Internal Hemorrhoids Pathogenesis and Contributing Factors

Pathophysiologic Mechanism

The American Gastroenterological Association notes that 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
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 2
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 3
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

The American Gastroenterological Association emphasizes that rigorous proof for most commonly believed risk factors is lacking, including inadequate fiber intake, prolonged sitting on the toilet, and chronic straining at stool 4
Constipation, diarrhea, pregnancy, and family history have all been proposed as contributing factors, but none have been rigorously proven 1
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 3

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 5
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 4

The European Society for Medical Oncology guidelines state that dietary habits, chronic inflammatory diseases, and the presence of hemorrhoids do not appear to predispose to epidermoid anal cancer, and notably do not list anal intercourse as a risk factor for hemorrhoids themselves, only for HPV-related anal cancer 6, 7
The American Gastroenterological Association emphasizes that rigorous proof for most commonly believed hemorrhoid risk factors is lacking, including many factors clinicians assume contribute to the condition 8, 9

Hemorrhoids develop from vascular and structural changes in the anal cushions, which contribute 15-20% of resting anal pressure, involving abnormal arteriovenous plexus dilation within the subepithelial space 9

The European Society for Medical Oncology guidelines warn that diagnosis is often delayed because bleeding is attributed to hemorrhoids when other pathology is present, and clinicians should not attribute hemorrhoids to sexual practices without evidence 6, 7
The American Gastroenterological Association emphasizes that most patients and many physicians tend to attribute any anorectal symptom to hemorrhoids incorrectly, and instead, focus on anal fissures, HPV-related pathology, and standard hemorrhoid risk factors such as constipation and pregnancy 9

The bright red bleeding characteristic of hemorrhoids results from the arterial oxygen tension caused by arteriovenous communications within the anal cushions 10
When the suspensory muscles stretch and the arteriovenous plexus dilates abnormally at the 3, 7, and 11 o'clock positions, symptomatic hemorrhoids develop, as reported in Gastroenterology 10