BIZARRE PAROSTEAL OSTEOCHONDROMATOUS PROLIFERATION OF BONE (NORA LESION)

Bizarre parosteal osteochondromatous proliferation was first described in 1983, when Nora et al. reported 35 examples of a proliferative les ion involving the small bones of the hands and, less often, the feet. No examples involving the large bones were reported. We present 65 cas es of this condition, five from the Mayo Clinic files and 60 from our consultation files, including 34 females and 31 males; patients' ages ranged from 8 to 73 years (average, 33.9 years). Thirty-six lesions in volved the hands, 10 the feet, 17 the long bones, one the skull, and o ne an unknown site. The long bones involved were the radius (three les ions), ulna (six), fibula (two), femur (three), tibia (two), and humer us (one lesion). Roentgenograms typically showed a heavily calcific ma ss attached to the underlying cortex and having a broad base. Histolog ically, a large amount of hypercellular cartilage showed maturation to trabecular bone, which frequently contained spindle cells in the inte rtrabecular spaces, an. appearance that could lead to a mistaken diagn osis of parosteal osteosarcoma. A helpful feature was the distinct blu e tinctorial characteristic of the bone in the lesion. Follow-up infor mation was available for 40 patients; approximately 55% had a recurren ce. No metastasis had been reported in any of the 65 cases. Bizarre pa rosteal osteochondromatous proliferations are a form of heterotopic os sification and should not be mistaken for chondrosarcoma or osteosarco ma.