SUBMUCOSAL MESENCHYMAL TUMORS OF THE MOUSE URINARY-BLADDER

A unique morphologic change has been described in the submucosa of the urinary bladder of mice since the 1950s. These lesions, variously ref erred to as vegetative changes, reactive lesions, submucosal granuloma s, leiomyosarcomas, atypical hemangiosarcomas, or submucosal mesenchym al tumors have been considered rare and of questionable etiology. Alth ough the morphologic criteria are fairly well defined, the pathobiolog y of the lesion is not well characterized and the previously listed no menclature reflects this uncertainty. The lesion may not be limited to the urinary bladder, the cell of origin is controversial, the biology is unknown, and whether the lesion is granulomatous, hypertrophy, hyp erplasia, metaplasia, or a benign or malignant neoplasm is not well de fined. Data compiled from multiple sources are discussed to review the strain of mouse most often affected, sex, age at diagnosis, anatomic location, incidence, descriptive morphology, immunohistochemical stain ing results, and other features of the submucosal mesenchymal tumor of the mouse urinary bladder. Presented are suggested terminology for th e lesion, submucosal mesenchymal tumor of the mouse urinary bladder; t he relevance of the tumor for human risk assessment; and discussion of the possible histogenesis of this lesion from primitive mesenchymal c ells of the submucosa (lamina propria) of the urinary bladder of mice.