The small lytic mass associated with the anterolateral cortex of the tibia metaphysis shows evidence of chondroid-type mineralization by radiography ("rings and arcs" pattern of calcification). The MR images nicely demonstrate the lesion originating from the superficial cortex, without intramedullary invasion. The absence of associated reactive marrow edema is suggestive of a benign etiology. The MR signal characteristics (T1 intermediate, T2 hyperintense) are typical of chondral tissue.
The differential diagnosis includes:
- periosteal (juxta-cortical) chondroma
- chondromyxoid fibroma (intramedullary >> juxta-cortical location, sclerotic rim, and radiographically apparent chondroid matrix is uncommon)
- non-epiphyseal chondroblastoma (classically T2 hypointense due to immature chondroid matrix, usually associated with reactive marrow edema)
The presentation and imaging appearance, including the lobulated and exophytic morphology, are most consistent a benign juxtacortical chondroma.
Soft, gray mass associated with a piece of bone. The mass measures approximately 2.0 x 2.0 x 1.7 cm. Sections show a cartilaginous neoplasm that has some degree of nuclear atypia and areas of myxoid changes. However, it is known that benign periosteal or juxtacortical chondromas can have atypia. Furthermore, the mass is relatively small, measuring 2.5 cm by imaging, and is well-circumscribed. Immunostains (Ki-67, p53) were indeterminate.
DIAGNOSIS: juxtacortical (periosteal) chondroma.