Internal Anal Sphincterotomy

Anatomy and Physiology

The anal canal can be described in 2 ways, the functional (surgical) or anatomic anal canal. The surgical anal canal is about 4 cm long and extends from the anal verge to the anorectal ring or puborectalis sling. The anatomic anal canal is approximately 2 cm long and starts at the anal verge extending to the dentate line.

The anal canal consists of 2 muscular structures, which are responsible for anal continence. The first of these structures is the internal anal sphincter, which is the inner layer of the muscular complex and is composed of smooth muscle. The internal anal sphincter is approximately 2.5 to 4 cm long and 2 to 3 mm thick.  Since the internal anal sphincter is an involuntary muscle, it is consistently contracted to prevent inadvertent loss of stool. During a bowel movement, the internal anal sphincter muscle relaxes, allowing for the expulsion of stool. The second muscular structure is the external anal sphincter, which is the outer muscular layer and is composed of striated muscle. The external anal sphincter is a muscular tube around the anal canal, which merges proximately with the puborectalis and the levator ani muscles. It is the voluntary muscle used during bowel movements.

Indications

Internal anal sphincterotomy is indicated in patients who have failed at least 6 weeks of conservative medical management. Typically, patients undergo medical management for 1 to 3 months. If it has failed, surgery is recommended.  Surgical candidates must have good fecal continence before the procedure to reduce the risk of postoperative fecal incontinence.

Contraindications

Patients with poor anal continence are typically not candidates for this procedure. As mentioned above, atypical fissure locations need a full evaluation for other diseases before surgical intervention.

Equipment

An assortment of various-sized anoscopes and an electrocautery surgical unit should be available. A Hill-Ferguson anal retractor comes in various sizes. A bovie-electrocautery device or an 11-blade scalpel is used depending on the surgeon's preference. A minor set, which contains a variety of instruments, is usually opened as well. 

Personnel

In addition to the surgeon, an anesthesiologist, nurse anesthetist, and a surgical scrub technician are necessary in the operating room. The surgeon and an assistant are sufficient when performing in an office setting.

Preparation

No preoperative preparation, such as bowel prep, is needed. The field is typically prepped with a local antiseptic solution of the surgeon's preference.

Antibiotics

Most cases do not require any preoperative intravenous antibiotics.

Anesthesia

A lateral internal anal sphincterotomy can be performed in the office using a local anesthetic, or it can be performed in the operating room under a regional or general anesthetic. The choice of anesthesia is decided based on patient and surgeon preference.  However, studies demonstrate a higher rate of fissure recurrence for internal anal sphincterotomy performed under local anesthetic alone.

Patient Positioning

The patient can be placed in the prone jackknife, lithotomy, or lateral decubitus position. This is determined by surgeon preference, patient body habitus, and patient comorbidities. A morbidly obese patient may not tolerate the jackknife and lithotomy position.  It is this surgeon's preference for lithotomy positioning.

Technique or Treatment

The patient is positioned per the surgeon's preference. The patient is then prepped and draped in the usual sterile fashion. Either a Hill-Ferguson retractor or an anoscope is inserted, and the anal canal is inspected for any other gross pathology. The fissure is usually in the posterior position and may be associated with a right posterior hemorrhoidal complex. The fissure and hemorrhoid may be excised, and the anal mucosa is then reapproximated using an absorbable suture. The procedure can be continued, closed, or opened at the surgeon's discretion.[5][6][7]

Open

A radial-oriented incision over the intersphincteric groove is made in the left lateral position through the anoderm exposing the internal anal sphincter muscle fibers. Using a hemostat or similar instrument, the internal anal sphincter is elevated off the external anal sphincter, and the muscle is divided to the level of the dentate line either using electrocautery or sharply. If divided sharply, one must ensure adequate hemostasis to prevent postoperative bleeding complications. The anoderm is left open to allow healing by the second intention or can be closed using an absorbable suture.

Closed

This technique palpates the intersphincteric groove at the left lateral position. With a finger in the anal canal, an 11-blade scalpel is inserted into the intersphincteric plane, ensuring it stays below the dentate line. The blade is then moved medially, dividing the internal sphincter. The incision is left open to allow for healing by secondary intention.

Complications

The major complication associated with internal anal sphincterotomy is anal incontinence. Up to 50% of patients experience transient incontinence, varying from the inability to control gas to loss of formed stool, resulting in soiling. However, anal incontinence resolves in the majority of patients.  In a meta-analysis of 22 retrospective and prospective studies, 4512 patients were followed for more than 2 years after a lateral internal sphincterotomy for the chronic anal fissure. In this study, the overall continence disturbance rate was 14%. The rate for major incontinence, defined as involuntary loss of feces, was less than 2%. Some experts have advocated limiting the sphincterotomy to the length of the fissure, which has been shown to reduce the risk of incontinence. However, this is associated with an increased risk for non-healing fissures or recurrence of fissures. Other minor complications of internal anal sphincterotomy include infection, bleeding, and fistula development.[8]

Clinical Significance

Anal fissures are a common cause of anal pain, affecting approximately 250,000 new patients every year in the United States. Although it is difficult to measure the true prevalence of the disease given the reluctance of patients to discuss anorectal issues, it is purported to have equal prevalence amongst men and women. Long-term recurrence is seen in patients who have typically only undergone medical therapy. It is rare to see patients who have undergone surgical treatment have relapsing symptoms. Further investigation must be done if the patient fails surgical management, which may suggest other pathologies.

Enhancing Healthcare Team Outcomes

Anal fissures often lead to a poor quality of life because of inappropriate or inadequate treatment. The primary caregiver should always refer these patients to a colorectal surgeon because of the enormous morbidity. The condition is best managed by an interprofessional team that includes a colorectal surgeon, dietitian, general surgeon, and a gastroenterologist. A proper anal internal sphincterotomy is required in adults to prevent fecal incontinence.