Anal fissures

An anal fissure is a laceration in the lining of the anal canal distal to the dentate line, which most commonly occurs in the posterior midline and is often caused by local trauma such as the passage of hard stool. Anal fissures can occasionally be seen in patients with leukemia, tuberculosis, and Crohn's disease ⁽¹⁰⁾. The pathogenesis involves a cycle of repeated trauma and injury.

The internal anal sphincter muscle, which is exposed beneath the tear, goes into spasm, pulling the edges of the fissure apart, impairing wound healing and leading to further tearing of the anal mucosa with subsequent passage of bowel movements. In addition, ischemia can contribute to the development of a chronic anal fissure ⁽¹¹⁾.

The diagnosis can usually be made from a classic clinical history in which the patient describes a tearing pain with the passage of hard stool, accompanied by bright red blood, which is usually limited to the surface of the stool or as a stain on the toilet paper. Most patients with an anal fissure cannot tolerate a digital rectal examination or anoscopy.

A fresh laceration usually signifies an acute fissure, whereas a chronic fissure has raised edges exposing the white horizontally oriented fibers of the internal sphincter at its base and is often accompanied by external skin tags distally and hypertrophied anal papillae proximally.

Therapy for anal fissures is aimed at breaking the cycle of sphincter spasm and tearing of anal mucosa and promoting subsequent healing of the fissure. Medical therapy is often successful, with the goals being relaxation of the internal anal sphincter, maintenance of atraumatic passage of stool, and analgesia ⁽¹²⁾. These goals can be accomplished with fiber supplementation, stool softeners, and warm sitz baths.

Topical anesthetic creams such as topical nitroglycerin can often soothe the inflamed anoderm in the setting of an acute fissure. Botulinum toxin*, which is a potent inhibitor of acetylcholine release from nerve endings, can be injected into the anal sphincter and can improve healing in patients with chronic fissures ⁽¹³⁾. Oral nifedipine, a calcium channel antagonist, has been tried as medical therapy under the proposed theory that it can reduce the resting internal anal sphincter pressure; controlled studies with long-term follow-up, however, are lacking ⁽¹⁴⁾.

If medical therapy fails, then surgical management can be performed using a lateral internal sphincterotomy to relax and reduce internal sphincter pressure ⁽¹⁵⁾. This technique divides the internal anal sphincter from its distal end for a distance equal to that of the fissure or up to the dentate line.

The sphincterotomy heals best if it is performed in the left or lateral position (not the anterior or posterior midline position) and can be divided in an open or closed fashion. Complications may include transient incontinence of flatus or stool or postoperative infections (2% of patients).