Case contributed by Dr Ahmed D. Abdulwahab


Few months of left knee pain with mild reduced range of movement.

Patient Data

Age: 20 years
Gender: Male

X-ray of the left knee joint show a well-defined lucent lesion in the medial femoral condyle with a narrow zone of transition with sclerotic borders containing faint chondroid calcifications with no signs of bone destruction or no periosteal reaction.  It does not appear to cross the growth plate and does not reach the articular surface.   Findings are suggestive of a chondroblastoma, but other differential diagnoses including Brodie abscess or clear cell chondrosarcoma are also considered and further imaging advised.


CT scan of the left knee joint showing a well defined intraosseous lytic lesion seen in the medial femoral condyle epiphysis with a sclerotic rim.  It is causing endosteal scalloping of the posterior lateral aspect of the medial femoral condyle with no cortical destruction with internal chondroid calcification (chondroid matrix). No soft tissue component, findings are more suggestive of a chondroblastoma.

Case Discussion

Chondroblastoma (also known as Codman Tumor) is a rare benign neoplasm of cartilagenous origin, it occurs mostly in males less than 20 yrs, which occurs most commonly in the epiphysis of long bones.  

Plain radiographs and CT will show a smooth or lobulated lucent lesion, thin sclerotic rim, possible endosteal scalloping, solid periosteal reaction, and internal chondroid calcification in 50% of cases.

On MRI it shows cartilage signal intensity (intermediate on T1 weighted images, high signal on T2 and STIR weighted images) and shows heterogeneous moderate post-contrast enhancement

Differentiating between a chondroblastoma and a clear cell chondrosarcoma can be difficult with MRI characteristics and patient age helping to differentiate.  

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