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Internal Anal Sphincterotomy

Editor: Jeffrey G. Deppen Updated: 10/3/2022 8:43:51 PM


An anal fissure is a common benign anorectal disease affecting both children and adults. It is defined as a painful linear tear in the posterior anoderm extending cephalad to the dentate line. Classically these are caused by a large, firm, forceful bowel movement. This results in cycles of recurring anal pain and bleeding leading to chronic anal fissures in as many as 40% of patients who develops fissures. An anal fissure can typically be diagnosed based on history alone. Patients will describe moderate to severe anal pain with bowel movements with variable amounts of bleeding. The bleeding is described as blood on the toilet paper with wiping. The pain commonly persists for 15 to 30 minutes following a bowel movement. The exposed internal anal sphincter frequently spasms, leading to significant pain. If this persists, this muscle becomes hypertrophied leading to nonhealing anal fissures. Typically, in children, these are self-limiting, whereas in adults these can require surgical intervention.  [1][2][3][4]

The majority of anal fissures (90%) are located in the posterior midline. Fissures can be located in the anterior midline in as many as 25% of females and 8% of males. Fissures in the lateral position should raise concern for other disease processes like inflammatory bowel disease or granulomatous diseases. 

There are several medical therapies including salves, fiber and topical nitroglycerin that aids in spontaneous closure early in the disease process. Surgical therapies include botulinum toxin injections, fissurectomy, advancement flaps, and internal lateral anal sphincterotomy. Surgical intervention is typically indicated with chronic fissures or for fissures that are not amenable to medical therapy. 

Internal lateral anal sphincterotomy was first introduced in 1951, by Eisenhammer. The procedure provides prompt symptomatic relief by reducing pathologically elevated pressures within the anal canal. The procedure has provided greater than 95% cure rate at 3 weeks post-procedure.  Currently, it is considered the gold standard surgical intervention.

Anatomy and Physiology

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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 in 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.


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 prior to the procedure to reduce the risk of postoperative fecal incontinence.


Patients with poor anal continence are typically not candidates for this procedure. Atypical fissure locations need a full evaluation for other diseases as mentioned above prior to surgical intervention.


An assortment of variously 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 are used depending on the surgeon preference. A minor set, which contains a variety of instruments is usually opened as well. 


In the operating room, in addition to the surgeon, the presence of an anesthesiologist or nurse anesthetist and a surgical scrub technician is necessary. When performing in an office setting, the surgeon and an assistant are sufficient.


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


Most cases do not require any preoperative intravenous antibiotics.


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 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 will be determined by surgeon preference, patient body habitus, and patient comorbidities. A morbidly obese patient may not tolerate jackknife and lithotomy position.  It is this surgeon's preference for lithotomy positioning.

Technique or Treatment

The patient is positioned per surgeon 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 located 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. At this point, at the surgeons' discretion, the procedure can either be continued in a closed or open fashion.[5][6][7]


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 once must ensure adequate hemostasis to prevent any postoperative bleeding complications. The anoderm is then left open to allow healing by second intention or can be closed using an absorbable suture.


With this technique, the intersphincteric groove is palpated at the left lateral position. With a finger in the anal canal, an 11-blade scalpel is inserted into the intersphincteric plane, ensuring to stay 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.


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 will resolve 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 shown to reduce the risk of incontinence. However, this is associated with an increased risk for non-healing fissure 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 disease given 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 that have typically only underwent medical therapy. It is rare to see patients who have undergone surgical treatment to have relapsing symptoms. Further investigation must be done if patient fails surgical management, as this 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 or nurse practitioner 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.



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