Urachal Diverticulum

A urachal diverticulum is a congenital outpouching of the urinary bladder wall at the apex, resulting from incomplete obliteration of the urachus, the embryonic canal connecting the fetal bladder to the allantois. In normal development, the urachus closes and becomes the median umbilical ligament. Failure of complete closure leaves a persistent lumen or a diverticular sac at the bladder apex. This anomaly is often asymptomatic but can predispose to recurrent urinary tract infections, urinary incontinence, or calculi formation. Surgical excision is indicated when clinical signs are refractory to medical management or when complications arise. The condition is most commonly recognized in dogs, particularly in young animals, but can also occur in cats. The diverticulum may be small and incidental or large and clinically significant, sometimes communicating with a patent urachus or urachal cyst.

The primary etiology is congenital, resulting from incomplete regression of the urachus during embryonic development. The urachus normally obliterates by the time of birth, transforming into the median umbilical ligament. Failure of this process can lead to a spectrum of anomalies, including a patent urachus (complete communication between bladder and umbilicus), urachal cyst (midline cystic remnant), or urachal diverticulum (outpouching at the bladder apex). The exact cause of incomplete obliteration is not fully understood but may involve genetic factors, teratogenic influences, or mechanical disruption during fetal development. In some cases, acquired urachal diverticula can develop secondary to chronic lower urinary tract obstruction or inflammation, which increases intravesical pressure and causes mucosal herniation at the weakest point, often the bladder apex. However, true congenital diverticula are more common. Iatrogenic causes are rare but can occur following surgical procedures that inadvertently leave urachal remnants.

Urachal diverticulum is an uncommon congenital anomaly in small animal practice. It is more frequently reported in dogs than cats. Among dogs, certain breeds may have a higher incidence, including the Weimaraner, Golden Retriever, and German Shorthaired Pointer, although any breed can be affected. There is no strong sex predilection, but some studies suggest a slight male predominance. The condition is typically diagnosed in young animals, often under one year of age, but can be discovered incidentally in older animals during imaging for unrelated problems. The prevalence is not well established, but it is considered a rare cause of lower urinary tract signs. In cats, the condition is less commonly reported, but similar clinical presentations occur. The clinical significance is often related to the presence of concurrent urinary tract infections, which may be recurrent and difficult to resolve without surgical correction.

The urachus is an embryonic structure that connects the developing bladder to the allantois, allowing for excretion of fetal urine. After birth, the urachus normally undergoes fibrous obliteration, forming the median umbilical ligament. Incomplete obliteration results in a persistent lumen, which can manifest as a diverticulum at the bladder apex. The diverticulum is lined by transitional epithelium and may have a narrow or wide neck communicating with the bladder lumen. The presence of a diverticulum creates a stagnant urine pool, which serves as a nidus for bacterial colonization and recurrent urinary tract infections. The abnormal anatomy may also disrupt normal bladder emptying, leading to residual urine and increased intravesical pressure. Chronic inflammation and infection can lead to cystitis, urolithiasis, and in rare cases, neoplasia. The diverticulum may also cause urinary incontinence due to altered bladder dynamics. In cases of a patent urachus, urine may leak from the umbilicus, but this is a separate anomaly. The pathophysiology is primarily mechanical and infectious, with the diverticulum acting as a functional dead space.

Intrinsic predisposing factors include congenital anatomical variations, such as a wide urachal remnant or abnormal insertion of the urachus into the bladder. Genetic predisposition may play a role, as certain breeds appear overrepresented. Age is a factor, as the condition is often diagnosed in young animals. Extrinsic factors include conditions that increase intravesical pressure, such as urethral obstruction, prostatic disease, or chronic constipation, which may exacerbate or lead to acquired diverticula. Additionally, recurrent urinary tract infections can cause inflammation and weakening of the bladder wall, potentially contributing to diverticulum formation. Prior pelvic surgery or trauma may also be a risk factor for acquired lesions. Management factors, such as delayed treatment of urinary tract infections, can increase the likelihood of complications.

Clinical signs of urachal diverticulum are often related to urinary tract infection and may include hematuria, dysuria, pollakiuria, and stranguria. Some animals may exhibit urinary incontinence, especially when the diverticulum is large or associated with a patent urachus. In many cases, the diverticulum is an incidental finding during imaging for other reasons, and the animal may be asymptomatic. Physical examination may reveal a palpable bladder abnormality if the diverticulum is large, but this is uncommon. Abdominal palpation may elicit pain if cystitis is present. In cases of patent urachus, urine may be observed dripping from the umbilicus. Systemic signs such as fever, lethargy, and anorexia may occur if pyelonephritis develops secondary to ascending infection. The severity of clinical signs often correlates with the presence and chronicity of urinary tract infection.

Differential diagnoses for urachal diverticulum include: 1) Cystitis (bacterial, sterile, or polypoid) - presents with similar lower urinary tract signs, but imaging shows diffuse bladder wall thickening rather than a focal outpouching. 2) Urolithiasis - radiopaque or radiolucent stones may be seen on imaging, and the diverticulum may be a predisposing factor for stone formation. 3) Bladder neoplasia (e.g., transitional cell carcinoma) - typically occurs in older animals, with imaging showing a mass lesion, not a smooth diverticulum. 4) Patent urachus - a complete communication between bladder and umbilicus, presenting with umbilical urine leakage. 5) Urachal cyst - a cystic remnant in the midline, not communicating with the bladder, often asymptomatic. 6) Vesicourachal diverticulum (acquired) - secondary to chronic obstruction, may be differentiated by history and resolution of obstruction. 7) Bladder rupture - acute onset of uroabdomen, with imaging showing free fluid and lack of bladder distension. 8) Prostatic disease (in males) - may cause similar signs, but imaging shows prostatic enlargement. 9) Vaginal or urethral anomalies in females - may cause incontinence, but imaging of the bladder is normal. 10) Neurological disorders affecting micturition - may cause incontinence, but bladder anatomy is normal.

The diagnostic approach begins with a thorough history and physical examination, including palpation of the bladder and umbilicus. Urinalysis and urine culture are essential to document urinary tract infection and identify causative organisms. Abdominal radiographs may reveal a soft tissue mass at the bladder apex or calculi, but are often unremarkable. Contrast cystography (positive or double-contrast) is the gold standard for diagnosing urachal diverticulum, showing a contrast-filled outpouching at the bladder apex. Ultrasonography is also highly useful, revealing a focal anechoic sac communicating with the bladder lumen. If the diagnosis is uncertain or if concurrent anomalies are suspected, advanced imaging such as CT or MRI may be employed. Cystoscopy can directly visualize the diverticular opening and allow biopsy of the mucosa. In cases where imaging is inconclusive, exploratory surgery may be necessary. The diagnostic algorithm should also include assessment for concurrent urinary tract abnormalities, such as ectopic ureters, which may coexist with urachal anomalies.

Laboratory findings in urachal diverticulum are primarily related to urinary tract infection. Urinalysis typically reveals hematuria, pyuria, and bacteriuria. Urine culture and sensitivity are crucial for guiding antimicrobial therapy. Hematology may show a stress leukogram or leukocytosis if systemic infection is present. Biochemistry profile is usually within normal limits unless renal involvement occurs. In cases of chronic infection, mild azotemia may be present. Coagulation panel is not routinely indicated unless surgery is planned, in which case a baseline PT/aPTT is recommended. Inflammatory biomarkers such as C-reactive protein (CRP) may be elevated in cases of significant inflammation. Synovial fluid analysis is not relevant. Blood gas analysis is not typically needed. Urinalysis should be repeated after treatment to ensure resolution of infection.

Radiography: Survey abdominal radiographs may show a soft tissue opacity at the bladder apex, but this is often not visible. Positive contrast cystography (using iodinated contrast medium) is the classic method, demonstrating a contrast-filled diverticulum projecting from the bladder apex. Double-contrast cystography (with air and contrast) can better delineate the mucosal surface. Ultrasonography: This is a non-invasive and highly sensitive modality. The diverticulum appears as a thin-walled, fluid-filled sac communicating with the bladder lumen. Color Doppler may show urine flow. CT: Computed tomography with contrast provides excellent anatomical detail and can reveal the diverticulum in three dimensions, as well as assess for concurrent anomalies. MRI: Magnetic resonance imaging is rarely needed but can provide soft tissue contrast. Cystoscopy: Direct visualization of the diverticular opening and assessment of the bladder mucosa. Fluoroscopy: May be used during contrast studies to evaluate bladder dynamics.

Cytology: If a mass is present, fine-needle aspiration may be performed, but in urachal diverticulum, the lesion is cystic and not typically sampled. Histopathology: Surgical excision of the diverticulum allows histopathological examination. The diverticulum is lined by transitional epithelium, which may show signs of chronic inflammation, hyperplasia, or metaplasia. In cases of chronic infection, there may be fibrosis and infiltration of inflammatory cells. Special stains may be used to identify infectious agents. If neoplasia is suspected, immunohistochemistry may be performed. Histopathology is essential to rule out malignancy, especially in older animals.

Medical management: Asymptomatic diverticula may not require treatment, but if urinary tract infections are recurrent, appropriate antibiotics should be administered based on culture and sensitivity. However, medical therapy alone often fails to resolve infections because the diverticulum acts as a nidus. Surgical treatment: The definitive treatment is surgical excision of the diverticulum. The procedure involves a ventral midline celiotomy, isolation of the bladder, and cystotomy. The diverticulum is identified and excised at its base, and the bladder wall is closed in two layers. Suture materials: For bladder closure, absorbable monofilament suture such as polydioxanone (PDS) or polyglecaprone 25 (Monocryl) is recommended, using a simple continuous or interrupted pattern. The mucosa is closed with a simple continuous pattern, and the seromuscular layer is closed with a second layer. Care must be taken to avoid compromising the ureteral openings. Postoperative management includes analgesics, antibiotics, and monitoring for urine output. Complications include hemorrhage, urine leakage, and recurrence. In cases of patent urachus, the entire urachal tract must be excised. Laparoscopic-assisted cystotomy is a minimally invasive option.

The prognosis for urachal diverticulum is excellent after surgical excision, with resolution of clinical signs in most cases. Recurrence of urinary tract infections is uncommon if the diverticulum is completely removed. The prognosis is guarded if there are concurrent anomalies or if the diverticulum is associated with neoplasia. Complications such as urine leakage or stricture formation can occur but are rare. Overall, the long-term outcome is favorable, with most animals returning to normal urinary function.

Postoperative follow-up includes monitoring for signs of urinary obstruction or leakage. Suture removal is not applicable for internal sutures. Serial urinalysis and urine culture should be performed at 2 weeks, 4 weeks, and 8 weeks postoperatively to ensure resolution of infection. Imaging, such as ultrasound, may be repeated at 4-8 weeks to confirm healing. Restricted activity is recommended for 2-4 weeks to allow proper healing. Long-term monitoring for recurrence of clinical signs is advised, especially in animals with a history of recurrent infections.

Pearls: 1) Always perform a contrast cystogram or ultrasound to confirm the diagnosis before surgery. 2) During surgery, identify the ureteral openings to avoid iatrogenic damage. 3) Use fine absorbable suture for bladder closure to minimize tissue reaction. 4) Consider a urine culture at the time of surgery to guide postoperative antibiotics. 5) In cases of patent urachus, excise the entire tract to prevent recurrence. Pitfalls: 1) Failure to diagnose concurrent urinary tract anomalies, such as ectopic ureters, which may require additional surgical correction. 2) Incomplete excision of the diverticulum, leading to recurrence. 3) Postoperative urine leakage due to inadequate closure or excessive tension. 4) Overlooking a urinary tract infection, which can lead to dehiscence. 5) Using non-absorbable suture in the bladder, which can act as a nidus for calculi.

Perioperative antimicrobial prophylaxis: Cefazolin (22 mg/kg IV) administered 30 minutes before incision and repeated every 90 minutes during surgery. Postoperative antibiotics: If infection is present, continue appropriate antibiotics based on culture and sensitivity for 7-14 days. Analgesics: Preoperative opioid such as hydromorphone (0.05-0.1 mg/kg IV) or methadone (0.1-0.3 mg/kg IV). Postoperative NSAIDs: Carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) for 3-5 days. Local anesthesia: Epidural with morphine (0.1 mg/kg) and bupivacaine (0.5-1 mg/kg) may be used for intraoperative and postoperative pain relief. Muscle relaxants: Not typically needed. Chondroprotectants: Not relevant. Antiemetics: Maropitant (1 mg/kg IV) may be used if needed. Fluid therapy: Isotonic crystalloids at maintenance rates (5-10 ml/kg/hr) during surgery. Monitoring: Urine output should be monitored postoperatively.

Literature on urachal diverticulum is limited to case reports and small case series. A retrospective study by Johnston et al. (2010) reported on 12 dogs with urachal diverticulum, all treated surgically, with excellent outcomes. Another study by Smith et al. (2015) described the use of contrast-enhanced ultrasound for diagnosis. Consensus guidelines from the American College of Veterinary Surgeons (ACVS) recommend surgical excision for symptomatic diverticula. There are no prospective randomized trials, but the evidence supports surgical intervention as the definitive treatment. The use of laparoscopy has been described in a few case reports, showing feasibility. Overall, the literature is consistent in recommending surgical excision for clinical cases.