What is the etiology of rectal fissures?

Etiology of Anal Fissures

The exact etiology of anal fissures is multifactorial, with the primary mechanism being internal anal sphincter hypertonia leading to decreased anodermal blood flow, creating an ischemic ulcer rather than simply mechanical trauma from hard stools. 1, 2

Primary Pathophysiological Mechanisms

• Internal anal sphincter hypertonia: Manometric studies have demonstrated a strong correlation between internal anal sphincter (IAS) hypertonia and decreased anodermal vascular blood flow, supporting the ischemic ulcer theory 1

• Mechanical trauma: While passage of hard stools can contribute to fissure development, it is not sufficient to explain their onset, as less than 25% of patients with anal fissures actually complain of constipation 1, 3

• Vascular insufficiency: Reduced blood flow to the posterior midline of the anal canal creates a vulnerable area prone to tearing and poor healing 2

Anatomical Considerations

• Location patterns:

  • Approximately 90% of anal fissures are located posteriorly in the midline 1
  • Anterior fissures occur in 10% of women versus 1% of men 1
  • More recent data suggests anterior fissures are more common than previously thought (12.6% in women and 7.7% in men) 3

• Atypical locations: Fissures that are lateral or multiple in number should raise suspicion for underlying conditions 1

Associated Conditions

When fissures occur off the midline or are multiple, investigation for underlying conditions is warranted, including:

• Inflammatory bowel disease (IBD) 1, 2
• Sexually transmitted infections (HIV, syphilis, herpes) 1, 2
• Anorectal cancer 1, 2
• Tuberculosis 1, 2
• Leukemia 1

Clinical Presentation

• Pain: The cardinal symptom, occurring during and after defecation in 90.8% of patients 3
• Bleeding: Bright red and scanty, present in 71.4% of patients 1, 3
• Bowel habits: Contrary to common belief, infrequent hard bowel movements occur in only 13.8% of patients with anal fissures 3

Important Clinical Distinctions

• Anal fissures must be distinguished from hemorrhoids, as symptoms can overlap but treatments differ 1
• Pain associated with anal fissures is typically more severe than with uncomplicated hemorrhoids 1
• Atypical fissures (lateral, multiple, non-healing) require more extensive evaluation to rule out serious underlying conditions 2

Common Pitfalls in Diagnosis

• Assuming hemorrhoids are the cause of anorectal symptoms without proper examination 1
• Failing to recognize atypical presentations that may indicate underlying disease 1
• Attributing anal pain solely to hemorrhoids when fissures are present (up to 20% of hemorrhoid patients have concomitant fissures) 1
• Missing other causes of anal pain such as perianal abscess 1

Understanding the multifactorial etiology of anal fissures is essential for proper diagnosis and treatment, with recognition that internal sphincter hypertonia and resulting ischemia play a more significant role than previously appreciated.