Painless hand mass

Abstract

AnswerBizarre parosteal osteochondromatous proliferation (Nora lesion) of the metacarpal. DiscussionRadiograph (Fig. 1) and CT ( Fig. 2) images show a wellcorticated osseous lesion originating from the dorsomedial surface of the second metacarpal neck. There is a slight irregularity of the underlying cortex, but no periosteal reaction or bone destruction. Although no visible cleavage plane separates the lesion from the second metacarpal, the medullary space of the lesion is noncontiguous with that of the underlying bone, and it lacks characteristic orientation away from the joint space as is seen with an osteochondroma. Clinically, a firm, immobile, nontender mass was palpated in the second intermetacarpal space. The overlying skin was normal in appearance. Because the patient had a limited range of motion at the second and third carpometacarpal joints, surgical excision was performed. Histopathology demonstrates fragments of bone and cartilage with areas of endochondral ossification and surrounding bland fibroblastic proliferation. The interface between forming bone and cartilage has a characteristic purple-blue staining quality (Fig. 3).First described by Nora et al. in 1983 (described in A b r a m ov i c i a nd S t e i ne r [1 ] ), b i za rr e pa ro st e al osteochondromatous proliferation (BPOP), also referred to as a BNora lesion,^is a rare, benign, locally aggressive osteochondromatous exostosis composed of bone and cartilage in a fibrous myxoid cell stroma without cellular atypia. Histologically, BPOP is characterized by the presence of a hypercellular fibrocartilaginous cap containing large, bizarre binucleate chondrocytes, with admixed areas of endochondral ossification maturing to trabecular bone. Bony trabeculae are histologically immature, with high osteoblastic activity and irregular calcification.Bizarre parosteal osteochondromatous proliferation most commonly arise from the periosteum of the metacarpals and metatarsals, with the hand affected four times more commonly Fig. 1 Anteroposterior radiograph of the right second to fourth metacarpals and proximal phalanges The case presentation can be found at