Skip to main content

Anorectal abscess

Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find one of our health articles more useful.

An anorectal abscess is a collection of pus in the anal or rectal region. It may be caused by infection of an anal fissure, sexually transmitted infections or blocked anal glands.

The following anatomical types have been identified1:

  • Perianal abscess: the most common (60%) - caused by direct extension of sepsis in the intersphincteric plane caudal to the perianal skin.

  • Ischiorectal abscess: (20%) - results from extension of sepsis through the external sphincter into the ischiorectal space.

  • Intersphincteric abscess: (5%) - depending on the effort made to find them, sepsis confined to the intersphincteric space.

  • Supralevator abscess: (4%) - produces horseshoe abscess track.

  • Postanal abscess: posteriorly based below the level of the ano-coccygeal ligament.

Continue reading below


  • High-risk groups include those with diabetes, immunocompromised patients, people who engage in receptive anal sex and patients with inflammatory bowel disease.

  • Deep rectal abscesses may be caused by intestinal disorders such as Crohn's disease or diverticulitis2.

  • Studies suggest that most patients are between the ages of 20 to 60 with a mean age of 40. The male-to-female ratio is 2:13.


  • Symptoms include painful, hardened tissue in the perianal area, discharge of pus from the rectum, a lump or nodule, tenderness at the edge of the anus, fever, constipation or pain associated with bowel movements.

  • The perianal pain is usually constant, throbbing and worse when sitting down.

  • A rectal examination may confirm the presence of an anorectal abscess.

  • Superficial perianal abscesses may occur in infants and toddlers. The abscess often appears as a swollen, red, tender lump at the edge of the anus. The infant may have discomfort but no other symptoms.

Continue reading below

Differential diagnosis


  • A digital rectal examination is usually sufficient for the diagnosis and the treatment planning of anal abscesses and fistulae.

  • Initial investigation will depend on presentation but may include a screen for sexually transmitted infections and/or investigation for inflammatory bowel disease, diverticular disease or lower gastrointestinal tract malignancy.

  • Proctosigmoidoscopy may be performed to exclude associated diseases.

  • MRI scan: allows the assessment of3:

    • Location of any fistular tracts.

    • Location of the internal and external opening(s) of any fistula.

    • Location of deep abscesses.

    • The state of the anorectal wall and the perirectal spaces.

    • Any damage to the anal sphincter.

  • Transperineal ultrasound may be a useful adjunct4.

Continue reading below

Associated diseases

Fistula in ano3

  • Fistulae occur in approximately 40% of patients with anorectal abscesses. Anorectal fistulae may also be associated with diverticular disease, inflammatory bowel disease, malignancy, tuberculosis and actinomycosis.

  • One study found that 68% of recurrent abscesses were associated with a fistula.

  • Goodsall's rule: an external opening situated behind the transverse anal line will open into the anal canal in the midline posteriorly. An anterior opening is usually associated with a radial tract. Goodsall's rule has been challenged as being inaccurate; cases have been reported where the external opening is off-midline5.

  • Fistulae may be classified as intersphincteric (25% in one study), trans-sphincteric (29.16%), suprasphincteric (8.33%), and extrasphincteric (12.5%). Extrasphincteric fistulae are usually not associated with intersphincteric sepsis6.


  • Prompt surgical drainage.

  • Medication for pain relief.

  • Traditionally, antibiotics have not been considered necessary unless there was an underlying condition such as diabetes or immunosuppression. However, one study found that postoperative prophylactic antibiotic therapy including ciprofloxacin and metronidazole played an important role in preventing fistula-in-ano formation after incision and drainage of a simple perianal abscess7.

  • A Cochrane review found that fistula surgery with abscess drainage significantly reduced recurrence or persistence of abscess/fistula, or the need for repeat surgery, compared to abscess drainage alone8.

  • Low fistulae: lay open with either fistulotomy or fistulectomy9.

  • High fistulae: may require a defunctioning proximal colostomy; there is also a risk of postoperative faecal incontinence10. Faecal diversion, however, is not always necessary. One study described the treatment of high fistula by fistulectomy and reconstruction (primary suture repair) of anal sphincter without stool diversion11.

  • An advancement flap (a section of mucosa removed from the anal lining) may be used to close the defect. This technique has been found particularly helpful in Crohn's disease12. A biosynthetic anal fistula plug has been developed and the National Institute for Health and Care Excellence (NICE) recommends its use, providing standard consent and audit procedures are followed13.

  • Clinical trials assessing adipose stem cells, collagen, dermal matrix and numerous other techniques are ongoing1415.


  • Systemic infection.

  • Fissure in ano occurs in up to 30% of patients (the risk is reduced by early surgical drainage).

  • Recurrence.

  • Scarring.


  • The outcome is good if the abscess is treated promptly.

  • Fistula in ano in children often resolves spontaneously and immediate surgical treatment should be withheld16.

Further reading and references

  1. Kelighley M; Anorectal Disorders in Master of Surgery, 2006.
  2. Lewis RT, Maron DJ; Anorectal Crohn's disease. Surg Clin North Am. 2010 Feb;90(1):83-97, Table of Contents.
  3. Abcarian H; Anorectal infection: abscess-fistula. Clin Colon Rectal Surg. 2011 Mar;24(1):14-21. doi: 10.1055/s-0031-1272819.
  4. Nevler A, Beer-Gabel M, Lebedyev A, et al; Transperineal ultrasonography in perianal Crohn's disease and recurrent cryptogenic fistula-in-ano. Colorectal Dis. 2013 Aug;15(8):1011-8. doi: 10.1111/codi.12204.
  5. Cirocco WC, Reilly JC; It is time to retire Goodsall's Rule: the Midline Rule is a more accurate predictor of the true and natural course of anal fistulas. Tech Coloproctol. 2020 Apr;24(4):317-321. doi: 10.1007/s10151-020-02167-z. Epub 2020 Feb 27.
  6. Sofic A, Beslic S, Sehovic N, et al; MRI in evaluation of perianal fistulae. Radiol Oncol. 2010 Dec;44(4):220-7. doi: 10.2478/v10019-010-0046-4. Epub 2010 Oct 14.
  7. Ghahramani L, Minaie MR, Arasteh P, et al; Antibiotic therapy for prevention of fistula in-ano after incision and drainage of simple perianal abscess: A randomized single blind clinical trial. Surgery. 2017 Nov;162(5):1017-1025. doi: 10.1016/j.surg.2017.07.001. Epub 2017 Aug 16.
  8. Malik AI, Nelson RL, Tou S; Incision and drainage of perianal abscess with or without treatment of anal fistula. Cochrane Database Syst Rev. 2010 Jul 7;(7):CD006827. doi: 10.1002/14651858.CD006827.pub2.
  9. Kim do S; Comparison of a fistulectomy and a fistulotomy with marsupialization in the management of a simple anal fistula: a randomized, controlled pilot trial. J Korean Soc Coloproctol. 2012 Apr;28(2):67-8. doi: 10.3393/jksc.2012.28.2.67. Epub 2012 Apr 30.
  10. Jordan J, Roig JV, Garcia-Armengol J, et al; Risk factors for recurrence and incontinence after anal fistula surgery. Colorectal Dis. 2010 Mar;12(3):254-60. doi: 10.1111/j.1463-1318.2009.01806.x. Epub 2009 Feb 7.
  11. Farag AFA, Elbarmelgi MY, Mostafa M, et al; One stage fistulectomy for high anal fistula with reconstruction of anal sphincter without fecal diversion. Asian J Surg. 2019 Aug;42(8):792-796. doi: 10.1016/j.asjsur.2018.12.005. Epub 2019 Feb 6.
  12. van Praag EM, Stellingwerf ME, van der Bilt JDW, et al; Ligation of the Intersphincteric Fistula Tract and Endorectal Advancement Flap for High Perianal Fistulas in Crohn's Disease: A Retrospective Cohort Study. J Crohns Colitis. 2020 Jul 9;14(6):757-763. doi: 10.1093/ecco-jcc/jjz181.
  13. Bioprosthetic plug insertion for anal fistula; NICE Interventional procedures guidance, September 2019
  14. Li P, Guo X; A review: therapeutic potential of adipose-derived stem cells in cutaneous wound healing and regeneration. Stem Cell Res Ther. 2018 Nov 8;9(1):302. doi: 10.1186/s13287-018-1044-5.
  15. Bobkiewicz A, Krokowicz L, Borejsza-Wysocki M, et al; A novel model of acellular dermal matrix plug for anal fistula treatment. Report of a case and surgical consideration based on first utility in Poland. Pol Przegl Chir. 2017 Aug 31;89(4):52-55. doi: 10.5604/01.3001.0010.3912.
  16. Afsarlar CE, Karaman A, Tanir G, et al; Perianal abscess and fistula-in-ano in children: clinical characteristic, management and outcome. Pediatr Surg Int. 2011 Oct;27(10):1063-8. doi: 10.1007/s00383-011-2956-7.

Article history

The information on this page is written and peer reviewed by qualified clinicians.

symptom checker

Feeling unwell?

Assess your symptoms online for free