Fluoroscopy-guided balloon dilation of a proximal urethral stricture caused by a urethral membrane in a female cat

Introduction

Feline urethral strictures are uncommon, usually occurring secondary to catheter-induced or pelvic trauma and most commonly within the mid–distal or distal urethra. Although rare, urethral strictures of presumed congenital origin have also been described in young cats. ¹ Diagnosis, management and confirmation of the aetiology of non-trauma-induced urethral strictures can be challenging owing to the sparseness of the current literature describing affected cases and a lack of histopathology due to tissue size and difficulty in sampling.^2–7 Several surgical options have been described for the treatment of urethral strictures. These are invasive procedures with significant complications and variable outcomes.^3,8–11 This report describes the successful management of a suspected congenital proximal urethral stricture in a female cat using minimally invasive fluoroscopy-guided balloon dilation. To our knowledge, this treatment modality has not been previously reported in cats.

Case description

A 2-year-old female neutered domestic shorthair cat was presented with a 5-week history of stranguria, pollakiuria and urinary incontinence. On initial presentation to the primary veterinarian the cat was reported to be excessively licking her vulva. This progressed to urinary incontinence when laying down and stranguria when urinating. Symptomatic treatment with cefovecin (8 mg/kg SC [Convenia; Zoetis]), meloxicam (0.05 mg/kg PO q24h [Metacam; Boehringer Ingelheim]), clomipramine (5 mg PO q24h [Clomicalm; Elanco]) and urinary diet did not lead to improvement; therefore, phenylpropanolamine (1.2 mg/kg PO q24h [Propalin; Vetoquinol]) was subsequently trialled. Owing to ongoing clinical signs, an exploratory coeliotomy was performed 3 weeks later. The primary veterinarian identified a thickened but grossly normal bladder. Ovariohysterectomy and bladder wall biopsy were performed. Histopathology revealed no abnormalities.

Physical examination at the referral institution was unremarkable aside from the bladder being medium sized but firm on abdominal palpation. The cat demonstrated urinary incontinence in the consultation.

Biochemistry and haematology, urinalysis and culture were performed. These were unremarkable apart from a mild elevation of urea (12.1 mmol/l[reference interval 2.7–9.2 mmol/l]). Feline leukaemia virus, feline immunodeficiency virus and coronavirus testing were negative.

Abdominal radiographs performed under sedation (ketamine 2.5 mg/kg [Ketavet; Zoetis] and midazolam 0.2 mg/kg [Hypnovel; Roche], IM) showed a markedly distended bladder causing dorsal displacement of the descending colon. Abdominal ultrasonography showed a focal thickening of the mid dorsal bladder wall. Mild right renal pelvic dilation and diverticuli were noted without ureteral dilation. Based on the clinical history, these findings were suspected to be due to a partial urethral obstruction causing chronic bladder distension. Urethral catheterisation using a 3.5 Fr urinary catheter (KatKath; Vigon Vet) was attempted but not possible. Therefore, cystoscopy was performed under general anaesthesia. This revealed a markedly dilated urethra with an abrupt narrowing near the bladder neck. The cystoscope was unable to traverse this narrowing, precluding visual assessment of the bladder lumen. A retrograde urethrogram was performed, which confirmed the presence of caudal urethral dilation with a sharp reduction in the proximal urethral diameter near the bladder neck (Figure 1). The urethral wall appeared smooth and regular. Based on the urethroscopic and urethrography findings, a diagnosis of urethral stricture was made.

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Figure 1

Retrograde urethrogram showing a sharp reduction in the proximal urethral diameter (black arrow) near the bladder neck, allowing only a thin trace of contrast into the bladder

The cat was discharged with meloxicam (0.05 mg/kg PO q24h) while interventional treatment options were being considered. The owner reported improvement of clinical signs and initially elected to continue monitoring. The cat re-presented 8 weeks later with ongoing dysuria and a distended, firm bladder. Repeat biochemistry was unremarkable. Repeated abdominal ultrasonography showed the development of bilateral renal pelvic and ureteral dilation. Owing to worsened clinical signs and progression of urinary tract obstruction on ultrasonography, the cat was admitted for fluoroscopy-guided balloon dilation of the urethral stricture.

The cat was anaesthetised. While in dorsal recumbency, a 9.5 Fr cystoscope (67030 BA; Karl Storz-Endoskope) was introduced into the distal urethra. The stricture was identified as a membranous structure arising from the urethral mucosa, with a very narrow lumen leading to the bladder neck (Figure 2). A 0.014-inch guidewire was introduced into the bladder across the urethral stricture, followed by placement of a 4 Fr micro-introducer to minimally dilate the stricture. This allowed passage of a 5 mm percutaneous transluminal angioplasty balloon dilation catheter (Sterling PTA Balloon; Boston Scientific). The positioning of the balloon was confirmed and monitored by fluoroscopy. The stricture was dilated with 5 ml of sterile saline introduced for 15 s into the balloon dilation catheter. Cystoscopic evaluation post-dilation revealed successful dilation of the stricture (Figure 3). The bladder lumen was evaluated with no abnormalities identified.

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Figure 2

Endoscopic image from the urethra at the level of the bladder neck. Membranous structure causing urethral stricture, with a small opening to the urinary bladder (black arrow), can be appreciated, preventing the cystoscope from reaching the bladder

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Figure 3

Urethral opening post-fluoroscopic-guided balloon dilation. Note the moderate inflammation of the urethral mucosa at the level of the stricture

The cat recovered uneventfully and was hospitalised for 48 h to monitor urination. Mild pollakiuria and dysuria were noted but resolved within 48 h. No urinary incontinence was noted. The cat was discharged with meloxicam (0.05 mg/kg PO q24h).

On re-evaluation 6 weeks post-stricture dilation, complete resolution of all clinical signs was reported. Serum biochemistry results were unremarkable. Abdominal ultrasonography showed resolution of the bilateral ureteral dilation with mild persistence of bilateral renal pelvic dilation. A retrograde urethrogram showed a marked improvement in the diameter of the proximal urethra at the site of the previous stricture (Figure 4). Subsequent follow-up was performed by telephone communication with both the referring veterinarian and owner. Twelve months after the procedure, the cat remained without clinical signs or complications.

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Figure 4

Six-week post-balloon dilation retrograde urethrogram. Marked improvement of the previously reported urethral stricture. Although some degree of reduction of the urethral diameter can be appreciated, good contrast flow into the bladder is noted

Discussion

Urethral obstruction is a common condition in cats. ¹² It can occur as a result of the presence of urethral plugs, urolithiasis, neoplasia, granuloma formation, bladder displacement or herniation, urethral stricture or idiopathic causes.^1,13,14 Strictures are defined as a reduction in the diameter of the lumen of a hollow structure. This occurs owing to the presence of cicatricial tissue as a result of inflammation and has been reported in hollow organs, such as the oesophagus, the rectum, the trachea, ureters and the urethra.^15,16 In the present case, the lesion was considered a stricture, as its location did not correlate with a natural narrowing point of the urethra. Furthermore, it was located proximally at it widest point. To our knowledge, the proximal nature of the stricture is thought to be a novel clinical finding, as previous literature only describes the presence of distal or mid urethral strictures in cats. ¹

Urethral strictures are usually sequelae of malignancy, pelvic trauma, severe inflammation or surgical intervention.^9,11,14 From the case history, stricture formation was considered congenital in origin based on signalment and the lack of trauma, urethral catheterisation or surgical intervention prior to presentation. In addition, the presence of the membranous structure separating both cavities suggests a congenital origin. Despite the lack of histopathology, it was considered to be a membrane based on the correlation of its clinical appearance and the definition of a membrane as a ‘thin layer of tissue separating two cavities’. ¹⁵ It was hypothesised that the membrane originated from the urethral mucosa. A similar finding has been reported in a dog with partial urethral obstruction, which was also suspected to be congenital in origin. ⁷

Urethral strictures typically present with clinical signs of dysuria and pollakiuria owing to partial or complete lower urinary tract obstruction.^17–19 In this case, the cat presented with similar dysuria, stranguria and incontinence. The mild uraemia noted on biochemistry analysis was considered either postprandial in nature or subclinical dehydration. The cat’s hydration status appeared clinically correct; however, subclinical dehydration can present with a marginal elevation of urea. ²⁰

Abdominal ultrasound and contrast radiography are common diagnostic tools when investigating urinary tract disorders.^21,22 In the present case, the abdominal ultrasound showed focal thickening of the dorsal bladder wall. This was suspected to represent the area previously biopsied by the referring veterinarian. The presence and location of the stricture was confirmed via retrograde positive contrast radiography, an imaging modality commonly used to diagnose urethral strictures.^2,9,12,18,19 Cystourethroscopy can also be used when investigating persistent lower urinary tract signs, providing a magnified internal image of the urinary tract. In this case, it identified the nature of the urethral obstruction, precluding placement of a urinary catheter. Cystourethroscopy also aids in performing interventional treatments.^23,24 Although considered a minimally invasive procedure, complications associated with cystoscopy include trauma to the urethral wall, urethritis, urethral and/or bladder rupture. ²³

Various surgical procedures (perineal, prepubic and subpubic urethrostomy) have been described for the treatment of proximal and distal urethral obstructions, mostly in male cats. Such procedures are rarely performed as they are associated with a high complication rate, including stricture formation, urinary leakage, recurrent urinary tract infections, dehiscence, skin necrosis and urinary incontinence.^8,25,26 In the present case, surgical treatment was not considered a valid option due to the proximal location of the stricture near to the bladder neck.

Bougienage, either digital or with specific instrumentation, has been described as a management method for oesophageal and rectal strictures in dogs.^27,28 A single case report of a urethral stricture as a consequence of perineal urethrostomy surgery in a cat was managed via bougienage with a successful outcome. ⁵ Although bou-gienage could be considered a management option for urethral stricture in cats, in the present case report the very narrow lumen of the membranous stricture was considered too small to be amenable for this technique.

Urethral balloon dilation is a common treatment modality for urethral strictures in humans, with similar outcomes to transurethral urethrotomy. The main complication is recurrence of the stricture in up to 25% of patients within the first 3 years. ²⁹ Urethroplasty offers the greatest chance for cure in humans and remains the gold standard in management of urethral strictures.^6,30 In veterinary medicine, limited cases of non-malignant urethral strictures have been reported in dogs^2,7,31,32 and cats.^5,17–19 To our knowledge, no other feline cases managed by balloon dilation have been reported. Only two of the canine cases reported were managed by fluoroscopy- and cystoscopy-guided balloon dilation,^2,31 with no associated complications or signs of re-obstruction noted 22 months post treatment. In the current case, follow-up retrograde urethrography showed persistent mild narrowing of the previous stricture site; however, there was normal flow of contrast into the bladder and resolution of clinical signs. This was considered a good outcome and repeat dilation was not necessary.

The placement of stents, self-expanding metallic stents (SEMS) and balloon-expandable metallic stents have been reported as treatment for urethral strictures and malignant urethral obstructions in both dogs and cats. Ureteral obstruction is the main concern with placement of SEMS for proximal urethral obstructions in cats, owing to a more caudal entrance of the ureters in the area of the trigone;^17,18 therefore, balloon dilation was the preferred treatment choice in this case.

Conclusions

To our knowledge, this is the first report of a young cat with a suspected congenital proximal urethral obstruction that was successfully managed by fluoroscopy-guided balloon dilation. Based on the promising results of this case report, fluoroscopy-guided balloon dilation should be considered a technique for management of urethral stricture in cats; although further studies with a larger caseload are required to fully endorse this technique in cats.