What is an anal fistula?
A fistula often starts when an infected anal gland forms an abscess. After the abscess drains, a tunnel can remain and cause repeated swelling, pain, pus or blood from an opening near the anus. The opening may seem to heal and then reopen.
The key question is how much of the anal sphincter muscle the tract crosses. A low simple fistula and a high branching fistula need different operations.
What are the symptoms of an anal fistula?
Common symptoms are:
- Pus, blood or fluid leaking from a small opening near the anus
- Painful swellings or boils near the anus that keep coming back
- Throbbing pain that eases when the swelling drains
- An opening that seems to heal and then reopens
- Fever with a painful swelling, which may be an abscess and needs urgent care
How is an anal fistula diagnosed?
Examination looks for openings, scars, active infection and existing continence. MRI of the pelvis is especially useful for a recurrent, branching or high fistula. Examination under anaesthesia may be needed to map and drain the tract safely.
Bowel symptoms or an unusual pattern may require tests for Crohn's disease, tuberculosis or another cause.
When does an anal fistula need surgery?
A persistent anal fistula requires definitive surgical intervention because spontaneous, permanent closure is rare. Any active acute abscess is drained promptly to eliminate infection. The surgical strategy is determined by the tract's height, branching anatomy, previous interventions, baseline continence and muscle integrity.
Treatment is matched to the fistula: simple, low tunnels are treated differently from complex tunnels that cross more of the sphincter muscle, with bowel control a priority.
How is an anal fistula treated, and what are the risks?
Two operations are offered, chosen by how much sphincter (control) muscle the fistula crosses: Fistulotomy and Fistulotomy with Sphincter Repair.
For simple, low fistulas that cross little or no muscle, fistulotomy opens and cleans the tunnel so it heals from the base, while protecting bowel control.
For higher or complex tunnels that cross more of the muscle, fistulotomy with sphincter repair is performed. The tunnel is opened and cleaned completely, and the divided muscle is stitched back together in the same operation to restore the muscle ring. This is also called fistulotomy with primary sphincteroplasty (FIPS). Your bowel control and the path of the fistula are checked before surgery, sometimes with an MRI scan.
Risks include wound discomfort, minor bleeding, slow healing, a change in bowel control and the fistula coming back.
Recovery after fistula surgery
Sit in a warm sitz bath (a tub of plain warm water) for 10–15 minutes, 2–3 times a day and after passing stool, and wash gently, so the wound heals cleanly from the base. After fistulotomy with sphincter repair, avoid hard stools and straining to protect the muscle repair while it heals. Stool softeners, high-fibre food and enough water keep motions smooth.
Urgent medical advice should be sought for fever, escalating pain, urinary retention, foul-smelling discharge or unexpected bleeding. Follow-up visits continue until the wound has fully healed, and any change in bowel control is checked.
When to seek urgent care
A painful swelling with fever, chills, spreading redness, difficulty passing urine or feeling very unwell may be an anal abscess and needs urgent drainage assessment. Antibiotics alone do not cure a drainable abscess.