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Anorectal varices
Anorectal varices are the dilation of collateral submucosal vessels due to backflow in the veins of the rectum. Typically this occurs due to portal hypertension which shunts venous blood from the portal system through the portosystemic anastomosis present at this site into the systemic venous system.〔Hunt AH. 'A contribution to the study of portal hypertension. Edinburgh: Livingstone, 1958: 61.〕 This can also occur in the oesophagus, causing oesophageal varices, and at the level of the umbilicus, causing caput medusae. Between 44% and 78% of patients with portal hypertension get anorectal varices.〔
==Pathogenesis==
Blood from the superior portion of the rectum normally drains into the superior rectal vein and via the inferior mesenteric vein to the liver as part of the portal venous system. Blood from the middle and inferior portions of the rectum is drained via the middle and inferior rectal veins. In portal hypertension, venous resistance is increased within the portal venous system; when the pressure in the portal venous system increases above that of the systemic, blood is shunted through the portosystemic anastomoses. The shunting of blood and consequential increase of pressure through the collateral veins causes the varicosities.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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