Small lymphocytic lymphoma involving an enlarging complex renal cyst.

A 47-year-old white man presented for evaluation of a complex right renal mass. He had a history of human immunodeficiency virus. Cervical lymph node biopsy had revealed small lymphocytic lymphoma. Computed tomographic scan disclosed diffuse mesenteric and retroperitoneal adenopathy consistent with chronic lymphocytic leukemia, as well as a 4.5-cm complex cystic right renal mass, which 17 months later enlarged to 6.2 cm. The mass resembled multiloculated cystic nephroma. Partial nephrectomy revealed infiltration of the cyst wall by small lymphocytic lymphoma. To our knowledge, this is the first reported case of lymphoma arising in or colonizing a renal cyst.