Development of septa in the urinary bladder of client-owned rabbits leading to urinary outflow obstruction, urinary retention, and urinary bladder distension.

Objective: To describe a novel condition in rabbits characterized by the development of septa in the urinary bladder leading to partial urinary outflow obstruction.

Methods: A multicenter retrospective case series was designed, including 7 rabbits presented from 2017 to 2023 that met 2 inclusion criteria: (1) underwent histopathology of the urinary bladder, and (2) had clinical evidence of membranes and septa in the urinary bladder through diagnostic imaging and/or necropsy. Clinical signs of urinary outflow obstruction and bladder distension were observed in all cases.

Results: Abdominal radiographs and ultrasound identified abnormalities consistent with septa in 5 of 7 and 1 of 3 cases, respectively. In all 7 rabbits, the septa were visible via rigid cystoscopy. In 6 cases, the septum developed in a dorsoventral/laterolateral plane, causing variable degrees of narrowing of the lumen of the bladder neck and accumulation of sediment cranial to it. In 1 case, the septum developed in a craniocaudal/laterolateral plane, dividing the bladder neck into dorsal and ventral portions. The most common histopathological findings in the septum included urothelial hyperplasia (7 of 7) and heterophilic, lymphocytic, and plasmocytic inflammation (5 of 7). One rabbit died while recovering from cystoscopy. In the remaining 6 cases, endoscopic removal of the septum resolved the clinical signs consistent with urinary outflow obstruction and urinary retention.

Conclusions: Rabbits can develop septa inside their urinary bladder. These benign proliferations can result in urinary outflow obstruction and urinary retention.

Clinical relevance: Rigid cystoscopy was effective for the diagnosis and treatment of urinary outflow obstruction and urinary retention.