Anal Fistula: Causes, Symptoms, Diagnosis, Treatment and Nursing Care

Anal fistula is an abnormal tunnel connecting the anal canal or lower rectum to the skin near the anus. It often develops after an anorectal abscess drains, then causes recurrent swelling, pain and discharge from a small skin opening. These nursing notes explain the anatomy, causes, types, assessment, diagnosis, treatment options, complications and practical nursing care while emphasizing protection of continence and timely referral.

Clinical safety: Severe or rapidly increasing anal pain, a tender swelling, fever, chills, spreading redness, difficulty passing urine, confusion or feeling very unwell may indicate an acute abscess or spreading infection. Arrange urgent clinical assessment. An abscess usually requires drainage; antibiotics alone are not a substitute. Do not probe or squeeze a suspected fistula. This lesson supports nursing education and does not replace examination, specialist advice, prescribing guidance or local referral protocols.

By the end of this lesson, the learner should be able to:

• Define fistula-in-ano and explain its usual relationship to an anal gland infection and abscess.
• Describe the common symptoms, relevant history and focused assessment findings.
• Outline the Parks classification and explain why the tract’s relationship to the sphincter matters.
• Identify red flags, complex disease and situations requiring urgent or specialist review.
• Summarize diagnostic investigations and common surgical approaches.
• Plan respectful perioperative and postoperative nursing care, including wound care, pain relief, bowel support and continence monitoring.

A fistula-in-ano is a persistent abnormal tract with an internal opening in the anal canal or, less commonly, the lower rectum, and an external opening on the perianal skin. The tract may contain granulation tissue and can remain open and drain intermittently. A person may have one external opening or several openings connected to a branching tract.

The anal canal is surrounded by internal and external sphincter muscles. These muscles help maintain continence. Anal glands open into small pits (anal crypts) near the dentate line. When a gland becomes blocked and infected, infection can form an abscess. If the abscess drains to the skin but the pathway between the gland and skin persists, a fistula may form. This is the common cryptoglandular pathway. Fistula can also occur with Crohn’s disease, tuberculosis, cancer, previous surgery, trauma or radiation injury.

Key nursing concept: The external opening may close temporarily while the deeper tract remains. Pus then collects again, producing a cycle of swelling and pain followed by spontaneous or surgical drainage. A closed-looking skin opening does not always mean the disease has resolved.

Risk factors and associated conditions guide the assessment, but they do not confirm a diagnosis. Avoid labelling a tract as “simple” or assuming it is caused by an abscess without clinician evaluation.

The Parks classification describes the relationship of the tract to the sphincter muscles. The classification helps the surgical team estimate how much sphincter is involved and choose an approach that balances healing with continence preservation.

“Simple” and “complex” are practical treatment descriptions rather than substitutes for anatomical assessment. Complexity may include a high tract, significant sphincter involvement, branching or horseshoe extension, multiple or recurrent openings, Crohn’s disease, radiation damage, previous failed repair, or a situation in which surgery could threaten continence. Anterior fistulas in women and patients with pre-existing continence problems also require particular care.

1. An anal gland becomes obstructed or infected, commonly near the anal crypts.
2. Infection spreads into surrounding tissue, forming an abscess and causing tenderness, pain, swelling and sometimes fever.
3. The abscess may be drained surgically or may discharge through the skin.
4. If the internal source and connecting tract persist, a fistula remains between the anal canal and skin.
5. Intermittent closure of the external opening can trap discharge, leading to renewed pressure, pain and another abscess.

Not every abscess develops into a fistula, and a fistula may become apparent only after the initial infection has settled. Recurrent or persistent drainage should therefore be reviewed rather than managed indefinitely as a superficial skin problem.

Symptoms vary with the tract’s size, position and whether it is draining. Common features include:

• A small opening, pit or area of granulation tissue near the anus.
• Intermittent discharge of pus, blood-stained fluid or mucus; some patients report an unpleasant smell.
• Perianal skin irritation, itching, soreness or maceration from ongoing moisture.
• Recurrent episodes of a painful lump or swelling, followed by discharge and temporary relief.
• Pain with sitting, walking or defecation, especially when the opening is blocked or an abscess is present.
• Occasional passage of gas or stool through an abnormal opening, depending on anatomy.

Fever, chills, spreading redness, rapidly worsening pain, weakness or urinary difficulty suggest acute infection or a deeper abscess rather than an uncomplicated, freely draining fistula. Some deep abscesses have little visible swelling, so severe rectal pressure or pain still needs assessment.

• Ask when symptoms began, how often swelling recurs, whether it drains spontaneously, and how much pain or discharge is present.
• Clarify discharge colour, odour, blood, relation to bowel movements and whether stool or gas passes through the opening.
• Ask about prior abscess drainage, fistula surgery, seton placement, wound healing, recurrence and baseline bowel continence.
• Assess bowel habit, constipation, diarrhoea, abdominal pain, weight loss, fever and other features of inflammatory bowel disease or systemic illness.
• Review diabetes, immune suppression, HIV status or risk when clinically relevant, current medicines, allergies, nutrition and previous pelvic or anorectal procedures.
• Explore effects on sleep, mobility, work, hygiene, relationships and emotional wellbeing. Use respectful language and protect privacy because embarrassment may delay care.

Explain the examination, obtain consent, provide a chaperone according to policy and maintain dignity. Inspect the perianal skin for an external opening, active drainage, redness, swelling, tenderness, scars, skin damage and the number or position of openings. Record observations objectively and report the patient’s pain and general condition.

A clinician may perform digital rectal examination or anoscopy when indicated and tolerated. An acute abscess can make examination extremely painful. Do not force an examination, insert instruments, squeeze a lesion or probe an opening as part of routine nursing care. A painful examination should be stopped and the clinician informed. If a fistula opening is not visible, intermittent closure does not exclude a tract.

Escalate urgently: fever or rigors; systemic toxicity, confusion or faintness; a hot, swollen, increasingly painful perianal area; spreading cellulitis; severe rectal pain or pressure without an obvious lump; urinary retention or difficulty passing urine; rapidly increasing discharge with deterioration; or signs of sepsis. Use local emergency and escalation pathways, particularly for immunocompromised patients and people with diabetes.

Many straightforward fistulas are identified from the history and clinical examination. Additional tests are selected by the clinician when the tract is deep, recurrent, branching, multiple, difficult to identify, associated with Crohn’s disease, or when an abscess is suspected but not visible.

Imaging is not required for every simple, clinically apparent fistula. The choice of investigation depends on the suspected anatomy, available services and specialist assessment.

Management depends on whether there is an active abscess, the anatomy and height of the tract, the amount of sphincter involved, the patient’s continence, associated disease and previous treatment. The surgical goal is to control infection and achieve durable healing while preserving sphincter function.

A painful abscess usually requires prompt incision and drainage. Antibiotics may be indicated for systemic infection, surrounding cellulitis, immunosuppression or selected comorbidities, as determined by the clinician and local protocol. Antibiotics alone do not replace drainage of a drainable abscess. A fistula may not be obvious at the time of drainage; attempts to forcefully locate or divide an uncertain tract can injure the sphincter.

For selected low, simple fistulas that involve little sphincter and have an acceptable continence risk, the surgeon may lay open the tract so it heals gradually from its base. Fistulotomy can be effective, but dividing too much sphincter can impair control of flatus or stool. The decision is individualized after assessment; it is not appropriate for every fistula.

A draining seton is a soft loop passed through the tract to keep it open and allow ongoing drainage. It may control sepsis and inflammation while a complex fistula is assessed or treated in stages. Patients should receive clear advice about expected drainage, hygiene, follow-up and whom to contact if the seton becomes displaced or symptoms worsen. A seton is not a reason to pull, cut or remove it without surgical instruction.

For complex or higher tracts, a surgeon may consider sphincter-preserving methods such as ligation of the intersphincteric fistula tract (LIFT) or an endorectal advancement flap. Other methods may be chosen according to anatomy and local expertise. These approaches aim to avoid cutting significant sphincter muscle, but no procedure guarantees healing or eliminates recurrence. Patients need a balanced discussion of benefits, recurrence and continence risks.

Perianal Crohn’s disease needs coordinated care between the colorectal or surgical team and the clinician managing inflammatory bowel disease. Medical treatment may be central, while surgery may be used to drain infection, control sepsis or support a broader treatment plan. Repeated operations that divide sphincter muscle can threaten continence, so treatment is individualized.

• Recurrent abscess: may occur when drainage stops but the tract remains.
• Persistent or recurrent fistula: some tracts fail to heal or recur after treatment, particularly when complex anatomy or underlying disease is present.
• Ongoing discharge and skin breakdown: moisture can cause irritation, excoriation, discomfort and odour.
• Continence impairment: sphincter injury or division may affect control of flatus or stool; assess baseline function and report changes.
• Delayed wound healing or infection: may be influenced by the extent of surgery, nutrition, diabetes, immune status, smoking and local wound conditions.
• Psychosocial distress: embarrassment, pain, odour and uncertainty can affect daily activities and mental wellbeing.

Follow-up is important even when symptoms improve. Recurrence, new swelling or continued discharge should prompt reassessment rather than repeated self-treatment.

• Assess pain, temperature, pulse, blood pressure, hydration and signs of infection; escalate deterioration promptly.
• Document baseline bowel function, continence, allergies, medicines, comorbidities and relevant previous procedures.
• Prepare the patient for imaging, EUA or surgery according to the prescribed plan and facility protocol. Verify identity, consent, procedure, fasting instructions and required checks.
• Provide a private opportunity for questions. Explain that examination or treatment may be uncomfortable and that the team will protect dignity and obtain consent.
• Support anxiety reduction with clear, nonjudgmental explanations. Avoid promising that one procedure will cure every fistula.

• Monitor vital signs, pain, bleeding, wound drainage, urinary function and general recovery according to the operation and local observation schedule.
• Use aseptic technique for wound care and follow the surgeon’s instructions for dressings, packing, irrigation or sitz baths. Not every procedure requires packing or the same wound routine.
• Explain that some drainage can be expected after a fistulotomy or while a draining seton is in place. Report increasing pain, fever, heavy bleeding, foul or suddenly increased discharge, spreading redness or systemic illness.
• Clean gently with water after bowel movements if advised; pat dry and protect surrounding skin. Avoid harsh soaps or inserting anything into the tract.
• Administer prescribed analgesia and reassess response. Encourage safe movement and comfortable positioning as tolerated.
• Monitor urination after anorectal surgery; report inability to void, suprapubic discomfort or painful retention promptly.
• Support early follow-up, wound review and communication with the surgical team, especially for patients with complex fistulas or Crohn’s disease.

• Encourage adequate oral fluids and a fibre-containing diet when appropriate and not contraindicated.
• Administer stool softeners or laxatives only as prescribed or permitted by local protocol, aiming to avoid straining and hard stool.
• Encourage patients to respond to the urge to defecate and avoid prolonged straining. Review diarrhoea as well as constipation because frequent loose stool can irritate perianal skin.
• Teach a gentle cleansing routine and use of a clean absorbent pad if drainage is present; change it regularly to protect skin and clothing.
• Offer privacy, reassurance and practical support. Ask about concerns related to odour, continence, intimacy, work and access to follow-up.

Use the surgeon’s order and local protocol for the specific operation. The procedure table summarizes core nursing actions and their rationale.

Use the surgeon’s order and local protocol for the specific operation. The procedure table summarizes core nursing actions and their rationale.

• Explain what a fistula is and why drainage may return if the internal tract remains.
• Follow the wound-care and medication plan provided by the surgical team; do not self-start leftover antibiotics or insert objects into the opening.
• Maintain gentle perianal hygiene, change pads when wet and protect the skin from persistent moisture.
• Use fluids, dietary fibre and prescribed bowel medicines to reduce straining, while reporting persistent diarrhoea or constipation.
• Attend follow-up even if the opening appears to close. Report renewed swelling, increasing pain, fever, spreading redness, heavy bleeding or a change in continence promptly.
• Seek urgent help for severe pain with fever, feeling faint or confused, difficulty passing urine or rapid deterioration.

Read the related Anal Fissure nursing notes and visit the Diploma in Nursing Direct curriculum.

A 38-year-old patient reports a tender lump beside the anus that has opened several times over the last two months. Yellow discharge stains the underwear, and the pain temporarily improves after drainage. Today the patient has worsening pain and feels feverish. The patient is embarrassed and worried about an examination.

1. Which symptoms suggest a persistent fistula, and which new symptoms raise concern for an acute abscess or spreading infection?
2. What focused history and observations should the nurse obtain first?
3. How should the nurse protect dignity and obtain consent during assessment?
4. Why should a nurse not probe the opening or assume antibiotics alone will resolve a suspected abscess?
5. What postoperative teaching may be needed if the patient receives drainage and later fistula surgery?

Suggested discussion: Repeated swelling followed by purulent drainage and temporary relief is consistent with a fistula pattern, but worsening pain and fever need urgent clinician assessment for abscess and systemic infection. Check vital signs, pain, general appearance, urinary symptoms, comorbidities and drainage; maintain privacy and explain each step. Do not probe the tract. A clinician determines the need for drainage, antibiotics and imaging. Teaching should cover wound hygiene, prescribed pain and bowel care, expected drainage, follow-up, continence changes and red flags.

Some symptoms may temporarily stop when an opening closes, but the underlying tract can remain and refill. Many fistulas need a procedure for durable healing. The appropriate plan depends on anatomy and the cause; Crohn’s-related disease needs coordinated medical and surgical care.

No. An abscess is a collection of infection and pus; a fistula is a persistent tunnel connecting the anal canal or rectum to the skin. An abscess can lead to a fistula, and a fistula can cause another abscess if drainage is blocked.

Antibiotics do not remove the tract and are not a substitute for draining a drainable abscess. A clinician may prescribe them in selected situations, such as systemic infection, extensive cellulitis or immune compromise. Follow local guidelines and the prescribed plan.

There can be a risk if sphincter muscle is divided or injured. The surgeon assesses the tract, baseline continence and individual risk, and may choose a sphincter-preserving or staged procedure for complex disease. New difficulty controlling gas or stool should be reported.

A draining seton keeps a tract open so fluid can drain and may control infection while a complex fistula is managed in stages. Follow the team’s hygiene and review instructions. Do not pull or remove the seton unless specifically instructed.

Seek urgent assessment for fever, chills, rapidly worsening anal pain, a new tender swelling, spreading redness, urinary difficulty, heavy bleeding, faintness, confusion or feeling very unwell.

• An anal fistula is an abnormal tract between the anal canal or lower rectum and perianal skin, commonly following an anal gland infection or abscess.
• Recurrent swelling and drainage are common; intermittent closure can lead to another painful abscess.
• The relationship of the tract to the sphincter muscles guides classification and surgical planning.
• Complex, recurrent, branching or Crohn’s-related fistulas may require imaging and specialist care.
• Drain an acute abscess promptly when indicated; antibiotics alone do not replace drainage.
• Fistulotomy is suitable only for selected tracts when sphincter and continence risk are acceptable; setons and sphincter-preserving methods may be considered for complex disease.
• Nursing care includes respectful assessment, infection monitoring, wound and skin care, pain control, bowel support, continence monitoring and clear follow-up advice.

Educational note: This material is for nursing students and health professionals. Apply current Uganda Ministry of Health guidance, facility protocols, professional scope of practice and the treating clinician’s plan. Individual diagnosis and treatment require clinical assessment.

1. Gaertner WB, Burgess PL, Davids JS, et al. The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula. Diseases of the Colon & Rectum. 2022;65(8):964–985. Official ASCRS guideline (PDF).
2. American Society of Colon and Rectal Surgeons. Abscess and Fistula Expanded Information. Patient and professional information.
3. Ministry of Health, Uganda. Uganda Clinical Guidelines, 2023. Use with current facility protocols and referral pathways. Uganda Ministry of Health guideline portal.