Hobnail hemangioma: a immunohistochemical study and literature review.

Hobnail hemangioma is a rare vascular lesion with unusual morphology, including bland cells with hobnail appearance, a biphasic grow pattern with superficial dilated vessels and slit-like vessels in a deeper portion of the lesion and the infiltrative pattern of later growth, which may cause misdiagnosis. The differential diagnosis with hemangioendothelioma variants, low grade angiosarcomas and Kaposi sarcoma is of particular concern. The lack of recognition of this uncommon entity may result in excessive and unnecessary treatment. Immunohistochemistry stains play an important role in hobnail hemangioma differential diagnosis. Here, we present the results of our researches and also review of the literature as well as discussion about usage of immunohistochemistry in the diagnosis of HH.