Targetoid hemosiderotic hemangioma: A review article

Targetoid hemosiderotic hemangioma (THH), also known as hobnail lymphatic malformation (HLL) or hobnail hemangioma, is an uncommon, acquired vascular lesion with a dynamic presentation and an unclear etiology. It predominantly affects adults with an age range from 9 to 78 years and has no gender predilection. The lesion is thought to arise from trauma, leading to micro-shunts between small lesional capillaries and adjacent lymphatic vessels.

This review article examines the clinical, histologic, and immunohistochemical characteristics of THH, and explores its differential diagnoses, including Kaposi's sarcoma, solitary angiokeratoma, retiform hemangioendothelioma, and Dabska tumor.

THH presents clinically as asymptomatic, well-circumscribed lesions with a central red-blue and/or brown papule surrounded by a peripheral ecchymotic ring, giving a "bull's-eye" or targetoid appearance. Histologically, THH exhibits dilated vascular channels lined by hobnail endothelial cells, red blood cell extravasation, hemosiderin deposition, and mild lymphohistiocytic infiltrates. Immunohistochemistry is positive for D2-40, a lymphatic endothelial marker.

Heightened awareness of the clinical appearance of these solitary targetoid lesions is important. Without clinical-pathologic correlation, the branching telangiectatic vessels and purpura seen in THH could suggest more concerning vascular lesions like Kaposi sarcoma.