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Anal Abscesses and Fistulas

An anal abscess is an infected cavity filled with pus around the anus.  Patients complain of a painful swelling around the anus, and along with fever. When the abscess ruptures through the skin around the anus – an anal fistula is formed.

An anal fistula is a small tunnel that connects an opening inside the anal canal to the skin near the anus. Most anal fistula form from a previous anal abscess though some are due to inflammatory bowel disease like Crohn’s or due to a cancer. This is why your doctor may recommend Colonoscopy to rule out these other conditions.


Most abscesses arise from infection of glands that open into the anal canal. There are usually 12 – 15 glands in normal people. When these gland get infected, pus forms resulting in an anal abscess. A patient with an abscess may have pain, redness or swelling in the area around the anal area or canal. Other common signs include feeling unwell, fever and chills. When the pus drains through the skin, the pain usually subsides but may recur if the infection builds up again. Patients with fistulas may have pain and fever as well as recurrent drainage from an opening near the anus. These symptoms tend to keep coming back in the same area every few weeks. 


Most anal abscesses or fistulas can be diagnosed and managed based on a simple clinical examination. Occasionally imaging studies such as endoanal ultrasound or an MRI scan can be helpful in the diagnosis and management of complex fistulas and may be used to visualize the fistula track.


Antibiotics alone are not effective in treating abscesses or fistula. Antibiotics may be needed, in addition to surgery, if a patient has immunity issues, specific heart valve conditions or Fournier’s gangrene (a bacterial infection of the skin and tissues under the skin).

The treatment of an abscess is surgical drainage under most circumstances. It is important that your surgeon be very familiar with treating abscesses and fistula. For most patients, abscess drainage is a simple procedure. An incision is made in the skin near the anus to allow the pus to escape. This is usually done in an operating theatre under general anesthesia as the area is usually exquisitely tender. Some patients can get more severe infections if their immunity is compromised like in diabetes, and can develop gangrene around the area which can become life threatening.

Surgery is nearly always needed to treat an anal fistula. In many patients, if the fistula track is superficial, a fistulotomy is performed. During this procedure, the fistula track is opened and the infected tissue cleared to allow healing from the bottom up. The success of the procedure depends upon correctly identifying the internal opening and dealing with it. If the internal opening is not dealt with, the fistula will recur and further surgery will be required to treat the problem.

The surgery usually requires cutting a small portion of the sphincter muscle. If a large amount of the sphincter muscle is divided this could lead to loss of bowel control (fecal incontinence). If the fistula track involves a large portion of the sphincter muscle, other more complicated procedures like a LIFT (LIgation of the Fistula Tract) or an Anal Advancement Flap may be required to treat the fistula without damaging the sphincter muscle.   

Occasionally, your doctor may place a Seton (a string) through the fistula tract to drain it and control the infection before performing another procedure to treat the fistula. This is commonly used in patients with recurrent fistulas who are suffering from Crohn’s disease as they are at high risk of incontinence from repeated anal surgery.


Most patients experience little pain following the operation. There will be discharge from the anal wound which can be easily managed by flushing the area with tap water. It isn’t necessary to apply any special antiseptic solutions or creams to the wound as these often irritate the tissues and may cause other problems. Your doctor may prescribe some antibiotics and pain killers in the immediate postoperative period.

Unfortunately, despite the best efforts of your doctor and appropriate treatment an abscess or a fistula can recur. If an abscess comes back, it suggests that perhaps there is a fistula that needs to be treated. If a fistula comes back, additional surgery will likely be required to identify the internal opening and treat the problem.