The prevalence and distribution of proliferative and metaplastic changes in normal appearing canine bladders

The prevalence and distribution of Brunn's nests, simple hyperplasia, simple squamous metaplasia, cystitis glandularis/cystica, atypical hyperplasia, and lymphocytic infiltration were studied by multiple histologic sections in 30 grossly normal urinary bladders obtained from a controlled population of dogs ranging in age from two to 14 years. The data were statistically analyzed using Fisher's exact test and logistic regression. A comparison of urothelial changes was made between dog and human. Brunn's nests were the most prevalent urothelial change and were observed at one or more locations in 80% of the cases. Simple hyperplasia was the second most common proliferative change and was observed at one or more locations in 66.7% of all cases. Brunn's nests (p less than 0.0001) and simple hyperplasia (p = .003) were significantly more likely to be found in the trigone. Simple squamous metaplasia was observed at one more more locations in 23.3% of all cases. Lymphocytic infiltration was observed in 20% of the animals; however, there was no statistically significant correlation between it and the urothelial changes. The trigone was by far the most common site (86.6% of all cases) for one or more lesions to be found. There was no evidence that inflammation was the cause of these urothelial changes. The data supports the concept that Brunn's nests, simple hyperplasia, and simple squamous metaplasia are normal variants of bladder urothelium in dogs and further that they are not precancerous changes. There was a similarity in prevalence, distribution, and significance of many urothelial changes between the dog and human which indicates that the dog is a good comparative model for studying diseases of the urinary bladder.