Gross and histopathologic characterization of feline cystitis.

Cystitis is a common diagnosis in feline clinical practice; however, studies examining the pathological aspects of this condition are limited. In this paper, we describe the gross, histological and epidemiological features of cystitis in cats, focusing on establishing the macroscopic presentation through post-mortem examinations in a retrospective study spanning 11 years. Seventy-five cases were selected. The mean age of the affected cats was 4.5 years and the majority of the cases were male (64/75; 85.3%). We identified three main macroscopic presentations: haemorrhagic (50/75; 66.7%), fibrinous and haemorrhagic (10/75; 13.3%), and fibrinous and ulcerative (9/75; 12%). Histological examination of the cases in the haemorrhagic pattern revealed primarily haemorrhage and urothelial erosion. The urinary bladder of the cats with fibrinous and haemorrhagic cystitis had diffuse mucosal and submucosal necrosis, along with haemorrhage and fibrin deposition. In the fibrinous and ulcerative pattern, there was diffuse necrosis of the mucosa and submucosa, fibrin deposition and neutrophil infiltrate. Fibrinoid necrosis of the urinary bladder blood vessel walls was common across all macroscopic presentations (56/75; 74.7%). Uroperitoneum and urethritis were the most frequent extravesical directly cystitis-related findings (17/75; 22.7%) and pulmonary oedema was the most frequent systemic finding (49/75; 65.3%). This study broadens the current understanding of the pathological features of feline cystitis, highlighting three major macroscopic presentations and the frequent occurrence of fibrinoid necrosis of the vessel walls in the urinary bladder.