Ossifying pyogenic granuloma: A rare variant usually not recognized.

Pyogenic granuloma (PG) represents a polypoid and lobular, capillary lesion, resembling granulation tissue, usually occurring on skin or mucosal surfaces. The occurrence of metaplastic ossification is extremely rare in PG. We present three cases of PG with metaplastic ossification. All three patients were men, aged 18-66 years. In all cases, the lesions occurred on the digits, particularly in or around the nail bed. Histopathologically, these superficial dermal-based tumors were characterized by classic features of PG, namely circumscribed, exophytic to polypoid proliferations of capillary-sized blood vessels in a lobular arrangement. The characteristic vascular component also was intimately associated with spicules and trabeculae of metaplastic bone formation rimmed by osteoblasts and osteoclasts. This osseous component was diffusely distributed in two cases and more localized in another. We speculate that ossification in PGs possibly represents a reactive process in response to chronic injury. We believe that ossifying PG is likely under-recognized and often mistaken for other entities also arising in the extremities and characterized by osseous metaplasia.