Pitfalls in the histopathologic diagnosis of pyogenic granuloma.

The term pyogenic granuloma (PG) is a misnomer. The histopathologic appearance is fairly characteristic, the lesion being in fact a lobular capillary hemangioma. The recognition of PG as a clinically polypoid or exophytic, circumscribed lesion is of importance to both the clinician and the pathologist, as this feature distinguishes PG from most malignant vascular tumors. Although PG may be multiple, especially on the skin, and necrosis is not uncommon, invasion of adjacent structures is not seen. Diagnostic pitfalls occur histologically when the characteristic lobular configuration of PG is not recognized because of a solid growth pattern of endothelial proliferation, the presence of brisk mitosis, intervascular stromal fibrosis or spindle cell proliferation, and occasionally an epithelioid appearance of endothelial cells. The different vascular neoplasms that may be confused with PG are discussed, and the clinical and histopathologic features of PG are emphasized.