Age / Sex : 5 / F

C.C.: painless swelling, right knee (D: a few years)

Dysplasia epiphysealis hemimelica (Trevor's disease)

Discussion

Findings:
1) Radiograph : Knee AP/ lateral - multiple ossifications are seen adjacent to medial side of proximal epiphysis the tibia - lobulated osseous mass protruding from epiphysis of medial femoral condyle
2) MRI : Coronal T2-weighted FSE, coronal and sagittal fat-suppressed 3D FLASH - Nodular ossifications extending from epiphyseal ossification center of tibia - Cartilaginous cap surrounds the ossifications and has a continuity with normal portion of hyaline cartilage - Enlarged posterior aspect of medial femoral condyle with irregular margin - Medial margin of the epiphyseal ossification center of medial femoral condyle is irregular

Differential Diagnosis:
- Dysplasia epiphysealis hemimelica - synovial osteochondromatosis

Diagnosis: Dysplasia epiphysealis hemimelica (Trevor's disease)

Discussion:
1. - a rare developmental bone dysplasia characterized by an osteocartilaginous mass arising from an epiphysis - histologic features are identical to those of an osteochondroma
2. Clinical findings - affect epiphyses in the lower limb (distal femur, proximal tibia > talus, other tarsal and carpal bones) - characteristically hemimelic (medial>lateral), multiple bone involvement (70%), no malignant transformation - nonhereditary, in children (2-14 years) - Sx : swelling > pain, valgus or varus deformity, and limb-length discrepancy - 3 forms based on the disease extent and distribution 1) localized form (monostotic involvement) 2) classic form (more than one area of osseous involvement in a single extremity) (2/3 of cases) 3) generalized or severe form (disease involving an entire single extremity)
3. Radiologic findings.
1) Radiographic findings - irregular mass with focal ossification arising from one side of the affected epiphysis or sesamoid bone - single or multiple, enlarge with skeletal growth, and may be associated with joint deformity - with maturation, the lesion ossifies and becomes confluent with the underlying bone. - premature closure of the physis with resultant deformity and occasional limb discrepancy may also be seen.
2) MRI - identifying the size and configuration of epiphyseal lesion (including unossified portion of the cartilageneous mass) - edema may be evident in both overgrown bone and normal epiphyseal bone, related to altered mechanical stress

References:
1. Resnick D. Diagnosis of bone and joint disorders, 4th ed. Philadelphia: Saunders, 2002; 3888-3894
2. Murphey MD, Choi JJ, Kransdorf MJ, et al. Imaging of osteochondroma: variants and complications with radiologic-pathologic correlation. Radiographics. 2000; 20(5): 1407-34.