Mucinous cystadenoma with malignant transformation arising in the renal pelvis

Mucinous cystadenoma with malignant transformation occupying the lower half portion of the right renal pelvis in a 69-year-old Japanese man was recorded. The patient had recent dysuria but no clinical history of pyelonephritis or urolithiasis. Under the clinical diagnosis of unusual renal cyst, the right total nephrectomy was performed. Grossly, the cystic tumor, 5 cm across, formed a monolocular lumen filled with mucins and showed no direct communication with the renal pelvis inside. Microscopically, the epithelial lining was characterized by a single layer of benign mucin producing columnar cells that scattered foci of non-invasive papillary projections with cell stratification and nuclear atypia suggestive of malignancy. Although there was non-specific chronic pyelitis, no pyelitis cystica et glandularis was encountered. Of circa 60 glandular neoplasms arising in the renal pelvis reported previously, adenomas are only five including two mucinous cystadenomas, while the remainder are adenocarcinomas. The histological findings of mucinous cystadenoma in the present case may represent the process of a transition from adenoma to adenocarcinoma. The result suggests the possibility that adenoma-carcinoma sequence may exist among the glandular neoplasma arising in the renal pelvis. The histogenesis was unclarified.