For horseshoe abscesses and fistulas, should an intersphincteric or ischiorectal approach be chosen?

Horseshoe Abscess and Fistula Management: Intersphincteric vs Ischiorectal Approach

For horseshoe abscesses and fistulas, the surgical approach depends on the anatomical location of the primary abscess cavity: intersphincteric horseshoe abscesses should be drained into the rectal lumen (possibly with limited internal sphincterotomy), while ischiorectal (ischioanal) horseshoe abscesses require external drainage through the overlying skin with counter-drainage of the lateral extensions. 1

Anatomical Classification Determines Surgical Approach

The Parks classification system guides treatment decisions by defining the relationship of the abscess to the sphincter complex 2:

• Intersphincteric abscesses: The infection runs through the intersphincteric space between the internal and external sphincters 2
• Ischiorectal abscesses: The infection penetrates through the external sphincter into the ischiorectal (ischioanal) fossa 2
• Horseshoe extensions: Secondary horizontal tracts that extend bilaterally from the primary abscess cavity 2

Specific Surgical Techniques by Location

Intersphincteric Horseshoe Abscesses

• Drain into the rectal lumen through the internal opening 1
• Consider limited internal sphincterotomy to facilitate drainage 1
• This approach avoids unnecessary external sphincter division and preserves continence 3

Ischiorectal Horseshoe Abscesses

• Drain externally through the overlying skin at the site of the lateral extensions 1
• Perform counter-drainage of both lateral ischiorectal extensions 4, 5
• Make the primary incision in the posterior midline to address the deep postanal space 6
• Keep incisions as close to the anal verge as possible to minimize potential fistula tract length 1

Critical Technical Considerations

The key to successful treatment is identifying and adequately draining the primary abscess cavity in the deep postanal space 4, 6:

• Failure to maintain prolonged drainage in the midline after primary fistulotomy is the main cause of recurrence (18% overall recurrence rate) 5
• Horseshoe-type abscess is itself a risk factor for recurrence 1
• The superficial external sphincter between its coccygeal origin and the anus should be preserved to avoid deformity and incontinence 3

Role of Seton Placement

Liberal use of setons is advocated for horseshoe abscesses and fistulas 5:

• Place a cutting seton in the posterior midline to drain the deep postanal space 6
• Additional draining setons may be needed for lateral extensions (average 3 setons total) 6
• Setons promote wound drainage and prevent premature wound closure 5
• Seton fistulotomy with counter-drainage has lower recurrence rates (18.1%) compared to primary fistulotomy alone (28.6%) 4
• Setons should be removed after resolution of induration and suppuration, typically after 1.6 months 6

Timing and Setting

Emergency drainage is indicated for 1:

• Sepsis, severe sepsis, or septic shock
• Immunosuppression
• Diabetes mellitus
• Diffuse cellulitis

Otherwise, drainage should occur within 24 hours 1. Young, fit patients without sepsis may undergo ambulatory surgery 1.

Common Pitfalls to Avoid

• Do not probe for fistulas during acute abscess drainage to avoid iatrogenic complications 2
• Ensure adequate postoperative care of the cavity to prevent recurrence 4
• Recognize that delayed time from disease onset to incision increases recurrence risk 1
• Inadequate drainage is associated with recurrence rates up to 44% 1