Most Common Site of Anal Fissure
Approximately 90% of anal fissures occur in the posterior midline of the anal canal, making this the overwhelmingly most common location. 1
Anatomical Distribution
The posterior midline represents the vast majority of all anal fissure cases, with the remaining 10% occurring anteriorly 1. There is a notable sex difference in anterior fissure distribution:
- Anterior midline fissures occur in approximately 10% of women versus only 1% of men 1
- Posterior midline fissures remain the dominant location regardless of sex 2, 1
Clinical Significance of Location
The location of a fissure has critical diagnostic and prognostic implications:
Typical (Midline) Fissures
- Posterior or anterior midline fissures are considered primary fissures and are usually idiopathic 3, 4
- These respond well to conservative management in approximately 50% of cases 2, 5
- Clinical examination alone is typically sufficient for diagnosis 5
Atypical (Off-Midline) Fissures
Lateral or multiple fissures mandate immediate evaluation for serious underlying pathology 2, 5, 1. These atypical locations should raise suspicion for:
- Crohn's disease or inflammatory bowel disease 2, 1, 4
- HIV/AIDS and associated secondary infections 2, 1
- Sexually transmitted diseases (syphilis, herpes) 1
- Anorectal cancer 1, 4
- Tuberculosis 2, 1
- Leukemia 2, 1
Anatomical Basis
Anal fissures are longitudinal tears in the squamous epithelium extending from the dentate line to the anal verge 1, 3. The posterior midline predominance is related to:
- Internal anal sphincter hypertonia correlating with decreased anodermal vascular blood flow in this location 1
- The posterior commissure being the area of poorest blood supply and highest mechanical stress during defecation 1
Diagnostic Approach
Fissures are best visualized by effacing the anal canal with opposing traction on the buttocks 2, 1. For typical posterior midline fissures presenting with classic symptoms (anal pain during and after defecation, bright red bleeding), no additional investigations are needed 5. However, atypical locations require endoscopy, CT, MRI, or endoanal ultrasound to rule out underlying pathology 5, 1.