Cystic Renal Oncocytoma: A Case Report with Review of the Literature

Abstract

Renal oncocytomas are benign, predominantly asymptomatic tumors that are usually found incidentally.  These tumors are typically solid, well-circumscribed, homogenous tan-brown lesions, often with a central fibrous scar. Histologically, the tumor cells are arranged in solid compact nests, acini and tubules of variable size, all within a hypocellular hyalinized stroma. In the literature, there are only five cases of cystic renal oncocytoma reported. Herein we present a case of cystic renal oncocytoma with the unusual gross appearance of multiloculation. It was found incidentally on imaging studies in the upper pole of the right kidney.  Grossly, it was a well-circumscribed 1.5 cm mass with a multiloculated cystic cut surface. Microscopically, the oncocytic cells were arranged along the septae that divided the mass into multiloculated cysts. Immunohistochemical staining of the tumor showed expression of kidney-specific cadherin in all the neoplastic cells, CK7 expression in 45% and PAX-2 expression in 60% of these cells. RCC and vimentin showed no reactivity within the tumor. The morphological features and immunohistochemical studies confirmed the diagnosis of a cystic renal oncocytoma.