EXTRASKELETAL OSSEOUS AND CARTILAGINOUS TUMORS OF THE EXTREMITIES

Extraskeletal osseous and cartilaginous tumors and tumorlike condition s of the extremities can often be differentiated radiologically; for t hose that cannot, knowledge of the spectrum of lesions will allow a su itably ordered differential diagnosis. Of the osseous lesions-myositis ossificans, fibro-osseous pseudotumor, fibrodysplasia ossificans prog ressiva soft-tissue osteoma, and extraskeletal osteosarcoma-all but my ositis ossificans are relatively rare. Myositis ossificans has a disti nct mineralization pattern that can be observed radiologically as a pe ripheral rim of lamellar bone. Fibro-osseous pseudotumor typically occ urs in the digits of the hand and lacks the well-defined zoning patter n of myositis ossificans. The cartilaginous entities include the true tumors, soft-tissue chondroma and extraskeletal chondrosarcoma, and th e tumorlike process, synovial osteochondromatosis. The tumors are rela tively rare; synovial osteochondromatosis commonly affects middle-aged men, especially in the knee, and is associated with osteoarthritis. T he differential diagnosis for these extraskeletal osseous and cartilag inous lesions includes soft-tissue sarcoma, benign mesenchymoma, malig nant mesenchymoma (rare), calcified tophi in gout. melorheostosis (rar e), pilomatricoma (rare), and tumoral calcinosis (rare).