Suspected anorectal abscess (adult)
Perianal or rectal pain, swelling, fever. Children: seek paediatric surgical advice.
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Colorectal SurgeryEmergency
Anorectal Abscess and Perianal Sepsis (ASCRS 2022)
Anorectal Abscess and Perianal Sepsis (ASCRS 2022): Suspected anorectal abscess (adult) → Clinical assessment → Signs of necrotising infection (Fournier...
Pathway Overview
17 steps
Algorithm Steps
17 total
01Start 02Action Clinical assessment
History, perineal examination and digital rectal examination
- Pain, swelling, fever; prior abscess, fistula or anorectal surgery
- Risk factors: diabetes, immunosuppression, neutropenia, HIV, Crohn's disease
- Look for fluctuance, cellulitis, an external fistula opening, necrosis or crepitus
- Check glucose, HbA1c and urine ketones (undiagnosed diabetes). High glucose or ketones: treat (DKA pathway if present); do not delay drainage
- Signs of sepsis: FBC, creatinine, CRP, lactate and blood cultures
- Differentials: thrombosed haemorrhoid, fissure, pilonidal disease, hidradenitis, cancer, STI
03Decision Signs of necrotising infection (Fournier's gangrene)?
Yes if any: crepitus, dusky or necrotic skin, rapidly spreading cellulitis, pain out of proportion, or severe sepsis
- Rapidly spreading cellulitis
- Crepitus on examination
- Dusky or necrotic skin
- Pain out of proportion to signs
- Severe sepsis or septic shock
- If Yes
04Warning Yes: suspected Fournier's gangrene or severe sepsis - emergency surgery now
Life-threatening. Resuscitate, call the senior surgeon and ICU. Theatre for debridement or urgent drainage. Imaging must not delay surgery.
- Theatre for debridement of all necrotic tissue as soon as possible
- Adult IV antibiotics now (CrCl >50 mL/min): meropenem 1 g 8-hourly PLUS vancomycin PLUS clindamycin 600 mg 8-hourly
- Vancomycin: load 25-30 mg/kg IV (max 2.5 g), then 15-20 mg/kg (max 2 g) 12-hourly; actual body weight; reduce frequency in renal impairment
05Action Fournier's: after the first debridement
Serial surgery and targeted antibiotics
- Send tissue for culture at the first operation
- Plan repeat debridement until no necrotic tissue remains
- De-escalate antibiotics by culture results and clinical response
- Multidisciplinary team (colorectal, urology, plastics, ICU); faecal diversion only if faecal soiling or sphincter damage makes it necessary
06End Fournier's: continue ICU and surgical care
Specialist inpatient care
If No07Action No necrotising signs: classify abscess site
The site decides the drainage route
- Perianal: superficial, next to the anal verge (most common)
- Ischiorectal: deeper, lateral buttock swelling
- Intersphincteric: rectal pain, little to see outside; felt on rectal examination
- Supralevator or high ischiorectal: pain may refer to perineum, lower back or buttocks; examination may look normal
- Horseshoe: crosses the midline through the deep postanal space
08Warning Before drainage: check high-risk groups
Neutropenia or other immunosuppression, Crohn's disease, high endocarditis risk (prosthetic valve, previous endocarditis, rheumatic heart disease). High glucose or ketones: treat (DKA pathway if present); do not delay drainage. Children: paediatric surgical advice.
- Neutropenia: IV antibiotics within 1 hour by the neutropenic fever protocol (adult, no penicillin allergy: piperacillin-tazobactam 4.5 g IV 6-hourly); haematology advice. Fluctuance: drain. No fluctuance: antibiotics first and early imaging.
- Crohn's disease: MRI; drain and place a loose seton; no fistulotomy unless a simple low fistula without proctitis; involve the IBD team
- High endocarditis risk (prosthetic valve, previous endocarditis, rheumatic heart disease, some congenital heart disease, heart transplant with valve disease): antibiotics before drainage
09Decision Simple superficial perianal abscess?
Yes: superficial, next to the anal verge, first episode, not immunosuppressed, no Crohn's disease; no imaging. No: occult, deep, recurrent, horseshoe, immunosuppressed or Crohn's disease; image (MRI preferred) if it will not delay drainage.
- Simple perianal abscess: no imaging
- Occult or deep abscess, recurrence, complex fistula: MRI preferred
- CT if MRI is not available quickly or a pelvic source is suspected
- Endoanal ultrasound where local skill exists
- If Yes
10Action Yes: superficial perianal abscess - incision and drainage
Drain promptly. This is the main treatment. Sepsis: IV antibiotics within 60 minutes; do not delay drainage.
- Incision close to the anal verge, large enough to drain; protect the sphincter
- Break up loculations
- No routine packing: less pain, same healing and recurrence
- Leave the wound open; no primary closure
- Fit, immunocompetent, small abscess, no sepsis: day-case or bedside drainage under local anaesthetic is possible
- Option: drainage catheter (for example Pezzer or Malecot)
11Decision Cellulitis, systemic infection or immunosuppression?
Antibiotics are not routine after drainage. Give them only for these indications.
- If Yes
12Action Yes: antibiotics with drainage
Drainage is still the main treatment
- Indications: cellulitis, systemic signs of infection, or immunosuppression (for example neutropenia, HIV, immunosuppressive drugs)
- Choice and dose: eTG or local guideline; cover skin and bowel flora. Neutropenia: neutropenic fever protocol
- MRSA risk or MRSA isolated with sepsis, raised or low white cell count: add anti-MRSA cover
- Send pus for culture if immunosuppressed, recurrent, non-healing or at risk of multidrug-resistant organisms
13Action Assess for fistula
30-70% have a fistula at presentation
- No obvious fistula: do not probe to look for one (false tract risk)
- Obvious low fistula with no or minimal sphincter involvement: fistulotomy may be done in selected patients
- Fistula through sphincter muscle: loose draining seton; definitive repair later
- No primary fistulotomy if complex, horseshoe, Crohn's disease, poor continence or prior anorectal surgery
- Goodsall's rule: reliable for anterior openings, less reliable for posterior
14Action Post-drainage care
Wound care and follow-up
- Leave the wound open; no packing
- Warm water baths or shower rinses for comfort and hygiene
- Regular analgesia; fibre and stool softeners
- Culture pus if the wound does not heal or the abscess recurs
- Surgical follow-up; return early if fever, spreading redness, worse pain or urinary retention
- Persistent discharge or recurrence: assess for fistula (MRI or examination under anaesthesia)
15Outcome Outcomes
Recurrence and fistula
- Recurrence up to 44%, most within 1 year
- Risk factors: inadequate drainage, loculations, horseshoe abscess, no primary fistulotomy
- Persistent fistula: refer for definitive fistula treatment
If No16Action No: no antibiotics after drainage
Uncomplicated abscess in a healthy patient: antibiotics do not improve healing or reduce recurrence
- Adequate drainage is the treatment
- Reassess if cellulitis spreads or fever persists
- Path rejoins step 13Shared downstream outcome
If No17Action No: deep or complex abscess - drain in theatre
Examination under anaesthesia. Sepsis: IV antibiotics within 60 minutes, then drain urgently; do not wait for imaging. Image first only if it will not delay drainage. The drainage route depends on the abscess origin.
- Intersphincteric: drain into the anal canal (internal sphincterotomy) or through the intersphincteric groove
- Supralevator from an intersphincteric abscess: drain through the rectal wall
- Supralevator from an ischiorectal abscess: drain through the perianal skin
- Supralevator from pelvic disease (diverticulitis, Crohn's disease): CT and treat the source; do not drain through the perineum
- Horseshoe: modified Hanley (open deep postanal space, counter-incisions, seton); no primary lay-open fistulotomy
- Wrong drainage route can create a complex fistula
- Path rejoins step 11Shared downstream outcome
Guideline Source
ASCRS Clinical Practice Guidelines for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula (Gaertner WB et al., Dis Colon Rectum 2022;65:964-985)
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. Children and infants need paediatric surgical advice.
- Fistula repair (seton, LIFT, flap) and Crohn's disease long-term care are covered only briefly.
- Fournier's gangrene: first steps only; antibiotic doses from Australian eTG-based regimen (Safer Care Victoria 2025) for normal renal function.
- Antibiotic choice for uncomplicated cellulitis follows local guidance (eTG).
Contraindicated Populations
Children and infants (paediatric surgical advice)Neutropenia or other immunosuppression (modified approach: antibiotics, early imaging)Crohn's disease (loose seton; avoid fistulotomy unless simple low fistula without proctitis)
Applicable Regions
AUUSEUUK
AU: Fournier's antibiotics follow Safer Care Victoria 2025 (adapted from eTG Antibiotic v16): meropenem 1 g IV 8-hourly plus vancomycin plus clindamycin 600 mg IV 8-hourly. Neutrophils are reported as x10^9/L (ANC 1.0 x10^9/L = 1000/mm3).
US: IDSA 2014 empiric necrotising infection regimens include vancomycin or linezolid plus piperacillin-tazobactam, a carbapenem, or ceftriaxone plus metronidazole.
Version 2Next review: 2027-09-30
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Frequently Asked Questions
What is the Anorectal Abscess and Perianal Sepsis (ASCRS 2022)?
The Anorectal Abscess and Perianal Sepsis (ASCRS 2022) is a emergency 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 (Gaertner WB et al., Dis Colon Rectum 2022;65:964-985).
What guideline is the Anorectal Abscess and Perianal Sepsis (ASCRS 2022) based on?
This algorithm is based on ASCRS Clinical Practice Guidelines for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula (Gaertner WB et al., Dis Colon Rectum 2022;65:964-985) (DOI: 10.1097/DCR.0000000000002473).
What are the limitations of the Anorectal Abscess and Perianal Sepsis (ASCRS 2022)?
Known limitations include: Adults only. Children and infants need paediatric surgical advice.; Fistula repair (seton, LIFT, flap) and Crohn's disease long-term care are covered only briefly.; Fournier's gangrene: first steps only; antibiotic doses from Australian eTG-based regimen (Safer Care Victoria 2025) for normal renal function.; Antibiotic choice for uncomplicated cellulitis follows local guidance (eTG).. Individual patient factors may require deviation from these recommendations.
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