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Hemorrhoids (cont.)

What is the difference between an internal, external, or thrombosed hemorrhoid?

  • An internal hemorrhoid is a swollen blood vessel that arises from within the rectum above the pectinate line. It causes no symptoms unless there is bleeding with a bowel movement, or if it prolapses and can be felt externally after if protrudes through the anus.
  • An external hemorrhoid arises from blood vessels that surround the anus beyond the pectinate line. They do not cause many problems unless they rapidly expand and clot. Usually this clot resolves spontaneously leaving residual skin.
  • A thrombosed external hemorrhoid occurs when the blood clot that forms in an external hemorrhoid does not resolve causing increased swelling and pain within the hemorrhoidal tissue.

What causes hemorrhoids?

Hemorrhoids are not arteries or veins, but instead are normal blood vessels called sinusoids that are located in the walls that surround the rectum and anus. When the venous pressure within these blood vessels increases, the hemorrhoids swell and dilate, because it is more difficult for blood to empty from them. This leads to the most common symptoms of bleeding and swelling.

Common situations that increase pressure within the hemorrhoidal blood vessels and lead to abnormalities include the following.

  • Straining to have a bowel movement. This may be due to constipation or diarrhea.
  • Prolonged sitting, including on the toilet
  • Lack of exercise
  • Low fiber diet
  • Obesity
  • Pregnancy
  • Colon cancers
  • Liver disease
  • Inflammatory bowel disease
  • Anal intercourse
  • Spinal cord injury

Picture of an internal, external, prolapsed, and thrombosed hemorrhoids
Medically Reviewed by a Doctor on 6/6/2016
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