• 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.
  • Classification:
    • 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

ALERT
Geriatric Considerations
Constipation is a common complication.

Pediatric Considerations

• Most common in infants
• More frequent in males

• Predominant age: All ages
• Predominant sex: Male > Female

Incidence Common

• 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
• Carcinoma

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)

• 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

Lab

• 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.

Imaging

• Lower GI series if inflammatory bowel disease suspected
• Pelvic MRI or endorectal ultrasound may be useful in complex or recurrent fistulas.

Diagnostic Procedures/Other

• 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

Pathological Findings

• 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

General Measures

• Appropriate health care: Outpatient surgery
• Sitz baths 3–4 times per day until definitive surgery

• Fistulotomy:
  • 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.
  • Sphincterotomy
• Fistulectomy:
  • Complete excision of tract (rarely indicated because of extensive tissue loss)
  • Sphincterotomy
• 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

1. Malik AI, Nelson RL. Surgical management of anal fistulae: A systematic review. Colorectal Dis. 2008;10:420–30.  [PMID:18479308]
2. 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]
3. 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]
4. Lewis RT, Maron DJ. Anorectal Crohn's disease. Surg Clin North Am. 2010;90:83–97, Table of Contents  [PMID:20109634]
5. 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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