[An unusual case of cystic nephroma protruding into the renal pelvis].

Cystic nephroma is a relatively rare and benign renal lesion of uncertain etiology. Approximately 200 cases have been described, but only a few cases of cystic nephroma with prominent renal pelvis involvement have been reported. Here, we report an unusual case of cystic nephroma that protruded into the renal pelvis. A 45-year-old woman hospitalized because of a right renal mass detected on clinical examination. The diagnosis of a malignant or benign lesion was not clear. A right nephroureterectomy was performed. The characteristics of the resected specimen were consistent with those of cystic nephroma. Macroscopic examination revealed that the giant lesion originated from the upper renal pelvis and extended into the renal pelvis. The patient is currently free from disease at eight months after the surgery. In general, this tumor arises from the renal parenchyma. To our knowledge, this is the fifth case report on cystic nephroma with prominent renal pelvis involvement.