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Anorectal Abscess and Anal Fistula

Medically reviewed by Last updated on May 27, 2022.

What is an anorectal abscess and anal fistula?

Anorectal abscess and anal fistula are conditions that often occur together. An anal fistula is an abnormal tunnel from the anus or rectum to the skin or another organ. It usually forms when there is an anorectal abscess. An anorectal abscess is a collection of pus from an infection in the anus or rectum.

What causes an anorectal abscess and anal fistula?

You might have been born with an anal fistula. An anorectal abscess is commonly caused by different kinds of bacteria. Bacteria may enter the skin through a tear or plugged glands in the anus, usually from constipation or trauma. Rectal enemas to help empty your bowel may also cause a tear. Conditions that weaken your immune system, such as cancer, may increase your risk. An anal fistula may form from an abscess that has ruptured or has been drained. It may occur in conditions affecting the intestine and after injury.

What are the signs and symptoms of an anorectal abscess?

  • A hard, red, tender lump, or swelling in the area near the opening of the anus
  • Fever
  • Pain in the lower abdomen or anus
  • Pain during a bowel movement

What are the signs and symptoms of an anal fistula?

  • Discharge of pus or blood from the anus
  • Pain around the anus that may be relieved as the discharge increases
  • Pain during a bowel movement

How are an anorectal abscess and anal fistula diagnosed?

Your healthcare provider will look for any swelling, redness, or opening of a fistula in your anal area. Your healthcare provider may also check your rectum by inserting a gloved finger into your anus. He may also try to feel abnormal tissue. You may need any of the following tests:

  • Anoscopy: A clear lotion is put onto a short plastic or metal tube. The tube is then gently pushed into your anus and up the rectum. Your healthcare provider can also take samples of bowel movement to be sent to a lab for tests.
  • Fistulography: This is a type of x-ray that shows how deep the fistula is and where it started. A probe or catheter (tube) will be inserted into the opening of the fistula. A dye may be put into the fistula tract (pathway) to make it show up better on the x-ray.
  • MRI: This machine uses magnetic waves to look at your intestine. This will help healthcare providers check the length of the fistula. You will need to lie still during an MRI. Never enter the MRI room with any metal objects. This can cause serious injury.
  • Sigmoidoscopy: A sigmoidoscopy test looks for changes in your intestinal (bowel) wall that may be caused by a disease or condition. This test may also help find the cause of bleeding or pain. A long, thin tube with a tiny camera on the end is put through your anus into your rectum (rear-end). It also goes to the part of your intestine called the sigmoid. Healthcare providers will look for problems in your rectum and lower colon. A small amount of tissue may be taken from the intestine wall and sent for tests. Follow your healthcare provider's instructions for what to do before, during and after the test.
  • Transanal ultrasound: This is a test that looks inside your rectum to check for a large fistula. A small tube is placed into your anus. Sound waves are used to show pictures of your organs and tissues on a monitor. Hydrogen peroxide may be injected into the tract of the fistula before the test.

How are an anorectal abscess and anal fistula treated?

  • Medicines:
    • Antibiotics: This medicine is given to help treat or prevent an infection caused by bacteria.
    • Pain medicine: This medicine may be given to ease your pain.
    • Stool softeners: This medicine makes it easier for you to have a bowel movement. You may need this medicine to treat or prevent constipation.
  • Procedures:
    • Incision and drainage: Your healthcare provider may break the abscess to drain the pus. This is done by making an incision in or near the affected area. A catheter (tube) may be put in place for some time to allow the remaining pus to drain.
    • Surgery: You may need to have surgery to drain a very large abscess. If you have a fistula, surgery may be done to open and clean up the fistula tract. This may be left open until it heals on its own.

What are the risks of an anorectal abscess or anal fissure?

Surgery used to treat an anorectal abscess or anal fistula may cause you to bleed too much. You may get another infection from the surgery. A fistula may form after treatment of the abscess. Surgery to treat a fistula may injure other body parts, including the sphincter muscles. This may lead to problems with controlling bowel movements. If left untreated, the infection may spread to other parts of your body and make you very sick. If an abscess is not treated, it may also return.

When should I contact my healthcare provider?

Contact your healthcare provider if:

  • You have a fever.
  • You have increased pain, redness, swelling, drainage, or bleeding in the area.
  • You have questions or concerns about your condition or care.

When should I seek immediate care?

Seek care immediately or call 911 if:

  • You have blood, pus, or a bad smelling discharge coming from your anus or vagina.
  • You have a very bad pain in your rectum or vagina that does not go away.
  • You have trouble breathing all of a sudden.
  • Your stools are black or have blood on them.

Care Agreement

You have the right to help plan your care. Learn about your health condition and how it may be treated. Discuss treatment options with your healthcare providers to decide what care you want to receive. You always have the right to refuse treatment. The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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