Inverted papilloma of the renal pelvis. Cytologic features of ureteral washings.

A case of rare inverted papilloma of the renal pelvis with cytologic study of ureteral washings is described. Cytologic findings included increased numbers of urothelial cell clusters with mild degenerative changes. Although cytology was helpful in establishing the presence of a papillary transitional-cell lesion, histologic analysis following resection was required to distinguish between the possibilities of transitional-cell carcinoma and inverted papilloma.