Answer: Renal medullary carcinoma

Histology: The tumor is centered in the renal pelvis, and is a high-grade adenocarcinoma associated with edematous, acutely inflamed stroma. Intarenal vascular invasion is readily identified. Cytologically, the tumor shows rhabdoid features; namely, vesicular chromatin, prominent nucleoli, and hyaline intracytoplasmic inclusions. In the stroma adjacent to the tumor, extravasated sickled red blood cells are present.

Discussion: True rhabdoid tumor of the kidney is a tumor of infants and young children. This diagnosis should be highly suspect in anyone over the age of 5 years. True rhabdoid tumors of the kidney are associated with mutations or deletions involving the INI1 gene on the long arm of chromosome 22. There is no association between this disorder and sickle cell trait. Renal medullary carcinomas typically show rhabdoid cytologic features and are easily mistaken for true rhabdoid tumors; in fact, in the initial description of rhabdoid tumor of the kidney (American Journal of Surgical Pathology 1989; 13: 439-458), the three cases in patients above the age of 5 have now proven to be renal medullary carcinomas (J. B. Beckwith, personal communication to P. Argani). Papillary renal cell carcinoma may show a tubular growth pattern, but is not associated with high cytologic grade and rhabdoid cytology as the current case is. Conventional renal cell carcinoma may show similar cytology when high-grade (rhabdoid features), but typically does not have the inflamed edematous stroma and association with sickled red blood cells as the renal medullary carcinoma.

Renal medullary carcinoma is a highly lethal carcinoma of the renal pelvis that is virtually restricted to patients who have sickle cell trait. It preferentially affects children and young adults, and is associated with a median survival of approximately 16 weeks.