Periosteal chondroma

Case contributed by Dr Gilcrease-Garcia

Presentation

Right lateral knee mass.

Patient Data

Age: 25 years old
X-ray

Right knee radiographs show an eccentric, cortically-based lytic lesion located at the anterolateral right proximal tibia (best visualized on oblique and lateral views). There is a small amount of internal chondroid calcification. The joint spaces of the knee are normal. No knee effusion, and no acute fracture.

MRI

Non-contrast MR of the knee shows a 2.5 x 1.8 cm T2 hyperintense, T1 intermediate multilobulated mass at the anterolateral proximal right tibial shaft, which appears to arise from the cortex or periosteum. There is T2 hyperintensity within the tibialis anterior muscle surrounding the mass, consistent with intramuscular edema. There is no evidence of significant bone marrow edema of the tibia.

Case Discussion

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:

The presentation and imaging appearance, including the lobulated and exophytic morphology, are most consistent a benign juxtacortical chondroma.

Histology

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.

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Case information

rID: 56933
Case created: 29th Nov 2017
Last edited: 3rd Dec 2017
Inclusion in quiz mode: Included

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