Anal fissure
Exam Tips
- Classic history: knife-like pain with defecation followed by prolonged burning pain and streaks of bright red blood.
- Posterior midline single fissure strongly suggests primary disease; lateral or multiple fissures should trigger a search for secondary causes (Crohn, STI, TB, malignancy).
- Do not perform routine digital rectal examination in a very painful suspected fissure in primary care.
- In children, link fissure to constipation-stool withholding cycle and ask safeguarding questions if findings are unexplained.
- In OSCE management, always include stool-softening strategy, analgesia, GTN counselling (headache), and explicit red-flag referral criteria.
- Visual recognition point: See Figure showing acute versus chronic fissure morphology (linear tear vs indurated ulcer with sentinel tag).
Definition
An anal fissure is a linear tear or ulcer in the squamous lining of the distal anal canal (anoderm), classically causing severe pain during and after defecation with small-volume bright red bleeding. Most are primary and lie in the posterior midline; fissures are termed acute if present for under 6 weeks and chronic if symptoms persist for 6 weeks or longer.
Pathophysiology
The dominant mechanism is a trauma-ischaemia cycle: passage of hard stool (or sometimes loose stool) causes an anoderm tear, pain triggers internal anal sphincter spasm, and raised resting sphincter tone reduces local blood flow (especially posterior midline watershed perfusion), impairing healing. Reduced nitric-oxide-mediated sphincter relaxation may contribute to persistent hypertonia. Chronic fissures develop fibrotic edges, exposed internal sphincter fibres, and often a sentinel skin tag, which further reduce spontaneous healing. See Figure: posterior midline fissure and internal sphincter spasm mechanism (anorectal anatomy diagram).
Risk Factors
- Constipation and passage of hard stool
- Stool withholding (especially in children), leading to larger/harder stools
- Diarrhoea or frequent loose stools
- Pregnancy and postpartum state (anterior fissures more common after childbirth)
- Anal trauma (anal intercourse, previous anorectal surgery, instrumentation)
- Increased internal anal sphincter tone
- Inflammatory bowel disease (particularly Crohn disease)
- Sexually transmitted infections (for example HIV, syphilis, herpes simplex)
- Colorectal/anal malignancy
- Drugs associated with constipation or mucosal injury (for example opioids, nicorandil, chemotherapy)
Clinical Features
Symptoms
- Severe sharp anal pain on defecation, often followed by deep burning pain lasting hours
- Small-volume bright red rectal bleeding on toilet paper or stool
- Tearing sensation when passing stool
- Fear of defecation and stool withholding
- In children: crying/pain during defecation with possible rectal bleeding
Signs
- Visible fissure on gentle buttock separation, usually single posterior midline lesion
- Acute fissure: superficial linear split with clean margins
- Chronic fissure: deeper/wider ulcer, indurated edges, possible visible internal sphincter fibres
- Sentinel skin tag or hypertrophied anal papilla in chronic disease
- Atypical features suggesting secondary cause: lateral location, multiple fissures, irregular ulcers
Investigations
Management
Lifestyle Modifications
- Soften stool with gradual fibre increase (whole grains, fruit, vegetables) plus adequate fluid intake
- Avoid straining and prolonged toilet sitting; discourage stool withholding
- Maintain gentle anal hygiene and keep perianal skin clean/dry
- Warm sitz baths, especially after bowel motions, for pain relief
- Treat underlying constipation or diarrhoea actively to break the trauma cycle
- Safety-net: return early if worsening pain, fever, discharge, persistent bleeding, or non-healing
Pharmacological Treatment
Simple analgesia
- Paracetamol 1 g orally every 4-6 hours when required (maximum 4 g/day)
- Ibuprofen 200-400 mg orally up to three times daily with food when required (typical max 1.2 g/day without specialist advice)
Use for post-defecation pain; avoid or use caution with NSAIDs in renal impairment, peptic ulcer disease, anticoagulation, and late pregnancy.
Topical local anaesthetic
- Lidocaine 5% ointment, apply 1-2 mL to anal canal shortly before defecation, short course (few days)
For severe pain; prolonged use may cause local sensitisation/irritation.
Topical nitrate (sphincter relaxant)
- Glyceryl trinitrate (GTN) 0.4% rectal ointment, apply intra-anally twice daily for 6-8 weeks
Consider in adults with primary fissure not improving after about 1 week of conservative care. Headache is common and can limit adherence. Avoid in pregnancy, breastfeeding, and children; avoid with phosphodiesterase-5 inhibitors (for example sildenafil/tadalafil) due to hypotension risk.
Bowel regulation (if constipation present)
- Macrogol oral powder sachets (for example 1-3 sachets daily, titrated to soft stool)
- Lactulose 15 mL twice daily, adjusted to response
Goal is consistently soft, easy-to-pass stool; tailor to age/comorbidity and reduce once bowel habit normalises.
Specialist/off-label topical calcium-channel blocker
- Diltiazem 2% rectal cream/ointment, typically applied twice daily for 6-8 weeks
Often used in secondary care when GTN is not tolerated; local formulary and prescribing governance apply.
Surgical / Interventional
- Botulinum toxin injection to internal anal sphincter (specialist setting)
- Lateral internal sphincterotomy for chronic/refractory fissure
- Fissurectomy with or without advancement flap in selected cases
- Urgent specialist referral if red-flag or atypical features suggest secondary pathology (including suspected cancer pathway where indicated)
Complications
- Failure to heal and progression to chronic fissure
- Recurrence, especially if bowel/lifestyle factors persist
- Faecal impaction from stool avoidance
- Local infection or perianal abscess
- Anorectal fistula (uncommon)
- Reduced quality of life due to persistent pain and fear of defecation
Prognosis
About half of acute primary fissures heal within 6-8 weeks with conservative treatment, and some resolve earlier. Around 40% of acute presentations may become chronic, and recurrence is common without sustained stool-softening and bowel-habit measures. Prognosis in secondary fissures depends mainly on the underlying disease.
Sources & References
🏥BMJ Best Practice(1)
💊BNF Drug References(1)
- Glyceryl trinitrate[management.pharmacological]
✅NICE Guidelines(1)
- Anal fissure[overview]
📖Textbook References(14)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 23, 24)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 708, 709)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 24)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 657)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 367, 368)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 359)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 359)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 660)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 367, 368)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 365)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 1265)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 1265, 1266)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 1265, 1266)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 1266, 1267)[context]