Scanning electron microscopy of upper urinary tract tumors.

Scanning electron microscopy (SEM) was performed on specimens from 16 patients with low-grade tumors, and 4 patients with benign lesions of the upper urinary tract. Pleomorphic microvilli could be seen at a low frequency on the majority of the tumor specimens as well as on surface cells of specimens from patients with inverted papilloma, fibroepithelial polyp, and hydronephrosis. The SEM appearance of the lining cells was similar whether the specimen was obtained from a patient with a tumor, or an inflammatory or proliferative lesion. Furthermore, pleomorphic microvilli were observed in five histologically normal bladders in which the covering cells had been rubbed off with a cold loop of a resectoscope. Pleomorphic microvilli are thus not morphologic markers of preneoplastic hyperplasia or tumor. It is likely that their presence merely reflects an increased rate of detachment of superficial epithelial cells which are replaced by cells from the deeper part of the epithelium. The demonstration of pleomorphic microvilli is therefore of questionable value in the preoperative diagnosis of tumors of the upper urinary tract and, consequently, their significance must be re-evaluated.