Will antibiotics clear an anal abscess?

Antibiotics alone do not usually clear an abscess, because the pus is walled off and the medicine cannot reach it. The abscess generally needs to be drained. Antibiotics may be given in addition if there is infection in the surrounding tissue or if you have other medical conditions.

Does every abscess lead to a fistula?

No. Roughly 25% to 30% of people who have an anal abscess go on to develop a fistula. Many heal completely after the abscess is drained.

Will fistula surgery affect my continence?

Protecting the sphincter muscle is a central consideration in planning fistula surgery, The path of the tunnel is mapped carefully beforehand. Some procedures carry a small risk to continence and others avoid cutting muscle. Dr Chen will discuss the specific risk for your fistula before you begin treatment.

Is anal fistula treatment claimable?

MediSave can be used for approved day surgery, meaning a procedure on MOH’s Table of Surgical Procedures where you are admitted and discharged the same day, and an Integrated Shield plan may cover part of the cost. Your own eligibility is worth confirming before the procedure.

Patient guide

Anal Fistula and Abscess

An anal abscess is a collection of pus that forms when a small gland inside the anus becomes blocked and infected. It usually needs to be drained. In about a third of cases a fistula follows: a small tunnel between the gland and the skin that rarely heals on its own and is treated surgically.

Medically reviewed by Dr Chen Chung Ming, FRCS (Edin), FAMS · Colorectal Surgeon

BUILD NOTE: this page was drafted for the refresh and has NOT yet been read by Dr Chen. Clinical content, and the medical-review byline above, must be confirmed by him before the domain cutover.

About Anal Abscess and Fistula

Small glands sit just inside the anus. If one becomes blocked and infected, pus collects and forms an abscess. About 90% of anal abscesses start this way, with infection of one of those glands.¹ An abscess is usually painful and needs to be drained rather than treated with antibiotics alone.

After an abscess has been drained or has burst on its own, a small tunnel can remain between the gland inside the anus and the skin outside. That tunnel is a fistula: an abnormal tract running between the skin near the anus and the anal canal, and occasionally the lower rectum.¹ Roughly 25% to 30% of people who have an anal abscess go on to develop one.¹ A fistula rarely heals without surgery.

Symptoms

An abscess usually causes:

Constant throbbing pain near the anus that is worse when sitting
A tender, red, swollen lump
Fever or feeling generally unwell

A fistula usually causes:

Ongoing discharge of pus, blood or fluid that stains underwear
Irritation or itching of the surrounding skin
Repeated episodes of swelling and pain that resolve and return

Contributing Factors

Most abscesses and fistulas arise from a blocked anal gland with no clear underlying cause. Some are associated with:

Crohn’s disease or other inflammatory bowel disease
Previous surgery or injury in the area
Diabetes or a weakened immune system
Certain infections, such as tuberculosis

How It Is Diagnosed

Diagnosis starts with your symptoms and an examination of the area. An abscess is often clear on examination. For a fistula, the aim is to map the path of the tunnel and how much of the anal sphincter muscle it crosses. This determines which operation is appropriate. The investigations used include anoscopy, sigmoidoscopy, colonoscopy, endoanal ultrasound, fistulography, MRI and anal manometry. Endoanal ultrasound gives a full picture of the tract, and MRI is used for difficult or recurrent fistulas.¹ An examination under anaesthesia may also be arranged to map the tract accurately.

Treatment

An abscess is treated by draining the pus, usually as a day procedure under anaesthesia. Antibiotics alone do not clear an abscess, although they may be given as well if there is surrounding infection.

A fistula is treated surgically. The choice depends on how much sphincter muscle the tunnel involves, since protecting continence is a priority:

Fistulotomy opens the tunnel so it heals from the base. It is the most common procedure for a simple fistula, where the tunnel involves little or none of the sphincter muscle.¹
A seton is a soft thread passed through the tunnel to keep it draining. It is used where the tunnel crosses a significant amount of sphincter muscle, so laying the tract open would put continence at risk.¹ It may be the only treatment needed, or a first step before a further operation.
LIFT, or ligation of the intersphincteric fistula tract, closes the tunnel between the sphincter muscles and avoids cutting them.
An advancement flap is used when laying the tract open is not appropriate. The internal opening is removed and closed with a flap of healthy tissue from inside the rectum.¹
Fibrin glue and the bioprosthetic plug avoid cutting muscle altogether. The glue is injected along the tunnel to seal it. The plug is a small cone of absorbable material placed in the tunnel to block it off. Neither puts continence at risk, but healing rates are less reliable than with the other methods, so they are not usually the first choice.¹

Fistulas are grouped as simple or complex. A simple fistula has a single short tract that crosses little sphincter muscle, with both openings close to the anus, no side branches or abscess cavity and no other underlying condition. Anything else, including a fistula that persists or recurs despite treatment, counts as complex.¹

After fistula surgery the routine is a high-fibre diet with plenty of fluid, stool bulking agents and softeners, pain relief, soaking the area in warm water several times a day to keep it clean, and a daily wound dressing at a nearby clinic for the first week.¹

Dr Chen will explain which approach suits your fistula, and the balance of healing and continence for each, before you decide. See also fissure and fistula surgery.

When to See a Doctor

See a doctor promptly if you have increasing pain and swelling near the anus, particularly with a fever, as an abscess usually needs draining without delay. Persistent discharge or a lump that keeps returning should also be assessed rather than managed at home.