Anal fissure

Overview

An anal fissure is a linear tear in the squamous mucosal lining of the anal canal, almost always at the posterior midline. A vicious cycle of pain → IAS spasm → raised anal pressure → ischaemia → impaired healing underlies chronicity.

Presentation

•Post-defecatory pain - intense burning/tearing lasting minutes to hours ('passing broken glass'); cardinal symptom

•Bright red rectal bleeding - small amount on toilet paper or pan; does not mix with stool

•Sentinel pile - hypertrophied skin tag at distal end of chronic fissure; 6 o'clock (posterior) or 12 o'clock (anterior)

•Secondary constipation - pain-avoidance of defecation perpetuates the cycle

•Location: posterior midline 90%, anterior midline 10%; anterior fissures more common postpartum

🚨

A lateral (off-midline) anal fissure must prompt investigation for a secondary cause - Crohn's disease, anal carcinoma, syphilis, or tuberculosis. New fissure in an elderly patient: consider malignancy.

Investigations

•Diagnosis is clinical - history and gentle perianal inspection; DRE performed cautiously or deferred (examination under anaesthesia if pain prohibitive)

•Proctoscopy/sigmoidoscopy or colonoscopy - if secondary pathology (IBD, malignancy) suspected, or atypically located/multiple fissures

Management

Acute fissure (<6 weeks): often resolves with conservative measures. Chronic fissure (>6 weeks): requires pharmacological treatment; refer to colorectal surgery if no response after 8 weeks.

•Conservative (all stages): high-fibre diet, adequate fluids, ispaghula husk (bulk-forming laxative; lactulose if not tolerated), lidocaine 5% ointment before defecation, regular paracetamol

•First-line (chronic fissure): topical GTN 0.4% ointment applied to anal margin twice daily - nitric oxide donor; relaxes IAS, improves blood flow

•Most common side effect: headache - main reason for discontinuation

•Second-line (GTN not tolerated/ineffective): topical diltiazem 2% cream - calcium channel blocker; similar efficacy to GTN, better tolerability (fewer headaches)

•If no pharmacological response after 8 weeks: refer to secondary care (colorectal surgery)

•Botulinum toxin injection into IAS - temporary chemical denervation (~3 months); effective but fissure may recur

•Lateral internal sphincterotomy (LIS) - gold standard; surgical division of part of IAS; healing rates >90%; risk of faecal incontinence 1-5% (must be part of informed consent)

🎯

GTN headache is the key reason to switch to topical diltiazem. If pharmacological treatment fails at 8 weeks, refer for botulinum toxin injection or lateral internal sphincterotomy.

Complications

•Chronic non-healing fissure - fibrosis, sentinel pile, hypertrophied anal papilla

•Faecal incontinence - recognised risk of LIS (1-5%)

•Perianal abscess or fistula-in-ano - secondary infection; if occurs, suggests secondary diagnosis