Anal Fistula: Symptoms, Types, Causes and Treatment

Anal fistula is a chronic and often distressing condition that affects people of all ages, but is most common in adults in their 30s and 40s. Characterized by an abnormal tunnel between the anal canal and the skin near the anus, an anal fistula can cause persistent discomfort, discharge, and even significant social embarrassment. Understanding the symptoms, types, causes, and modern treatments is crucial for patients and clinicians alike. This article provides a comprehensive, evidence-based overview, synthesizing the latest research to help you grasp the essentials and complexities of this often misunderstood proctological problem.

Symptoms of Anal Fistula

Living with an anal fistula can have a profound impact on daily comfort, emotional wellbeing, and overall quality of life. Recognizing the symptoms early is key to prompt diagnosis and effective treatment. While pain and discharge are the hallmark symptoms, there are several other signs and associated issues to be aware of.

Symptom	Description	Impact on Life	Source(s)
Pain	Persistent or intermittent anal pain	Discomfort, anxiety	2 3 4 15
Discharge	Pus or blood from external opening	Hygiene issues, odor	2 3 4 15
Swelling	Perianal swelling, redness	Reduced mobility	4
Soiling	Staining of underwear	Social embarrassment	1 2
Incontinence	Inability to control gas or stool	Reduced quality of life	1 2 3
Urgency	Sudden need to defecate	Anxiety, lifestyle impact	2
Fever	Occasionally with abscess formation	Systemic illness	4

Table 1: Key Symptoms

Pain and Discomfort

Pain is the most common and persistent symptom, often described as throbbing or aching, and may worsen with sitting, movement, or defecation. Pain can be continuous or flare up intermittently, especially during episodes of acute infection or abscess formation 2 3 4 15.

Discharge and Soiling

Many patients notice pus or blood-stained discharge from a small opening near the anus. This can be persistent or intermittent, leading to soiling of underwear and associated odor, which can cause significant embarrassment and distress 2 3 4 15.

Swelling and Redness

Acute episodes, such as when a fistula is associated with an abscess, can result in visible swelling, redness, and warmth around the anus. Fever may also occur in these cases, signaling a spreading infection 4.

Continence Issues

Some individuals experience varying degrees of incontinence, ranging from minor soiling to inability to control gas or even loose stools. These symptoms can be a result of the disease itself or, more commonly, a complication of surgical treatment 1 2 3.

Impact on Quality of Life

The persistent nature of symptoms, particularly pain, discharge, and incontinence, can significantly reduce quality of life. Patients may feel embarrassed, anxious, and less able to participate in daily or social activities 2 3.

Types of Anal Fistula

Not all anal fistulas are alike. Their classification is important because it determines both the complexity of the disease and the best approach to treatment. The anatomic path taken by the fistula tract through the sphincter muscles forms the basis of most widely used classifications.

Type	Description	Prevalence	Source(s)
Intersphincteric	Tract lies between internal and external sphincter	Most common (54%)	6 7 4
Transsphincteric	Crosses both sphincters to perianal skin	21%	7 4 8
Suprasphincteric	Extends above external sphincter	3%	7 8 4
Extrasphincteric	Bypasses sphincters, connects to rectum	3%	7 4
Superficial	Tract does not involve sphincter muscles	16%	7
Complex (e.g. RIFIL)	Multiple or high tracts, horseshoe extensions	Challenging cases	8

Table 2: Anal Fistula Types

Classification Systems

The Parks classification is commonly used in Western countries and divides fistulas into five main types based on their relationship to the sphincter muscles: intersphincteric, transsphincteric, suprasphincteric, extrasphincteric, and superficial 6 7. Japan often uses the Sumikoshi classification, but the underlying principle is similar: to guide treatment by mapping the fistula’s complexity and involvement with the sphincters 4.

Simple vs. Complex Fistulas

• Simple fistulas: Typically intersphincteric or low transsphincteric, involve minimal sphincter muscle, and are easier to treat with a lower risk of incontinence 9 18.
• Complex fistulas: Involve a significant portion of the sphincter, may have multiple tracts or extensions (e.g., RIFIL), are more difficult to manage, and have a higher risk of recurrence or treatment-related complications 8 9 16.

Rare and Challenging Types

Recently, MRI studies have identified complicated variants such as RIFIL (roof of ischiorectal fossa inside levator-ani muscle), which are highly complex, have a higher rate of recurrence, and often require advanced imaging for diagnosis and planning 8.

Causes of Anal Fistula

Understanding the causes of anal fistula is key for prevention and effective management. While most fistulas develop after an infection, several risk factors and underlying diseases can contribute to their formation.

Cause	Mechanism/Description	Notable Risk Factors	Source(s)
Cryptoglandular	Infection of anal glands via anal crypts	Most common cause	4 10 11 12 15
Inflammatory Bowel Disease (IBD)	Particularly Crohn’s disease	Diarrhea, weight loss, pain	5 15
Lifestyle Factors	Obesity, sedentary habits, high-salt diet	Smoking, alcohol, spicy foods	13
Medical Conditions	Diabetes, dermatoses, prior anorectal surgery	Hyperlipidemia	13
Other Infections	Tuberculosis, HIV, malignancy	Immunosuppression	11 15

Table 3: Main Causes and Risk Factors

Cryptoglandular Infection

The vast majority of anal fistulas originate from an infection in the anal glands. Bacteria enter through the anal crypts, causing an abscess in the intersphincteric space. When this abscess fails to resolve, it may form a persistent track to the skin, becoming a fistula 4 10 11 12 15. Multiple bacteria can be involved, but the chronic phase does not appear to be driven by any specific pathogen 11.

Inflammatory Bowel Disease

Anal fistulas can be the first sign of Crohn’s disease, a type of inflammatory bowel disease. Patients presenting with chronic diarrhea, weight loss, and abdominal pain in addition to fistula symptoms should be evaluated for underlying IBD 5 15. Notably, around 7% of patients operated on for anal fistula may subsequently be diagnosed with Crohn’s 5.

Lifestyle and Medical Risk Factors

Certain lifestyle factors—high body mass index, excessive salt or spicy food intake, sedentary lifestyle, smoking, and alcohol use—increase the risk of developing an anal fistula. Medical conditions such as diabetes and hyperlipidemia, as well as a history of anorectal surgery, also contribute 13.

Rare Causes

Less commonly, anal fistulas can result from specific infections (e.g., tuberculosis, HIV), malignancy, or trauma 11 15. These cases require tailored investigation and management.

Treatment of Anal Fistula

Treating anal fistula is a balance between eradicating the disease and preserving continence. There is no universal solution; the approach depends on the fistula's type, complexity, and patient factors. Here, we break down the main treatment strategies, their risks, and key considerations.

Treatment	Indication/Type	Success/Complications	Source(s)
Fistulotomy	Simple, low fistulas	High cure, some incontinence	3 18 15
Seton Placement	Complex or high tracts	Preserves continence	2 3 4 15
Advancement Flap	Sphincter-sparing, complex cases	Good healing, low incontinence	1 16
LIFT Procedure	Intersphincteric/complex, sphincter-sparing	Lowest incontinence risk	9 16
Fistula Plug/Fibrin Glue	Sphincter-sparing, variable success	Modest results, low risk	16
VAAFT, FiLaC, OTSC	Novel, minimally invasive	Promising, more data needed	14 17 16

Table 4: Main Treatment Options

Conventional Surgical Approaches

Fistulotomy—the laying open of the fistula tract—remains the gold standard for simple, low-lying fistulas, with cure rates over 90%. However, even in these cases, up to 12% of patients may experience some degree of continence impairment postoperatively 3 18 15.

Seton Placement involves threading a thin material through the fistula to promote drainage and fibrosis, allowing the tract to heal slowly without cutting the sphincter, thus preserving continence. Loose setons are often used for complex or high tracts and can be left in place for extended periods 2 3 15.

Sphincter-Sparing Techniques

Advancement Flap is a technique where healthy tissue is used to cover the internal opening after the diseased tract is removed. It is especially useful for complex fistulas, with high healing rates and minimal risk of major incontinence 1 16.

LIFT (Ligation of the Intersphincteric Fistula Tract) is a newer, minimally invasive, sphincter-sparing option, with the best outcomes for minimizing post-operative incontinence, both in simple and complex fistulas 9 16.

Plugs and Glues use biological materials to fill or seal the tract. Their advantages include low risk of incontinence, but cure rates are variable (24–88%), often due to material displacement 16.

Novel and Minimally Invasive Methods

VAAFT (Video-Assisted Anal Fistula Treatment), FiLaC (Fistula Laser Closure), and OTSC (Over-the-Scope Clip) are innovative techniques that offer promising short-term results, with healing rates of 64–100% and very low morbidity. However, long-term data and standardized protocols are still lacking, and these methods are mainly reserved for difficult cases or patients who have failed other treatments 14 17 16.

Outcomes and Quality of Life

The primary goals are to eradicate the fistula, prevent recurrence, and maintain continence. Recurrence rates and complications vary by technique and fistula complexity. Fecal incontinence, even if minor (e.g., soiling, loss of gas control), can have a profound impact on quality of life 1 2 18.

Key Considerations:

• Imaging (MRI/Ultrasound) is often used for complex or recurrent cases to guide surgical planning 3 8 15.
• Underlying Disease: In patients with Crohn’s disease or other systemic illnesses, medical management may be necessary in addition to surgical intervention 5 15.
• Patient Selection: Sphincter-sparing approaches are preferable in patients at higher risk of incontinence, such as those with pre-existing weakness or complex fistula anatomy 9 16 18.

Conclusion

Anal fistula is a challenging condition that requires a nuanced, individualized approach. Early recognition of symptoms and accurate classification are vital for successful management. Surgical treatment remains the mainstay, but the choice of technique must balance cure rates with preservation of continence and quality of life.

Key Takeaways:

• Anal fistula typically presents with pain, discharge, swelling, and sometimes incontinence, all of which can significantly impair quality of life 2 3 4.
• The main types are intersphincteric, transsphincteric, suprasphincteric, extrasphincteric, and superficial, with complex variants posing greater treatment challenges 6 7 8.
• Most cases are caused by cryptoglandular infection, but Crohn’s disease and lifestyle factors also play important roles 4 5 10 11 13.
• Treatment is tailored to the fistula’s complexity, ranging from fistulotomy for simple cases to advanced sphincter-sparing or minimally invasive procedures for complex disease 1 9 14 16 18.
• Maintaining continence and minimizing recurrence are the central goals of therapy, with patient quality of life as a primary consideration 2 3 9 18.

If you suspect you have symptoms of an anal fistula, seek timely medical evaluation. With modern surgical techniques and a careful, patient-centered approach, most people can achieve lasting relief and a return to normal life.