Anal Fissure
Summary
An anal fissure is a longitudinal tear in the distal anoderm (lining of the anal canal), extending from the dentate line to the anal verge. It is one of the most painful conditions in medicine, disproportionate to the small size of the lesion. 90% are Posterior Midline due to the relatively poor blood supply in this zone (ischaemic watershed). The pathology is a vicious cycle: Trauma -> Pain -> Hypertonia (Spasm) of the Internal Anal Sphincter -> Ischaemia of the fissure edges -> Failure to heal -> Chronic Fissure. [1,2]
Key Facts
- Mechanism: The Internal Anal Sphincter (IAS) is in a constant state of spasm. This high pressure squeezes the perforating arterioles, starving the fissure of oxygen. Healing requires Chemical or Surgical relaxation of the muscle.
- The "Sentinel Pile": In chronic fissures (>6 weeks), the body attempts to heal creating granulation tissue, resulting in a Hypertrophied Anal Papilla internally and a Sentinel Skin Tag externally.
- Location Rules:
- Posterior Midline: 90% (Men), 60% (Women).
- Anterior Midline: 10% (Men), 40% (Women - post-childbirth).
- Lateral: RED FLAG. Always suspect secondary pathology (Crohn's, HIV, Syphilis, TB).
Clinical Pearls
The "Assault" Exam: Do NOT perform a Digital Rectal Exam (PR) on a patient with an acute fissure. It is excruciating and unnecessary. Diagnosis is by Inspection alone (gently parting the buttocks).
Headaches: GTN ointment works by donating Nitric Oxide. This relaxes the sphincter, but also dilates cerebral vessels. 50% of patients get a "thumping" headache. Warn them, or they will stop using it.
Botox: Think of it as a "Medical Sphincterotomy". It paralyzes the muscle for 3 months, giving the fissure a window of opportunity to heal without the permanent incontinence risk of cutting the muscle.
Incidence
- Common in young adults (20-40 years).
- Equal gender distribution (though anterior more common in women).
- Common in post-partum period and infants.
The Ischaemic Cycle
- Trauma: Hard stool or Diarrhoea tears the anoderm.
- Pain: Nerve endings exposed.
- Spasm: Reflex hypertonicity of Internal Sphincter.
- Ischaemia: High pressure exceeds capillary perfusion pressure of the posterior commissure.
- Chronicity: Fissure broadens, edges undermine, sentinel pile forms.
Symptoms
- Position: Left Lateral.
- Inspect: Gently separate buttocks.
- Findings:
- Acute: Clean, superficial laceration.
- Chronic: Indurated edges, visible Internal Sphincter fibres at base (white transverse fibres), Sentinel Pile.
Diagnostic
- EUA (Examination Under Anaesthesia): If pain prevents exam or to rule out cancer/abscess.
- Colonoscopy / Flex Sig: Only if rectal bleeding is atypical or suspect Crohn's/Cancer.
Management Algorithm
ANAL FISSURE DIAGNOSED
↓
CONSERVATIVE (6 weeks)
(Fibre, Fluids, Sitz Bath,
Lidocaine, Nifedipine)
↓
┌─────────────┴─────────────┐
HEALED NOT HEALED
(Continue fibre) (Chronic Fissure)
↓
MEDICAL THERAPY (1st Line)
- GTN 0.4% Ointment BD
- OR Diltiazem 2% BD
↓
┌─────────┴─────────┐
HEALED PERSISTENT
↓ ↓
Recurrence? SURGICAL REFERRAL
↓
┌──────┴──────┐
BOTOX LIS
(Safe) (Gold Std)
1. Conservative (Acute)
- Diet: High fibre, fluids.
- Laxatives: Osmotic (Macrogol/Lactulose). Keep stool soft.
- Analgesia: Lidocaine ointment prior to defecation.
- Warm Baths: Relaxes sphincter.
- Success: 50% of acute fissures heal.
2. Medical (Chronic - "Chemical Sphincterotomy")
- GTN 0.4% Ointment (Rectogesic):
- Dose: Pea-sized amount to anal margin BD.
- Side Effect: Headache.
- Efficacy: 60-70%.
- Diltiazem 2% / Nifedipine Ointment:
- Mechanism: Calcium Channel Blocker.
- Benefit: Fewer headaches than GTN. Often unlicensed special.
3. Surgical
- Botulinum Toxin A (Botox):
- Injection into Internal Sphincter (Inter-sphincteric space).
- Efficacy: 60-80%.
- Risk: Temporary incontinence (flatus) less than 5%.
- Lateral Internal Sphincterotomy (LIS):
- Gold Standard (95% cure).
- Division of the distal third of the Internal Sphincter.
- Risk: Permanent incontinence (minor leakage) in 3-10%. Generally reserved for those who fail Botox or have severe pain.
- Fistula-in-ano: Infection of fissure base.
- Anal Stenosis: Scarring.
- Incontinence: Iatrogenic from surgery.
- Acute fissures often heal.
- Chronic fissures rarely heal without intervention.
- Recurrence is common (50%) if constipation returns.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Anal Fissure | ACPGBI (2008) / ASCRS | GTN/Diltiazem first line. LIS reserved for failures due to incontinence risk. |
| NICE CKS | UK | Refer if not healed after 8 weeks of non-surgical treatment. |
Landmark Trials
1. Nelson's Meta-analysis (Cochrane)
- Findings: GTN is significantly better than placebo. LIS is significantly better than GTN. Botox is equivalent to GTN but fewer side effects.
What is an Anal Fissure?
It is a small tear in the skin of the anus, like a paper cut.
Why won't it heal?
Because it's in a bad place. Every time you go to the toilet, it gets stretched open. Also, the pain makes the ring muscle go into a tight spasm, which cuts off the blood supply. It's like trying to heal a cut on your knuckle while making a fist all day.
How do the creams work?
The special creams (GTN) contain medicine to relax the muscle. This brings blood back to the area and allows the cut to heal naturally.
Will I need surgery?
Only if the creams don't work. The surgery involves a tiny cut to the muscle to relax it permanently.
Primary Sources
- Perry WB, et al. Practice parameters for the management of anal fissures (3rd revision). Dis Colon Rectum. 2010;53:1110-1115.
- Nelson RL, et al. Non surgical therapy for anal fissure. Cochrane Database Syst Rev. 2012.
- Cross KL, et al. The Management of Anal Fissure: ACPGBI Position Statement. Colorectal Dis. 2008.
Common Exam Questions
- Surgery: "Patient with HIV has lateral fissure. Diagnosis?"
- Answer: Biopsy to rule out Lymphoma/Ca/Ulcer. Do not treat as simple fissure.
- Pharmacology: "Mechanism of GTN?"
- Answer: Nitric Oxide donor -> cGMP -> Smooth muscle relaxation.
- Anatomy: "Which muscle is cut in LIS?"
- Answer: Internal Anal Sphincter (Distal third). Never external (voluntary).
- Clinical: "Sentinel Pile location?"
- Answer: Distal/External to the fissure.
Viva Points
- Crohn's Fissures: Do NOT perform LIS. The sphincter is often already weak, and the wound won't heal. Use medical management or Infliximab.
- Anal Advancement Flap: "V-Y Flap". Used for fissures in patients with low sphincter pressure (who cannot have LIS).
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.