Targetoid hemosiderotic hemangioma: A review article.

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.