Perianal Pain, Swelling or Discharge
Adults only (not for children). Ask about continence, prior anorectal surgery, obstetric injury and Crohn's disease. Examine the perineum and do a DRE. Neutropenia: no routine DRE; image instead.
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Colorectal SurgeryManagement
Perianal Abscess and Fistula Management (ASCRS)
Perianal Abscess and Fistula Management (ASCRS): Perianal Pain, Swelling or Discharge → Exclude Necrotising Infection (Fournier's Gangrene) First → Necr...
Pathway Overview
20 steps
Algorithm Steps
20 total
01Start 02Warning Exclude Necrotising Infection (Fournier's Gangrene) First
Life-threatening. The diagnosis is clinical. Do not delay surgery for imaging.
- Crepitus, skin necrosis, bullae or dusky skin
- Pain out of proportion; swelling or tenderness beyond the erythema
- Rapid spread or systemic toxicity (sepsis, confusion)
03Decision Necrotising Infection Suspected?
Any sign in the warning above.
- If Yes
04Action Suspected Fournier's Gangrene: Emergency Surgery
Resuscitate. Emergency surgical review. Debride in theatre as soon as possible.
- Start empirical IV antibiotics now: gram-positive, gram-negative, anaerobic and MRSA cover (local guideline)
- Do not delay surgery for imaging. CT only if stable
- Send tissue for culture at the first operation
- Check glucose, HbA1c and urine ketones
05End Fournier's Gangrene: Critical Care and Team Care
Repeat debridement until no necrotic tissue remains. Colorectal, urology and critical care teams.
If No06Decision No Necrotising Infection: Abscess Present?
Fluctuance, induration or a tender swelling. A deep abscess can show few external signs.
- If Yes
07Warning Abscess: Check for Sepsis, Diabetes, Immunosuppression or Heart Valve Risk
Sepsis, diabetes or immunosuppression: emergency drainage. Prosthetic heart valve or previous endocarditis: antibiotics before drainage.
- Sepsis, spreading cellulitis, diabetes or immunosuppression: drain as an emergency
- Antibiotics for cellulitis, sepsis, immunosuppression, prosthetic heart valve or previous endocarditis (give before drainage). Not for a simple abscess in a well patient
- Neutropenia without fluctuance: antibiotics alone may come first. No routine DRE; image (CT or MRI). Urgent surgical and haematology advice
08Action Abscess: Prompt Incision and Drainage
Drain within 24 h, sooner if the warning above applies. Keep the incision close to the anal verge. Do not cut the sphincter.
- Small perianal abscess, fit, immunocompetent, no sepsis: day-case or bedside drainage
- Deep (ischiorectal, intersphincteric, supralevator) or horseshoe abscess: drain under anaesthesia (EUA)
- Intersphincteric: drain into the anal canal. Supralevator from an intersphincteric abscess: through the rectal wall. From an ischiorectal abscess: through the perianal skin. Source unclear: image first (CT or MRI)
- Do not probe for a fistula if none is obvious
- Check glucose, HbA1c and urine ketones for undiagnosed diabetes
09Decision Fistula Seen at Drainage?
- If Yes
10Decision Fistula Seen: Suitable for Fistulotomy Now?
Yes only for a subcutaneous or low simple fistula in a selected patient. No if Crohn's, incontinence, anterior fistula in a woman, prior obstetric or sphincter injury, any sphincter involvement, or doubt.
- If Yes
11End Suitable: Fistulotomy at Drainage, Then Follow-Up
Lay open the subcutaneous or low simple fistula. Review wound healing and continence. Recurrent abscess, discharge or new incontinence: assess as a fistula (MRI or endoanal US, colorectal review).
If No12Action Not Suitable or in Doubt: Loose Draining Seton
Place a loose draining seton through the tract. Do not cut the sphincter now. Plan staged repair after the sepsis settles.
13Action Seton in Place, or Fistula Without Abscess: Assess
Before definitive surgery, record continence, prior anorectal surgery, obstetric injury and Crohn's disease. MRI or endoanal US for a recurrent or complex fistula, or Crohn's.
- Classify by relation to the sphincters (Parks)
- EUA if the tract is unclear
14Decision Fistula Type?
Crohn's disease: Crohn's step. Otherwise complex: transsphincteric >30% of external sphincter, suprasphincteric, extrasphincteric, horseshoe, recurrent, branching, anterior in a woman, or with radiation, cancer, incontinence or chronic diarrhoea. Simple: none of these.
- Simple
15End Simple Fistula, Normal Continence: Fistulotomy
Lay-open fistulotomy for intersphincteric or low transsphincteric fistula (<30% of external sphincter). Not for anterior fistula in a woman, prior obstetric or sphincter injury, incontinence, recurrent fistula or Crohn's: use sphincter-sparing surgery.
- Complex
16End Complex Fistula: Sphincter-Sparing Surgery
Loose draining seton to control sepsis, then staged repair: advancement flap, or LIFT for transsphincteric fistula. Cutting seton only in selected cases. Plug and fibrin glue work poorly.
- Crohn's
17End Crohn's Fistula: Combined Surgical and Medical Care
Drain sepsis. Loose draining seton plus biologic (anti-TNF) therapy with gastroenterology. No surgery if asymptomatic. Fistulotomy only for a selected simple low fistula. Refractory: diversion or proctectomy.
If No18End No Fistula Seen: Wound Care and Follow-Up
Abscess recurs in up to 44%, mostly within 1 year. 30-50% later develop a fistula. Recurrent abscess or persistent discharge: assess for fistula.
If No19Decision No Abscess: Signs of Fistula?
External opening, chronic discharge or recurrent swelling.
- If Yes
- Path rejoins step 13Shared downstream outcome
If No20End No Abscess or Fistula: Consider Other Causes
Severe pain, fever or urinary retention with few signs: suspect a deep abscess. Image (MRI, CT or endoanal US) or EUA. Otherwise consider fissure, thrombosed haemorrhoid, pilonidal disease, hidradenitis, Crohn's, STI or neoplasm.
Guideline Source
ASCRS Clinical Practice Guidelines for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula (2022)
Clinical Safety Information
Clinical Decision Support — Not a Substitute for Clinical Judgment
Individual patient factors may require deviation from these recommendations.
Known Limitations
- Adults only. Not validated for children.
- Crohn's disease, immunosuppression and neutropenia need specialist-led care.
- Rectovaginal fistula is not covered.
- Choice of fistula operation needs a colorectal surgeon; every sphincter operation carries an incontinence risk.
Contraindicated Populations
Children (guideline evidence is from adults)Rectovaginal or anovaginal fistula
Applicable Regions
USAUUKEU
AU: Empirical antibiotic choice: Therapeutic Guidelines (Antibiotic) and local guidelines.
US: ASCRS 2022 guideline.
Version 2Next review: 2027-09-30
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Frequently Asked Questions
What is the Perianal Abscess and Fistula Management (ASCRS)?
The Perianal Abscess and Fistula Management (ASCRS) is a management clinical algorithm for Colorectal Surgery. It provides a structured decision tree to guide clinical decision-making, based on ASCRS Clinical Practice Guidelines for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula (2022).
What guideline is the Perianal Abscess and Fistula Management (ASCRS) based on?
This algorithm is based on ASCRS Clinical Practice Guidelines for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula (2022) (DOI: 10.1097/DCR.0000000000002473).
What are the limitations of the Perianal Abscess and Fistula Management (ASCRS)?
Known limitations include: Adults only. Not validated for children.; Crohn's disease, immunosuppression and neutropenia need specialist-led care.; Rectovaginal fistula is not covered.; Choice of fistula operation needs a colorectal surgeon; every sphincter operation carries an incontinence risk.. Individual patient factors may require deviation from these recommendations.
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