Anal fistula

An anal fistula is a small, abnormal tunnel that connects the anal canal or rectum to the skin around the anus. Most develop after an anal abscess — a pocket of pus — that drained incompletely and left a persistent tract. Fistulas do not heal on their own and almost always need surgery.

Symptoms

• Persistent drainage of pus, blood, or faecal matter from a small opening in the skin near the anus
• Pain, especially when sitting or passing stools
• Swelling or a lump near the anus
• Skin irritation around the opening
• Fever and general illness during an active abscess
• Sometimes painful bowel movements

Causes

• Anal abscess — the most common cause
• Crohn's disease — fistulas are common in Crohn's, often complex
• Tuberculosis — TB fistulas are relatively more common in India than in Western populations; distinguishing TB from Crohn's matters for treatment
• Trauma or previous surgery
• Radiation therapy, hidradenitis suppurativa, rarely cancer

Diagnosis

A doctor can often diagnose an anal fistula on examination. Further tests may include:

• Examination under anaesthesia — allows the surgeon to trace the tract
• MRI of the pelvis — maps complex or recurrent fistulas
• Endoanal ultrasound
• Investigations for underlying conditions (Crohn's, TB)

Treatment

Surgery is the mainstay. The right procedure depends on the fistula's path relative to the sphincter muscles:

• Fistulotomy — cutting open the tract so it heals as a flat scar. Works well for simple low fistulas.
• Seton placement — a thread or drain passed through the tract to drain infection and, over time, allow gradual healing. Used for complex fistulas to protect continence.
• Advancement flap surgery — covering the internal opening with a flap of healthy tissue
• LIFT procedure (ligation of the intersphincteric fistula tract)
• VAAFT (video-assisted anal fistula treatment) and fibrin glue / plugs — minimally invasive options with variable success
• For Crohn's-related or TB-related fistulas — treating the underlying disease is essential alongside surgery

A key surgical challenge is balancing complete removal of the fistula with preserving the sphincter muscles (for continence). Colorectal surgeons or general surgeons experienced with anorectal conditions should handle complex cases.