Appendiceal cystadenoma mimicking a cystic renal mass.

We report the first case of appendiceal mucinous cystadenoma associated with the kidney. A 57-year-old man with chronic renal failure presented with a right renal mass. During laparoscopic nephrectomy, frozen analysis of a tubular structure extending from the mass showed appendiceal tissue. The mass, appendix, and what was believed to be the right kidney were removed. Pathologic examination demonstrated mucinous cystadenoma of the appendix. No renal tissue was identified, but the patient refused further treatment. This case demonstrates that mucinous cystadenomas arising from retroperitoneal structures might mimic renal neoplasms and should be considered in the differential diagnosis of cystic renal masses.