An anal abscess is an infected cavity filled with pus near the anus or rectum.  These typically are the result of an infection in the internal glands of the anus. Occasionally, an anal gland can be clogged with bacteria, fecal material or foreign matter 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 known as a fistula-in-ano) is frequently the result of a previous or current anal abscess. This occurs in up to 50% of patients with abscesses. Normal anatomy includes small glands just inside the anus. The fistula is the tunnel that forms under the skin and connects the clogged infected glands to an abscess. A fistula can be present with or without an abscess and may connect just to the skin of the buttocks near the anal opening.


Anal abscesses are classified by their location in relation to the muscles of the anus and rectum, and their treatment and complexity vary depending on their size and location.

Fistulas are also classified by their relationship to the muscles that allow us to control our stool. As well, these classifications are important in helping the surgeon make treatment decisions.


Anorectal pain, swelling, redness of the skin around the anus and fever are the most common symptoms of an abscess. Occasionally, rectal bleeding or urinary symptoms, such as trouble initiating a urinary stream or painful urination, may be present.

Patients with fistulas commonly have history of a previously drained anal abscess. Anorectal pain, drainage from the perianal skin, irritation of the perianal skin, and sometimes rectal bleeding, can be presenting symptoms of a fistula-in-ano.


Your colorectal surgeon will perform a careful history regarding anorectal symptoms and past medical history, followed by a physical examination. The physician will examine the external anus as well as performing a digital rectal exam.

When diagnosing an anal fistula, your surgeon will be looking for an external opening that drains pus, blood or stool.. Heaped up tissue at the external opening suggests a longstanding fistula. A digital rectal exam may produce pus from the external opening. Some fistulas will close spontaneously and the drainage may come and go, making them hard to identify at the time of the office visit.



American Society of Colorectal Surgeons