Why is an Examination Under Anesthesia (EUA) of the rectum recommended during incision and drainage of a perianal abscess?

Examination Under Anesthesia (EUA) of the Rectum During Perianal Abscess Drainage

An examination under anesthesia (EUA) of the rectum is strongly recommended during incision and drainage of perianal abscesses to identify underlying fistulas, ensure complete drainage, and significantly reduce recurrence rates.

Rationale for Performing EUA During Perianal Abscess Drainage

Identification of Underlying Fistulas

• Approximately 30-35% of perianal abscesses have an associated fistula that can be identified during EUA 1, 2
• Without proper identification and treatment, these fistulas can lead to recurrent abscesses requiring repeat surgeries
• EUA allows for complete inspection of the fistula tract that would otherwise be difficult or impossible in an awake patient due to pain 3

Benefits of EUA-Guided Drainage

1. Higher cure rates and reduced recurrence:

   • Patients who undergo EUA prior to treatment have:
     • Better initial response rates (100% vs. 82.6%) 3
     • Significantly lower recurrence rates (44% vs. 79%) 3
     • Longer time to recurrence (13.5 months vs. 3.6 months) 3

2. Improved anatomical assessment:

   • Allows identification of:
     • Occult supralevator abscesses
     • Complex anal fistulas
     • Multiple abscess loculations 1
     • Horseshoe extensions

3. Appropriate treatment selection:

   • Enables proper decision-making regarding:
     • Fistulotomy for low fistulas not involving sphincter muscles 1
     • Seton placement for fistulas involving sphincter muscles 1
     • Proper drainage technique based on abscess location (perianal, ischioanal, intersphincteric, or supralevator) 1

Clinical Evidence Supporting EUA

A landmark study of 1023 patients with anorectal abscesses found that careful examination under regional anesthesia allowed for identification of fistulas in 34.7% of cases. When these fistulas were treated during the initial procedure, recurrence rates dropped from 3.7% to 1.8% 2.

More recent evidence confirms these findings:

• A Cochrane review showed significant reduction in recurrence, persistent abscess/fistula, or need for repeat surgery when fistulas were identified and treated at the time of abscess drainage (RR=0.13,95% CI 0.07-0.24) 4
• A 2021 systematic review and meta-analysis demonstrated that proper identification and treatment of high perianal abscesses with seton drainage (identified through EUA) resulted in:
  • Higher clinical cure rates
  • Shorter wound healing time
  • Lower pain scores
  • Reduced anal fistula formation
  • Lower abscess recurrence rates 5

Practical Approach to EUA During Perianal Abscess Drainage

1. Positioning and anesthesia:

   • Lithotomy or prone jackknife position
   • Regional or general anesthesia to allow complete relaxation and thorough examination

2. Systematic examination:

   • Digital rectal examination to assess for internal openings
   • Careful inspection of the entire perianal area
   • Gentle probing of the abscess cavity to identify fistula tracts
   • Evaluation of sphincter involvement

3. Treatment decisions based on findings:

   • For simple perianal abscesses without fistula: incision and drainage only
   • For low fistulas not involving sphincter: primary fistulotomy with abscess drainage 1
   • For fistulas involving sphincter muscles: loose draining seton placement 1
   • For supralevator abscesses: drainage via appropriate route (rectal or external) based on origin 1

Pitfalls and Caveats

• Avoid blind probing: Guidelines suggest against aggressive probing to search for fistulas when not obvious, as this can create iatrogenic complications 1
• Sphincter preservation: Always assess sphincter involvement before deciding on fistulotomy to prevent incontinence
• Recognize special populations: Patients with Crohn's disease benefit particularly from EUA with seton placement prior to medical therapy 3
• Follow-up planning: Even with proper EUA, approximately 3-5% of cases may develop recurrent abscesses requiring repeat intervention 6

By performing a thorough EUA of the rectum during perianal abscess drainage, surgeons can significantly improve outcomes, reduce recurrence rates, and minimize the need for repeat procedures, ultimately improving patient morbidity and quality of life.