Decreased vascularization of retroperitoneal kaposiform hemangioendothelioma induced by treatment with sirolimus explains relief of symptoms.

Kaposiform hemangioendothelioma (KHE) is a vascular tumor with poor prognosis. We present a child with progressive disability, extreme pain, and autonomic dysfunction due to a retroperitoneal KHE where radiologic characteristics were essential for diagnosis and monitoring of response to therapy. He received sirolimus, and the symptomatology resolved completely. Repeat MRIs revealed fast marked decrease in vascularity of the tumor, although the volume was not significantly affected. We suggest that the sirolimus-induced tumor de-vascularization may explain the clinical and coagulopathy improvement.