Cellular pseudosarcomatous fibroepithelial stromal polyp of the renal pelvis.

Cellular pseudosarcomatous fibroepithelial stromal polyp is an underrecognized lesion described in the lower female genital tract. We here report the clinical, histological, and immunohistochemical features of a cellular pseudosarcomatous fibroepithelial stromal polyp located in the renal pelvis. A 47-year-old woman was referred with a 4-month history of left flank pain and gross hematuria. Left radical nephrectomy was performed. Gross pathological examination showed irregular pedunculated polypoid masses that had developed from the renal pelvis. Histologically, spindle cells with a patternless appearance were seen. The cells were of different sizes and had discernible cytoplasmic bipolar processes. Atypical stromal cells and atypical mitoses were also found. This case represents a typical cellular pseudosarcomatous fibroepithelial stromal polyp, probably developing from a reactive hyperplastic process involving the subepithelial stroma.