What is the appropriate workup for a rectovaginal fistula?

Workup for Rectovaginal Fistula

MRI pelvis without and with IV gadolinium contrast is the preferred imaging modality for evaluating rectovaginal fistulas, providing superior visualization of fistulous tracts, active inflammation, and associated abscesses. 1, 2

Initial Clinical Assessment

History and Physical Examination

• Identify pathognomonic symptoms: passage of stool, gas, or odorous mucopurulent discharge from the vagina (often confused with incontinence), dyspareunia, perineal pain, and recurrent vaginal infections 1, 2
• Determine fistula height: Distinguish between high fistulas (rectovaginal—communicating with rectum proximal to anal sphincter, often involving posterior vaginal fornix) versus low fistulas (anovaginal—communicating from anal sphincter complex to lower half of vagina), as this dictates surgical approach 1, 2
• Assess for complexity features: Look for multiple external openings, associated pain or fluctuation suggesting abscess, or signs of underlying inflammatory bowel disease 2
• Evaluate anal sphincter integrity: Document any sphincter damage that may require concurrent repair 3

Imaging Evaluation

Primary Imaging Modality

• MRI pelvis without and with IV gadolinium contrast is the gold standard, offering superior contrast resolution for evaluating fistulous tracts, with IV gadolinium being essential for detecting active inflammation in fistulous tracts and abscesses 1, 2
• Transvaginal ultrasound should be considered as part of the assessment for best definition of vulvar or vaginal openings 4

Alternative Imaging Options

• CT pelvis with IV contrast has comparable diagnostic utility for visualizing fluid collections, abscesses, and fistulous tracts when MRI is contraindicated or unavailable 1, 2
• Fluoroscopic vaginography demonstrates 79% sensitivity and 100% positive predictive value for fistulous tract identification 1, 2
• Transrectal ultrasound shows 100% positive predictive value for identifying the anorectal opening and 93% for identifying the vaginal opening 1, 2
• Endoluminal biplane ultrasonography can accurately determine internal openings in the rectum or vagina and identify concomitant branches and abscesses in the rectovaginal septum 5

Anatomical Documentation Requirements

Structured Reporting Elements

• Document internal opening position: Specify whether in anus or rectum 4, 1
• Describe track characteristics: Note the course of the fistulous tract 4, 1
• Identify vaginal or vulvar opening location: Report as left or right 4, 1
• Classify complexity: Simple fistulas versus complex fistulas (those with extensions, multiple external openings, complicated by abscess, urogenital involvement, or anorectal stricture) require fundamentally different management approaches 4, 2

Associated Findings to Report

• Abscess presence: Document anatomical location, size (largest diameter in two perpendicular planes), presence of horseshoe abscess, and relation to fistula 4
• Signs of proctitis: Include in the report as this may influence patient management 4
• Sphincter integrity assessment: Essential when surgery is being considered 4

Microbiological Evaluation

• Obtain vaginal cultures: Polymicrobial enteric flora with anaerobes (Bacteroides, fusobacteria, anaerobic cocci) is highly specific for fistulous bowel communication 1, 2
• Interpret culture patterns: Polymicrobial bacteremia with mixed enteric organisms including E. coli, enterococci, and anaerobes is highly suggestive of enteric fistula, whereas a single vaginal swab showing only E. coli and GBS lacks the polymicrobial anaerobic pattern typical of fecal contamination 1

Critical Exclusions

Rule Out Malignancy

• Evaluate for underlying malignancy: Approximately 11% of rectovaginal fistulas are caused by underlying malignancy, making imaging evaluation for soft tissue mass, wall thickening, or malignant lymphadenopathy crucial 2

Assess for Sepsis

• Control sepsis before repair: Untreated fistulas can progress to sepsis, making early recognition and treatment crucial 1, 2
• Allow tract maturation: Prior to attempting repair, sepsis must be controlled and the tract allowed to mature over a period of 3 to 6 months 6

Timing Considerations

• Interval imaging after acute surgery: An interval of at least 4 weeks is recommended for examinations performed after first presentation requiring acute perianal surgery 4
• Combined assessment: When patients have symptoms of suspected perianal fistula and small-bowel disease at initial presentation, combine bowel and pelvic assessment by combining intestinal and pelvic MRI or intestinal ultrasound with endoanal ultrasound or perineal ultrasound for fistula to allow procedures in a single visit 4

Common Pitfalls to Avoid

• Do not confuse with incontinence: The passage of stool or gas from the vagina is pathognomonic for rectovaginal fistula, not simple incontinence 1, 2
• Do not use contrast enema: Fluoroscopic contrast enema is not useful because it cannot assess the presence or absence of an abscess or fistula tract 4
• Do not delay imaging for malignancy evaluation: Given the 11% malignancy rate, always evaluate for underlying neoplasm 2