Anal fistula
Other namesAnal fistulae, fistula-in-ano
This is a modified version of the original by Armin Kübelbeck [CC BY 3.0 (], via Wikimedia Commons, Specifically, it was made fistula-specific by removing abscess labels.
Different types of anal fistula
SpecialtyGeneral surgery

Anal fistula is a chronic abnormal communication between the anal canal and the perianal skin.[1] An anal fistula can be described as a narrow tunnel with its internal opening in the anal canal and its external opening in the skin near the anus.[2] Anal fistulae commonly occur in people with a history of anal abscesses. They can form when anal abscesses do not heal properly.[3]

Anal fistulae originate from the anal glands, which are located between the internal and external anal sphincter and drain into the anal canal.[4] If the outlet of these glands becomes blocked, an abscess can form which can eventually extend to the skin surface. The tract formed by this process is a fistula.[5]

Abscesses can recur if the fistula seals over, allowing the accumulation of pus. It can then extend to the surface again – repeating the process.[5]

Anal fistulae per se do not generally harm, but can be very painful, and can be irritating because of the drainage of pus (it is also possible for formed stools to be passed through the fistula). Additionally, recurrent abscesses may lead to significant short term morbidity from pain and, importantly, create a starting point for systemic infection.[5]

Treatment, in the form of surgery, is considered essential to allow drainage and prevent infection. Repair of the fistula itself is considered an elective procedure which many patients opt for due to the discomfort and inconvenience associated with an actively draining fistula.[5][3]

Signs and symptoms

Anal fistulae can present with the following symptoms:[4]

  • pain
  • swelling
  • tenderness
  • fever
  • unpleasant odor


Intersphincteric fistula in the lower anal canal. Ultrasound image where the fistula is labeled with a letter F.

Diagnosis is by examination, either in an outpatient setting or under anaesthesia (referred to as EUA or Examination Under Anaesthesia). The fistula may be explored by using a fistula probe (a narrow instrument). In this way, it may be possible to find both openings. The examination can be an anoscopy. Diagnosis may be aided by performing a fistulogram, proctoscopy and/or sigmoidoscopy. Possible findings:



Depending on their relationship with the internal and external sphincter muscles, fistulae are classified into five types:

Differential diagnosis

Other conditions in which infected perianal "holes" or openings may include pilonidal cyst.


There are several stages to treating an anal fistula:

Definitive treatment of a fistula aims to stop it recurring. Treatment depends on where the fistula lies, and which parts of the internal and external anal sphincters it crosses. However, treatment is challenging as complete eradication of the anal sphincters may lead to continence impairment, but failure to excise the affected areas results in recurrence. Those already treated for recurring anal fistula are at higher risk to experience re-recurrence of the disease. [1]

Japan: A man with an anal fistula. From the Yamai no Soshi, late 12th century.

The VAAFT procedure is done in two phases, diagnostic and operative. Before the procedure, the patient is given a spinal or general anaesthetic and is placed in the lithotomy position (legs in stirrups with the perineum at the edge of the table). In the diagnostic phase, the fistuloscope is inserted into the fistula to locate the internal opening in the anus and to identify any secondary tracts or abscess cavities. The anal canal is held open using a speculum and irrigation solution is used to give a clear view of the fistula tract. Light from the fistuloscope can be seen from inside the anal canal at the location of the internal opening of the fistula, which helps to locate the internal opening. In the operative phase of the procedure, the fistula tract is cleaned and the internal opening of the fistula is sealed. To do this, the surgeon uses the unipolar electrode, under video guidance, to cauterise material in the fistula tract. Necrotic material is removed at the same time using the fistula brush and forceps, as well as by continuous irrigation. The surgeon then closes the internal opening from inside the anal canal using stitches and staples.


Some people will have an active infection when they present with a fistula, and this requires clearing up before definitive treatment can be decided.

Antibiotics can be used as with other infections, but the best way of healing infection is to prevent the buildup of pus in the fistula, which leads to abscess formation. This can be done with a seton.


A literature review published in 2018 showed an incidence as high as 21 people per 100,000. "Anal fistulas are 2–6 times more prevalent in males than females, with the condition occurring most frequently in patients in their 30s and 40s."[20]

See also


  1. ^ Madoff, Robert D.; Melton-Meax, Genevieve B. (2020). "136. Diseases of the rectum and anus: anal fistula". In Goldman, Lee; Schafer, Andrew I. (eds.). Goldman-Cecil Medicine. Vol. 1 (26th ed.). Philadelphia: Elsevier. p. 935. ISBN 978-0-323-55087-1.
  2. ^ a b "Anorectal sinuses and fistulae". Archived from the original on 2018-06-05. Retrieved 2016-07-03.
  3. ^ a b c d e f "Colorectal Surgery – Anal Fistula". Retrieved 2016-07-03.
  4. ^ a b Mappes, H. J.; Farthmann, E. H. (2001-01-01). Anal abscess and fistula. Zuckschwerdt.
  5. ^ a b c d "Anorectal Fistula". Merck Manual Consumer Version. Retrieved 2016-06-27.
  6. ^ a b Parks AG, Gordon PH, Hardcastle JD (1976). "A classification of fistula-in-ano". Br J Surg. 63 (1): 1–12. doi:10.1002/bjs.1800630102. PMID 1267867. S2CID 204100917.
  7. ^ Morris J, Spencer JA, Ambrose NS (May 2000). "MR imaging classification of perianal fistulas and its implications for patient management". Radiographics. 20 (3): 623–35. doi:10.1148/radiographics.20.3.g00mc15623. PMID 10835116.
  8. ^ Garg P (13 April 2017). "Comparing existing classifications of fistula-in-ano in 440 operated patients: Is it time for a new classification?". Int J Surg. 42: 34–40. doi:10.1016/j.ijsu.2017.04.019. PMID 28414118.
  9. ^ a b c d Parks, A. G.; Gordon, P. H.; Hardcastle, J. D. (1976-01-01). "A classification of fistula-in-ano". The British Journal of Surgery. 63 (1): 1–12. doi:10.1002/bjs.1800630102. ISSN 0007-1323. PMID 1267867. S2CID 204100917.
  10. ^ a b c d e Shawki, Sherief; Wexner, Steven D (2011-07-28). "Idiopathic fistula-in-ano". World Journal of Gastroenterology. 17 (28): 3277–3285. doi:10.3748/wjg.v17.i28.3277. ISSN 1007-9327. PMC 3160530. PMID 21876614.
  11. ^ Hippocrates, "On Fistulae", translation by Francis Adams, Internet Classics Archive, Massachusetts Institute of Technology
  12. ^ Garg P, Song J, Bhatia A, Kalia H, Menon GR (October 2010). "The efficacy of anal fistula plug in fistula-in-ano: a systematic review". Colorectal Disease. 12 (10): 965–70. doi:10.1111/j.1463-1318.2009.01933.x. PMID 19438881. S2CID 30693484.
  13. ^ Rojanasakul A (September 2009). "LIFT procedure: a simplified technique for fistula-in-ano". Tech Coloproctol. 13 (3): 237–40. doi:10.1007/s10151-009-0522-2. PMID 19636496. S2CID 11643866.
  14. ^ Rojanasakul A, Pattanaarun J, Sahakitrungruang C, Tantiphlachiva K (March 2007). "Total anal sphincter saving technique for fistula-in-ano; the ligation of intersphincteric fistula tract". J Med Assoc Thai. 90 (3): 581–6. PMID 17427539.
  15. ^ van Onkelen, RS; Gosselink, MP; Schouten, WR (February 2012). "Is it possible to improve the outcome of transanal advancement flap repair for high transsphincteric fistulas by additional ligation of the intersphincteric fistula tract?". Diseases of the Colon and Rectum. 55 (2): 163–6. doi:10.1097/DCR.0b013e31823c0f74. PMID 22228159. S2CID 25873518.
  16. ^ Prosst RL, Herold A, Joos AK, Bussen D, Wehrmann M, Gottwald T, Schurr MO (September 2012). "The anal fistula claw: the OTSC clip for anal fistula closure". Colorectal Disease. 14 (9): 1112–7. doi:10.1111/j.1463-1318.2011.02902.x. PMID 22122680. S2CID 2605631.
  17. ^ Prosst RL, Ehni W (July 2012). "The OTSC Proctology clip system for anorectal fistula closure: the 'anal fistula claw': case report". Minim Invasive Ther Allied Technol. 21 (4): 307–12. doi:10.3109/13645706.2012.692690. PMID 22657572. S2CID 23099041.
  18. ^ Prosst RL, Ehni W, Joos AK (September 2013). "The OTSC Proctology clip system for anal fistula closure: first prospective clinical data". Minim Invasive Ther Allied Technol. 22 (5): 255–9. doi:10.3109/13645706.2013.826675. PMID 23971828. S2CID 25219225.
  19. ^ Mennigen R, Laukötter M, Senninger N, Rijcken E (April 2015). "The OTSC(®) proctology clip system for the closure of refractory anal fistulas". Tech Coloproctol. 19 (4): 241–6. doi:10.1007/s10151-015-1284-7. PMID 25715788. S2CID 23284320.
  20. ^ Yamana, Tetsuo (July 25, 2018). "PRACTICE GUIDELINES-Japanese Practice Guidelines for Anal Disorders II. Anal fistula". J Anus Rectum Colon. 2 (3): 103–109. doi:10.23922/jarc.2018-009. PMC 6752149. PMID 31559351.