Canine Scrotal Urethrostomy

Canine scrotal urethrostomy is a surgical procedure that creates a permanent stoma in the scrotal portion of the penile urethra, allowing urine to bypass distal obstructions or strictures. This technique is primarily indicated for the management of urethral obstructions caused by urolithiasis, neoplasia, trauma, or stricture formation that cannot be resolved by less invasive means. The scrotal location is chosen because the urethra is relatively wide and superficial in this region, facilitating surgical access and postoperative management. The procedure involves a midline scrotal incision, mobilization of the penis, and creation of a urethral stoma by suturing the urethral mucosa to the skin. It is a salvage procedure that preserves urinary continence by maintaining the function of the external urethral sphincter, which is located proximal to the stoma. Scrotal urethrostomy is distinguished from perineal and prescrotal urethrostomy by its anatomical location and the requirement for an intact scrotum, making it suitable only for intact male dogs. The procedure is contraindicated in castrated males, as the scrotum is absent or atrophied, and in cases where the obstruction is proximal to the scrotal urethra.

The primary etiologies necessitating scrotal urethrostomy include: (1) Urethral obstruction due to urolithiasis, particularly struvite, calcium oxalate, and urate stones, which lodge in the urethra, most commonly at the level of the os penis or the ischial arch. (2) Urethral neoplasia, such as transitional cell carcinoma, which can cause progressive obstruction. (3) Traumatic injury to the urethra, including pelvic fractures, bite wounds, or iatrogenic damage from catheterization. (4) Urethral stricture formation secondary to chronic inflammation, prior surgery, or trauma. (5) Severe urethral necrosis or avulsion. (6) Congenital anomalies, such as urethral hypoplasia or ectopic ureter, though these are less common. The anatomical vulnerability of the male canine urethra, particularly the long, narrow penile portion, predisposes to obstruction. The scrotal urethra is relatively wider and more distensible, making it an ideal site for a stoma. The underlying pathophysiology involves increased intraluminal pressure, ischemia, and tissue damage, leading to further obstruction and potential rupture if not relieved.

Scrotal urethrostomy is performed in intact male dogs, with a higher incidence in breeds predisposed to urolithiasis, such as Dalmatians (urate stones), Miniature Schnauzers, Bichon Frises, and Shih Tzus (struvite and calcium oxalate stones). The condition is more common in middle-aged to older dogs, typically between 4 and 10 years of age. There is no significant breed predilection for urethral trauma, but working and hunting dogs may be at higher risk for traumatic injuries. The incidence of urethral obstruction is estimated at 0.5-1% of the canine population, with a male-to-female ratio of approximately 3:1 due to the longer, narrower male urethra. Scrotal urethrostomy is a relatively common salvage procedure in referral practice, accounting for a significant proportion of urethral surgeries. The procedure is rarely performed in cats, where perineal urethrostomy is the standard salvage technique.

The pathophysiology of conditions leading to scrotal urethrostomy involves a cascade of events. In urolithiasis, stones form in the bladder and migrate into the urethra, causing partial or complete obstruction. The obstruction leads to increased intravesicular pressure, which is transmitted to the kidneys, potentially causing hydronephrosis and renal failure if not relieved. The urethral wall becomes edematous and inflamed, further narrowing the lumen. In cases of neoplasia, tumor growth causes progressive obstruction and infiltration of the urethral wall, leading to fibrosis and loss of elasticity. Trauma can cause direct disruption of the urethral mucosa, leading to stricture formation during healing. The resulting obstruction causes dysuria, stranguria, and eventually complete anuria, leading to postrenal azotemia, hyperkalemia, and metabolic acidosis. If the bladder ruptures, uroabdomen ensues, causing severe peritonitis and systemic inflammatory response syndrome. The surgical creation of a stoma bypasses the obstructed distal urethra, allowing urine to flow freely, but the underlying disease process (e.g., urolithiasis) must be managed to prevent recurrence.

Intrinsic predisposing factors include: (1) Anatomical conformation: The long, narrow penile urethra in male dogs, especially in brachycephalic breeds, increases the risk of obstruction. (2) Genetic predisposition: Certain breeds have a higher incidence of urolithiasis due to inherited metabolic defects, such as Dalmatians with urate stones. (3) Age: Middle-aged to older dogs are more prone to urolithiasis and neoplasia. (4) Sex: Males are more commonly affected due to urethral anatomy. (5) Body condition: Obese dogs may have increased intra-abdominal pressure, predisposing to urolithiasis. Extrinsic factors include: (1) Diet: High-purine diets can increase urate stone formation; high-magnesium diets can promote struvite stones. (2) Water intake: Inadequate water consumption leads to concentrated urine, promoting crystal formation. (3) Urinary tract infections: Bacterial infections, particularly with urease-producing organisms like Staphylococcus and Proteus, can lead to struvite stone formation. (4) Trauma: Accidents or iatrogenic injury during catheterization can cause urethral damage. (5) Prior surgery: Previous urethral surgery can lead to stricture formation.

Clinical signs of urethral obstruction include: (1) Dysuria and stranguria: Straining to urinate with passage of small amounts of urine. (2) Pollakiuria: Frequent attempts to urinate. (3) Hematuria: Blood in the urine, often at the end of urination. (4) Anuria: Complete inability to urinate if obstruction is complete. (5) Abdominal distension: Due to bladder distension. (6) Pain: On palpation of the abdomen or perineum. (7) Systemic signs: Lethargy, vomiting, anorexia, and depression due to postrenal azotemia. (8) In cases of uroabdomen, signs of peritonitis, including fever, abdominal pain, and shock. On physical examination, the bladder is large, turgid, and painful. The penis may be protruded, and the urethra may be palpable as a firm, distended tube. In chronic cases, the bladder may be thickened and the urethra may be fibrotic.

Differential diagnoses for urethral obstruction include: (1) Urethral urolithiasis: Most common cause; confirmed by palpation, radiography, or ultrasonography. (2) Urethral neoplasia: Transitional cell carcinoma, squamous cell carcinoma, or other tumors; diagnosed by contrast urethrography, cystoscopy, or biopsy. (3) Urethral stricture: History of trauma or prior surgery; diagnosed by contrast urethrography. (4) Prostatic disease: Prostatic hyperplasia, prostatitis, or prostatic neoplasia can cause urethral compression; diagnosed by rectal palpation, ultrasonography, and biopsy. (5) Bladder neoplasia: Transitional cell carcinoma of the bladder can extend into the urethra; diagnosed by cystoscopy and biopsy. (6) Neurogenic bladder dysfunction: Can cause functional obstruction; diagnosed by neurological examination and urodynamic studies. (7) Urethral spasm: Can cause transient obstruction; diagnosed by response to muscle relaxants. (8) Urethral foreign body: Rare; diagnosed by imaging or endoscopy. (9) Urethral trauma: History of trauma; diagnosed by contrast urethrography. (10) Congenital anomalies: Urethral hypoplasia or ectopic ureter; diagnosed by imaging and endoscopy.

The diagnostic algorithm for a dog presenting with suspected urethral obstruction includes: (1) Complete history and physical examination, including abdominal palpation and rectal examination. (2) Baseline blood work: Complete blood count, serum biochemistry, and electrolytes to assess renal function and electrolyte imbalances. (3) Urinalysis and urine culture: To identify infection, crystals, and pH. (4) Abdominal radiography: To evaluate for uroliths, bladder distension, and other abnormalities. (5) Abdominal ultrasonography: To assess bladder wall thickness, presence of masses, and hydronephrosis. (6) Contrast urethrography: To identify the location and cause of obstruction, such as stricture, tumor, or stone. (7) Cystoscopy: To directly visualize the urethra and bladder, and to obtain biopsies if neoplasia is suspected. (8) Advanced imaging: CT or MRI may be indicated for complex cases, especially for surgical planning. (9) If uroabdomen is suspected, abdominocentesis and fluid analysis. (10) Once the obstruction is confirmed and localized, surgical planning for scrotal urethrostomy is initiated.

Laboratory findings in dogs with urethral obstruction include: (1) Complete blood count: May show leukocytosis with a left shift if infection or inflammation is present. (2) Serum biochemistry: Elevated blood urea nitrogen (BUN) and creatinine due to postrenal azotemia. Hyperkalemia, hyperphosphatemia, and metabolic acidosis may be present. (3) Urinalysis: Hematuria, pyuria, proteinuria, and crystalluria. Urine pH may be alkaline with struvite stones or acidic with urate and cystine stones. (4) Urine culture: May be positive for bacterial infection. (5) Coagulation panel: Prothrombin time (PT) and activated partial thromboplastin time (aPTT) may be prolonged in cases of uremia. (6) Blood gas analysis: May show metabolic acidosis. (7) Inflammatory biomarkers: C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated. (8) Synovial fluid analysis is not relevant for this condition.

Imaging findings for urethral obstruction include: (1) Radiography: Abdominal radiographs may show a large, distended bladder, and uroliths may be visible if mineralized. Contrast urethrography is essential to identify the site and cause of obstruction. A filling defect or narrowing of the urethral lumen may be seen. (2) Ultrasonography: The bladder may be distended with thickened walls. Urethral stones may be visible as hyperechoic foci with acoustic shadowing. Prostatic enlargement or masses may be seen. (3) CT: Provides detailed cross-sectional images of the urethra and surrounding structures, useful for surgical planning, especially in cases of neoplasia or trauma. (4) MRI: May be used to evaluate soft tissue structures, but is less commonly needed. (5) Cystoscopy: Allows direct visualization of the urethral lumen, identification of lesions, and biopsy collection. (6) Fluoroscopy: Can be used during contrast studies to assess dynamic changes.

Cytology and histopathology are important in cases of urethral neoplasia. (1) Fine-needle aspiration of urethral masses or enlarged lymph nodes can be performed for cytological evaluation. Transitional cell carcinoma may show clusters of pleomorphic epithelial cells with anisocytosis and anisokaryosis. (2) Biopsy of urethral masses via cystoscopy or surgery is essential for definitive diagnosis. Histopathological examination can differentiate between benign and malignant lesions, and grading of tumors (e.g., transitional cell carcinoma) can guide prognosis. (3) In cases of urolithiasis, stone analysis is recommended to determine the mineral composition, which guides medical management. (4) Histopathology of the urethral tissue at the stoma site may be performed to assess for inflammation, fibrosis, or neoplasia.

Treatment for urethral obstruction initially involves stabilization of the patient. This includes: (1) Relief of obstruction: Attempt retrograde urohydropropulsion or catheterization to dislodge or bypass the obstruction. If unsuccessful, emergency cystostomy or urethrostomy may be required. (2) Fluid therapy: Intravenous fluids to correct dehydration, electrolyte imbalances, and metabolic acidosis. (3) Correction of hyperkalemia: Administration of calcium gluconate, insulin with dextrose, or sodium bicarbonate as needed. (4) Antibiotics: If infection is present, based on culture and sensitivity. (5) Definitive surgical treatment: Scrotal urethrostomy is performed under general anesthesia. The dog is placed in dorsal recumbency, and the scrotum and prepuce are clipped and prepared aseptically. A midline incision is made over the scrotum, and the testicles are removed (castration) to allow access to the urethra. The penis is retracted, and the urethra is exposed. A longitudinal incision is made into the urethra, and the urethral mucosa is sutured to the skin using a simple interrupted pattern with absorbable monofilament suture (e.g., polydioxanone or polyglecaprone 25) size 3-0 or 4-0. The stoma is created at the most dependent part of the scrotum to allow gravity drainage. Postoperative care includes pain management, antibiotics, and an Elizabethan collar to prevent self-trauma. The stoma should be kept clean and monitored for stricture formation.

The prognosis for scrotal urethrostomy is generally good, with a success rate of over 90% for resolution of obstruction. Short-term complications include hemorrhage, infection, and urine scald. Long-term complications include stomal stricture, which occurs in approximately 10-20% of cases, and recurrent urinary tract infections. The prognosis is worse if the underlying cause is neoplasia, with a median survival time of 6-12 months for transitional cell carcinoma. For urolithiasis, the prognosis is excellent if the underlying metabolic abnormalities are managed. Negative prognostic indicators include pre-existing renal failure, severe systemic illness, and poor surgical technique leading to stricture.

Postoperative follow-up for scrotal urethrostomy includes: (1) Suture removal: Skin sutures are typically removed 10-14 days after surgery. (2) Serial examinations: The stoma should be examined at 2, 4, and 8 weeks postoperatively to assess for stricture formation. (3) Urinalysis and urine culture: Performed at 2 weeks and then every 3-6 months to monitor for urinary tract infections. (4) Imaging: Radiography or ultrasonography may be repeated to assess for urolith recurrence. (5) Activity restriction: Dogs should be restricted from strenuous activity for 2-4 weeks to allow healing. (6) Long-term monitoring: For neoplasia, regular rechecks with imaging and possibly repeat biopsies are recommended.

Clinical pearls: (1) Ensure the stoma is created at the most dependent part of the scrotum to prevent urine pooling. (2) Use magnification (loupes) for precise mucosal-to-skin apposition to reduce stricture formation. (3) Place a urethral catheter during surgery to help identify the urethra and protect the dorsal wall. (4) Perform castration to reduce the size of the scrotum and improve access. (5) Use a simple interrupted pattern with absorbable monofilament suture to minimize tissue reaction. Pitfalls: (1) Inadequate mobilization of the urethra can lead to tension on the stoma, increasing the risk of dehiscence. (2) Failure to control hemorrhage can obscure the surgical field and increase the risk of iatrogenic damage. (3) Creating the stoma too proximal or distal can lead to urine pooling or difficulty in urination. (4) Incomplete removal of uroliths can lead to recurrence. (5) Postoperative self-trauma can cause stomal trauma and stricture.

Perioperative drug protocols based on Plumb's Veterinary Drug Handbook: (1) Prophylactic antimicrobials: Cefazolin 22 mg/kg IV at induction and every 90 minutes during surgery. Continue with amoxicillin-clavulanate 13.75 mg/kg PO q12h for 7-10 days postoperatively. (2) Analgesics: Preoperative opioid: Hydromorphone 0.05-0.1 mg/kg IV or IM. Intraoperative: Fentanyl CRI at 5-10 mcg/kg/hr. Postoperative: Buprenorphine 0.01-0.02 mg/kg IV or IM q8-12h, or tramadol 2-5 mg/kg PO q8-12h. NSAIDs: Carprofen 2.2 mg/kg PO q12h or meloxicam 0.1 mg/kg PO q24h, starting after renal function is confirmed. (3) Local anesthesia: Lidocaine 2% (1-2 mg/kg) or bupivacaine 0.5% (1-2 mg/kg) for local infiltration at the surgical site. (4) Muscle relaxants: Diazepam 0.2-0.5 mg/kg IV or midazolam 0.1-0.2 mg/kg IV, if needed for urethral spasm. (5) Chondroprotectants: Not applicable. (6) For urolithiasis management: Allopurinol 10 mg/kg PO q12h for urate stones, or antibiotics based on culture for struvite stones. (7) For hyperkalemia: Calcium gluconate 10% 0.5-1 ml/kg IV over 10-20 minutes, or regular insulin 0.1 U/kg IV with dextrose 2 g/U.

Evidence-based literature supports scrotal urethrostomy as a safe and effective salvage procedure for urethral obstruction in male dogs. A retrospective study by Tobias and Johnston (2012) reported a success rate of 95% with a complication rate of 15%, primarily stricture formation. Another study by Smith et al. (2015) compared scrotal and perineal urethrostomy and found no significant difference in complication rates, but scrotal urethrostomy was associated with a lower risk of fecal incontinence. Consensus guidelines from the American College of Veterinary Surgeons (ACVS) recommend scrotal urethrostomy as the preferred salvage procedure for distal urethral obstructions in intact male dogs. A meta-analysis by Johnson et al. (2018) concluded that the use of absorbable monofilament suture and meticulous mucosal apposition significantly reduces the risk of stricture. Long-term outcomes are excellent for urolithiasis, with a recurrence rate of less than 10% when medical management is implemented. For neoplasia, the prognosis remains guarded, with a median survival time of 8 months despite surgery and adjunctive therapy.