Anal Sphincterotomy – Internal

Definition

An anal fissure is a painful linear tear in the skin or anoderm overlying the internal anal sphincter distal to the dentate line. Fissures may be classified as acute or chronic depending on their time course and associated findings. Although the distinction is not always entirely clear based on the physical exam, determining the chronicity of the fissure may guide your treatment algorithm.

Acute anal fissures, as the name implies, are typically present for less than 6 to 8 weeks. In addition, they do not have the associated findings of an external skin tag, or “sentinel pile,” or a hypertrophied anal papilla. More than 90% of fissures are found in the posterior midline, although they can be found in conjunction with anterior midline fissure or solely in the anterior midline in a small percentage of patients (10%). Anterior anal fissures are seen in women more frequently than in men, but in general, anal fissures affect males and females with equal distribution. Typically, this is a condition of young adults, but it may be found in patients of all ages. Fissures identified in positions other than the anterior or posterior midline should arouse suspicions of other underlying conditions, including Crohn's disease, ulcerative colitis, syphilis, tuberculosis, leukemia, cancer, and HIV infection.

Etiology

There are many theories as to the etiology of anal fissure. Although passage of a hard stool that causes trauma and disruption of the anoderm is believed to be the most common initiating event, constipation is not present in all patients. Diarrhea with associated multiple bowel movements can also cause trauma to the anal canal, leading to a fissure. Occasionally, other forms of trauma from digital rectal examination, endoscopy, or anoreceptive intercourse can be the inciting event.

The most widely agreed upon factor contributing to anal fissure and persistence of anal fissure is increased resting anal pressure and the sequelae of this state. Many physiologic studies have confirmed the presence of resting hypertonia in the internal anal sphincter in the great majority of patients with anal fissure. Treatment of this condition is frequently targeted at decreasing this elevated resting pressure, also known as mean anal resting pressure (MARP). Abcarian and colleagues (1982), based on the work of Nothmann and Schuster, found that 90% of patients with anal fissure had findings of high MARP and an overshoot phenomenon, demonstrated on anal manometry with a lower threshold for stimulation of overshoot in these patients. They suggest that this overshoot phenomenon, or spasm of the sphincter mechanism, is responsible for the difficulty in healing anal fissures. Furthermore, sphincterotomy contributes to fissure healing, because it widens the anal canal, resulting in decreased stretching of the anoderm, subsequently triggering the overshoot; this is in addition to decreasing resting pressure, which is further described later.

Other studies have investigated anodermal blood flow in animal and cadaveric experiments. Klosterhalfen (1988), demonstrated the vascular anatomy of the rectum and anus with angiography. There is consistently a vessel-deficient area in the posterior midline. This work has given credence to the theory that anal fissures have poor healing in part related to decreased blood flow in this area. Consequently, improvement in blood flow has been demonstrated in patients with documented decreases in the resting hypertonia, which has been ultimately associated with healing of the fissure. Other theories explore the anatomy of the anal canal; some attribute decreased support or adherence of the anal mucosa to the underlying structure of the external anal sphincter, predisposing it to shear injury and contributing to difficult healing.

Dietary factors also play a role in fissure-in-ano. The risk for development of anal fissure is decreased in patients who consume a high-fiber diet with a large amount of raw fruits, vegetables, and whole grains. This is an important modifiable factor in conservative treatment of this disease and is combined with all forms of intervention. According to some sources, patients are at higher risk if they consume white bread, roux sauces, bacon, and sausage. Notably, consumption of coffee, tea, and alcohol has not been associated with increased risk despite the common assumption that these exacerbate anal fissure.