Anal Abscess and Fistula

Anal Abscess and Fistula

An anal abscess is an infected cavity filled with pus near the anus or rectum. An anal fistula (also called fistula-in-ano) is a small tunnel that tracks from an opening inside the anal canal to an outside opening in the skin near the anus. An anal fistula often results from a previous or current anal abscess. As many as 50% of people with an abscess get a fistula. However, a fistula can also occur without an abscess.


Small glands just inside the anus are part of normal anatomy. If the glands in the anus become clogged, this may result in an infection. When the infection is serious, it often leads to an abscess. Bacteria, feces or foreign matter can also clog the anal glands and cause an abscess to form. Crohn’s disease, cancer, trauma, and radiation can increase the risk of infections and fistulas.


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 ill or tired, fever and chills. Patients with fistulas have similar symptoms, as well as drainage from an opening near the anus. A fistula is suspected if these symptoms tend to keep coming back in the same area every few weeks. 


Most anal abscesses or fistulas are diagnosed and managed based on clinical findings. Occasionally, imaging studies such as ultrasound, CT scan or MRI can help in the diagnosis and management of deeper abscesses and may be used to visualize the fistula tunnel.


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. Colorectal surgeons are experts in this area. For most patients, an abscess can be drained surgically through a simple procedure. An incision is made in the skin near the anus to drain the infection. This can be done at your surgeon’s office with local anesthetic or in an operating room under general anesthesia. Some patients with more severe disease may require multiple surgeries to take care of the problem. Patients who tend to get more severe infections due to diabetes or immunity problems may need to be hospitalized.

Surgery is nearly always needed to treat an anal fistula. In many patients, if the fistula is not too deep, a fistulotomy is performed. During this surgery, the fistula track will be opened to allow healing from the bottom up. The surgery may require dividing a small portion of the sphincter muscle. A large amount of the sphincter muscle is not divided as this could lead to problems with bowel control (fecal incontinence)

in some patients. If the fistula track does involve a large portion of the sphincter muscle, other more involved surgeries are done to treat the fistula without harming the sphincter muscle. More difficult cases may require multiple surgeries.

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 widespread cellulitis (a bacterial infection of the skin and tissues under the skin). Providing your physician with an accurate medical history and undergoing a physical exam are important steps in deciding if antibiotics are required. 

Post-Treatment Prognosis

Your surgeon will advise you on proper postsurgical care. Unfortunately, despite proper treatment and complete healing, an abscess or fistula can come back. 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 treat the problem.

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