Anal fistula (or perianal fistula) is an abnormal connection between the last part of the intestine and the skin near the anus. It forms a narrow tunnel and can cause pain, redness, and bleeding from the anus.
In many cases, an anal fistula develops after an anal abscess. It can also be linked to inflammatory bowel conditions, such as Crohn’s disease, or to diverticulitis.
Treatment is almost always surgical. If an anal fistula is suspected, especially after a prior abscess, evaluation by a colorectal surgeon is recommended to confirm the diagnosis and begin appropriate treatment.
Anal fistula symptoms
The main symptoms of an anal fistula include:
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An opening in the skin around the anus;
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Redness or swelling in the area;
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Pain or discomfort with bowel movements, sitting, or walking;
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Drainage of pus, blood, or stool through the fistula opening;
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Fever.
Abdominal pain, diarrhea, loss of appetite, weight loss, and nausea may also occur if the fistula becomes infected or inflamed.
In these cases, evaluation by a colorectal surgeon is recommended to confirm a perianal fistula and select the most appropriate treatment.
Confirming a diagnosis
Diagnosis of a perianal or anal fistula is made by a colorectal surgeon based on symptoms, medical history, and a physical exam with inspection of the anal area.
The doctor may also order tests to assess the fistula tunnel and help identify the underlying cause, such as anoscopy, endoanal ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), or fistulography.
Possible causes
The main causes of a perianal or anal fistula include:
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Anal infection;
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Trauma to the anal area;
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Radiation therapy for anal cancer;
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Prostate inflammation caused by radiation therapy;
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Complicated vaginal delivery requiring an episiotomy;
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Inflammatory bowel diseases, such as Crohn’s disease or diverticulitis.
These conditions can raise the risk of developing a perianal or anal fistula. However, in most cases, it is related to a perianal abscess, which may occur due to obstruction or infection of anal glands.
Treatment options
Treatment for a perianal or anal fistula should be managed by a colorectal surgeon and is usually done with surgery to help prevent complications such as infection or fecal incontinence.
Anal fistula surgery
Surgery for a perianal or anal fistula, called an anal fistulectomy, is typically performed as follows:
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General anesthesia or epidural anesthesia is given;
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An anal probe is inserted to assess the fistula and determine whether there is a single tunnel or a complex fistula with multiple tunnels;
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An incision is made over the fistula to expose the tunnel between the intestine and the skin;
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Damaged tissue is removed from inside the fistula;
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A special thread is placed inside the fistula to help promote healing;
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Stitches are placed to close the wound.
Other surgical approaches may also be used, including grafts, plugs, and special suture threads called setons.
The best technique depends on the type of fistula and the condition that caused it, such as Crohn’s disease, where medications like infliximab may be needed before any surgery.
Recovery time
After surgery, a hospital stay of at least 24 hours is often needed. After discharge, rest for 2 to 3 days is usually recommended, along with taking the antibiotics and anti-inflammatory medications prescribed to help prevent infection and reduce pain and discomfort.
To lower the risk of infection, the area should be cleaned with water and a pH-neutral soap, and dressings should be changed as directed.
It is normal for the wound to bleed slightly during recovery, especially when wiping with toilet paper. However, if bleeding is heavy or there is sharp pain, follow-up with a doctor is important.
During the first week, a high-fiber, low-residue diet may be recommended, since stool buildup can increase pressure on the anal area and make healing more difficult.
Red flag symptoms
Immediate evaluation by a colorectal surgeon is recommended if any of the following occurs:
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Bleeding from the anus;
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Worsening pain, redness, or swelling;
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Fever above 100.4°F (38°C);
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Difficulty urinating.
Medical evaluation is also important if constipation occurs and does not improve after 3 days, even with the use of laxatives.