- Inflammatory tract with 1 opening in the anal canal and another in perianal skin.
- Fistulas occur spontaneously or secondary to perirectal abscess. Most fistulas originate in the anal crypts at the anorectal junction:
- Goodsall rule:
- If external opening is anterior to an imaginary line drawn horizontally through anal canal, fistula usually runs directly into anal canal. Positive predictive value (PPV) is ~70%.
- If external opening is posterior to line, fistula usually curves to posterior midline of anal canal. PPV is ~40%.
- In children, tract is usually straight.
- Intersphincteric: Fistula is confined to the intersphincteric plane (most common).
- Trans-sphincteric: Fistula connects intersphincteric plane with ischiorectal fossa by perforating the external sphincter.
- Suprasphincteric: Fistula connects intersphincteric plane with ischiorectal fossa but loops over external sphincter.
- Extrasphincteric: Fistula connects rectum to perineal skin but passes external to sphincter.
- System(s) affected: Gastrointestinal; Skin/Exocrine
- Synonym(s): Fistula-in-ano; Anal fistula
Constipation is a common complication.Pediatric Considerations
- Most common in infants
- More frequent in males
- Predominant age: All ages
- Predominant sex: Male > Female
- Injection of internal hemorrhoids, puncture wound from eggshells or fish bones, foreign objects, enema tip injuries
- Ruptured anal hematoma
- Prolapsed internal hemorrhoid
- Acute appendicitis, salpingitis, diverticulitis
- Inflammatory bowel disease (chronic ulcerative colitis, Crohn disease)
- Previous perirectal abscess
- Radiation treatment to perineum/pelvis
- Trauma, either internal or external
Prevention or prompt treatment of anorectal abscess
- Erosion of anal canal
- Extension from infection from a tear in lining of anal canal
- Infecting organism is commonly Escherichia coli (other enteric pathogens may also contribute to infection)
Commonly Associated Conditions
- Possibly associated with penetrating injury, intestinal tuberculosis, ulcerative colitis
- Hidradenitis suppurativa
- Crohn disease
- History of perianal drainage
- History of perianal pain
- History of perianal abscesses in 26–37% (may be higher in recurrent abscesses) (1)[A]
- Constant or intermittent drainage or discharge (drainage may be purulent, bloody, or fecal)
- Firm, tender perianal mass
- External anal sphincter pain during and after defecation
- Spasm of external anal sphincter during and after defecation
- Anal bleeding
- Discoloration of skin surrounding fistula
- Fistulous opening frequently granulose or scarred
- Possible fever (uncommon)
- Perineal or perianal draining orifice
- Recurrent perianal abscesses in identical location
- Small palpable lesion sometimes identified on rectal exam at level of anal crypts
Diagnostic Tests and Interpretation
- CBC (usually not indicated)
- Serologic testing using perinuclear antineutrophil cytoplasmic antibody and anti-Saccharomyces cerevisiae antibody if inflammatory bowel disease (i.e., Crohn disease) suspected
- Consider rapid plasma reagin for recurrent fistulas in sexually active patients to rule out syphilis.
- Lower GI series if inflammatory bowel disease suspected
- Pelvic MRI or endorectal ultrasound may be useful in complex or recurrent fistulas.
- Proctoscopy or sigmoidoscopy
- Colonoscopy and esophagogastroduodenoscopy if Crohn disease suspected
- Probe inserted into tract to determine its course (be careful not to create an artificial opening); best done at time of surgery
- Injection of dilute methylene blue into abscess cavity at time of surgery may be helpful in demonstrating fistula
- Fistulous tract may be simple or multiple
- Fistulous tract has primary opening in anal crypt; secondary opening in anal skin, para-anal skin, perineal skin, or in rectal mucous membrane
- Anal sinus: Opens in anal crypt
- Termination of sinus is blind and located in para-anal or pararectal tissue.
- Pilonidal sinus
- Perianal abscess
- Urethroperineal fistulas
- Ischiorectal abscess
- Submucous or high muscular abscess
- Pelvirectal abscess (rare)
- Rule out: Crohn disease, carcinoma, retrorectal tumors
- Broad-spectrum antibiotic if active infection:
- Cephalexin (Keflex)
- Cefadroxil (Duricef)
- Ampicillin-sulbactam (Unasyn)
- Amoxicillin-clavulanate (Augmentin)
- Cefoxitin or piperacillin/tazobactam (Zosyn) for IV use
- Stool-softening laxative
- Appropriate health care: Outpatient surgery
- Sitz baths 3–4 times per day until definitive surgery
- Surgical incision of entire length of fistula (unroofing) (2)[A]
- Mucosal tract should be cauterized or curetted.
- Consider fistulotomy at time of initial abscess drainage if fistula tract can be identified.
- Complete excision of tract (rarely indicated because of extensive tissue loss)
- Consider Seton stitch placement (especially for suprasphincteric or trans-sphincteric fistulas) (2)[A].
- Endorectal advancement flap closure for complex fistulas (2)[A]
- General anesthesia or regional anesthesia usually required (usually done as outpatient procedure in children)
- Consider use of fibrin glue in selected cases of anal fistulas (2)[A],(3)[A]:
- There is slightly lower healing rate in fibrin glue-treated patients.
- Very low incontinence rate following fibrin glue
- Repeat applications of fibrin glue improve results.
- Fistulas in Crohn disease (2)[A],(4)[B]:
- Asymptomatic fistulas may not need treatment.
- Simple fistulas treated with unroofing
- Complex fistulas treated with advancement flap or long-term Setons
- Fibrin glue may be of benefit in patients with complex fistulae or Crohn disease (1)[A].
- May require a diverting stoma
- Occasional patients may require proctectomy.
- Aggressive treatment of Crohn disease
- Postoperative: Sitz baths several times per day
- Avoid constipation.
Resume work and normal activity as soon as possible.
Patient Monitoring Frequent follow-up examinations following surgery to ensure complete healing and assess continence
Clear liquid diet until GI function returns
- Surgical results usually excellent
- No major difference between the various techniques used as far as recurrence rates are concerned (5)[A]
- Postoperative healing:
- 4–5 weeks for perianal fistulas
- 12–16 weeks for deeper fistulas
- <1/3 of patients with Crohn disease who have active proctitis demonstrate significant healing following surgical intervention (4)[B].
- Postoperative healing may occur within 2–3 weeks in children.
- Recurrence rates 2–9% in simple fistulas (2)[A]
- Healing may be significantly delayed in patients with Crohn disease.
- Constipation (urge to defecate may be suppressed due to pain)
- Rectovaginal fistula
- Partial incontinence of fecal material if sphincter is divided
- Delayed wound healing
- Low-grade carcinoma may develop in long-standing fistulas.
- Recurrent anorectal fistula if fistula is incompletely opened or excised
- Chronic intermittent infections
- Sepsis (rarely)
Hammond TM, Grahn MF, Lunniss PJ. Fibrin glue in the management of anal fistulae. Colorectal Dis. 2004;6:308–19.
Anorectal Abscess; Crohn Disease
565.1 Anal fistula
- K60.5 Anorectal fistula
- K60.3 Anal fistula
- K60.4 Rectal fistula
72779005 Anorectal fistula (disorder)
- Suspect anorectal fistula when patient complains of constant or intermittent perianal drainage or discharge (drainage may be purulent, bloody, or fecal).
- Surgery is the definitive treatment and usually produces excellent results.
- Antibiotics should be reserved for acute infection.
Timothy L. Black, MD
- Malik AI, Nelson RL. Surgical management of anal fistulae: A systematic review. Colorectal Dis. 2008;10:420–30. [PMID:18479308]
- Whiteford MH, Kilkenny J, Hyman N, et al. Practice parameters for the treatment of perianal abscess and fistula-in-ano (revised). Dis Colon Rectum. 2005;48:1337–42. [PMID:15933794]
- 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. [PMID:19912660]
- Lewis RT, Maron DJ. Anorectal Crohn's disease. Surg Clin North Am. 2010;90:83–97, Table of Contents [PMID:20109634]
- Jacob TJ, Perakath B, Keighley MR. Surgical intervention for anorectal fistula. Sao Paulo Med J. 2011;129(2):120–1. PMID: 2160379
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