Describe the aetiology, clinical features and management of anal fissure.

Aetiology of Anal Fissure

The exact aetiology of anal fissures is often multifactorial, but the primary initiating factor is thought to be trauma to the anal canal. This trauma typically leads to a tear in the anoderm, which can then perpetuate a vicious cycle of pain and sphincter spasm.

Primary Anal Fissures (Idiopathic)

Most anal fissures (around 90%) are considered primary, meaning they have no clear underlying cause beyond direct trauma and associated physiological responses.

• Trauma from Stool Passage: The most common cause is the passage of large, hard stools, often due to chronic constipation, which overstretches the anal canal. Conversely, prolonged or severe diarrhoea can also cause irritation and tearing.
• Internal Anal Sphincter Hypertonicity: This is a key pathophysiological factor. The internal anal sphincter (IAS) maintains the resting pressure of the anal canal. In many patients with anal fissures, there is hypertonicity and hypertrophy of the IAS, leading to elevated anal canal resting pressures. This increased tension reduces blood flow (ischemia) to the posterior midline of the anal canal, which is already a relatively poorly perfused area, impairing healing and perpetuating the fissure.
• Lack of Nitric Oxide Synthase: Some theories suggest a deficiency in nitric oxide synthase, which is needed to generate nitric oxide, a substance that helps relax the sphincter.

Secondary Anal Fissures

These fissures are associated with an identifiable underlying condition or systemic disease. They often occur in atypical locations (e.g., lateral positions, rather than the posterior or anterior midline), can be multiple, or have an irregular outline.

• Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can lead to anal fissures, often with deeper, irregular ulcers.
• Infections: Sexually transmitted infections (STIs) such as syphilis, herpes, chlamydia, HIV, and tuberculosis can cause perianal ulcerations that may present as fissures.
• Anal Trauma:
  • Childbirth trauma (perineal lacerations).
  • Anal intercourse.
  • Previous anal surgery (scarring can cause stenosis or tethering, making the area more susceptible to trauma).
  • Foreign body insertion.
• Malignancy: Squamous cell anal carcinoma can present as a non-healing fissure.
• Other systemic conditions: Leukemia, dermatologic conditions like psoriasis.

Clinical Features of Anal Fissure

The clinical presentation varies slightly between acute and chronic fissures, though pain and bleeding are universal symptoms.

Acute Anal Fissure

An acute fissure appears as a fresh, superficial linear tear, much like a paper cut.

• Severe Pain: The hallmark symptom is intense, sharp pain during defecation, often described as "passing glass." This pain typically persists for several minutes to hours after a bowel movement, due to sustained internal anal sphincter spasm.
• Bright Red Bleeding: Usually minimal, appearing as streaks on toilet paper or stool, or occasionally a few drops in the toilet bowl. Significant bleeding is uncommon.
• Constipation: Patients often develop a fear of defecation due to anticipated pain, leading to voluntary withholding of stools, which exacerbates constipation and hardens stools, perpetuating the cycle.
• Anal Spasm: A feeling of tightness or cramping in the anal region.

Chronic Anal Fissure

A fissure is considered chronic if it persists for more than 6-8 weeks. Chronic fissures are deeper and often have distinct morphological changes due to repeated injury and healing attempts.

• Pain: Similar to acute fissures, but sometimes the intensity may reduce over time and become more cyclical. However, it still significantly interferes with daily life.
• Bleeding: Continues to be bright red and usually minimal.
• Associated Lesions (Fissure Triad): Chronic fissures are often accompanied by:
  • Sentinel Pile: A hypertrophied skin tag distal to the fissure, formed by edema and fibrosis.
  • Hypertrophied Anal Papilla: An enlarged papilla located proximal to the dentate line.
  • Visible Internal Anal Sphincter Fibers: The base of the fissure may expose the white, glistening fibers of the internal anal sphincter.
• Pruritus Ani: Itching around the anus due to irritation.
• Discharge: Rarely, some serous or purulent discharge may be present, particularly if infection supervenes.

Management of Anal Fissure

The primary goals of management are pain relief, reduction of internal anal sphincter spasm, promotion of healing, and prevention of recurrence. Management typically follows a stepped approach, starting with conservative measures.

1. Conservative (First-line) Management

This is effective for most acute fissures and should be the initial approach for all patients.

• Dietary Modifications:
  • High-fiber diet: Increasing dietary fiber (fruits, vegetables, whole grains) helps soften stools and increase bulk, facilitating easier passage.
  • Adequate Fluid Intake: Essential for maintaining soft stool consistency.
• Stool Softeners/Laxatives: Medications like psyllium (bulk-forming laxative) or lactulose (osmotic laxative) help make stools softer and easier to pass, reducing trauma during defecation.
• Sitz Baths: Warm water baths (15-20 minutes, 2-3 times daily, especially after bowel movements) help relax the anal sphincter, reduce pain, and promote blood flow to the area, aiding healing.
• Topical Anaesthetics: Lidocaine jelly or other local anaesthetics can be applied before defecation to temporarily relieve pain.

2. Pharmacological Management

These are typically used for chronic fissures or acute fissures unresponsive to conservative measures. The aim is to reduce IAS tone and improve blood flow.

Medication Type	Mechanism of Action	Examples and Usage	Side Effects
Topical Nitrates	Release nitric oxide, causing smooth muscle relaxation (including IAS) and vasodilation, improving blood flow.	0.2% or 0.4% Glyceryl Trinitrate (GTN) ointment, applied twice daily for 6-8 weeks.	Headache (most common, due to systemic absorption), dizziness, hypotension.
Topical Calcium Channel Blockers (CCBs)	Block calcium influx into smooth muscle cells, leading to relaxation of the IAS and increased blood flow.	2% Diltiazem cream or 0.2% Nifedipine ointment, applied twice daily for 6-8 weeks.	Fewer systemic side effects than GTN, but can cause mild headache or dizziness.
Botulinum Toxin A Injection	Causes temporary paralysis of the internal anal sphincter, reducing spasm and promoting healing. Acts as a "chemical sphincterotomy."	Injected directly into the internal anal sphincter. Effect lasts approximately 3 months. May be used when topical agents fail.	Temporary faecal incontinence (especially to flatus), local pain at injection site. Superior healing rates reported.

3. Surgical Management

Surgical options are considered when medical treatments fail, particularly for chronic fissures.

• Lateral Internal Sphincterotomy (LIS):
  • Description: Considered the gold standard for chronic anal fissures unresponsive to medical therapy. It involves a controlled, partial division of the internal anal sphincter muscle, usually laterally (to avoid nerve damage), which permanently reduces sphincter tone.
  • Outcome: Highly effective with high healing rates (over 90%) and significant pain relief.
  • Risk: Small risk of permanent or transient faecal incontinence (especially to flatus), though generally low when performed carefully.
• Fissurectomy with Advancement Flap:
  • Description: Excision of the fissure along with a skin or mucosal advancement flap to cover the defect. Reserved for complex or refractory fissures, especially those with significant scarring, or those at risk of incontinence after sphincterotomy (e.g., in patients with pre-existing sphincter weakness, Crohn's disease related fissures, or anterior fissures in women).
• Other less common procedures: Anal dilation (less favored due to uncontrolled sphincter tearing and higher risk of incontinence), posterior midline sphincterotomy (higher risk of keyhole deformity and incontinence).

Management of secondary fissures primarily focuses on treating the underlying cause (e.g., immunomodulators for Crohn's disease, antibiotics for infections) alongside symptomatic relief.