A case of pararenal angiomyolipoma arising from an existing exophytic angiomyolipoma.

A 52-year-old healthy woman with a congenital solitary right kidney presented with an incidentally found pararenal mass. Computed tomography and magnetic resonance imaging revealed an exophytic mass in the right kidney consistent with an angiomyolipoma and an additional enhancing pararenal mass that contained fatty elements. Differential diagnosis of the mass included liposarcoma and angiomyolipoma. Upon exploration, the exophytic angiomyolipoma was found to be contiguous with the pararenal mass via an isthmus of fatty tissue. Frozen sections were taken from both masses which confirmed that both were angiomyolipoma. This is the first case reported in the literature wherein an angiomyolipoma extended extrarenally and formed a significantly larger pararenal mass.