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Anal Fistula


An anal fistula, also known as a fistula-in-ano, is an abnormal tract or cavity which runs outwards from an internal opening in the anorectal lumen to an external opening on the skin of the perineum or buttock. The fistula usually originates in the infected crypt of a anorectal abscess and tracks to the external opening [1].


An anal fistula causes chronic purulent, fecal or serosanguineous discharge with skin irritation. Intermittent swelling, pain and even fever occur due to fecal stasis in the tract; spontaneous rupture and discharge results in temporary improvement. A "water can" appearance is seen when there is prolonged disease course with secondary track formation [5].

Anal fistulas have been classified into the four general types by Parks et al, based on correlation with anatomical structures to facilitate surgical strategy: Intersphincteric, transsphincteric, suprasphincteric and extrasphincteric fistulas [6].

  • Nicholls, Evaluation and management of perianal abscess and anal fistula: a consensus statement developed by the Italian Society of Colorectal Surgery (SICCR), Techniques in Coloproctology, 19, 10, (595), (2015).[doi.org]
  • Romberg-Camps, Liekele E. Oostenbrug, Daisy M.A.E. Jonkers, Laurents P.S. Stassen, Ad A.M. Masclee, Marieke J. Pierik and Stéphanie O.[doi.org]
  • RESULTS: Thirteen patients were lost to follow-up and 21 were withdrawn, primarily to undergo an alternative treatment. The fistula healing rates at 6 and 12 months were 41% (95% CI, 30%-52%; total n 74) and 49% (95% CI, 38%-61%; total n 73).[ncbi.nlm.nih.gov]


The aim is to determine the site of the internal and external openings, the course of the primary track, the presence of secondary extensions, and the presence of other conditions complicating the fistula [7].

  • A full medical and surgical history is necessary to gain information about sphincter strength and associated conditions. 
  • Palpation reveals an indurated tract or cord. Probing under anesthesia and instillation of dilutehydrogen peroxide via the external opening are useful methods of determining the anatomy of the fistula tract(s). 

Special investigations

  • Anal manometry
  • Endoanal ultrasound to assess sphincter integrity for surgical planning
  • Magnetic resonance imaging (MRI) to demonstrate secondary extensions
  • In complex and recurrent cases, fistulography may be necessary
  • Computerised tomography (CT)

Laboratory investigations

  • Blood work is required in preoperative workup and in presence of clinical signs of sepsis
  • Wound culture is indicated if infectious etiologies such as syphilis or HIV are suspected
  • Workup for Crohn disease if relevant
  • Tissue biopsy and histopathological examination if malignancy is suspected
Entamoeba Histolytica
  • This case report provides the outlook that yields the novel insight into the possible role of Entamoeba histolytica in the pathogenesis and persistence of the fistulous tract.[ncbi.nlm.nih.gov]


Treatment of anal fistula is mainly surgical and depends on the location of the fistula and any evidence of sepsis or a large abscess [8].


Concurrent presence of an inflammatory bowel disease warrants consultation with a gastroenterologist. Asymptomatic anal fistula in presence of Crohn disease is managed conservatively because of post-surgical recurrence and poor healing. Antibiotics are given only in cases with sepsis or cellulitis. Analgesics can be given for the pain


  • Fistulotomy, or laying open, is the surest way of eradicating a fistula. However, it involves division of all structures lying between the external and internal openings. Fistulotomy is done for fistulas located at the lower position [9]. 
  • Fistulectomy. This technique involves coring out of the fistula, usually bydiathermy cautery; it allows better definition of fistula anatomy in terms of the relation of the track to the sphincters and the presence of secondary extensions.
  • Staged fistulotomy. Only primary tracks are divided with secondary tracks kept open. In the second stage the track is divided after enough time is given for healing of the wound.
  • Loose setons. For long-term palliation and effective drainage. Also used with other techniques to simplify the tract and create fibrosis.
  • Cutting setons. To eradicate fistulas effectively without sacrificing the sphincters.
  • Advancement flap. High fistulas often require closure of the internal opening and performance of an advancement flap which aims to preserve both anatomy and function.

New experimental treatments

  • For anal fistulas in patients with Crohn disease, local injections of allogeneic mesenchymal stem cells derived from adipose tissues have been used. 
  • Glues, to plug and seal the track and allow ingrowth of healthy tissue to replace the granulation tissue after surgical treatment

Long-term postoperative complications 

  • Recurrence
  • Incontinence (stool)
  • Anal stenosis 
  • Prolonged wound healing

Recurrence and continence rates

0-18% recurrence rate has been reported in standard fistulotomy, with 3-7% rate of incontinence. With surgery using seton, a recurrence rate of 0-17% has been reported, with 0-17% rate of incontinence. Surgical technique using mucosal advancement flap results in 1-17% recurrence and 6-8% incontinence.


Anal fistulae can be treated satisfactorily with surgery. Fistulas persist when the source of infection in anorectal abscess, has not been identified or adequately drained, when the diagnosis is incorrect, when postoperative care is insufficient, or in the presence of Crohn disease, malignancy, radiation proctitis, or unusual infection. Malignancy can rarely arise in a long-standing fistula tract.


Most anal fistulas result from a previous anorectal abscess. Infection of an anal crypt glands leads to involvement of the intramuscular spaces and anorectal abscess. Sometimes the abscess bursts spontaneously draining in the skin leading to the development of a chronic fistula. Following surgical drainage of an abscess, occasionally a granulation tissue-lined tract is left behind that can lead to an anal fistula [2].

Other causes of anal fistulas are:


Non-specific anal fistulae are more common in men than women (1.8:1). The overall incidence is about 9 cases per 100,000 population per year. The most common age group is third to fifth decades of life, mean age of patients being 38.3 years. Various studies have shown that 7 to 40 % cases of anorectal abscess result in the formation of a fistula tract [3].

Sex distribution
Age distribution


The majority of primary anal fistulas originate in anal crypts which become infected, leading to abscess formation. The surgical opening or rupture of the abscess leads to the formation of an anal fistula. The fistula tract is lined with some amount of granulation tissue. Although majority of anal fistula are non-specific, idiopathic or cryptoglandular, they can also be found in patients with inflammatory bowel disease, particularly Crohn disease, some other diseases of the intestines, and HIV infection. Anorectal abscesses and fistulas occur in approximately 30% of HIV patients [4].


Identifying the source of infection, removal of the infected crypt of an anorectal abscess and complete eradication of infection is crucial to prevent development of an anal fistula [10].


An anal fistula is an abnormal communication between the anorectal lumen (the internal opening) and the perianal area (the external opening). Anorectal fistulae are commonly classified based on the relationship of the primary track to the external anal sphincter. Most fistulas arise from the incomplete resolution, treatment or drainage of an anorectal abscess, which leads to the chronic process of fistula formation. An anal fistula may be associated with an underlying disease such as tuberculosis or Crohn disease.

Symptoms range from the minor discomfort of perianal irritation and pus discharge to more serious sepsis. The treatment of choice is the surgical opening of the tract to drain the infection and eradicate the fistulous tract. Complete drainage and good postoperative care of an anorectal abscess are essential to prevent the development of anal fistula.

Patient Information

  • Definition: An anal fistula is an abnormal connection between the end of the large intestine, known as the anal canal, and the skin around the anus. The external opening of the fistula looks like a hole in the skin near the anus. 
  • Cause: The common cause of an anal fistula is bursting or incomplete treatment of an infection with collection of pus in the anal area. An anal fistula is more common in patients of Crohn disease, HIV, diverticulosis and other diseases that affect the intestines. Any prior radiation therapy in anal region, anal surgery, cancers of the blood, and anal trauma also increase the risk of developing an anal fistula. 
  • Symptoms: There may be pus discharge from the anus leading to irritation of the surrounding skin. There may be bleeding, pain and pus discharge during a bowel movement. You may have a sensation of a swelling or an opening near the anus. 
  • Diagnosis: The surgeon will examine the fistula by inserting a gloved finger into the anus to ascertain the position and extent of the fistula. A probing of the tract may be required under anaesthesia. The surgeon may also use a proctoscope or a sigmoidoscope, which are endoscopes for examining the rectal and the lower colon. If you have a recurrent or complex case of anal fistula, ultrasound, MRI or CT examinations may be required. 
  • Treatment: Anal fistula can be effectively treated with surgery to close the abnormal tract and treat the infection. 



  1. Scoma JA, Salvati EP, Rubin RJ. Incidence of fistulas subsequent to anal abscesses. Dis Colon Rectum 1974; 17:357.
  2. Piazza DJ, Radhakrishnan J. Perianal abscess and fistula-in-ano in children. Dis Colon Rectum 1990; 33:1014.
  3. Nordgren S, Fasth S, Hultén L. Anal fistulas in Crohn's disease: incidence and outcome of surgical treatment. Int J Colorectal Dis 1992; 7:214.
  4. Coremans G, Margaritis V, Van Poppel HP, et al. Actinomycosis, a rare and unsuspected cause of anal fistulous abscess: report of three cases and review of the literature. Dis Colon Rectum 2005; 48:575.
  5. Parks AG, Gordon PH, Hardcastle JD. A classification of fistula-in-ano. Br J Surg 1976; 63:1. 
  6. Schouten WR, Briel JW, Auwerda JJ. Relationship between anal pressure and anodermal blood flow. The vascular pathogenesis of anal fissures. Dis Colon Rectum. Jul 1994;37(7):664-9.
  7. Cirocco WC, Reilly JC. Challenging the predictive accuracy of Goodsall's rule for anal fistulas. Dis Colon Rectum 1992; 35:537.
  8. Steele SR, Kumar R, Feingold DL, Rafferty JL, Buie WD. Practice parameters for the management of perianal abscess and fistula-in-ano. Dis Colon Rectum. Dec 2011;54(12):1465-74.
  9. Abbas MA, Jackson CH, Haigh PI. Predictors of outcome for anal fistula surgery. Arch Surg. Sep 2011;146(9):1011-6.
  10. Cho DY. Controlled lateral sphincterotomy for chronic anal fissure. Dis Colon Rectum. May 2005;48(5):1037-41.

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Last updated: 2019-07-11 22:17