Anal Fistula Types: Simple vs Complex

Introduction

Anal fistula is a common medical condition in India that causes discomfort, pain, and sometimes persistent infection around the anus. A fistula is an abnormal tunnel that connects the inside of the anal canal or rectum to the skin near the anus. It often results from an infection in an anal gland that fails to heal properly.

Understanding the difference between simple and complex anal fistulas is crucial for effective treatment. The choice of treatment depends on the fistula type, its anatomy, and any underlying health problems. In this article, we explain the types of anal fistulas, how to differentiate between simple and complex fistulas, their symptoms, diagnosis, and treatment options.

What is an Anal Fistula?

An anal fistula develops when an infection in the anal glands spreads, leading to an abscess (collection of pus). If the abscess drains but the pathway remains, it forms a fistula. Patients may experience ongoing discharge, discomfort, and sometimes pain.

The fistula connects the anal canal (internal opening) to a hole or opening on the skin near the anus (external opening). The main goal of treatment is to eliminate the fistula and prevent recurrence while preserving anal sphincter function.

Anatomy of Anal Fistula

The anal canal contains several glands that help lubricate stool passage. These glands open just inside the anus and drain into the anal canal. Infection or blockage of these glands can cause an abscess and subsequently a fistula.

Fistulas have two openings:

• Internal opening: The point where the fistula begins inside the anal canal or rectum.
• External opening: The skin opening where pus or fluid drains outside near the anus.

Based on their course through different muscles and tissues, fistulas are classified into simple and complex types.

Simple Anal Fistula:

A simple anal fistula is a straightforward fistulous tract that usually crosses minimal muscle and tissue. It has a lower risk of complications and is easier to treat.

Features of a simple fistula:

• Usually low or superficial in location.
• The tract passes through or below the superficial anal sphincter muscles only.
• Only one internal opening exists.
• No significant branching or multiple tracts.
• No associated disease like Crohn’s or tuberculosis.
• It is commonly caused by anorectal abscesses.

Simple fistulas most often present with minimal symptoms apart from intermittent pus discharge or slight pain.

Complex Anal Fistula:

Complex fistulas have multiple tracts, high involvement of muscles, or association with other illnesses. They pose a challenge for treatment due to the risk of damaging the anal sphincter and resulting in incontinence if treated improperly.

Features of a complex fistula:

• High or extensive involvement of muscles, passing through or above the external sphincter (trans-sphincteric, supra-sphincteric, or extra-sphincteric types).
• Multiple tracts or branching fistulas.
• More than one internal or external opening.
• Associated with other diseases like Crohn’s disease, tuberculosis, cancer, or radiation injury.
• May involve strictures or scarring from previous treatment or infection.
• Recurrent fistulas after surgery.

Complex fistulas cause more persistent symptoms, including chronic discharge, severe pain, and sometimes fecal incontinence from muscle damage.

Types of Anal Fistulas According to Anatomy

The Parks classification, widely used by surgeons, divides fistulas into:

1. Intersphincteric: The tract runs between the internal and external sphincter muscles. Most intersphincteric fistulas are simple.
2. Transsphincteric: Passing through both internal and external sphincters into the ischiorectal fossa. Usually complex.
3. Suprasphincteric: Encircle the external sphincter and extend above it.
4. Extrasphincteric: Rare. The tract extends from the rectum or sigmoid colon to the skin without involving the sphincter.

Simple fistulas tend to be intersphincteric or low transsphincteric; complex fistulas are high transsphincteric, suprasphincteric, or extrasphincteric.

Symptoms of Simple vs Complex Fistulas

Both types may present similarly but with differences in severity and persistence.

Common symptoms include:

• Recurrent pain and swelling near the anus
• Pus or foul-smelling discharge from the external opening
• Redness or irritation of the surrounding skin
• Bleeding or itching near the anus
• Fever in case of active infection or abscess

However:

• Simple fistulas typically cause mild pain and occasional discharge.
• Complex fistulas produce more severe symptoms, frequent discharge, persistent infection, and may cause difficulties with bowel control.

Diagnosis of Anal Fistulas

Correct diagnosis and classification are essential before starting treatment.

Steps include:

• Clinical Examination: Inspection for external openings, digital rectal examination to feel any induration or tract.
• Probing the Fistula: Gently passing a thin instrument through the external opening to determine the path of the tract. This is done carefully to avoid creating more damage.
• Imaging Studies:
  • MRI (Magnetic Resonance Imaging): The gold standard for detailed mapping of fistula anatomy and planning treatment.
  • Endoanal Ultrasound: Useful in some settings to visualize the tract and sphincter involvement.
  • Fistulogram: X-ray with contrast injected into the tract to see its course.
• Additional Tests: If an underlying condition like tuberculosis or Crohn’s disease is suspected, blood tests, biopsy, or colonoscopy may be necessary.

Treatment of Anal Fistulas: Simple vs Complex Approaches

The treatment goal is to heal the fistula completely, prevent recurrence, and maintain anal continence.

Treatment of Simple Fistulas

Simple fistulas normally respond well to surgical treatment with low risks.

• Fistulotomy:
  The most common and effective surgery for simple fistulas. The surgeon opens the fistulous tract completely and allows it to heal by secondary intention. It is safe because the fistula passes through less sphincter muscle.
• Marsupialization:
  Sometimes after fistulotomy, the edges are sutured to the wound to help faster healing.
• Seton Placement:
  If any concern about sphincter involvement exists, a draining seton (a thread or rubber band) may be placed to keep the tract open and reduce inflammation before definitive surgery.
• Post-operative care:
  Sitz baths, stool softeners, and maintaining hygiene aid recovery.

Healing rates for simple fistulas with fistulotomy are high, around 90-95%.

Treatment of Complex Fistulas

Complex fistulas are challenging due to high involvement of anal sphincter muscles and multiple tracts. Aggressive treatment risks incontinence if not done carefully.

Treatment options include:

• Seton Placement:
  Loose setons help drain the infection without cutting muscle. This controls sepsis and prepares for further treatment.
• Advancement Flap Surgery:
  The internal opening is covered with a flap of rectal or anal mucosa. This closes the fistula without cutting sphincter muscle. Best for complex fistulas with minimal sphincter involvement.
• Ligation of Intersphincteric Fistula Tract (LIFT):
  This newer procedure involves identification and ligation of the fistula tract between sphincter muscles. It preserves continence and has good results in selected cases.
• Fibrin Glue or Plug:
  These minimally invasive methods seal the fistula tract but often show variable success.
• Fistulectomy:
  Complete excision of the fistula tract. Used selectively due to risk of incontinence.
• Management of Associated Diseases:
  Underlying Crohn’s disease or tuberculosis must be treated medically along with fistula surgery.
• Repeated or staged surgeries are often needed to ensure healing without damage.

Risks and Complications Based on Fistula Type

• Simple fistulas heal well with minimal risk.
• Complex fistulas have a higher chance of recurrence and complications such as:
  • Anal incontinence (if too much muscle is cut)
  • Infection or abscess reformation
  • Fistula persistence or multiple tracts
  • Impact on quality of life

When to See a Doctor?

If you notice any of the following, consult a surgeon promptly:

• Persistent or recurrent pus or discharge near the anus
• Painful swelling or redness in the anal area
• Fever with anal pain
• Any difficulty with bowel control or stool leakage
• History of tuberculosis, inflammatory bowel disease, or prior fistula surgery

Early diagnosis improves outcomes and reduces complications.

Prevention and Care

Though not all fistulas are preventable, reducing risk factors helps:

• Treat anal abscesses early and completely
• Manage constipation with fibre-rich diet and hydration
• Maintain strict personal hygiene
• Avoid straining during bowel movements
• Timely medical attention for anorectal pain or discharge

Conclusion

Anal fistulas cause significant discomfort and require proper diagnosis for effective treatment. Distinguishing simple from complex fistulas helps doctors plan the best course.

Simple fistulas have straightforward anatomy, lower risk to sphincter muscles, and usually heal well with fistulotomy. Complex fistulas involve multiple tissues and require careful, often multi-step treatment to avoid incontinence and recurrence.

With advances in diagnostics and surgical techniques, most anal fistulas heal well with minimal impact on quality of life. We encourage maintaining good bowel habits, hygiene, and following medical advice closely to achieve the best results.