Perianal Abscess & Anal Fistula
Causes, symptoms and treatment. A perianal abscess is an infected cavity of pus near the anus/rectum. An anal fistula is usually a tunnel (track) that forms after an abscess and connects the anal canal to the skin.
Rapid pain, swelling near the anus, fever/chills and feeling unwell.
Persistent discharge from an opening near the anus; irritation and intermittent pain.
Anal abscess & anal fistula: causes, symptoms and treatment
What is an anal abscess or fistula?
A perianal abscess is an infected cavity filled with pus near the anus or rectum and often develops quickly, causing pain and swelling. An anal fistula is usually the result of a previous abscess and forms a track between the anal canal and the skin.
What causes a perianal abscess?
Small glands just inside the anus can become blocked. If infected, an abscess can develop. Certain conditions (such as colitis or other inflammation of the intestine) can make infection more likely.
What causes a fistula in ano?
A fistula often forms when an abscess bursts or has not fully resolved after drainage, leaving a tunnel from the anal gland to the skin. If the outer opening closes, a recurrent abscess may develop. Fistula can also be associated with Crohn’s disease or ulcerative colitis, and occurs more commonly in men.
What are the symptoms?
- Abscess: pain and swelling around the anus, fatigue, fever/chills, feeling unwell.
- Fistula: discharge of pus from an opening near the anus (sometimes relieves pain), irritation, discomfort, occasional bleeding, fever/malaise.
Seek urgent assessment if you have severe anal pain with fever/chills or a rapidly enlarging swelling.
Does an abscess always become a fistula? About one third do not recur, one third recur as abscess, and around one third to one half can go on to develop a fistula.
How is it diagnosed?
Diagnosis is often made by careful clinical examination. Sometimes scans (MRI/CT/ultrasound) are needed, or an examination under anaesthetic to fully assess the anal region.
How is a perianal abscess treated?
Some abscesses burst and drain spontaneously. New abscesses often require drainage via a small incision near the anus to release pus and relieve pressure. Superficial abscesses may be drained under local anaesthetic, but many are drained under general anaesthetic (often day case/overnight). Larger abscesses or people prone to severe infection (e.g., diabetes or reduced immunity) may need a longer stay.
How can a fistula be treated?
Surgery is usually needed to cure an anal fistula and is best performed by a specialist colorectal surgeon. Surgery may be staged. A common first step is inserting a seton (a stitch/drain through the tract) to allow ongoing drainage, with definitive surgery often 6–8 weeks later.
Common operations include:
- Fistulotomy: opening the fistula tract to heal into a flattened scar (often 1–2 months).
- Seton suture/drain: left in place to drain or sometimes tightened gradually.
- Rectal advancement flap: for complex fistula or high incontinence risk; reported effectiveness ~70%.
- Fibrin glue: the only non-surgical option described; simple but poor long-term results.
- Bioprosthetic plug: plug to block internal opening; early success reported, long-term uncertain.
- LIFT procedure: ligation of the intersphincteric fistula tract (selected cases).
Key consideration: Your surgeon chooses the safest option based on how much sphincter muscle is involved (to minimise incontinence risk), Crohn’s disease, and (in women) childbirth plans.
Recovery & aftercare
Discomfort after fistula surgery is often mild to moderate for about a week and controlled with pain relief. Soaking the area in warm water may help. Stool softeners (e.g., lactulose) or a bulk fibre laxative may be recommended. It may be necessary to wear a gauze pad to absorb drainage. Bowel movements generally do not affect healing.
Recurrence and long-term effects
If properly healed, the problem usually does not return, but following specialist advice helps reduce recurrence. Potential complications include infection, bowel incontinence and recurrence of the fistula. After fistulotomy, recurrence risk is reported around 21% (varies by procedure). If you already have weak anal sphincter muscles, bowel control issues can worsen after surgery—discuss any concerns with your surgeon.
Can I be treated at the Glasgow Colorectal Centre?
Yes—Glasgow Colorectal Centre surgeons are experienced in managing patients with perianal abscesses and fistulas.