Bizarre parosteal osteochondromatous proliferation (Nora's lesion) of the sesamoid: a case report.

We report the a case of Nora's lesion (Bizarre Parosteal Osteochondromatous Proliferation) of the sesamoid. A 32-year-old woman presented with a painless, enlarging mass of two years duration on the plantar aspect of the first metatarsophalangeal joint of the left foot. Radiographs, Computerized Tomographs and Magnetic Resonance images, initially suggested a parosteal osteosarcoma arising from the tibial sesamoid. The mass was excised, and a histological diagnosis of Bizarre Parosteal Osteochondromatous Proliferation of bone (Nora's lesion) was made. The aggressive growth of this lesion may suggest a neoplasm clinically. Histological features, however, are those of a reactive lesion.