Benign lymphangioendothelioma presenting as a giant flank mass.

Benign lymphangioendothelioma is a rare lesion of controversial etiology and a histopathologic mimic of Kaposi sarcoma and so-called 'well-differentiated' angiosarcoma. Its most typical clinical presentation is as a slowly expanding, erythematous patch or plaque; it rarely presents as a large mass. We report the second case of a giant benign lymphangioendothelioma, which arose as a serpiginous mass involving most of the flank of an elderly male with no prior radiation exposure and with a remote history of herpes zoster infection. A biopsy revealed numerous anastomosing vascular channels extending from the superficial dermis to the subcutis that were dilated to progressively slit-like in architecture. The endothelial cells lacked cytologic atypia, hobnailing, or significant mitotic activity, and human herpesvirus-8 expression was absent. Positivity for podoplanin (D2-40) was observed in the endothelial cells, supporting a lymphatic phenotype. Furthermore, the lesional cells lacked immunohistochemical expression of Wilms tumor 1, providing further support of a malformative - rather than neoplastic - pathogenesis.