Tumour-like lesions of the urinary bladder.

There are a number of benign epithelial proliferations in the bladder that may be difficult to distinguish from carcinomas, including urothelial carcinoma and its variants, squamous cell carcinoma and adenocarcinoma. If misdiagnosed, there is the potential for over treatment, with its attendant risk of complications, as well as errors relating to prognostic assessment. In the case of the misdiagnosis of high grade proliferative lesions that mimic invasive carcinoma, unnecessary radical surgery, chemotherapy and radiotherapy may result. Similarly, the misdiagnosis of lesions that have the appearance of low grade carcinoma can prompt a lifetime of radiological investigation and cystoscopies. In this review, we discuss a variety of entities that may be diagnostically challenging and emphasise the importance of identifying key morphological features that have diagnostic utility. We also highlight the importance of relevant clinical information and the clinical settings in which these lesions may occur. In this review we have divided the lesions on the basis of morphology in order to facilitate discussion relating to the differential diagnosis. The architectural patterns we discuss include papillary lesions (polypoid/papillary cystitis and papillary urothelial hyperplasia), pseudocarcinomatous proliferations (pseudocarcinomatous urothelial hyperplasia, florid proliferation of von Brunn nests and fibroepithelial polyps), glandular lesions (intestinal metaplasia and müllerianosis) and lesions with several different patterns (prostatic type urethral polyps and nephrogenic adenoma or metaplasia).