Anal Fissure
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Direct answer
An anal fissure is a longitudinal ulcer in the squamous-lined anal canal distal to the dentate line, occurring in the posterior midline in about 90 per cent of cases, where a relatively ischaemic corner and a hypertonic internal sphincter impair healing. The presentation is excruciating pain during and after defecation with bright red blood streaking the stool, contrasting with the painless bleeding of haemorrhoids. Acute fissures heal with fibre, sitz baths and topical agents — glyceryl trinitrate 0.2 per cent or diltiazem 2 per cent, which chemically relax the internal sphincter and heal roughly half to two-thirds; botulinum toxin injection raises healing further. Chronic fissures with a sentinel tag, hypertrophied anal papilla and exposed internal sphincter fibres that fail medical therapy are treated by lateral internal sphincterotomy, the gold standard, with a small risk of soiling.
What you must remember
- Position: posterior midline in roughly 90 per cent, anterior midline in most of the rest (anterior fissures commoner in women); multiple or lateral fissures suggest Crohn's disease, tuberculosis, HIV, syphilis or haematological disease.
- Symptom triad: severe tearing pain on defecation lasting hours, bright red bleeding on the paper, and constipation from fear of defecation — a self-perpetuating cycle.
- Chronicity signs: sentinel pile (skin tag) distally, hypertrophied anal papilla proximally, indurated edges, and horizontal exposed fibres of the internal sphincter at the base.
- Chemical sphincterotomy: topical GTN 0.2 per cent (dose-limiting headache is the main adverse effect) or diltiazem 2 per cent, for 6–8 weeks; combined with stool bulking and sitz baths.
- Botulinum toxin injection of the internal sphincter heals most chronic fissures temporarily-to-permanently with fewer headaches than nitrates.
- Lateral internal sphincterotomy divides the distal one-third to one-half of the internal sphincter with high cure rates but a small risk of soiling; anal dilatation (Lord's procedure) is obsolete due to uncontrolled sphincter injury.
- Fissures in Crohn's disease are treated conservatively — medical therapy of the underlying disease, avoiding sphincterotomy.
Common confusion
Fissure is confused with a painful thrombosed external haemorrhoid and with fistula. The fissure's pain is cutting pain during stool passage with streaking haematochezia, while a thrombosed pile is a constant painful lump; fissure pain is disproportionate to the tiny visible ulcer. The second error is diagnosing a 'fissure' that is off the midline or multiple — this is the exam's cue to think of Crohn's, tuberculosis or HIV rather than to proceed to sphincterotomy.
Exam-focused takeaway
Know the posterior midline predilection and its ischaemic-hypertonia explanation, the drug strengths (GTN 0.2 per cent, diltiazem 2 per cent), the order of therapy from fibre to nitrates to botox to sphincterotomy, and the classic side effect of nitrates (headache). Stems contrast painful (fissure) with painless (haemorrhoid) bleeding per rectum, and ask the operation for a chronic fissure with failed medical therapy — lateral internal sphincterotomy, never anal dilatation.
Frequently asked questions
Why are anal fissures usually posterior?
The posterior midline is a watershed of anal canal blood supply compressed by the contracted sphincter at high pressure, so with hypertonia the posterior corner is relatively ischaemic and fails to heal.
What is the first-line medical treatment?
Stool bulking with fibre and adequate fluids, warm sitz baths, and a topical chemical sphincterolytic — glyceryl trinitrate 0.2 per cent or diltiazem 2 per cent — for 6–8 weeks.
Why does GTN fail or get abandoned?
Nitrate headache is dose-limiting in a substantial proportion of patients, and tachyphylaxis with reduced efficacy develops, leading to a switch to diltiazem or botulinum toxin.
When is sphincterotomy indicated and what does it risk?
For chronic fissures failing 6–8 weeks of medical therapy or recurring after botox; it risks minor soiling in a small proportion.