Benign polyps with prostatic-type epithelium of the urethra and the urinary bladder. A suggestion of histogenesis based on histologic and immunohistochemical studies.

The clinicohistologic features of seven urethral and four urinary bladder polyps with prostatic-type epithelium are described. The average age of the patients was 50 years. Seven patients had prior cystoscopies and in none of them was the lesion noted initially. Histologically the lesions were papillary or polypoid and the surface was lined predominantly by prostatic-type epithelium with interspersed transitional epithelial cells or by transitional epithelium with interspersed prostatic-type epithelial cells. The prostatic-type columnar cells contained foamy, faintly eosinophilic cytoplasm, which stained strongly for prostate specific antigen and prostatic acid phosphatase. In all the lesions, there were prostatic acini in the underlying fibrovascular stroma, which was devoid of smooth muscle. The intermingling of prostatic-type cells and transitional epithelium, on the surface of the polyps, the absence of lesions at previous cystoscopies, the coexistence of cystitis cystica glandularis (a metaplastic lesion), and the older age group of our patients suggest that the prostatic-type epithelium in the polyps of urethra and urinary bladder is an acquired lesion, most likely a metaplastic response of transitional epithelium, which embryologically was multipotential.