Fistula-in-Ano management

Definition

Fistula-in-ano is an abnormal epithelialized tract that connects the anal canal or rectum to the perianal skin. It commonly develops following a previous anorectal abscess due to cryptoglandular infection but may also occur secondary to inflammatory, infectious, traumatic, or malignant conditions.

Risk Factors

• Previous perianal abscess

• Crohn's Disease

• Diabetes mellitus

• Tuberculosis

• Anorectal trauma

• Pelvic radiotherapy

• Immunosuppression (e.g., HIV infection, malignancy)

Classification (Parks Classification)

Simple Fistulas

1. Intersphincteric fistula

2. Low transsphincteric fistula

Complex Fistulas

1. High transsphincteric fistula

2. Suprasphincteric fistula

3. Extrasphincteric fistula

4. Multiple tracts, recurrent fistulas, or fistulas associated with Crohn’s disease, tuberculosis, malignancy, or radiation injury

Clinical Presentation

Symptoms

• Persistent or recurrent purulent perianal discharge

• Intermittent bloody discharge

• Perianal pain or discomfort

• Pruritus ani

• Swelling around the anus

• Recurrent perianal abscesses

• Soiling of undergarments

History

• Previous anorectal abscess (present in most patients)

• Previous anorectal surgery

• History suggestive of Crohn’s disease or tuberculosis

Signs

• External opening with discharge near the anus

• Palpable fibrous tract

• Perianal induration or scarring

• Multiple openings in complex disease

Investigations

Initial Evaluation

• Clinical examination including digital rectal examination

• Examination under anesthesia (EUA) when necessary

Imaging

• Pelvic MRI (gold standard for delineating fistula anatomy and identifying secondary tracts)

• Endoanal ultrasonography (EAUS)

• Fistulography (rarely used)

Additional Investigations (When Indicated)

• Colonoscopy if Crohn’s disease is suspected

• HIV testing

• Tuberculosis investigations

• Biopsy of atypical or suspicious tracts to exclude malignancy

Non-Pharmacological Management

• Maintain good perianal hygiene

• Warm sitz baths

• Control underlying conditions (diabetes, Crohn’s disease, tuberculosis)

• Nutritional optimization

• Smoking cessation

Pharmacological Treatment

Antibiotics alone do not cure fistula-in-ano and should not be used as definitive treatment.

If Associated Cellulitis or Active Infection

A: Metronidazole (PO) 400 mg 8-hourly for 5–7 days

AND/OR

A: Ciprofloxacin (PO) 500 mg 12-hourly for 5–7 days

Particularly useful in patients with Crohn’s disease-associated fistulas.

Pain Management

A: Paracetamol (PO) 500–1000 mg 6–8 hourly when required

Surgical Management

Surgery is the definitive treatment.

Options

• Fistulotomy (preferred for simple low fistulas)

• Fistulectomy

• Seton placement (for high or complex fistulas)

• Advancement flap repair

• Ligation of Intersphincteric Fistula Tract (LIFT)

• Fibrin glue injection

• Anal fistula plug

The choice of procedure depends on:

• Fistula anatomy

• Degree of sphincter involvement

• Risk of postoperative incontinence

• Presence of underlying disease

Referral

Refer to a surgeon or colorectal specialist if:

• Complex fistula is suspected

• Recurrent disease

• Associated Crohn’s disease or tuberculosis

• Multiple fistulous tracts

• Suspicion of malignancy

• Fecal incontinence is present

Patient Education

• Explain that fistula-in-ano usually requires surgical treatment.

• Encourage adherence to follow-up appointments.

• Maintain good anal hygiene.

• Seek medical attention for increasing pain, fever, swelling, or recurrent abscess formation.

Complications

• Recurrent perianal abscess

• Recurrent fistula formation

• Fecal incontinence

• Sepsis

• Malignant transformation (rare, usually in longstanding fistulas)