OVERVIEW

What is an anal fistula?

An anal fistula, short for anorectal fistula, is a chronic granulomatous tract between the skin around the anus and the rectum/anal canal. Simply put, it occurs when the rectum or anal canal becomes abnormally connected to the surrounding skin due to various causes.

An anal fistula typically consists of three parts: the internal opening, the fistula tract, and the external opening. The internal opening is located inside the anal canal, usually as a single opening, while the external opening(s) appear on the perianal skin, which may be one or multiple. The external opening continuously discharges pus, blood, or even feces. Anal fistulas often persist and recur repeatedly, with complex anal fistulas being one of the challenging conditions in colorectal surgery ^[1].

A minority of anal fistulas may only have an internal opening and a fistula tract, representing a special type of the condition.

Is anal fistula common?

Yes. Anal fistula is one of the common colorectal surgical diseases.

Who is more prone to anal fistula?

People of any age can develop it, but it is more common in young and middle-aged males ^[1].

Can anal fistula become malignant?

In most cases, anal fistulas do not turn malignant. However, long-standing, unhealed fistulas may develop into rectal cancer ^[2].

What are the types of anal fistulas?

1. Based on etiology, they can be divided into:
   • Specific anal fistulas: Caused by conditions like Crohn's disease, tuberculosis, or lymphogranuloma. These tend to recur if the underlying disease is not controlled.
   • Non-specific anal fistulas: Result from general pyogenic infections. These respond well to treatment and are less likely to recur.
2. Based on the presence of openings:
   • Single internal opening fistula (blind fistula): Only has an internal opening and a tract, without an external opening.
   • Internal-external fistula: Has both internal and external openings, with the tract connecting them.
3. Based on involvement of the anorectal ring:
   • High anal fistula: Located above the anorectal ring.
   • Low anal fistula: Located below the anorectal ring.
     Note: The anorectal ring is a muscular structure encircling the anal canal, crucial for maintaining continence and defecation. Damage to these muscles may lead to fecal incontinence.
4. Based on the shape of the fistula tract:
   • Straight fistula: The tract is linear.
   • Curved fistula: The tract is bent.
   • Horseshoe fistula: External openings on both sides of the anus, with a horseshoe-shaped tract.
5. Based on the relationship with the anal sphincters (internal and external sphincters), classified as (Parks classification):
   • Intersphincteric fistula: Passes between the internal and external sphincters.
   • Transsphincteric fistula: Traverses both the internal and deep/external sphincters.
   • Suprasphincteric fistula: Extends above the levator ani muscle before descending to the skin.
   • Extrasphincteric fistula: Passes through the levator ani, directly connecting to the rectum.
     Note: Parks classification is widely used by doctors to guide surgical planning ^[3].
6. Based on the number of openings and tracts:
   • Simple anal fistula: Single tract.
   • Complex anal fistula: Multiple openings and tracts ^[4].

SYMPTOMS

What are the manifestations of anal fistula?

The main manifestations of anal fistula include continuous or intermittent discharge of pus, bloody or mucus-like secretions, and even fecal matter from the external opening. Persistent irritation from these secretions can lead to dampness, itching, and eczema around the anal skin.

When the external opening heals, pus trapped in the fistula may cause noticeable swelling, pain around the anus, and even systemic infection symptoms such as fever, chills, and fatigue. These symptoms may temporarily improve after the abscess ruptures, but the cycle of anal fistula → abscess formation → anal fistula may recur repeatedly, creating a vicious cycle.

During examination, doctors may observe single or multiple external openings on the perianal skin, with pus or bloody discharge upon pressure ^[1].

What serious complications can anal fistula cause?

If left untreated, persistent infection in anal fistula may spread to surrounding tissues, leading to complications such as rectovaginal fistula (only in females) and acute necrotizing fasciitis of the perineum. In severe cases, it may cause sepsis, septic shock, or even death ^[1].

Additionally, recurrent anal fistula may increase the risk of malignant transformation ^[2].

CAUSES

What are the causes of anal fistula?

1. Perianal and perirectal abscesses: Over 90% of anal fistulas develop from "perianal and perirectal abscesses" ^[1]. When the anal crypt glands in the anal canal become infected by bacteria, they may suppurate, and the accumulated pus forms a perianal or perirectal abscess. If not treated promptly, the abscess may rupture, discharge pus, and form a fistula, leading to the development of an anal fistula ^[1].
   If the external opening of the fistula heals, preventing pus from draining, another abscess may form, creating a vicious cycle. If the infection spreads further, it may cause severe systemic infection. Chronic anal fistulas may develop multiple external openings and branch tracts, which can interconnect, forming complex anal fistulas.

2. Other diseases: Crohn's disease, lymphogranuloma venereum, tuberculosis, rectal tumors, anal canal trauma, etc., are also common causes of anal fistulas, accounting for about 10% of cases ^[1].

Why do anal fistulas develop multiple external openings?

After an abscess ruptures, the discharged pus and bacteria may spread to adjacent areas, forming new abscesses. When these abscesses rupture, new external openings may form. This cycle repeats, leading to the formation of multiple external openings ^[1].

DIAGNOSIS

What tests do anal fistula patients need to undergo for accurate diagnosis?

1. Digital rectal examination: During the consultation, the doctor will examine the anus and perform a "digital rectal examination." For this procedure, the doctor or nurse wears gloves, lubricates the fingertip (usually the index finger of the right hand) with petroleum jelly, and inserts it into the patient's anus and rectum to check for lumps or other abnormalities.
2. Anoscopy: The doctor inserts an anoscope into the anus to examine the internal condition, checking whether the anal sinuses are congested, depressed, or discharging pus. Such findings may indicate the location of the internal opening of the fistula.
3. Probe examination: If an anal fistula is suspected, the doctor may use a thin, flexible probe inserted through the external opening to gently explore the fistula tract, aiding in diagnosis.
4. Methylene blue injection: A white gauze strip is first placed in the anus, and 5% methylene blue is injected into the fistula tract through the external opening. The stained area on the gauze helps determine the location of the internal opening.
5. Fistulography: For high or complex fistulas, fistulography with iodized oil may be required. The general procedure involves: positioning under X-ray, injecting the contrast agent iodized oil into the fistula tract through a catheter from the external opening, observing the distribution and path of the oil, and taking X-ray images from multiple angles to assess the condition ^[1].
6. Endoanal ultrasound: An ultrasound probe is inserted into the anal canal to determine the size and depth of an abscess. This is a commonly used, quick, and non-invasive imaging method, though its accuracy is slightly lower than that of MRI.
7. Magnetic resonance imaging (MRI): Currently one of the most effective diagnostic tools for anal fistulas. It helps clarify the type of fistula before surgery and rules out other potential causes in recurrent cases ^[3].

TREATMENT

Which department should be consulted for anal fistula?

This condition should be treated in the general surgery or colorectal surgery department of a formal medical institution.

How should anal fistula be treated?

Anal fistula is difficult to heal on its own and mostly requires surgical treatment. There are many surgical methods, such as fistulotomy, fistulectomy, and seton placement.

1. Fistulotomy: The anal fistula is cut open, directly exposing the external opening, fistula tract, and internal opening, allowing the wound to heal through granulation tissue growth. Commonly used for treating low anal fistulas.
2. Fistulectomy: The entire fistula tract is removed, cutting into healthy tissue without suturing, allowing the surgical wound to heal naturally. Commonly used for treating simple anal fistulas.
3. Seton placement: A rubber band or chemically corrosive thread is used to apply mechanical pressure, slowly cutting through the anal fistula. The seton falls off after about two weeks, and the fistula heals. Suitable for high anal fistulas, elderly patients with a history of anal surgery, those with poor anal sphincter function, or cases where the fistula tract's relationship with the sphincter is unclear ^[3].

The choice of surgical method depends on whether and how much the anal sphincter is involved. Some complex anal fistula cases may require multiple procedures or staged surgeries to achieve a cure.

Regardless of the chosen method, the principle is to effectively treat the anal fistula while minimizing damage to the anal sphincter to avoid postoperative fecal incontinence ^[1].

Can anal fistula surgery be performed at any time?

No, surgery should be performed only when the fistula tract has matured. Fistula maturation refers to the tract becoming dense, free of acute inflammation, and without redness, swelling, or pain in the surrounding tissues. A professional doctor must assess whether the fistula has matured, and the surgery timing should be determined after consultation.

Why is anal fistula surgery not sutured?

Leaving the wound unsutured allows pus and tissue fluids to drain promptly, promoting healthy tissue growth and wound healing. Suturing may create a dead space where pus cannot drain, leading to delayed healing.

What additional treatments are needed after anal fistula surgery?

Postoperative patients require nutritional support, hydration, electrolyte replenishment, and antibiotics (e.g., gentamicin, penicillin) to control infection. Additionally, patients who undergo fistulectomy or fistulotomy should have regular wound dressing changes until the wound heals ^[1].

What complications may arise after anal fistula surgery?

1. Fecal incontinence: Temporary fecal incontinence due to pain or acute inflammation is common shortly after surgery and usually resolves within 2–3 days. Permanent fecal incontinence is rare and often results from damage to the rectal-anal ring, requiring surgical or other treatments.
2. Rectal prolapse: Postoperative scarring may lead to rectal mucosal prolapse, which typically requires symptomatic treatment, such as using an abdominal or T-band to reposition the prolapsed rectum.
3. Anal stenosis: Postoperative narrowing may cause difficulty in defecation or thinner stools. If stenosis occurs, anal dilation therapy is needed after the surgical wound heals. This involves using fingers or specialized instruments like dilators under medical supervision ^[4].

Is anal fistula prone to recurrence?

Some patients may experience recurrence after surgery, particularly those with high complex fistulas, horseshoe fistulas, or specific fistulas (e.g., caused by Crohn's disease or intestinal tuberculosis). Recurrence is associated with high fistula location, internal openings in the rectum, multiple internal openings, or failure to locate the internal opening during surgery ^[1].

DIET & LIFESTYLE

What should patients pay attention to in their daily life after being discharged from anal fistula surgery?

The following aspects should be noted:

1. Exercise: Patients should engage in activities based on their tolerance. Avoid weight-bearing, running, jumping, or other strenuous exercises within two weeks after surgery, and refrain from using ring-shaped cushions within three months post-operation.
2. Diet: Consume a high-fiber diet for the first two weeks after surgery and drink at least two liters of water daily to prevent constipation.
3. Perianal hygiene: Take warm sitz baths 2-3 times a day for 15 minutes each time within one month after surgery. Use soft wet wipes instead of toilet paper to clean the anus after each bowel movement and keep the perianal area dry.

Is sitz bath effective for treating anal fistula?

A sitz bath involves sitting in a shallow basin of warm water for cleansing. It helps maintain skin cleanliness and relieve local pain but has minimal therapeutic effect on anal fistula.

PREVENTION

Can Anal Fistula Be Prevented?

Anal fistulas are mostly caused by perianal or perirectal abscesses, so actively treating such abscesses can effectively prevent their occurrence. Prevention can be approached from the following aspects:

1. Rest adequately: Ensure sufficient sleep, avoid staying up late, and prevent weakened immunity;
2. Maintain good bowel habits: Keep stools regular to avoid constipation or diarrhea;
3. Practice perianal hygiene: Clean the perianal area daily with warm water and change underwear frequently;
4. Exercise regularly: Avoid prolonged sitting and choose suitable physical activities;
5. Seek medical attention promptly: Consult a doctor if symptoms like perianal pus discharge, itching, or eczema occur.