What is the management for a fistula with discharge located posterior to the anal sphincter?

Management of Posterior Anal Fistula with Discharge

For a fistula with discharge located posterior to the anal sphincter, MRI (option D) is the recommended initial management approach to accurately characterize the fistula anatomy before surgical intervention. 1

Diagnostic Approach

MRI is superior for evaluating complex anal fistulas for several reasons:

• MRI provides detailed anatomical information about the fistula tract, including:

  • Primary and secondary tracts
  • Internal opening location
  • Relationship to sphincter muscles
  • Presence of associated abscesses
  • Supralevator extension
  • Horseshoe ramifications 1

• While endoanal ultrasound can be used for fistula assessment, MRI demonstrates higher accuracy in evaluating secondary extensions in complex fistulas 1

• Posterior fistulas require careful assessment as they may involve the sphincter complex in various ways, and improper management could lead to incontinence 1

Why MRI is Superior to Other Options

1. Fistulogram (Option A): Less accurate than MRI for defining the complete anatomy of complex fistulas and may miss secondary tracts or abscesses 1

2. Fistulotomy and marsupialization (Option B): Should not be performed without proper imaging assessment first, especially for trans-sphincteric fistulas, as this could lead to sphincter damage and incontinence 1

3. Lateral internal sphincterotomy (Option C): Inappropriate for fistula management; this procedure is primarily indicated for anal fissures, not fistulas 2

Management Algorithm After MRI Assessment

Once MRI characterization is complete, treatment should follow this pathway:

1. For simple subcutaneous fistulas (not involving sphincter muscle):

   • Fistulotomy can be performed safely 1

2. For trans-sphincteric fistulas (involving sphincter muscles):

   • Place a loose draining seton rather than immediate fistulotomy 1
   • This preserves sphincter function while allowing drainage

3. For complex fistulas with features such as:

   • Multiple tracts
   • Horseshoe extensions
   • Supralevator extension
   • Sphincter involvement
   • Consider specialized techniques after complete imaging assessment 3, 4

Important Considerations

• Posterior fistulas are more common (90% of anal fistulas are located posteriorly in the midline) 2

• MRI has been shown to correctly classify primary fistula tracts in up to 90% of cases compared to surgical findings 1

• Recent studies have identified highly complex fistula types (such as RIFIL - Roof of Ischiorectal Fossa Inside Levator-ani muscle) that require precise MRI diagnosis to prevent recurrence 3

• The accuracy of MRI for detecting suprasphincteric fistulas is higher than endoanal ultrasound, which is particularly important for posterior fistulas that may have complex extensions 5

By starting with MRI assessment, you can accurately classify the fistula and plan the most appropriate surgical intervention while minimizing the risk of sphincter damage and recurrence.