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There is an expansile soft tissue mass arising from the medial metaphysoepiphyseal region of the distal femur with a cortical breach and extension to the adjacent soft tissues of the knee, surrounding the medial collateral ligament and extending to the medial aspect of the intercondylar notch. It shows a low signal on T1, inhomogeneous high signal on T2 with a peripheral hypointense rim, and oedematous infiltration of the surrounding bone marrow. The postcontrast sequences show a heterogeneous enhancement with a peripheral rim-like corresponding most likely to the fibrovascular septation between lobules of hyaline cartilage.