What causes rectal fissures?

What Causes Rectal (Anal) Fissures

Anal fissures are longitudinal tears in the anal mucosa caused primarily by internal anal sphincter hypertonia and resulting anodermal ischemia, though the exact etiology remains incompletely understood. 1, 2

Primary Pathophysiologic Mechanisms

The dominant theory centers on internal anal sphincter dysfunction rather than simple mechanical trauma:

• Internal anal sphincter hypertonia correlates strongly with decreased anodermal vascular blood flow, creating an ischemic environment that prevents healing and promotes fissure formation 1, 2
• Manometric studies demonstrate elevated anal sphincter pressures in patients with anal fissures, supporting the ischemic ulcer theory 1
• Contrary to common belief, less than 25% of patients with anal fissures actually complain of constipation, indicating that hard stool passage alone is insufficient to explain their development 1, 2

Contributing Factors

While mechanical trauma from bowel movements is implicated, it is not universally present:

• Hard bowel movements are associated with fissure development but are not found in all patients 3
• The passage of hard stools may trigger the initial tear, but sphincter hypertonia and ischemia perpetuate the condition 4

Anatomical Patterns Suggesting Underlying Causes

The location of the fissure provides critical diagnostic information:

• Approximately 90% of anal fissures occur in the posterior midline, with anterior fissures representing 10% in women versus only 1% in men 1, 2
• Lateral or multiple fissures are atypical and should prompt investigation for underlying conditions including inflammatory bowel disease (particularly Crohn's disease), HIV/AIDS, syphilis, herpes, tuberculosis, anorectal cancer, or leukemia 1, 2, 5

Secondary Causes to Consider

When fissures present atypically, specific etiologies must be excluded:

• Inflammatory bowel disease (especially Crohn's disease) can manifest with atypical fissure locations 1, 5
• Sexually transmitted infections including HIV, syphilis, and herpes 2, 5
• Malignancy of the anorectum 2, 5
• Infectious causes such as tuberculosis 2, 5
• Anal trauma from anoreceptive intercourse 6

Clinical Implications

Understanding the ischemic pathophysiology guides treatment selection:

• The goal of both medical and surgical treatment is to reduce internal anal sphincter tone, thereby improving blood flow to the anoderm 4
• Treatments that temporarily decrease anal pressures (chemical sphincterotomy with botulinum toxin or topical agents) or permanently reduce sphincter tone (lateral internal sphincterotomy) address the underlying pathophysiology rather than just the mechanical trauma 5, 4

Key Diagnostic Pitfall

Do not assume all midline posterior fissures are idiopathic without proper evaluation:

• Even typical-appearing fissures that fail conservative management warrant consideration of underlying conditions 1
• Chronic fissures displaying sentinel tags, hypertrophied papillae, fibrosis, or visible internal sphincter muscle at the base indicate prolonged disease requiring more aggressive intervention 2, 5