What is the initial workup for a rectovaginal fistula?

Initial Workup for Rectovaginal Fistula

The initial workup for a rectovaginal fistula should include contrast-enhanced pelvic MRI as the first-line imaging procedure, followed by proctosigmoidoscopy to evaluate for concomitant rectal inflammation, and examination under anesthesia (EUA) for definitive diagnosis and classification. 1

Clinical Presentation and Diagnosis

Patients with rectovaginal fistulas typically present with:

• Passage of stool, gas, or odorous mucopurulent discharge from the vagina
• Dyspareunia
• Perineal pain
• Recurrent vaginal infections
• Symptoms may be confused with incontinence 1

Physical Examination

• Direct inspection of the vagina and rectum is essential
• Careful examination of the vestibule is critical as endoscopy alone may miss the fistula
• Assess for associated conditions:
  • Anal stenosis
  • Presacral masses
  • Active rectal inflammation 1, 2

Diagnostic Algorithm

1. Contrast-enhanced pelvic MRI:

   • First-line imaging modality
   • Helps visualize fistula tract, associated abscesses, and underlying etiology
   • Provides information on fistula location, complexity, and surrounding tissues 1

2. Proctosigmoidoscopy:

   • Essential to evaluate for concomitant rectal inflammation
   • Presence of active rectal disease has significant prognostic and therapeutic implications
   • Should be performed routinely in the initial evaluation 1

3. Endoanal ultrasound (EUS):

   • Good alternative if rectal stenosis is excluded
   • May be enhanced with hydrogen peroxide injection into the fistula tract
   • Less accurate for high or complex fistulas 1

4. Examination under anesthesia (EUA):

   • Gold standard for definitive diagnosis in the hands of an experienced surgeon
   • Allows for direct visualization and classification of the fistula
   • Permits assessment of associated abscesses that require drainage
   • Increases the specificity and sensitivity of MRI and EUS when combined 1

5. CT with IV contrast:

   • May be used if MRI is unavailable
   • Water-soluble rectal contrast can help delineate fistulous tracts
   • Less sensitive than MRI but useful for detecting underlying etiology 1

Classification of Rectovaginal Fistulas

Rectovaginal fistulas are classified as:

1. By location:

   • High fistulas (rectovaginal): Communication to the rectum proximal to the anal sphincter, often involving posterior vaginal fornix
   • Low fistulas (anovaginal): Communication from anal sphincter complex to lower half of vagina 1

2. By complexity:

   • Simple or complex (most commonly used classification in clinical practice) 1

Etiology Assessment

Identifying the underlying cause is crucial for treatment planning:

• Obstetric or vaginal trauma (88% of cases)
• Crohn's disease (9% of cases)
• Radiation
• Pelvic infections
• Malignancies
• Iatrogenic injury or postoperative complications 1

Important Considerations and Pitfalls

• Do not rely solely on endoscopy for diagnosis, as it may miss the fistula; direct inspection under anesthesia is key 2
• Avoid barium contrast in favor of water-soluble contrast to prevent complications if surgery is needed 1
• Rule out perianal abscesses which must be drained before any definitive treatment 1
• Evaluate for active rectal inflammation as this significantly impacts treatment approach and success rates 1
• Allow fistula tract to mature over 3-6 months before attempting definitive repair 3
• Consider sphincter status when planning treatment, as this affects surgical approach selection 3

By following this systematic diagnostic approach, clinicians can accurately identify and characterize rectovaginal fistulas, which is essential for appropriate treatment planning and optimal patient outcomes.