Nephrogenic adenoma of the urinary bladder: a comparison of its cytologic and histopathologic features in ten cases

We studied the cytologic features of ten cases of nephrogenic adenoma, a benign proliferative lesion of urothelium that is typically associated with prior trauma or urothelial irritation. The typical cytologic features consisted of numerous vacuolated polygonal cells, including signet-ring-like cells, that were isolated or formed papillae or loose groups. Columnar cells and occasional glandular structures were also seen. The cells typically exhibited no or only mild nuclear atypia. There was often a background of acute inflammation. The differential diagnosis of urinary cytologic specimens with these features includes degenerative changes, changes induced by instrumentation, and, most importantly, adenocarcinoma and low-grade papillary transitional-cell carcinoma.