at vertebral level TX. The aorta passes posteriorly to the diaphragm at the midline at vertebral level TXII. Numerous other structures that pass between the thorax and abdomen pass through or posterior to the diaphragm. The breasts, consisting of mammary glands, superficial fascia, and overlying skin, are in the pectoral region on each side of the anterior thoracic wall (Fig. 3.9).


Anatomy_Gray

Anatomy_Gray. The breasts, consisting of mammary glands, superficial fascia, and overlying skin, are in the pectoral region on each side of the anterior thoracic wall (Fig. 3.9). Vessels, lymphatics, and nerves associated with the breast are as follows: Branches from the internal thoracic arteries and veins perforate the anterior chest wall on each side of the sternum to supply anterior aspects of the thoracic wall. Those branches associated mainly with the second to fourth intercostal spaces also supply the anteromedial parts of each breast. Lymphatic vessels from the medial part of the breast accompany the perforating arteries and drain into the parasternal nodes on the deep surface of the thoracic wall. Vessels and lymphatics associated with lateral parts of the breast emerge from or drain into the axillary region of the upper limb. Lateral and anterior branches of the fourth to sixth intercostal nerves carry general sensation from the skin of the breast.


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Anatomy_Gray. Lateral and anterior branches of the fourth to sixth intercostal nerves carry general sensation from the skin of the breast. When working with patients, physicians use vertebral levels to determine the position of important anatomical structures within body regions.


Anatomy_Gray

Anatomy_Gray. The horizontal plane passing through the disc that separates thoracic vertebrae TIV and TV is one of the most significant planes in the body (Fig. 3.10) because it: passes through the sternal angle anteriorly, marking the position of the anterior articulation of the costal cartilage of rib II with the sternum. The sternal angle is used to find the position of rib II as a reference for counting ribs (because of the overlying clavicle, rib I is not palpable); separates the superior mediastinum from the inferior mediastinum and marks the position of the superior limit of the pericardium; marks where the arch of the aorta begins and ends; passes through the site where the superior vena cava penetrates the pericardium to enter the heart; is the level at which the trachea bifurcates into right and left main bronchi; and marks the superior limit of the pulmonary trunk. Venous shunts from left to right


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Anatomy_Gray. Venous shunts from left to right The right atrium is the chamber of the heart that receives deoxygenated blood returning from the body. It lies on the right side of the midline, and the two major veins, the superior and inferior venae cavae, that drain into it are also located on the right side of the body. This means that, to get to the right side of the body, all blood coming from the left side has to cross the midline. This left-to-right shunting is carried out by a number of important and, in some cases, very large veins, several of which are in the thorax (Fig. 3.11). In adults, the left brachiocephalic vein crosses the midline immediately posterior to the manubrium and delivers blood from the left side of the head and neck, the left upper limb, and part of the left thoracic wall into the superior vena cava.


Anatomy_Gray

Anatomy_Gray. The hemiazygos and accessory hemiazygos veins drain posterior and lateral parts of the left thoracic wall, pass immediately anterior to the bodies of thoracic vertebrae, and flow into the azygos vein on the right side, which ultimately connects with the superior vena cava. The arrangement of vessels and nerves that supply the thoracic wall reflects the segmental organization of the wall. Arteries to the wall arise from two sources: the thoracic aorta, which is in the posterior mediastinum, and a pair of vessels, the internal thoracic arteries, which run along the deep aspect of the anterior thoracic wall on either side of the sternum.


Anatomy_Gray

Anatomy_Gray. the wall, mainly along the inferior margin of each rib (Fig. 3.12A). Running with these vessels are intercostal nerves (the anterior rami of thoracic spinal nerves), which innervate the wall, related parietal pleura, and associated skin. The position of these nerves and vessels relative to the ribs must be considered when passing objects, such as chest tubes, through the thoracic wall. Dermatomes of the thorax generally reflect the segmental organization of the thoracic spinal nerves (Fig. 3.12B). The exception occurs, anteriorly and superiorly, with the first thoracic dermatome, which is located mostly in the upper limb, and not on the trunk. The anterosuperior region of the trunk receives branches from the anterior ramus of C4 via supraclavicular branches of the cervical plexus. The highest thoracic dermatome on the anterior chest wall is T2, which also extends into the upper limb. In the midline, skin over the xiphoid process is innervated by T6.


Anatomy_Gray

Anatomy_Gray. The highest thoracic dermatome on the anterior chest wall is T2, which also extends into the upper limb. In the midline, skin over the xiphoid process is innervated by T6. Dermatomes of T7 to T12 follow the contour of the ribs onto the anterior abdominal wall (Fig. 3.12C). All preganglionic nerve fibers of the sympathetic system are carried out of the spinal cord in spinal nerves T1 to L2 (Fig. 3.13). This means that sympathetic fibers found anywhere in the body ultimately emerge from the spinal cord as components of these spinal nerves. Preganglionic sympathetic fibers destined for the head are carried out of the spinal cord in spinal nerve T1. The thoracic wall is expandable because most ribs articulate with other components of the wall by true joints that allow movement, and because of the shape and orientation of the ribs (Fig. 3.14).


Anatomy_Gray

Anatomy_Gray. The thoracic wall is expandable because most ribs articulate with other components of the wall by true joints that allow movement, and because of the shape and orientation of the ribs (Fig. 3.14). A rib’s posterior attachment is superior to its anterior attachment. Therefore, when a rib is elevated, it moves the anterior thoracic wall forward relative to the posterior wall, which is fixed. In addition, the middle part of each rib is inferior to its two ends, so that when this region of the rib is elevated, it expands the thoracic wall laterally. Finally, because the diaphragm is muscular, it changes the volume of the thorax in the vertical direction. Changes in the anterior, lateral, and vertical dimensions of the thoracic cavity are important for breathing. Innervation of the diaphragm


Anatomy_Gray

Anatomy_Gray. Changes in the anterior, lateral, and vertical dimensions of the thoracic cavity are important for breathing. Innervation of the diaphragm The diaphragm is innervated by two phrenic nerves that originate, one on each side, as branches of the cervical plexus in the neck (Fig. 3.15). They arise from the anterior rami of cervical nerves C3, C4, and C5, with the major contribution coming from C4. The phrenic nerves pass vertically through the neck, the superior thoracic aperture, and the mediastinum to supply motor innervation to the entire diaphragm, including the crura (muscular extensions that attach the diaphragm to the upper lumbar vertebrae). In the mediastinum, the phrenic nerves pass anteriorly to the roots of the lungs.


Anatomy_Gray

Anatomy_Gray. The tissues that initially give rise to the diaphragm are in an anterior position on the embryological disc before the head fold develops, which explains the cervical origin of the nerves that innervate the diaphragm. In other words, the tissue that gives rise to the diaphragm originates superior to the ultimate location of the diaphragm. Spinal cord injuries below the level of the origin of the phrenic nerve do not affect movement of the diaphragm. The cylindrical thorax consists of: a wall, two pleural cavities, the lungs, and the mediastinum.


Anatomy_Gray

Anatomy_Gray. The cylindrical thorax consists of: a wall, two pleural cavities, the lungs, and the mediastinum. The thorax houses the heart and lungs, acts as a conduit for structures passing between the neck and the abdomen, and plays a principal role in breathing. In addition, the thoracic wall protects the heart and lungs and provides support for the upper limbs. Muscles anchored to the anterior thoracic wall provide some of this support, and together with their associated connective tissues, nerves, and vessels, and the overlying skin and superficial fascia, define the pectoral region. The pectoral region is external to the anterior thoracic wall and helps anchor the upper limb to the trunk. It consists of: a superficial compartment containing skin, superficial fascia, and breasts; and a deep compartment containing muscles and associated structures. Nerves, vessels, and lymphatics in the superficial compartment emerge from the thoracic wall, the axilla, and the neck.


Anatomy_Gray

Anatomy_Gray. Nerves, vessels, and lymphatics in the superficial compartment emerge from the thoracic wall, the axilla, and the neck. The breasts consist of mammary glands and associated skin and connective tissues. The mammary glands are modified sweat glands in the superficial fascia anterior to the pectoral muscles and the anterior thoracic wall (Fig. 3.16). The mammary glands consist of a series of ducts and associated secretory lobules. These converge to form 15 to 20 lactiferous ducts, which open independently onto the nipple. The nipple is surrounded by a circular pigmented area of skin termed the areola. A well-developed, connective tissue stroma surrounds the ducts and lobules of the mammary gland. In certain regions, this condenses to form well-defined ligaments, the suspensory ligaments of breast, which are continuous with the dermis of the skin and support the breast. Carcinoma of the breast creates tension on these ligaments, causing pitting of the skin.


Anatomy_Gray

Anatomy_Gray. In nonlactating women, the predominant component of the breasts is fat, while glandular tissue is more abundant in lactating women. The breast lies on deep fascia related to the pectoralis major muscle and other surrounding muscles. A layer of loose connective tissue (the retromammary space) separates the breast from the deep fascia and provides some degree of movement over underlying structures. The base, or attached surface, of each breast extends vertically from ribs II to VI, and transversely from the sternum to as far laterally as the midaxillary line.


Anatomy_Gray

Anatomy_Gray. The base, or attached surface, of each breast extends vertically from ribs II to VI, and transversely from the sternum to as far laterally as the midaxillary line. The breast is related to the thoracic wall and to structures associated with the upper limb; therefore, vascular supply and drainage can occur by multiple routes (Fig. 3.16): laterally, vessels from the axillary artery—superior thoracic, thoraco-acromial, lateral thoracic, and subscapular arteries; medially, branches from the internal thoracic artery; the second to fourth intercostal arteries via branches that perforate the thoracic wall and overlying muscle. Veins draining the breast parallel the arteries and ultimately drain into the axillary, internal thoracic, and intercostal veins. Innervation of the breast is via anterior and lateral cutaneous branches of the second to sixth intercostal nerves. The nipple is innervated by the fourth intercostal nerve. Lymphatic drainage of the breast is as follows:


Anatomy_Gray

Anatomy_Gray. Lymphatic drainage of the breast is as follows: Approximately 75% is via lymphatic vessels that drain laterally and superiorly into axillary nodes (Fig. 3.16). Most of the remaining drainage is into parasternal nodes deep to the anterior thoracic wall and associated with the internal thoracic artery. Some drainage may occur via lymphatic vessels that follow the lateral branches of posterior intercostal arteries and connect with intercostal nodes situated near the heads and necks of ribs. Axillary nodes drain into the subclavian trunks, parasternal nodes drain into the bronchomediastinal trunks, and intercostal nodes drain either into the thoracic duct or into the bronchomediastinal trunks. The breast in men is rudimentary and consists only of small ducts, often composed of cords of cells, that normally do not extend beyond the areola. Breast cancer can occur in men. Muscles of the pectoral region


Anatomy_Gray

Anatomy_Gray. Muscles of the pectoral region Each pectoral region contains the pectoralis major, pectoralis minor, and subclavius muscles (Fig. 3.17 and Table 3.1). All originate from the anterior thoracic wall and insert into bones of the upper limb. The pectoralis major muscle is the largest and most superficial of the pectoral region muscles. It directly underlies the breast and is separated from it by deep fascia and the loose connective tissue of the retromammary space. The pectoralis major has a broad origin that includes the anterior surfaces of the medial half of the clavicle, the sternum, and related costal cartilages. The muscle fibers converge to form a flat tendon, which inserts into the lateral lip of the intertubercular sulcus of the humerus. The pectoralis major adducts, flexes, and medially rotates the arm. The subclavius and pectoralis minor muscles underlie the pectoralis major:


Anatomy_Gray

Anatomy_Gray. The pectoralis major adducts, flexes, and medially rotates the arm. The subclavius and pectoralis minor muscles underlie the pectoralis major: The subclavius is small and passes laterally from the anterior and medial part of rib I to the inferior surface of the clavicle. The pectoralis minor passes from the anterior surfaces of ribs III to V to the coracoid process of the scapula. Both the subclavius and pectoralis minor pull the tip of the shoulder inferiorly. A continuous layer of deep fascia, the clavipectoral fascia, encloses the subclavius and pectoralis minor and attaches to the clavicle above and to the floor of the axilla below.


Anatomy_Gray

Anatomy_Gray. A continuous layer of deep fascia, the clavipectoral fascia, encloses the subclavius and pectoralis minor and attaches to the clavicle above and to the floor of the axilla below. The muscles of the pectoral region form the anterior wall of the axilla, a region between the upper limb and the neck through which all major structures pass. Nerves, vessels, and lymphatics that pass between the pectoral region and the axilla pass through the clavipectoral fascia between the subclavius and pectoralis minor or pass under the inferior margins of the pectoralis major and minor. The thoracic wall is segmental in design and composed of skeletal elements and muscles. It extends between: the superior thoracic aperture, bordered by vertebra TI, rib I, and the manubrium of the sternum; and the inferior thoracic aperture, bordered by vertebra TXII, rib XII, the end of rib XI, the costal margin, and the xiphoid process of the sternum.


Anatomy_Gray

Anatomy_Gray. The skeletal elements of the thoracic wall consist of the thoracic vertebrae, intervertebral discs, ribs, and sternum. There are twelve thoracic vertebrae, each of which is characterized by articulations with ribs. A typical thoracic vertebra has a heart-shaped vertebral body, with roughly equal dimensions in the transverse and anteroposterior directions, and a long spinous process (Fig. 3.18). The vertebral foramen is generally circular and the laminae are broad and overlap with those of the vertebra below. The superior articular processes are flat, with their articular surfaces facing almost directly posteriorly, while the inferior articular processes project from the laminae and their articular facets face anteriorly. The transverse processes are club shaped and project posterolaterally. Articulation with ribs A typical thoracic vertebra has three sites on each side for articulation with ribs.


Anatomy_Gray

Anatomy_Gray. Articulation with ribs A typical thoracic vertebra has three sites on each side for articulation with ribs. Two demifacets (i.e., partial facets) are located on the superior and inferior aspects of the body for articulation with corresponding sites on the heads of adjacent ribs. The superior costal facet articulates with part of the head of its own rib, and the inferior costal facet articulates with part of the head of the rib below. An oval facet (transverse costal facet) at the end of the transverse process articulates with the tubercle of its own rib. Not all vertebrae articulate with ribs in the same fashion (Fig. 3.19): The superior costal facets on the body of vertebra TI are complete and articulate with a single facet on the head of its own rib—in other words, the head of rib I does not articulate with vertebra CVII. Similarly, vertebra TX (and often TIX) articulates only with its own ribs and therefore lacks inferior demifacets on the body.


Anatomy_Gray

Anatomy_Gray. Similarly, vertebra TX (and often TIX) articulates only with its own ribs and therefore lacks inferior demifacets on the body. Vertebrae TXI and TXII articulate only with the heads of their own ribs—they lack transverse costal facets and have only a single complete facet on each side of their bodies. There are twelve pairs of ribs, each terminating anteriorly in a costal cartilage (Fig. 3.20). Although all ribs articulate with the vertebral column, only the costal cartilages of the upper seven ribs, known as true ribs, articulate directly with the sternum. The remaining five pairs of ribs are false ribs: The costal cartilages of ribs VIII to X articulate anteriorly with the costal cartilages of the ribs above. Ribs XI and XII have no anterior connection with other ribs or with the sternum and are often called floating ribs.


Anatomy_Gray

Anatomy_Gray. Ribs XI and XII have no anterior connection with other ribs or with the sternum and are often called floating ribs. A typical rib consists of a curved shaft with anterior and posterior ends (Fig. 3.21). The anterior end is continuous with its costal cartilage. The posterior end articulates with the vertebral column and is characterized by a head, neck, and tubercle. The head is somewhat expanded and typically presents two articular surfaces separated by a crest. The smaller superior surface articulates with the inferior costal facet on the body of the vertebra above, whereas the larger inferior facet articulates with the superior costal facet of its own vertebra. The neck is a short flat region of bone that separates the head from the tubercle. The tubercle projects posteriorly from the junction of the neck with the shaft and consists of two regions, an articular part and a nonarticular part:


Anatomy_Gray

Anatomy_Gray. The tubercle projects posteriorly from the junction of the neck with the shaft and consists of two regions, an articular part and a nonarticular part: The articular part is medial and has an oval facet for articulation with a corresponding facet on the transverse process of the associated vertebra. The raised nonarticular part is roughened by ligament attachments. The shaft is generally thin and flat with internal and external surfaces. The superior margin is smooth and rounded, whereas the inferior margin is sharp. The shaft bends forward just laterally to the tubercle at a site termed the angle. It also has a gentle twist around its longitudinal axis so that the external surface of the anterior part of the shaft faces somewhat superiorly relative to the posterior part. The inferior margin of the internal surface is marked by a distinct costal groove. Distinct features of upper and lower ribs The upper and lower ribs have distinct features (Fig. 3.22).


Anatomy_Gray

Anatomy_Gray. Distinct features of upper and lower ribs The upper and lower ribs have distinct features (Fig. 3.22). Rib I is flat in the horizontal plane and has broad superior and inferior surfaces. From its articulation with vertebra TI, it slopes inferiorly to its attachment to the manubrium of the sternum. The head articulates only with the body of vertebra TI and therefore has only one articular surface. Like other ribs, the tubercle has a facet for articulation with the transverse process. The superior surface of the rib is characterized by a distinct tubercle, the scalene tubercle, which separates two smooth grooves that cross the rib approximately midway along the shaft. The anterior groove is caused by the subclavian vein, and the posterior groove is caused by the subclavian artery. Anterior and posterior to these grooves, the shaft is roughened by muscle and ligament attachments.


Anatomy_Gray

Anatomy_Gray. Rib II, like rib I, is flat but twice as long. It articulates with the vertebral column in a way typical of most ribs. The head of rib X has a single facet for articulation with its own vertebra. Ribs XI and XII articulate only with the bodies of their own vertebrae and have no tubercles or necks. Both ribs are short, have little curve, and are pointed anteriorly. The adult sternum consists of three major elements: the broad and superiorly positioned manubrium of the sternum, the narrow and longitudinally oriented body of the sternum, and the small and inferiorly positioned xiphoid process (Fig. 3.23). Manubrium of the sternum The manubrium of the sternum forms part of the bony framework of the neck and the thorax. The superior surface of the manubrium is expanded laterally and bears a distinct and palpable notch, the jugular notch (suprasternal notch), in the midline.


Anatomy_Gray

Anatomy_Gray. The superior surface of the manubrium is expanded laterally and bears a distinct and palpable notch, the jugular notch (suprasternal notch), in the midline. On either side of this notch is a large oval fossa for articulation with the clavicle. Immediately inferior to this fossa, on each lateral surface of the manubrium, is a facet for the attachment of the first costal cartilage. At the lower end of the lateral border is a demifacet for articulation with the upper half of the anterior end of the second costal cartilage. Body of the sternum The body of the sternum is flat. The anterior surface of the body of the sternum is often marked by transverse ridges that represent lines of fusion between the segmental elements called sternebrae, from which this part of the sternum arises embryologically.


Anatomy_Gray

Anatomy_Gray. The lateral margins of the body of the sternum have articular facets for costal cartilages. Superiorly, each lateral margin has a demifacet for articulation with the inferior aspect of the second costal cartilage. Inferior to this demifacet are four facets for articulation with the costal cartilages of ribs III to VI. At the inferior end of the body of the sternum is a demifacet for articulation with the upper demifacet on the seventh costal cartilage. The inferior end of the body of the sternum is attached to the xiphoid process. The xiphoid process is the smallest part of the sternum. Its shape is variable: it may be wide, thin, pointed, bifid, curved, or perforated. It begins as a cartilaginous structure, which becomes ossified in the adult. On each side of its upper lateral margin is a demifacet for articulation with the inferior end of the seventh costal cartilage.


Anatomy_Gray

Anatomy_Gray. A typical rib articulates with: the bodies of adjacent vertebrae, forming a joint with the head of the rib; and the transverse process of its related vertebra, forming a costotransverse joint (Fig. 3.24). Together, the costovertebral joints and related ligaments allow the necks of the ribs either to rotate around their longitudinal axes, which occurs mainly in the upper ribs, or to ascend and descend relative to the vertebral column, which occurs mainly in the lower ribs. The combined movements of all of the ribs on the vertebral column are essential for altering the volume of the thoracic cavity during breathing. Joint with head of rib


Anatomy_Gray

Anatomy_Gray. Joint with head of rib The two facets on the head of the rib articulate with the superior facet on the body of its own vertebra and with the inferior facet on the body of the vertebra above. This joint is divided into two synovial compartments by an intra-articular ligament, which attaches the crest to the adjacent intervertebral disc and separates the two articular surfaces on the head of the rib. The two synovial compartments and the intervening ligament are surrounded by a single joint capsule attached to the outer margins of the combined articular surfaces of the head and vertebral column. Costotransverse joints are synovial joints between the tubercle of a rib and the transverse process of the related vertebra (Fig. 3.24). The capsule surrounding each joint is thin. The joint is stabilized by two strong extracapsular ligaments that span the space between the transverse process and the rib on the medial and lateral sides of the joint:


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Anatomy_Gray. The costotransverse ligament is medial to the joint and attaches the neck of the rib to the transverse process. The lateral costotransverse ligament is lateral to the joint and attaches the tip of the transverse process to the roughened nonarticular part of the tubercle of the rib. A third ligament, the superior costotransverse ligament, attaches the superior surface of the neck of the rib to the transverse process of the vertebra above. Slight gliding movements occur at the costotransverse joints. The sternocostal joints are joints between the upper seven costal cartilages and the sternum (Fig. 3.25). The joint between rib I and the manubrium is not synovial and consists of a fibrocartilaginous connection between the manubrium and the costal cartilage. The second to seventh joints are synovial and have thin capsules reinforced by surrounding sternocostal ligaments.


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Anatomy_Gray. The joint between the second costal cartilage and the sternum is divided into two compartments by an intraarticular ligament. This ligament attaches the second costal cartilage to the junction of the manubrium and the body of the sternum. Interchondral joints occur between the costal cartilages of adjacent ribs (Fig. 3.25), mainly between the costal cartilages of ribs VII to X, but may also involve the costal cartilages of ribs V and VI. Interchondral joints provide indirect anchorage to the sternum and contribute to the formation of a smooth inferior costal margin. They are usually synovial, and the thin fibrous capsules are reinforced by interchondral ligaments.


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Anatomy_Gray. The joints between the manubrium and the body of the sternum and between the body of the sternum and the xiphoid process are usually symphyses (Fig. 3.25). Only slight angular movements occur between the manubrium and the body of the sternum during respiration. The joint between the body of the sternum and the xiphoid process often becomes ossified with age. A clinically useful feature of the manubriosternal joint is that it can be palpated easily. This is because the manubrium normally angles posteriorly on the body of the sternum, forming a raised feature referred to as the sternal angle. This elevation marks the site of articulation of rib II with the sternum. Rib I is not palpable, because it lies inferior to the clavicle and is embedded in tissues at the base of the neck. Therefore, rib II is used as a reference for counting ribs and can be felt immediately lateral to the sternal angle.


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Anatomy_Gray. In addition, the sternal angle lies on a horizontal plane that passes through the intervertebral disc between vertebrae TIV and TV (see Fig. 3.10). This plane separates the superior mediastinum from the inferior mediastinum and marks the superior border of the pericardium. The plane also passes through the end of the ascending aorta and the beginning of the arch of the aorta, the end of the arch of the aorta and the beginning of the thoracic aorta, and the bifurcation of the trachea, and just superior to the pulmonary trunk (see Fig. 3.79 and 3.86). Intercostal spaces lie between adjacent ribs and are filled by intercostal muscles (Fig. 3.26). Intercostal nerves and associated major arteries and veins lie in the costal groove along the inferior margin of the superior rib and pass in the plane between the inner two layers of muscles.


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Anatomy_Gray. Intercostal nerves and associated major arteries and veins lie in the costal groove along the inferior margin of the superior rib and pass in the plane between the inner two layers of muscles. In each space, the vein is the most superior structure and is therefore highest in the costal groove. The artery is inferior to the vein, and the nerve is inferior to the artery and often not protected by the groove. Therefore, the nerve is the structure most at risk when objects perforate the upper aspect of an intercostal space. Small collateral branches of the major intercostal nerves and vessels are often present superior to the inferior rib below. Deep to the intercostal spaces and ribs, and separating these structures from the underlying pleura, is a layer of loose connective tissue, called endothoracic fascia, which contains variable amounts of fat.


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Anatomy_Gray. Superficial to the spaces are deep fascia, superficial fascia, and skin. Muscles associated with the upper limbs and back overlie the spaces. Muscles of the thoracic wall include those that fill and support the intercostal spaces, those that pass between the sternum and the ribs, and those that cross several ribs between costal attachments (Table 3.2). The muscles of the thoracic wall, together with muscles between the vertebrae and ribs posteriorly (i.e., the levatores costarum and serratus posterior superior and serratus posterior inferior muscles) alter the position of the ribs and sternum and so change the thoracic volume during breathing. They also reinforce the thoracic wall. The intercostal muscles are three flat muscles found in each intercostal space that pass between adjacent ribs (Fig. 3.27). Individual muscles in this group are named according to their positions: The external intercostal muscles are the most superficial.


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Anatomy_Gray. The external intercostal muscles are the most superficial. The internal intercostal muscles are sandwiched between the external and innermost muscles. The innermost intercostal muscles are the deepest of the three muscles. The intercostal muscles are innervated by the related intercostal nerves. As a group, the intercostal muscles provide structural support for the intercostal spaces during breathing. They can also move the ribs.


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Anatomy_Gray. The eleven pairs of external intercostal muscles extend from the inferior margins (lateral edges of costal grooves) of the ribs above to the superior margins of the ribs below. When the thoracic wall is viewed from a lateral position, the muscle fibers pass obliquely anteroinferiorly (Fig. 3.27). The muscles extend around the thoracic wall from the regions of the tubercles of the ribs to the costal cartilages, where each layer continues as a thin connective tissue aponeurosis termed the external intercostal membrane. The external intercostal muscles are most active in inspiration.


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Anatomy_Gray. The eleven pairs of internal intercostal muscles pass between the most inferior lateral edge of the costal grooves of the ribs above, to the superior margins of the ribs below. They extend from parasternal regions, where the muscles course between adjacent costal cartilages, to the angle of the ribs posteriorly (Fig. 3.27). This layer continues medially toward the vertebral column, in each intercostal space, as the internal intercostal membrane. The muscle fibers pass in the opposite direction to those of the external intercostal muscles. When the thoracic wall is viewed from a lateral position, the muscle fibers pass obliquely posteroinferiorly. The internal intercostal muscles are most active during expiration.


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Anatomy_Gray. The innermost intercostal muscles are the least distinct of the intercostal muscles, and the fibers have the same orientation as the internal intercostals (Fig. 3.27). These muscles are most evident in the lateral thoracic wall. They extend between the inner surfaces of adjacent ribs from the medial edge of the costal groove to the deep surface of the rib below. Importantly, the neurovascular bundles associated with the intercostal spaces pass around the thoracic wall in the costal grooves in a plane between the innermost and internal intercostal muscles.


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Anatomy_Gray. The subcostales are in the same plane as the innermost intercostals, span multiple ribs, and are more numerous in lower regions of the posterior thoracic wall (Fig. 3.28A). They extend from the internal surfaces of one rib to the internal surface of the second (next) or third rib below. Their fibers parallel the course of the internal intercostal muscles and extend from the angle of the ribs to more medial positions on the ribs below. The transversus thoracis muscles are found on the deep surface of the anterior thoracic wall (Fig. 3.28B) and in the same plane as the innermost intercostals. The transversus thoracis muscles originate from the posterior aspect of the xiphoid process, the inferior part of the body of the sternum, and the adjacent costal cartilages of the lower true ribs. They pass superiorly and laterally to insert into the lower borders of the costal cartilages of ribs III to VI. They most likely pull these latter elements inferiorly.


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Anatomy_Gray. The transversus thoracis muscles lie deep to the internal thoracic vessels and secure these vessels to the wall. Vessels that supply the thoracic wall consist mainly of posterior and anterior intercostal arteries, which pass around the wall between adjacent ribs in intercostal spaces (Fig. 3.29). These arteries originate from the aorta and internal thoracic arteries, which in turn arise from the subclavian arteries in the root of the neck. Together, the intercostal arteries form a basket-like pattern of vascular supply around the thoracic wall. Posterior intercostal arteries originate from vessels associated with the posterior thoracic wall. The upper two posterior intercostal arteries on each side are derived from the supreme intercostal artery, which descends into the thorax as a branch of the costocervical trunk in the neck. The costocervical trunk is a posterior branch of the subclavian artery (Fig. 3.29).


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Anatomy_Gray. The remaining nine pairs of posterior intercostal arteries arise from the posterior surface of the thoracic aorta. Because the aorta is on the left side of the vertebral column, those posterior intercostal vessels passing to the right side of the thoracic wall cross the midline anterior to the bodies of the vertebrae and therefore are longer than the corresponding vessels on the left. In addition to having numerous branches that supply various components of the wall, the posterior intercostal arteries have branches that accompany lateral cutaneous branches of the intercostal nerves to superficial regions. The anterior intercostal arteries originate directly or indirectly as lateral branches from the internal thoracic arteries (Fig. 3.29).


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Anatomy_Gray. The anterior intercostal arteries originate directly or indirectly as lateral branches from the internal thoracic arteries (Fig. 3.29). Each internal thoracic artery arises as a major branch of the subclavian artery in the neck. It passes anteriorly over the cervical dome of the pleura and descends vertically through the superior thoracic aperture and along the deep aspect of the anterior thoracic wall. On each side, the internal thoracic artery lies posterior to the costal cartilages of the upper six ribs and about 1 cm lateral to the sternum. At approximately the level of the sixth intercostal space, it divides into two terminal branches: the superior epigastric artery, which continues inferiorly into the anterior abdominal wall (Fig. 3.29); and the musculophrenic artery, which passes along the costal margin, goes through the diaphragm, and ends near the last intercostal space.


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Anatomy_Gray. Anterior intercostal arteries that supply the upper six intercostal spaces arise as lateral branches from the internal thoracic artery, whereas those supplying the lower spaces arise from the musculophrenic artery. In each intercostal space, the anterior intercostal arteries usually have two branches: One passes below the margin of the upper rib. The other passes above the margin of the lower rib and meets a collateral branch of the posterior intercostal artery. The distributions of the anterior and posterior intercostal vessels overlap and can develop anastomotic connections. The anterior intercostal arteries are generally smaller than the posterior vessels.


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Anatomy_Gray. In addition to anterior intercostal arteries and a number of other branches, the internal thoracic arteries give rise to perforating branches that pass directly forward between the costal cartilages to supply structures external to the thoracic wall. These vessels travel with the anterior cutaneous branches of the intercostal nerves. Venous drainage from the thoracic wall generally parallels the pattern of arterial supply (Fig. 3.30). Centrally, the intercostal veins ultimately drain into the azygos system of veins or into internal thoracic veins, which connect with the brachiocephalic veins in the neck. Often the upper posterior intercostal veins on the left side come together and form the left superior intercostal vein, which empties into the left brachiocephalic vein. Similarly, the upper posterior intercostal veins on the right side may come together and form the right superior intercostal vein, which empties into the azygos vein.


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Anatomy_Gray. Similarly, the upper posterior intercostal veins on the right side may come together and form the right superior intercostal vein, which empties into the azygos vein. Lymphatic vessels of the thoracic wall drain mainly into lymph nodes associated with the internal thoracic arteries (parasternal nodes), with the heads and necks of ribs (intercostal nodes), and with the diaphragm (diaphragmatic nodes) (Fig. 3.31). Diaphragmatic nodes are posterior to the xiphoid and at sites where the phrenic nerves penetrate the diaphragm. They also occur in regions where the diaphragm is attached to the vertebral column. Parasternal nodes drain into bronchomediastinal trunks. Intercostal nodes in the upper thorax also drain into bronchomediastinal trunks, whereas intercostal nodes in the lower thorax drain into the thoracic duct.


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Anatomy_Gray. Nodes associated with the diaphragm interconnect with parasternal, prevertebral, and juxta-esophageal nodes, brachiocephalic nodes (anterior to the brachiocephalic veins in the superior mediastinum), and lateral aortic/lumbar nodes (in the abdomen). Superficial regions of the thoracic wall drain mainly into axillary lymph nodes in the axilla or parasternal nodes. Innervation of the thoracic wall is mainly by the intercostal nerves, which are the anterior rami of spinal nerves T1 to T11 and lie in the intercostal spaces between adjacent ribs. The anterior ramus of spinal nerve T12 (the subcostal nerve) is inferior to rib XII (Fig. 3.32). A typical intercostal nerve passes laterally around the thoracic wall in an intercostal space. The largest of the branches is the lateral cutaneous branch, which pierces the lateral thoracic wall and divides into an anterior branch and a posterior branch that innervate the overlying skin.


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Anatomy_Gray. The intercostal nerves end as anterior cutaneous branches, which emerge either parasternally, between adjacent costal cartilages, or laterally to the midline, on the anterior abdominal wall, to supply the skin. In addition to these major branches, small collateral branches can be found in the intercostal space running along the superior border of the lower rib. In the thorax, the intercostal nerves carry: somatic motor innervation to the muscles of the thoracic wall (intercostal, subcostal, and transversus thoracis muscles), somatic sensory innervation from the skin and parietal pleura, and postganglionic sympathetic fibers to the periphery. Sensory innervation of the skin overlying the upper thoracic wall is supplied by cutaneous branches (supraclavicular nerves), which descend from the cervical plexus in the neck. In addition to innervating the thoracic wall, intercostal nerves innervate other regions: The anterior ramus of T1 contributes to the brachial plexus.


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Anatomy_Gray. In addition to innervating the thoracic wall, intercostal nerves innervate other regions: The anterior ramus of T1 contributes to the brachial plexus. The lateral cutaneous branch of the second intercostal nerve (the intercostobrachial nerve) contributes to cutaneous innervation of the medial surface of the upper arm. The lower intercostal nerves supply the muscles, skin, and peritoneum of the abdominal wall. The diaphragm is a thin musculotendinous structure that fills the inferior thoracic aperture and separates the thoracic cavity from the abdominal cavity (Fig. 3.34 and see Chapter 4). It is attached peripherally to the: xiphoid process of the sternum, costal margin of the thoracic wall, ends of ribs XI and XII, ligaments that span across structures of the posterior abdominal wall, and vertebrae of the lumbar region. From these peripheral attachments, muscle fibers converge to join the central tendon. The pericardium is attached to the middle part of the central tendon.


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Anatomy_Gray. From these peripheral attachments, muscle fibers converge to join the central tendon. The pericardium is attached to the middle part of the central tendon. In the median sagittal plane, the diaphragm slopes inferiorly from its anterior attachment to the xiphoid, approximately at vertebral level TVIII/IX, to its posterior attachment to the median arcuate ligament, crossing anteriorly to the aorta at approximately vertebral level TXII. Structures traveling between the thorax and abdomen pass through the diaphragm or between the diaphragm and its peripheral attachments: The inferior vena cava passes through the central tendon at approximately vertebral level TVIII. The esophagus passes through the muscular part of the diaphragm, just to the left of midline, approximately at vertebral level TX. The vagus nerves pass through the diaphragm with the esophagus. The aorta passes behind the posterior attachment of the diaphragm at vertebral level TXII.


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Anatomy_Gray. The vagus nerves pass through the diaphragm with the esophagus. The aorta passes behind the posterior attachment of the diaphragm at vertebral level TXII. The thoracic duct passes behind the diaphragm with the aorta. The azygos and hemiazygos veins may also pass through the aortic hiatus or through the crura of the diaphragm. Other structures outside the posterior attachments of the diaphragm lateral to the aortic hiatus include the sympathetic trunks. The greater, lesser, and least splanchnic nerves penetrate the crura.


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Anatomy_Gray. Other structures outside the posterior attachments of the diaphragm lateral to the aortic hiatus include the sympathetic trunks. The greater, lesser, and least splanchnic nerves penetrate the crura. The arterial supply to the diaphragm is from vessels that arise superiorly and inferiorly to it (see Fig. 3.34). From above, pericardiacophrenic and musculophrenic arteries supply the diaphragm. These vessels are branches of the internal thoracic arteries. Superior phrenic arteries, which arise directly from lower parts of the thoracic aorta, and small branches from intercostal arteries contribute to the supply. The largest arteries supplying the diaphragm arise from below it. These arteries are the inferior phrenic arteries, which branch directly from the abdominal aorta.


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Anatomy_Gray. Venous drainage of the diaphragm is by veins that generally parallel the arteries. The veins drain into: the brachiocephalic veins in the neck, the azygos system of veins, or abdominal veins (left suprarenal vein and inferior vena cava). The diaphragm is innervated by the phrenic nerves (C3, C4, and C5), which penetrate the diaphragm and innervate it from its abdominal surface. Contraction of the domes of the diaphragm flattens the diaphragm, thereby increasing thoracic volume. Movements of the diaphragm are essential for normal breathing. One of the principal functions of the thoracic wall and the diaphragm is to alter the volume of the thorax and thereby move air in and out of the lungs. During breathing, the dimensions of the thorax change in the vertical, lateral, and anteroposterior directions.


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Anatomy_Gray. During breathing, the dimensions of the thorax change in the vertical, lateral, and anteroposterior directions. Elevation and depression of the diaphragm significantly alter the vertical dimensions of the thorax. Depression results when the muscle fibers of the diaphragm contract. Elevation occurs when the diaphragm relaxes. Changes in the anteroposterior and lateral dimensions result from elevation and depression of the ribs (Fig. 3.35). The posterior ends of the ribs articulate with the vertebral column, whereas the anterior ends of most ribs articulate with the sternum or adjacent ribs.


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Anatomy_Gray. Because the anterior ends of the ribs are inferior to the posterior ends, when the ribs are elevated, they move the sternum upward and forward. Also, the angle between the body of the sternum and the manubrium may become slightly less acute. When the ribs are depressed, the sternum moves downward and backward. This “pump handle” movement changes the dimensions of the thorax in the anteroposterior direction (Fig. 3.35A). As well as the anterior ends of the ribs being lower than the posterior ends, the middles of the shafts tend to be lower than the two ends. When the shafts are elevated, the middles of the shafts move laterally. This “bucket handle” movement increases the lateral dimensions of the thorax (Fig. 3.35B). Any muscles attaching to the ribs can potentially move one rib relative to another and therefore act as accessory respiratory muscles. Muscles in the neck and the abdomen can fix or alter the positions of upper and lower ribs.


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Anatomy_Gray. Two pleural cavities, one on either side of the mediastinum, surround the lungs (Fig. 3.37): Superiorly, they extend above rib I into the root of the neck. Inferiorly, they extend to a level just above the costal margin. The medial wall of each pleural cavity is the mediastinum. Each pleural cavity is lined by a single layer of flat cells, mesothelium, and an associated layer of supporting connective tissue; together, they form the pleura. The pleura is divided into two major types, based on location: Pleura associated with the walls of a pleural cavity is parietal pleura (Fig. 3.37). Pleura that reflects from the medial wall and onto the surface of the lung is visceral pleura (Fig. 3.37), which adheres to and covers the lung.


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Anatomy_Gray. Pleura that reflects from the medial wall and onto the surface of the lung is visceral pleura (Fig. 3.37), which adheres to and covers the lung. Each pleural cavity is the potential space enclosed between the visceral and parietal pleurae. They normally contain only a very thin layer of serous fluid. As a result, the surface of the lung, which is covered by visceral pleura, directly opposes and freely slides over the parietal pleura attached to the wall. The names given to the parietal pleura correspond to the parts of the wall with which they are associated (Fig. 3.38): Pleura related to the ribs and intercostal spaces is termed the costal part. Pleura covering the diaphragm is the diaphragmatic part. Pleura covering the mediastinum is the mediastinal part. The dome-shaped layer of parietal pleura lining the cervical extension of the pleural cavity is cervical pleura (dome of pleura or pleural cupola).


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Anatomy_Gray. The dome-shaped layer of parietal pleura lining the cervical extension of the pleural cavity is cervical pleura (dome of pleura or pleural cupola). Covering the superior surface of the cervical pleura is a distinct dome-like layer of fascia, the suprapleural membrane (Fig. 3.38). This connective tissue membrane is attached laterally to the medial margin of the first rib and behind to the transverse process of vertebra CVII. Superiorly, the membrane receives muscle fibers from some of the deep muscles in the neck (scalene muscles) that function to keep the membrane taut. The suprapleural membrane provides apical support for the pleural cavity in the root of the neck.


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Anatomy_Gray. In the region of vertebrae TV to TVII, the mediastinal pleura reflects off the mediastinum as a tubular, sleeve-like covering for structures (i.e., airway, vessels, nerves, lymphatics) that pass between the lung and mediastinum. This sleeve-like covering and the structures it contains forms the root of the lung. The root joins the medial surface of the lung at an area referred to as the hilum of the lung. Here, the mediastinal pleura is continuous with the visceral pleura. The parietal pleural is innervated by somatic afferent fibers. The costal pleura is innervated by branches from the intercostal nerves, and pain would be felt in relation to the thoracic wall. The diaphragmatic pleura and the mediastinal pleura are innervated mainly by the phrenic nerves (originating at spinal cord levels C3, C4, and C5). Pain from these areas would refer to the C3, C4, and C5 dermatomes (lateral neck and the supraclavicular region of the shoulder).


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Anatomy_Gray. The peripheral reflections of parietal pleura mark the extent of the pleural cavities (Fig. 3.39). Superiorly, the pleural cavity can project as much as 3 to 4 cm above the first costal cartilage but does not extend above the neck of rib I. This limitation is caused by the inferior slope of rib I to its articulation with the manubrium. Anteriorly, the pleural cavities approach each other posterior to the upper part of the sternum. However, posterior to the lower part of the sternum, the parietal pleura does not come as close to the midline on the left side as it does on the right because the middle mediastinum, containing the pericardium and heart, bulges to the left.