Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Insufficiency fractures also occur at fairly predictable aThomas Jefferson University Hospital, Philadelphia, Pennsylvania. bResearch Author, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania. cPanel Chair, Mayo Clinic Arizona, Phoenix, Arizona. dUniversity of Wisconsin School of Medicine and Public Health, Madison, Wisconsin. eMichigan State University, East Lansing, Michigan; American Academy of Orthopaedic Surgeons. fPenn State Health Milton S. Hershey Medical Center, Hershey, Pennsylvania. gMayo Clinic, Rochester, Minnesota. hHospital for Special Surgery, New York, New York. iBrigham & Women's Hospital, Boston, Massachusetts; Committee on Emergency Radiology-GSER. jMayo Clinic Arizona, Glendale, Arizona, Primary care physician. kUniversity of Virginia Health System, Charlottesville, Virginia. lMedical University of South Carolina, Charleston, South Carolina; North American Spine Society. mDuke University Medical Center, Durham, North Carolina. nUniversity of Missouri Health Care, Columbia, Missouri. oPenn State Milton S. Hershey Medical Center, Hershey, Pennsylvania and Uniformed Services University of the Health Sciences, Bethesda, Maryland. pSpecialty Chair, VA San Diego Healthcare System, San Diego, California. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization. Reprint requests to: publications@acr.org Stress (Fatigue-Insufficiency) Fracture sites, including the sacrum, supra-acetabular ilium, superior and inferior pubic rami, and pubic bone. These patients often present with intractable low back and/or pelvic pain [16].


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Bone Scan Whole Body with SPECT or SPECT/CT Area of Interest The bone scan was regarded for many years as the reference standard for detecting stress-induced injuries and was valued for its sensitivity. Dobrindt et al [17] reported the sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of bone scintigraphy for detection of stress injuries as 92.9%, 73.8%, 83.3%, 78.0%, and 91.2%, respectively. Planar scintigraphy combined with single-photon emission CT (SPECT) is more accurate in diagnosing stress injuries than planar scintigraphy alone [18]. The objection to the studies quoting high accuracy for bone scintigraphy is that, in all of them, positive bone scintigraphy is taken as the reference standard for detecting stress fractures and therefore sensitivity is 100%. However, depending on the staging criteria for bone scintigraphy pattern, the abnormalities may in fact be stress reactions rather than actual stress fractures [19-21]. Nonetheless, bone scintigraphy shows stress fractures days to weeks earlier than radiographs in many instances and differentiates between osseous and soft tissue injury as well. CT Area of Interest With IV Contrast There is no relevant literature to support the use of CT area of interest with intravenous (IV) contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without and With IV Contrast There is no relevant literature to support the use of CT area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without IV Contrast CT is not supported for the initial imaging of suspected stress fractures but may offer an adjunct role when other imaging modalities are equivocal [22], particularly in the pelvis or sacrum.


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Although superior to radiography, it is less sensitive than nuclear scintigraphy or MRI [23]. The benefit of CT seems to lie in its specificity, ranging from 88% to 98% in a recent meta-analysis regarding accuracy of imaging modalities for lower extremity stress fractures, and thus may confirm a finding suspected to represent stress fracture on MRI [24]. CT may also be useful in cases where MRI results are equivocal. MRI Area of Interest Without and With IV Contrast There is no relevant literature to support the use of MRI area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. MRI Area of Interest Without IV Contrast MRI demonstrates stress abnormalities as early as bone scintigraphy and with as much sensitivity [25-28]. In the absence of an actual stress fracture, stress reaction, or muscle/tendon injuries can be identified using fluid-sensitive sequences. Thus, MRI may be considerably more specific than scintigraphy [22,23]. The recent literature supports MRI as the procedure of choice for early diagnosis of both fatigue and insufficiency types of stress fractures, outperforming all other modalities [15,22,23,29-39]. Fluid-sensitive sequences are the favored initial sequence for MRI screening [40]. Short tau inversion recovery (STIR) and T1-weighted images demonstrate a fracture line surrounded by edema. MRI of an osseous stress injury contains prognostic as well as diagnostic information [41,42]. Radiography Area of Interest Radiographs are insensitive for stress fracture in the early stages of injury and in elderly patients with underlying osteoporosis. However, if symptoms have been present for at least 10 to 14 days, radiographs can achieve sensitivity of 30% to 70%, making them an effective screening tool [43]. If the findings on radiographs are conclusive for stress fracture, often no further imaging needs to be performed.


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Detection of osseous change is limited in areas covered by prominent overlapping soft tissue or bowel gas [31]. If the osseous reaction involves cortical bone, then endosteal/periosteal callus may be visible with or without a fracture line through the cortex. If the trabecular bone is involved, then stress fractures are often more subtle, progressing from patchy areas of increased density into linear areas of sclerosis, oriented perpendicular to the trabeculae. US Area of Interest There is increasing evidence of the usefulness of ultrasound (US) in the early diagnosis of stress fractures of the extremities [44,45]. Although later US findings of stress fractures, including subcutaneous edema, periosteal thickening, cortical bone irregularity, local hyperemia [44-46], and periosteal callus are often nonspecific, these Stress (Fatigue-Insufficiency) Fracture findings provide useful information in the setting of suspected stress fracture. Because US cannot evaluate the subcortical bone, trabecular stress fractures may be missed. Variant 2: Adult. Suspect stress fracture, excluding vertebrae. Radiographs negative or indeterminate. Next imaging study. Area of Interest: pelvis, ankle, elbow, femur, foot, forearm, hand, hip, humerus, knee, leg tib/fib, ribs, sacrum, shoulder, or wrist. Bone Scan Whole Body with SPECT or SPECT/CT Area of Interest Bone scintigraphy shows stress fractures days to weeks earlier than radiographs in many instances and differentiates between osseous and soft tissue injury as well. Although bone scan was regarded as the reference standard examination for many years, MRI demonstrates stress abnormalities as early as bone scintigraphy and with as much sensitivity [25-28].


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Because standard planar whole body bone scintigraphy is often nonspecific and supplemental imaging is frequently required, there is consensus in the literature that MRI should supersede bone scintigraphy as the imaging examination of choice for suspected stress fracture when radiographs are negative [31]. CT Area of Interest With IV Contrast There is no relevant literature to support the use of CT area of interest with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without and With IV Contrast There is no relevant literature to support the use of CT area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without IV Contrast CT is not supported as the next imaging study for suspected stress fractures following radiographs but may offer an adjunctive role when other imaging modalities are equivocal [22]. Although superior to radiography, it is less sensitive than nuclear scintigraphy and MRI [23]. CT is useful in cases where MRI results are equivocal. MRI Area of Interest Without and With IV Contrast There is no relevant literature to support the use of MRI area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. MRI Area of Interest Without IV Contrast MRI outperforms radiography, bone scintigraphy, and CT with recent literature supporting MRI as the procedure of choice for making an early diagnosis of both fatigue and insufficiency fractures [15,22,23,29-39]. MRI of an osseous stress injury contains prognostic as well as diagnostic information [41,42].


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Radiography Area of Interest Repeat In 10-14 Days Short-term (10-14 days) follow-up radiographs are more sensitive than initial radiographs secondary to overt bone reaction in the location of the stress fracture. Follow-up radiographic sensitivity is reported to be 30% to 70% [43]. Detection of osseous change is more limited in areas covered by prominent overlapping soft tissue [31]. If the osseous reaction involves cortical bone, then endosteal/periosteal callus may be visible with or without a fracture line through the cortex. If the trabecular bone is involved, then stress fractures are often more subtle, progressing from patchy areas of increased density into linear areas of sclerosis, oriented perpendicular to the trabeculae. US Area of Interest There is increasing evidence of the usefulness of US in the early diagnosis of stress fractures of the extremities [44,45]. Although later US findings of stress fractures, including subcutaneous edema, periosteal thickening, cortical bone irregularity, local hyperemia [44-46], and periosteal callus are often nonspecific, these findings provide useful information in the setting of suspected stress fracture. Because US cannot evaluate the subcortical bone, trabecular stress fractures may be missed. Variant 3: Adult. Suspect pelvis or hip or sacrum stress fracture. Pregnant patient. Radiographs negative or indeterminate. Next imaging study. Area of Interest: pelvis, hip, or sacrum. Pelvic and hip insufficiency fractures have varied presentations and often insidious onset. Patients frequently present with intractable lower back or pelvic pain, with loss of mobility, independence, and symptom exacerbation Stress (Fatigue-Insufficiency) Fracture with weight bearing [47]. Insufficiency fractures occur in patients with abnormal bone, be it from osteoporosis, irradiated bone, or resumption of activity.


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Imaging findings of pregnancy-related sacral fractures are similar to sacral insufficiency fractures related to involutional osteoporosis, with the exception that patients will be in their reproductive years and in the last trimester of pregnancy or recently postpartum [56,57]. Bone Scan Whole Body with SPECT or SPECT/CT Area of Interest Bone scintigraphy and CT are both associated with radiation exposure to the fetus in a pregnant patient. For reference, the approximate mean fetal absorbed dose from a pelvis radiograph is 1.1 mGy, from a pelvis CT is 25 mGy, and from a bone scintigraphy is 4.6 mGy (early in pregnancy) and 1.8 mGy (at 9 months estimated gestational age) [62]. Because bone scintigraphy is often nonspecific and supplemental imaging is frequently required, there is consensus in the literature that cross-sectional imaging should supersede bone scintigraphy as the imaging of choice for suspected insufficiency fracture when the radiograph is negative, regardless of the risks of radiation exposure [31]. CT Area of Interest With IV Contrast There is no relevant literature to support the use of CT area of interest with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without and With IV Contrast There is no relevant literature to support the use of CT area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without IV Contrast CT and bone scintigraphy are both associated with radiation exposure to the fetus in a pregnant patient [62]. Therefore, MRI is preferred. MRI Area of Interest Without and With IV Contrast There is no relevant literature to support the use of MRI area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury.


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. MRI Area of Interest Without IV Contrast Given the importance of recognizing these high-risk fractures in the femoral head and neck, MRI is the preferred second-line study after initial negative radiographs to prevent delayed diagnosis. MRI does not use ionizing radiation, has excellent sensitivity, and allows for definitive diagnosis. MRI typically demonstrates linear T1 and T2 hypointense signal, representing fracture lines, and T1 hypointense and T2 hyperintense signal in the surrounding bone marrow, representing associated edema. MRI demonstrates stress abnormalities as early as bone scintigraphy and with as much sensitivity [25-28]. Stress (Fatigue-Insufficiency) Fracture In addition to confirming a suspected stress fracture, MRI may also demonstrate other reasons for occult pelvic pain, such as soft tissue abnormalities or the subchondral hip or supra-acetabular stress fractures described in some patients with osteoporosis [57]. Radiography Area of Interest Repeat In 10-14 Days A follow-up radiographic examination has increased sensitivity compared to initial radiographs [43] but is less sensitive than MRI. US Area of Interest There is increasing evidence of the usefulness of US in the early diagnosis of stress fractures of the distal extremities [44,45] and may allow visualization of posterior sacral fractures without the risk of ionizing radiation. However, definitive diagnosis of suspected hip or pelvic fractures should not be delayed by choosing US as the second-line study following negative or indeterminate radiographs, considering that additional imaging may be required following a negative or US indeterminate examination. Patients at high-risk for fracture completion include patients with osteoporosis, those on bisphosphonate therapy, and athletes.


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Stress fractures in this population that are not identified and managed in a timely fashion can progress to more serious fractures and complications (eg, risk of fatty emboli in completed femoral shaft fractures). Preventive strategies, including identifying and modifying risk factors, may help deter progression to complete fracture [42,63,64]. Certain stress fractures are considered high risk based on a tendency for nonunion or delayed union. High-risk stress fractures include the anterior tibial diaphysis, lateral femoral neck and femoral head, patella, medial malleolus, navicular, fifth metatarsal base, proximal second metatarsal, tibial hallux sesamoid, and talus [65]. CT Area of Interest With IV Contrast There is no relevant literature to support the use of CT area of interest with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. Stress (Fatigue-Insufficiency) Fracture CT Area of Interest Without and With IV Contrast There is no relevant literature to support the use of CT area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without IV Contrast CT is not supported as the next imaging study for suspected stress fractures following radiographs but may offer an adjunctive role when other imaging modalities are equivocal [22]. Although superior to radiography, it is less sensitive than nuclear scintigraphy or MRI [23]. The benefit of CT seems to lie in its specificity, ranging from 88% to 98% in a recent meta-analysis regarding accuracy of imaging modalities for lower extremity stress fractures and thus may confirm a finding suspected to represent stress fracture on MRI [24].


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. MRI Area of Interest Without and With IV Contrast There is no relevant literature to support the use of MRI area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. MRI Area of Interest Without IV Contrast MRI is beneficial after initial negative radiographs to prevent delayed diagnosis. MRI has excellent sensitivity, and it allows for definitive diagnosis. MRI typically demonstrates linear T1 and T2 hypointense signal, representing fracture lines, and T1 hypointense and T2 hyperintense signal in the surrounding bone marrow, representing associated edema. MRI demonstrates stress abnormalities as early as bone scintigraphy but with more specificity [25-28]. US Area of Interest There is increasing evidence of the usefulness of US in the early diagnosis of stress fractures of the distal extremities [44,45] and may allow for visualization of posterior sacral fractures. However, definitive diagnosis of suspected hip or pelvic fractures should not be delayed by choosing US as the second-line study following negative or indeterminate radiographs, considering that additional imaging may be required following a negative or US indeterminate examination. Variant 5: Adult. Suspect subchondral stress fracture at an extremity joint. Radiographs negative or indeterminate. Next imaging study. Area of Interest: pelvis, ankle, elbow, femur, foot, forearm, hand, hip, humerus, knee, leg tib/fib, shoulder, or wrist. Bone Scan Whole Body with SPECT or SPECT/CT Area of Interest Normal bone scintigraphy generally excludes a diagnosis of stress fracture, and the patient can return to normal activity. Tc-99m-methyl diphosphonate is a marker of bone perfusion and bone turnover [68]. Relative uptake is dependent on both the perfusion of a region of bone as well as the area of the mineralization front of bone (eg, osteoid).


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Thus, there will be focal uptake in any location of new bone formation. Although bone scintigraphy is very sensitive for stress reactions, including subchondral stress fractures, in most cases it lacks specificity, with synovitis, arthritis, degenerative joint disease, stress reactions, and tumor appearing similar. Supplemental imaging with MRI may be necessary for conclusive diagnosis or to avoid false positives [66]. Because planar bone scintigraphy is often nonspecific and supplemental imaging is frequently required, there is consensus in the literature that cross-sectional imaging should supersede planar bone scintigraphy as the imaging of choice for suspected stress fractures when the radiograph is negative [31]. CT Area of Interest With IV Contrast There is no relevant literature to support the use of CT area of interest with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without and With IV Contrast There is no relevant literature to support the use of CT area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. Stress (Fatigue-Insufficiency) Fracture CT Area of Interest Without IV Contrast CT is not supported as the next imaging study for suspected subchondral stress fractures following radiographs but may offer an adjunctive role when other imaging modalities are equivocal [22]. Although superior to radiography, it is less sensitive than nuclear scintigraphy or MRI [23]. The value of CT in the setting of suspected subchondral stress fracture primarily lies in detection of articular surface collapse and sclerosis that could indicate secondary necrosis. CT is useful in cases in which MRI results are equivocal.


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. MRI Area of Interest Without and With IV Contrast There is no relevant literature to support the use of MRI area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. MRI Area of Interest Without IV Contrast MRI is beneficial after initial negative radiographs to prevent delayed diagnosis. MRI has excellent sensitivity and allows for definitive diagnosis. Radiography Area of Interest Repeat In 10-14 Days In general, follow-up radiographic examination has increased sensitivity compared to initial radiographs [43]. However, subchondral insufficiency fractures are typically radiographically occult until collapse or flattening of the articular surface occurs, at which point morbidity is significantly increased. Therefore, MRI without IV contrast should be considered as the next imaging study after initial negative radiographs to prevent delay in diagnosis and preventative treatment. US Area of Interest US does not allow evaluation of subchondral bone and so provides no benefit in this scenario. Variant 6: Adult. Positive stress fracture on radiographs, excluding vertebrae. Need for determining extent (ie, for surgical planning, return to activity) or associated complication (ie, osteonecrosis or delayed healing). Next imaging study. Area of Interest: pelvis, ankle, elbow, femur, foot, forearm, hand, hip, humerus, knee, leg tib/fib, ribs, sacrum, shoulder, or wrist. After a diagnosis of stress fracture is made, additional imaging is typically not needed. Most patients are followed clinically until they are pain free, at which time they can increase activity in a controlled manner [14]. Fractures in the long bones may be followed up by radiography, CT, MRI, or a combination thereof as needed to determine full extent of involvement.


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Occasionally, once activity/weightbearing is increased, an unexpected incomplete response to conservative therapy becomes evident with the return of pretreatment symptoms. In this situation, it is recommended that follow-up imaging be performed as well as re-evaluation of the original imaging studies to determine whether the true etiology of pain was obscured or simply misdiagnosed. CT Area of Interest With IV Contrast There is no relevant literature to support the use of CT area of interest with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without and With IV Contrast There is no relevant literature to support the use of CT area of interest without and with IV contrast because it does not provide added information over noncontrast imaging with regard to stress injury. CT Area of Interest Without IV Contrast CT is useful in identifying possible etiologies in delayed healing after conservative therapy for suspected stress fracture, such as osteoid osteoma or suspected completion of fracture. Stress (Fatigue-Insufficiency) Fracture MRI Area of Interest Without and With IV Contrast MRI with IV contrast may be useful in identifying complications of stress fracture such as osteonecrosis or in suspected osteoid osteoma or tumor causing persistent symptoms or delayed healing after conservative therapy for suspected stress fracture. MRI Area of Interest Without IV Contrast MRI is useful in identifying complications of stress fracture such as osteonecrosis or in suspected osteoid osteoma or tumor causing persistent symptoms or delayed healing after conservative therapy for suspected stress fracture. In athletes, MRI can be used to predict time to return to play on initial diagnosis.


Stress Fatigue Insufficiency Fracture Including Sacrum Excluding Other Vertebrae PCAs. Fredericson et al [71] retrospectively correlated return to activity with an MRI grading system based on the pattern of periosteal and marrow edema on T1-weighted and fat-suppressed T2-weighted sequences. Similar findings were confirmed in other studies [13,72,73], including that the finding of abnormal cortical signal intensity or a fracture line was of prognostic value [73] and that MRI performed better in predicting return to activity than radiographs, bone scintigraphy, or CT [72,74]. A recent prospective study in university athletes found that MRI grading severity, total-body bone mineral density evaluated by dual-energy X-ray absorptiometry, and location of injury (ie, cortical or trabecular bone) were important variables for predicting time to full return to sport [42]. In this study, periosteal edema as described by Fredericson et al [71] was not associated with return to sport. Using the modified grading scale and a multiple regression model, for every 1-unit increase in MRI grade, the time to full return to sport increased by approximately 48 days [42]. Furthermore, trabecular stress injuries (eg, femur neck and pubic bone) were associated with a longer time to return to sport than cortical bone stress injuries. In addition, decreased bone mineral density leads to increased time to return to sport. Therefore, bone mineral density provides additional diagnostic and prognostic information [42]. The model of MRI grade, trabecular versus cortical bone site, and total-body bone mineral density accounted for 68% of the variation in time to return to sport [42]. Although further studies are needed, optimization of bone mass may reduce risk of sustaining stress injuries or possibly reduce recovery time in athletes with these injuries.


Multiple Gestations

Multiple Gestations.  Introduction/Background The incidence of twin pregnancies has been rising, largely attributable to the increasing use of artificial reproductive techniques [1]. Compared with singletons, twin pregnancies carry a higher risk of complications [2]. These include maternal hypertensive disorders, growth disturbances, preterm labor, premature rupture of membranes, and other conditions, some of which are unique to monochorionic (MC) twins such as twin-twin transfusion syndrome (TTTS) [3-5]. Compared with singletons, twins face an approximately 5-fold increase in fetal death and a 7-fold increase in neonatal death, primarily due to complications of prematurity [2]. Multiple gestations are also at a higher risk for congenital anomalies, placenta previa, and vasa previa. Importantly, chorionicity determines the prognosis of multiple gestations [2]. People carrying twin or higher-order multiple pregnancies will typically undergo more ultrasound (US) examinations than those carrying singletons [9]. Most will, at minimum, undergo a first trimester dating scan, a nuchal translucency (NT) scan at 11 to 14 weeks, an anatomy scan at 18 to 22 weeks, and 1 or more scans in the third trimester to assess growth. MC pregnancies undergo more frequent follow-up, influenced by the presence of complications and institutional practice [2,9,13]. Some of these high-risk pregnancies will be candidates for fetal intervention. Special Imaging Considerations First trimester fetal anatomy evaluation and fetal echocardiography are available at many institutions [14-16]. Advancement of US technology has allowed improved imaging at earlier gestational ages making this feasible. Indications for detailed first trimester obstetric US were summarized by American Institute of Ultrasound in Medicine (AIUM) and endorsed by other key societies, with relevant International Classification of Diseases, 10th Revision (ICD-10) codes provided [15,16]. Reprint requests to: publications@acr.org


Multiple Gestations

Multiple Gestations. Multiple Gestations Fetal Doppler can include umbilical artery (UA), middle cerebral artery (MCA), and ductus venosus. At some institutions, all 3 are performed together as an obstetric Doppler evaluation. Ductus venosus evaluation is performed as a part of fetal echocardiography evaluation. Fetal imaging with MRI is being increasingly used for pregnancies complicated by congenital anomalies or complications related to MC gestations [17,18]. Both neurologic and nonneurologic indications exist for fetal imaging. In MC twins, fetal MRI is helpful for assessing intracranial injury that may occur following spontaneous single fetal demise or after an in utero intervention such as laser ablation of intertwin vascular connections [18,19]. Details on risk to the fetus, guidelines on screening for pregnancy, minimizing radiation exposure, and risk assessment can be found in the ACR-SPR Practice Parameter for Imaging Pregnant or Potentially Pregnant Adolescents and Women with Ionizing Radiation [20]. Gadolinium contrast is a relatively contraindicated in pregnancy, which is discussed in detail in the ACR Manual on Contrast Media [21] and the ACR Gadolinium Pregnancy Screening Statement [22]. Most importantly, there are currently no established indications for using gadolinium for MRI evaluation of twin pregnancy or fetal conditions, in general. OR Discussion of Procedures by Variant The variants discussed are presented in approximate order of gestational age. This discussion is almost entirely focused on twin pregnancies because twins represent 98% of multiple gestations, and the vast majority of data relate to twins. It is recognized that higher risks occur in the setting of triplets and higher-order multiples [23]. Variant 1: Known or suspected multiple gestations. Monochorionic or dichorionic. First trimester. Initial imaging. In this variant, the patient is clinically known or suspected to be pregnant with twins or higher order multiples.


Multiple Gestations

Multiple Gestations. Multiple gestation pregnancies are most often detected in the first trimester. Sometimes a point-of-care US may have been performed. At the time of this evaluation, the most important assessments include ascertaining the location of the pregnancy, identifying the number of gestational sacs, and determining the chorionicity and amnionicity [24]. An NT sonogram performed between 11 and 14 weeks has been incorporated into many practices. If not previously imagined, multiple gestations can sometimes be detected on that examination. MRI Fetal Without and With IV Contrast Fetal MRI without and with intravenous (IV) contrast is not useful as an initial imaging modality for the evaluation of known or suspected multiple gestations. Gadolinium contrast administration is avoided during pregnancy and is used only in exceptional circumstances. There is no relevant literature regarding the use of fetal MRI without and with IV contrast in these patients. Sometimes a gestational sac may be identified incidentally during imaging for other reasons. These patients are usually referred to US for further evaluation. MRI Fetal Without IV Contrast Fetal MRI without IV contrast is not useful as an initial imaging modality for the evaluation of known or suspected multiple gestations. There is no relevant literature regarding the use of fetal MRI without IV contrast in these patients. Sometimes a gestational sac may be identified incidentally during imaging for other reasons. These patients are usually referred to US for further evaluation. US Assessment for TTTS Complications affecting MC twins such as TTTS and other conditions related to a single shared placenta usually develop after 14 weeks and do not occur in the first trimester [9]. Hence, US assessment for TTTS is not useful in the first trimester [9]. However, embryonic crown-rump length (CRL) measurements are performed during Multiple Gestations transabdominal and transvaginal imaging of the pregnant uterus.


Multiple Gestations

Multiple Gestations. If there is an intertwin discrepancy in CRL or NT measurements, this may be an early marker for TTTS [9]. US Cervix Transvaginal Transvaginal US (TVUS) of the cervix can be performed to confirm that the cervix is closed and is done along with TVUS of the pregnant uterus. An open cervix indicates a high risk for miscarriage. Cervical length measurement is not recommended in the first trimester. In studies specifically evaluating twin pregnancies, routine TVUS assessment of cervical length in the first trimester (as a component of standard management of low-risk twins) has not been shown to predict preterm labor or to be associated with improved outcomes [25,26]. In an asymptomatic and low-risk twin population, a single transvaginal cervical length between 16 and 20 weeks was not predictive of spontaneous preterm birth before 34 weeks, and hence cervical length measurement in the first trimester is of limited value [25,26]. US Duplex Doppler Fetal Middle Cerebral Artery US Doppler of the fetal MCA is not useful as an initial imaging modality for the evaluation of known or suspected multiple gestations. Fetal organogenesis is usually completed by 11 to 12 weeks, at which time identifiable fetal anatomic parts have developed. Until organogenesis completion around 12 weeks, a separate fetal MCA is not identifiable, and hence fetal MCA Doppler cannot be performed. Hence, this examination is not useful in the first trimester. US Duplex Doppler Fetal Umbilical Artery US duplex Doppler of the fetal UA is not useful as an initial imaging modality for the evaluation of known or suspected multiple gestations [9]. In the early first trimester, an identifiable UA cannot reliably be assessed. An identifiable UA is present in the late first trimester; however, there is still no role for UA assessment in the first trimester [9]. US Echocardiography Fetal US echocardiography has no role in the initial imaging in the first trimester [9].


Multiple Gestations

Multiple Gestations. US Pregnant Uterus Biophysical Profile Biophysical profile (BPP) is performed in the second and third trimesters, and there is no role for this in the first trimester. US Pregnant Uterus Transabdominal In the first trimester, the main goal of imaging is to confirm the presence and location of the gestational sacs, determine chorionicity and amnionicity, provide pregnancy dating, and document embryonic or fetal cardiac activity [9]. This is accomplished using transabdominal and TVUS. Once the in utero location of the gestational sac(s) is confirmed, recognition of possible multiple pregnancy is made and gestational age is determined [9]. Gestational age assessment is most accurate at the first US imaging and can be done using mean sac diameter or CRL measurements. In multiple gestations, all attempts should be made to establish the chorionicity and amnionicity at the earliest imaging encounter [9]. TVUS has the highest accuracy for this assessment. In a DC diamniotic gestation, 2 separate gestation sacs each with surrounding echogenic chorionic reactions are identified. A single gestation sac with peripheral chorionic reaction is seen with MC multiple gestations. The presence of thin intertwin membrane corresponds to diamniotic pregnancy. Very early on, the amnion may not yet have formed or be visible. Thus, lack of identification of an intertwin membrane does not necessarily indicate monoamnionicity. The intertwin membrane is typically identified by 10 weeks on TVUS. Although it has been suggested that the number of yolk sacs can be used as an indicator for assessing amnionicity, this determination can sometimes be erroneous [27]. Hence, attempt should be made to demonstrate a thin intertwin membrane as an indication of diamniotic pregnancy, which can more often be achieved by TVUS imaging or at the next US examination [9,27].


Multiple Gestations

Multiple Gestations. Authors have reported significant correlation between intertwin CRL discrepancy and outcomes including birthweight discordance, small for gestational age birth weight, preterm delivery, chromosomal abnormalities, structural anomalies, and spontaneous fetal loss [29-32]. Severe CRL discordance (>16%) can be associated with Multiple Gestations US Pregnant Uterus Transvaginal In addition to transabdominal US of the pregnant uterus, TVUS can be performed, especially earlier in gestation, to confirm the number of sacs, to assess chorionicity and amnionicity [24]. When an intertwin membrane is not seen transabdominally, TVUS can be attempted because of superior resolution [9]. Variant 2: Multiple gestations. Monochorionic or dichorionic. First trimester. First trimester ultrasound performed. Next imaging study. In this variant, the patient is known to be carrying a multiple gestation pregnancy and is in the first trimester. The chorionicity has likely been established at a prior US. Often, the amnionicity has also been identified; however, in some cases, definitive confirmation of amnionicity needs to be done. This can be achieved by demonstrating the intertwin membrane at the next imaging study. NT US measurements and first trimester anatomy screening evaluation can be performed at the next imaging study [9,14]. NT measurements for twins are specific screening unique to each twin, whereas cell-free DNA testing techniques cannot separate the genetic information specific to each twin. Documentation of the presence of embryonic cardiac motion and assessment of complications such as early pregnancy failure or subchorionic hemorrhage can also occur. MRI Fetal Without and With IV Contrast Fetal MRI without and with IV contrast is not useful as a next imaging study for the evaluation of known or suspected multiple gestations. There is no relevant literature regarding the use of fetal MRI without and with IV contrast for evaluation of patients with multiple gestations in the first trimester.


Multiple Gestations

Multiple Gestations. MRI Fetal Without IV Contrast Fetal MRI without IV contrast is not useful as a next imaging study for the evaluation of known or suspected multiple gestations. There is no relevant literature regarding the use of fetal MRI without IV contrast for the evaluation of patients with multiple gestations in the first trimester. US Cervix Transvaginal US cervix transvaginal can be performed as the next imaging study to assess the cervix. In studies specifically evaluating low-risk twin pregnancies, routine TVUS assessment of cervical length in the first trimester (as a component of standard management) has not been shown to predict preterm labor or to be associated with improved outcomes [25,26]. US Duplex Doppler Fetal Middle Cerebral Artery US Doppler of the fetal MCA is not useful as the next imaging study for the evaluation of known or suspected multiple gestations. Early in pregnancy, a discrete fetal MCA is not identifiable, and fetal MCA Doppler cannot be performed. Hence, this examination is not useful in the first trimester [9]. US Duplex Doppler Fetal Umbilical Artery US Doppler of the fetal UA is not routinely used as the next imaging study for the evaluation of known or suspected multiple gestations. An identifiable UA is present in the late first trimester [9]. There is no established role for UA assessment at this gestational age, and hence this examination is not indicated in the first trimester. Multiple Gestations US Echocardiography Fetal US echocardiography can be performed in the first trimester between 12 weeks 0 days and 13 weeks 6 days. Indications for detailed first trimester obstetric US and fetal echocardiography were summarized by AIUM and endorsed by other key societies and include both maternal and fetal indications.


Multiple Gestations

Multiple Gestations. These include but are not limited to previous fetus or child with a congenital, genetic, or chromosomal anomaly; known or suspected fetal abnormality detected by US in the current pregnancy; and fetus at increased risk for a congenital anomaly based on the following: 35 years of age or older at delivery, maternal pregestational diabetes, pregnancy conceived via in vitro fertilization, multiple gestations, teratogen exposure, enlarged NT, positive screening test results for aneuploidy including cell-free DNA screening and serum only, or combined first trimester screening [15,16]. US Pregnant Uterus Biophysical Profile BPP is performed in the second and third trimesters, and there is no role for this in the first trimester. As in singleton pregnancies, increased NT measurements are associated with an increased risk of aneuploidy and structural anomalies; markedly increased NT is associated with a greater risk of subsequent demise [33]. In MC twin pairs, markedly discordant NT can be a marker for early-onset TTTS [37]. However, normal fetal anatomy and karyotype were the most common outcomes among MC diamniotic twins with discordant NTs [38]. Some studies of MC diamniotic twins have shown that NT discordance is more predictive of adverse fetal outcomes than CRL discordance [39]. Others, including Allaf et al [40], found that NT and CRL discordances were not predictive of overall adverse outcomes in MC diamniotic twin pregnancies, although this varies with the severity of discordance. Both parameters (NT and CRL discrepancy) had high negative predictive value; thus, the absence of discordance is reassuring [39]. US Pregnant Uterus Transvaginal As with transabdominal US of the pregnant uterus, a next TVUS study in the first trimester can be performed for confirming cardiac motion, demonstrating the intertwin membrane (if not previously visualized) and NT measurements.


Multiple Gestations

Multiple Gestations. TVUS imaging is routinely performed in some institutions or can be done as needed, when the transabdominal evaluation is considered incomplete or suboptimal. If prior history of cesarean delivery or uterine instrumentation is present, assessment for placenta accreta spectrum can be performed. MRI Fetal Without and With IV Contrast MRI fetal without and with IV contrast does not have a role in the second trimester anatomy evaluation. Gadolinium contrast is usually not administered for fetal indications. Multiple Gestations MRI Fetal Without IV Contrast MRI fetal without IV contrast does not have a role in the initial second trimester anatomy evaluation. MRI fetal without IV contrast can be considered for multiple gestations if an abnormality is noted in the second trimester anatomy US. It can also be considered when maternal factors, such as soft tissue attenuation, limit sonographic evaluation of the fetus. In all cases, anatomy evaluation with MRI without IV contrast is performed after an US examination has been performed. US Assessment for TTTS With very rare exceptions, DC twins with separate placentas do not develop TTTS or other complications associated with placental sharing and vascular connections. Hence, US assessment for TTTS is not useful for DC or multichorionic twins. US Duplex Doppler Fetal Middle Cerebral Artery US duplex Doppler fetal MCA is not useful for complications of multiple pregnancies at the second trimester anatomy scan. If there is a risk for fetal anemia or if hydrops is noted during evaluation, fetal MCA Doppler can be performed and interpreted using established nomograms [45]. US Duplex Doppler Fetal Umbilical Artery US duplex Doppler fetal UA is not useful for complications of multiple pregnancies at the second trimester anatomy scan. However, if growth restriction is noted during evaluation, fetal UA Doppler can be performed.


Multiple Gestations

Multiple Gestations. US Echocardiography Fetal Multiple gestations are at higher risk for cardiac defects, and echocardiography is very useful in the second trimester. This is particularly relevant for DC twin pregnancies conceived using assisted reproductive technologies because these groups are at increased risk of congenital heart disease [46]. US Pregnant Uterus Biophysical Profile BPP is performed in late second and third trimesters, and there is no role in the first trimester. There is no role for BPP at the time of second trimester anatomy scan. US Pregnant Uterus Transvaginal Transvaginal examination of the pregnant uterus and cervix can be performed as an adjunct for limited transabdominal fetal evaluation. Additional indications include assessment of the cervix and placenta and detection of vasa previa. Typically, TVUS imaging is performed only if transabdominal evaluation is considered suboptimal Multiple Gestations or incomplete and never as the only approach for second trimester anatomy evaluation. If prior history of cesarean delivery or uterine instrumentation is present, assessment for placenta accreta spectrum can be performed. MRI Fetal Without and With IV Contrast MRI fetal without and with IV contrast does not have a role in the second trimester anatomy evaluation. Gadolinium contrast is usually not administered for fetal indications. MRI Fetal Without IV Contrast MRI fetal without IV contrast does not have a role in the second trimester anatomy evaluation. MRI fetal without IV contrast can be considered for the next imaging after an abnormality is noted on the second trimester anatomy sonogram. It can also be considered when maternal factors such as soft tissue attenuation limit evaluation of the fetus on US. In all cases, anatomy evaluation with MRI without IV contrast is performed after an US has previously been done. Historically, reports suggested measuring cervical length at each visit to triage for risk of preterm labor.


Multiple Gestations

Multiple Gestations. However, more recent literature has questioned the significance and usefulness of this practice because of a lack of proven effective interventions. In twin pregnancies, cervical length measuring <1.5 cm has been shown to be predictive of preterm labor, regardless of management strategies [43]. Multiple Gestations Vasa previa and velamentous cord insertion are more commonly present in MC multiple gestations. Both of these conditions are associated with adverse pregnancy outcome and deserve dedicated evaluation at this point in pregnancy [47]. There is also a higher frequency of vasa previa when velamentous cord insertion is found; if overlooked, this may result in acute fetal hemorrhage, distress, and potential demise at the time of delivery. For this reason, examiners should be aware of the possibility of vasa previa, especially in MC pregnancies [49]. US Duplex Doppler Fetal Middle Cerebral Artery Fetal MCA Doppler assessment is performed to detect the presence of TAPS [3,20,50,51]. In contrast to evaluation for TTTS, there are no clear established guidelines addressing whether evaluation for TAPS should be part of routine second trimester anatomy evaluation. This may be optionally considered on a case-by-case basis, for example, when imaging signs of TTTS are present [9]. Some authors are advocating for routine antenatal screening for TAPS in MC gestations [50]. US Duplex Doppler Fetal Umbilical Artery US duplex Doppler fetal UA is essential for second trimester evaluation of MC twins and should be performed at the time of anatomy evaluation [9]. This is helpful for the staging of TTTS, TAPS, and growth discordant twins. US Echocardiography Fetal Multiple gestations are at higher risk for cardiac defects, and an echocardiogram is recommended in the second trimester. The risk of cardiac anomalies has been reported to be 2% in uncomplicated MC twins and 5% in cases of TTTS, particularly among recipient twins [52,53].


Multiple Gestations

Multiple Gestations. The risk of a structural congenital cardiac anomaly in at least 1 of an MC MA twin pair is 8 times that of a MC diamniotic twin pair [9]. In addition, if 1 MC twin is affected, the risk of the co-twin having a cardiac anomaly is higher. For these reasons, fetal echocardiography should be considered in MC gestations [9]. US Pregnant Uterus Biophysical Profile BPP is performed in late second and third trimesters. There is no role for BPP at the time of second trimester anatomy scan. Placental cord insertion of each twin should be documented in the second trimester. Marginal or velamentous cord insertion are common among MC pregnancies, with velamentous cord insertion present in up to 22% of MC twins [54]. Velamentous cord insertion in MC twins increases the risk of adverse outcome, including small for gestational age and sFGR, lower gestational age at birth, and intrauterine fetal demise [55]. There is also a higher frequency of vasa previa when a velamentous cord insertion is found, especially in MC pregnancies [49]. Velamentous cord insertion in 1 or both twins is associated with increased risk of TTTS, and the risk of discordant growth is determined by both discordance in insertion sites and velamentous cord insertion in 1 twin [56,57]. In a study by Saito et al [57], 27% of twin pairs with abnormal cord insertions (defined as twin pair with velamentous cord insertions and/or marginal cord insertion in 1 or both twins) developed TTTS compared with 7% of twin pairs with normal cord insertions in both. If prior history of cesarean delivery or uterine instrumentation is present, assessment for placenta accreta spectrum can be performed. US Pregnant Uterus Transvaginal Transvaginal examination of the pregnant uterus and cervix can be performed as an adjunct for limited transabdominal fetal evaluation. Additional indications include assessment of the cervix and placenta and detection of vasa previa.


Multiple Gestations

Multiple Gestations. Typically, transvaginal imaging is performed only if transabdominal evaluation is considered suboptimal or incomplete and never as the only approach for second trimester anatomy evaluation. If prior history Multiple Gestations of cesarean delivery or uterine instrumentation is present, assessment for placenta accreta spectrum can be performed. MRI Fetal Without and With IV Contrast MRI fetal without and with IV contrast does not have a role in growth and antepartum surveillance of DC or multichorionic gestations. Gadolinium contrast is usually not administered for fetal indications. MRI Fetal Without IV Contrast MRI fetal without IV contrast does not have a role in growth and antepartum surveillance of DC or multichorionic gestations. It is usually reserved for problem-solving when an anatomic abnormality is identified. US Assessment for TTTS DC twins with separate placentas do not develop TTTS or other complications associated with a single shared placenta. Hence, this evaluation is not useful for growth and antepartum surveillance of DC or multichorionic twins. US Cervix Transvaginal US cervix transvaginal evaluation for antepartum surveillance is useful for assessing cervical length, vasa, and placenta previa. Any cervical pathology, such as a myoma or other masses, that may preclude vaginal delivery should also be assessed. Usually, a transabdominal examination is performed first, followed by transvaginal imaging if the initial evaluation is inadequate. Historically, reports suggested measuring cervical length at each visit to triage for risk of preterm labor. However, more recent literature has questioned the significance and usefulness of this practice, recommending against cervical length measurement after 26 weeks. In twin pregnancies, cervical length measuring <1.5 cm has been shown to be predictive of preterm labor, regardless of management strategies [43].


Multiple Gestations

Multiple Gestations. If placenta previa or low-lying placenta has been suggested previously, assessment of the location of placental edge can be performed on surveillance examinations. US Duplex Doppler Fetal Middle Cerebral Artery If there is a risk for fetal anemia or if fetal hydrops is noted during evaluation, fetal MCA Doppler can be performed and interpreted using established nomograms. US duplex Doppler fetal MCA is generally not useful for surveillance of uncomplicated DC or multichorionic gestations. US Duplex Doppler Fetal Umbilical Artery If growth restriction or amniotic fluid abnormalities (oligohydramnios) are noted during antepartum surveillance, fetal UA Doppler can be performed. US duplex Doppler fetal UA is generally not useful for surveillance of uncomplicated DC or multichorionic gestations. US Echocardiography Fetal Echocardiography can be performed for surveillance of DC or multichorionic gestations when cardiac defects or secondary cardiac decompensation is suspected or observed. Uncomplicated DC or multichorionic gestations do not need routine fetal echocardiographic follow-up. US Pregnant Uterus Biophysical Profile BPP can be performed in the late second and third trimesters for assessing fetal well-being. To date, there are insufficient data in the literature to suggest that antenatal surveillance of twins with BPP is beneficial in the setting Multiple Gestations of reactive nonstress test or in the absence of associated risk factors [62,63]. US Pregnant Uterus Transabdominal Transabdominal US of the pregnant uterus remains the mainstay for the evaluation of DC or multichorionic gestations. At each US scan, the following should be assessed: fetal biometry, amniotic fluid volume, and key features of fetal anatomy. Due to variability and SDs in measurements, growth assessment, and biometry are usually performed no more frequently than every 2 weeks. It is suggested that the discordance in estimated fetal weights be calculated and documented at each scan.


Multiple Gestations

Multiple Gestations. If prior history of cesarean delivery or uterine instrumentation is present, assessment for placenta accreta spectrum can be performed. US Pregnant Uterus Transvaginal Transvaginal examination of the pregnant uterus and cervix can be performed as an adjunct for limited transabdominal fetal evaluation. Additional indications include assessment of the cervix and placenta and detection of vasa previa. Typically, transvaginal imaging is performed only if transabdominal evaluation is considered suboptimal or incomplete. If prior history of cesarean delivery or uterine instrumentation is present, assessment for placenta accreta spectrum can be performed. Variant 6: Multiple gestations. Monochorionic twins. Growth and antepartum surveillance. In this variant, the patient is known to be pregnant with uncomplicated MC multiple gestation. The fetuses have been demonstrated to share a single placenta. Given the higher incidence of growth disturbance, congenital abnormalities, and complications unique to MC twinning, assessment of growth and surveillance for fetal well- being is indicated. In addition to monitoring fetal size and interval growth, ongoing evaluation includes amniotic fluid assessment and the search for possible development of TTTS, TAPS, or sFGR. Typically, surveillance begins at 16 weeks for MC twins, with fetal biometry performed every 2 to 3 weeks [9,12]. Assessment for potential TTTS or other complications of MC twinning is performed every 2 weeks [9,12]. If there is discordance in fetal size or amniotic fluid volume, shorter interval surveillance may be warranted [13]. MRI Fetal Without and With IV Contrast MRI fetal without and with IV contrast does not have a role in growth and antepartum surveillance of MC gestations. Gadolinium contrast is usually not administered for fetal indications. MRI Fetal Without IV Contrast MRI fetal without IV contrast can be useful for antepartum surveillance for a known abnormality.


Multiple Gestations

Multiple Gestations. In MC twins, fetal MRI has been used to assess for brain injury that may occur after fetal intervention or following spontaneous in utero demise of a co-twin [17]. This examination is usually not indicated for uncomplicated multiple gestations. In a study by Kawaguchi et al [13], the incidence of unexpected critical complications in patients with MC diamniotic twin pregnancies was significantly lower in those undergoing weekly US, suggesting that weekly sonographic evaluation for patients with MC diamniotic pregnancy may be more effective for the early detection of impending intrauterine fetal death and/or TTTS. US Cervix Transvaginal US cervix transvaginal evaluation for antepartum surveillance is useful for assessing cervical length, vasa, and placenta previa. Any cervical pathology, such as myoma or other masses, that may preclude vaginal delivery should also be assessed. Usually, a transabdominal examination is performed first, followed by transvaginal imaging if the initial evaluation is inadequate. Historically, reports suggested measuring cervical length at each visit to triage for risk of preterm labor. However, more recent literature has questioned the significance and usefulness of this practice, recommending against cervical length measurement after 26 weeks. In twin pregnancies, cervical length measuring <1.5 cm has been shown to be predictive of preterm labor, regardless of management strategies [43]. If placenta previa or low-lying placenta has been suggested previously, assessment of location of placental edge can be performed. Multiple Gestations US Duplex Doppler Fetal Middle Cerebral Artery Fetal MCA Doppler assessment is performed to detect the presence of TAPS [3,50,51]. This can be done at serial surveillance examinations, with US evaluation for TTTS and UA Doppler interrogation, as frequently as indicated by fetal status [9,50]. US Duplex Doppler Fetal Umbilical Artery US duplex Doppler fetal UA is essential for antepartum surveillance of MC twins.


Multiple Gestations

Multiple Gestations. This information is critical for the detection and staging of TTTS and for the evaluation of fetuses diagnosed with sFGR [9,42]. US Pregnant Uterus Biophysical Profile BPP can be performed in the third trimester to assess fetal well-being. Frequency of BPP can be determined based on the presence of risk factors and impending complications [53,64]. To date, there are insufficient data in the literature to suggest that antenatal surveillance of twins with BPP is beneficial in the setting of reactive nonstress test or in the absence of associated risk factors [62,63]. US Pregnant Uterus Transabdominal Transabdominal US of the pregnant uterus continues to be the mainstay for the evaluation and surveillance of MC twins. For MC twins, sonographic surveillance usually begins at 16 weeks and is done every 2 weeks thereafter [9,12]. Due to variability and SDs in measurements, growth and biometry is usually performed no more frequently than every 2 weeks. The discordance in estimated fetal weights should be calculated and documented at each scan. If prior history of cesarean delivery or uterine instrumentation is present, assessment for placenta accreta spectrum can be performed. US Pregnant Uterus Transvaginal Transvaginal examination of the pregnant uterus and cervix can be performed as an adjunct for limited transabdominal fetal evaluation. Additional indications include assessment of the cervix and placenta and detection of vasa previa. Typically, transvaginal imaging is performed only if transabdominal evaluation is considered suboptimal or incomplete. If prior history of cesarean delivery or uterine instrumentation is present, assessment for placenta accreta spectrum can be performed. Variant 7: Multiple gestations. Dichorionic or multichorionic higher order multiples or monochorionic gestations. Known abnormality or discordance between fetuses (fluid, size, weight). Growth and antepartum surveillance.


Multiple Gestations

Multiple Gestations. In this variant, multiple gestations of all chorionicity and amnionicity have a known abnormality detected on a previous examination and are receiving surveillance imaging. MRI Fetal Without and With IV Contrast MRI fetal without and with IV contrast does not have a role in growth and antepartum surveillance of MC, DC, or multichorionic gestations. Gadolinium contrast is usually not administered for fetal indications. MRI Fetal Without IV Contrast MRI fetal without IV contrast can be useful for antepartum surveillance for a known abnormality. In DC and multichorionic twins, this can be indicated for multiple reasons, in particular, to evaluate neurologic, thoracic, and abdominal structural anomalies and associated complications. In MC twins, fetal MRI has been useful in the assessment of intracranial injury that may occur related to TTTS after fetal intervention or following spontaneous in utero demise of a co-twin. Cerebral injury can affect approximately 18% of co-twin survivors after single fetal demise in MC twin pregnancies, and follow-up evaluation of these cases can improve detection rate of such damage [65,66]. MRI evaluation of complicated MC multiple gestations can be useful for estimating neurologic injury associated with TTTS, TAPS, sFGR, and fetal interventions [65]. In a study, postnatal follow-up of all survivors shown to have normal fetal MRI demonstrated normal neurologic outcome, but only 1 of 3 survivors with cerebral lesions at fetal MRI demonstrated normal neurologic outcome [65]. Brain injury of the surviving co-twin after single fetal demise in MC pregnancies is usually of ischemic origin and spares the brainstem and cerebellum [67]. Focal brain lesions are more frequent in pregnancies complicated by TTTS or in Multiple Gestations those in whom an intervention has been performed [67]. Robinson et al [18] showed that MRI provided additional information over a prenatal US in 5 of 33 patients (15%) altering prognosis and patient counseling.


Multiple Gestations

Multiple Gestations. Additional findings on MRI included occipital lobe infarction, hemispheric injury, dural sinus thrombosis, polymicrogyria, and intraventricular hemorrhage. In this series, US was normal in 2 patients and underrepresented parenchymal injury in the remaining 3 patients [18]. Kocaoglu et al [68] demonstrated that abnormal cerebral imaging findings on MRI due to hypoxic-ischemic injury or hemorrhage can be seen at the beginning of the second trimester and do not correlate with the current US staging system; however, they do correlate with decreased survival. Hence, it has been suggested that fetal MRI-based detection of cerebral abnormalities could be included in the TTTS staging system as an independent risk factor and incorporated in the prenatal evaluation of complicated MC gestations [68]. In a study including 49 MC multiple gestations with single fetal demise, median gestational age at time of co-twin death was 25 weeks and median interval between single fetal loss and live birth was 61 days, with median gestational age at delivery 36 weeks [17]. Severe cerebral injury was diagnosed in 26% of the survivors and was detected antenatally on MRI in 4 of 50 (8%) cases. Abnormal cerebral findings predominantly resulted from hypoxic- ischemic injury resulting in cystic periventricular leukomalacia, MCA infarction, or injury to basal ganglia, thalamus, and/or cortex [17]. Risk factors associated with severe cerebral injury were advanced gestational age at time of single fetal demise, development of TTTS before co-twin loss, and lower gestational age at birth [17]. US Assessment for TTTS DC twins with separate placentas do not typically develop TTTS or other complications associated with a single shared placenta. Hence, this evaluation is not useful for growth and antepartum surveillance of complicated DC or multichorionic twins.


Multiple Gestations

Multiple Gestations. US Cervix Transvaginal US cervix transvaginal evaluation for antepartum surveillance for all multiple gestations is useful for assessing cervical length, vasa, and placenta previa. Any cervical pathology, such as myoma or other masses, that may preclude vaginal delivery should also be assessed. Usually, a transabdominal examination is performed first, followed by transvaginal imaging if the initial evaluation is inadequate. Historically, reports suggested measuring cervical length at each visit to triage for risk of preterm labor. However, more recent literature has questioned the significance and usefulness of this practice, recommending against cervical length measurement after 26 weeks. In twin pregnancies, cervical length measuring <1.5 cm has been shown to be predictive of preterm labor, regardless of management strategies [43]. If placenta previa or low-lying placenta has been suggested previously, assessment of the location of placental edge can be performed. US Duplex Doppler Fetal Middle Cerebral Artery For DC twins and multichorionic multiples, if there is a risk for fetal anemia or fetal hydrops is noted during surveillance, fetal MCA Doppler can be performed and interpreted using established nomograms. US duplex Multiple Gestations Doppler fetal MCA can be useful for surveillance of complicated DC or multichorionic gestations when there is concern for fetal anemia. Prognostic importance of MCA-PSV for outcome after laser ablation for TTTS has been reported. In a study by Trieu et al [74], there was no correlation between the incidence of elevated MCA-PSV before laser and fetal survival up to 7 days after laser. In contrast, the presence of an MCA-PSV above 1.5 MoM in the former donor twin 48 hours following laser was associated with higher risk for intrauterine fetal demise of the former donor within a week after surgery [74]. US duplex Doppler fetal UA is essential for antepartum surveillance of complicated MC twins.


Multiple Gestations

Multiple Gestations. This information is critical for detecting and staging TTTS and for evaluating fetuses diagnosed with sFGR. Doppler studies may show absence or reversal of EDF in the UA of the donor, information that is used in staging TTTS [70]. US Echocardiography Fetal Echocardiography can be performed for surveillance of DC or multichorionic gestations when cardiac defects or secondary cardiac decompensation is expected or observed. Multiple Gestations for fetal intervention. Fetoscopic laser ablation of placental vascular anastomoses can help reverse cardiac dysfunction, even in the most severe cases of TTTS [80]. Finneran et al [80] showed that laser treatment for TTTS causes rapid improvement in the cardiac function of recipient fetuses and that preoperative recipient myocardial performance index does not correlate with survival of either twin postoperatively. Hence, monitoring of cardiac function should be continued even after fetal intervention has been performed [80-82]. US Pregnant Uterus Biophysical Profile BPP can be performed in late second and third trimesters for assessing fetal well-being for all multiple pregnancies. US Pregnant Uterus Transabdominal Transabdominal US of the pregnant uterus continues to be the mainstay for surveillance imaging of complicated multiple gestations. Complicated multiple gestations require sonographic surveillance at frequent intervals varying between 2 to 3 days to 2 to 3 weeks based on the abnormality and fetal status [9]. Higher-risk gestations merit frequent surveillance. Due to variability and SDs in measurements, growth and biometry is usually performed no more frequently than every 2 weeks [9]. The discordance in estimated fetal weights should be calculated and documented at each scan in which growth and fetal weight estimates are performed. If prior history of cesarean delivery or uterine instrumentation is present, assessment for placenta accreta spectrum can be performed.


Abdominal Aortic Aneurysm Follow up Without Repair .  Introduction/Background Abdominal aortic aneurysm (AAA) is defined as an aneurysmal dilation of the abdominal aorta of at least 3 cm in diameter. This entity has a high degree of morbidity and mortality in the event of rupture [1,2]. To mitigate this risk, screening programs have been widely instituted to identify small, developing aneurysms. Such screening reduces morbidity and health care costs related to this disease [3-8]. An increasing number of aneurysms are identified incidentally on ultrasound (US) and cross-sectional imaging, creating a growing cohort of patients with known AAA [9-12]. The reported prevalence of AAA in persons >65 years of age ranges from 1.7% to 4.5% for men and 0.5% to 1.3% for women [11,13,14]. Special Imaging Considerations For the purposes of distinguishing between CT and CT angiography (CTA), ACR Appropriateness Criteria topics use the definition in the Practice Parameter for the Performance and Interpretation of Body Computed Tomography Angiography (CTA) [25]. All elements are essential: 1) timing, 2) reconstructions/reformats, and 3) 3-D renderings. Standard CTs with contrast also include timing issues and recons/reformats. Only in CTA, however, is 3-D rendering a required element. This corresponds to the definitions that the CMS has applied to the Current Procedural Terminology codes. aResearch Author, UT Southwestern Medical Center, Dallas, Texas. bUT Southwestern Medical Center, Dallas, Texas. cPanel Chair, UT Southwestern Medical Center, Dallas, Texas. dPanel Vice-chair, University of Michigan Health System, Ann Arbor, Michigan. eMayo Clinic, Rochester, Minnesota. fTufts University School of Medicine, Boston, Massachusetts; Society for Vascular Surgery. gUniversity of Wisconsin, Madison, Wisconsin. hMassachusetts General Hospital, Boston, Massachusetts. iUniversity of Alabama at Birmingham, Birmingham, Alabama. jMayo Clinic, Rochester, Minnesota. kUniversity of Michigan Health System, Ann Arbor, Michigan.


Abdominal Aortic Aneurysm Follow up Without Repair . lLoyola University Medical Center, Maywood, Illinois. mColumbia University Medical Center, New York, New York. nUT Southwestern Medical Center, Dallas, Texas. oSpecialty Chair, UMass Memorial Medical Center, Worcester, Massachusetts. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through society representation on expert panels. Participation by representatives from collaborating societies on the expert panel does not necessarily imply individual or society endorsement of the final document. Reprint requests to: publications@acr.org AAA Follow-up (Without Repair) Discussion of Procedures by Variant Variant 1: Asymptomatic abdominal aortic aneurysm surveillance (without repair). US Duplex Doppler Aorta Abdomen US is the most widely studied and utilized imaging tool for evaluating an AAA, both for screening and during surveillance. US has been verified as having consistent measurement accuracy, which can approximate the accuracy demonstrated by CT and MRI or MR angiography (MRA) [17,18,26,27]. Studies have reported that US may underestimate the maximum AAA diameter by 4 mm, on average, and the interobserver measurement difference can range from 2 to 10 mm with US compared with <2 mm using CT [27-31]. Evidence is still lacking as to whether these differences are clinically impactful. Variation in accuracy is believed to be related to measurement technique. For example, there is debate as to whether to place the measurement caliper on the outer or inner edge of the vessel, without clear consensus on an ideal methodology [31]. Finally, no significant difference between rate of growth measurements between US and CT has been found [18,32]. US is also less capable of identifying specific aneurysm features beyond diameter, such as intraluminal thrombus or adjacent inflammation, both of which are more easily identified on CT [21,33,34].


Abdominal Aortic Aneurysm Follow up Without Repair . CTA Abdomen and Pelvis CTA of the abdomen and pelvis presents many benefits over the other modalities. Relative to US, CTA is considered slightly more accurate at determining aneurysm diameter [27,30,31]. The use of iodinated contrast carries its own risks and contraindications that require consideration [35]. CT Abdomen and Pelvis The majority of evidence regarding AAA surveillance using CT is based on CTA data and is primarily related to contrast bolus timing. Contrast-enhanced CT is well established in the literature and is capable of identifying aortic aneurysms, with many papers discussing incidental AAA identification [9,11,13]. There is no specific literature regarding the use of noncontrast CT in the surveillance of AAA. One study reviewed the incidence of AAA incidentally found during CT colonography. This included patients who underwent CT imaging, some with and others without the use of intravenous (IV) contrast. This review did not distinguish the difference between those patients [11]. This technique could theoretically be of use in patients with chronic renal disease who have aneurysms less amenable to imaging by US. Noncontrast imaging can be employed in CTA protocols to evaluate for calcification, with spectral CT scanners offering virtual noncontrast reconstructions as an alternative. MRI Abdomen and Pelvis There is no relevant literature regarding the use of MRI for AAA surveillance in this setting; although, MRI may be useful in some cases. Similar to CT, there is excellent reproducibility in measurements between MRI examinations, a critical characteristic in monitoring for subtle changes in AAA size. Aortography Abdomen There is no relevant literature regarding the use of conventional angiography in the surveillance of AAA. Noninvasive techniques to monitor aneurysm characteristics make this invasive option less reasonable.


Lower Urinary Tract Symptoms Suspicion of Benign Prostatic Hyperplasia.  Initial assessment of LUTS includes obtaining relevant medical history, performing a focused physical examination, and assessing symptom severity by one of several validated questionnaires. The International Prostate Symptom Score (IPSS) is used most commonly in the United States, and other validated questionnaires include the International Consultation on Incontinence Questionnaire and the Danish Prostate Symptom Score. These scores identify dominant symptoms (storage or voiding) and can be used to monitor response to therapy. Voiding charts (eg, frequency-volume chart) can be created by the patient to actively record several days of voiding time and volume. A physical examination should include an abdominal examination for bladder distention, a detailed genitourinary examination for any stricturing disease or urethral mass, a digital rectal examination to assess prostate size, and a neurological examination of the perineum and lower limbs. Digital rectal examination can be inaccurate for volume estimation and cancer detection and is most useful for identifying an enlarged prostate with volume >50g [4]. Initial laboratory analysis may include prostate serum antigen level if desired, following appropriate shared decision-making discussion. Urinalysis can be obtained to evaluate for urinary tract infection, glucosuria and proteinuria as cause of urinary frequency, and microhematuria. Urinalysis results may lead to an additional workup beyond the scope of this topic [1,2,5]. Pressure flow urodynamics is considered the reference standard for determining the underlying cause of LUTS and differentiating between storage and voiding abnormalities. Watchful waiting with lifestyle modifications is appropriate for patients without bothersome symptoms. For patients with moderate to severe symptoms, medical therapy with 1-adrenoceptor antagonists is a first-line therapy.


Lower Urinary Tract Symptoms Suspicion of Benign Prostatic Hyperplasia. The 5 -reductase inhibitors can be helpful for patients with prostate volume >40 mL [6]. The muscarinic receptor antagonists and phosphodiesterase type 5 inhibitors can be used for storage symptoms [6]. Transurethral resection of the prostate is the standard surgical treatment for prostate volume 30 to 80 mL, with surgery or transurethral holmium laser enucleation for prostate volume >80 mL [6]. Other interventional options include laser ablation, transurethral needle or microwave ablation, transurethral resection, and prostate artery embolization. Treatment decisions vary by prostate volume and patient comorbidities [6,7]. aMayo Clinic, Jacksonville, Florida. bPanel Chair, University of Chicago, Chicago, Illinois. cPanel Vice-Chair, Duke University Medical Center, Durham, North Carolina. dMemorial Sloan Kettering Cancer Center, New York, New York. eMcGill University, Montreal, Quebec, Canada. fMayo Clinic, Rochester, Minnesota. gUrology Clinics of North Texas, Dallas, Texas; American Urological Association. hUniversity of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; American Society of Nephrology. iUPMC, Pittsburgh, Pennsylvania; American Urological Association. jCleveland Clinic, Cleveland, Ohio. kStanford University Medical Center, Stanford, California. lOttawa Hospital Research Institute and the Department of Radiology, The University of Ottawa, Ottawa, Ontario, Canada. mEmory University Hospital, Atlanta, Georgia. nNational Institutes of Health, Bethesda, Maryland. oThe University of Texas MD Anderson Cancer Center, Houston, Texas. pUniversity of Washington, Seattle Cancer Care Alliance, Seattle, Washington. qSpecialty Chair, University of Alabama at Birmingham, Birmingham, Alabama. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through society representation on expert panels.


Lower Urinary Tract Symptoms Suspicion of Benign Prostatic Hyperplasia. Participation by representatives from collaborating societies on the expert panel does not necessarily imply individual or society endorsement of the final document. Reprint requests to: publications@acr.org Lower Urinary Tract Symptoms-Suspicion of BPH Discussion of Procedures by Variant Variant 1: Lower urinary tract symptoms. Suspicion of benign prostatic hyperplasia. Initial imaging. Radiography Abdomen Radiographs do not directly image the prostate and are of low diagnostic yield in patients with LUTS [8]. A distended bladder may be visible on radiographs as a pelvic mass; however, the timing of last void is usually unavailable, making this appearance a finding of uncertain significance. Bladder stones can be identified on radiographs. Radiography Intravenous Urography Intravenous urography is now rarely performed as it has been replaced by CT urography at most centers [9]. Positive yield of intravenous urography for BOO is <15% [10,11]. In patients with stones, hematuria, or atypical history, CT urography may be considered for further evaluation [12]. Fluoroscopy Retrograde Urethrography Retrograde urethrography does not directly image the prostate or provide adequate evaluation of prostate size. It may be useful if urethral stricture is considered as a cause of urinary obstruction. Fluoroscopy Voiding Cystourethrography Voiding cystourethrography does not directly image the prostate or provide adequate evaluation of prostate size. It may be useful if urethral stricture is considered as a cause of urinary obstruction. TRUS Prostate Grayscale transrectal ultrasound (TRUS) is the most commonly used modality to image the prostate. Although more invasive, TRUS measurement of prostate volume is more accurate than digital rectal examination or pelvic US [13,14], though correlation between TRUS and pelvic US is consistent when bladder volumes are <400 mL [15].


Lower Urinary Tract Symptoms Suspicion of Benign Prostatic Hyperplasia. Prostate volume has low correlation with initial symptoms [16] but may predict symptom progression and response to 5 -reductase inhibitors, as well as guide surgical procedures [6]. The addition of spectral Doppler assessment is not helpful to differentiate benign from malignant areas [17], and further study of prostate arterial resistive index measurement is needed to determine clinical usefulness [18]. US Pelvis US is the preferred method to assess bladder volume and postvoid residual over catheterization and can be performed with a specific bladder scan unit or pelvic US. A measurable postvoid residual can be seen with both BOO and decreased detrusor function. Although no current postvoid residual threshold value can diagnose BOO or guide treatment [1,2], a persistent postvoid residual >100 mL or increasing postvoid residual over time may predict acute urinary retention, poor response to medical treatment, and deterioration of symptoms [1,19]. US measurement of bladder wall thickness includes the entire width of the bladder wall, whereas detrusor wall thickness measures the hypoechoic muscle between the more echogenic mucosa and adventitia. A study of 157 patients, of which 48 had BOO by urodynamics, identified optimal cutoff of 3.7-mm wall thickness for identifying patients with BOO by receiver operator curve analysis [25]. Although detrusor wall thickening has been shown to increase in BOO, the ratio of bladder to detrusor thickness depends on degree of bladder filling [28]. US-estimated bladder weight can be calculated from bladder volume and wall thickness, assuming a spherical shape. This value may also correlate with BOO and acute urinary retention [29,30]. Lower Urinary Tract Symptoms-Suspicion of BPH US Kidneys Retroperitoneal Routine imaging of the upper urinary tract with renal US is not usually indicated in uncomplicated LUTS [1,2,31].


Left Lower Quadrant Pain

Left Lower Quadrant Pain.  Introduction/Background The differential diagnosis for left lower quadrant pain includes gastrointestinal, gynecologic, urologic, and body wall pathology. These conditions range from the benign and self-limited to life-threatening surgical emergencies. Along with patient history, physical examination, and laboratory tests, imaging is often critical to limit the differential diagnosis and identify life-threatening abnormalities [1]. Appropriate imaging triage for patients with left lower quadrant pain should address the diagnostic possibilities and consider which imaging modality can best add clinically relevant information to help guide management. In older patients, early diagnosis is important because this population has a higher rate of comorbid disease-related complications [2-6]. Furthermore, symptoms and clinical findings may be nonspecific in this population, with atypical presentation of common diseases. Acute colonic diverticulitis is the most common explanation for left lower quadrant pain, and the prevalence is rising. There was a 50% increase in diverticulitis events between 2000 and 2007 [6,7]. Colonic diverticulitis, which results from inflammation of colonic diverticula, is common in Western populations, likely due to inadequate dietary fiber. Approximately 10% of the Western population has diverticulosis at 40 years of age; this increases to 70% or more in older patients. It has been estimated that between 5% and 25% of patients with diverticulosis will develop diverticulitis [3,8]. Although the most common cause of adult left lower quadrant pain is acute diverticulitis of the sigmoid or descending colon, other common causes of left lower quadrant pain include colitis, inflammatory bowel disease, epiploic appendagitis, bowel obstruction, hernia, ovarian and fallopian tube pathology, pyelonephritis, and urolithiasis [6,9]. Many of these conditions can present with symptoms that overlap with the acute presentation of diverticulitis.


Left Lower Quadrant Pain

Left Lower Quadrant Pain. Special Imaging Considerations Diverticulitis and Colon Cancer: Perforated colon cancer can mimic diverticulitis [10]. CT findings that suggest colon cancer rather than diverticulitis include abnormal pericolic lymph nodes (>1 cm in short axis and/or rounded) or a luminal mass [10-12]. Patients with uncomplicated diverticulitis do not have a higher risk of colon cancer than the general population [10]. The prevalence of colon cancer in patients with uncomplicated diverticulitis has been reported to be 0.5% to 0.9% [10,13,14]. Colonoscopy after a diagnosis of uncomplicated diverticulitis is not indicated in the general population. [10,15]. Colonoscopy may have a role in the following situations: 1) patients for whom colonoscopy is indicated for colon cancer screening but in whom it has not yet been performed, 2) patients with abnormal pericolic lymph node(s), 3) patients with a luminal colon mass, and 4) patients with an uncertain diagnosis (eg, inflammatory bowel disease or ischemic colitis) [16]. Colonoscopy in general should be avoided in aUniversity of California San Francisco, San Francisco, California. bPanel Chair, University of Wisconsin Hospital & Clinics, Madison, Wisconsin. cPanel Vice-Chair, University of California San Diego, San Diego, California. dPenn State Milton S. Hershey Medical Center, Hershey, Pennsylvania. eUniversity of Texas Health Science Center at Houston and McGovern Medical School, Houston, Texas; American Gastroenterological Association. fMedstar Georgetown University Hospital, Washington, District of Columbia, Primary care physician. gNYU Grossman School of Medicine, New York, New York. hMemorial Sloan Kettering Cancer Center, New York, New York. iMassachusetts General Hospital, Boston, Massachusetts. jOregon Health and Science University, Portland, Oregon. kCleveland Clinic, Cleveland, Ohio. lSentara Norfolk General Hospital/Eastern Virginia Medical School, Norfolk, Virginia; American College of Emergency Physicians.


Left Lower Quadrant Pain

Left Lower Quadrant Pain. mDuke Signature Care, Durham, North Carolina; American College of Physicians. nMallinckrodt Institute of Radiology, Saint Louis, Missouri; Committee on Emergency Radiology-GSER. oUniversity of North Carolina at Chapel Hill, Chapel Hill, North Carolina. pUniversity of California San Diego, San Diego, California. qMcMaster University, Hamilton, Ontario, Canada; Commission on Nuclear Medicine and Molecular Imaging. rSpecialty Chair, Virginia Commonwealth University Medical Center, Richmond, Virginia. The American College of Radiology seeks and encourages collaboration with other organizations on the development of the ACR Appropriateness Criteria through representation of such organizations on expert panels. Participation on the expert panel does not necessarily imply endorsement of the final document by individual contributors or their respective organization. Reprint requests to: publications@acr.org Left Lower Quadrant Pain the setting of acute diverticulitis because of the risk of perforation; if indicated, it usually is deferred until the acute event has resolved. Use of Oral and Rectal Contrast Media for CT: Neither oral nor rectal contrast is required for the routine evaluation of left lower quadrant pain. More than 20 studies have found no benefit for oral contrast in the evaluation of abdominal pain in the emergency department [17]. Rectal contrast may have a limited role in evaluating for perforation after surgical intervention. OR Discussion of Procedures by Variant Variant 1: Left lower quadrant pain. Initial imaging. This variant applies if there is nonspecific pain in the left lower quadrant with a broad differential diagnosis including gastrointestinal, gynecologic, urologic, and body wall pathology. If diverticulitis is primarily suspected, please refer to Variant 2 (suspected diverticulitis) or Variant 3 (suspected complication of diverticulitis). CT Abdomen and Pelvis CT is the most useful examination for left lower quadrant pain [16,19].


Left Lower Quadrant Pain

Left Lower Quadrant Pain. It is accurate and guides appropriate management, regardless of patient sex or patient body habitus [20]. CT is sensitive for small quantities of extraluminal intraperitoneal or retroperitoneal air [21,22]. Extraluminal air can be a critical finding indicating luminal perforation and often has surgical implications. Colonic diverticulitis is a common cause of small-volume extraluminal air at CT. Large-volume extraperitoneal air is more commonly seen with peptic ulcer disease or anastomotic dehiscence but can indicate a large-caliber perforation from diverticulitis [21]. Mortality rates are higher in patients with larger amounts of extraluminal air [21]. Fluoroscopic Contrast-Enhanced Enema Contrast-enhanced enema is not generally useful as the initial imaging test in patients with left lower quadrant pain. Although it may hold some utility in sigmoid and small bowel pathology, contrast enema would be of little value in the work up of other potential etiologies of left lower quadrant pain including gynecologic or urologic conditions. No recent studies in the utility of fluoroscopic contrast-enhanced enema and left lower quadrant pain have been published. Left Lower Quadrant Pain MRI Abdomen and Pelvis MRI is not useful for the initial evaluation of acute abdominal pain [1,12]. It is less sensitive for extraluminal air and urinary tract calculi, is more time-consuming to perform, requires an active screening process for indwelling devices and metal, and is more subject to motion artifacts in symptomatic patients. Few have compared the diagnostic accuracy of CT and MRI for the evaluation of left lower quadrant pain. In a 2013 pilot study, 30 consecutive patients with either sigmoid colon cancer (n = 15) or recent treatment for acute diverticulitis (n = 15) were imaged with CT or unenhanced MRI (T2-weighted and diffusion-weighted imaging) [12].


Left Lower Quadrant Pain

Left Lower Quadrant Pain. MRI was found to be more accurate than CT for the differentiation of cancer from diverticulitis (sensitivity: 100% versus 67%, specificity: 100% versus 93%) [12]. There are no large studies confirming the diagnostic accuracy of MRI for the general evaluation of patients with left lower quadrant pain. Radiography Abdomen and Pelvis Radiography is not useful as the initial imaging test for the general population of patients with left lower quadrant pain because CT is more accurate. Radiography can identify large volume extraluminal air, can diagnose ileus or bowel obstruction, or may diagnose urolithiasis. CT is more sensitive and specific for each of those entities. Radiography may play a role in the triage of severely ill patients with a surgical abdomen, but CT is used in most cases. Variant 2: Left lower quadrant pain. Suspected diverticulitis. Initial imaging. Diverticulitis is suspected in patients with left lower quadrant pain, fever, and leukocytosis. However, this triad is present in only approximately 25% of patients with diverticulitis [6,26]. Misdiagnosis based on clinical assessment alone has been reported to be between 34% and 68% [6,27,28]. CT Abdomen and Pelvis CT is the most useful examination for patients with suspected colonic diverticulitis because of its reproducibility, superior diagnostic accuracy (98%) [16,19], accuracy for alternative diagnoses with a similar presentation [9,16], risk-stratification of patients for operative versus nonoperative treatment [8,30-32], and inpatient versus outpatient triage [33,34]. CT diagnosis of uncomplicated acute diverticulitis in the emergency department can prevent unneeded hospital admission [3,5]. This is because most colonic diverticulitis is uncomplicated and can be managed with outpatient antibiotics [11]. Juszczyk et al [5] showed that early CT for acute diverticulitis can reduce hospital admission by more than 50% and shorten hospital length of stay.


Left Lower Quadrant Pain

Left Lower Quadrant Pain. IV contrast material is commonly used to improve the characterization and detection of subtle bowel wall abnormalities and complications of diverticulitis (eg, abscess) [2,29]. However, for most patients, IV or intracavitary contrast material is not necessary for the diagnosis of diverticulitis [35,36]. Left Lower Quadrant Pain CT may also help predict which patients are likely to experience recurrent diverticulitis and thereby augment triage between surveillance and operative management [39]. Colonic wall thickness at the site of diverticulitis and extent of diverticulitis-related complication may predict recurrent diverticulitis. Dickerson et al [39] showed that patients with colonic wall thicknesses <9 mm had a 19% recurrence risk at 1 year compared with a 40% recurrence if the wall thickness was >15 mm. Numerous CT classification systems for diverticulitis have been proposed but none are widely integrated into clinical practice. For example, the Hinchey classification uses CT findings to differentiate between uncomplicated and complicated disease [29,40,41]. Endoscopic classification systems for predicting occurrence, recurrence, and need for surgery are undergoing validation. In patients requiring colonoscopy for colon cancer screening, CT colonography has been proposed as an alternative to colonoscopy [16,42]. Fluoroscopic Contrast-Enhanced Enema Contrast-enhanced enema is not useful as the initial imaging test in patients with suspected diverticulitis because CT is more accurate and easier to obtain [16]. Because diverticulitis is mainly an extramucosal process, and contrast enema shows only the secondary effects of inflammation on the colon, the evaluation of extraluminal abnormalities, such as abscesses and pericolonic fat inflammation, is limited. Contrast-enhanced enema can be used to assess for complications of diverticulitis (eg, fistula) and for presurgical planning before colonic resection (ie, assess length of stricture and colonic motility) [16].


Left Lower Quadrant Pain

Left Lower Quadrant Pain. MRI Abdomen and Pelvis In 2021, Jerjen et al [43] published a systematic review of the use of MRI for the diagnosis of acute colonic diverticulitis. The authors found that the diagnostic accuracy of MRI for diverticulitis is likely less than that of CT but insufficiently studied. Published estimates of diagnostic accuracy have been limited by study-related biases and small sample sizes. At present, there are insufficient published data to support the routine use of MRI for the diagnosis of suspected diverticulitis. Findings of diverticulitis at MRI are like those at CT: colonic diverticula, thickened diverticulum(la), and inflammation in the pericolic fat, with or without complication (eg, abscess, fistula, perforation). MRI is less sensitive than CT for small-volume extraluminal gas and is more affected by patient motion than CT. Abbreviated MR protocols are being explored to reduce acquisition time and enable emergency department evaluation for suspected diverticulitis, but this remains a research application. Radiography Abdomen and Pelvis Radiography is not useful as the initial imaging test for the general population of patients with suspected diverticulitis because CT is more accurate. Radiography can identify large volume extraluminal air or bowel obstruction. CT is more sensitive and specific for both. Radiography may play a role in the triage of severely ill patients with a surgical abdomen, but CT is used in most cases. US Abdomen Transabdominal Although US is the initial imaging test for suspected diverticulitis in some European countries and the developing world, it still is not widely used in the United States, possibly in part due to a larger obese population. Acute diverticulitis is diagnoseable by US using the following criteria [25]: 1. Short-segment colonic wall thickening (>5 mm) 2. Inflamed diverticulum in the thickened area (hypoechoic and surrounded by hyperechoic fat) 3. Noncompressible hyperechoic pericolic tissue


Left Lower Quadrant Pain

Left Lower Quadrant Pain. Meta-analyses and prospective studies have demonstrated sensitivity and positive predictive value of graded compression US for diverticulitis of >90%. The accuracy is modestly less than that of CT, but especially so in obese patients and in patients with distal sigmoid diverticulitis. US likely has lower specificity than CT and is less likely to identify an alternative diagnosis. Furthermore, US requires a higher level of training for the diagnosis of diverticulitis than does CT. Dirks et al [25] estimate that a minimum of 500 examinations is required for competency. If used as the initial imaging test at the bedside (eg, point of care), US may hypothetically reduce the number of CT scans performed without a negative effect on patient care, with CT used in inconclusive cases or when the US is negative. US also has the benefit of being noninvasive. Variant 3: Left lower quadrant pain. Suspected complication(s) of diverticulitis. Initial imaging. CT Abdomen and Pelvis CT is the most useful examination for patients with suspected complications of colonic diverticulitis because of its reproducibility, superior diagnostic accuracy [16,19], accuracy for alternative diagnoses with a similar presentation [9,16], risk-stratification of patients for operative versus nonoperative treatment [8,30-32], and inpatient versus outpatient triage [33,34]. IV and oral contrast material may improve diagnosis of abscess by distinguishing from adjacent bowel. Unenhanced CT with oral contrast is less accurate than contrast-enhanced CT with oral contrast for the characterization of complications of diverticulitis but is superior to unenhanced CT without oral contrast [32]. Combining unenhanced CT with contrast-enhanced CT (biphasic imaging) is unnecessary and not recommended [23]. CT can predict unfavorable outcomes from acute diverticulitis. Longer segments of involved colon, retroperitoneal abscess, and extraluminal air have been associated with recurrence, failure of medical management, and need for surgery.