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Anatomy_Gray. Blood from the lower limbs and the pelvis may drain via a series of collateral vessels, some of which include the superficial inferior epigastric veins, which run in the superficial fascia. These anastomose with the superior, superficial, and deep epigastric venous systems to drain into the internal thoracic veins, which in turn drain into the brachiocephalic veins and the superior vena cava. After the initial inferior vena cava thrombosis, the veins of the anterior abdominal wall and other collateral pathways hypertrophy to accommodate the increase in blood flow. A 52-year-old woman visited her family physician with complaints of increasing lethargy and vomiting. The physician examined her and noted that compared to previous visits she had lost significant weight. She was also jaundiced, and on examination of the abdomen a well-defined 10-cm rounded mass was palpable below the liver edge in the right upper quadrant (Fig. 4.185).


Anatomy_Gray

Anatomy_Gray. The clinical diagnosis was carcinoma of the head of the pancreas. It is difficult to appreciate how such a precise diagnosis can be made clinically when only three clinical signs have been described. The patient’s obstruction was in the distal bile duct. When a patient has jaundice, the causes are excessive breakdown of red blood cells (prehepatic), hepatic failure (hepatic jaundice), and posthepatic causes, which include obstruction along the length of the biliary tree. The patient had a mass in her right upper quadrant that was palpable below the liver; this was the gallbladder. In healthy individuals, the gallbladder is not palpable. An expanded gallbladder indicates obstruction either within the cystic duct or below the level of the cystic duct insertion (i.e., the bile duct). The patient’s vomiting was related to the position of the tumor.


Anatomy_Gray

Anatomy_Gray. The patient’s vomiting was related to the position of the tumor. It is not uncommon for vomiting and weight loss (cachexia) to occur in patients with a malignant disease. The head of the pancreas lies within the curve of the duodenum, primarily adjacent to the descending part of the duodenum. Any tumor mass in the region of the head of the pancreas is likely to expand and may encase and invade the duodenum. Unfortunately, in this patient’s case, this happened, producing almost complete obstruction. Further discussion with the patient revealed that she was vomiting relatively undigested food soon after each meal. A CT scan demonstrated further complications.


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Anatomy_Gray. A CT scan demonstrated further complications. In the region of the head and neck of the pancreas are complex anatomical structures, which may be involved with a malignant process. The CT scan confirmed a mass in the region of the head of the pancreas, which invaded the descending part of the duodenum. The mass extended into the neck of the pancreas and had blocked the distal part of the bile duct and the pancreatic duct. Posteriorly the mass had directly invaded the portal venous confluence of the splenic and superior mesenteric veins, producing a series of gastric, splenic, and small bowel varices. This patient underwent palliative chemotherapy, but died 7 months later. A 44-year-old woman had been recently diagnosed with melanoma on the toe and underwent a series of investigations.


Anatomy_Gray

Anatomy_Gray. This patient underwent palliative chemotherapy, but died 7 months later. A 44-year-old woman had been recently diagnosed with melanoma on the toe and underwent a series of investigations. Melanoma (properly called malignant melanoma) can be an aggressive form of skin cancer that spreads to lymph nodes and multiple other organs throughout the body. The malignant potential is dependent upon its cellular configuration and also the depth of its penetration through the skin. The patient developed malignant melanoma in the foot, which spread to the lymph nodes of the groin. The inguinal lymph nodes were resected; however, it was noted on follow-up imaging that the patient had developed two metastatic lesions within the right lobe of the liver. Surgeons and physicians considered the possibility of removing these lesions. A CT scan was performed that demonstrated the lesions within segments V and VI of the liver (Fig. 4.186).


Anatomy_Gray

Anatomy_Gray. Surgeons and physicians considered the possibility of removing these lesions. A CT scan was performed that demonstrated the lesions within segments V and VI of the liver (Fig. 4.186). The segmental anatomy of the liver is important because it enables the surgical planning for resection. The surgery was undertaken and involved identifying the portal vein and the confluence of the right and left hepatic ducts. The liver was divided in the imaginary principal plane of the middle hepatic vein. The main hepatic duct and biliary radicals were ligated and the right liver was successfully resected. The segments remaining included the left lobe of the liver.


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Anatomy_Gray. The segments remaining included the left lobe of the liver. The patient underwent a surgical resection of segments V, VI, VII, and VIII. The remaining segments included IVa, IVb, I, II, and III. It is important to remember that the lobes of the liver do not correlate with the hepatic volume. The left lobe of the liver contains only segments II and III. The right lobe of the liver contains segments IV, V, VI, VII, and VIII. Hence, cross-sectional imaging is important when planning surgical segmental resection. A 55-year-old man developed severe jaundice and a massively distended abdomen. A diagnosis of cirrhosis of the liver was made, and further confirmatory tests demonstrated that the patient had significant ascites (free fluid within the peritoneal cavity). A liver biopsy was necessary to confirm the cirrhosis, but there was some debate about how this biopsy should be obtained (eFig. 4.187).


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Anatomy_Gray. In patients with cirrhosis it is important to determine the extent of the cirrhosis and the etiology. History, examination, and blood tests are useful and are supported by complex radiological investigations. To begin treatment and determine the prognosis, a sample of liver tissue must be obtained. However, there are important issues to consider when taking a liver biopsy from a patient with suspected cirrhosis. One issue is liver function. The liver function of patients with suspected liver disease is poor, as demonstrated by the patient’s jaundice—an inability to conjugate bilirubin. Importantly, because some liver products are blood-clotting factors involved in the clotting cascade, the blood-clotting ability of patients with severe liver disease is significantly impaired. These patients therefore have a high risk of bleeding. Another issue is the presence of ascites.


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Anatomy_Gray. Another issue is the presence of ascites. Normally the liver rests against the lateral and anterior abdominal walls. This direct contact can be useful for care after a liver biopsy has been obtained. After the procedure, the patient lies over the region where the biopsy has been obtained and the weight of the liver stems any localized bleeding. When patients have significant ascites, the liver cannot be compressed against the walls of the abdomen and blood may pour freely into the ascitic fluid. The patient has ascites, so another approach for a liver biopsy must be considered. The patient was referred to the radiology department for a transjugular liver biopsy.


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Anatomy_Gray. The patient has ascites, so another approach for a liver biopsy must be considered. The patient was referred to the radiology department for a transjugular liver biopsy. The skin around the jugular vein in the neck was anesthetized. Access was obtained through insertion of a needle and a guidewire. The guidewire was advanced through the right internal jugular vein and into the right brachiocephalic vein. It entered the superior vena cava, was passed along the posterior wall of the atrium, and entered the superior aspect of the inferior vena cava. A catheter was inserted over the wire and directed into the right hepatic vein. Using a series of dilators, the hole was enlarged and a biopsy needle was placed over the wire and into the right hepatic vein. The liver was biopsied through the right hepatic vein and the biopsy sample was removed. A simple suture was used to close the internal jugular vein in the neck, and minor compression stemmed any blood flow.


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Anatomy_Gray. Assuming that the biopsy needle does not penetrate the liver capsule, it is not important how much the patient bleeds from the liver, because this bleeding will enter the hepatic vein and is immediately returned to the circulation. A 30-year-old man had a diffuse and poorly defined epigastric mass. Further examination revealed asymmetrical scrotal enlargement. As part of her differential diagnosis, the resident considered the possibility that the man had testicular cancer with regional abdominal para-aortic nodal involvement (the lateral aortic, or lumbar, nodes). A primary testicular neoplasm is the most common tumor in men between the ages of 25 and 34 and accounts for between 1% and 2% of all malignancies in men. A family history of testicular cancer and maldescent of the testis are strong predisposing factors. Spread of the tumor is typically to the lymph node chains that drain the testes.


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Anatomy_Gray. Spread of the tumor is typically to the lymph node chains that drain the testes. The testes develop from structures adjacent to the renal vessels in the upper abdomen, between the transversalis fascia and the peritoneum. They normally migrate through the inguinal canals into the scrotum just before birth. The testes take with them their arterial supply, their venous drainage, their nerve supply, and their lymphatics. A computed tomography scan revealed a para-aortic lymph node mass in the upper abdomen and enlarged lymph nodes throughout the internal and common iliac lymph node chains. Assuming the scrotal mass was a carcinoma of the testes, which would normally drain into the lateral aortic (lumbar) nodes in the upper abdomen, it would be very unusual for iliac lymphadenopathy to be present. Further examination of the scrotal mass was required.


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Anatomy_Gray. Further examination of the scrotal mass was required. A transillumination test of the scrotum on the affected side was positive. An ultrasound scan revealed normal right and left testes and a large fluid collection around the right testis. A diagnosis of a right-sided hydrocele was made. Scrotal masses are common in young males, and determining the exact anatomical site of the scrotal mass is of utmost clinical importance. Any mass that arises from the testis should be investigated to exclude testicular cancer. Masses that arise from the epididymis and scrotal lesions, such as fluid (hydrocele) or hernias, are also clinically important but are not malignant. The ultrasound scan revealed fluid surrounding the testis, which is diagnostic of a hydrocele. Simple cysts arising from and around the epididymis (epididymal cysts) can be easily defined. A diagnosis of lymphoma was suspected.


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Anatomy_Gray. A diagnosis of lymphoma was suspected. Lymphoma is a malignant disease of lymph nodes. Most lymphomas are divided into two specific types, namely Hodgkin’s lymphoma and non-Hodgkin’s lymphoma. If caught early the prognosis following radical chemotherapy is excellent.


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Anatomy_Gray. The patient underwent a biopsy, which was performed from the posterior approach. He was placed in the prone position in the computed tomography (CT) scanner. A fine needle with a special cutting device was used to obtain a lymph node sample. A left-sided approach was used because the inferior vena cava is on the right side and the nodes were in the para-aortic regions (i.e., the biopsy needle would have to pass between the inferior vena cava and the aorta from a posterior approach, which is difficult). The skin was anesthetized using local anesthetic at the lateral border of the quadratus lumborum muscle. The needle was angled at approximately 45° within the quadratus lumborum muscle and entered the retroperitoneum to lie beside the left-sided para-aortic lymph nodes. Because this procedure is performed using CT guidance, the operator can advance the needle slowly, taking care not to “hit” other retroperitoneal structures.


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Anatomy_Gray. A good biopsy was obtained and the diagnosis was Hodgkin’s lymphoma. The patient underwent chemotherapy and 2 years later is in full remission and leads an active life. A 35-year-old man had a soft mass approximately 3 cm in diameter in the right scrotum. The diagnosis was a right indirect inguinal hernia. What were the examination findings? The mass was not tender and the physician was not able to “get above it.” The testes were felt separate from the mass, and a transillumination test (in which a bright light is placed behind the scrotum and the scrotal sac is viewed from the front) was negative. (A positive test occurs when the light penetrates through the scrotum.) When the patient stood up, a positive cough “impulse” was felt within the mass. After careful and delicate maneuvering, the mass could be massaged into the inguinal canal, so emptying from the scrotum. When the massaging hand was removed, the mass recurred in the scrotum.


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Anatomy_Gray. After careful and delicate maneuvering, the mass could be massaged into the inguinal canal, so emptying from the scrotum. When the massaging hand was removed, the mass recurred in the scrotum. An indirect inguinal hernia enters the inguinal canal through the deep inguinal ring. It passes through the inguinal canal to exit through the superficial inguinal ring in the aponeurosis of the external oblique muscle. The hernia sac lies superior and medial to the pubic tubercle and enters into the scrotum within the spermatic cord. A direct inguinal hernia passes directly through the posterior wall of the inguinal canal. It does not pass down the inguinal canal. If large enough, it may pass through the superficial inguinal ring and into the scrotum.


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Anatomy_Gray. A 25-year-old man developed severe pain in the left lower quadrant of his abdomen. The pain was diffuse and relatively constant but did ease for short periods of time. On direct questioning the patient indicated that the pain was in the inguinal region and radiated posteriorly into his left infrascapular region (loin). A urine dipstick was positive for blood (hematuria). A diagnosis of a ureteric stone (calculus) was made. The patient’s initial infrascapular pain, which later radiated to the left groin, relates to passage of the ureteric stone along the ureter. The origin of the pain relates to ureteral distention. A series of peristaltic waves along the ureter transport urine along the length of the ureter from the kidney to the bladder. As the ureteric stone obstructs the kidney, the ureter becomes distended, resulting in an exacerbation of the pain. The peristaltic waves are superimposed upon the distention, resulting in periods of exacerbation and periods of relief.


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Anatomy_Gray. The pain is referred. The visceral afferent (sensory) nerve fibers from the ureter pass into the spinal cord, entering the first and second lumbar segments of the spinal cord. Pain is thus referred to cutaneous regions innervated by somatic sensory nerves from the same spinal cord levels. The patient was investigated by a CT scan. Traditionally, a plain radiograph was used to look for the radiopaque stone (90% of renal stones are radiopaque) and this often proceeded to intravenous urography to determine precise location of renal stones. Currently, low-dose CT of the collecting system is used to visualize the renal stones and pinpoint the level of obstruction, using low radiation dose and no intravenous contrast.


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Anatomy_Gray. An ultrasound scan may also be useful to assess for pelvicaliceal dilation and may reveal stones at the pelviureteral junction or the vesicoureteric junction. Ultrasound is also valuable for assessing other causes of obstruction (e.g., tumors at and around the ureteric orifices in the bladder) and is particularly useful in pregnant women when imaging with the use of radiation is a concern. Usually an intravenous urogram would be carried out to enable assessment of the upper urinary tracts and precise location of the stone. Not infrequently, CT scans of the abdomen are also obtained. These scans not only give information about the kidneys, ureters, and bladder but also show the position of the stone and other associated pathology. If this patient’s infrascapular pain was on the right and predominantly within the right lower abdomen, appendicitis would also have to be excluded. A CT scan would enable differentiation of appendicitis and urinary colic.


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Anatomy_Gray. A 27-year-old woman was admitted to the surgical ward with appendicitis. She underwent an appendectomy. It was noted at operation that the appendix had perforated and there was pus within the abdominal cavity. The appendix was removed and the stump tied. The abdomen was washed out with warm saline solution. The patient initially made an uneventful recovery, but by day 7 she had become unwell, with pain over her right shoulder and spiking temperatures. This patient had developed an intraabdominal abscess. Any operation on the bowel may involve peritoneal contamination with fecal contents and fecal flora. This may not be appreciated at the time of the operation. Over the postoperative period an inflammatory reaction ensued and an abscess cavity developed, filling with pus. Typically, the observation chart revealed a “swinging” pyrexia (fever). The most common sites for abscess to develop are the pelvis and the hepatorenal recess.


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Anatomy_Gray. The most common sites for abscess to develop are the pelvis and the hepatorenal recess. When a patient is in the supine position, the lowest points in the abdominal and pelvic cavities are the posterior superior aspect of the peritoneal cavity (the hepatorenal recess) and, in women, the recto-uterine pouch (pouch of Douglas). The shoulder pain suggested that the abscess was in the hepatorenal recess and that the pain was referred from the diaphragm. The motor and sensory innervation of the diaphragm is from nerves C3 to C5. The somatic pain sensation from the parietal peritoneum covering the undersurface of the diaphragm is carried into the spinal cord by the phrenic nerve (C3 to C5) and is interpreted by the brain as coming from skin over the shoulder—a region supplied by other somatic sensory nerves entering the same levels of the spinal cord as those from the diaphragm. A chest radiograph demonstrated elevation of the right hemidiaphragm.


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Anatomy_Gray. A chest radiograph demonstrated elevation of the right hemidiaphragm. This elevation of the right hemidiaphragm was due to the pus tracking from the hepatorenal space around the lateral and anterior aspect of the liver to sit on top of the liver in a subphrenic position. An ultrasound scan demonstrated this collection of fluid. The abscess cavity could be clearly seen by placing the ultrasound probe between ribs XI and XII. The inferior border of the right lower lobe lies at rib X in the midaxillary line. When the probe is placed between ribs XI and XII the ultrasound waves pass between the intercostal muscles and the parietal pleura laterally on the chest wall, and continue through the parietal pleura overlying the diaphragm into the cavity of the abscess, which lies below the diaphragm.


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Anatomy_Gray. Drainage was not done by an intercostal route. Instead, using CT guidance and local anesthesia, a subcostal drain was established and 1 liter of pus was removed (eFig. 4.188). It is important to bear in mind that placing a drain through the pleural cavity into the abdominal cavity effectively allows intraabdominal pus to pass into the thoracic cavity, and that this may produce an empyema (pus in the pleural space). The patient made a slow and uneventful recovery.


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Anatomy_Gray. The patient made a slow and uneventful recovery. A 45-year-old man developed a low-grade rectal carcinoma just above the anorectal margin. He underwent an abdominoperineal resection of the tumor and was left with a left lower abdominal colostomy (see below). Unfortunately, the man’s wife left him for a number of reasons, including lack of sexual desire. He “turned to drink” and over the ensuing years developed cirrhosis. He was brought into the emergency room with severe bleeding from enlarged veins around his colostomy. An emergency transjugular intrahepatic portosystemic shunt was created, which stopped all bleeding (eFigs. 4.189 and 4.190). He is now doing well in a rehabilitation program. A colostomy was necessary because of the low site of the tumor.


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Anatomy_Gray. A colostomy was necessary because of the low site of the tumor. Carcinoma of the colon and rectum usually develops in older patients, but some people do get tumors early in life. Most tumors develop from benign polyps, which undergo malignant change. As the malignancy develops it invades through the wall of the bowel and then metastasizes to local lymphatics. The tumor extends within the wall for a few centimeters above and below its origin. Lymphatic spread is to local and regional lymph nodes and then to the pre-aortic lymph node chain. These drain eventually into the thoracic duct.


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Anatomy_Gray. When this man was assessed for surgery, the tumor was so close to the anal margin that resection of the sphincters was necessary to be certain that the tumor margins were clear. The bowel cannot be joined to the anus without sphincters because the patient would be fecally incontinent. At surgery the tumor was excised, including the locoregional lymph node chains and the peritumoral fat around the rectum. The free end of the sigmoid colon was brought through a hole in the anterior abdominal wall. The bowel was then carefully sutured to the anterior abdominal wall to allow placement of a bag to collect the feces. This is a colostomy. Contrary to their usual immediate negative reaction to having a bag on the anterior abdominal wall, most patients cope extremely well, especially if they have been cured of cancer.


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Anatomy_Gray. Contrary to their usual immediate negative reaction to having a bag on the anterior abdominal wall, most patients cope extremely well, especially if they have been cured of cancer. This patient’s pelvic nerves were damaged. The radical pelvic surgical dissection damaged the pelvic parasympathetic nerve supply necessary for erection of the penis. Unfortunately, this was not well explained to the patient, which in some part led to the failure of his relationship. With any radical surgery in the pelvis, the nerves that supply the penis or clitoris may be damaged, so interfering with sexual function. This patient was bleeding from stomal varices. As he developed a serious drinking problem, his liver became cirrhotic and this damaged the normal liver architecture. This in turn increased the blood pressure in the portal vein (portal hypertension).


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Anatomy_Gray. In patients with portal hypertension small anastomoses develop between the veins of the portal system and the veins of the systemic circulation. These portosystemic anastomoses are usually of little consequence; however, at the gastroesophageal junction, they lie in a submucosal and mucosal position and are subject to trauma. Torrential hemorrhage may occur from even minor trauma, and death may ensue following blood loss. These varices require urgent treatment, which includes injecting sclerosant substances, banding, and even surgical ligation.


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Anatomy_Gray. Fortunately, most of the other portosystemic anastomoses are of relatively little consequence. In patients with colostomies, small veins may develop between the veins of the large bowel (portal system drainage) and cutaneous veins on the anterior abdominal wall (systemic veins). If these veins become enlarged because of portal hypertension, they are subject to trauma as feces are passed through the colostomy. Torrential hemorrhage may ensue if they are damaged. A procedure was carried out to lower the portal pressure. To reduce the pressure in the portal vein in this patient, several surgical procedures were considered. These included sewing the side of the portal vein onto the inferior vena cava (portacaval shunt) and sewing the splenic vein onto the renal vein (a splenorenal shunt). These procedures, however, require a large abdominal incision and are extremely complex. As an alternative, it was decided to create a transjugular intrahepatic portosystemic shunt.


Anatomy_Gray

Anatomy_Gray. Creating a transjugular intrahepatic portosystemic shunt is a relatively new technique that may be carried out under local anesthesia. Using a right internal jugular approach, a long needle is placed through the internal jugular vein, the superior vena cava, and the right atrium, into the inferior vena cava. The right hepatic vein is cannulated and, with special steering wires, a needle is passed through the hepatic substance directly into the right branch of the portal vein. A small balloon is passed over the wire and through the hepatic substance and is inflated. After the balloon has been removed, a metallic stent (a flexible wire tube) is placed across this tract in the liver to keep it open. Blood now freely flows from the portal vein into the right hepatic vein, creating a portosystemic shunt.


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Anatomy_Gray. As a result of this procedure, the pressure in this patient’s portal system is lower and similar to that of the systemic venous system, so reducing the potential for bleeding at the portosystemic anastomoses (i.e., the colostomy). A 62-year-old man came to the emergency department with swelling of both legs and a large left varicocele (enlarged and engorged varicose veins around the left testis and within the left pampiniform plexus of veins). The patient was known to have a left renal cell carcinoma and was due to have this operated on the following week. Anatomically it is possible to link all of the findings with the renal cell carcinoma by knowing the biology of the tumor. Renal cell carcinoma tends to grow steadily and predictably. Typically, when the tumor is less than 3 to 4 cm, it remains confined to the kidney. Large tumors have the propensity to grow into the renal vein, the inferior vena cava and the right atrium and through the heart into the pulmonary artery.


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Anatomy_Gray. The tumor grew into the renal vein. As the tumor grew into the renal vein it blocked off all tributaries draining into the vein, the largest of which is the left testicular vein. This blockage of the left testicular vein caused a dilation of the veins around the left testis (a varicocele occurred). The swollen legs were accounted for by caval obstruction. The tumor grew along the renal vein and into the inferior vena cava toward the heart. Renal tumors can grow rapidly; in this case the tumor grew rapidly into the inferior vena cava, occluding it. This increased the pressure in the leg veins, resulting in swelling and pitting edema of the ankles. The patient unfortunately died on the operating table.


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Anatomy_Gray. The patient unfortunately died on the operating table. In this patient’s case, a “tongue” of tumor grew into the inferior vena cava. At the time of surgery, the initial dissection mobilized the kidney on its vascular pedicle; however, a large portion of tumor became detached in the inferior vena cava. The tumor embolus passed through the right atrium and right ventricle and occluded the pulmonary artery. This could not be cleared at the time of surgery, and the patient succumbed. A 65-year-old businessman came to the emergency department with severe lower abdominal pain that was predominantly central and left sided. He had pain radiating into the left loin, and he also noticed he was passing gas and fecal debris as he urinated. A CT scan of his abdomen and pelvis was performed (eFig. 4.191).


Anatomy_Gray

Anatomy_Gray. A CT scan of his abdomen and pelvis was performed (eFig. 4.191). The CT scan demonstrated a collection of fluid (likely a pelvic abscess) in the left iliac fossa. Associated with this collection of fluid was significant bowel wall thickening of the sigmoid colon and multiple small diverticula arising throughout the sigmoid colon. Gas was present in the bladder. An obstruction was noted in the left ureter and the left pelvicalyceal system. The patient underwent an urgent operation.


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Anatomy_Gray. The patient underwent an urgent operation. As the surgeons entered into the abdominal cavity through a midline incision, the tissues in the left iliac fossa were significantly inflamed. The surgeon used his hand to mobilize the sigmoid colon and entered a cavity from which there was a “whoosh” of pus as indicated on the CT scan. The pus was washed out and drained. The sigmoid colon was remarkably thickened and inflamed and stuck to the dome of the bladder. Careful finger dissection revealed a small perforation in the dome of the bladder, allowing the passage of fecal material and gas into the bladder and producing the patient’s symptoms of pneumaturia and fecaluria. The sigmoid colon was resected. The rectal stump was oversewn and the descending colon was passed through the anterior abdominal wall to form a colostomy. The bladder was catheterized and the small hole in the dome of the bladder was oversewn.


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Anatomy_Gray. The patient had a difficult postoperative period in the intensive care unit where he remained pyrexial and septic. The colostomy began to function well. An ultrasound was performed and demonstrated the continued dilation in the left kidney, and the patient underwent a nephrostomy. Under ultrasound guidance a drainage catheter was placed into the renal pelvis through the renal cortex on the left. A significant amount of pus was drained from the renal tract initially; however, after 24 hours urine passed freely. The likely cause for the obstruction was the inflammation around the distal ureter on the left. It is also possible that a small ureteric perforation occurred, allowing bacteria to enter the urinary tract. The patient made a further uneventful recovery with resumption of normal renal function and left the hospital.


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Anatomy_Gray. The patient made a further uneventful recovery with resumption of normal renal function and left the hospital. On return to the surgeon in the outpatient clinic some weeks later, the patient did not wish to continue with his colostomy and bag. Further to discussion, surgery was planned to “rejoin” the patient. At operation the colostomy was “taken down” and the rectal stump was identified. There was, however, a significant gap between the bowel ends. To enable the bowel to be sutured, the descending colon was mobilized from the posterior abdominal wall. An anastomosis was performed and the patient left the hospital 1 week later and currently remains well. A 72-year-old man was brought to the emergency department with an abdominal aortic aneurysm (an expansion of the infrarenal abdominal aorta). The aneurysm measured 10 cm, and after discussion with the patient it was scheduled for repair. The surgical and endovascular treatment options were explained to the patient.


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Anatomy_Gray. The surgical and endovascular treatment options were explained to the patient. Treatment of abdominal aortic aneurysms has been, for many years, an operative procedure where the dilation (ballooning) of the aorta is resected and a graft is sewn into position. A modern option is to place a graft to line the aneurysm from within the artery (endovascular aneurysm repair). In this technique the surgeon dissects the femoral artery and makes a small hole in it. The graft is compressed within a catheter and the catheter is passed through the femoral artery and the iliac arterial system into the distal abdominal aorta. The graft can then be released inside the aorta, effectively relining it to prevent further expansion of the aneurysm. Occasionally the relined aneurysm may continue to enlarge after the endovascular graft has been placed and a cause needs to be identified.


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Anatomy_Gray. Occasionally the relined aneurysm may continue to enlarge after the endovascular graft has been placed and a cause needs to be identified. A Doppler ultrasound investigation of the abdomen and a CT scan revealed there was flow between the endovascular lining and the wall of the aneurysm. The likely sources for this bleeding were assessed. The graft usually begins below the level of the renal arteries and divides into two limbs that end in the common iliac arteries. The aneurysm may continue to be fed from any vessels between the graft and the aneurysm wall. These vessels can include the lumbar arteries and the inferior mesenteric artery. Interestingly, blood usually flows from the abdominal aorta into the inferior mesenteric artery and the lumbar arteries; however, with the changes in flow dynamics with the graft in place, blood may flow in the opposite direction through these branches, thereby leading to enlargement of the aneurysm.


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Anatomy_Gray. Blood flow was from the superior mesenteric artery into the aneurysm sac. Above the level of the graft the superior mesenteric artery arises normally. From the right colic and middle colic branches a marginal branch around the colon anastomoses, in the region of the splenic flexure, with marginal branches from the inferior mesenteric artery (this can become a hypertrophied vessel known as the marginal artery of Drummond). In this situation, blood passed retrogradely into the inferior mesenteric artery, filling the aneurysm and allowing it to remain pressurized and expand. The inferior mesenteric artery was ligated laparoscopically and the aneurysm failed to expand further. Over the ensuing 6 months the aneurysm contracted. The patient remains fit and healthy, with two small scars in the groin. 412.e1 412.e2 Fig. 4.1, cont’d Conceptual Overview • Relationship to Other Regions Fig. 4.13, cont’d Fig. 4.15, cont’d Fig. 4.47, cont’d. Fig. 4.50, cont’d In the clinic—cont’d


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Anatomy_Gray. 412.e1 412.e2 Fig. 4.1, cont’d Conceptual Overview • Relationship to Other Regions Fig. 4.13, cont’d Fig. 4.15, cont’d Fig. 4.47, cont’d. Fig. 4.50, cont’d In the clinic—cont’d In the clinic—cont’d In the clinic—cont’d In the clinic—cont’d In the clinic—cont’d In the clinic—cont’d In the clinic—cont’d In the clinic—cont’d In the clinic—cont’d In the clinic—cont’d Surface Anatomy • How to Find the Superficial Inguinal Ring Surface Anatomy • Visualizing Structures at the LI Vertebral Level Surface Anatomy • Using Abdominal Quadrants to Locate Major Viscera Surface Anatomy • Where to Find the Spleen The pelvis and perineum are interrelated regions associated with the pelvic bones and terminal parts of the vertebral column. The pelvis is divided into two regions: The superior region related to upper parts of the pelvic bones and lower lumbar vertebrae is the false pelvis (greater pelvis) and is generally considered part of the abdominal cavity (Fig. 5.1).


Anatomy_Gray

Anatomy_Gray. The superior region related to upper parts of the pelvic bones and lower lumbar vertebrae is the false pelvis (greater pelvis) and is generally considered part of the abdominal cavity (Fig. 5.1). The true pelvis (lesser pelvis) is related to the inferior parts of the pelvic bones, sacrum, and coccyx, and has an inlet and an outlet. The bowl-shaped pelvic cavity enclosed by the true pelvis consists of the pelvic inlet, walls, and floor. This cavity is continuous superiorly with the abdominal cavity and contains elements of the urinary, gastrointestinal, and reproductive systems. The perineum (Fig. 5.1) is inferior to the floor of the pelvic cavity; its boundaries form the pelvic outlet. The perineum contains the external genitalia and external openings of the genitourinary and gastrointestinal systems. Contains and supports the bladder, rectum, anal canal, and reproductive tracts


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Anatomy_Gray. Contains and supports the bladder, rectum, anal canal, and reproductive tracts Within the pelvic cavity, the bladder is positioned anteriorly and the rectum posteriorly in the midline. As it fills, the bladder expands superiorly into the abdomen. It is supported by adjacent elements of the pelvic bone and by the pelvic floor. The urethra passes through the pelvic floor to the perineum, where, in women, it opens externally (Fig. 5.2A) and in men it enters the base of the penis (Fig. 5.2B). Continuous with the sigmoid colon at the level of vertebra SIII, the rectum terminates at the anal canal, which penetrates the pelvic floor to open into the perineum. The anal canal is angled posteriorly on the rectum. This flexure is maintained by muscles of the pelvic floor and is relaxed during defecation. A skeletal muscle sphincter is associated with the anal canal and the urethra as each passes through the pelvic floor.


Anatomy_Gray

Anatomy_Gray. The pelvic cavity contains most of the reproductive tract in women and part of the reproductive tract in men. In women, the vagina penetrates the pelvic floor and connects with the uterus in the pelvic cavity. The uterus is positioned between the rectum and the bladder. A uterine (fallopian) tube extends laterally on each side toward the pelvic wall to open near the ovary. In men, the pelvic cavity contains the site of connection between the urinary and reproductive tracts. It also contains major glands associated with the reproductive system—the prostate and two seminal vesicles. Anchors the roots of the external genitalia In both genders, the roots of the external genitalia, the clitoris and the penis, are firmly anchored to: the bony margin of the anterior half of the pelvic outlet, and a thick, fibrous, perineal membrane, which fills the area (Fig. 5.3). The roots of the external genitalia consist of erectile (vascular) tissues and associated skeletal muscles.


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Anatomy_Gray. The roots of the external genitalia consist of erectile (vascular) tissues and associated skeletal muscles. The pelvic inlet is somewhat heart shaped and completely ringed by bone (Fig. 5.4). Posteriorly, the inlet is bordered by the body of vertebra SI, which projects into the inlet as the sacral promontory. On each side of this vertebra, wing-like transverse processes called the alae (wings) contribute to the margin of the pelvic inlet. Laterally, a prominent rim on the pelvic bone continues the boundary of the inlet forward to the pubic symphysis, where the two pelvic bones are joined in the midline. Structures pass between the pelvic cavity and the abdomen through the pelvic inlet. During childbirth, the fetus passes through the pelvic inlet from the abdomen, into which the uterus has expanded during pregnancy, and then passes through the pelvic outlet.


Anatomy_Gray

Anatomy_Gray. During childbirth, the fetus passes through the pelvic inlet from the abdomen, into which the uterus has expanded during pregnancy, and then passes through the pelvic outlet. The walls of the true pelvis consist predominantly of bone, muscle, and ligaments, with the sacrum, coccyx, and inferior half of the pelvic bones forming much of them. Two ligaments—the sacrospinous and the sacrotuberous ligaments—are important architectural elements of the walls because they link each pelvic bone to the sacrum and coccyx (Fig. 5.5A). These ligaments also convert two notches on the pelvic bones—the greater and lesser sciatic notches—into foramina on the lateral pelvic walls. Completing the walls are the obturator internus and piriformis muscles (Fig. 5.5B), which arise in the pelvis and exit through the sciatic foramina to act on the hip joint. The diamond-shaped pelvic outlet is formed by both bone and ligaments (Fig. 5.6). It is limited anteriorly in the midline by the pubic symphysis.


Anatomy_Gray

Anatomy_Gray. The diamond-shaped pelvic outlet is formed by both bone and ligaments (Fig. 5.6). It is limited anteriorly in the midline by the pubic symphysis. On each side, the inferior margin of the pelvic bone projects posteriorly and laterally from the pubic symphysis to end in a prominent tuberosity, the ischial tuberosity. Together, these elements construct the pubic arch, which forms the margin of the anterior half of the pelvic outlet. The sacrotuberous ligament continues this margin posteriorly from the ischial tuberosity to the coccyx and sacrum. The pubic symphysis, ischial tuberosities, and coccyx can all be palpated. The pelvic floor, which separates the pelvic cavity from the perineum, is formed by muscles and fascia (Fig. 5.7).


Anatomy_Gray

Anatomy_Gray. The pelvic floor, which separates the pelvic cavity from the perineum, is formed by muscles and fascia (Fig. 5.7). Two levator ani muscles attach peripherally to the pelvic walls and join each other at the midline by a connective tissue raphe. Together they are the largest components of the bowlor funnel-shaped structure known as the pelvic diaphragm, which is completed posteriorly by the coccygeus muscles. These latter muscles overlie the sacrospinous ligaments and pass between the margins of the sacrum and the coccyx and a prominent spine on the pelvic bone, the ischial spine. The pelvic diaphragm forms most of the pelvic floor and in its anterior regions contains a U-shaped defect, which is associated with elements of the urogenital system. The anal canal passes from the pelvis to the perineum through a posterior circular orifice in the pelvic diaphragm. The pelvic floor is supported anteriorly by: the perineal membrane, and muscles in the deep perineal pouch.


Anatomy_Gray

Anatomy_Gray. The pelvic floor is supported anteriorly by: the perineal membrane, and muscles in the deep perineal pouch. The perineal membrane is a thick, triangular fascial sheet that fills the space between the arms of the pubic arch, and has a free posterior border (Fig. 5.7). The deep perineal pouch is a narrow region superior to the perineal membrane. The margins of the U-shaped defect in the pelvic diaphragm merge into the walls of the associated viscera and with muscles in the deep perineal pouch below. The vagina and the urethra penetrate the pelvic floor to pass from the pelvic cavity to the perineum. The pelvic cavity is lined by peritoneum continuous with the peritoneum of the abdominal cavity that drapes over the superior aspects of the pelvic viscera, but in most regions, does not reach the pelvic floor (Fig. 5.8A).


Anatomy_Gray

Anatomy_Gray. The pelvic viscera are located in the midline of the pelvic cavity. The bladder is anterior and the rectum is posterior. In women, the uterus lies between the bladder and rectum (Fig. 5.8B). Other structures, such as vessels and nerves, lie deep to the peritoneum in association with the pelvic walls and on either side of the pelvic viscera. The perineum lies inferior to the pelvic floor between the lower limbs (Fig. 5.9). Its margin is formed by the pelvic outlet. An imaginary line between the ischial tuberosities divides the perineum into two triangular regions. Anteriorly, the urogenital triangle contains the roots of the external genitalia and, in women, the openings of the urethra and the vagina (Fig. 5.9A). In men, the distal part of the urethra is enclosed by erectile tissues and opens at the end of the penis (Fig. 5.9B). Posteriorly, the anal triangle contains the anal aperture.


Anatomy_Gray

Anatomy_Gray. Posteriorly, the anal triangle contains the anal aperture. The cavity of the true pelvis is continuous with the abdominal cavity at the pelvic inlet (Fig. 5.10A). All structures passing between the pelvic cavity and abdomen, including major vessels, nerves, and lymphatics, as well as the sigmoid colon and ureters, pass via the inlet. In men, the ductus deferens on each side passes through the anterior abdominal wall and over the inlet to enter the pelvic cavity. In women, ovarian vessels, nerves, and lymphatics pass through the inlet to reach the ovaries, which lie on each side just inferior to the pelvic inlet. Three apertures in the pelvic wall communicate with the lower limb (Fig. 5.10A): the obturator canal, the greater sciatic foramen, and the lesser sciatic foramen.


Anatomy_Gray

Anatomy_Gray. Three apertures in the pelvic wall communicate with the lower limb (Fig. 5.10A): the obturator canal, the greater sciatic foramen, and the lesser sciatic foramen. The obturator canal forms a passageway between the pelvic cavity and the adductor region of the thigh, and is formed in the superior aspect of the obturator foramen, between bone, a connective tissue membrane, and muscles that fill the foramen. The lesser sciatic foramen, which lies inferior to the pelvic floor, provides communication between the gluteal region and the perineum (Fig. 5.10B). The pelvic cavity also communicates directly with the perineum through a small gap between the pubic symphysis and the perineal membrane (Fig. 5.10B). The pelvic cavity projects posteriorly


Anatomy_Gray

Anatomy_Gray. The pelvic cavity also communicates directly with the perineum through a small gap between the pubic symphysis and the perineal membrane (Fig. 5.10B). The pelvic cavity projects posteriorly In the anatomical position, the anterior superior iliac spines and the superior edge of the pubic symphysis lie in the same vertical plane (Fig. 5.11). Consequently, the pelvic inlet is angled 50°–60° forward relative to the horizontal plane, and the pelvic cavity projects posteriorly from the abdominal cavity. Meanwhile, the urogenital part of the pelvic outlet (the pubic arch) is oriented in a nearly horizontal plane, whereas the posterior part of the outlet is positioned more vertically. The urogenital triangle of the perineum therefore faces inferiorly, while the anal triangle faces more posteriorly. Important structures cross the ureters in the pelvic cavity


Anatomy_Gray

Anatomy_Gray. Important structures cross the ureters in the pelvic cavity The ureters drain the kidneys, course down the posterior abdominal wall, and cross the pelvic inlet to enter the pelvic cavity. They continue inferiorly along the lateral pelvic wall and ultimately connect with the base of the bladder. An important structure crosses the ureters in the pelvic cavity in both men and women—in women, the uterine artery crosses the ureter lateral to the cervix of the uterus (Fig. 5.12A), and in men, the ductus deferens crosses over the ureter just posterior to the bladder (Fig. 5.12B). The prostate in men and the uterus in women are anterior to the rectum In men, the prostate gland is situated immediately anterior to the rectum, just above the pelvic floor (Fig. 5.13). It can be felt by digital palpation during a rectal examination.


Anatomy_Gray

Anatomy_Gray. In men, the prostate gland is situated immediately anterior to the rectum, just above the pelvic floor (Fig. 5.13). It can be felt by digital palpation during a rectal examination. In both sexes, the anal canal and the lower rectum also can be evaluated during a rectal examination by a clinician. In women, the cervix and lower part of the body of the uterus also are palpable. However, these structures can more easily be palpated with a bimanual examination where the index and middle fingers of a clinician’s hand are placed in the vagina and the other hand is placed on the lower anterior abdominal wall. The organs are felt between the two hands. This bimanual technique can also be used to examine the ovaries and uterine tubes. The perineum is innervated by sacral spinal


Anatomy_Gray

Anatomy_Gray. The perineum is innervated by sacral spinal Dermatomes of the perineum in both men and women are from spinal cord levels S3 to S5, except for the anterior regions, which tend to be innervated by spinal cord level L1 by nerves associated with the abdominal wall (Fig. 5.14). Dermatomes of L2 to S2 are predominantly in the lower limb. Most of the skeletal muscles contained in the perineum and the pelvic floor, including the external anal sphincter and external urethral sphincter, are innervated by spinal cord levels S2 to S4. Much of the somatic motor and sensory innervation of the perineum is provided by the pudendal nerve from spinal cord levels S2 to S4. Nerves are related to bone


Anatomy_Gray

Anatomy_Gray. Much of the somatic motor and sensory innervation of the perineum is provided by the pudendal nerve from spinal cord levels S2 to S4. Nerves are related to bone The pudendal nerve is the major nerve of the perineum and is directly associated with the ischial spine of the pelvis (Fig. 5.15). On each side of the body, these spines and the attached sacrospinous ligaments separate the greater sciatic foramina from the lesser sciatic foramina on the lateral pelvic wall. The pudendal nerve leaves the pelvic cavity through the greater sciatic foramen and then immediately enters the perineum inferiorly to the pelvic floor by passing around the ischial spine and through the lesser sciatic foramen (Fig. 5.15). The ischial spine can be palpated transvaginally in women and is the landmark that can be used for administering a pudendal nerve block. Parasympathetic innervation from spinal cord levels S2 to S4 controls erection


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Anatomy_Gray. Parasympathetic innervation from spinal cord levels S2 to S4 controls erection The parasympathetic innervation from spinal cord levels S2 to S4 controls genital erection in both women and men (Fig. 5.16). On each side, preganglionic parasympathetic nerves leave the anterior rami of the sacral spinal nerves and enter the inferior hypogastric plexus (pelvic plexus) on the lateral pelvic wall. The two inferior hypogastric plexuses are inferior extensions of the abdominal prevertebral plexus that forms on the posterior abdominal wall in association with the abdominal aorta. Nerves derived from these plexuses penetrate the pelvic floor to innervate the erectile tissues of the clitoris in women and the penis in men. Muscles and fascia of the pelvic floor and perineum intersect at the perineal body


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Anatomy_Gray. Muscles and fascia of the pelvic floor and perineum intersect at the perineal body Structures of the pelvic floor intersect with structures in the perineum at the perineal body (Fig. 5.17). This poorly defined fibromuscular node lies at the center of the perineum, approximately midway between the two ischial tuberosities. Converging at the perineal body are: the levator ani muscles of the pelvic diaphragm, and muscles in the urogenital and anal triangles of the perineum, including the skeletal muscle sphincters associated with the urethra, vagina, and anus. The course of the urethra is different in men In women, the urethra is short and passes inferiorly from the bladder through the pelvic floor and opens directly into the perineum (Fig. 5.18A).


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Anatomy_Gray. The course of the urethra is different in men In women, the urethra is short and passes inferiorly from the bladder through the pelvic floor and opens directly into the perineum (Fig. 5.18A). In men the urethra passes through the prostate before coursing through the deep perineal pouch and perineal membrane and then becomes enclosed within the erectile tissues of the penis before opening at the end of the penis (Fig. 5.18B). The penile part of the male urethra has two angles: The more important of these is a fixed angle where the urethra bends anteriorly in the root of the penis after passing through the perineal membrane. Another angle occurs distally where the unattached part of the penis curves inferiorly—when the penis is erect, this second angle disappears. It is important to consider the different courses of the urethra in men and women when catheterizing patients and when evaluating perineal injuries and pelvic pathology.


Anatomy_Gray

Anatomy_Gray. It is important to consider the different courses of the urethra in men and women when catheterizing patients and when evaluating perineal injuries and pelvic pathology. The pelvis is the region of the body surrounded by the pelvic bones and the inferior elements of the vertebral column. It is divided into two major regions: the superior region is the false (greater) pelvis and is part of the abdominal cavity; the inferior region is the true (lesser) pelvis, which encloses the pelvic cavity. The bowl-shaped pelvic cavity is continuous above with the abdominal cavity. The rim of the pelvic cavity (the pelvic inlet) is completely encircled by bone. The pelvic floor is a fibromuscular structure separating the pelvic cavity above from the perineum below.


Anatomy_Gray

Anatomy_Gray. The perineum is inferior to the pelvic floor and its margin is formed by the pelvic outlet. The perineum contains: the terminal openings of the gastrointestinal and urinary systems, the external opening of the reproductive tract, and the roots of the external genitalia. The bones of the pelvis consist of the right and left pelvic (hip) bones, the sacrum, and the coccyx. The sacrum articulates superiorly with vertebra LV at the lumbosacral joint. The pelvic bones articulate posteriorly with the sacrum at the sacro-iliac joints and with each other anteriorly at the pubic symphysis. The pelvic bone is irregular in shape and has two major parts separated by an oblique line on the medial surface of the bone (Fig. 5.19A): The pelvic bone above this line represents the lateral wall of the false pelvis, which is part of the abdominal cavity. The pelvic bone below this line represents the lateral wall of the true pelvis, which contains the pelvic cavity.


Anatomy_Gray

Anatomy_Gray. The pelvic bone below this line represents the lateral wall of the true pelvis, which contains the pelvic cavity. The linea terminalis is the lower two-thirds of this line and contributes to the margin of the pelvic inlet. The lateral surface of the pelvic bone has a large articular socket, the acetabulum, which, together with the head of the femur, forms the hip joint (Fig. 5.19B). Inferior to the acetabulum is the large obturator foramen, most of which is closed by a flat connective tissue membrane, the obturator membrane. A small obturator canal remains open superiorly between the membrane and adjacent bone, providing a route of communication between the lower limb and the pelvic cavity. The posterior margin of the bone is marked by two notches separated by the ischial spine: the greater sciatic notch, and the lesser sciatic notch. The posterior margin terminates inferiorly as the large ischial tuberosity.


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Anatomy_Gray. The posterior margin terminates inferiorly as the large ischial tuberosity. The irregular anterior margin of the pelvic bone is marked by the anterior superior iliac spine, the anterior inferior iliac spine, and the pubic tubercle. Components of the pelvic bone Each pelvic bone is formed by three elements: the ilium, pubis, and ischium. At birth, these bones are connected by cartilage in the area of the acetabulum; later, at between 16 and 18 years of age, they fuse into a single bone (Fig. 5.20). Of the three components of the pelvic bone, the ilium is the most superior in position. The ilium is separated into upper and lower parts by a ridge on the medial surface (Fig. 5.21A).


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Anatomy_Gray. Of the three components of the pelvic bone, the ilium is the most superior in position. The ilium is separated into upper and lower parts by a ridge on the medial surface (Fig. 5.21A). Posteriorly, the ridge is sharp and lies immediately superior to the surface of the bone that articulates with the sacrum. This sacral surface has a large L-shaped facet for articulating with the sacrum and an expanded, posterior roughened area for the attachment of the strong ligaments that support the sacro-iliac joint (Fig. 5.21). Anteriorly, the ridge separating the upper and lower parts of the ilium is rounded and termed the arcuate line. The arcuate line forms part of the linea terminalis and the pelvic brim. The portion of the ilium lying inferiorly to the arcuate line is the pelvic part of the ilium and contributes to the wall of the lesser or true pelvis.


Anatomy_Gray

Anatomy_Gray. The portion of the ilium lying inferiorly to the arcuate line is the pelvic part of the ilium and contributes to the wall of the lesser or true pelvis. The upper part of the ilium expands to form a flat, fan-shaped “wing,” which provides bony support for the lower abdomen, or false pelvis. This part of the ilium provides attachment for muscles functionally associated with the lower limb. The anteromedial surface of the wing is concave and forms the iliac fossa. The external (gluteal) surface of the wing is marked by lines and roughenings and is related to the gluteal region of the lower limb (Fig. 5.21B). The entire superior margin of the ilium is thickened to form a prominent crest (the iliac crest), which is the site of attachment for muscles and fascia of the abdomen, back, and lower limb and terminates anteriorly as the anterior superior iliac spine and posteriorly as the posterior superior iliac spine.


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Anatomy_Gray. A prominent tubercle, the tuberculum of the iliac crest, projects laterally near the anterior end of the crest; the posterior end of the crest thickens to form the iliac tuberosity. Inferior to the anterior superior iliac spine of the crest, on the anterior margin of the ilium, is a rounded protuberance called the anterior inferior iliac spine. This structure serves as the point of attachment for the rectus femoris muscle of the anterior compartment of the thigh and the iliofemoral ligament associated with the hip joint. A less prominent posterior inferior iliac spine occurs along the posterior border of the sacral surface of the ilium, where the bone angles forward to form the superior margin of the greater sciatic notch. The anterior and inferior part of the pelvic bone is the pubis (Fig. 5.21). It has a body and two arms (rami).


Anatomy_Gray

Anatomy_Gray. The anterior and inferior part of the pelvic bone is the pubis (Fig. 5.21). It has a body and two arms (rami). The body is flattened dorsoventrally and articulates with the body of the pubic bone on the other side at the pubic symphysis. The body has a rounded pubic crest on its superior surface that ends laterally as the prominent pubic tubercle. The superior pubic ramus projects posterolaterally from the body and joins with the ilium and ischium at its base, which is positioned toward the acetabulum. The sharp superior margin of this triangular surface is termed the pecten pubis (pectineal line), which forms part of the linea terminalis of the pelvic bone and the pelvic inlet. Anteriorly, this line is continuous with the pubic crest, which also is part of the linea terminalis and pelvic inlet. The superior pubic ramus is marked on its inferior surface by the obturator groove, which forms the upper margin of the obturator canal.


Anatomy_Gray

Anatomy_Gray. The inferior ramus projects laterally and inferiorly to join with the ramus of the ischium. The ischium is the posterior and inferior part of the pelvic bone (Fig. 5.21). It has: a large body that projects superiorly to join with the ilium and the superior ramus of the pubis, and a ramus that projects anteriorly to join with the inferior ramus of the pubis. The posterior margin of the bone is marked by a prominent ischial spine that separates the lesser sciatic notch, below, from the greater sciatic notch, above. The most prominent feature of the ischium is a large tuberosity (the ischial tuberosity) on the posteroinferior aspect of the bone. This tuberosity is an important site for the attachment of lower limb muscles and for supporting the body when sitting.


Anatomy_Gray

Anatomy_Gray. The sacrum, which has the appearance of an inverted triangle, is formed by the fusion of the five sacral vertebrae (Fig. 5.22). The base of the sacrum articulates with vertebra LV, and its apex articulates with the coccyx. Each of the lateral surfaces of the bone bears a large L-shaped facet for articulation with the ilium of the pelvic bone. Posterior to the facet is a large roughened area for the attachment of ligaments that support the sacro-iliac joint. The superior surface of the sacrum is characterized by the superior aspect of the body of vertebra SI and is flanked on each side by an expanded wing-like transverse process termed the ala. The anterior edge of the vertebral body projects forward as the promontory. The anterior surface of the sacrum is concave; the posterior surface is convex. Because the transverse processes of adjacent sacral vertebrae fuse lateral to the position of the intervertebral foramina and lateral to the bifurcation of spinal nerves into posterior and


Anatomy_Gray

Anatomy_Gray. is convex. Because the transverse processes of adjacent sacral vertebrae fuse lateral to the position of the intervertebral foramina and lateral to the bifurcation of spinal nerves into posterior and anterior rami, the posterior and anterior rami of spinal nerves S1 to S4 emerge from the sacrum through separate foramina. There are four pairs of anterior sacral foramina on the anterior surface of the sacrum for anterior rami, and four pairs of posterior sacral foramina on the posterior surface for the posterior rami. The sacral canal is a continuation of the vertebral canal that terminates as the sacral hiatus.


Anatomy_Gray

Anatomy_Gray. The small terminal part of the vertebral column is the coccyx, which consists of four fused coccygeal vertebrae (Fig. 5.22) and, like the sacrum, has the shape of an inverted triangle. The base of the coccyx is directed superiorly. The superior surface bears a facet for articulation with the sacrum and two horns, or cornua, one on each side, that project upward to articulate or fuse with similar downward-projecting cornua from the sacrum. These processes are modified superior and inferior articular processes that are present on other vertebrae. Each lateral surface of the coccyx has a small rudimentary transverse process, extending from the first coccygeal vertebra. Vertebral arches are absent from coccygeal vertebrae; therefore no bony vertebral canal is present in the coccyx.


Anatomy_Gray

Anatomy_Gray. The sacrum articulates superiorly with the lumbar part of the vertebral column. The lumbosacral joints are formed between vertebra LV and the sacrum and consist of: the two zygapophysial joints, which occur between adjacent inferior and superior articular processes, and an intervertebral disc that joins the bodies of vertebrae LV and SI (Fig. 5.23A). These joints are similar to those between other vertebrae, with the exception that the sacrum is angled posteriorly on vertebra LV. As a result, the anterior part of the intervertebral disc between the two bones is thicker than the posterior part. The lumbosacral joints are reinforced by strong iliolumbar and lumbosacral ligaments that extend from the expanded transverse processes of vertebra LV to the ilium and the sacrum, respectively (Fig. 5.23B).


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Anatomy_Gray. The sacro-iliac joints transmit forces from the lower limbs to the vertebral column. They are synovial joints between the L-shaped articular facets on the lateral surfaces of the sacrum and similar facets on the iliac parts of the pelvic bones (Fig. 5.24A). The joint surfaces have an irregular contour and interlock to resist movement. The joints often become fibrous with age and may become completely ossified.


Anatomy_Gray

Anatomy_Gray. Each sacro-iliac joint is stabilized by three ligaments: the anterior sacro-iliac ligament, which is a thickening of the fibrous membrane of the joint capsule and runs anteriorly and inferiorly to the joint (Fig. 5.24B); the interosseous sacro-iliac ligament, which is the largest, strongest ligament of the three, and is positioned immediately posterosuperior to the joint and attaches to adjacent expansive roughened areas on the ilium and sacrum, thereby filling the gap between the two bones (Fig. 5.24A,C); and the posterior sacro-iliac ligament, which covers the interosseous sacro-iliac ligament (Fig. 5.24C).


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Anatomy_Gray. The pubic symphysis lies anteriorly between the adjacent surfaces of the pubic bones (Fig. 5.25). Each of the joint’s surfaces is covered by hyaline cartilage and is linked across the midline to adjacent surfaces by fibrocartilage. The joint is surrounded by interwoven layers of collagen fibers and the two major ligaments associated with it are: the superior pubic ligament, located above the joint, and the inferior pubic ligament, located below it. In the anatomical position, the pelvis is oriented so that the front edge of the top of the pubic symphysis and the anterior superior iliac spines lie in the same vertical plane (Fig. 5.26). As a consequence, the pelvic inlet, which marks the entrance to the pelvic cavity, is tilted to face anteriorly, and the bodies of the pubic bones and the pubic arch are positioned in a nearly horizontal plane facing the ground.


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Anatomy_Gray. The pelvises of women and men differ in a number of ways, many of which have to do with the passing of a baby through a woman’s pelvic cavity during childbirth. The pelvic inlet in women is circular (Fig. 5.27A) compared with the heart-shaped pelvic inlet (Fig. 5.27B) in men. The more circular shape is partly caused by the less distinct promontory and broader alae in women. The angle formed by the two arms of the pubic arch is larger in women (80°–85°) than it is in men (50°–60°). The ischial spines generally do not project as far medially into the pelvic cavity in women as they do in men. The true pelvis is cylindrical and has an inlet, a wall, and an outlet. The inlet is open, whereas the pelvic floor closes the outlet and separates the pelvic cavity, above, from the perineum, below.


Anatomy_Gray

Anatomy_Gray. The pelvic inlet is the circular opening between the abdominal cavity and the pelvic cavity through which structures traverse between the abdomen and pelvic cavity. It is completely surrounded by bones and joints (Fig. 5.28). The promontory of the sacrum protrudes into the inlet, forming its posterior margin in the midline. On either side of the promontory, the margin is formed by the alae of the sacrum. The margin of the pelvic inlet then crosses the sacro-iliac joint and continues along the linea terminalis (i.e., the arcuate line, the pecten pubis or pectineal line, and the pubic crest) to the pubic symphysis. The walls of the pelvic cavity consist of the sacrum, the coccyx, the pelvic bones inferior to the linea terminalis, two ligaments, and two muscles. Ligaments of the pelvic wall


Anatomy_Gray

Anatomy_Gray. The walls of the pelvic cavity consist of the sacrum, the coccyx, the pelvic bones inferior to the linea terminalis, two ligaments, and two muscles. Ligaments of the pelvic wall The sacrospinous and sacrotuberous ligaments (Fig. 5.29A) are major components of the lateral pelvic walls that help define the apertures between the pelvic cavity and adjacent regions through which structures pass. The smaller of the two, the sacrospinous ligament, is triangular, with its apex attached to the ischial spine and its base attached to the related margins of the sacrum and the coccyx. The sacrotuberous ligament is also triangular and is superficial to the sacrospinous ligament. Its base has a broad attachment that extends from the posterior superior iliac spine of the pelvic bone, along the dorsal aspect and the lateral margin of the sacrum, and onto the dorsolateral surface of the coccyx. Laterally, the apex of the ligament is attached to the medial margin of the ischial tuberosity.


Anatomy_Gray

Anatomy_Gray. These ligaments stabilize the sacrum on the pelvic bones by resisting the upward tilting of the inferior aspect of the sacrum (Fig. 5.29B). They also convert the greater and lesser sciatic notches of the pelvic bone into foramina (Fig. 5.29A,B). The greater sciatic foramen lies superior to the sacrospinous ligament and the ischial spine. The lesser sciatic foramen lies inferior to the ischial spine and sacrospinous ligament between the sacrospinous and sacrotuberous ligaments. Muscles of the pelvic wall Two muscles, the obturator internus and the piriformis, contribute to the lateral walls of the pelvic cavity. These muscles originate in the pelvic cavity but attach peripherally to the femur. The obturator internus is a flat, fan-shaped muscle that originates from the deep surface of the obturator membrane and from associated regions of the pelvic bone that surround the obturator foramen (Fig. 5.30 and Table 5.1).


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Anatomy_Gray. The muscle fibers of the obturator internus converge to form a tendon that leaves the pelvic cavity through the lesser sciatic foramen, makes a 90° bend around the ischium between the ischial spine and ischial tuberosity, and then passes posterior to the hip joint to insert on the greater trochanter of the femur. The obturator internus forms a large part of the anterolateral wall of the pelvic cavity. The piriformis is triangular and originates in the bridges of bone between the four anterior sacral foramina. It passes laterally through the greater sciatic foramen, crosses the posterosuperior aspect of the hip joint, and inserts on the greater trochanter of the femur above the insertion of the obturator internus muscle (Fig. 5.30 and Table 5.1).


Anatomy_Gray

Anatomy_Gray. A large part of the posterolateral wall of the pelvic cavity is formed by the piriformis. In addition, this muscle separates the greater sciatic foramen into two regions, one above the muscle and one below. Vessels and nerves coursing between the pelvic cavity and the gluteal region pass through these two regions. Apertures in the pelvic wall Each lateral pelvic wall has three major apertures through which structures pass between the pelvic cavity and other regions: the obturator canal, the greater sciatic foramen, and the lesser sciatic foramen. At the top of the obturator foramen is the obturator canal, which is bordered by the obturator membrane, the associated obturator muscles, and the superior pubic ramus (Fig. 5.31). The obturator nerve and vessels pass from the pelvic cavity to the thigh through this canal.


Anatomy_Gray

Anatomy_Gray. The greater sciatic foramen is a major route of communication between the pelvic cavity and the lower limb (Fig. 5.31). It is formed by the greater sciatic notch in the pelvic bone, the sacrotuberous and the sacrospinous ligaments, and the spine of the ischium. The piriformis muscle passes through the greater sciatic foramen, dividing it into two parts. The superior gluteal nerves and vessels pass through the foramen above the piriformis. Passing through the foramen below the piriformis are the inferior gluteal nerves and vessels, the sciatic nerve, the pudendal nerve, the internal pudendal vessels, the posterior femoral cutaneous nerves, and the nerves to the obturator internus and quadratus femoris muscles. The lesser sciatic foramen is formed by the lesser sciatic notch of the pelvic bone, the ischial spine, the sacrospinous ligament, and the sacrotuberous ligament (Fig. 5.31).


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Anatomy_Gray. The lesser sciatic foramen is formed by the lesser sciatic notch of the pelvic bone, the ischial spine, the sacrospinous ligament, and the sacrotuberous ligament (Fig. 5.31). The tendon of the obturator internus muscle passes through this foramen to enter the gluteal region of the lower limb. Because the lesser sciatic foramen is positioned below the attachment of the pelvic floor, it acts as a route of communication between the perineum and the gluteal region. The pudendal nerve and internal pudendal vessels pass between the pelvic cavity (above the pelvic floor) and the perineum (below the pelvic floor), by first passing out of the pelvic cavity through the greater sciatic foramen and then looping around the ischial spine and sacrospinous ligament to pass through the lesser sciatic foramen to enter the perineum. The nerve to obturator internus follows a similar course.


Anatomy_Gray

Anatomy_Gray. The pelvic outlet is diamond shaped, with the anterior part of the diamond defined predominantly by bone and the posterior part mainly by ligaments (Fig. 5.32). In the midline anteriorly, the boundary of the pelvic outlet is the pubic symphysis. Extending laterally and posteriorly, the boundary on each side is the inferior border of the body of the pubis, the inferior ramus of the pubis, the ramus of the ischium, and the ischial tuberosity. Together, the elements on both sides form the pubic arch. From the ischial tuberosities, the boundaries continue posteriorly and medially along the sacrotuberous ligament on both sides to the coccyx. Terminal parts of the urinary and gastrointestinal tracts and the vagina pass through the pelvic outlet. The area enclosed by the boundaries of the pelvic outlet and below the pelvic floor is the perineum.


Anatomy_Gray

Anatomy_Gray. The area enclosed by the boundaries of the pelvic outlet and below the pelvic floor is the perineum. The pelvic floor is formed by the pelvic diaphragm and, in the anterior midline, the perineal membrane and the muscles in the deep perineal pouch. The pelvic diaphragm is formed by the levator ani and the coccygeus muscles from both sides. The pelvic floor separates the pelvic cavity, above, from the perineum, below. The pelvic diaphragm The pelvic diaphragm is the muscular part of the pelvic floor. Shaped like a bowl or funnel and attached superiorly to the pelvic walls, it consists of the levator ani and the coccygeus muscles (Fig. 5.34 and Table 5.2).


Anatomy_Gray

Anatomy_Gray. The pelvic diaphragm’s circular line of attachment to the cylindrical pelvic wall passes, on each side, between the greater sciatic foramen and the lesser sciatic foramen. Thus: the greater sciatic foramen is situated above the level of the pelvic floor and is a route of communication between the pelvic cavity and the gluteal region of the lower limb; and the lesser sciatic foramen is situated below the pelvic floor, providing a route of communication between the gluteal region of the lower limb and the perineum. The two levator ani muscles originate from each side of the pelvic wall, course medially and inferiorly, and join together in the midline. The attachment to the pelvic wall follows the circular contour of the wall and includes: the posterior aspect of the body of the pubic bone, a linear thickening called the tendinous arch, in the fascia covering the obturator internus muscle, and the spine of the ischium.


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Anatomy_Gray. At the midline, the muscles blend together posterior to the vagina in women and around the anal aperture in both sexes. Posterior to the anal aperture, the muscles come together as a ligament or raphe called the anococcygeal ligament (anococcygeal body) and attaches to the coccyx. Anteriorly, the muscles are separated by a U-shaped defect or gap termed the urogenital hiatus. The margins of this hiatus merge with the walls of the associated viscera and with muscles in the deep perineal pouch below. The hiatus allows the urethra (in both men and women), and the vagina (in women), to pass through the pelvic diaphragm (Fig. 5.34). The levator ani muscles are divided into at least three collections of muscle fibers, based on site of origin and relationship to viscera in the midline: the pubococcygeus, the puborectalis, and the iliococcygeus muscles.


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Anatomy_Gray. The pubococcygeus originates from the body of the pubis and courses posteriorly to attach along the midline as far back as the coccyx. This part of the muscle is further subdivided on the basis of association with structures in the midline into the puboprostaticus (levator prostatae), the pubovaginalis, and the puboanalis muscles. A second major collection of muscle fibers, the puborectalis portion of the levator ani muscles, originates, in association with the pubococcygeus muscle, from the pubis and passes inferiorly on each side to form a sling around the terminal part of the gastrointestinal tract. This muscular sling maintains an angle or flexure, called the perineal flexure, at the anorectal junction. This angle functions as part of the mechanism that keeps the end of the gastrointestinal system closed.


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Anatomy_Gray. The final part of the levator ani muscle is the iliococcygeus. This part of the muscle originates from the fascia that covers the obturator internus muscle. It joins the same muscle on the other side in the midline to form a ligament or raphe that extends from the anal aperture to the coccyx. The levator ani muscles help support the pelvic viscera and maintain closure of the rectum and vagina. They are innervated directly by branches from the anterior ramus of S4 and by branches of the pudendal nerve (S2 to S4). The two coccygeus muscles, one on each side, are triangular and overlie the sacrospinous ligaments; together they complete the posterior part of the pelvic diaphragm (Fig. 5.34 and Table 5.2). They are attached, by their apices, to the tips of the ischial spines and, by their bases, to the lateral margins of the coccyx and adjacent margins of the sacrum.


Anatomy_Gray

Anatomy_Gray. The coccygeus muscles are innervated by branches from the anterior rami of S3 and S4 and participate in supporting the posterior aspect of the pelvic floor. The perineal membrane and deep The perineal membrane is a thick fascial, triangular structure attached to the bony framework of the pubic arch (Fig. 5.36A). It is oriented in the horizontal plane and has a free posterior margin. Anteriorly, there is a small gap (blue arrow in Fig. 5.36A) between the membrane and the inferior pubic ligament (a ligament associated with the pubic symphysis). The perineal membrane is related above to a thin space called the deep perineal pouch (deep perineal space) (Fig. 5.36B), which contains a layer of skeletal muscle and various neurovascular elements.


Anatomy_Gray

Anatomy_Gray. The deep perineal pouch is open above and is not separated from more superior structures by a distinct layer of fascia. The parts of the perineal membrane and structures in the deep perineal pouch, enclosed by the urogenital hiatus above, therefore contribute to the pelvic floor and support elements of the urogenital system in the pelvic cavity, even though the perineal membrane and deep perineal pouch are usually considered parts of the perineum. The perineal membrane and adjacent pubic arch provide attachment for the roots of the external genitalia and the muscles associated with them (Fig. 5.36C). The urethra penetrates vertically through a circular hiatus in the perineal membrane as it passes from the pelvic cavity, above, to the perineum, below. In women, the vagina also passes through a hiatus in the perineal membrane just posterior to the urethral hiatus.


Anatomy_Gray

Anatomy_Gray. Within the deep perineal pouch, a sheet of skeletal muscle functions as a sphincter, mainly for the urethra, and as a stabilizer of the posterior edge of the perineal membrane (Fig. 5.37 and Table 5.3). Anteriorly, a group of muscle fibers surround the urethra and collectively form the external urethral sphincter. Two additional groups of muscle fibers are associated with the urethra and vagina in women. One group forms the sphincter urethrovaginalis, which surrounds the urethra and vagina as a unit. The second group forms the compressor urethrae, on each side, which originate from the ischiopubic rami and meet anterior to the urethra. Together with the external urethral sphincter, the sphincter urethrovaginalis and compressor urethrae facilitate closing of the urethra.


Anatomy_Gray

Anatomy_Gray. In both men and women, a deep transverse perineal muscle on each side parallels the free margin of the perineal membrane and joins with its partner at the midline. These muscles are thought to stabilize the position of the perineal body, which is a midline structure along the posterior edge of the perineal membrane. The perineal body is an ill-defined but important connective tissue structure into which muscles of the pelvic floor and the perineum attach (Fig. 5.38). It is positioned in the midline along the posterior border of the perineal membrane, to which it attaches. The posterior end of the urogenital hiatus in the levator ani muscles is also connected to it.


Anatomy_Gray

Anatomy_Gray. The deep transverse perineal muscles intersect at the perineal body; in women, the sphincter urethrovaginalis also attaches to the perineal body. Other muscles that connect to the perineal body include the external anal sphincter, the superficial transverse perineal muscles, and the bulbospongiosus muscles of the perineum. The pelvic viscera include parts of the gastrointestinal system, the urinary system, and the reproductive system. The viscera are arranged in the midline, from front to back; the neurovascular supply is through branches that pass medially from vessels and nerves associated with the pelvic walls. Pelvic parts of the gastrointestinal system consist mainly of the rectum and the anal canal, although the terminal part of the sigmoid colon is also in the pelvic cavity (Fig. 5.39).


Anatomy_Gray

Anatomy_Gray. Pelvic parts of the gastrointestinal system consist mainly of the rectum and the anal canal, although the terminal part of the sigmoid colon is also in the pelvic cavity (Fig. 5.39). The rectum is continuous: above, with the sigmoid colon at about the level of vertebra SIII, and below, with the anal canal as this structure penetrates the pelvic floor and passes through the perineum to end as the anus. The rectum, the most posterior element of the pelvic viscera, is immediately anterior to and follows the concave contour of the sacrum. The anorectal junction is pulled forward (perineal flexure) by the action of the puborectalis part of the levator ani muscle, so the anal canal moves in a posterior direction as it passes inferiorly through the pelvic floor.


Anatomy_Gray

Anatomy_Gray. In addition to conforming to the general curvature of the sacrum in the anteroposterior plane, the rectum has three lateral curvatures; the upper and lower curvatures to the right and the middle curvature to the left. The lower part of the rectum is expanded to form the rectal ampulla. Finally, unlike the colon, the rectum lacks distinct taeniae coli muscles, omental appendices, and sacculations (haustra of the colon). The anal canal begins at the terminal end of the rectal ampulla where it narrows at the pelvic floor. It terminates as the anus after passing through the perineum. As it passes through the pelvic floor, the anal canal is surrounded along its entire length by the internal and external anal sphincters, which normally keep it closed.


Anatomy_Gray

Anatomy_Gray. The lining of the anal canal bears a number of characteristic structural features that reflect the approximate position of the anococcygeal membrane in the fetus (which closes the terminal end of the developing gastrointestinal system in the fetus) and the transition from gastrointestinal mucosa to skin in the adult (Fig. 5.39B). The upper part of the anal canal is lined by mucosa similar to that lining the rectum and is distinguished by a number of longitudinally oriented folds known as anal columns, which are united inferiorly by crescentic folds termed anal valves. Superior to each valve is a depression termed an anal sinus. The anal valves together form a circle around the anal canal at a location known as the pectinate line, which marks the approximate position of the anal membrane in the fetus.


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Anatomy_Gray. Inferior to the pectinate line is a transition zone known as the anal pecten, which is lined by nonkeratinized stratified squamous epithelium. The anal pecten ends inferiorly at the anocutaneous line (“white line”), or where the lining of the anal canal becomes true skin. Given the position of the colon and rectum in the abdominopelvic cavity and its proximity to other organs, it is extremely important to accurately stage colorectal tumors: a tumor in the pelvis, for example, could invade the uterus or bladder. Assessing whether spread has occurred may involve ultrasound scanning, computed tomography, and magnetic resonance imaging. The pelvic parts of the urinary system consist of the terminal parts of the ureters, the bladder, and the proximal part of the urethra (Fig. 5.40).


Anatomy_Gray

Anatomy_Gray. The pelvic parts of the urinary system consist of the terminal parts of the ureters, the bladder, and the proximal part of the urethra (Fig. 5.40). The ureters enter the pelvic cavity from the abdomen by passing through the pelvic inlet. On each side, the ureter crosses the pelvic inlet and enters the pelvic cavity in the area anterior to the bifurcation of the common iliac artery. From this point, it continues along the pelvic wall and floor to join the base of the bladder. In the pelvis, the ureter is crossed by: the ductus deferens in men, and the uterine artery in women. The bladder is the most anterior element of the pelvic viscera. Although it is entirely situated in the pelvic cavity when empty, it expands superiorly into the abdominal cavity when full (Fig. 5.40). The empty bladder is shaped like a three-sided pyramid that has tipped over to lie on one of its margins (Fig. 5.41A). It has an apex, a base, a superior surface, and two inferolateral surfaces.


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Anatomy_Gray. The empty bladder is shaped like a three-sided pyramid that has tipped over to lie on one of its margins (Fig. 5.41A). It has an apex, a base, a superior surface, and two inferolateral surfaces. The apex of the bladder is directed toward the top of the pubic symphysis; a structure known as the median umbilical ligament (a remnant of the embryological urachus that contributes to the formation of the bladder) continues from it superiorly up the anterior abdominal wall to the umbilicus.


Anatomy_Gray

Anatomy_Gray. The base of the bladder is shaped like an inverted triangle and faces posteroinferiorly. The two ureters enter the bladder at each of the upper corners of the base, and the urethra drains inferiorly from the lower corner of the base. Inside, the mucosal lining on the base of the bladder is smooth and firmly attached to the underlying smooth muscle coat of the wall—unlike elsewhere in the bladder where the mucosa is folded and loosely attached to the wall. The smooth triangular area between the openings of the ureters and urethra on the inside of the bladder is known as the trigone (Fig. 5.41B). The inferolateral surfaces of the bladder are cradled between the levator ani muscles of the pelvic diaphragm and the adjacent obturator internus muscles above the attachment of the pelvic diaphragm. The superior surface is slightly domed when the bladder is empty; it balloons upward as the bladder fills. Neck of bladder


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Anatomy_Gray. Neck of bladder The neck of the bladder surrounds the origin of the urethra at the point where the two inferolateral surfaces and the base intersect. The neck is the most inferior part of the bladder and also the most “fixed” part. It is anchored into position by a pair of tough fibromuscular bands, which connect the neck and pelvic part of the urethra to the posteroinferior aspect of each pubic bone. In women, these fibromuscular bands are termed pubovesical ligaments (Fig. 5.42A). Together with the perineal membrane and associated muscles, the levator ani muscles, and the pubic bones, these ligaments help support the bladder. In men, the paired fibromuscular bands are known as puboprostatic ligaments because they blend with the fibrous capsule of the prostate, which surrounds the neck of the bladder and adjacent part of the urethra (Fig. 5.42B).


Anatomy_Gray

Anatomy_Gray. Although the bladder is considered to be pelvic in the adult, it has a higher position in children. At birth, the bladder is almost entirely abdominal; the urethra begins approximately at the upper margin of the pubic symphysis. With age, the bladder descends until after puberty when it assumes the adult position. The urethra begins at the base of the bladder and ends with an external opening in the perineum. The paths taken by the urethra differ significantly in women and men. In women, the urethra is short, being about 4 cm long. It travels a slightly curved course as it passes inferiorly through the pelvic floor into the perineum, where it passes through the deep perineal pouch and perineal membrane before opening in the vestibule that lies between the labia minora (Fig. 5.45A).


Anatomy_Gray

Anatomy_Gray. The urethral opening is anterior to the vaginal opening in the vestibule. The inferior aspect of the urethra is bound to the anterior surface of the vagina. Two small para- urethral mucous glands (Skene’s glands) are associated with the lower end of the urethra. Each drains via a duct that opens onto the lateral margin of the external urethral orifice. In men, the urethra is long, about 20 cm, and bends twice along its course (Fig. 5.45B). Beginning at the base of the bladder and passing inferiorly through the prostate, it passes through the deep perineal pouch and perineal membrane and immediately enters the root of the penis. As the urethra exits the deep perineal pouch, it bends forward to course anteriorly in the root of the penis. When the penis is flaccid, the urethra makes another bend, this time inferiorly, when passing from the root to the body of the penis. During erection, the bend between the root and body of the penis disappears.


Anatomy_Gray

Anatomy_Gray. The urethra in men is divided into preprostatic, prostatic, membranous, and spongy parts. Preprostatic part. The preprostatic part of the urethra is about 1 cm long, extends from the base of the bladder to the prostate, and is associated with a circular cuff of smooth muscle fibers (the internal urethral sphincter). Contraction of this sphincter prevents retrograde movement of semen into the bladder during ejaculation. Prostatic part. The prostatic part of the urethra (Fig. 5.45C) is 3 to 4 cm long and is surrounded by the prostate. In this region, the lumen of the urethra is marked by a longitudinal midline fold of mucosa (the urethral crest). The depression on each side of the crest is the prostatic sinus; the ducts of the prostate empty into these two sinuses.


Anatomy_Gray

Anatomy_Gray. Midway along its length, the urethral crest is enlarged to form a somewhat circular elevation (the seminal colliculus). In men, the seminal colliculus is used to determine the position of the prostate gland during transurethral transection of the prostate. A small blind-ended pouch—the prostatic utricle (thought to be the homologue of the uterus in women)—opens onto the center of the seminal colliculus. On each side of the prostatic utricle is the opening of the ejaculatory duct of the male reproductive system. Therefore the connection between the urinary and reproductive tracts in men occurs in the prostatic part of the urethra. Membranous part. The membranous part of the urethra is narrow and passes through the deep perineal pouch (Fig. 5.45B). During its transit through this pouch, the urethra, in both men and women, is surrounded by skeletal muscle of the external urethral sphincter.


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Anatomy_Gray. Spongy urethra. The spongy urethra is surrounded by erectile tissue (the corpus spongiosum) of the penis. It is enlarged to form a bulb at the base of the penis and again at the end of the penis to form the navicular fossa (Fig. 5.45B). The two bulbo-urethral glands in the deep perineal pouch are part of the male reproductive system and open into the bulb of the spongy urethra. The external urethral orifice is the sagittal slit at the end of the penis. The reproductive system in men has components in the abdomen, pelvis, and perineum (Fig. 5.47A). The major components are a testis, epididymis, ductus deferens, and ejaculatory duct on each side, and the urethra and penis in the midline. In addition, three types of accessory glands are associated with the system: a single prostate, a pair of seminal vesicles, and a pair of bulbo-urethral glands.


Anatomy_Gray

Anatomy_Gray. The design of the reproductive system in men is basically a series of ducts and tubules. The arrangement of parts and linkage to the urinary tract reflects its embryological development. The testes originally develop high on the posterior abdominal wall and then descend, normally before birth, through the inguinal canal in the anterior abdominal wall and into the scrotum of the perineum. During descent, the testes carry their vessels, lymphatics, and nerves, as well as their principal drainage ducts, the ductus deferens (vas deferens) with them. The lymph drainage of the testes is therefore to the lateral aortic or lumbar nodes and pre-aortic nodes in the abdomen, and not to the inguinal or pelvic lymph nodes.


Anatomy_Gray

Anatomy_Gray. Each ellipsoid-shaped testis is enclosed within the end of an elongated musculofascial pouch, which is continuous with the anterior abdominal wall and projects into the scrotum. The spermatic cord is the tube-shaped connection between the pouch in the scrotum and the abdominal wall. The sides and anterior aspect of the testis are covered by a closed sac of peritoneum (the tunica vaginalis), which originally connected to the abdominal cavity. Normally after testicular descent, the connection closes, leaving a fibrous remnant.


Anatomy_Gray

Anatomy_Gray. Each testis (Fig. 5.47B) is composed of seminiferous tubules and interstitial tissue surrounded by a thick connective tissue capsule (the tunica albuginea). Spermatozoa are produced by the seminiferous tubules. The 400 to 600 highly coiled seminiferous tubules are modified at each end to become straight tubules, which connect to a collecting chamber (the rete testis) in a thick, vertically oriented linear wedge of connective tissue (the mediastinum testis), projecting from the capsule into the posterior aspect of the gonad. Approximately 12 to 20 efferent ductules originate from the upper end of the rete testis, penetrate the capsule, and connect with the epididymis.


Anatomy_Gray

Anatomy_Gray. The epididymis courses along the posterolateral side of the testis (Fig. 5.47B). It has two distinct components: the efferent ductules, which form an enlarged coiled mass that sits on the posterior superior pole of the testis and forms the head of the epididymis; and the true epididymis, which is a single, long coiled duct into which the efferent ductules all drain, and which continues inferiorly along the posterolateral margin of the testis as the body of the epididymis and enlarges to form the tail of the epididymis at the inferior pole of the testis. During passage through the epididymis, spermatozoa acquire the ability to move and fertilize an egg. The epididymis also stores spermatozoa until ejaculation. The end of the epididymis is continuous with the ductus deferens.


Anatomy_Gray

Anatomy_Gray. The ductus deferens is a long muscular duct that transports spermatozoa from the tail of the epididymis in the scrotum to the ejaculatory duct in the pelvic cavity (Fig. 5.47A). It ascends in the scrotum as a component of the spermatic cord and passes through the inguinal canal in the anterior abdominal wall. After passing through the deep inguinal ring, the ductus deferens bends medially around the lateral side of the inferior epigastric artery and crosses the external iliac artery and the external iliac vein at the pelvic inlet to enter the pelvic cavity. The duct descends medially on the pelvic wall, deep to the peritoneum, and crosses the ureter posterior to the bladder. It continues inferomedially along the base of the bladder, anterior to the rectum, almost to the midline, where it is joined by the duct of the seminal vesicle to form the ejaculatory duct.


Anatomy_Gray

Anatomy_Gray. Between the ureter and ejaculatory duct, the ductus deferens expands to form the ampulla of the ductus deferens. The ejaculatory duct penetrates through the prostate gland to connect with the prostatic urethra. Each seminal vesicle is an accessory gland of the male reproductive system that develops as a blind-ended tubular outgrowth from the ductus deferens (Fig. 5.47A). The tube is coiled with numerous pocket-like outgrowths and is encapsulated by connective tissue to form an elongate structure situated between the bladder and rectum. The seminal vesicle is immediately lateral to and follows the course of the ductus deferens at the base of the bladder. The duct of the seminal vesicle joins the ductus deferens to form the ejaculatory duct (Fig. 5.48). Secretions from the seminal vesicle contribute significantly to the volume of the ejaculate (semen).


Anatomy_Gray

Anatomy_Gray. The prostate is an unpaired accessory structure of the male reproductive system that surrounds the urethra in the pelvic cavity (Figs. 5.47A and 5.48). It lies immediately inferior to the bladder, posterior to the pubic symphysis, and anterior to the rectum. The prostate is shaped like an inverted rounded cone with a larger base, which is continuous above with the neck of the bladder, and a narrower apex, which rests below on the pelvic floor. The inferolateral surfaces of the prostate are in contact with the levator ani muscles that together cradle the prostate between them. The prostate develops as 30 to 40 individual complex glands, which grow from the urethral epithelium into the surrounding wall of the urethra. Collectively, these glands enlarge the wall of the urethra into what is known as the prostate; however, the individual glands retain their own ducts, which empty independently into the prostatic sinuses on the posterior aspect of the urethral lumen (see Fig. 5.45C).


Anatomy_Gray

Anatomy_Gray. Secretions from the prostate, together with secretions from the seminal vesicles, contribute to the formation of semen during ejaculation. The ejaculatory ducts pass almost vertically in an anteroinferior direction through the posterior aspect of the prostate to open into the prostatic urethra. The bulbo-urethral glands (see Fig. 5.47A), one on each side, are small, pea-shaped mucous glands situated within the deep perineal pouch. They are lateral to the membranous part of the urethra. The duct from each gland passes inferomedially through the perineal membrane, to open into the bulb of the spongy urethra at the root of the penis. Together with small glands positioned along the length of the spongy urethra, the bulbo-urethral glands contribute to lubrication of the urethra and the pre-ejaculatory emission from the penis.