Causes of Internal Hemorrhoids
Internal hemorrhoids develop from abnormal swelling of the anal cushions, stretching of their suspensory muscles, and dilation of the submucosal arteriovenous plexus, though the exact pathogenesis remains unknown despite commonly cited risk factors. 1
Pathophysiologic Mechanism
The fundamental process involves structural changes to normal anal anatomy:
Anal cushions are normal vascular structures consisting of connective tissue surrounding arteriovenous communications between terminal branches of the superior rectal arteries and rectal veins, suspended by smooth muscle that arises from the conjoined longitudinal muscle layer. 1
Symptomatic hemorrhoids arise when these cushions become abnormally enlarged, leading to stretching of the suspensory muscles and prolapse of upper anal and lower rectal tissue through the anal canal. 1
Elevated anal resting pressure has been consistently demonstrated in patients with hemorrhoids compared to controls, though whether this elevated pressure causes or results from enlarged hemorrhoids remains unclear; resting tone normalizes after hemorrhoidectomy. 1
Commonly Cited Contributing Factors (With Important Caveats)
The American Gastroenterological Association emphasizes that rigorous proof for most commonly believed risk factors is lacking. 1 Despite widespread clinical belief, the following factors have not been rigorously proven:
Inadequate fiber intake, prolonged sitting on the toilet, and chronic straining at stool are widely believed by clinicians to contribute to symptomatic hemorrhoids, yet rigorous proof of such beliefs is lacking. 1
Constipation, diarrhea, pregnancy, and family history have all been proposed as contributing factors, but none have been rigorously proven. 1
Functional constipation and dyssynergic defecation are significantly more prevalent in patients with hemorrhoids (OR 2.09), suggesting a potential causal relationship through high straining forces during paradoxical contractions. 2
Pregnancy as a Special Circumstance
Pregnancy is associated with hemorrhoids in approximately 80% of pregnant persons, more commonly during the third trimester due to compression of the rectum by the gravid uterus. 3
Only 0.2% of pregnant women require urgent hemorrhoidectomy for incarcerated prolapsed hemorrhoids, indicating that while pregnancy is associated with hemorrhoids, severe complications remain rare. 1
Clinical Pitfall to Avoid
The prevalence of constipation is significantly higher in patients with hemorrhoids compared to controls, and anal pressures remain elevated even after rubber band ligation, suggesting that addressing underlying defecation disorders may be important for preventing recurrence rather than treating hemorrhoids alone. 2