• General:
    • Normal venous sinusoids of the distal rectum and proximal anal canal
    • Normal vascular cushions of anal canal that contribute to anal continence
    • Arteriovenous shunt system exists at the level of the internal hemorrhoids that accounts for the bright red blood per rectum
  • When the hemorrhoids become symptomatic, hemorrhoid disease develops
  • Do not cause pain unless thrombosed or strangulated
  • Discrete masses of thick submucosa contain:
    • Blood vessels
    • Smooth muscle
    • Elastic and connective tissue
  • Sliding down of part of anal canal lining
  • External hemorrhoids:
    • Vessels situated below dentate line
    • Covered by skin/anoderm
    • Drain to internal iliac veins
  • Internal hemorrhoids:
    • Submucosal vessels above dentate lines
    • Drain to portal system
    • Usually at left lateral, right posterolateral, and right anterolateral positions
    • Grade 1: Painless, bleeding
    • Grade 2: Prolapse with bowel movement (BM), spontaneously reduce
    • Grade 3: Prolapse with BM, require manual reduction
    • Grade 4: Chronically prolapsed, not reducible


  • Exact cause unknown
  • Gravitational forces and abdominal pressure cause distention of the sinusoids
  • Associated with straining and irregular bowel habits:
    • Hard, bulky stools or diarrhea cause tenesmus/straining
    • Push anal cushions out of anal canal
    • Weaken submucosal tissue leading to prolapse
  • Higher resting anal pressures:
    • Erect posture
  • Heredity:
    • Absence of valves in veins
  • Increased intraabdominal pressure:
    • Ascites
    • Pregnancy
  • Portal hypertension

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