Bizarre Parosteal Osteochondromatous Proliferation

**Semantic type:** Neoplastic Process

**Definition:** A benign lesion that usually affects the proximal small bones of the hands or feet. Grossly it consists of a cartilage cap and a bony stalk. Microscopically it is characterized by the presence of spindle cells, cartilage, and bone, usually in a disorganized pattern compared to subungual exostosis. Enlarged (bizarre) chondrocytes are present in the cartilage. Swelling with or without pain is present. Recurrences following resection have been reported in approximately half of cases.

**Synonyms:** - BPOP - Nora Lesion - Nora's Lesion