Where are fissures typically located?

Typical Location of Anal Fissures

Anal fissures are most commonly located in the midline, with approximately 90% occurring posteriorly in the midline of the anal canal. 1

Anatomical Distribution

• Posterior midline fissures are the most common location, representing the majority of all anal fissures 1
• Anterior midline fissures occur less frequently, seen in approximately 10% of women versus only 1% of men 1
• Lateral or multiple fissures are rare and should raise suspicion for underlying conditions 1

Atypical Fissure Locations and Associated Conditions

When fissures occur off the midline (lateral) or are multiple, they warrant further evaluation for underlying conditions such as:

• Inflammatory bowel disease (IBD) 1
• Sexually transmitted diseases (HIV, syphilis, herpes) 1
• Anorectal cancer 1
• Tuberculosis 1
• Leukemia 1
• Other infectious causes 1

Anatomical Description

• Anal fissures are longitudinal tears in the squamous epithelium at or just inside the anal verge 1
• They can extend from the dentate line to the anal verge 1
• Chronic fissures may display signs of chronicity including:
  • Sentinel skin tag just distal to the fissure 1
  • Hypertrophied anal papilla at the proximal margin 1
  • Fibrosis 1
  • Visible internal sphincter muscle at the fissure base 1

Pathophysiology

• Anal fissures result from multiple factors including mechanical trauma, sphincter spasm, and ischemia 2
• Internal anal sphincter hypertonia correlates with decreased anodermal vascular blood flow 1
• Contrary to common belief, less than 25% of patients with anal fissures complain of constipation 1
• The initial lesion is typically a tear in the anoderm caused by overstretching of the anal canal 3

Clinical Relevance

• Understanding the typical location helps in diagnosis and treatment planning 1
• Atypical locations should prompt investigation for underlying conditions 1
• The posterior midline location is more susceptible to trauma and has poorer blood supply, explaining the predominance of fissures in this location 3

Diagnostic Approach

• Fissures are best visualized by effacing the anal canal with opposing traction on the buttocks 1
• End-viewing endoscopes cannot visualize fissures effectively 1
• In cases of severe pain, examination under anesthesia may be warranted 1
• For atypical fissures, additional investigations such as endoscopy, CT scan, MRI, or endoanal ultrasound may be necessary 1