Clinical case study: Treatment of incontinence with hydraulic occluder placement

canine incontinence
Penny the dog

Case study by Dr Benjamin McRae & subedited by Phil Tucak

This case demonstrates the surgical management of urinary incontinence in a young female dog. Penny is a three-year-old female spayed American Staffordshire terrier, who presented to her regular vet with signs of urinary incontinence at approximately nine months of age. The owners reported that she would often wet the bed, and dribble urine while conscious. Penny had been acquired by her owners from the RSPCA in Queensland and had been desexed when she was approximately six months of age. 

Initial empirical treatment with amoxicillin-clavulanic acid 250mg orally twice daily for a suspected urinary tract infection was unsuccessful. A complete blood count, serum biochemistry and urinalysis including culture and sensitivity were performed and were all unremarkable, except for variable USG results ranging from concentrated to isosthenuric. Penny was trialled on both phenylpropanolamine and stilboestrol treatments without success.

Penny was referred to the Veterinary Specialists of Sydney (VSOS) internal medicine service when she was approximately 18 months of age. She underwent an abdominal ultrasound and cystoscopy performed by a registered specialist in small animal internal medicine, Dr Karina Graham. Ultrasound examination of the abdomen and, importantly, the lower urinary tract was unremarkable. On cystoscopic examination both ureterovesicular junctions were in anatomically normal positions, ruling out ectopic ureters as a cause of her incontinence. 

The urethra itself was noted to be wider than normal. Veterinary specific collagen was injected into the submucosa via endoscopy to bulk up and form out-pouching of the mucosa to narrow the urethral lumen. Bupivicaine 2.5mg/ml was instilled into the urethra prior to recovery. Penny was discharged on amoxicillin-clavulanic acid 375mg PO BID for three days, and a single subcutaneous injection of carprofen 4mg/kg was administered on recovery from anaesthesia. 

Initial communication by the regular vet with the owners suggested a good response to the procedure, with only minimal dribbling of urine and no more bedwetting. However a follow-up four months later revealed that the incontinence, including bedwetting and leaking of urine, returned approximately six weeks after the procedure. Penny was re-started on phenylpropanolamine and stilboestrol, and the possibility of surgical placement of a hydraulic occluder was discussed. 

Refractory urinary incontinence (RUI) is a complex and often multifactorial problem in dogs with urinary sphincter mechanism incontinence (USMI), particularly those with urogenital anatomical defects, such as Penny’s wide urethra. 

RUI refers to cases where medical therapy involving the use of drugs like phenylpropanoloamine, or submucosal bulking agents such as collagen have not been successful. Patient-controlled hydraulic urethral sphincter occluders have been used in humans for decades, and their use was first reported in dogs in 2004. Hydraulic occluders are made of an incomplete silicone ring that encircles the urethra, and is connected to a percutaneous port through which saline is injected to inflate the occluder and narrow the lumen of the urethra. 

After a consultation with Dr Karina Graham, the owners consented to the placement of a hydraulic occluder. Surgery was performed by Drs Graham and Andrew Levien. A caudal laparotomy was performed and the bladder identified. A babcock forcep was used to retract the bladder cranially and the urethra was catheterised with a 6Fr Foley catheter, allowing the urethra to be gently dissected from the vagina. 

canine incontinence
Figure 1. Collagen injection into the urethra. Figure 2. Following collagen injection. 
Figures 3 and 4. Endoscopic images taken during urethroscopy showing the decreased diameter of the urethral lumen with 0% inflation and 100% inflation of the occluder respectively.
Figure 5. The bladder exteriorised during the procedure. Figure 6. Abdominal radiograph showing the subcutaneous access port for hydraulic occluder inflation.

The circumference of the urethra was measured using a penrose drain, and estimated to be approximately 40mm. A 12x14mm hydraulic occluder was selected and primed with saline. The occluder tubing was introduced through the body wall, placed around the urethra and secured using 0-Prolene simple interrupted suture. The vascular access port was secured to the fascia using 0-Prolene simple interrupted suture. The abdomen was lavaged and closed routinely. 

Penny was discharged on amoxicillin-clavulanic acid 22.5mg/kg orally twice daily for two weeks, as well as meloxicam 0.1mg/kg orally once daily and tramadol 5mg/kg orally three times daily. The following day she was reported to be comfortable, and urinating normally at home, although the flow was not as forceful as normal. 

A recheck cystoscopy for hydraulic occluder inflation was scheduled for six weeks post-operatively with Dr Graham. A six-week delay in inflation is recommended to allow revascularisation of the dissected portion of periurethral tissue and minimise the risk of urethral atrophy. 

At the six-week recheck, Penny was anaesthetised and a repeat cystoscopy was performed. Various inflation volumes and their effect on the hydraulic occluder were documented.

For reference, the volumes required to inflate the hydraulic occluder:

0.00mls – 100% open

0.20mls – 75% open

0.25mls – 50% open

0.40mls – 25% open 

0.70ml – 0% open 

The occluder was inflated with 0.20mls of saline. The owners were advised that if Penny showed any signs of urinary obstruction 0.05mls would be removed. If she remained incontinent, then 0.05mls was to be added each week until the incontinence had resolved. Stilboestrol was still being given at this time, and it was recommended that this medication be withdrawn. 

Following the hydraulic occluder placement, Penny’s owners have not noted any episodes of incontinence unless she gets very excited. She had a short period of increased urination frequency, however this coincided with another dog staying with her, and was suspected to be behavioural. 

Despite the success seen in this case, hydraulic occluders are not without risks. One serious complication seen in 17% of patients of one study is urethral stricture formation. Post-operative urinary tract infections were diagnosed in 61% of animals, and stranguria/pollakiuria were seen in 6/18 and 2/18 dogs respectively. For this reason, the procedure is only recommended in dogs that are refractory to medical management.

Dr Benjamin McRae BSc BVMS, Veterinary Surgeon

canine incontinence

Dr Benjamin McRae completed his Bachelor of Veterinary Medicine and Surgery at Perth’s Murdoch University in 2013. Initially he worked in general practice and emergency settings around Australia, and has now commenced an internship in small animal surgery at Veterinary Specialists of Sydney (VSOS).

He was drawn to VSOS because of the respected team and the chance to be part of a world-class animal treatment centre. His main area of interest is minimally invasive surgery, particularly laparoscopy. 


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