Anal abscess is a cavity filled with pus near the anus or rectum.

Fistula is frequently the result of a previous or current anal abscess, seen in nearly 50% of patients with abscesses. The small glands inside the anus become infected leading to an abscess. The fistula is a tunnel/canal that forms under the skin that connects the infected gland to the abscess or skin. The fistula can occur with or without an abscess. Other diseases that can lead to fistulas are Crohn’s disease, radiation, trauma and malignancy.

How it occurs?

Abscess is due to infection of the anal glands. After the drainage of the abscess, a tunnel (fistula) may appear/persist, connecting the infected anal gland to the skin. This occurs in up to 50% of abscesses. If the opening on the skin heals when fistula is present, a recurrent abscess may develop.

Patients may have pain and swelling around the anus. Fever may also accompany.

Any tests?

CT scan or MRI may be helpful in the diagnosis of deeper abscesses or identification of the fistula tunnel for treatment types.

Treatment

The treatment of abscess is surgery. This is generally performed under general anesthesia. Antibiotics alone are not used for anal abscess treatment.

For fistula treatment, surgery is the mainstay. It could be performed in multiple steps depending on the fistula type. The surgery could be performed during the drainage of an abscess. Sometimes fistula appears after weeks to years following initial abscess drainage.

Despite proper treatment, both abscesses and fistulas can recur.

(Simplified from Patient Eduction Brochures of The American Society of Colon and Rectal Surgeons)