Hemorrhoids Are Vascular Structures with Arteriovenous Communications
Hemorrhoids are vascular structures—specifically, they consist of connective tissue cushions surrounding direct arteriovenous communications between arteries and veins, making them neither purely arterial nor purely venous. 1
Anatomic Composition
The American Gastroenterological Association guidelines clearly define the structural nature of hemorrhoids 1:
- Hemorrhoids consist of connective tissue cushions surrounding direct arteriovenous communications between the terminal branches of the superior rectal arteries and the superior, inferior, and middle rectal veins
- These are located in the subepithelial space of the anal canal
- Anal subepithelial smooth muscle suspends and contributes to the bulk of the hemorrhoidal cushions
- They are normal anatomic structures present from infancy, not pathologic entities
Clinical Significance of the Arteriovenous Nature
The arteriovenous composition has important clinical implications 1:
- Hemorrhoidal bleeding is characteristically bright red due to the arterial oxygen tension caused by arteriovenous communications within the anal cushions
- Blood may drip or squirt into the toilet bowl, reflecting the arterial component
- This distinguishes hemorrhoidal bleeding from darker venous bleeding from more proximal sources
Research confirms this vascular architecture 2:
- Increased caliber and arterial blood flow in terminal branches of the superior rectal artery correlate with hemorrhoid appearance
- Mean arterial caliber in hemorrhoid patients: 1.87 mm vs. 0.92 mm in controls (P < 0.001)
- Arterial blood flow significantly higher: 33.9 vs. 11.9 cm/second (P < 0.01)
Important Distinction: Not Varicosities
Hemorrhoids are NOT varicose veins 3:
- They are vascular cushions composed of arterioles, venules, and arteriolar-venular communications
- Portal hypertension does not cause hemorrhoids
- Rectal varices from portal hypertension are distinct entities requiring different treatment
This understanding guides modern treatments like rectal artery embolization, which targets the arterial supply to reduce blood flow and alleviate symptoms 4, 5.