Anal Abscess (Anal Fistula or Fistula-in-ano)

Anal Abscess (Anal Fistula or Fistula-in-ano)

An anal abscess is an infected cavity filled with pus occurs around the anus or rectum. It is mostly the result of an acute infection in the internal glands of the anus. Sometimes obstructed and inflamed by bacteria, feces or foreign matter can clog an anal gland and tunnel into the tissue around the anus or rectum, where it may then collect in a cavity called an abscess.

An anal fistula (also commonly called fistula-in-ano) is mostly the result of a previous or current anal abscess. A fistula is an abnormal opening of the skin that connects a clogged gland inside the anal canal to the outside skin.

Symptoms of Anal Abscesses

Superficial anal abscesses are often associated with:

  • Pain, which is usually constant, throbbing, and worse when sitting down
  • Skin irritation around the anus, including swelling, redness, and tenderness
  • Discharge of pus
  • Constipation or pain associated with bowel movements

Deeper anal abscesses may also be associated with:

  • Fever
  • Chills
  • Malaise

Occasionally, fever is the only symptom of deep anal abscesses.

Can the abscess or fistula recur?

As previously mentioned, up to 50% of abscesses may re-present as another abscess/ frank fistula.

Causes of Anal Abscesses

These include:

  • An anal fissure, a tear in the anal canal, that becomes infected
  • Sexually transmitted infections
  • Blocked anal glands

Risk factors for anal abscesses include:

  • Colitis
  • Inflammatory bowel disease such as Crohn’s disease or ulcerative colitis
  • Diabetes
  • Diverticulitis
  • Pelvic inflammatory disease
  • Being the receptive partner in anal sex
  • Use of medications such as prednisone

Diagnosis of Anal Abscesses

A clinical assessment — including a digital rectal exam — is sufficient to diagnose an anal abscess. But some patients may require further tests to screen for:

  • inflammatory bowel disease
  • Diverticular disease
  • Rectal cancer
  • Sexually transmitted infections

In occasional cases, an examination may be done under anesthesia. The doctor may also ask for Endo-anal ultrasonography, a CT scan, or an MRI.

What are the treatments for an anal fistula?

Surgery is mostly recommended to cure an anal fistula. The surgery is performed by a colorectal surgeon. The objective of the surgery is a balance between getting rid of the fistula while protecting the anal sphincter muscles, which could cause incontinence if damaged.

Fistulas in which there is no or little sphincter muscle involved are treated with a Fistulotomy (the skin and muscle over the tunnel are cut open to convert it from a tunnel to an open groove). This procedure permits the fistula tract to heal from the bottom up.

In the case of complex fistula, the surgeon may have to place a special drain called a Seton, which remains in place for at least 6 weeks. After a seton is placed, a second operation is almost always performed:

  • A fistulotomy, or
  • An advancement flap procedure (the fistula is covered with a flap, or piece of tissue, taken from the rectum, like a trap door), or
  • A Ligation of the Intersphincteric Fistula Tract (LIFT) procedure (the skin above the fistula is opened up, the sphincter muscles are spread, and the fistula is tied off).

Fistula surgery is usually done on an outpatient basis, which means the patient can go home the same day. Patients who have very large or deep fistula tunnels may have to stay in the hospital after the surgery. Some fistulas may require several operations to get rid of the fistula.


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