Introduction
A 10-month-old spayed female ferret presented to Angell Animal Medical Center for frequent straining to urinate and defecate, occasional hematochezia and intermittent, reducible prolapse of the rectal mucosa. The ferret was current on all vaccines, housed indoors and fed on both a proprietary ferret diet and grain-free cat food. The ferret was bright, alert, and responsive with a firm, enlarged bladder and reactive on caudal abdominal palpation. A 3-mm umbilical swelling, yellow staining around the vulva and a mild 1- to 2-mm rectal prolapse were present. Serum biochemical analysis revealed a normal BUN (43 mg/dL; reference range, 12 to 43 mg/dL) and elevated creatinine (1.3 mg/dL; reference range, 0.2 to 0.6 mg/dL), but other findings were unremarkable. The PCV was 31% (reference range, 46.0% to 57.0%) and TS concentration was 6.9 g/dL (reference range, 5.3 to 7.2 g/dL).
Diagnostics Findings and Interpretation
Plain radiographs revealed an ovoid cystolith (15 X 24 mm) with a ureterolith (6 X 8 mm) at the level of the left distal ureter (Figure 1). During hospitalization, lactated Ringer solution (continuous rate infusion at 120 mL/kg/h, IV), clavamox (13 mg/kg, PO, q 12 h), prazosin (0.1 mg/kg, PO, q 8 h), and buprenorphine (0.05 mg/kg, IV, q 6 h) were administered.
Given the concern for a urinary obstruction, the ferret was anesthetized for exploratory laparotomy. A ventral cystotomy was performed to remove a large, solitary calculus from the bladder. Bilateral calculi in the distal ureters could not be manually passed into the bladder. They were left in situ until evaluation of ureteral patency could be assessed by ultrasound. The previously noted umbilical swelling was found to be a patent urachus, which was ligated with 3-0 PDS and resected. Bladder and abdominal wall closure was routine.
The ferret recovered well from the surgery. Abdominal ultrasonography revealed moderate hydronephrosis of the left kidney and hydroureter due to an 8 mm calculus present at the distal left ureter (Figure 2); the left kidney was enlarged up to 4 cm with a thick heterogenous hypoechoic subcapsular region that measured 9 mm thick. There was loss of corticomedullary distinction and moderate pyelectasia of 6 mm. The right kidney had mild pyelectasia of 2 mm. There was a 5 mm calculus in the distal right ureter causing mild dilation of the ureter. At the time of ultrasound, the PCV had decreased to 18.5% and the TS concentration was 4.0 g/dL. This was attributed to subscapular hemorrhage seen around the left kidney. Owners were informed that a blood transfusion might be necessary. An aerobic urine culture was obtained by cystocentesis and the ferret was started empirically on enrofloxacin (10 mg/kg, PO, q 12 h) in addition to the previously prescribed clavamox.
Recheck abdominal ultrasonography 2 days after the cystotomy showed progressive dilation of the left renal pelvis now measuring approximately 9 mm in depth (previously 6 mm). There was also progression of the echogenic fluid surrounding the left kidney. The right kidney was unchanged in appearance. The ferret was suspected to have a left ureteral obstruction while the right ureter remained patent.
Treatment and Outcome
Given the progressive left hydronephrosis, surgery was performed to re-route the left ureter with ureteroneocystostomy. The bladder was exteriorized and the previous cystotomy sutures removed to access the interior of the bladder. The distal left ureter was ligated with 2 circumferential sutures using 4-0 PDS and transected proximal to the ligatures. Hemostats were used to create a stoma in the bladder wall and pull the transected left ureter through the new stoma. Simple interrupted sutures of 4-0 PDS were used to attach the ureteral mucosa to the bladder mucosa. A tom cat was passed through the lumen to ensure patency before closing the bladder. The bladder was leak tested and the surgical site lavaged with saline and suctioned prior to routine closure of the bladder and abdominal wall. Nocita (5.3 mg/kg, SC, once) was administered along the incision site. Postoperative analgesia after both procedures was provided by fentanyl (continuous rate infusion at 3 mcg/kg/h, IV, for 1 day). The ureterolith and previously removed cystolith were submitted to the Minnesota Urolith Center for analysis.
The following day the ferret had an excellent appetite, and successfully urinated with mild hematuria. A chemistry panel revealed a normal BUN concentration (26 mg/dL) and improved creatinine concentration (0.8 mg/dL). The PCV was 25% and TS was 4.7 g/dL. A focal ultrasonographic evaluation showed progressive pyelectasia of the left kidney (Figure 3), with the renal pelvis now measuring 14 mm in depth (previously 9 mm). Left sided perirenal fluid accumulation was relatively unchanged and the pyelectasia of the right kidney remained stable.
Aerobic urine culture grew Staphylococcus pseudintermedius and Pasteurella sp. Enrofloxacin was recommended and continued due to its predictable effectiveness on sensitivity testing. Quantitative urolith analysis confirmed the uroliths were 100% struvite. A change to a balanced, high-quality, commercial ferret diet was advised. The ferret was discharged 10 days after presentation and owners were encouraged to pursue periodic bloodwork and ultrasonographic evaluation rechecks.
The ferret was reevaluated 3 weeks following discharge. The owners reported no health concerns and physical examination findings were within normal limits. A CBC and chemistry panel revealed no abnormalities. Recheck abdominal ultrasonography showed resolution of the left renal pyelectasia and hydroureter (Figure 4). There was moderate-to-severe remodeling of the left kidney with poor corticomedullary definition and irregular margins secondary to prior renal insult. The right kidney was relatively unchanged in appearance with mild persistent pyelectasia. The previously detected right distal ureteral calculus was not apparent.
Comments
Hydronephrosis and hydroureter are infrequently reported in ferrets. Ligation of the ureter, seen as a potential complication of ovariohysterectomy, is most commonly associated with hydronephrosis and hydroureter.1,2 However, ureteral obstruction secondary to calculi formation is rarely documented and the incidence of ureterolithiasis causing hydronephrosis and hydroureter is unknown in ferrets.2 In cases of unilateral obstruction, adequate function of the remaining kidney may delay diagnosis. Female ferrets that are severely affected by urolithiasis may develop rectal or vaginal prolapse and potentially fatal hemorrhage.1,2 Given the history of severe stranguria, the authors suspect that the rectal prolapse was related to the ferret’s urinary obstruction rather than an incidental finding.
Results of physical examination and diagnostic imaging are important for the diagnosis and management of ferrets with ureteral and cystic calculi obstruction. Plain radiographs were used to evaluate the entire urinary tract and confirmed the presence of uroliths. Evidence of worsening hydronephrosis of the left kidney on serial ultrasonographic exams confirmed obstruction secondary to ureterolithiasis. Persistent right renal pyelectasia could be a result of polyuria or an indication of mild, early obstruction secondary to the right ureteral calculus. In similar cases of ureterolithiasis, retrograde pyelography, intravenous excretory urography and ultrasonographic evaluation should be considered prior to surgery. These procedures were indicated, but not available at the time of presentation.
Potential risks and complications of ureteroneocystostomy surgery in the immediate postoperative period include hemorrhage, uroabdomen and stricture formation. The long-term complications and risks of re-obstruction after ureteral surgery remain unknown in ferrets. However, resolution of clinical signs in this case suggests that ureteroneocystostomy may be a therapeutic option for ureteral calculus obstruction in ferrets. Successful placement of a subcutaneous ureteral bypass (SUB) system may be attempted in the future if standardized devices become available for smaller exotic species.3,4
Cystic and ureteral calculi in ferrets are often a result of improper husbandry and being fed poor quality diets rather than a balanced commercial ferret diet.2,5 Despite the strong correlation between grain-free diets and cystine urolith formation, quantitative urolith analysis confirmed the ferret had struvite calculi.5 Analysis of calculi composition and an appropriate diet plan are essential in the long-term management of urolithiasis in ferrets. While recurrence of struvite uroliths following surgery is unknown, the ferret was started on a high-quality ferret diet to prevent future urolithiasis. Due to their predicted effectiveness on aerobic urine culture results, clavamox and enrofloxacin were administered and continued several days past resolution of the ferret’s clinical signs.
To the authors’ knowledge, this is the first report of a ureteroneocystostomy procedure to treat a ferret with urolithiasis. However, no long-term data are available to determine the risks and prognosis following this surgery. Whether the affected kidney and ureter will remain functional is unclear, and it is yet to be determined whether late-occurring complications will develop as the ferret ages. Nevertheless, the short-term outcome was successful for the ferret of this report.
Acknowledgments
No third-party funding or support was received in connection with this case report. The authors declare that there were no conflicts of interest.
References
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