What is the workup for a rectovaginal fistula (rectovaginal fistula)?

Workup for Rectovaginal Fistula

Magnetic resonance imaging (MRI) with intravenous contrast is the preferred initial imaging modality for the diagnosis and evaluation of rectovaginal fistulas. 1, 2

Initial Diagnostic Approach

Clinical Assessment

• Evaluate for key symptoms:
  • Passage of stool, gas, or mucopurulent secretions through vagina
  • Dyspareunia and perineal pain
  • Recurrent vaginal infections
  • Symptoms that may mimic fecal incontinence

Diagnostic Imaging

1. MRI with intravenous contrast

   • Highest precision for detecting fistulous tracts
   • Superior visualization of associated abscesses
   • Evaluation of secondary extensions
   • Identification of underlying etiology 2

2. Endoanal/endorectal ultrasound

   • Alternative when MRI is unavailable
   • Limitations include operator dependence and difficulty in patients with pain 2
   • Transvaginal ultrasound should be considered as part of assessment for better definition of vulvar or vaginal openings 1

3. Additional imaging options (based on specific clinical scenarios):

   • Fluoroscopic vaginography - useful for visualizing the tract from vagina 2
   • Contrast enema - limited sensitivity (7.7-34%) but may detect subtle fistulas 2
   • CT with intravenous contrast - sensitivity of 76.5% for detecting fistulas 2

Essential Endoscopic Evaluation

• Proctosigmoidoscopy
  • Mandatory to assess for concomitant rectal inflammation
  • Presence of active rectal disease significantly impacts management approach and prognosis 1, 2
  • Helps identify underlying causes (Crohn's disease, malignancy, etc.)

Gold Standard Confirmation

• Examination under anesthesia (EUA)
  • Performed by an experienced colorectal surgeon
  • Approximately 90% accurate in detecting and correctly classifying fistulas 1
  • Includes visual inspection, palpation, and probing of fistula tracks
  • Should be considered when other imaging is inconclusive or when planning surgical intervention

Etiology Assessment

Always evaluate for underlying causes:

• Obstetric trauma (88% of cases) 2
• Crohn's disease (9% of cases) 2
• Malignancy (approximately 11% of colovaginal fistulae) 1, 2
• Radiation therapy to pelvic area 2
• Pelvic infections (diverticulitis, tuberculosis) 2
• Iatrogenic causes (surgical complications) 1, 3

Classification

Document the fistula characteristics according to:

1. Anatomical location:

   • Position of internal opening (anus/rectum)
   • Track characteristics
   • Position of vaginal/vulvar opening (left, right) 1

2. Complexity:

   • Simple vs. complex fistula classification 1
   • Parks classification system for anatomic precision 1

Common Pitfalls to Avoid

• Failing to perform proctosigmoidoscopy to evaluate rectal inflammation
• Relying solely on conventional fistulography
• Not considering underlying malignancy when imaging shows soft tissue mass, wall thickening, or suspicious lymphadenopathy 1, 2
• Inadequate timing of follow-up imaging (at least 4 weeks recommended after acute perianal surgery) 1

Special Considerations

• For patients with suspected Crohn's disease, consider combining bowel and pelvic assessment in a single visit 1
• For suspected malignancy-associated fistulas, additional cancer staging workup is necessary
• Rectovaginal fistulas require a multidisciplinary approach involving colorectal surgery, gynecology, and gastroenterology 1