Von Brunn’s nests in the ureter of two cats

Introduction - Von Brunn’s nests and cysts are submucosal benign urothelial processes, related to irritative stimuli. They are common findings in the urinary bladder of human beings. Very few cases have been described in dogs and cats. Materials and Methods - We report macroscopic, histopathological and, in one case, immunohistochemical features of these rare forms in the left ureters of two cats, after ureterectomy due to urinary obstruction. Results - In both cases, macroscopical findings were coherent with an isolated, nodular and compact mass of 2.5 cm diameter. Microscopic examination showed considerable thickening of the muscular wall due to multifocal fibrosis, multifocal lacking of the lining epithelium in transverse sections of the ureteral lumen, and foci of urothelial islands in the lamina propria without any cytological atypia or mitosis and with occasional central cystic cavities. Multifocal areas of oedema, hyperemia/hemorrhage, angiogenesis and mild to moderate widespread lymphoplasmacytic infiltrates were also present. The cystic cavities contained macrophages full of lipofuscin, hemosiderin, erythrocytes and eosinophilic amorphous material. In one case, urothelial islands showed intense immunoreactivity for pan-cytokeratin (CK AE1/AE3). Inflammation was poor in the other case, where the urothelium appeared multifocally dilated with focal mucous metaplasia. In both cases, such findings and the anamnesis allowed us to hypothesize that the presence of epithelial islands was consistent with a hyperplastic condition, known as von Brunn’s nests and cysts. Conclusions - It is important to know the histological features of von Brunn nests, since it is not always easy to distinguish these islands from a well-differentiated urothelial carcinoma.