Bizarre Parosteal Osteochondromatous Proliferation (Nora's Lesion) of the Hand: A Report of Two Atypical Cases.

Bizarre parosteal osteochondromatous proliferation (BPOP), also called Nora's lesion, is an unusual, benign, bony lesion frequently found in the hand. Originally, two of the key radiological features used to describe such lesions were: (1) a lack of corticomedullar continuity and (2) an origin from the periosteal aspect of an intact cortex. The authors present 2 unique cases of histologically proven BPOP in which the integrity of the cortex was affected. In the first case there was medullary continuity, and in the second case there was saucerization of the underlying cortical bone. The authors support that simple X-ray evaluation is insufficient to diagnose BPOP in atypical cases. Careful axial CT scanning or MRI may prove helpful. Taking into account these new notions, histopathology gains greater importance as a diagnostic tool for this particular group of entities.