What are the features of inverted papilloma of the urinary tract? How does it differ from papillary urothelial carcinoma? Is there a malignant counterpart of inverted papilloma? What are the differential diagnoses?

Abstract

Inverted papilloma of the urothelial tract is a benign tumor that affects men more frequently than women. More than 90% of inverted papillomas are located in the trigone, bladder neck, and prostatic urethra; and they seldom recur after surgical removal. They may also occur in the upper urinary tract including the renal pelvis and ureters. An intimate association with the proliferative disorders, including von Brunn’s nests, cystitis cystica, and cystitis glandularis, suggests their close histogenetic relationship. It is not clear whether inverted papilloma is indeed a neoplasm. Occasionally, inverted papilloma shows some histologic atypias, such as nuclear enlargement, prominent nucleoli, and mitotic figures, or exophitic papillary growth; but their clinical significance remains unknown. Although uncommon, urothelial carcinomas may exhibit an endophytic growth pattern (carcinoma with inverted growth pattern). It is imperative to distinguish inverted papilloma from urothelial carcinoma with an inverted growth pattern.