Anorectal Fistula

• Jordan Klebanoff, M.D.
• Babak Vakili, M.D.

 Basic Information

Definition

An anorectal fistula is an inflammatory tract with a secondary (external) opening in the perianal skin and a primary (internal) opening in the anal canal at the dentate line. Anorectal fistulae usually originate as a complication of a perianal abscess. Anorectal fistulae can be classified as follows (based on their relationship to the anal sphincter complex):

1. 1.

   Intersphincteric: fistula track passes within the intersphincteric plane to the perianal skin (most common)

2. 2.

   Transsphincteric (Fig E1): fistula track passes from the internal opening, through the internal and external sphincter, and into the ischiorectal fossa to the perianal skin (frequent)

   

3. 3.

   Suprasphincteric: after passing through the internal sphincter, fistula tract passes above the puborectalis and then tracts downward, lateral to the external sphincter, into the ischiorectal space to the perianal skin (uncommon); if abscess cavity extends cephalad, a supralevator abscess possibly palpable on rectal examination

4. 4.

   Extrasphincteric: fistula tract passes from the rectum, above the levators, through the levator muscles to the ischiorectal space and perianal skin (rare)

5. 5.

   Submucosal: originate at the level of the dentate line in an infected crypt not involving the sphincter muscles

With a horseshoe fistula, the tract passes from one ischiorectal fossa to the other behind the rectum.

Synonym

1. Fistula-in-ano

ICD-10CM CODES
K60.3	Anal fistula
K60.5	Anorectal fistula

Epidemiology & Demographics

1. •

   Common in all ages (average age is 39 years)

2. •

   Occurs twice as often in men as compared to women (12.1/100,000 vs. 5.5/100,000)

3. •

   Associated with inflammatory bowel disease and constipation

4. •

   Pediatric age group: more common in infants; boys more than girls

Physical Findings & Clinical Presentation

1. •

   Acute stage: perianal swelling, pain with defecation, and fever

2. •

   Chronic stage: history of rectal drainage or bleeding; previous abscess with drainage

3. •

   Tender external fistulous opening, within 2 to 3 cm of the anal verge, with purulent or serosanguineous drainage on compression; the greater the distance from the anal margin, the greater the probability of a complicated upward extension

4. •

   Goodsall’s rule:

   1. 1.

      Location of the internal opening related to the location of the external opening.

   2. 2.

      With external opening anterior to an imaginary line drawn horizontally across the midpoint of the anus: fistulous tract runs radially into the anal canal.

   3. 3.

      With opening posterior to the transanal line: tract is usually curvilinear, entering the anal canal in the posterior midline.

   4. 4.

      Exception to this rule: an external anterior opening that is >3 cm from the anus. In this case the tract may curve posteriorly and end in the posterior midline.

5. •

   If perianal abscess recurs, presence of a fistula is suggested.

Etiology

1. •

   Most common: nonspecific cryptoglandular infection (skin or intestinal flora)

2. •

   Fistulas more common when intestinal microorganisms are cultured from the anorectal abscess

3. •

   Tuberculosis

4. •

   Lymphogranuloma venereum

5. •

   Actinomycosis

6. •

   Inflammatory bowel disease (IBD): Crohn’s disease, ulcerative colitis

7. •

   Trauma: surgery (episiotomy, prostatectomy), foreign bodies, anal intercourse

8. •

   Malignancy: carcinoma, leukemia, lymphoma

9. •

   Treatment of malignancy: surgery, radiation

Diagnosis

Differential Diagnosis

1. •

   Hidradenitis suppurativa

2. •

   Pilonidal sinus

3. •

   Bartholin’s gland abscess or sinus

4. •

   Infected perianal sebaceous cysts

Workup

1. •

   Digital rectal examination:

   1. 1.

      Assess sphincter tone and voluntary squeeze pressure

   2. 2.

      Determine the presence of an extraluminal mass

   3. 3.

      Identify an indurated fistula tract

   4. 4.

      Palpate an internal opening or pit

2. •

   Gentle probing of external orifice to avoid creating a false tract; 50% do not have clinically detectable opening

3. •

   Anoscopy

4. •

   Proctosigmoidoscopy to exclude inflammatory or neoplastic disease

5. •

   All studies done under adequate anesthesia

Laboratory Tests

1. •

   Complete blood count

2. •

   Rectal biopsy if diagnosis of IBD or malignancy suspected; biopsy of external orifice is useless

Imaging Studies

1. •

   Colonoscopy or barium enema if:

   1. 1.

      Diagnosis of IBD or malignancy is suspected

   2. 2.

      History of recurrent or multiple fistulas

   3. 3.

      Patient <<25 yr

2. •

   Small bowel series: occasionally obtained for reasons similar to previously

3. •

   Fistulography: unreliable but may be helpful in complicated fistulas

4. •

   Endoanal ultrasound, MRI, or CT scan can be considered preoperatively

Treatment

Nonpharmacologic Therapy

Sitz baths

Pharmacologic Therapy (Rarely Recommended)

1. •

   Immunomodulators (Infliximab)

Acute General Rx

1. •

   Treatment of choice: surgery

2. •

   Broad-spectrum antibiotic given if:

   1. 1.

      Cellulitis present

   2. 2.

      Patient is immunocompromised

   3. 3.

      Valvular heart disease present

   4. 4.

      Prosthetic devices present

3. •

   Stool softener/laxative

Chronic Rx

1. •

   Surgery

2. •

   Surgical goals are as follows:

   1. 1.

      Cure the fistula

   2. 2.

      Prevent recurrence

   3. 3.

      Preserve sphincter function

   4. 4.

      Minimize healing time

3. •

   Methods for the management of anal fistulas: fistulotomy, fistulectomy, setons (Fig. E2) (maintains fistula patent for drainage while spontaneous healing occurs), fibrin glue (clot formation within the fistulous tract), fistula plugs (Fig. E3) (promote closure of fistula), LIFT procedure, rectal advancement flaps, and colostomy

Disposition

Outpatient surgery

Referral

Refer to a surgeon with expertise in this area.

Pearls & Considerations

Comments

1. •

   HIV-positive and diabetic patients with perirectal abscesses/fistulas are true surgical emergencies.

2. •

   Risk of septicemia, Fournier’s gangrene, and other septic complications make immediate drainage imperative.

Suggested Reading

• E.B. Sneider, J.A. Maykel: Anal abscess and fistula. Gastroenterol Clin N Am. 42:773–784 2013

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