Anal Fistula

An anal fistula is an abnormal tunnel that forms between the inside of the anal canal and the skin around the anus. Most anal fistulas develop as a result of a previous anal abscess.

Inside the anal canal are small glands which can occasionally become blocked and infected. This infection may lead to an abscess — a painful collection of pus near the anus. When the abscess drains, either spontaneously or surgically, a persistent tunnel can remain connecting the infected gland to the skin. This tunnel is known as an anal fistula.

Anal fistulas usually do not heal on their own and commonly require surgery for definitive treatment.

Symptoms

Common symptoms of an anal fistula include:

• Persistent or intermittent discharge near the anus

• Recurrent swelling or abscess formation

• Pain around the anus

• Irritation of the surrounding skin

• Bleeding

• Discomfort with sitting or bowel motions

• A small opening or lump near the anus

Some patients notice cyclical symptoms where swelling and pain improve temporarily after drainage, before recurring again.

Causes

More than 90% of anal fistulas are related to previous infection of an anal gland (cryptoglandular infection). Other less common causes include:

• Crohn's disease

• Previous anorectal surgery or trauma

• Radiation therapy

• Infection

• Obstetric injury

• Rarely, cancer

Classification

Anal fistulas are classified according to their relationship to the anal sphincter muscles. Some fistulas are simple and involve only a small amount of sphincter muscle, while others are more complex and involve a larger portion of the continence mechanism.

Determining the course of the fistula is important in planning treatment while preserving bowel control.

Assessment

Diagnosis is usually based on symptoms and examination. An external opening on the skin is often visible.

Further assessment may include:

• Digital rectal examination

• Anoscopy

• Examination under anaesthetic

• MRI scan or endoanal ultrasound for complex fistulas

Imaging is particularly useful for recurrent or complex fistulas and for fistulas associated with Crohn’s disease.

Treatment

Surgery is usually required to treat anal fistulas. The aim of treatment is to eliminate the fistula while preserving anal sphincter function and continence.

Treatment options depend on the complexity and location of the fistula and may include:

• Fistulotomy

• Seton placement

• Advancement flap procedures

• LIFT procedure (ligation of intersphincteric fistula tract)

• Other sphincter-preserving techniques

Simple fistulas are often highly treatable with surgery, while more complex fistulas may require staged or multiple procedures.

Patients with fistulas related to Crohn’s disease often require combined medical and surgical management.