AI Summary Overview
Quick Glance: Common Anal Fistula Symptoms
Symptoms of anal fistula change depending on whether the tract is draining or blocked. Some of the common symptoms of anal fistula in both cases are given below:
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Pain near the anus that feels dull, sore or throbbing
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Pain that becomes worse while sitting or passing stool
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Pus or an unpleasant-smelling discharge from an opening near the anus
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A small hole in the skin that keeps draining
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Red or swollen skin around the affected area
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Blood-stained discharge
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A tender lump that reduces after pus drains
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Occasional difficulty controlling bowel movements
Repeated discharge from the same opening is an important symptom of an anal fistula.
Anal Fistula Symptoms That Should Not Be Ignored
Changes in drainage, pain, or bowel control can indicate a blockage, abscess formation, or a more complex tract. The following symptoms of anal fistula should not be ignored and necessitate medical evaluation:
| Symptom | What It May Indicate |
| Persistent pus or foul-smelling discharge | An open fistula tract draining infected fluid |
| Painful swelling beside the anus | A new or recurrent anal abscess |
| Recurrent pain and swelling in the same area | A persistent fistula with repeated abscess formation |
| Fever with anal pain or swelling | Active infection or abscess formation requiring prompt assessment |
| Blood or stool leaking through a skin opening | A connection between the anal canal and skin |
| Increasing redness and warmth around the anus | Local infection or inflammation |
| Difficulty controlling wind or stool | Anorectal or sphincter dysfunction that requires specialist evaluation |
| Several draining openings | A branching or complex fistula |
The external opening alone cannot show the full route or complexity of a fistula. Examination and, when necessary, imaging are used to establish its relationship with the anal sphincter muscles.
Why Do Anal Fistula Symptoms Occur?
Most anal fistulas develop after an infection of a small gland inside the anus causes an abscess. When the abscess drains, a tunnel can remain between the anal canal and the skin. Fluid or pus can then continue to drain through the opening, causing irritation and sometimes blood-stained discharge.
When the external opening drains freely, pressure falls, and pain may improve. If it closes while the fistula remains, infected fluid can collect again and cause renewed swelling, throbbing pain or another abscess. Crohn's disease is another important cause of recurrent or multiple perianal fistulas.
Anal Fistula Symptoms That Require Immediate Medical Attention
Urgent medical care is recommended if anal fistula symptoms suddenly become much worse or you start feeling unwell with fever or chills:
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Severe or rapidly worsening anal pain
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Fast-growing swelling around the anus, buttocks or perineum
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High temperature, chills or shaking
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Redness spreading from the painful area
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Difficulty passing urine
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Confusion, faintness or unusual drowsiness
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Rapid breathing or a racing heartbeat
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Heavy bleeding that does not stop
Fever with worsening pain and little or no drainage can indicate a blocked abscess. Infection can also spread faster in people with diabetes or reduced immunity.
Symptoms of Anal Fistula Based on Type
The route through or around the sphincter muscles determines the anatomical type of anal fistula. The main symptoms of anal fistula based on its types are mentioned below:
| Type | Symptoms |
| Intersphincteric fistula | Pain, swelling and discharge from an opening close to the anus |
| Transsphincteric fistula | Recurrent drainage from an opening farther from the anus; deeper pain and swelling |
| Suprasphincteric fistula | Deep anal or pelvic pain, repeated abscesses and external drainage |
| Extrasphincteric fistula | Deep infection and discharge from a tract beginning above the anal canal |
Symptoms alone cannot identify the fistula type. Pelvic MRI, endoanal ultrasound or examination under anaesthesia helps detect and treat its route.
Anal Fistula Symptoms in Women
A fistula extending between the rectum and vagina has a different symptom from a tract opening beside the anus. Women may notice gas or stool passing through the vagina, repeated vaginal infections or discharge with a strong smell in such cases.
Anal Fistula Symptoms in Children
Anal fistulas can occur in infants and children. In infants, parents may first notice a recurring red or swollen area beside the anus or pus draining during a nappy change.
Possible signs of anal fistula that parents may notice include:
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Recurrent swelling beside the anus
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Redness or tenderness
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Pus draining from a small opening
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Repeated abscess formation
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Irritability when the area is touched
In an older child, multiple or recurrent perianal fistulas occurring with persistent diarrhoea, abdominal pain, poor growth, or weight loss should be medically assessed promptly for an underlying disorder such as Crohn's disease.
Can You Have an Anal Fistula Without Symptoms?
An anal fistula may cause very few symptoms when it drains freely. A small persistent opening, occasional moisture, underwear staining or intermittent discharge may be the only noticeable signs.
Symptoms can also come and go. If the opening temporarily closes, fluid may build up again and cause renewed pain and swelling.
When Can Anal Fistula Symptoms Become Life-Threatening?
An anal fistula itself is rarely life-threatening. Serious risk arises when an associated abscess or infection spreads into deeper tissues or affects the whole body. The table below lists such symptoms and explains why they can be serious:
| Symptoms | Why It Is Serious |
| Severe anal or pelvic pain with rapidly increasing swelling and fever | These symptoms may indicate a deep abscess that requires urgent drainage and treatment. |
| Rapidly spreading redness or swelling of the buttock or perineum with severe pain | Infection may be spreading through surrounding soft tissues. |
| High fever, confusion, rapid breathing or extreme weakness | These may indicate sepsis caused by a severe infection. |
| Severe perineal pain with rapidly progressing swelling, skin discolouration and marked illness | These rare symptoms may indicate a necrotising soft-tissue infection requiring emergency treatment. |
| Fainting, marked weakness or dizziness with substantial rectal bleeding | Significant blood loss requires emergency assessment and may indicate another gastrointestinal or anorectal condition. |
People with diabetes or reduced immune function may develop more serious infections and may need a lower threshold for urgent assessment when anal pain, swelling or fever develops.
How are Anal Fistula Symptoms Diagnosed?
Anal fistula diagnosis involves finding both the skin opening and the internal route of the tract. Doctors use the following examinations to assess the depth, branches and relationship with the sphincter muscles:
| Diagnostic Test or Assessment | Purpose |
| Symptom and medical history | Reviews abscesses, discharge, bowel symptoms, Crohn’s disease, surgery and injury |
| External examination | Checks for an opening, redness, swelling, scars and drainage |
| Digital rectal examination | Assesses the anal canal and surrounding tissues for tenderness or abnormalities when appropriate |
| Anoscopy or proctoscopy | Examines the inside of the anus and lower rectum |
| Pelvic MRI | Can help identify fistula tracts, deeper abscesses and their relationship with the anal sphincter |
| Endoanal ultrasound | Examines the fistula and anal sphincter using sound waves |
| CT scan | May be used in selected cases to assess deep pelvic infection or abscess when clinically appropriate |
| Examination under anaesthesia | Allows a surgeon to inspect and trace the tract |
| Blood tests | May assess infection, inflammation or an underlying illness but do not diagnose the fistula itself |
A colorectal surgeon often confirms a straightforward fistula through examination. Imaging becomes more useful for recurrent, complex or Crohn’s-related disease.
FAQs
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Q1. What can be the first sign of an anal fistula?
Ans: An anal fistula may first cause recurrent swelling or tenderness around the anus. Some people may instead notice pus or unpleasant-smelling fluid repeatedly staining their underwear. -
Q2. Does an anal fistula always cause pain?
Ans: No. If the fistula keeps draining, there may be little pain. Pain often gets worse when the opening closes, and pus starts to build up. -
Q3. Which anal fistula symptoms need medical attention?
Ans: See a doctor for anal fistula if you have a fever, increasing pain, a growing lump, repeated discharge or redness spreading around the anus. Problems controlling bowel movements also need assessment.
