Normal Anatomical Position of Hemorrhoids
Most people have three hemorrhoidal cushions located in the subepithelial space of the anal canal, classically positioned at the right anterior, right posterior, and left lateral locations, though this "typical" configuration occurs in only 19% of individuals. 1
Anatomical Location and Structure
Hemorrhoids are normal structural components of the anal canal present from infancy, not pathological entities unless they become symptomatic. 1 They are located in the subepithelial space of the anal canal and consist of connective tissue cushions surrounding direct arteriovenous communications between terminal branches of the superior rectal arteries and the superior, inferior, and middle rectal veins. 1
Key Anatomical Features:
- Number: Typically three cushions, though anatomical variation is common 1
- Classic positions (occurring only 19% of the time):
- Right anterior
- Right posterior
- Left lateral 1
- Structural support: Anal subepithelial smooth muscle arises from the conjoined longitudinal muscle layer, passes through the internal anal sphincter, and inserts into the subepithelial vascular space, suspending and contributing to the bulk of the hemorrhoidal cushions 1
Classification by Position Relative to Dentate Line
Hemorrhoids are defined as internal or external according to their position relative to the dentate line. 1
Internal Hemorrhoids:
- Located above the dentate line 1, 2
- Covered by columnar epithelium 3
- Originate from the superior hemorrhoidal plexus
- Contribute to anal continence and sensitivity 3
External Hemorrhoids:
- Located below the dentate line 1, 2
- Covered by anoderm (modified squamous epithelium) 4
- Originate from the inferior hemorrhoidal plexus 4
- Highly innervated by somatic pain receptors, causing significant pain when thrombosed 4
Physiological Function
These cushions serve critical normal functions:
- Contribute approximately 15-20% of resting anal pressure 1
- Serve as a conformable plug to ensure complete closure of the anal canal 1
- Aid in maintaining fecal continence 3
Clinical Pitfall
A common error is assuming all anorectal symptoms are due to hemorrhoids. 1 The presence of hemorrhoidal cushions is normal anatomy—only their enlargement, prolapse, or thrombosis constitutes hemorrhoidal disease requiring treatment. The wide anatomical variation (with the "classic" three-cushion configuration present in less than one-fifth of people) means clinicians should not expect uniform positioning across all patients. 1