Pediatric Pelvis.

The development of the pelvis follows a predictable pattern of ossification that involves the maturation of bone, synchondroses, and apophyses. These growth centers appear and close at distinct times during skeletal maturity and give rise to structural changes in the pelvis that can be distinctively appreciated on various imaging modalities. Accurate interpretation of radiologic images requires knowledge of skeletal development because the varying appearance of the maturing pediatric pelvis may be mistaken for pathology. In addition, many normal features within the pelvis can be erroneously perceived as injury. This article incorporates a multimodality review of normal pelvic maturation, a discussion of developmental variants, and a description of common injuries unique to the pediatric pelvis.

Imaging in pediatric spondyloarthritis.

PURPOSE OF REVIEW: Imaging is used in the diagnosis of peripheral and axial disease in juvenile spondyloarthritis (JSpA). Imaging of the joints and entheses in children and adolescents can be challenging for those unfamiliar with the appearance of the maturing skeleton. These differences are key for rheumatologists and radiologists to be aware of. RECENT FINDINGS: In youth, skeletal variation during maturation makes the identification of arthritis, enthesitis, and sacroiliitis difficult. A great effort has been put forward to define imaging characteristics seen in healthy children in order to more accurately identify disease. Additionally, there are novel imaging modalities on the horizon that are promising to further differentiate normal physiologic changes versus disease. SUMMARY: This review describes the current state of imaging, limitations, and future imaging modalities in youth, with key attention to differences in imaging interpretation of the peripheral joints, entheses, and sacroiliac joint in youth and adults.

Musculoskeletal imaging in neonates: use of ultrasound.

High-resolution US is a practical, cost-effective modality to evaluate the musculoskeletal system in neonates. US can be performed portably in the neonatal intensive care unit so that the critically ill infant can be evaluated with minimal distress. Sonography is noninvasive and does not require sedation; typical questions that might require the use of MRI or CT in older children can be rapidly resolved with US. Dynamic imaging can be used in real time to stress joints and see how articular structures relate. Given the advantages of US within the neonatal population, it has been widely used to evaluate for neonatal fractures, congenital joint abnormalities, limb deficiencies as well as muscular and soft-tissue abnormalities.

Whole-body magnetic resonance imaging in the evaluation of children with fever without a focus.

BACKGROUND: Fever without a focus is defined as a temperature of 38° C or higher as the single presenting symptom. After extensive investigation, a large percentage (12-67%) of cases remain undiagnosed. OBJECTIVE: To assess the diagnostic value of whole-body magnetic resonance imaging (WB-MRI) in children with fever without a focus. MATERIALS AND METHODS: A retrospective study was performed to identify children who underwent WB-MRI for fever without a focus. Ninety-two children, 50 boys, with a mean age of 6.1 years were included. A multidisciplinary team of physicians completed in consensus a medical record review that included: 1) immune status, 2) underlying chronic conditions, 3) hospitalization status at onset of fever, and 4) results of tissue, body fluid cultures and biopsies. Original MRI reports were evaluated. WB-MRI studies were categorized into helpful WB-MRI and not helpful WB-MRI. RESULTS: A final diagnosis for the cause of the fever was available for 68/92 cases (73.9%), which were determined to be infectious in 33/68 (48.5%), oncological in 3/68 (4.4%), rheumatological etiologies in 23/68 (33.8%) and miscellaneous in 9/68 (13.2%) cases. WB-MRI was found to be helpful in 62/92 cases (67.4%) and not helpful in 30/92 cases (32.6%). WB-MRI was 10.2 times less likely to be helpful in immunosuppressed children and almost 5.7 times less likely to be helpful in cases of prolonged fever (>3 weeks) at the time of MRI (P≤0.01). CONCLUSION: WB-MRI provides helpful information in approximately 2/3 of children with fever without a focus. In most cases, it was helpful to exclude the need of further investigation.

Intraoperative Contrast-Enhanced Ultrasound Imaging of Femoral Head Perfusion in Developmental Dysplasia of the Hip: A Feasibility Study.

OBJECTIVES: Developmental dysplasia of the hip (DDH) is one of the most common developmental deformities of the lower extremity. Although many children are successfully treated with a brace or harness, some require intraoperative closed or open reduction and spica casting. Surgical reduction is largely successful to relocate the hip; however, iatrogenic avascular necrosis is a major source of morbidity. Recent research showed that postoperative gadolinium-enhanced magnetic resonance imaging (MRI) can depict hip perfusion, which may predict a future incidence of avascular necrosis. As contrast-enhanced ultrasound (CEUS) assesses blood flow in real time, it may be an effective intraoperative alternative to evaluate femoral head perfusion. Here we describe our initial experience regarding the feasibility of intraoperative CEUS of the hip for the assessment of femoral head perfusion before and after DDH reduction. METHODS: This single-institution retrospective Institutional Review Board-approved study with a waiver of informed consent evaluated intraoperative hip CEUS in children with DDH compared to postoperative contrast-enhanced MRI. Pediatric radiologists, blinded to prior imaging findings and outcomes, reviewed both CEUS and MRI examinations separately and some time from the initial examination both independently and in consensus. RESULTS: Seventeen patients had 20 intraoperative CEUS examinations. Twelve of 17 (70.6%) had prereduction hip CEUS, postreduction hip CEUS, and postreduction gadolinium-enhanced MRI. Seven of 12 (58.3%) were evaluable retrospectively. All CEUS studies showed blood flow in the femoral epiphysis before and after reduction, and all MRI studies showed femoral head enhancement after reduction. The CEUS and MRI for all 7 patients also showed physeal blood flow. CONCLUSIONS: Contrast-enhanced ultrasound is a feasible intraoperative tool for assessing adequate blood flow after hip reduction surgery in DDH.

Magnetic resonance imaging of the fetal musculoskeletal system.

Diagnosing musculoskeletal pathology requires understanding of the normal embryological development. Intrinsic errors of skeletal development are individually rare but are of paramount clinical importance because anomalies can greatly impact patients' lives. An accurate assessment of the fetal musculoskeletal system must be performed to provide optimal genetic counseling as well as to drive therapeutic management. This manuscript reviews the embryology of skeletal development and the appearance of the maturing musculoskeletal system on fetal MRI. In addition, it presents a comprehensive review of musculoskeletal fetal pathology along with postnatal imaging.

Normal hip joint fluid volumes in healthy children of different ages, based on MRI volumetric quantitative measurement.

BACKGROUND: While magnetic resonance imaging (MRI) of the pelvis and hips is common in pediatric patients, to date there are no data on the quantification of normal hip joint fluid volume in this patient population. OBJECTIVE: We sought to assess the feasibility and reliability of quantitative hip joint fluid measurement in the pediatric population to estimate the normal volume of fluid in a pediatric hip joint. MATERIALS AND METHODS: Seventy healthy children ages 8-17 years underwent a pelvic MRI including a large field of view coronal T2 fat-saturated sequence where hips were entirely imaged. Following 3 training sessions, 2 readers with experience in musculoskeletal imaging performed volumetric quantitative measurements of hip fluid (140 hips) using semiautomated pixel-based thresholding on custom MATLAB software. RESULTS: The mean processing time per hip was 2 min, 41 s. The mean volume of fluid in a hip joint was 2.1 mL (range: 0.38-5.41 mL), increasing slightly with age. Volumes were also greater in boys than in girls (P=0.004). Intra-observer and interobserver agreement were high (intra-class correlation coefficients 0.93 and 0.98, respectively), with mean volume differences of 0.04 mL for intra-observer and 0.09 mL for interobserver. CONCLUSION: A semiautomated pixel-based thresholding approach was feasible and reliable for measuring joint fluid in pediatric hip MRI. The average fluid volume of 2.1 mL can represent a visually substantial quantity of fluid per MRI slice, particularly in small children, and should not be misinterpreted as a joint effusion.

MRI of the Sacroiliac Joint in Healthy Children.

To listen to the podcast associated with this article, please select one of the following: iTunes, Google Play, or direct download. OBJECTIVE. Increasing reliance on MRI for the evaluation of sacroiliitis requires that radiologists be familiar with the normal appearance of the developing sacroiliac joint. We describe age-related MRI features of the sacroiliac joints in healthy children. SUBJECTS AND METHODS. Seventy healthy children from three age groups-prepubertal (8-10 years), peripubertal (11-13 years), and approaching skeletal maturity (14-17 years)-completed questionnaires and underwent sacroiliac joint MRI. Imaging studies were evaluated by three experienced pediatric radiologists. Metaphyseal-equivalent signal intensity, nonperiarticular osteitis, cartilage volume, joint fluid, enthesitis, and surface cortex irregularities were evaluated. Metaphyseal-equivalent signal intensity was evaluated using an ordinal grading system (types I-IV). Intraclass correlation coefficients were calculated to assess interrater reliability. RESULTS. Increased metaphyseal-equivalent signal intensity (types I and II) was present in most prepubertal children and in less than 10% of the group approaching skeletal maturity. More prepubertal girls had type I signal than boys, but signal progressed to type IV signal faster in girls than in boys. None of the subjects had subchondral marrow edema, but four subjects had nonperiarticular osteitis. Cartilage volumes decreased with advancing age in girls and, on average, were lower in girls than in boys of the same age. One subject had measurable joint fluid. Cortex irregularities were common (57.1%), most frequently seen along the iliac bone (51.4% ilium vs 11.4% sacrum, p < 0.01) and in the upper quadrants (42.8% upper vs 27.1% lower, p = 0.01). CONCLUSION. We provide valuable reference MRI descriptions of the healthy pediatric sacroiliac joint that should improve our ability to distinguish between normal and pathologic findings.

Magnetic resonance imaging of elbow injuries in children.

Evaluating elbow injuries is challenging because of the complex anatomy of the joint. In children, injury patterns depend on the sports-specific mechanism as well as the stage of skeletal maturity. This article reviews the anatomy of the elbow and common injury patterns seen in children, with an emphasis on MRI and the throwing athlete. Imaging pitfalls specific to children are described.

Extended field of view magnetic resonance imaging for suspected osteomyelitis in very young children: is it useful?

BACKGROUND: Osteomyelitis is a challenging diagnosis for clinicians, particularly in very young children. At our institution, the magnetic resonance imaging (MRI) protocol in suspected osteomyelitis for children 5 years of age or younger includes a large field of imaging regardless of the clinical site of concern. OBJECTIVE: To determine if extended field of view (FOV) MRI contributes important information in young children with suspected osteomyelitis. MATERIALS AND METHODS: A retrospective study was performed including children 5 years of age or younger with suspected osteomyelitis from January 2011 to September 2015. All children underwent coronal fluid-sensitive MRI from neck to feet. Focused imaging was performed as necessary on abnormal sites depicted on survey imaging. Two radiologists reviewed the imaging findings, which were compared to the clinical outcome. RESULTS: We studied 51 children with a mean age of 2.2 years (range: 21 days-5.5 years); 53% were boys. Osteomyelitis was depicted by MRI in 20 subjects (39.2%). Survey coronal fluid-sensitive imaging was accomplished by adding a single fluid-sensitive series in 1 child, 2 series in 31 children, 3 series in 16 children and 4 series in 3 children. Survey imaging added a median total time of 6:51 min to the examination (range: 2.29-20.54 min). Extended FOV imaging added important information in 11/51 subjects (21.6%), in 6 cases (11.8%) of infection and in 5 cases (9.8%) by suggesting alternative diagnoses. CONCLUSION: The addition of extended FOV MRI in young children with suspected osteomyelitis added important clinical information in 21.6% of patients while only adding a median of 6:51 min to the examination. It is our experience that in children ≤5 years of age with suspected osteomyelitis, extended FOV imaging adds important information and may result in changes in management.

Correlation between diffusion tensor imaging parameters of the distal femoral physis and adjacent metaphysis, and subsequent adolescent growth.

BACKGROUND: Diffusion-tensor imaging (DTI) depicts the movement of water through columns of cartilage and newly formed bone and provides information about velocity of growth and growth potential. OBJECTIVE: To determine the correlation between DTI tractography parameters of the distal femoral physis and metaphysis and the height change after DTI in pubertal and post-pubertal children. MATERIALS AND METHODS: We retrospectively analyzed DTI images of the knee in 47 children with a mean age of 14.1 years in a 2-year period. In sagittal echoplanar DTI studies, regions of interest were placed in the femoral physis. Tractography was performed using a fractional anisotropy threshold of 0.15 and a maximum turning angle of 40°. The sample was divided to assess short-term and long-term growth after DTI. Short-term growth (n=25) was the height change between height at MRI and 1 year later. Long-term growth (n=36) was the height gain between height at MRI and at the growth plateau. RESULTS: For the short-term group, subjects with larger tract volume (R2=0.40) and longer track lengths (R2=0.38) had larger height gains (P<0.01). For the long-term group, subjects with larger tract volume (R2=0.43) and longer track lengths (R2=0.32) had a larger height gain at the growth plateau (P<0.01). Intra- and inter-observer variability were good-excellent. CONCLUSION: Follow-up data of growth 1 year after DTI evaluation and at skeletal maturity confirms that DTI parameters are associated with the amount of post-imaging growth.

Evaluating growth failure with diffusion tensor imaging in pediatric survivors of high-risk neuroblastoma treated with high-dose cis-retinoic acid.

BACKGROUND: The survival of patients with high-risk neuroblastoma has increased with multimodal therapy, but most survivors demonstrate growth failure. OBJECTIVE: To assess physeal abnormalities in children with high-risk neuroblastoma in comparison to normal controls by using diffusion tensor imaging (DTI) of the distal femoral physis and adjacent metaphysis. MATERIALS AND METHODS: We prospectively obtained physeal DTI at 3.0 T in 20 subjects (mean age: 12.4 years, 7 females) with high-risk neuroblastoma treated with high-dose cis-retinoic acid, and 20 age- and gender-matched controls. We compared fractional anisotropy (FA), normalized tract volume (cm3/cm2) and tract concentration (tracts/cm2) between the groups, in relation to height Z-score and response to growth hormone therapy. Tractography images were evaluated qualitatively. RESULTS: DTI parameters were significantly lower in high-risk neuroblastoma survivors compared to controls (P<0.01), particularly if the patients were exposed to both cis-retinoic acid and total body irradiation (P<0.05). For survivors and controls, DTI values were respectively [mean ± standard deviation]: tract concentration (tracts/cm2), 23.2±14.7 and 36.7±10.5; normalized tract volume (cm3/cm2), 0.44±0.27 and 0.70±0.21, and FA, 0.22±0.05 and 0.26±0.02. High-risk neuroblastoma survivors responding to growth hormone compared to non-responders had higher FA (0.25±0.04 and 0.18±0.03, respectively, P=0.02), and tract concentration (tracts/cm2) (31.4±13.7 and 14.8±7.9, respectively, P<0.05). FA, normalized tract volume and tract concentration were linearly related to height Z-score (R2>0.31; P<0.001). Qualitatively, tracts were nearly absent in all non-responders to growth hormone and abundant in all responders (P=0.02). CONCLUSION: DTI shows physeal abnormalities that correlate with short stature in high-risk neuroblastoma survivors and demonstrates response to growth hormone treatment.

Normal meniscal dimensions at different patient ages-MRI evaluation.

OBJECTIVE: The purpose of this work is to evaluate the normal meniscal and tibial dimensions in relation to age and gender in different children using conventional MRI sequences. MATERIALS AND METHODS: Morphometric measurements of the menisci were retrospectively performed on knee MRIs of children (< 18 years). All knee MRIs over a 7-year period were collected. Exclusion criteria included: prior knee surgery or diseases involving the knee joint. A total of 186 children were included, 110 boys and 76 girls, with a mean age of 8.2 years (range, 0.3-17.8 years). Menisci and tibial measurement changes with age and gender as well as differences between the medial and lateral menisci were evaluated. RESULTS: The medial menisci measurements increased with age (p value < 0.001). The lateral menisci measurements increased with age (p value < 0.001), except for the coronal meniscal width (p = 0.084). Coronal and sagittal percentage of meniscal coverage of the tibia decreased with age (p < 0.001). Medial menisci have greater sagittal width and anterior horn height than lateral menisci (p value < 0.001). Lateral menisci are larger in their coronal width and height, and sagittal posterior horn height in comparison to medial menisci (p < 0.001). CONCLUSIONS: Menisci increase in all dimensions in correlation with age; except in the coronal meniscal width, which is a useful dimension to diagnose discoid meniscus on MRI, based on this, it would seem that the currently published size criteria, based on adults, could be applicable to children. The tibia has a faster rate dimension increase in correlation with age in comparison to the menisci.

Ankle and Foot Injuries in the Young Athlete.

Injuries to the ankle and foot are common in the young athlete, especially with increasing participation and high levels of competitiveness in youth sports programs. Knowledge of the normal development of the foot and ankle is crucial to understand age-specific injury patterns because acute or chronic/repetitive stress to the developing skeleton results in injuries that differ from those seen in adults. Congenital abnormalities may also predispose children to increased risk of injury and pain. Radiologists must be aware of these distinctions to diagnose and classify injuries correctly for optimum treatment. We describe common and unique foot and ankle injuries in the young athlete. Throughout the article we focus not only on imaging findings but also on the mechanism of injury.

MR imaging features of cuboid fractures in children.

BACKGROUND: Cuboid fractures are rare, usually occult on initial radiographs and are often underdiagnosed. MRI is more sensitive than radiographs for detecting acute, non-displaced cuboid fractures in adults, but only case reports have described these findings in children. OBJECTIVE: To summarize the MR and clinical features of cuboid fractures and compare MR findings with initial and follow-up radiographs in a cohort of children. MATERIALS AND METHODS: A retrospective search for patients <18 years of age with cuboid fractures was performed during a 10-year period at a large tertiary children's hospital. Subjects with cuboid fractures reported on MRI and available clinical history were included. MR images were evaluated for fracture location, fracture morphology, percentage of marrow edema in the cuboid, subchondral disruption, and associated tendon or ligamentous injury. Initial and short-term follow-up radiographs were also reviewed when available. RESULTS: Nineteen children ages 18 months to 17 years (mean: 9.0 years, standard deviation: 4.1 years, 63% boys) were diagnosed with cuboid fractures by MRI. Most cases of cuboid fractures are related to acute trauma (63%) but can be seen as stress fractures (16%). Most fractures (17/19, 89%) were linear in configuration. Fractures were most commonly adjacent to the tarsometatarsal joint (10/19, 52%). The degree of marrow edema was variable. Ligamentous injury was seen in two patients and tendon pathology was seen in one, all adolescents. Initial radiographs (n=10) were negative in 9 cases (90%). All available follow-up radiographs (n=12, obtained 19-42 days after MRI) demonstrated sclerosis in the region of the fracture. CONCLUSION: MR-depicted cuboid fractures in children typically occur in isolation. The fractures were most commonly adjacent to the tarsometatarsal joint and linear in morphology. Initial radiographs were usually normal and follow-up radiographs depicted sclerosis at the site of fracture in all available cases.

Docking of the Femoral Head Following Closed Reduction for DDH: Does it Really Occur?

BACKGROUND: It has been suggested that the femoral head can "dock" deeper into the acetabulum after initial closed reduction (CR) for developmental dysplasia of the hip (DDH). The purpose of this study was to quantify the interval change in femoral head position between immediate postoperative magnetic resonance imaging (MRI) and follow-up imaging at ~3 weeks. METHODS: A retrospective review of 29 patients (30 hips) who underwent CR and spica casting for DDH was conducted. Immediate postoperative and average 3-week follow-up MRI scans in spica were performed on all patients. On both scans, 2 blinded reviewers measured the following indices: the distance between the femoral head and the acetabulum on midcoronal and midaxial images, the displacement of the center of femoral head from Hilgenreiner's line in the coronal and axial plane, and the left-right displacement of the center of femoral head from Perkins line. Measurements were averaged between the 2 reviewers and the interval change in femoral head position between the immediate postoperative and follow-up scans were compared. RESULTS: There were 26 female individuals and 3 male individuals in our series with a mean age of 7.6 months (range, 4 to 13 mo). Follow-up MRI scans were performed at an average of 23.8 days (range, 13 to 46 d). On the basis of the averaged measurements from both readers, the distance between the femoral head and the acetabulum decreased significantly on coronal measurement and on all 3 axial measurements between initial and follow-up MRI. In addition, the position of the femoral head became significantly more medial, more anterior, and more cranial relative to the acetabulum. The interrater correlation coefficient between both readers across all measurements was 0.731. CONCLUSIONS: These findings provide evidence that femoral head position within the acetabulum improves even over a short time period following initial CR for DDH, suggesting that the "docking" phenomenon may in fact occur. LEVEL OF EVIDENCE: Level IV-therapeutic study.

Diffusion-Tensor Imaging of the Physes: A Possible Biomarker for Skeletal Growth-Experience with 151 Children.

Purpose To determine the changes of diffusion-tensor imaging (DTI) and tractography in the distal femur and proximal tibia related to age, sex, and height. Materials and Methods Following institutional review board approval, with waiver of consent and with HIPAA compliance, the authors retrospectively analyzed DTI images of the knee in 151 children, 73 girls (median age, 14.1 years; range, 6.5-17.8 years) and 78 boys (median age, 16.6 years; range, 6.9-17.9 years), studied from January 2013 to October 2014. At sagittal echo-planar DTI (20 directions, b values of 0 and 600 sec/mm2), regions of interest were placed in the tibial and femoral physes. Using a fractional anisotropy threshold of 0.15 and an angle threshold of 40°, the authors performed tractography and measured apparent diffusion coefficient (ADC) and tract length and volume. Changes related to age, sex, and height were evaluated by using fitted nonlinear polynomial functions on bootstrapped samples. Results Femoral tract volume and length increased and then decreased with age (P < .001); the peaks of femoral tract volume are consistent with the growth spurt, occurring earlier in girls (10.8 years) than in boys (13.0 years) (P < .001). Girls had smaller tract volumes in comparison to boys (P = .013). ADC peaks 2 years earlier than tract volume (girls at 9.3 years, boys at 11.0 years). Girls with greater than 50th percentile of height had longer tracts and greater tract volumes compared with girls with less than 50th percentile (P < .020). DTI parameters of boys do not correlate with percentile of height (P > .300). Conclusion DTI of the physis and metaphysis shows greater tract length and volumes in subjects who are at ages when the growth is fastest. ADC and tract length and volume have an earlier and smaller peak in girls than in boys. Femoral tract length and volume are larger in taller girls. © RSNA, 2017.

MRI of Native Knee Cartilage Delamination Injuries.

OBJECTIVE: The purpose of this article is to describe the normal imaging appearance of cartilage and the pathophysiologic findings, imaging appearance, and surgical management of cartilage delamination. CONCLUSION: Delamination injuries of knee cartilage signify surgical lesions that can lead to significant morbidity without treatment. These injuries may present with clinical symptoms identical to those associated with meniscal injury, and arthroscopic identification can be difficult, thereby creating a role for imaging diagnosis. A low sensitivity of imaging identification of delamination injury of the knee is reported in the available literature, although vast improvements in MRI of cartilage have since been introduced.

Ultrasound imaging of synovial inflammation in juvenile idiopathic arthritis.

Juvenile idiopathic arthritis (JIA) is the most common rheumatic entity of childhood. The hallmark feature of all subtypes is joint inflammation. Imaging is used to evaluate the extent and severity of inflammation, degree of joint damage and response to treatment, which in turn impacts patient management. Ultrasound has become a useful adjunct to clinical examination because it shows promise in evaluating clinical and subclinical inflammation (synovitis, enthesitis) as well as cartilage and bone erosive changes. However more collaborative research is needed to help define the normal appearance of the growing skeleton, clarify the significance of subclinical findings and develop useful definitions, imaging protocols and scoring systems of disease.