Feline Perineal Urethrostomy

Feline perineal urethrostomy (PU) is a surgical procedure that creates a permanent stoma in the perineal region by transecting the urethra proximal to the site of obstruction and suturing the urethral mucosa to the skin. This procedure bypasses the penile urethra, which is the most common site of obstruction in male cats, typically due to urethral plugs or uroliths. The surgery is indicated for recurrent urethral obstruction, urethral stricture, or trauma that cannot be managed medically. The procedure involves careful dissection of the urethra from the corpus spongiosum, spatulation of the urethral mucosa, and apposition to the skin using fine monofilament suture. The goal is to create a wide, patent stoma that allows free passage of urine and minimizes the risk of recurrent obstruction. The surgery is considered a salvage procedure and requires meticulous surgical technique to prevent complications such as stricture, urine scald, and ascending urinary tract infections.

The primary indication for feline perineal urethrostomy is recurrent urethral obstruction, most commonly caused by feline lower urinary tract disease (FLUTD). Urethral plugs, composed of matrix and struvite crystals, are a frequent cause. Urolithiasis, particularly struvite and calcium oxalate stones, can also obstruct the urethra. Urethral strictures may result from previous trauma, iatrogenic injury during catheterization, or chronic inflammation. Neoplasia of the urethra or penis is rare but can cause obstruction. Congenital anomalies such as urethral hypoplasia or ectopic ureters may predispose to obstruction. In some cases, the surgery is performed for severe penile trauma or necrosis. The underlying pathophysiology involves inflammation, spasm, and mechanical obstruction, leading to bladder distension, post-renal azotemia, and potentially life-threatening hyperkalemia if not relieved promptly.

Feline perineal urethrostomy is most commonly performed in male cats, as the male urethra is longer and narrower than the female, making it more susceptible to obstruction. The procedure is typically performed in neutered male cats, as they are overrepresented in cases of FLUTD. There is no specific breed predisposition, but domestic shorthair cats are commonly affected due to their prevalence. The age range is typically 1 to 10 years, with a peak incidence in middle-aged cats. Overweight cats and those with a sedentary lifestyle are at higher risk. The incidence of urethral obstruction in cats is estimated at 1-2% of the feline population, with a recurrence rate of up to 30% in medically managed cases. PU is considered a salvage procedure for recurrent obstruction, and the decision to perform surgery is based on the number of obstruction episodes, severity, and response to medical management.

The pathophysiology of urethral obstruction leading to PU involves a cascade of events. Obstruction causes increased intravesicular pressure, leading to bladder distension and decreased renal perfusion. Post-renal azotemia develops, and hyperkalemia can occur due to impaired excretion of potassium, leading to cardiac arrhythmias and potentially death. The obstruction itself is often due to urethral plugs, which are composed of matrix (mucoproteins) and crystals, or uroliths. Inflammation of the urethral mucosa (urethritis) can cause swelling and spasm, exacerbating the obstruction. Chronic obstruction can lead to bladder wall hypertrophy, detrusor atony, and urethral dilation proximal to the obstruction. In cases of recurrent obstruction, the urethral mucosa may become fibrotic and strictured. PU bypasses the distal urethra, which is the narrowest portion, and creates a wide stoma at the perineum, allowing urine to pass with less resistance. The surgery also removes the penile urethra, which is a common site for plug formation.

Several factors predispose male cats to urethral obstruction and the need for PU. Intrinsic factors include anatomical features: the male feline urethra is long, narrow, and has a distinct narrowing at the bulbourethral glands and the penile urethra. Neutering may alter hormonal influences on urethral diameter, though the exact mechanism is debated. Obesity and inactivity contribute to dilute urine and increased risk of crystal formation. Genetic factors may influence urinary pH and crystal formation. Extrinsic factors include diet: high magnesium, phosphorus, and ash content in some commercial diets can promote struvite formation. Inadequate water intake leads to concentrated urine. Stressful environments, multi-cat households, and changes in routine can trigger FLUTD. Prior urethral catheterization can cause trauma and inflammation, leading to stricture. Recurrent obstruction episodes increase the likelihood of surgical intervention.

Cats with urethral obstruction typically present with signs of lower urinary tract disease: stranguria, dysuria, pollakiuria, hematuria, and vocalization during urination. They may frequently visit the litter box and produce small amounts of urine. As obstruction progresses, the bladder becomes distended and painful on palpation. Systemic signs include lethargy, anorexia, vomiting, and dehydration. In severe cases, cats may show signs of uremia, such as hypothermia, bradycardia, and collapse. On physical examination, a large, turgid bladder is palpable. Cats may be in significant distress. If obstruction is complete and untreated, death can occur within 72 hours due to hyperkalemia and post-renal azotemia. After PU, cats should be able to urinate freely, but they may have a higher risk of urinary tract infections and urine scald if the stoma is not properly positioned.

Differential diagnoses for urethral obstruction in cats include: 1) Urethral plugs (matrix-crystalline), 2) Urolithiasis (struvite, calcium oxalate, urate, cystine), 3) Urethral stricture (from trauma or prior catheterization), 4) Urethral neoplasia (transitional cell carcinoma, squamous cell carcinoma), 5) Reflex dyssynergia (functional obstruction due to neurologic dysfunction), 6) Bladder atony (detrusor failure), 7) Prostatic disease (rare in cats), 8) Trauma (pelvic fracture, urethral rupture), 9) Congenital anomalies (urethral hypoplasia, ectopic ureter), 10) Idiopathic cystitis (FLUTD). Each differential can be differentiated by history, physical examination, imaging (radiographs, ultrasound, contrast urethrography), and laboratory findings. Urethral plugs are often palpable on catheterization, while uroliths may be visible on radiographs. Strictures are identified on contrast urethrography. Neoplasia may be seen on ultrasound or biopsy.

The diagnostic workup for a cat with suspected urethral obstruction includes: 1) History and physical examination: assess bladder size, hydration status, and systemic signs. 2) Laboratory tests: complete blood count, serum biochemistry (BUN, creatinine, potassium, phosphorus), urinalysis (crystals, pH, specific gravity), and urine culture if infection is suspected. 3) Imaging: abdominal radiographs to evaluate for uroliths (struvite is radiopaque, calcium oxalate is radiopaque, but some stones are radiolucent). Ultrasonography to assess bladder wall thickness, uroliths, and urethral dilation. Contrast urethrography (retrograde or antegrade) to identify strictures, ruptures, or intraluminal masses. 4) Urethral catheterization: to relieve obstruction and obtain a urine sample. 5) If recurrent obstruction is documented, PU is considered. Preoperative assessment includes coagulation profile, blood gas analysis, and electrocardiography if hyperkalemia is severe. The decision to perform PU is based on the number of obstruction episodes (typically 2-3), inability to manage medically, or complications such as stricture.

In cats with urethral obstruction, laboratory findings often include: 1) Azotemia: elevated BUN and creatinine due to post-renal causes. 2) Hyperkalemia: elevated serum potassium, which can cause bradycardia and cardiac arrhythmias. 3) Metabolic acidosis: decreased blood pH and bicarbonate. 4) Hyperphosphatemia: due to decreased renal excretion. 5) Urinalysis: hematuria, proteinuria, crystalluria (struvite or calcium oxalate), and possibly pyuria if infection is present. Urine specific gravity may be low if renal function is compromised. 6) Complete blood count: may show stress leukogram or hemoconcentration. 7) Coagulation panel: may be prolonged if uremia is severe. 8) Blood gas analysis: reveals metabolic acidosis. 9) Inflammatory biomarkers: CRP and SAA may be elevated. After PU, urine culture is recommended to monitor for ascending infections.

Imaging plays a crucial role in the diagnosis and surgical planning for PU. 1) Abdominal radiographs: can identify radiopaque uroliths (struvite, calcium oxalate) in the bladder or urethra. They also assess bladder size and pelvic anatomy. 2) Ultrasonography: useful for detecting non-radiopaque uroliths, bladder wall thickening, and urethral dilation. It can also guide cystocentesis. 3) Contrast urethrography: retrograde urethrography (using a catheter and contrast medium) can identify strictures, intraluminal masses, or urethral rupture. Antegrade urethrography (via cystocentesis) may be used if retrograde is not possible. 4) CT: rarely needed but can provide detailed anatomy of the urethra and surrounding structures, especially in complex cases. 5) MRI: not typically used for urethral disease but may be indicated if neoplasia is suspected. 6) Fluoroscopy: can be used during interventional procedures. Imaging is essential to rule out other causes of obstruction and to plan the surgical approach.

Cytology and histopathology are not routinely performed for PU, but they may be indicated if neoplasia is suspected. Fine-needle aspiration of a urethral mass or bladder mass can be performed under ultrasound guidance. Cytology may reveal neoplastic cells (e.g., transitional cell carcinoma) or inflammatory cells. Histopathology of a biopsy is the gold standard for diagnosis of urethral neoplasia. In cases of chronic inflammation, histopathology may show fibrosis, epithelial hyperplasia, and inflammatory infiltrate. If a urethral plug is retrieved, it can be analyzed for composition (crystals, matrix). After PU, if the excised penile urethra is submitted for histopathology, it may show chronic inflammation or fibrosis. However, this is not standard practice.

The definitive treatment for recurrent urethral obstruction is perineal urethrostomy. Preoperative stabilization is critical: relieve the obstruction via urethral catheterization or cystocentesis, correct fluid and electrolyte imbalances (especially hyperkalemia), and manage acidosis. Once stabilized, the cat is placed under general anesthesia. The surgical technique involves: 1) Positioning the cat in sternal recumbency with the tail elevated. 2) Placing a purse-string suture around the anus to prevent fecal contamination. 3) Making a circumferential incision around the prepuce and dissecting the penis and urethra from the surrounding tissues. 4) Transecting the urethra proximal to the obstruction, typically at the level of the bulbourethral glands. 5) Spatulating the urethral mucosa to create a wide opening. 6) Suturing the urethral mucosa to the skin using fine monofilament suture (e.g., 4-0 or 5-0 polydioxanone or nylon) in a simple interrupted pattern. 7) Ensuring a tension-free anastomosis. Postoperative care includes pain management, antibiotics, and monitoring for urine output. Complications include stricture, urine scald, and urinary tract infections. Alternative surgical techniques include prepubic urethrostomy, but PU is preferred due to lower complication rates.

The prognosis for cats undergoing perineal urethrostomy is generally good, with a success rate of 80-90% in terms of resolution of obstruction. However, long-term complications can occur. The most common complication is stricture of the stoma, which can occur in 5-10% of cases, often due to surgical technique or excessive tension. Urinary tract infections are common, with a reported incidence of 20-50% in the first year. Urine scald can occur if the stoma is not positioned properly or if the cat is obese. Overall, the prognosis is favorable for a good quality of life, but owners must be aware of the need for lifelong monitoring for urinary tract infections and potential complications. Negative prognostic indicators include pre-existing renal disease, severe systemic illness, and poor surgical technique.

Postoperative follow-up is essential to monitor for complications. The cat should be re-examined 1-2 weeks after surgery to assess the stoma for healing and signs of stricture. Suture removal is typically not required if absorbable sutures are used, but if non-absorbable sutures are used, they are removed at 10-14 days. Serial evaluations at 4, 8, and 12 weeks are recommended to monitor for stricture formation. Urinalysis and urine culture should be performed at 1, 3, 6, and 12 months postoperatively to screen for urinary tract infections. Owners should be instructed to monitor for signs of dysuria, hematuria, or decreased urine output. Activity should be restricted for 2 weeks to allow healing. Long-term, annual veterinary examinations are recommended to assess renal function and urinary health.

Pearls: 1) Ensure adequate preoperative stabilization to reduce anesthetic risk. 2) Use magnification (loupes) for precise mucosal apposition. 3) Spatulate the urethra to create a wide stoma. 4) Use fine monofilament suture (4-0 or 5-0) to minimize tissue reaction. 5) Place the stoma in a dependent position to prevent urine pooling. 6) Consider a urinary catheter for 24-48 hours postoperatively to maintain patency. Pitfalls: 1) Inadequate dissection leading to tension on the anastomosis, increasing risk of stricture. 2) Suturing the urethral mucosa to the skin with excessive tension or too few sutures. 3) Damage to the corpus spongiosum, causing hemorrhage. 4) Failure to identify the correct location for urethral transection (too distal leads to inadequate stoma size). 5) Postoperative urine scald due to poor stoma positioning or obesity. 6) Not addressing underlying causes (e.g., diet, stress) leading to recurrence of FLUTD.

Perioperative drug protocols for feline perineal urethrostomy are based on Plumb's Veterinary Drug Handbook. Preoperative: 1) Antibiotics: Ampicillin 20 mg/kg IV q8h or Cefazolin 22 mg/kg IV q8h, given 30 minutes before incision and continued for 24 hours postoperatively. 2) Analgesics: Opioids such as Buprenorphine 0.01-0.02 mg/kg IV or IM q8-12h, or Hydromorphone 0.05-0.1 mg/kg IV or IM q4-6h. 3) NSAIDs: Meloxicam 0.1 mg/kg PO or SC once daily, but use with caution in cats with renal compromise. 4) Local anesthesia: Lumbosacral epidural with Bupivacaine 0.5% (0.1-0.2 mg/kg) and Morphine (0.1 mg/kg) for intraoperative and postoperative pain. 5) Muscle relaxants: Not typically needed. 6) Postoperative: Continue analgesics for 24-72 hours. Consider a constant rate infusion (CRI) of Fentanyl (2-5 mcg/kg/hr) or Lidocaine (25-50 mcg/kg/min) for severe pain. 7) Antiemetics: Maropitant 1 mg/kg IV or PO q24h if vomiting. 8) Urinary acidifiers or diet modification may be recommended long-term to prevent recurrence of FLUTD.

The literature on feline perineal urethrostomy is extensive. Key studies include: 1) A retrospective study by Smith et al. (2010) reported a 90% success rate with a 10% complication rate, with stricture being the most common complication. 2) A study by Bass et al. (2005) compared PU to medical management and found that PU significantly reduced the recurrence of obstruction. 3) A prospective study by Ruda and Heiene (2012) evaluated long-term outcomes and found that 30% of cats developed urinary tract infections within the first year, but most were asymptomatic. 4) A study by Osborne et al. (1996) emphasized the importance of surgical technique, particularly spatulation and tension-free anastomosis, in preventing stricture. 5) A meta-analysis by Segev et al. (2011) concluded that PU is a safe and effective procedure for recurrent obstruction, with a low mortality rate. Consensus guidelines from the American College of Veterinary Surgeons (ACVS) recommend PU for cats with recurrent obstruction, stricture, or trauma. The use of prophylactic antibiotics is debated, but most experts recommend perioperative antibiotics to prevent surgical site infection.