Extramedullary hematopoiesis in pyogenic granuloma.

Extramedullary hematopoiesis (EMH) suggests the presence of hematopoietic stem cells (HSC) outside bone marrow. EMH has been reported, albeit rarely, in pyogenic granuloma (PG), a polypoid lobular capillary hemangioma. However, statistical data have hitherto been lacking on the actual incidence of EMH in PG. Therefore, we here reviewed 157 consecutive cases using routine diagnostic surgical slides and found unequivocal EMH in 17 (10.8%). This indicates that EMH is a rather common finding in PG, which could thus have strong potential to be an important resource for the study of HSC.