Case 68: Identifying the Correct Matrix on Radiographs

37-years old presented with a knee swelling

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Case:

37-years old presented with a knee swelling. Only films were available for review.

The radiograph shows an expansile osteolytic lesion in the distal femur with thinning of the anterior cortex with a narrow zone of transition without periosteal reaction or cortical break, epimetaphyseal and extending into the diaphysis (Fig. 1).

Fig 1A

Fig 1B

This suggests a slow-growing, perhaps benign or low grade malignant lesion.

An epi-metaphyseal, juxtamedullary lesion in this age group should trigger a diagnosis of giant cell tumor (GCT), but GCTs rarely have sclerotic rims.

More importantly there is a matrix (arrow in Fig. 1B), which shows a rings and arcs appearance, suggestive of cartilage.

A cartilage tumor like this is too big and eccentric for an enchondroma, though rarely a chondroblastoma or chondromyxoid fibroma could be this big. Both would show marrow edema on MRI presenting as “benign aggressive lesions”. If not, then this is a chondrosarcoma, either Gd 1 or Gd 2.

The CT (Fig. 2) confirms the chondroid matrix.

Fig. 2

The axial T2 MRI (Figs. 3, 4) shows the typical lobulated septate appearance of a cartilage tumor with no marrow edema on the sagittal STIR (FIg. 5) image.

Fig. 3

Fig. 4

Fig. 5

The histopathology (Figs. 6, 7) show a Gd II chondrosarcoma.

Fig. 6

Fig. 7

A careful perusal of the radiographs often allows us to make a reasonable diagnosis. The MRI then helps confirm and the histopath then validates. Reading an MRI without the radiograph can lead to all sorts of problems

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Other Chondrosarcoma cases

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• 68 Cases

• 16 Cases of the Day

• 5 Lectures