Dual-Energy Computed Tomography for Diagnosis and Monitoring Attempted Medical Management of a Large Urate Urolith in a Desert Tortoise (Gopherus agassizii)

Abstract

An estimated 29-yr-old male zoo-housed desert tortoise (Gopherus agassizii) presented for endoscopic liver biopsies as part of a diagnostic workup for recurrent, profound anemia and hypoalbuminemia. Suspected cystoliths were identified during endoscopy, but were not visible on conventional radiographs. Dual-energy computed tomography (DECT) imaging confirmed the presence of a large urate urolith filling the majority of the bladder. Because of the recent clinical illness, the tortoise was considered a poor surgical candidate. Medical management consisting of urinary alkalinization with potassium citrate, vibration therapy, and daily warm water soaks was elected. Following institution of medical therapies, the tortoise began passing pieces of urate stone that were 0.25–2.0 cm in diameter during daily soaks. A recheck DECT scan at 2 months indicated the urolith was approximately one third the initial size, suggesting medical therapy was effectively treating the urolith. Unfortunately, after 5 months of medical therapy, the stone had increased in size again on the follow-up DECT scan. This case report suggests that medical management may be a potential option for large urate cystoliths in desert tortoises, although more research is needed to further refine effective therapeutics for such cases. The use of DECT imaging was essential in this case because it enabled confirmation of stone presence, identification of urolith composition, and monitoring of response to therapy.