BASICS
DESCRIPTION
- An anorectal fistula is an open communication between an anal abscess and the perirectal skin.
- Anorectal fistulas typically form from an abscess of the anal crypt glands.
- The classification of fistulas grades severity and guides treatment. Five subtypes are described:
- Submucosal or superficial: The fistula tracks beneath the submucosa and does not involve the sphincter mechanism (not classified under original Park classification).
- Intersphincteric: The fistula travels along the intersphincteric plane (Park type 1).
- Transsphincteric: The fistula traverses through the internal and external sphincter (type 2).
- Suprasphincteric: The fistula originates at the dentate line and loops over the external sphincter, to the ischiorectal fossa (type 3).
- Extrasphincteric (rare): high in the anal canal, (proximal to dentate line), does not involve sphincter complex (type 4)
- Fistulas can also be classified as low or high:
- Low fistulas involve the distal 1/3 of the external sphincter muscle.
- High fistulas involve more of the external sphincter.
- Fistulas may be simple or complex:
- Simple fistulas are low and include superficial, intersphincteric, or low transsphincteric fistulas. They also involve only one communicating tract and are not associated with inflammatory bowel disease (IBD) or other organs (bladder).
- Complex fistulas are higher along the gastrointestinal (GI) tract, have multiple tracts, involve other organs, are recurrent, or are associated with IBD or radiation.
- System(s) affected: GI; skin/exocrine
- Synonym(s): fistula-in-ano; anal fistula
EPIDEMIOLOGY
- The true prevalence is unknown because anorectal pain is commonly attributed to hemorrhoids.
- Mean age of presentation for anal abscess and fistula is 40 years (range 20 to 60).
- Predominant sex: Males are twice as likely to develop an abscess and/or fistula compared with females.
- Lifetime risk of developing fistula is 20-40% in Crohn disease patients.
ETIOLOGY AND PATHOPHYSIOLOGY
- Inspissated debris in an obstructed anal crypt gland results in suppuration and abscess formation along the path of least resistance in the perianal and perirectal spaces (cryptoglandular theory).
- Abscess rupture or drainage leads to an epithelialized track or fistula formation in ~1/3 of patients.
- Fistula formation also occurs in patients with IBD.
- Patients undergoing pelvic radiation are predisposed to fistula formation.
- Immunocompromised patients with primary perianal actinomycosis can (rarely) develop fistula-in-ano.
- Anorectal mucosal laceration due to rectal foreign bodies or trauma can cause abscess and fistula formation.
RISK FACTORS
- IBD (Crohn disease)
- Pelvic radiation
- Perianal trauma; previous anorectal abscess
- Pelvic carcinoma or lymphoma
- Ruptured anal hematoma
- Abscess formation due to acute appendicitis, salpingitis, or diverticulitis
- Tuberculosis (rare); syphilis; lymphogranuloma venereum
- Immunocompromised state (actinomycosis)
GENERAL PREVENTION
- Perianal hygiene
- Prevention or prompt treatment of anorectal abscess; management of commonly associated conditions or risk factors
COMMONLY ASSOCIATED CONDITIONS
- Anorectal abscess
- IBD (Crohn disease)
- Diabetes
- Chronic steroid treatment
DIAGNOSIS
HISTORY
- Perianal pain, pruritis, purulent (often malodorous) perianal drainage, and perirectal skin lesions
- Intermittent rectal pain is worse with defecation or sitting.
- Fever most common with abscesses, generally not common with fistulas
PHYSICAL EXAM
- Excoriations or inflammation of perianal skin
- Visible orifice; induration if opening is incomplete or blind
- Anorectal abscess palpated as an indurated or fluctuant tender perianal mass or small tender palpable lesion on rectal exam at level of anal crypt
- Anoscopy may reveal an internal orifice.
- Goodsall rule can assist in determining course of the fistula tract (more predictive with posterior external anal openings):
- If external opening is anterior to an imaginary line drawn transversely through the anal canal, fistula usually runs directly (radially) into the anal canal.
- If external opening is within 3 cm of anal verge and posterior to line, fistula leads to a curved tract, with an internal opening in posterior commissure (except for a long anterior fistula).
- In children, tract is usually straight.
DIFFERENTIAL DIAGNOSIS
- Pilonidal sinus; Hidradenitis suppurativa
- Hemorrhoids; Anal fissure, ulcer, or sores
- Infected inclusion cyst
- Urethroperineal fistulas
- Ischiorectal or high muscular abscess
- Rule out: Crohn disease, carcinoma, lymphoma, tuberculosis, chronic Chlamydia trachomatis infection, actinomycosis in immunocompromised, acute untreated pelvic inflammatory condition
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
- Imaging helps define perianal anatomy.
- MRI and endoscopic ultrasound are preferred.
- MRI has ~80-90% overall concordance with surgical examination under anesthesia; accuracy improves with dedicated pelvic MRI to allow better resolution.
- Angulation of fistula from internal opening correlates with the type of fistula (acute angle likely high transsphincteric; obtuse angle likely lower fistula).
- Fistulography (insertion of catheter into external opening of fistula and injection of radiographic contrast material) is not preferred and generally not accurate when evaluating perianal disease. Fistulography is reserved for patients who may have a fistula between the rectum and another organ (such as bladder).
- CT is limited in evaluating perianal fistula tracts; more helpful for large perianal abscesses and inflammation
- Consider testing for syphilis for recurrent fistulas in sexually active patients.
Diagnostic Procedures/Other
- Anoscopy or sigmoidoscopy
- Colonoscopy and esophagogastroduodenoscopy if Crohn disease is suspected
- Probing into the tract may be done under anesthesia prior to surgery to determine course of fistula.
- Injection of dilute methylene blue or hydrogen peroxide intraoperatively may help identify internal opening.
TREATMENT
GENERAL MEASURES
- Surgical treatment is definitive (1)[A].
- Optimal surgical treatment based on correct fistula classification
- Goals of treatment include resolving the inflammatory process, maintaining continence, and preventing recurrence.
- Sitz baths 3 to 4 times per day until definitive surgery
MEDICATION
- Medical management with antibiotics and immunosuppressive agents plays a role in the treatment of fistulas due to Crohn disease, particularly if patients are minimally symptomatic.
- Studies have shown improvement (reduced pain, discharge, and induration) and healing in up to 80% of patients with 8 weeks of treatment using oral metronidazole in patients with Crohn disease.
- Use of infliximab has also been shown to be effective in healing perianal Crohn fistulas but has been associated with a high rate of recurrence.
- Antibiotics may be indicated if patients have signs of sepsis or an active infection with a concurrent anorectal abscess.
- Consider surgery in Crohn patients who fail long-term medical therapy.
SURGERY/OTHER PROCEDURES
- Choice of surgical procedure is a balance between achieving cure, avoiding recurrence, and maintaining fecal incontinence (2)[A].
- Low transsphincteric and simple intersphincteric fistulas can be treated with simple fistulotomy or fibrin sealant (fistula plug) (3)[A].
- Fistula plugs can be used as initial treatment for high transsphincteric fistulas. If the fistula recurs, then an advancement flap may be necessary.
- Complex fistulas should be treated with an endorectal advancement flap, which closes the internal opening of the fistula with a mobilized flap of healthy mucosal and submucosal tissue.
- Fistulotomy opens ("unroofs") the entire fistula tract (4)[B].
- Fistula tract is cauterized or curetted and tract is marsupialized to promote healing.
- Lower rates of recurrence compared to incision and drainage alone
- Fistulotomy results in incontinence in about 12% of patients with simple fistulas, compared with almost 50% of patients with complex fistulas.
- A seton is a reactive suture or elastic that is used for drainage (noncutting seton) or to allow scarring of the tract (cutting seton). Cutting setons are tightened at regular intervals to allow slow cutting through the tract and causing scarring. Setons may be placed for complex fistulas treated with fistulotomy, for those that involve >30% of the external sphincter, are proximal to the dentate line, or are categorized as high transsphincteric fistulas.
- Postoperative: typically a same-day procedure; Sitz baths (Sit in warm bath for 20 minutes 3 to 4 times per day and after bowel movements.)
- Aggressive bowel regimen to prevent constipation
- Patients undergoing anal fistulotomy may benefit postoperatively from the use of topical application of sucralfate.
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Resumption of activity as tolerated after surgery
Patient Monitoring
Anoscopy at 3 to 6 months following procedure; frequent follow-up to ensure complete healing and assess continence
DIET
High-fiber diet
PROGNOSIS
Postoperative healing:
- 4 to 5 weeks for perianal fistulas
- 12 to 16 weeks for deeper fistulas
- Postoperative healing may occur within 2 to 3 weeks in children.
- Healing may be delayed in Crohn disease.
COMPLICATIONS
- Fecal incontinence
- Constipation
- Rectovaginal fistula
- Delayed wound healing
- Low-grade carcinoma may develop in long-standing fistulas.
- Recurrent anorectal fistula if fistula is incompletely treated
REFERENCES
11 Whiteford MH, Kilkenny JIII, Hyman N, et al. Practice parameters for the treatment of perianal abscess and fistula-in-ano (revised). Dis Colon Rectum. 2005;48(7):1337-1342.22 Malik AI, Nelson RL. Surgical management of anal fistulae: a systematic review. Colorectal Dis. 2008;10(5):420-430.33 Cirocchi R, Farinella E, La Mura F, et al. Fibrin glue in the treatment of anal fistula: a systematic review. Ann Surg Innov Res. 2009;3:12.44 Rizzo JA, Naig AL, Johnson EK. Anorectal abscess and fistula-in-ano: evidence-based management. Surg Clin North Am. 2010;90(1):45-68.
ADDITIONAL READING
- A ba-bai-ke-re MM, Wen H, Huang HG, et al. Randomized controlled trial of minimally invasive surgery using acellular dermal matrix for complex anorectal fistula. World J Gastroenterol. 2010;16(26):3279-3286.
- Gupta PJ, Heda PS, Shrirao SA, et al. Topical sucralfate treatment of anal fistulotomy wounds: a randomized placebo-controlled trial. Dis Colon Rectum. 2011;54(6):699-704.
- Jacob TJ, Perakath B, Keighley MR. Surgical intervention for anorectal fistula. Cochrane Database Syst Rev. 2010;(5):CD006319.
- Lewis RT, Maron DJ. Anorectal Crohn's disease. Surg Clin North Am. 2010;90(1):83-97.
- Mishra A, Shah S, Nar AS, et al. The role of fibrin glue in the treatment of high and low fistulas in ano. J Clin Diagn Res. 2013;7(5):876-879.
- Niyogi A, Agarwal T, Broadhurst J, et al. Management of perianal abscess and fistula-in-ano in children. Eur J Pediatr Surg. 2010;20(1):35-39.
SEE ALSO
Anorectal Abscess; Crohn Disease
CODES
ICD10
- K60.5 Anorectal fistula
- K60.3 Anal fistula
- K60.4 Rectal fistula
ICD9
565.1 Anal fistula
SNOMED
- 72779005 Anorectal fistula
- 197155003 intersphincteric fistula (disorder)
- 261827001 high anal fistula (disorder)
- 235793000 Suprasphincteric anal fistula (disorder)
- 360428006 Transsphincteric anal fistula (disorder)
CLINICAL PEARLS
- Suspect anorectal fistula in patients with perianal pain, pruritis, purulent drainage, and perirectal skin lesions.
- Surgery is the traditional mainstay of treatment in patients who do not have Crohn disease.
- MRI or endoscopic ultrasound are the modalities of choice to define the anatomy of anorectal fistulas.