Anal fistula or fistula-in-ano involves the formation of a hollow cavity, lined with granulation tissue. It connects to a primary opening inside the anal canal. These arise due to cryptogranular infections that lead to perirectal abscess formations, which is an acute inflammatory event. An inflammatory tract forms between the skin and the anal canal.

Classification
The Parks classification system relative to the sphincter muscle categorizes anal fistulas as follows:

• Intersphincteric fistulas: they track along the intersphincteric plane and end in the perianal skin
• Extrasphincteric fistulas: start in the high canal; encircles all of the sphincter and ends in the skin of the buttocks
• Transsphinteric fistulas: run across the external sphincter and go into the ischiorectal fossa ending in the buttocks’ skin
• Suprasphincteric fistulas: encircle the complete sphincter and run through the anal crypt

There are two types of anal fistulas: Simple and complex.

• Simple anal fistulas are inclusive of intersphincteric and transsphincteric fistulas
• Complex anal fistulas are inclusive of suprasphincteric fistulas, horseshoe fistulas, extrasphincteric fistulas, and IBD related fistulas.

Causes

• Infected anal crypts with formation of an abscess that ruptures
• Draining of ischiorectal abscesses into fistulous tracts
• Crohn’s disease or any inflammatory bowel disease
• Diverticulitis
• Reaction to foreign body
• LGV or lymphogranuloma venereum
• Syphilis
• Chlamydia
• Actinomycosis
• Exposure to radiation
• HIV disease

Signs and symptoms

• Persistent throbbing pain that worsens when sitting down
• Irritation of skin around the anus
• Swelling, redness and tenderness in the area surrounding the anus
• Pus or blood discharge
• Constipation
• Pain during bowel movements
• Fever
• Abdominal pain
• Change in bowel habits
• Weight loss

Diagnosis

• Physical examination of the rectal area will reveal abscess along with the anal fistula, signs of inflammation, tumour, erythema, oedema, pain and high temperature. Patient history will be examined for IBD, diverticulitis, tuberculosis, radiation therapy, and HIV infection.
• Digital rectal examination of the fibrous cord is conducted.
• Fistulography – a contrast is injected through the internal opening and images of the fistula tract are taken.
• Endorectal ultrasonography – a 7 or 10 MHz of ultrasound transducer is passed into the anal canal to differentiate between sphincteric lesions.
• Barium enema – is done to examine multiple fistulas.
• MRI – will evaluate complex and recurrent fistulas.
• CT scan – is helpful in the drainage of delineated fluid pockets.
• Anal manometry – is done to evaluate the sphincter mechanism pressure.

Treatment and medication
Anal fistulas require surgical therapy for proper and complete healing. Antibiotics are recommended for patients with sepsis or overlying cellulitis. Laxatives are prescribed for the easy passage of stools. Vasodilators provide muscle relaxation and relieve anal spasms. Diazepam will ease sphincter spasms. Calcium channel blockers decrease resting anal pressure.
We use the highly-recommended multi-disciplinary approach to manage perianal fistulas associated with IBDs such as Crohn’s disease.