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July 2016

Cat: Urinary bladder: Urothelial (transitional cell) papilloma



Cat, domestic shorthair, adult.


Urinary bladder: Urothelial (transitional cell) papilloma.


In the urinary bladder presented with a yellowish discolored, extensively proliferative and papillary, yet firm approximately 4.3 x 4.1 x 1.7 cm mass arising from the mucosal surface. On the cut surface, the mass displayed a clearly visible demarcation from the Tunica muscularis. Bar: 0.5 cm.


The female, neutered feral cat presented with anorexia, polydipsia, apathy and severe anemia. The latter was confirmed by a hematocrit of 9.7 %. Further blood parameters included lymphopenia as well as elevated urea, creatinine, and elevated liver enzymes. The cat was euthanized with poor prognosis.
Necropsy revealed a urothelial papilloma which was confirmed by histology. The papilloma filled approximately 80 % of the bladder´s lumen. The remaining lumen was filled with approximately 3 ml of coagulated blood.
Further lesions involved moderate generalized muscle atrophy, a moderate, diffuse, hepatic lipidosis and a moderate, chronic, multifocal to coalescing, lymphoplasmacytic nephritis with moderate fibrosis.

Despite epithelial tumors making up to 95 % of urinary bladder neoplasms, benign lesions are rarely found. The urothelial papilloma is histologically characterized by a thin fibrous stalk covered by a normal urothelial lining. Epithelial metaplasia with superficial necrosis and hemorrhage may occur. Signs of mitoses, invasion or inflammation are absent.
Papillomas are not known to have any breed or sex predisposition. Depending on their location, they may lead to obstruction, followed by urinary retention and hydronephrosis.
Malignant progression into transitional cell carcinomas has been observed in experimental cases, however, there is no supporting data on spontaneous progression.

Picture and authored by: Nancy Erickson, Department of Veterinary Pathology, Freie Universitaet Berlin, Germany