AKT · Gastroenterology/Anorectal

Anal fissure

Tear in the anoderm (hard stool/constipation; posterior midline)

Overview

A painful tear in the squamous lining of the anal canal, usually in the posterior midline, from hard stool/constipation. Causes severe PAIN on defecation ('passing glass') with a small amount of bright-red blood. Acute fissures heal with stool softening and topical GTN/diltiazem (which relax the sphincter); chronic ones may need botulinum toxin or sphincterotomy. Lateral/multiple fissures → look for an underlying cause (Crohn, infection, malignancy).

Recognise

Severe PAIN on and after defecation (sharp, 'tearing/passing glass'), often with a streak of bright-red blood and anal spasm
Posterior MIDLINE location (most); a sentinel skin tag/hypertrophied papilla in chronic fissures
Associated with constipation/hard stool; high anal sphincter tone perpetuates it (ischaemia)

Red flags

LATERAL or multiple fissures → consider Crohn, infection (HIV/syphilis/TB) or anal cancer — investigate
Non-healing despite treatment

Differentials & how to tell them apart

HaemorrhoidsPAINLESS bleeding (unless thrombosed) — fissure is pain-dominant

Perianal abscessthrobbing pain + swelling/fluctuance + systemic upset

Crohn's perianal diseaseatypical/lateral fissures, skin tags, fistulae

Anal cancermass/ulcer not healing — biopsy

Investigations

Clinical (gentle inspection — examination is painful; PR often deferred acutely). Investigate atypical (lateral/multiple/non-healing) fissures for secondary causes.

Management

Stool softeners + topical GTN/diltiazem (botulinum toxin/sphincterotomy if chronic)

1Soften stool (fibre, fluids, laxatives), analgesia and sitz baths. Add topical GTN or diltiazem to relax the sphincter and promote healing.Gate: A LATERAL or multiple/non-healing fissure is atypical — investigate for an underlying cause (Crohn, infection, anal cancer) rather than treating as a simple posterior-midline fissure
2Chronic/refractory → botulinum toxin injection or lateral internal sphincterotomy (counsel re incontinence risk); treat any underlying cause.

Stool softeners + fibre/fluids + analgesia/sitz baths — first-line — break the constipation-pain cycle

Topical GTN or diltiazem — relaxes the internal sphincter (reduces tone/ischaemia) to allow healing; GTN → headache

Botulinum toxin / lateral internal sphincterotomy — chronic/refractory fissures (sphincterotomy risks incontinence)

Key points

Severe pain on defecation + a streak of bright blood + posterior midline tear = anal fissure → soften stool + topical GTN/diltiazem. Lateral/multiple fissures aren't 'simple' — think Crohn/infection/cancer.

Monitor & prognosis

Healing; recurrence.

Most acute fissures heal; chronic ones are more stubborn.

Source: NICE CKS Anal fissure