An anal fissure is a longitudinal tear or ulcer in the squamous epithelium lining the anal canal, extending from the dentate line distally towards the anal verge. The vast majority over 90% occur in the posterior midline, where the anoderm is least supported by the underlying external sphincter and blood supply is most tenuous. A smaller proportion occur anteriorly more commonly in women following childbirth. Fissures are classified as acute (less than 6 weeks duration, with a fresh linear tear and well-defined edges) or chronic (persisting beyond 6 weeks, characterised by a triad of a deep ulcer with indurated edges, a hypertrophied anal papilla proximally, and a sentinel skin tag distally). The underlying pathophysiology involves a cycle of pain triggering internal anal sphincter spasm, which in turn reduces anodermal blood flow and impairs healing perpetuating the fissure. Predisposing factors include chronic constipation, hard stools, prolonged straining, low-fibre diet and prior anorectal surgery.
Symptoms
The hallmark symptom is severe, sharp anal pain during and after defaecation often described as passing broken glass which may persist for minutes to hours following bowel opening due to prolonged reflex sphincter spasm. This pain-defaecation association frequently leads patients to defer bowel movements, worsening constipation and perpetuating the cycle of injury. Bright red rectal bleeding is common, typically seen as a small streak on the toilet paper or surface of the stool. Pruritus ani and perianal discharge may accompany chronic fissures. A tender sentinel skin tag at the anal verge is often the visible external marker of an underlying chronic fissure and may be the only finding tolerated on examination in an acutely symptomatic patient.
Diagnosis
The diagnosis is entirely clinical. Gentle parting of the buttocks usually reveals the fissure directly at the posterior midline without the need for instrumentation. Digital rectal examination and proctoscopy though ideal are frequently impossible in the acute setting due to severe pain and sphincter spasm and should be deferred until after initial treatment has provided sufficient relief. Fissures occurring off the midline, multiple fissures or those failing standard treatment should raise suspicion for an underlying condition such as Crohn's disease, sexually transmitted infection, tuberculosis or anal malignancy, warranting further investigation including biopsy.
Treatment
Conservative management is first-line for acute fissures high-fibre diet, adequate fluid intake, stool softeners, warm sitz baths and topical local anaesthetic preparations to break the pain-spasm cycle, achieving healing in up to 50% of acute cases. For chronic or refractory fissures, topical pharmacological sphincterotomy is the mainstay glyceryl trinitrate (GTN) 0.4% ointment applied twice daily reduces internal sphincter pressure and improves anodermal perfusion, healing 50–70% of chronic fissures, though headache is a common limiting side effect. Topical diltiazem 2% cream offers comparable efficacy with a superior side-effect profile and is increasingly preferred. Botulinum toxin injection into the internal sphincter provides temporary chemical sphincterotomy and is effective in 60–80% of cases, particularly those failing topical therapy. Lateral Internal Sphincterotomy (LIS) surgical division of the lower third of the internal anal sphincter is the definitive treatment, achieving healing rates exceeding 95% and representing the gold standard for chronic fissures unresponsive to medical management, though it carries a small risk of permanent faecal incontinence that must be discussed with the patient prior to surgery.