Hobnail hemangioma ("targetoid hemosiderotic hemangioma"): clinicopathologic and immunohistochemical analysis of 62 cases.

Hobnail hemangioma, also known as "targetoid hemosiderotic hemangioma", represents a distinctive, benign vascular tumor, characterized histologically by a biphasic growth pattern of dilated vascular structures in the superficial dermis lined by prominent hobnail endothelial cells, and collagen dissecting, rather narrow neoplastic vessels in deeper parts of the lesion. We analyzed the clinicopathologic and immunohistochemical features in a series of 62 cases. Patient age range was 6-72 years (median: 32 years); 34 patients were male and 25 female. Clinically, a broad variation of diagnoses ranging from hemangioma to dermal melanocytic nevus and fibrous histiocytoma was suggested. Nineteen tumors arose in the lower and 13 in the upper extremities, 12 on the back, 8 in the buttock and hip region, and one case on the chest wall. Follow-up information on 35 patients (range from 1 to 4 years; mean: 1.5 years) revealed no local recurrence nor systemic metastasis. All neoplasms were located in the dermis and showed a broad morphologic spectrum in dependence of the age of the lesions. In addition to lesions resembling cavernous lymphangioma or lymphangioma circumscriptum, neoplasms were seen with morphologic features reminiscent to retiform hemangioendothelioma, progressive lymphangioma and so-called Dabska's tumor. Immunohistochemistry performed in 28 cases showed positive staining of tumor cells for CD31 in all cases tested, whereas only 3 out of 28 cases stained completely positive for CD34. In addition 4 out of 8 cases stained positively for vascular endothelial growth factor receptor-3 (VEGFR-3). Neoplastic endothelial cells were surrounded by actin-positive pericytes in only 7 out of 27 cases tested. Hobnail hemangioma occurs more frequently in male patients and arises commonly in the extremities and the trunk. Histologic and immunohistochemcial features suggest a lymphatic line of differentiation for this distinctive vascular neoplasm.