Unilateral Hydronephrosis and Partial Ureteral Obstruction by Entrapment in a Granuloma in a Spayed Dog

Introduction

Ureteral obstruction leads to restriction of urine flow, which may result in a uremic crisis, changes in the structure of the kidney and ureter, and loss of renal function. Mechanical obstruction of a ureter can result from intraluminal obstruction, mural lesions, or extraluminal compression. Causes of extramural ureteral obstruction in the dog include pelvic masses, bladder neoplasms, prostatic neoplasms, trauma, and ligation;¹ however, to the authors’ knowledge, this is the first report of unilateral partial occlusion of the ureter caused by entrapment in an ovarian pedicle granuloma associated with suture material reaction.

Case Report

A6-year-old, spayed female, mixed-breed dog weighing 14.2 kg was presented for persistent anorexia and lethargy that had lasted 3 to 4 days, as well as polyuria, polydipsia, and urinary incontinence that had persisted for about 1 month. Physical examination revealed moderate dehydration (5% to 7%) and lethargy. Initial diagnostic tests included a serum biochemical panel, a complete blood count (CBC), thoracic and abdominal radiographs, and a urinalysis.

Abnormalities included uremia (blood urea nitrogen [BUN] 131.2 mg/dL, reference range 9.1 to 31.9 mg/dL; creatinine 11.1 mg/dL, reference range 0.2 to 1.6 mg/dL); hyperphosphatemia (11.5 mg/dL, reference range 1.6 to 6.3 mg/dL); mild hypokalemia (3.2 mEq/L, reference range 3.4 to 5.2 mEq/L); and mild hyperchloremia (120 mEq/L, reference range 102 to 117 mEq/L). Other biochemical and CBC parameters were within normal limits. Thoracic and abdominal radiographs showed a severely enlarged left kidney and a small right kidney. Urinalysis showed diluted urine (urine specific gravity 1.014 g/dL). Abdominal ultrasonography showed severe left hydronephrosis and a small right kidney with a thin renal cortex. The left renal pelvis was distended, measuring 6 × 3.5 cm on the midsagittal plane. Lactated Ringer’s solution was administered continuously (10 mL/kg per hour for the first 12 hours, then 7 mL/kg per hour for 12 hours), and a urethral catheter was used for closed urine collection to quantify urine output. Continuous urine production was confirmed, and a serum biochemical panel obtained 12 hours later showed mildly improved BUN (100.8 mg/dL), creatinine (9.6 mg/dL), and phosphate (9.4 mg/dL).

On the second day of hospitalization, excretory urography (800 mg/kg of iodine was given as iohexol^a intravenously [IV]) was performed, and right lateral and ventrodorsal views were made at 0, 1, 3, 5, 10, and 20 minutes after iohexol injection. Hydronephrosis and hydroureter due to partial ureteral occlusion in the cranial part of the left ureter and a small right kidney were noted [Figures 1A, 1B]. The right ureter, caudal two-thirds of the left ureter, and the urinary bladder were unremarkable. Since a definitive cause of the ureteral obstruction was not identified, an exploratory laparotomy was performed the following day. A preoperative biochemical panel showed partially improved renal values (BUN 79.0 mg/dL, creatinine 6.8 mg/dL).

The dog was administered atropine sulfate (0.05 mg/kg body weight subcutaneously [SC]), morphine hydrochloride (0.5 mg/kg intramuscularly), and diazepam (0.5 mg/kg IV) prior to induction with ketamine hydrochloride (5 mg/kg IV). Anesthesia was maintained with isoflurane in oxygen. Pain management included epidural analgesia with morphine hydrochloride (0.1 mg/kg) and bupivacaine (0.2 mg/kg) after induction.

Exploratory laparotomy showed an enlarged left kidney; a distended left ureter cranial to a 2-cm, irregular, firm mass just caudal to the left kidney; and a small right kidney. The distended left ureter was approximately 2.5 cm in length and approximately 1.0 cm at its maximum diameter. The mass was located so close to the left kidney that complete resection was considered likely to injure the renal pelvis. The left ureter caudal to the mass appeared to be of normal size. Function of the right kidney was thought to be impaired because of the presenting azotemia; therefore, relief of the obstruction was considered necessary to preserve the function of the left kidney.

A 5-French polypropylene catheter with two side holes was introduced through the left renal capsule into the renal pelvis as a nephrostomy tube. Urine under pressure exited from the left renal pelvis when an 18-gauge needle was introduced as a trochar. Renal descensus was performed by moving the left kidney caudally and suturing the renal capsule to the lateral abdominal wall, using 3-0 polydioxanone. A ureteroureterostomy (end-to-side ureteral anastomosis) was performed. The left ureter was transected approximately 0.5 cm caudal to the obstruction; the caudal end of the cranial aspect of the ureter was ligated just cranial to the mass; and the caudal segment of the left ureter was mobilized cranially by carefully detaching it from surrounding tissues to minimize tension at the anastomosis site. A 9-mm longitudinal incision was made in the cranial left ureter, and the cranial tip of the caudal ureteral segment was spatulated to widen the ureteral orifice. The spatulated cranial tip of the caudal segment of left ureter was sutured to the longitudinal incision in the side of the cranial segment, using a simple interrupted pattern of 4-0 polyglactin 910.

An incisional biopsy (approximately one-fourth of the mass) was obtained from the ventral aspect of the mass that appeared to be trapping the ureter. The right ovarian pedicle, bladder, and uterine stump appeared to be grossly normal. Closure was routine following irrigation of the abdomen. The nephrostomy tube was secured to the skin using a finger-trap suture technique, and it was connected to a closed urine collection system. A urethral catheter was also maintained for quantification of urine output. The dog was stable during anesthesia, and recovery was uneventful.

The dog was stable postoperatively and regained its appetite and vigor. The nephrostomy tube did not function, presumably because of tube dislodgement or blockage;¹ however, urine was collected from the urethral catheter. The azotemia improved during the first two postoperative days (postoperative day 1: BUN 70.0 mg/dL, creatinine 6.8 mg/dL; day 2: BUN 70.0 mg/dL, creatinine 4.5 mg/dL; day 3: BUN 44.2 mg/dL, creatinine 3.1 mg/dL), and no clinical signs indicated urine leakage. The dog was discharged 6 days postoperatively in good general physical condition, and azotemia was improved (BUN 37.3 mg/dL, creatinine 2.9 mg/dL).

After discharge, urinary incontinence (occasional urine dribbling after urination with a small bladder) lasted for 2 months. Urinalysis and neurological examinations were unremarkable and showed gradual improvement. Abdominal radiography and ultrasonography 1 and 4 months postoperatively showed reduced hydronephrosis. The dog has been doing well with no clinical signs of ureteral stenosis 3 years after the surgery, and BUN, creatinine, and phosphate were within normal limits (16.5 mg/dL, 1.5 mg/dL, 3.2 mg/dL, respectively) 3 years after surgery. Macroscopic examination of the sample of the mass revealed a small piece of black, braided suture material in the center, which was assumed to be used for ligation of ovarian vessels during the ovariohysterectomy (OVH) performed 5 years prior to presentation. The OVH was the only surgery performed on this dog. Histologically, the mass mainly consisted of macrophages and degenerate neutrophils with fibrous tissue proliferation, suggesting chronic pyogranulomatous inflammation [Figure 2]. Considering the possibility of Mycobacterium spp. infection, periodic acid-Schiff staining was performed and found to be negative for acid-fast organisms.

Discussion

In reports describing complications associated with OVH, ovarian pedicle granulomas are rare.^2–9 In the case presented here, granuloma formation from a reaction to the suture material used in the OVH performed 5 years previously was suspected to be causing partial ureteral obstruction. Histopathological findings were consistent with pyogranulomatous inflammation with fibrous connective tissue. Most of the neutrophils were degenerate, which may suggest chronic inflammation rather than acute suppurative inflammation. The exact etiology of this inflammatory response remained unclear; however, suture material in the center of the biopsied mass and the chronic nature of the histopathological findings strongly suggested that chronic pyogranulomatous inflammation against the suture material led to granuloma formation with fibrous tissue proliferation, which then gradually entrapped the left ureter.

Although no histopathological evidence suggested bacterial infection in this case, further investigations would need to be considered to completely rule out infection. Mycobacteriosis can cause pyogranulomatous inflammation; however, no acid-fast organisms were identified. Since the right ovarian pedicle and uterine body appeared grossly normal intraoperatively, and no evidence of infectious disease was seen, the reason remains unknown as to why this pyogranulomatous inflammation only occurred at the left ovarian pedicle.

Entrapment of a ureter in a ligature associated with OVH has been reported shortly after the procedure.^4–6 One report has documented bilateral chronic ureteral obstruction secondary to OVH, with bilateral ureteric stenosis in the bladder trigone due to the presence of uterine stump scar tissue around the caudal portion of both ureters.⁸ To our knowledge, no reports have described chronic obstruction of the cranial ureter due to entrapment by fibrous tissue secondary to chronic pyogranulomatous inflammation presumably from a suture reaction. The type of suture material remains unknown in this case, but its presence 5 years after surgery would suggest a nonabsorbable material was used. Clinicians should be aware of this potential complication following OVH. Polyglactin 910 suture material was used for the ureteral anastomosis, because it provides good knot security, it is absorbable, and it does not stimulate a significant inflammatory response.

The normal diameter of the canine ureter, as measured using contrast-enhanced helical computed tomography, ranges from 1.3 to 2.7 mm.¹⁰ Healing of the ureter occurs by fibrous tissue replacement.¹ Given the small size and healing mechanism of the ureter, ureteral anastomosis is technically difficult and associated with a relatively high incidence of postoperative stricture or urine leakage.^2,11 Although urine diversion by placement of a ureteral stent or a nephrostomy tube has been recommended to minimize such complications, ureteral stenting is known to increase tension at the anastomosis site and cause stricture formation and infection.^1,12 Increasing the diameter of the anastomosis site by spatulation (as performed in this case) also can help to reduce the risk of postoperative ureteral stricture.

The nephrostomy tube in this case failed to function 1 day after surgery, presumably because of tube dislodgement or blockage. Since the urethral catheter seemed to be collecting appropriate amounts of urine, the nephrostomy tube was removed. No additional complications suggesting ureteral obstruction or urine leakage were noticed. Tube dislodgement is the most common problem with a nephrostomy tube attached to the skin, where the mobility of the skin allows the tube tip to migrate.^1,11 Some surgeons place an active peritoneal drain near the ureteral anastomosis site to detect urine leakage instead of placing a nephrostomy tube, because nephrostomy tubes are associated with leakage and tube obstruction.¹

Urinary incontinence in this dog was suspected to be from urethral sphincter incompetence, but the owner’s description was not specific enough to distinguish the pattern of urinary incontinence. The owner did not pursue treatment, because the incontinence was intermittent and gradually improving. Vesicovaginal fistula was considered unlikely based on the gradual improvement.

The prognosis for recovery of renal function after relief of a ureteral obstruction depends on a number of factors, such as the etiology, duration, and degree of obstruction. Relief of unilateral complete obstruction after 4 days resulted in nearly complete return of renal function. Relief after 14 days resulted in a 46% recovery of glomerular filtration rate and tubular function by 4 months. Relief of obstruction after 40 days resulted in little recovery of renal function.^13–15 In contrast to the rapid irreversibility of renal function following relief of a complete obstruction, partial ureteral obstruction results in less severe destruction and more complete return of function after relief.¹⁶

Extreme asymmetry in renal size is characteristic of the so-called “big kidney-little kidney syndrome,” which is usually associated with unilateral ureteral obstruction.¹⁷ The small kidney usually has end-stage renal failure, which supported our decision to not perform a left nephrectomy in this dog. Evaluating the function of each kidney requires nuclear scintigraphy, which is not legally permitted for dogs in our country (Japan). Because of the small size of the right kidney, we believed the left kidney was more functional than the right. The values of the BUN, creatinine, and phosphate improved and were well maintained for 3 years postoperatively.

Conclusion

Although ureteral obstruction due to entrapment by the granulomatous lesion secondary to OVH is very rare, the importance of suture material selection, less traumatic tissue handling, surgical skill, and strict aseptic technique should be addressed in a variety of surgical procedures including OVH. Although the underlying cause of chronic pyogranulomatous inflammation remained unclear, the possibility of an undetected infectious agent still remains open. In dealing with ureteral obstruction, assessment of the extent of renal damage is essential for therapeutic strategy planning.

Acknowledgments

We appreciate Dr. Hiroshi Fujita, BVSc, for preparing figures; Dr. Kyle Mathews, DVM, Diplomate ACVS, PhD, for great advice; and Dr. Tetsushi Yamagami, DVM, MS, PhD, for histopathological diagnosis.