Definition and Overview

An intersphincteric fistula is an abnormal tract found near the anus or rectum. It is one of the four types of inflammatory tracts that develop due to infection and anorectal abscess. The other three are suprasphincteric, transsphincteric, and extrasphincteric fistulas. These are hollow tracts that form inside the body when the anal crypt gland is obstructed due to bacterial overgrowth, which leads to the formation of pus. The fistula serves as a passageway for pus to drain to an external opening.

Fistulas are classified based on their anatomic location, whether or not they connect two internal organs, and the number of their openings. Among the four, intersphincteric perianal fistula is the most common accounting for approximately 70% of all anal fistulas caused by perianal abscess. It is followed by transsphincteric fistulas, which account for about 25% of all the cases.

Intersphincteric fistula-in-ano is called as such because it begins between the internal and external sphincter muscles and ends in the anus. Sphincter muscles are the ring-like muscles that surround, contract, and close a body opening (such as the anus).

Anal fistulas can also be either complex or simple. Simple cases involve low intersphincteric and transsphincteric fistulas crossing less than 30% of the external sphincter. Meanwhile, the case is considered complex if it is associated with a medical condition including chronic diarrhea, preexisting incontinence, and inflammatory bowel disease. Suprasphincteric and extrasphincteric fistulas fall under this category.

Causes of the Condition

90% of all cases of fistula-in-ano develop due to an acute infection in the anal gland. This is usually caused by fecal or foreign matter or bacteria. Such can clog the anal gland around the anus and can lead to the development of pus, which can then spread to the muscular wall of the anal sphincters. Once the infection has progressed to the intersphincteric space, it can extend to the adjacent perirectal spaces. In the majority of cases, the resulting abscess remains contained within the intersphincteric space until the condition is treated with surgery.

The condition can occur spontaneously or secondary to a perianal abscess. It can be caused by various conditions including chlamydial infections, Crohn’s disease, tuberculosis, inflammatory bowel disease (IBD), radiation therapy, diverticulitis, steroid therapy, HIV infection, and anal fissures, among others.

Key Symptoms

The most common symptoms of intersphincteric fistulas include swelling, irritation of the perianal skin, anorectal pain, bloody or purulent (with pus) discharge, itching, fever, and unpleasant odour. A small number of patients also experience urinary symptoms and rectal bleeding. In severe cases, the condition can lead to systemic infection.

Who to See and Types of Treatments Available

Intersphincteric fistula treatment begins with a careful assessment of the condition and its severity. Patients exhibiting symptoms mentioned above undergo traditional 2D and 3D endoanal ultrasound to determine the exact position and path of the fistula tract. CT scan and intersphincteric fistula MRI are also often performed to accurately identify internal openings and map the fistula tract. If patients have an active infection, they are placed under antibiotic therapy for at least a week before any treatment method is initiated.

Simple cases involving small or shallow fistula and minimal sphincter muscle are treated with a surgical procedure (fistulotomy) that aims to open the fistula tunnel and convert it to a groove, allowing the fistula to heal from the inside out. Another option is a procedure that involves injecting fibrin glue into the fistula with the hope that it will eventually be incorporated into the surrounding tissue.

Fistulotomy can be combined with Seton techniques in immunocompromised patients as well as those with complex and recurrent fistulas and if the fistula passes through a significant portion of the anal sphincter muscle. Seton, which is a piece of surgical thread, is inserted right in the fistula where it is left for up to eight weeks to drain pus and to help it heal. Tighter Seton can also be used to cut through the fistula but this technique requires several procedures. Its advantage, however, is that it allows for the progressive division of the sphincter muscle so incontinence can be avoided.

Patients with an increased risk of suffering from incontinence can undergo endoanal advancement flap. This avoids the division of the sphincter muscles and involves covering the opening of the fistula with healthy tissue. This is often reserved for complex fistulas or those with multiple tracts and affect up to 50% of the external sphincter. Although it has high success rates, 50% of patients suffering from other conditions such as Crohn’s disease and cancer have reported failure as well as mild to moderate incontinence.

Another sphincter muscle-sparing technique is called LIFT or ligation of the intersphincteric fistula tract. The procedure, which involves accessing the fistula between the sphincter muscles, is also considered for complex cases. In this method, surgeons use an incision in the anal canal to map the fistula’s exact location in the intersphincteric tract. Once the location has been identified, a tube is inserted through the external opening of the fistula on the buttocks. The area is then cleaned out and any infected tissue is removed before the openings are sealed.

Pain after intersphincteric fistula surgery is expected and is commonly managed with painkillers and laxatives. Before being discharged, patients are given instructions to help them recover faster. They are often advised to take sitz baths at home and to avoid constipation.

The recurrence rate for intersphincteric fistula is very high. In fact, up to 50% of patients who have undergone treatment suffer from the same condition months after full recovery.

References:

  • Steele SR, Kumar R, Feingold DL, Rafferty JL, Buie WD. Standards Practice Task Force of the American Society of Colon and Rectal Surgeons. Practice parameters for the management of perianal abscess and fistula-in-ano. Dis Colon Rectum. 2011. 54(12):1465-1475.

  • Gunawardhana PA, Deen KI. Comparison of hydrogen peroxide instillation with Goodsall's rule for fistula-in-ano. ANZ J Surg. 2001. 71(6):472-474.

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