Urolithiasis and transitional cell carcinoma of the bladder in a Wistar rat.

Urolithiasis and carcinoma of the urinary bladder are generally uncommon in rats. In particular, spontaneous urolithiasis and carcinoma of the bladder in young rats has not yet been reported. Our case concerns the unexpected finding of urolithiasis of the bladder and left kidney of an apparently healthy 4-mo-old male Wistar rat. The bladder was filled with 28 white, round to oval calculi of various sizes. The kidney presented a single unevenly shaped calculus in the pelvis. Histology revealed, in addition to urolithiasis, a grade II papillary transitional cell carcinoma of the bladder, with muscle invasion and neoplastic extension to the left renal pelvic epithelium. No previous experimental procedure or dietetic manipulation had occurred, which could be held responsible for these findings. These unusual findings indicate that, unknown to researchers, unapparent factors can affect the health status of even relatively young experimental animals. Asymptomatic disease, such as the unknown presence of a tumor, potentially can affect many parameters and thus influence research results.