Caudal vascular hamartoma accompanied by aberrant arteriovenous structures in a dog

A 9-year-old, female German Shepherd Dog presented with a firm bulging lesion at the tip of the tail. Histologically, the lesion was characterized by numerous poorly circumscribed clusters of vascular structures resembling capillaries that were separated by normal or mucinous connective tissues. The capillary-like vascular structures were composed of several layers: a single von Willebrand factor-positive endothelial cell layer with round, oval, or flattened hyperchromatic nuclei; and 1 or 2 surrounding spindle-shaped smooth muscle actin-positive pericyte layers. In the deep portion of the lesion, there were large vessels that showed morphological aberrations. These thin-to-thick-walled blood vessels corresponded to arteries and veins of varying diameters and were surrounded by fibrosis. The present case report describes a rare cutaneous vascular hamartoma, accompanied by aberrant arteriovenous structures.