PEDIATRIC RADIOLOGY: Musculoskeletal Radiology
Case Author: Ricardo Restrepo, MD, Miami Children’s Hospital
History
14-year-old boy with right knee pain for 3 months who reports no trauma when asked about it.
Imaging Findings
Frontal radiograph of the knee (A) shows a well-defined round lucent lesion involving the medial femoral condyle (arrow). Coronal fat-suppressed T2-weighted MR image (B) shows a rounded intramedullary epiphysial lesion of intermediate signal intensity (asterisk) in the medial femoral condyle with surrounding soft-tissue and bone marrow edema. Sagittal T1-weighted MR image (C) shows the round epiphysial lesion (arrow) as an area of intermediate signal intensity with a fluid-fluid level. Axial fat-suppressed gadolinium-enhanced T1-weighted MR image (D) shows enhancement of the adjacent marrow and soft-tissue edema (arrows) with mild enhancement of the lesion (asterisk).
- Aneurysmal bone cyst
- Brodie abscess
- Chondroblastoma
- Osteochondritis dissecans
Diagnosis
Chondroblastoma
Teaching Points
Aneurysmal bone cyst is a misnomer. The lesion consists of large vascular spaces filled with blood and hemosiderin and lined with giant cells. It can be primary or secondary, the latter originating from an existing lesion. The lesions are more commonly metaphysial in location but can occur anywhere in the bone. At MRI, multiple intralesional fluid-fluid levels are a characteristic finding. Brodie abscess is a subacute form of osteomyelitis. It occurs in the metaphysis of the long bones and can be round, oval, or serpiginous. It is lytic and has well-defined sclerotic borders. Chondroblastoma is an uncommon tumor that originates in the epiphysis or apophysis. The most common locations are the knee and shoulder. Chondroblastoma occurs at an average age of 20 years. As with any bone tumor, the diagnosis is first suggested on radiographs. MRI is performed to narrow the differential diagnosis and to further characterize the lesion. The most common location of osteochondritis dissecans in the knee is the lateral aspect of the medial femoral condyle. The cause is unclear but probably is multifactorial, chronic repetitive stress playing an important role. Osteochondritis dissecans is divided into juvenile and adult types according to the state of the physial plate. The type is juvenile when the physial plate is still open, and this type has a better prognosis than the adult type.
Suggested Readings
Brien EW, Mirra JM, Kerr R. Benign and malignant cartilage tumors of bone and joint: their anatomic and theoretical basis with an emphasis on radiology, pathology and clinical biology. Skeletal Radiol 1999; 26:325–335
Wootton-Gorges SL. MR imaging of primary bone tumors and tumor-like conditions in children. Magn Reson Imaging Clin N Am 2009; 17:469–487
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