Anorectal Fistula

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Chapter 12 Anorectal Fistula

INTRODUCTION

Description: An anorectal fistula involves communication between the anal or rectal canal and the perineum.

Prevalence: Common. For women, 5.6/100,000 population. The male-to-female ratio is 1.8 : 1.

Predominant Age: Any, average late 30s.

Genetics: No genetic pattern.

ETIOLOGY AND PATHOGENESIS

Causes: Anorectal fistulae may arise spontaneously or result from the drainage of a perirectal abscess. Patients with anal fistulae should be evaluated for the possibility of inflammatory bowel disease.

Risk Factors: Although Crohn’s disease and tuberculosis are recognized risk factors, in most patients a predisposing cause is not apparent. Other risk factors include tears, puncture wounds, and internal hemorrhoids; less commonly carcinoma, radiation therapy, actinomycoses, tuberculosis, and chlamydial infections increase risk.

DIAGNOSTIC APPROACH

Workup and Evaluation

Laboratory: No evaluation indicated.

Imaging: If inflammatory bowel disease is suspected, lower gastrointestinal series. Fistulography (accuracy rate 16% to 48%) or magnetic resonance imaging (MRI; becoming the study of choice when evaluating complex fistulae; shown to reduce recurrence rates by identifying unknown extensions).

Special Tests: None indicated.

Diagnostic Procedures: History, physical examination, probe of fistulous tract. Anoscopy, proctoscopy, or sigmoidoscopy may be helpful.

Pathologic Findings

Inflammation and granulation change from chronic infection. Tract may be single or multiple. Internal opening is generally within an anal crypt.

FOLLOW-UP

Patient Monitoring: Close follow-up during postoperative period, routine health care thereafter.

Prevention/Avoidance: None.

Possible Complications: Constipation, rectovaginal fistula, recurrence.

Expected Outcome: Healing is generally good after surgical excision, although recurrence resulting from underlying disease is common.

MISCELLANEOUS

Other Notes: Goodsall-Salmon law states that fistulae with an external opening anterior to a plane passing transversely through the center of the anus will follow a straight radial course to the dentate line. Fistulae with their openings posterior to this line will follow a curved course to the posterior midline. Exceptions to this rule are external openings more than 3 cm from the anal verge, which almost always originate as a primary or secondary tract from the posterior midline, consistent with a previous horseshoe abscess.

Pregnancy Considerations: No effect on pregnancy, although may affect the choice of an episiotomy site.

ICD-9-CM Codes: 565.1.

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Quah HM, Tang CL, Eu KW, et al. Meta-analysis of randomized clinical trials comparing drainage alone vs primary sphincter-cutting procedures for anorectal abscess-fistula. Int J Colorectal Dis. 2006;21:602. Epub 2005 Nov 30

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