Tumor-like lesions of the urinary bladder.

Tumor-like lesions of the urinary bladder are reviewed emphasizing those that are most diagnostically challenging for the pathologist and may result in serious errors in patient care if misinterpreted. The first category considered, pseudocarcinomatous proliferations, represents an area of bladder pathology only recently appreciated as being particularly treacherous because of the extent to which irregular islands of benign epithelial cells may seemingly penetrate the lamina propria and cause confusion with carcinoma. Somewhat orderly proliferations of this type have been known for years, von Brunn's nests, and are rarely a challenge for the experienced, but proliferations of an irregular nature such as may be seen most often as a result of prior radiation therapy, but sometimes due to chemotherapy or even ischemia, represent a challenging interpretation. The clinical history may be very important in arriving at the correct diagnosis as is the appreciation that the morphology, although architecturally problematic, is different from that of any of the familiar patterns of invasive carcinoma. Florid epithelial proliferations in fibroepithelial polyps are also briefly noted. Within the category of glandular proliferations, emphasis is placed on the wide spectrum of morphology of nephrogenic adenoma including its pseudoinfiltrative pattern and occasional propensity for tiny tubules to be misconstrued as signet-ring cells. The spectrum of müllerian glandular lesions including the relatively recently described mucinous variant, endocervicosis, is reviewed. The reactive papillary proliferation, papillary-polypoid cystitis, is then discussed. This entity has long been known but has recently been re-emphasized. Other non-neoplastic papillary lesions include florid papillary forms of nephrogenic adenoma. The past 25 years has seen a great expansion of knowledge concerning non-neoplastic spindle cell proliferations, including those related to a prior procedure, the postoperative spindle cell nodule and those without such a history, variously designated inflammatory pseudotumor, pseudosarcomatous myofibroblastic proliferation, or even other terms. The morphologic spectrum is explored and it is recommended that the two categories be retained.