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Cause and Management of Anal Stenosis


Introduction

Anal stenosis (also referred to as anal stricture) is an abnormal narrowing of the anus that often occurs after colon and rectal surgery. The diagnosis of anal stenosis is suggested by a history of constipation and difficulty in passing stool. Patients often have a history of anal surgery, inflammatory bowel disease, radiation treatment, or anorectal infection. The diagnosis is confirmed by physical examination.

Definition

The anal canal may be defined as the part of the alimentary tract from the anal verge to the anorectal ring (at the level of the levator muscle). Scarring and contracture may occur in a narrow bandlike fashion at the anal verge or occasionally may involve the entire anal canal with a thick, unyielding contracture. Severe stenosis may be defined by the inability to pass an 11-mm scope or the index finger into the anal canal. Stenosis of this degree is usually symptomatic and often requires operative treatment.

Sometimes the stenosis is due to an abnormally high tone in the internal sphincter. This condition is sometimes referred to as anismus (internal sphincter spasm). Anal manometry may be of value in documenting the spasm; a “saw tooth” pressure pattern is common. If the stenosis is due to scarring or a tumor, manometry is not very helpful. However, measurement of rectal compliance, anorectal sensation, and the integrity of the rectoanal inhibitory reflex will complete the picture of the patient’s adaptation to his or her condition.

Classification of Anal Stenosis

Cause

Anal stenosis may be broadly classified by its cause ( Box 10-1 ).

BOX 10-1
Common Causes of Anal Stenosis

  • Sphincter spasm (anal fissure)

  • Postoperative scarring

  • Anastomotic stenosis

  • Inflammatory bowel disease

  • Chronic suppuration

  • Chronic diarrhea

  • Radiation

  • Venereal disease

  • Congenital malformation (imperforate anus, stenosis, or membrane)

  • Neoplasm (benign or malignant anal, perianal, or rectal lesions)

  • Trauma (lacerations, crush, thermal injury, chemical injury)

  • Infection (tuberculosis, lymphogranuloma venereum, schistosomiasis, syphilis, actinomycosis)

  • Ischemia

Spasm

Anal spasm (anismus) causes a tight anal canal that is painful and impossible to examine in the office. One of the common causes of internal sphincter spasm is an anal fissure. However, the spasm of a fissure is not a true stenosis. Painful anal spasm is an indication for examination with use of an anesthetic. Narrowing associated with spasm will disappear as the anesthetic relaxes the sphincters, whereas a stricture due to scarring will persist. Stenosis associated with internal sphincter spasm and a painful anal fissure is generally treated with a lateral internal sphincterotomy, which is discussed in Chapter 3 .

Postoperative Scarring

Postoperative scarring is the most common cause of an anal stenosis. The anal canal is a small oval tube, and incisions made in the mucosa heal with contracture, producing a circular scar that inevitably tightens. This outcome is characteristic of all circular wounds, such as anastomoses. Ileal pouch–anal anastomoses can be hand sewn or stapled. Stapled anastomoses are prone to weblike strictures because of the diverting ileostomy, but these strictures are easily dilated at the time of stoma closure. Hand-sewn anastomoses can form denser strictures that may be symptomatic, often requiring repeated dilations. Anal stenosis is also common after a hand-sewn coloanal anastomosis for rectal cancer, especially when neoadjuvant radiation has been administered. The radiation makes stenosis relatively resistant to dilation, and thus frequent stretching with use of an anesthetic may be needed.

Anal mucosal stripping after stapled ileal pouch–anal anastomosis for retained anal transition zone is a potent cause of a dense anal stenosis. To avoid this consequence, consider stripping half the circumference at one operation and the other half later, after the first half has healed.

Postoperative strictures at the anal verge or in the external anal canal are usually due to excision of excessive amounts of anoderm during anorectal operations—especially hemorrhoidectomy—or overambitious electrocoagulation/excision of anal warts.

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