Magnetic Resonance Imaging Indirect Signs for Anterior Instability of the Lateral Meniscus in Pediatric and Adolescent Patients.

BACKGROUND: Anterior instability (AI) of the LM is potentially debilitating in young patients. The use of magnetic resonance imaging (MRI) to diagnose AI is limited due to the lack of reliable and accurate MRI findings. The ability to identify AI preoperatively would potentially improve the diagnosis and treatment of this pathology. This study presents a novel MRI finding ("phantom sign") for the detection of AI of the LM and demonstrates its reliability and accuracy. METHODS: Three independent blinded reviewers performed retrospective review of preoperative MRI for all patients who underwent LM repair between July 1, 2019, and March 31, 2022, at a single center. Positive phantom sign was defined as abnormal signal intensity on MRI of the anterior horn of the LM on the coronal sequence at the anterior tibial insertion of the anterior cruciate ligament (ACL). Preoperative MRI was also evaluated for other signs of LM anterior instability. Intrarater and inter-rater reliability was assessed for rater scoring of presence of pathology on MRI. Predictive ability of each imaging finding with at least good (ICC 0.6 or above) reliability was also evaluated based on documented intraoperative findings. RESULTS: Fifty-five preoperative MRIs of arthroscopically treated LM tears were reviewed. Median age was 15 years (range 6 to 20), and 21 patients (38.2%) were female. Twenty-seven patients (49.1%) had a discoid meniscus. LM AI was present on arthroscopy for 25 knees (45.45%), and among these, 21 had discoid morphology. Interrater reliability was substantial for phantom sign (ICC 0.71, 97.5% CI: 0.55-0.82), posterior displacement (ICC 0.71, 97.5% CI: 0.55-0.82), and posterior "megahorn" (ICC 0.76, 97.5% CI: 0.62-0.85). On predictive analysis, phantom signs were 98% sensitive and 76.7% specific for LM AI. Posterior displacement and posterior megahorn were specific for AI (both 93.34%), though with limited sensitivity (32% and 28.6%, respectively). CONCLUSIONS: Phantom sign is a reliable and sensitive MRI finding for anterior instability, even in the absence of frank displacement on preoperative MRI. A positive finding should prompt a thorough arthroscopic evaluation of the anterior horn of the LM. LEVEL OF EVIDENCE: Level III-case control study.

Rapid artificial intelligence solutions in a pandemic-The COVID-19-20 Lung CT Lesion Segmentation Challenge.

Artificial intelligence (AI) methods for the automatic detection and quantification of COVID-19 lesions in chest computed tomography (CT) might play an important role in the monitoring and management of the disease. We organized an international challenge and competition for the development and comparison of AI algorithms for this task, which we supported with public data and state-of-the-art benchmark methods. Board Certified Radiologists annotated 295 public images from two sources (A and B) for algorithms training (n=199, source A), validation (n=50, source A) and testing (n=23, source A; n=23, source B). There were 1,096 registered teams of which 225 and 98 completed the validation and testing phases, respectively. The challenge showed that AI models could be rapidly designed by diverse teams with the potential to measure disease or facilitate timely and patient-specific interventions. This paper provides an overview and the major outcomes of the COVID-19 Lung CT Lesion Segmentation Challenge - 2020.

Chest X-ray lung imaging features in pediatric COVID-19 and comparison with viral lower respiratory infections in young children.

RATIONALE: Chest radiography (CXR) is a noninvasive imaging approach commonly used to evaluate lower respiratory tract infections (LRTIs) in children. However, the specific imaging patterns of pediatric coronavirus disease 2019 (COVID-19) on CXR, their relationship to clinical outcomes, and the possible differences from LRTIs caused by other viruses in children remain to be defined. METHODS: This is a cross-sectional study of patients seen at a pediatric hospital with polymerase chain reaction (PCR)-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (n = 95). Patients were subdivided in infants (0-2 years, n = 27), children (3-10 years, n = 27), and adolescents (11-19 years, n = 41). A sample of young children (0-2 years, n = 68) with other viral lower respiratory infections (LRTI) was included to compare their CXR features with the subset of infants (0-2 years) with COVID-19. RESULTS: Forty-five percent of pediatric patients with COVID-19 were hospitalized and 20% required admission to intensive care unit (ICU). The most common abnormalities identified were ground-glass opacifications (GGO)/consolidations (35%) and increased peribronchial markings/cuffing (33%). GGO/consolidations were more common in older individuals and perihilar markings were more common in younger subjects. Subjects requiring hospitalization or ICU admission had significantly more GGO/consolidations in CXR (p < .05). Typical CXR features of pediatric viral LRTI (e.g., hyperinflation) were more common in non-COVID-19 viral LRTI cases than in COVID-19 cases (p < .05). CONCLUSIONS: CXR may be a complemental exam in the evaluation of moderate or severe pediatric COVID-19 cases. The severity of GGO/consolidations seen in CXR is predictive of clinically relevant outcomes. Hyperinflation could potentially aid clinical assessment in distinguishing COVID-19 from other types of viral LRTI in young children.

Rapid Artificial Intelligence Solutions in a Pandemic - The COVID-19-20 Lung CT Lesion Segmentation Challenge.

Artificial intelligence (AI) methods for the automatic detection and quantification of COVID-19 lesions in chest computed tomography (CT) might play an important role in the monitoring and management of the disease. We organized an international challenge and competition for the development and comparison of AI algorithms for this task, which we supported with public data and state-of-the-art benchmark methods. Board Certified Radiologists annotated 295 public images from two sources (A and B) for algorithms training (n=199, source A), validation (n=50, source A) and testing (n=23, source A; n=23, source B). There were 1,096 registered teams of which 225 and 98 completed the validation and testing phases, respectively. The challenge showed that AI models could be rapidly designed by diverse teams with the potential to measure disease or facilitate timely and patient-specific interventions. This paper provides an overview and the major outcomes of the COVID-19 Lung CT Lesion Segmentation Challenge - 2020.

Pediatric lung imaging features of COVID-19: A systematic review and meta-analysis.

RATIONALE: Pediatric COVID-19 studies have been mostly restricted to case reports and small case series, which have prevented the identification of specific pediatric lung disease patterns in COVID-19. The overarching goal of this systematic review and meta-analysis is to provide the first comprehensive summary of the findings of published studies thus far describing COVID-19 lung imaging data in the pediatric population. METHODS: A systematic literature search of PubMed was performed to identify studies assessing lung-imaging features of COVID-19 pediatric patients (0-18 years). A single-arm meta-analysis was conducted to obtain the pooled prevalence and 95% confidence interval (95% CI). RESULTS: A total of 29 articles (n = 1026 children) based on chest computerized tomography (CT) images were included. The main results of this comprehensive analysis are as follows: (1) Over a third of pediatric patients with COVID-19 (35.7%, 95% CI: 27.5%-44%) had normal chest CT scans and only 27.7% (95% CI: 19.9%-35.6%) had bilateral lesions. (2) The most typical pediatric chest CT findings of COVID-19 were ground-glass opacities (GGO) (37.2%, 95% CI: 29.3%-45%) and the presence of consolidations or pneumonic infiltrates (22.3%, 95% CI: 17.8%-26.9%). (3) The lung imaging findings in children with COVID-19 were overall less frequent and less severe than in adult patients. (4) Typical lung imaging features of viral respiratory infections in the pediatric population such as increased perihilar markings and hyperinflation were not reported in children with COVID-19. CONCLUSION: Chest CT manifestations in children with COVID-19 could potentially be used for early identification and prompt intervention in the pediatric population.

Overcoming Challenges for Successful PACS Installation in Low-Resource Regions: Our Experience in Nigeria.

In this paper, we walk you through our challenges, successes, and experience while participating in a Global Health Outreach Project at the University College Hospital (UCH) Ibadan, Nigeria. The scope of the project was to install a Picture Archive and Communication System (PACS) to establish a centralized viewing network at UCH's Radiology Department, for each of their digital modalities. Installing a PACS requires robust servers, the ability to retrieve and archive studies, ensuring workstations can view studies, and the configuration of imaging modalities to send studies. We anticipated that we might experience hurdles for each of these requirements, due to limited resources and without the availability to make a site visit prior to the start of the project. While we ultimately experienced delays and troubleshooting was required at each turn of the install, with the help of dedicated volunteers both on and off-site and the UCH staff, our shared goal was accomplished.

Advances in Diagnostic Imaging in Pediatric Gastroenterology.

PURPOSE OF REVIEW: The purpose is to provide a review of cross-sectional imaging updates in the assessment of gastrointestinal diseases, relevant to clinical practice and research. RECENT FINDINGS: New magnetic resonance imaging contrast agents (Eovist) are taken up by hepatocytes and excreted via the biliary tree. As such, a lesion will retain contrast only if hepatocytes are present, which aids in refining the differential diagnosis. Magnetic resonance enterography is a method for non-invasively diagnosing and following various GI conditions, predominantly inflammatory bowel disease. Contrast-enhanced ultrasound uses gas-filled microbubbles providing superb temporal resolution most notably in the arterial phase, which aids in differentiating lesions. Elastography is a new technique which assesses stiffness of liver for evaluating fibrosis. These new techniques provide more accurate diagnoses and information, often limiting ionizing radiation exposure from other modalities. While ultrasound will still remain the initial imaging modality, familiarity with these other options is valuable for appropriate pathology workup.

Ultrasound-Based Phenotyping of Lateral Ventricles to Predict Hydrocephalus Outcome in Premature Neonates.

OBJECTIVE: Prediction of post-hemorrhagic hydrocephalus (PHH) outcome-i.e., whether it requires intervention or not-in premature neonates using cranial ultrasound (CUS) images is challenging. In this paper, we present a novel fully-automatic method to perform phenotyping of the brain lateral ventricles and predict PHH outcome from CUS. METHODS: Our method consists of two parts: ventricle quantification followed by prediction of PHH outcome. First, cranial bounding box and brain interhemispheric fissure are detected to determine the anatomical position of ventricles and correct the cranium rotation. Then, lateral ventricles are extracted using a new deep learning-based method by incorporating the convolutional neural network into a probabilistic atlas-based weighted loss function and an image-specific adaption. PHH outcome is predicted using a support vector machine classifier trained using ventricular morphological phenotypes and clinical information. RESULTS: Experiments demonstrated that our method achieves accurate ventricle segmentation results with an average Dice similarity coefficient of 0.86, as well as very good PHH outcome prediction with accuracy of 0.91. CONCLUSION: Automatic CUS-based ventricular phenotyping in premature newborns could objectively and accurately predict the progression to severe PHH. SIGNIFICANCE: Early prediction of severe PHH development in premature newborns could potentially advance criteria for diagnosis and offer an opportunity for early interventions to improve outcome.

Pediatric Radiology Fellowship Creation as an International Education Outreach Effort in Ethiopia.

BACKGROUND: In 2008, there were no pediatric radiologists in Ethiopia, a country of 100 million people. The radiology residency programs lacked training in pediatric imaging acquisition and interpretation. OBJECTIVE: We established an accredited local pediatric radiology fellowship program in Ethiopia. METHODS: With assistance from US faculty from the Children's Hospital of Philadelphia, Ethiopian radiologists created a 2-year fellowship training program in a university-based Ethiopian radiology residency program that incorporated formal lectures and seminars, case tutorials, journal clubs, teleradiological conferences, paper presentations, and online courses from collaborating institutions. Formal accreditation of the program was achieved from the university, and core values were established to ensure sustainability and self-sufficiency. The Ethiopian institution provided funding for the fellows, and US faculty volunteered their time. RESULTS: In 2015, 2 radiologists were recruited to the new fellowship; after graduation in 2017, they formed the first pediatric radiology section at the Ethiopian institution. Three new fellows were recruited in 2019, and the program is now self-sustaining. Pediatric imaging training has also been added to the radiology residency. CONCLUSIONS: Establishing a pediatric radiology fellowship in a country with high need but little existing faculty expertise is feasible through outreach efforts.

Normal development imaging pitfalls and injuries in the pediatric shoulder.

The skeletal maturation of the shoulder has been well documented on radiographic and cadaveric studies. Recent increased use of MRI has provided increased understanding of the soft-tissue and osseous changes that occur during development. Thus recognizing normal maturation, imaging manifestations and pitfalls is crucial when evaluating the pediatric shoulder joint. At birth, the humeral diaphysis, midportion of the clavicle, and the body of the scapula are ossified, while the remainder of the bones of the shoulder are composed of non-ossified cartilaginous precursors. During growth, cartilaginous apophyses and epiphyses of the shoulder develop numerous secondary ossification centers, which fuse with the primary ossification centers to form the complete bony components of the shoulder. Additionally changes in the morphology of the growth plates as well as marrow signal occur in an organized manner. This paper affords the reader with an understanding of the normal development of three major components of skeletal maturation in the shoulder: ossification centers, growth plates and marrow signal. These topics are further subdivided into the glenoid, proximal humerus and acromioclavicular joint. We also provide a focus on distinguishing normal anatomy from imaging pitfalls related to skeletal maturation.

Anteroposterior Radiograph of the Ankle with Cross-Sectional Imaging Correlation.

The focus of this article is to illustrate various pathologic entities and variants, heralding disease about the ankle, based on scrutiny of AP radiographs of the ankle, with correlative findings on cross-sectional imaging. Many of these entities can only be detected on the AP ankle radiograph and, if not recognized, may lead to delayed diagnosis and persistent morbidity to the patient. However, a vigilant radiologist, equipped with the knowledge of the characteristic appearance and typical locations of the imaging findings, should be able to make the crucial initial diagnosis and surmise additional findings to be confirmed on cross-sectional imaging.

Imaging features of glenoid bare spot in a pediatric population.

OBJECTIVE: The bare spot (BaS) is a central, well-circumscribed focal defect in the glenoid articular surface, with reported adult incidence of 1-2%. We aimed to reassess MRI features of BaS in the pediatric population and determine its etiology. MATERIALS AND METHODS: A retrospective search of our database from June 2014 to October 2015 was performed for shoulder MRI in patients between 5 and 25 years and then subdivided into four groups: group 1, 5-10 years; group 2, 10-15 years; group 3, 15-18 years; group 4, 20-25 years. BaS was defined as a well-marginated, central defect of increased signal in the articular surface of the glenoid, seen on at least two planes, without evidence of underlying glenoid pathology. Presence, location and size along with clinical indications were documented. RESULTS: A final cohort of 253 patients revealed 23 BaS, 3.5% in group 1, 20% in group 2, 5% in group 3 and 4% in group 4. There was a significantly higher incidence in group 2 (p = 0.007) compared to group 3 and p = 0.002 compared to group 4. Location was mainly central. Mean size was significantly bigger in group 2 compared to group 3 and 4. Distribution showed the highest number at 14-15 years of age. Instability was higher in groups 3 and 4. CONCLUSION: Incidence of BaS in group 2 was significantly higher than in other age groups and higher than in adults. BaS was also larger compared to other populations. These findings support a developmental theory, explained by the centripetal ossification of the glenoid.

Implementing ultrasound-guided hydrostatic reduction of intussusception in a low-resource country in Sub-Saharan Africa: our initial experience in Ethiopia.

BACKGROUND: Despite advances in non-invasive radiological techniques for the treatment of intussusception, management of the entity still remains exclusively surgical in many developing countries, including Ethiopia. Fluoroscopic units are rare or mostly dysfunctional. Ultrasound scanners are more commonly available. Ultrasound-guided hydrostatic reduction (USGHR) was recently introduced to the main referral hospital in Ethiopia, and subsequently has been adopted as the initial management option for intussusception. PURPOSE: The aim of this study was to evaluate our experience with USGHR in Ethiopia and measure the impact on patient care. METHODS: A prospective study was conducted between July 2014 and August 2015 on all pediatric patients, with US-confirmed intussusception, at the Tikur Anbessa Specialized Teaching Hospital in Addis Ababa, Ethiopia. All patients, excluding those with signs of peritonitis, bowel ischemia, or symptoms lasting longer than 4 days, were selected to undergo USGHR. RESULTS: A total of 53 children were diagnosed with intussusception, confirmed via ultrasound. Following exclusion criteria, USGHR was attempted in 47 of the patients. Forty-one of the 47 patients (87.2%) had successful reduction, resulting in a 77% overall rate of successful non-operative management in all patients with intussusception. CONCLUSION: The rate of operative reduction of intussusception decreased by 77% following the introduction of USGHR as the initial non-surgical intervention. Therefore, we believe USGHR should be fully implemented in our hospital, and recommend that this study serves as an example to other institutions in our country as well as in other developing countries facing similar challenges.

Growth plate injury at the base of the coracoid: MRI features.

PURPOSE: To assess the MRI features of growth plate injury at the base of the coracoid process. MATERIALS AND METHODS: Subjects were identified through retrospective search of our department imaging database and teaching files and the teaching files of two outside academic institutions. The coracoid base growth plate was examined with attention to widening, irregularity, abnormal signal intensity of the growth plate, and the presence of adjacent soft tissue edema. The apposing coracoid and scapular bony surfaces were examined for signal intensity and morphology. RESULTS: Shoulder MRIs in eight patients with coracoid base growth plate disturbances were retrospectively reviewed (7 males, 1 female, mean age 15 years). Growth plate injury manifested as widening, irregularity and increased signal, apposing bony marrow edema and hypertrophy, and surrounding soft tissue edema. Five subjects were athletes (football, archery, basketball, swimming, rugby), two had a history of neuromuscular disorders, and one subject presented after a fall. Clinical indications included: rule out labral tear (n = 3), rule out rotator cuff tear or fracture after fall (n = 1), nonspecific pain (n = 1), shoulder subluxation, rule out glenoid pathology (n = 1, patient with underlying neuromuscular disorder), muscular dystrophy with shoulder pain (n = 1), and impingement (n = 1). Coracoid growth plate injury was not suspected clinically in any of the patients. CONCLUSION: Awareness of the imaging appearance of coracoid base growth plate injury can aid in a more accurate diagnosis of shoulder MRI studies in young pediatric athletes. While uncommon, coracoid growth plate injury should be considered when assessing children with shoulder symptomatology.

The frondiform ligament and pseudotenosynovitis of the extensor digitorum longus tendon: MRI evaluation with cadaveric correlation.

OBJECTIVE: Fluid along the frondiform ligament, the sinus tarsi stem of the inferior extensor retinaculum (IER), can approximate the extensor digitorum longus (EDL), at times simulating tenosynovitis. Our purpose, based on MRI and cadaveric studies, was to further evaluate this scantly described phenomenon, to identify associated findings and to alert the radiologists to the potential pitfall of over diagnosing EDL tenosynovitis. MATERIALS AND METHODS: Two musculoskeletal radiologists retrospectively reviewed the radiology reports and MRI studies of 258 ankle MRI exams, performed at our institution, for fluid along the frondiform ligament extending toward the EDL. No patient had EDL pathology clinically. MRI was performed in two cadaveric ankles following injection of the sinus tarsi and EDL tendon sheath, under ultrasound guidance. RESULTS: Altogether, 31 MRIs demonstrated fluid extending from the sinus tarsi along the frondiform ligament toward the EDL. In 30 cases (97 %), the fluid partially surrounded the tendon, without tendon sheath distension. Based on the radiology reports, in 11 of the 31 cases (35 %), the fluid was misinterpreted as abnormal. Most common associated findings included ligamentous injury, posterior tibial tendon (PTT) tear, flat-foot, and osteoarthrosis. In the cadavers, fluid extended along the frondiform ligament toward the EDL after sinus tarsi injection; there was no communication between EDL tendon sheath and the sinus tarsi. CONCLUSION: Fluid within the sinus tarsi can extend along the frondiform ligament and partially surround the EDL, manifesting as pseudotenosynovitis. This phenomenon, often seen with ligamentous tears or PTT dysfunction, should not be misdiagnosed as true pathology of the EDL.

Normal skeletal development and imaging pitfalls of the calcaneal apophysis: MRI features.

OBJECTIVE: Heel pain in children and secondary MR imaging (MRI) of the hindfoot have been increasing in incidence. Our purpose is to illustrate the, previously unreported, MRI stages in development of the posterior calcaneal apophysis, with attention to imaging pitfalls. This should aid in distinguishing normal growth from true disease. MATERIAL AND METHODS: Consecutive ankle MRIs in children <18 years, from 2008-2014, were subdivided into 0≤5, 5≤10, 10≤15 and 15≤18 age groups and retrospectively reviewed for development of the calcaneal apophysis. RESULTS: 204 ankle MRI studies in 188 children were identified. 40 studies were excluded with final cohort of 164 studies in 154 patients (82 boys, 72 girls). The calcaneal apophysis was cartilaginous until age 5. Foci of decreased as well as increased signal were embedded in cartilage, prior to ossification. Early, secondary ossification centers appeared in plantar third of the apophysis in 100% of children by age 7. Increased T2 signal in the ossifications was seen in 30% of children. Apohyseal fusion began at 12 and was complete in 78% of 14≤15 year olds and in 88% of 15≤18 year olds. Curvilinear low signal in the ossification centers, paralleling, but distinguished from growth plate, and not be confused with fracture line, was common. CONCLUSION: Development of the posterior calcaneus follows a unique sequence. Apophyseal fusion occurs earlier than reported in the literature. Familiarity with this maturation pattern, in particular the apophyseal increased T2 signal and the linear low signal paralleling the growth plate, will avoid misinterpreting it for pathology.

Evaluation of an initiative to reduce radiation exposure from CT to children in a non-pediatric-focused facility.

We would like to share our experience of reducing pediatric radiation exposure. Much of the recent literature regarding successes of reducing radiation exposure has come from dedicated children's hospitals. Nonetheless, over the past two decades, there has been a considerable increase in CT imaging of children in the USA, predominantly in non-pediatric-focused facilities where the majority of children are treated. In our institution, two general hospitals with limited pediatric services, a dedicated initiative intended to reduce children's exposure to CT radiation was started by pediatric radiologists in 2005. The initiative addressed multiple issues including eliminating multiphase studies, decreasing inappropriate scans, educating referring providers, training residents and technologists, replacing CT with ultrasound or MRI, and ensuring availability of pediatric radiologists for consultation. During the study period, the total number of CT scans decreased by 24 %. When accounting for the number of scans per visit to the emergency department (ED), the numbers of abdominal and head CT scans decreased by 37.2 and 35.2 %, respectively. For abdominal scans, the average number of phases per scan decreased from 1.70 to 1.04. Upon surveying the pediatric ED staff, it was revealed that the most influential factors on ordering of scans were daily communication with pediatric radiologists, followed by journal articles and lectures by pediatric radiologists. We concluded that a non-pediatric-focused facility can achieve dramatic reduction in CT radiation exposure to children; however, this is most effectively achieved through a dedicated, multidisciplinary process led by pediatric radiologists.

Normal Skeletal Maturation and Imaging Pitfalls in the Pediatric Shoulder.

A growing number of magnetic resonance (MR) imaging studies of the shoulder are being performed as a result of greater and earlier participation of children and adolescents in competitive sports such as softball and baseball. However, scant information is available regarding the MR imaging features of the normal sequential development of the shoulder. The authors discuss the radiographic and MR imaging appearances of the normal musculoskeletal maturation patterns of the shoulder, with emphasis on (a) development of secondary ossification centers of the glenoid (including the subcoracoid and peripheral glenoid ossification centers); (b) development of preossification and secondary ossification centers of the humeral head and the variable appearance and number of the secondary ossification centers of the distal acromion, with emphasis on the formation of the os acromiale; (c) development of the growth plates, glenoid bone plates, glenoid bare area, and proximal humeral metaphyseal stripe; and (d) marrow signal alterations in the distal humerus, acromion, and clavicle. In addition, the authors discuss various imaging interpretation pitfalls inherent to the normal skeletal maturation of the shoulder, examining clues that may help distinguish normal development from true disease (eg, osteochondral lesions, labral tears, abscesses, fractures, infection, tendon disease, acromioclavicular widening, and os acromiale). Familiarity with the timing, location, and appearance of maturation patterns in the pediatric shoulder is crucial for correct image interpretation.

MR imaging of entrapment neuropathies of the lower extremity. Part 1. The pelvis and hip.

Entrapment neuropathies can manifest with confusing clinical features and therefore are often underrecognized and underdiagnosed at clinical examination. Historically, electrophysiologic evaluation has been considered the mainstay of diagnosis. Today, cross-sectional imaging, particularly magnetic resonance (MR) imaging and specifically MR neurography, plays an increasingly important role in the work-up of entrapment neuropathies. MR imaging is a noninvasive operator-independent technique that allows identification of the underlying cause of injury, differentiation between surgically treatable and untreatable causes, and guidance of selective diagnostic anesthetic nerve blocks. Pathologic conditions affecting the lumbosacral plexus and major motor and mixed nerves of the pelvis and hip include neuropathies of the lumbosacral plexus, femoral nerve, lateral femoral cutaneous nerve, obturator nerve, and sciatic nerve; piriformis muscle syndrome; and injury of the gluteal nerves. Diagnosis of entrapment neuropathies of the pelvis and hip with MR imaging requires familiarity with the normal MR imaging anatomy and awareness of the anatomic and pathologic factors that put peripheral nerves at risk for injury.