Solid variant of aneurysmal bone cyst: a case report with bilateral involvement of the distal femoral metaphyses.

An extremely rare case of bilateral, symmetrical involvement of distal femoral metaphyses by the solid variant of aneurysmal bone cyst (ABC) in a boy aged 13 years is described. Although there is no difference between the conventional ABC and the solid variant in terms of clinical and radiological presentation, the lesion is solid, composed of fibrohistiocytic cells with abundant giant cells and/or areas of florid, heterotopic ossification, while aneurysmal channels are sparse or absent. The lesion needs to be differentiated from giant cell tumour of bone, when the osteoclastic component predominates, while fibrous dysplasia, osteoblastoma and even osteosarcoma need to be excluded any time ossification is prominent. Careful evaluation of the clinical, radiological and pathological findings is necessary.