Bizarre Parosteal Osteochondromatous Proliferation of the Hand: A Report of an Atypical Case and Current Concepts.

Bizarre parosteal osteochondromatous proliferation (BPOP), or Nora's lesion, is an unusual, benign, bony lesion often found in the tubular small bones of the hand and foot. In general, two characteristic radiological signs are used to diagnose the lesion, namely, (1) the absence of corticomedullar continuity and (2) BPOP developed from the parosteal surface of bones with an intact underlying cortex. Here, we present an atypical case of Nora's lesion of the proximal phalanx of the index finger, in which BPOP was diagnosed only histologically, with preoperative imaging examinations (X-ray and MRI) suggesting another lesion (enchondroma). Therefore, imaging (X-ray and MRI) alone may be inadequate to achieve the correct diagnosis of the lesion because many cartilaginous neoplasms may surround a broad range of lesions that mimic BPOP. Only histopathological evidence can confirm the correct diagnosis of the lesion.