Bizarre parosteal osteochondromatous proliferation (Nora lesion): a report of 3 cases and a review of the literature.

© 2008 Association médicale canadienne B parosteal osteochondromatous proliferation (BPOP), as defined by Nora and colleagues in 1983 (also called Nora lesion), is a rare lesion. About 160 cases of BPOP have been presented in the literature to date. The lesion is an exophytic outgrowth from the cortical surface consisting of bone, cartilage and fibrous tissue. It usually affects the proximal and middle phalanges, and the metacarpal or metatarsal bones. The hands are 4 times more commonly affected than the feet; however, lesions in the long bones, skull, maxilla and metatarsophalangeal sesamoid have been reported. The lesion affects patients of any age, but most are in their 20s and 30s with no sex predilection. This benign lesion of the bone might be mistaken for malignant processes because of the high frequency of recurrence, the occasional quick growth and atypical histologic appearance. Along with a review of the literature, we discuss the cases of 3 patients with this rare lesion to illustrate the histologic, radiologic and clinical features as well as the different etiologic theories on BPOP. Case reports