Morphology of the urinary bladder following long-term experimental irritation of the urothelium

10 female beagle whelps received an artificial urinary calculus (1.5 ml of a rapidly polymerizing methyl-methacrylate) by means of a transurethral procedure. The X-ray, cytological, endoscopic and bioptic findings were followed in a long-term experiment. After a period of 61 months, precancerous urothelial changes (n = 1) and invasive urothelial microcarcinomas were found (n = 2). Typical changes from earlier controls were pseudopapillary follicular cystites. Chronic irritation of the urothelium is shown to be an important factor in the pathogenesis of urinary bladder carcinoma. Decisive is the length of the period of irritation rather than the actual material used in making the pellet.