Hobnail Hemangioma: A Case Report.

Hobnail hemangioma is a small, solitary, benign vascular tumor that shows a biphasic histological pattern of dilated vascular spaces in the superficial dermis and narrow vascular structures in the deeper dermis. In the superficial dermis, dilated, irregular, thin-walled vascular spaces are lined by plump endothelial cells with large nuclei which protrude into the lumina like hobnails. A 43-year-old Japanese man presented with an 11×8-mm bluish-red macule surrounding a 6×3-mm violaceous, slightly elevated papule of the lumbar region of 6 months' duration. Total resection was performed under local anesthesia. Microscopic examination revealed a biphasic pattern with dilated superficial vessels whose endothelial cells were plump with intraluminal papillary projections, showing a "hobnail" appearance, in the papillary layer and upper dermis, and vascular spaces forming slitlike spaces, some of them dissecting collagen fibers, in the deeper dermis. Neither true atypia nor mitotic figures were present. The findings were consistent with those of hobnail hemangioma. Immunohistochemical analysis of the endothelia of the superficial vessels showed that CD31 and D2-40 were expressed, factor VIII was focally expressed, and CD34 and α-SMA were not expressed. In the endothelia of the deeper vessels, CD31, CD34, factor VIII, and α-SMA were expressed, but D2-40 was not expressed. These findings suggest that hobnail hemangioma also shows a biphasic immunohistochemical pattern because of its origin from both lymphatic vessels and blood vessels.