Extraskeletal osteochondroma of the foot.

Extraskeletal osteochondroma, an infrequently encountered benign lesion, is described in 1 patient who presented with a slow-growing, relatively painful mass on the dorsal side of his right foot, in the 3rd toe web. Radiographs and magnetic resonance imaging studies demonstrated a radio-opaque extraskeletal mass. Excision biopsy revealed a well-defined and lobulated, firm, calcified, extraskeletal mass, which was easily enucleated. Histologic examination revealed mature chondroid tissues with bland-looking chondrocytes and ossified tissues. The diagnosis of an extraskeletal osteochondroma should be considered when a discrete ossified mass is localized in the soft tissues of the distal extremities. A case of pathologically proven extraskeletal osteochondroma is presented together with clinical, radiologic, and magnetic resonance imaging findings, and a literature review.