Anal fistula

Last updated date: 08-Mar-2023

Originally Written in English

Anal fistula

Anal fistula


An anorectal fistula connects the anorectal canal to the perianal region. It is a morbid disease that usually emerges after perianal abscess drainage and needs careful monitoring to detect and treat. The classification of fistulas is essential for directing therapy. The majority of therapy is surgical management, although knowledge of innovative medicines and sphincter-preserving techniques, as well as preoperative imaging, are critical aspects in providing patients with different treatment options while preserving sphincter integrity.

Anal fistula definition

An anal fistula is a short tunnel that connects an abscess, a cavity in the anus that is diseased, to a skin hole around the anus.

The external orifice via which feces are discharged from the body is known as the anus. Several tiny glands that produce mucus are located just inside the anus. These glands can occasionally become clogged and infected, resulting in an abscess. A fistula can form in about half of these abscesses.

A perirectal abscess, whether surgically or spontaneously drained, can still result in a fistula in up to 40% of cases. However, spontaneously draining abscesses have a greater risk of fistula development, up to 66%. The average incidence has been found to be 8.6 per 100,000 people. The occurrence of an acute or chronic anal fistula can be stressful for patients and lead to a decrease in quality of life. They are frequently categorized according to their anatomical locations.



Anorectal fistulas are quite infrequent, with an annual incidence of 1-8 per 10,000 people. Crohn's disease may be responsible for up to 25% of cases in the Western Hemisphere. It is twice as frequent in men as in women and generally appears in the third to fifth decade of life. Obesity, diabetes, hyperlipidemia, a history of anorectal surgery, and even excessive salt intake are all risk factors for perirectal fistula.

Smoking has also been linked to the development of perianal abscess and fistulas, as well as recurring anal fistulas in specific operations. Patients under the age of 40, as well as those with recurrent anal abscesses, may be prone to the formation of an anal fistula.



An anal fistula is an epithelialized connection between the anal canal and the exterior peri-anal region with inflammatory and granulation tissue. The fistula cannot heal due to the distal blockage. Because cells are constantly being changed over, debris accumulates in the fistula tract, causing blockage and preventing healing. The usage of a seton and how it permits fistulas to heal is proof of this, since setons allow continual draining of the fistula and typically results in the fistula migrating and mending.


Causes of Anal fistula 

Anal abscesses and clogged anal glands are the most common anal fistula causes. An anal fistula can also occur due to the following less prevalent conditions; 

For more information see : Chlamydia infection 

  • Tuberculosis
  • Diverticulitis (a condition where small pouches develop in the large intestine and get inflamed) 
  • Cancer 

Complicated vaginal births with third or fourth-degree rips or the need for an episiotomy may lead to anal fistula; yet, these fistulas frequently heal spontaneously. Surgical treatment for nonhealing obstetric associated anal fistulas is determined by the location of the fistula as well as vaginal involvement. A recto-vaginal fistula becomes an ano-rectovaginal fistula when it is distal to the dentate line. Obstetrical trauma, which is usually accompanied with a traumatic vaginal delivery, is one of the causes. Patients who have an episiotomy are more likely to suffer from sphincter damage and fecal incontinence.

Although the involuntary internal sphincter accounts for the bulk of resting anal tone, the external sphincter, which is made up of striated voluntary muscle fibers, is essential for maintaining fecal continence. It is innervated by three nerve branches: the external perineal nerve anteriorly, the inferior rectal nerve posteromedially, and an extra posterior branch emerging from either S4 or the inferior rectal nerve in 31% of instances.


Anal Fistula Risk Factors 

Anal Fistula Risk Factors 

You have a 50 percent probability of having an anal fistula if you get an anal abscess. Even if your abscess clears on its own, you're still at risk of developing a fistula. 

Also, certain disorders affecting your lower digestive system or anal region might put you at high risk. Some of these conditions are Crohn’s disease, colitis, chronic diarrhea, radiation therapy treatment for rectal cancer. 


Classification of Anorectal Fistulas

  • A transphincteric fistula
  • A high intersphincteric fistula
  • A suprasphincteric fistula
  • Extrasphincteric fistula

Anorectal fistulas are characterized by their tract location relative to the internal and external sphincters. 


Intersphincteric Fistulas:

Because most abscesses form between these sphincters, the most frequent kind is an intersphincteric fistula. That is the one that passes the internal sphincter and then leads to the exterior of the anus. Because the therapy does not impact the external sphincter, a fistulotomy successfully handles these, or laying open of the fistulous tract, and seldom causes incontinence. The most frequent form of fistula is an intersphincteric fistula, which accounts for 50-80% of all cryptoglandular fistulas.


Transsphincteric Fistulas:

A trans-sphincteric fistula is one that extends from one side of the external sphincter to the other before leaving in the perianal region, so affecting both sphincters. Because of this, transsphincteric fistulas provide a management problem and frequently need more sophisticated or tiered therapy.

However, using a seton to progressively "lower" the tract and make it less engaged with the external sphincter may allow migration of the tract and a fistulotomy at a later date while maintaining the patient's continence. The amount of the external sphincter involvement determines the risk of postoperative incontinence, as a partial sphincterotomy is frequently tolerated. However, if the fistula involves the bulk of the sphincter, incontinence will occur after a full division.


Suprasphincteric Fistulas:

These fistula tracts pass above to the external sphincter, cross the puborectal muscle, and then turn caudal to their external entrance. As a result, they bypass the internal sphincter and the puborectal muscle while avoiding the external sphincter. When these individuals appear with a perirectal abscess, it may not be evident on inspection, but pain on the digital rectal exam will be present.

Again, owing of their high tract, the use of a seton before fistulotomy may be explored in these situations. A fistulectomy is similar to a fistulotomy in that the whole fistula tract is removed, either abruptly or with cautery. Historically, radical fistulectomy was the primary therapy for anal fistula; however, fistulotomy was chosen since it promoted better sphincter function, was a less invasive technique, and healed quicker.


Extrasphincteric Fistulas:

These fistulas frequently develop in the proximal rectum rather than the anus and are frequently the result of a treatment. Their external entrance is in the perianal region, and the tract ascends to reach the anal canal above the dentate line.


Signs and Symptoms of Anal Fistula 

Signs and Symptoms of Anal Fistula 

In patients who have not recently had a perirectal abscess drained, a detailed history, complete examination of systems, and physical exam are required to determine the source of fistula. On an abdominal exam, patients with inflammatory bowel disease may be sensitive and have a history of bloody diarrhea, abdominal discomfort, or systemic symptoms such as weight loss or fever. A detailed sexual history is essential since lymphogranuloma venereum can produce a perianal fistula in some cases.

A history of malignancy or pelvic radiation is required, as radiation fistulas are frequently documented, and therapy should be coordinated with the patient's cancer care. A history of rash or a history of several new sexual partners should raise the possibility of syphilis. A patient with a persistent cough or a history of TB may arrive with an anorectal fistula if he or she is from an endemic zone. Multiple draining fistulas, fistulas in unusual sites, and chronic or recurring fistulas should raise suspicions of a systemic process.

The following are the signs and symptoms of anal fistula;

  • Bleeding
  • Bowel movements associated with pain. 
  • Drainage (pus discharge) from the hole surrounding the anus that is bloody or foul-smelling. After the fistula drains, the pain may subside. 
  • Fever, chills, and feeling generally exhausted.
  • Frequent occurrence anal abscesses
  • Skin irritation around the anus due to drainage
  • Swelling and pain near the anus


Anal Fistula Diagnosis 

Anal Fistula Diagnosis

An anal fistula diagnosis usually involves examining the region surrounding the anus. The doctor will search the skin for any opening (the fistula tract). After that, he or she will attempt to assess the depth of the tract as well as its direction of travel. There will almost always be drainage from the external hole.

Other anal fistulas are not visible on the surface of the skin. In such instance, the doctor might have to order the following tests;

  • An anoscopy, which is a technique that involves looking inside the rectum and anus with a specific device. 
  • An MRI or an ultrasound of the anal region to acquire a better image of the fistula tract. 
  • To diagnose the fistula, the healthcare provider may have to look at you in the surgery room. This procedure is known as an examination under anesthesia.

If the doctor discovers a fistula, he or she may order more testing to evaluate if the problem is associated with Crohn's disease, an inflammatory bowel disease.

Fistulas develop in about 25 percent of persons who have Crohn's disease. X-rays, blood tests, and colonoscopies are among the tests used in these studies. 

A colonoscopy is a technique that involves inserting a flexible, illuminated device into the colon through the anus. It's done with conscious sedation, which is a type of light anesthetic.


CT scan and CT Fistulogram

Computerized tomography is beneficial for diagnosing abscesses and drainable fluid collections because it is rapid and easy to employ in the vast majority of clinical settings. Although it is not as sensitive or specific as pelvic MRI for anal fistula classification. A CT scan may be the most appropriate imaging to speed diagnosis and treatment for a patient in the clinical context if an acute infection of an anal fistula or an underlying abscess is suspected and a rapid diagnosis is required.

CT-fistulography is a valuable and efficient method for finding fistula tracts prior to surgery in the outpatient clinic. However, trained radiologists must read the pictures, and a qualified surgeon must be ready to inject the contrast for the scan. When compared to MRI, it may be less expensive. When attempting to conserve money or in patients who are unwilling or unable to have an MRI, it should be considered in complicated anal fistula preoperative planning. Multidetector CT has been used with equal success in detecting fistulous tracts and underlying abscesses. 


Anal Fistula Treatment 

Anal Fistula Treatment 

Anal fistulas don’t usually heal on their own; hence surgery is necessary to repair them. There are various procedures to address the issue. The optimum solution for you will be determined by the location of the anal fistula, as well as whether it is a single channel or branches off in multiple directions. 

To determine the optimum treatment, you may need an initial evaluation of the region under general anesthetic while asleep. The surgeon will discuss the many alternatives with you and recommend the one that is best for you. Anal fistula surgery is normally performed under general anesthesia. In many circumstances, there is no need to remain in the hospital overnight. 

The goal of surgery is to seal the fistula and prevent sphincter muscle damage or injury. Sphincter muscles are the ring of muscles that normally open and close the anus. They could also lead to bowel control problems (bowel incontinence). 

The major surgical treatment alternatives of anal fistula include; 

  • Fistulotomy

A fistulotomy is the most common form of surgery for an anal fistula. It includes cutting the fistula open throughout its whole length and allowing it to recover as a flat scar. 

A fistulotomy is also the most successful treatment for most anal fistulas. Yet, it's generally only appropriate for fistulas that don't pass out a lot of the sphincter muscles since the risk of incontinence is lower. 

If a tiny piece of the anal sphincter muscle must be cut during the procedure, the surgeon will make every effort to minimize the risk of incontinence. However, the doctor may recommend another operation instead of the risk of incontinence is exceptionally high.

  • An advancement flap procedure 

Sometimes, an anal fistula runs via the anal sphincter muscles, and a fistulotomy is likely to cause incontinence. The doctor may recommend an advancement flap procedure in such cases. It entails scraping out or cutting the fistula and sealing the opening where it gets into the gut using a flap of tissue. This can be obtained from the rectum, the colon's last section. 

This procedure has a lesser success rate, unlike a fistulotomy; however, it prevents cutting the anal sphincter muscles.

  • Seton approach 

If the anal fistula crosses through a large part of the anal sphincter muscle, the surgeon may suggest a seton at first. This is a piece of surgery thread that usually remains in the fistula for a few weeks to help maintain the fistula open. This enables it to drain and heal without having to cut the sphincter muscles. 

Fistulas can drain with loose setons, but they are not cured. Tighter setons can help slowly cut through a fistula to facilitate healing. This could involve a number of operations, which the surgeon will talk about with you. 

Alternatively, they may recommend doing numerous fistulotomy treatments, each time carefully opening up the small piece of the fistula, or a different treatment altogether. 

  • LIFT procedure 

The ligation of the intersphincteric fistula tract (LIFT) is a procedure that doctors use to treat fistulas passing through the anal sphincter muscles. It’s also a suitable option for conditions that are too risky to be treated with a fistulotomy.

The procedure involves creating a cut in the skin over the fistula and pulling the sphincter muscles apart. After that, the surgeon will seal the fistula on either end and cut it open to make it lie flat. 

This method has shown some positive outcomes so far. However, since it has only been available for a few years, further research is necessary to see how well it is effective in the short and long run. 

  • Endoscopic ablation 

An endoscope (a tiny tube attached to a camera on the tip) is inserted into the fistula during this surgery. The fistula is subsequently sealed with an electrode that is passed via the endoscope. Endoscopic ablation is usually effective, and there are no severe safety issues.

  • Fibrin glue 

Fibrin glue treatment is the only non-surgical treatment alternative for anal fistulas at the moment. The procedure involves injecting glue into the anal fistula when under general anesthesia to minimize pain. The purpose of glue is to seal the fistula and promotes healing.

However, it is less effective, unlike fistulotomy for uncomplicated fistulas. On the other hand, the effects aren't always permanent. Still, it’s a good option for a fistula that runs through the anal sphincter muscles since they don't require cutting. 


Surgery works successfully for the majority of anal fistulas. Your surgeon may advise that you soak the damaged area in a warm bath, called a sitz bath. They can also recommend taking stool softeners or laxatives for a week following the surgery.

You might experience pain or discomfort in the anal region following surgery. The doctor will thus likely administer a local anesthetic like lidocaine and even prescribe pain medication. 

If the treatment and recovery of abscess and fistula are successful, they are unlikely to return.


Complications of Anal Fistula 

Complications of Anal Fistula

Treatment for an anal fistula, like any other form of treatment, comes with a range of risks and complications. The following are some of the primary dangers: 

  • Infection: Sometimes, infection of the surgical area might occur and may necessitate treatment with antibiotics. For severe instances, hospitalization could be necessary. 
  • Fistula recurrence: Despite undergoing a surgical procedure, the fistula can sometimes reappear.
  • Bowel incontinence: Most forms of anal fistula treatment have the risk of bowel incontinence. However, severe incontinence is uncommon, and efforts can be made to avoid it.

The risk level you face will be determined by factors such as the location of the fistula and the operation you undergo. Consult the surgeon about the possible dangers associated with the surgery they prescribe.


Differential Diagnosis

The differential diagnosis for anal fistula comprises, first and foremost, all of the typical anorectal disorders encountered in the office of a primary care practitioner or a general or colorectal surgeon.

  • Anal fissure
  • Anal warts
  • Condyloma acuminate
  • Hemorrhoids
  • Perianal abscess
  • Solitary rectal ulcer syndrome

In addition to these, there are infectious, benign, and malignant processes which may present as or appear as an anal fistula such as

  • Crohn disease
  • Hidradenitis suppurativa
  • Anal cancer
  • Anorectal fistula can be caused by an unusual presentation of anal sexually transmitted infections. Anorectal sexually transmitted illnesses include syphilis, herpes, gonorrhea, and chlamydia, as well as Calymmatobacterium granulomatosis-caused granuloma inguinal.
  • In HIV-positive individuals who arrive with anal fistula symptoms, a diagnosis of probable Kaposi sarcoma as well as lymphoma is made. 




The prognosis of an anorectal fistula varies depending on the cause. Healing rates for simple cryptoglandular anal fistulas approach 80%, whereas those for complicated fistulas are about 60% after sphincter maintaining surgery. Setons have been utilized with great effectiveness, with recovery rates ranging from 80 to 90 percent after six months. In general, a fistula treated with a fistulotomy or fistulectomy should be completely healed within 12 weeks, depending on the extent of the lesion.

If the discharge is increasing or prolonged up to the twelfth week, the fistula has recurred or has not closed entirely. Incomplete division of the fistula in a fistulotomy or incomplete resection or obliteration of the tract in a fistulectomy are two causes of surgical failure. Failure of the LIFT operation might result from leaving a lengthy fistula tract behind or from insufficient closure of the fistula tract.

If the flap fails in anal-cutaneous or rectal mucosal advancement flap procedures, the fistula will either not heal or recur. Smoking is a risk factor for failure of flap therapy as well as Crohn's disease. This is frequently due to the flap's insufficient blood supply, as indicated by increased healing rates when the muscle layer is utilised in the flap.

Failure of anal fistula plugs to allow fistulas to heal can be due to a variety of factors, including inadequate internal coverage of the plug, insufficient debridement of the fistula tract, and early dislodgement of the fistula plug. If the tract has not migrated sufficiently to allow the fistula to heal, setons removed too early may result in the fistula not mending. Some setons can cause a lower fistula, which necessitates a fistulotomy for full healing.

Additional operations are done to address recurrent fistula depending on the initial surgery performed. When a fistula recurs, an MRI can assist detect its progress, and an anesthetic exam can help describe the fistula tract. Treatment is determined on the type of fistula present, which may differ between recurrent and complicated fistula. Because repeated anorectal procedures increase the risk of incontinence, a sphincter-preserving method is best used in the treatment of recurrent fistula, especially if a fistulotomy or fistulectomy was the first therapy.



An anal fistula is a tiny tunnel that forms around the anus between the end of the bowel and the skin. They're frequently caused by an infection around the anus, which results in a pus collection (abscess) in adjacent tissue.

Anal fistulas can cause a variety of unpleasant symptoms, including discomfort and skin irritation. In addition, they do go away on their own. In most anal fistula cases, surgery is advised.