Reactive proliferation of endothelial cells and pericytes associated with arteriovenous malformation

Arteriovenous malformation (AVM) is a structural vascular abnormality with no proliferation of cellular components. We report on a 53-year-old man who presented with a 15-year history of a progressively enlarging nodule on his lower lip. A dark-reddish, easy-bleeding nodule diagnosed as AVM was resected to reduce the volume and troublesome bleeding. Histologically, the nodule revealed that the proliferating cellular area was composed of endothelial cells and pericytes in addition to the area of dilated vessels. We speculated that the cell proliferation developed secondary to AVM. We also discuss the histological differential diagnosis of spindle cell hemangioma and pseudo-Kaposi's sarcoma.