Inverted papilloma of the urinary tract – a review of the literature

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Inverted papilloma of the genitourinary tract is an uncommon neoplasm. Some urothelial carcinomas exhibit prominent inverted growth patterns that may pose a diagnostic dilemma. The presence of multiple inverted papillomas, their frequent recurrence and association with transitional cell carcinoma may lead to conflicting clinical conclusions regarding their biological behaviour and hence there is a need to review the literature. Internet databases including PubMed, Google Scholar, Google and Educus were searched to identify publications on inverted papilloma. Thirty-four publications formed the foundation for this review of the literature. The results revealed that inverted papilloma is a rare endophytic urothelial neoplasm that is most commonly found in the urinary bladder and less commonly in the upper urinary tract and urethra. Inverted papillomas are more common in men than in women and may present with obstructive or irritating voiding symptoms or haematuria. Inverted papilloma of the prostatic urethra may present with perineal pain whereas inverted papilloma of the upper renal tract may present with haematuria and loin pain. Inverted papillomas may be difficult to differentiate from inverted urothelial carcinomas but exhibit an absence of, or only few, atypical cells whereas inverted urothelial carcinomas exhibit atypia. Immunohistochemistry can be of assistance as urothelial carcinomas are positive for Ki-67 and p53, fluorescence in situ hybridization (FISH) and cytokeratin 20; however, inverted papillomas generally do not express these markers. FISH analysis can often detect chromosomal anomalies in urothelial carcinomas, but chromosomal abnormalities are absent in inverted papillomas. Inverted papillomas are endophytic and, when they are completely resected or excised, they do not initially recur; however, urothelial carcinomas recur and may progress. Inverted papillomas rarely coexist with urothelial carcinomas and malignant transformation has rarely been reported in inverted papillomas. Microscopic examination may enable inverted papillomas to be classified as the more common classic trabecular subtype or the glandular subtype.