Intrarenal foreign body presenting as a solid tumor.

A 45-year-old man underwent radical nephrectomy for an asymptomatic solid renal mass radiographically interpreted as a tumor. The pathologic examination revealed an intrarenal sponge forgotten during nephrolithotomy performed 5 years previously. The sponge was surrounded by a thick fibrous capsule. This case suggests that foreign body should be included in the differential diagnosis of a suspected renal mass in patients with a history of previous surgery.