Synopsis
Recognise superficial and occult perianal sepsis, drain abscesses without dangerous delay, and plan sphincter-preserving investigation and treatment of anal fistulae.
- Most anal abscesses arise from infected anal glands, but Crohn disease, hidradenitis, trauma, malignancy, tuberculosis and sexually transmitted infection can produce similar or recurrent disease.
- A superficial abscess causes constant throbbing pain, focal tenderness and swelling; an ischiorectal or supralevator collection may have few external signs despite severe deep pain.
- Antibiotics alone do not replace drainage of a drainable anorectal abscess, even when they transiently reduce fever.
- Persistent discharge, a recurrent abscess or an external opening after drainage suggests an anal fistula connecting epithelium to perianal skin.
- Do not probe aggressively through an acute abscess cavity in an attempt to find a tract; creating a false passage can injure sphincter and complicate later repair.
- MRI pelvis is the preferred map for recurrent, complex, horseshoe, supralevator or Crohn-associated fistula; simple disease may be defined at examination under anaesthesia.
- Fistulotomy can cure a simple low tract, whereas sphincter-involving disease often needs a draining seton or another staged continence-preserving approach.
- Baseline continence, obstetric injury, previous fistula surgery and Crohn activity must be documented before choosing any operation that divides sphincter.
Key red flags
Constant escalating anal pain, focal erythema, warmth, swelling and exquisite tenderness, sometimes with fever or spontaneous pus, usually permit a clinical diagnosis and urgent drainage referral.
Severe rectal, pelvic or buttock pain with fever, urinary retention or systemic illness but little surface change suggests ischiorectal, intersphincteric or supralevator sepsis and needs urgent imaging or examination under anaesthesia.
Pain out of proportion, rapidly advancing discoloration, bullae, crepitus, shock or confusion indicates possible Fournier gangrene; normal-looking early skin does not exclude fascial spread.
Investigation priorities
Identify sepsis, necrosis and a drainable superficial focus rapidly.
Management branches
Focal fluctuant swelling or deep clinical suspicion of a collection.
- Assess physiology, give analgesia, establish intravenous access when unwell and involve the emergency general or colorectal surgical team promptly; keep the patient nil by mouth if theatre is likely.
- Drain the abscess adequately under appropriate anaesthesia, opening loculations while protecting sphincter; send pus for culture in recurrent, unusual, immunocompromised or treatment-resistant infection.
- Use systemic antibiotics in sepsis, spreading cellulitis, immune compromise or another locally defined indication, but never regard them as definitive treatment for an undrained collection.
- Provide wound, hygiene and bowel advice plus explicit review for persistent discharge or recurrent swelling, which may reveal a fistula after the acute cavity heals.