Bizarre parosteal osteochondromatous proliferations of the hands and feet.

We report 35 cases of peripheral skeletal osteochondromatous tumefactions which are both histologically and radiologically distinctive. The ages of the patients ranged from 14 to 74 years, with no sex predilection. Symptoms were related to the tumefaction. None of the patients had antecedent physical trauma or radiation. All lesions occurred on proximal phalanges, metatarsals, or metacarpals. Primary treatment was usually excision, and the gross appearance was typically that of a small osteochondroma. Histologically, the lesion exhibited marked proliferative activity, irregular bony-cartilaginous interfaces, and enlarged, bizarre, and binucleate chondrocytes, mimicking chondrosarcoma. Radiologically, the proliferations lacked both central continuity of the tumor with the underlying osseous medulla and "flaring" of the adjacent cortices. In 18 cases, the lesions recurred after primary excision, and at least eight lesions recurred twice. In spite of the rate of recurrence and the disturbing histologic appearance of these proliferations, behavior as a malignant tumor is either very rare or nonexistent.