Dual-Energy Computed Tomography for Diagnosis and Monitoring Attempted Medical Management of a Large Urate Urolith in a Desert Tortoise (Gopherus agassizii)
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.Abstract
Dorsoventral (A) and lateral beam (B) radiographs of a desert tortoise (Gopherus agassizii) revealed an empty gastrointestinal tract, but were otherwise unremarkable. No urolith was visible on conventional digital radiographs. These radiographs were taken during the same procedure as the endoscopy images in Figure 2, which clearly show a cystolith.
Endoscopic images acquired through a prefemoral approach of a desert tortoise (Gopherus agassizii). A white, gritty mass was present within the urinary bladder in the caudal coelom in both images (A) and (B). These images were taken during the same procedure as the radiographs in Figure 1, which show no evidence of a cystolith.
Initial dual-energy computed tomography (DECT) of a desert tortoise (Gopherus agassizii). Initial DECT showed a large urate urolith (arrows) in the left lobe of the bladder in both the axial (A) and coronal (B) planes. These are both 70-keV monoenergetic images.
Follow-up dual-energy computed tomography (DECT) of a desert tortoise (Gopherus agassizii) after 2 months of urinary alkalinization treatment. DECT showed a reduction in size of the urolith (arrows) in the right lobe of the bladder in both the axial (A) and coronal (B) planes. The uroliths were reduced in size, enabling movement from the left lobe into the right lobe of the bladder.
Follow-up dual-energy computed tomography (DECT) of a desert tortoise (Gopherus agassizii) after 5 months of urinary alkalinization treatment. DECT showed recurrence of the urolith (arrows) in the left lobe of the bladder in both the axial (A) and coronal (B) planes.
Cystoliths removed during a cysotomy via a prefemoral approach of a desert tortoise (Gopherus agassizii). The single calculus was fragmented to facilitate removal. In total, 27 white, semifriable pieces ranging in size from 4 to 25 mm in diameter were removed.
Four axial CT images of a desert tortoise (Gopherus agassizii). (A) Image was generated from the 140-kV acquisitions. (B) Image is the 70-keV monoenergetic image reconstructed from the 80- and 140-kV acquisitions. (C and D) Water(iodine) and iodine(water) image reconstructed from the same data. Note that the iodine(water) image allows easy differentiation between the noncalcified cystoliths on the left, and the calcification on the right.
