Anal Fissure 

An anal fissure (seen in the images below) is a painful linear tear or crack in the distal anal canal, which, in the short term, usually involves only the epithelium and, in the long term, involves the full thickness of the anal mucosa.

For excellent patient education resources, visit eMedicine's Esophagus, Stomach, and Intestine Center. Also, see eMedicine's patient education articles Anal Abscess, Rectal Pain, and Rectal Bleeding.

Recent studies

Grucela et al assessed the ability of 198 physicians from different specialties to accurately diagnose 7 common, benign anal pathologic conditions. Physicians in the study provided written diagnoses after viewing images of anal abscess, fissure, and fistula; prolapsed internal hemorrhoid; thrombosed external hemorrhoid; condyloma acuminata; and full-thickness rectal prolapse. The authors recorded a 53.5% overall diagnostic accuracy rate among the physicians, with highest accuracy rate (70.4%) found among surgeons; the accuracy rate for the remainder of the group was less than 50%. The proportion of correct diagnoses was lowest for hemorrhoidal conditions and was highest for condylomata and rectal prolapse. Diagnostic accuracy was not found to be associated with length of physician experience. Grucela et al recommended that improvements be made in physician education concerning common, benign anal disorders.^[1]

Frequency

Anal fissures develop with equal frequency in both sexes; they tend to occur in younger and middle-aged persons.

The exact etiology of anal fissures is unknown, but the initiating factor is thought to be trauma from the passage of a particularly hard or painful bowel movement. Low-fiber diets, such as those lacking in raw fruits and vegetables, are associated with the development of anal fissures. No occupations are associated with a higher risk for the development of anal fissures. Prior anal surgery is a predisposing factor because scarring from the surgery may cause either stenosis or tethering of the anal canal, which makes it more susceptible to trauma from hard stool.^[2]

Initial minor tears in the anal mucosa due to a hard bowel movement probably occur often, and, in most people, these heal rapidly without long-term sequelae. In patients with underlying abnormalities of the internal sphincter, these injuries progress to acute and chronic anal fissures. Studies of the internal anal sphincter and of anal canal physiology have been performed with varied results, but at least 1 abnormality is likely present in the internal anal sphincter of many anal fissure patients.

The most commonly observed abnormalities are hypertonicity^[3] and hypertrophy of the internal anal sphincter, leading to elevated anal canal and sphincter resting pressures. The internal sphincter maintains the resting pressure of the anal canal; anal-rectal manometry can be used to measure this pressure. Most patients with anal fissures have an elevated resting pressure, which returns to normal levels after surgical sphincterotomy.

The posterior anal commissure is the most poorly perfused part of the anal canal. In patients with hypertrophied internal anal sphincters, this delicate blood supply is further compromised, thus rendering the posterior midline of the anal canal relatively ischemic.

This is thought to account for why many fissures do not heal spontaneously and may last for several months. Pain accompanies each bowel movement as this raw area is stretched and the injured mucosa is abraded by the stool. The internal sphincter also begins to spasm when a bowel movement is passed, which has 2 effects. First, the spasm itself is painful; second, the spasm further reduces the blood flow to the posterior midline and the anal fissure, contributing to the poor healing rate.

See Etiology.

Typically, the symptoms of an anal fissure are relatively specific, and the diagnosis can often be made based on history findings alone. The patient reports severe pain during a bowel movement, with the pain lasting several minutes to hours afterward. The pain recurs with every bowel movement, and the patient commonly becomes afraid or unwilling to have a bowel movement, leading to a cycle of worsening constipation, harder stools, and more anal pain. Approximately 70% of patients note bright red blood on the toilet paper or stool. Occasionally, a few drops may fall in the toilet bowl, but significant bleeding does not usually occur with an anal fissure.

Initially, the fissure is just a tear in the anal mucosa and is defined as an acute anal fissure. If the fissure persists over time, it progresses to a chronic fissure that can be distinguished by its classic features. The fibers of the internal anal sphincter are visible in the base of the chronic fissure, and often, an enlarged anal skin tag is present distal to the fissure and hypertrophied anal papillae are present in the anal canal proximal to the fissure.

Most anal fissures occur in the posterior midline, with the remainder occurring in the anterior midline (99% of men, 90% of women). Two percent of patients have anterior and posterior fissures. Fissures occurring off the midline should raise the possibility of other etiologies (eg, Crohn disease), an infectious etiology (eg, sexually transmitted disease, acquired immunodeficiency syndrome [AIDS]^[4] ), or cancer.

Failure of medical therapy to resolve the acute fissure is an indication for surgical intervention. The presence of a symptomatic chronic fissure is also an indication for surgery because few of these heal spontaneously.

Thorough knowledge of the anatomy of the anal canal is vital for surgical treatment of an anal fissure.

Anal canal

The anal canal has 2 definitions. The first is the functional, or surgical, anal canal, and the second is the anatomic anal canal. The terms are often used interchangeably, even though they do not mean the same thing. The surgical anal canal is approximately 4 cm long and extends from the anal verge or intersphincteric groove, distally, to the anorectal ring, proximally. The anatomic anal canal is only approximately 2 cm long and extends from the anal verge, distally, to the dentate line, proximally.

Anal verge

The anal verge is an anocutaneous line approximately 2 cm distal to the dentate line. The anal verge marks the beginning of the anal canal.

Dentate line

The dentate line is the junction of the ectoderm and endoderm in the anal canal.

Internal anal sphincter

The internal anal sphincter is a smooth muscle that is the most distal extension of the inner circular smooth muscle of the colon and the rectum. It is 2.5-4 cm long and is normally 2-3 mm thick. The internal sphincter is not under voluntary control and is continuously contracted to prevent unplanned loss of stool.

External anal sphincter

The external anal sphincter is striated muscle that forms a circular tube around the anal canal. Proximally, it merges with the puborectalis muscle and the levator ani to form a single complex. Control of the external anal sphincter is voluntary.

The main contraindication to surgery for an anal fissure is impaired fecal continence, because this could be worsened with surgery. This contraindication mostly applies to patients with minor incontinence (occasional seeping). Patients with gross fecal incontinence (solid material) rarely develop fissures; however, those with irritable bowel syndrome and incontinence to liquid stool can develop fissures if they become constipated. These patients are at the most risk for surgical treatment of an anal fissure, because their typical bowel pattern is loose and more difficult to control.