Reactive angioendotheliomatosis in an infant.

Reactive cutaneous angioendotheliomatosis (RCA) is an uncommon benign disease characterized by intravascular proliferation of endothelial cells. The observation of RCA in infants is exceedingly rare. We describe a case of RCA in a 3-month-old infant. The lesions were characterized by six small purpuric papules (1-2 mm in diameter), distributed on the thighs and neck. The general condition of the patient was good, with no lymphadenopathy, systemic involvement, or fever. The histopathologic features of a papule were characterized by the presence of cohesive aggregates of large mononucleated cells protruding into the lumina of dilated vessels and filling some of them completely. Neither an inflammatory infiltrate nor a proliferation of pericytes were present around blood vessels. Intravascular proliferating cells demonstrated positive staining for Ulex europaeus agglutinin 1 (UEA-1) and for Factor VIII-RA and CD34 antigens. The course of the disease was unremarkable with persistence of the lesions for 8 months; no treatment was started.