How to examine a post-surgical rectovaginal fistula?

Examination of Post-Surgical Rectovaginal Fistula

MRI pelvis without and with IV contrast or CT pelvis with IV contrast are the most appropriate initial imaging modalities for examining a post-surgical rectovaginal fistula, as they provide detailed visualization of fistulous tracts and associated complications.

Clinical Presentation Assessment

• Patients with rectovaginal fistulas typically present with passage of stool, gas, or odorous mucopurulent discharge from the vagina, which may be confused with incontinence 1
• Other common symptoms include dyspareunia, perineal pain, and recurrent vaginal infections 1
• Determine if the fistula is high (rectovaginal) or low (anovaginal) based on symptoms and physical examination findings 1

Imaging Evaluation

First-Line Imaging Options

• MRI pelvis without and with IV contrast:

  • Provides superior contrast resolution for evaluating fistulous tracts 1
  • IV gadolinium contrast is essential as active inflammation in fistulous tracts enhances avidly, and abscesses show rim-like enhancement 1
  • Diffusion-weighted sequences increase fistula conspicuity (100% sensitivity) and help discriminate between inflammatory mass and abscess (100% sensitivity, 90% specificity) 1

• CT pelvis with IV contrast:

  • Alternative to MRI with comparable diagnostic utility 1
  • IV contrast is preferred to help visualize and characterize fluid collections, abscesses, and fistulous tracts 1
  • Water-soluble rectal contrast may help delineate the fistula tract 1

Specialized Imaging Techniques

• Fluoroscopic vaginography:

  • High sensitivity (79%) and positive predictive value (100%) for fistulous tract identification 1
  • Performed using a large-gauge Foley catheter placed in the vaginal lumen with water-soluble contrast injection 1
  • Limitations include occlusion of low fistulas by the Foley catheter balloon 1

• Transrectal ultrasound:

  • Can be useful in certain clinical scenarios with improved detection rates in recent studies 1
  • Positive predictive value of 100% for identifying the anorectal opening and 93% for identifying the vaginal opening 1
  • Hydrogen peroxide may be injected into external openings to enhance visualization of fistula tracts 1

Anatomical Classification

• High fistulas (rectovaginal): Communications to the rectum proximal to the anal sphincter, often involving the posterior vaginal fornix 1
• Low fistulas (anovaginal): Communications from the anal sphincter complex to the lower half of the vagina 1
• Complex fistulas: Those with extensions, multiple external openings, complicated by abscess, urogenital involvement, or anorectal stricture 1

Detailed Examination Documentation

• Document the position of internal opening (anus/rectum), track characteristics, and vaginal or vulvar opening location (left, right) 1
• Report the size of any associated abscess at its largest diameter in two perpendicular planes 1
• Note any signs of proctitis, as this may influence patient management 1
• Assess for secondary extensions, horseshoe configuration, or multiple external openings 1

Common Pitfalls and Caveats

• Avoid using barium contrast for imaging studies as it may spill into the peritoneal cavity or spaces of the extraperitoneal pelvis; water-soluble contrast is preferred 1
• Be aware that endoanal ultrasound has limitations in identifying complex fistulas with secondary branches, occluded branches, and fistulas that extend beyond the field of view 1
• Recognize that the height of abnormalities in the anal canal and distances reported on imaging should be considered indicative rather than absolute 1
• Understand that in patients with recurrent disease, it may be impossible to distinguish tracts with active inflammation from those with fibrosis and granulation tissue 1

By following this comprehensive approach to examining post-surgical rectovaginal fistulas, clinicians can accurately characterize the fistula anatomy and associated complications, which is essential for planning appropriate management strategies and improving patient outcomes.