Middle hemorrhoidal

Unlike the small intestine and upper colon, the vasculature draining the rectal cavity does not totally direct the blood supply to the liver. The lower and middle hemorrhoidal veins of the rectum bypass, at least... 

In the absence of fecal material, the rectum has a small amount of fluid, (about 2 m) with a pH about 7. The rectum is perfused by the superior, middle, and inferior hemorrhoidal veins. The inferior hemorrhoidal vein (closest to the anal sphincter) and the middle hemorrhoidal vein feed into the vena cava and back to the heart. The superior hemorrhoidal vein joins the mesenteric circulation, which feeds into the hepatic portal vein and then to the liver. 

The IMA supplies colon distal to the splenic flexure including the descending colon, sigmoid colon, and rectum. When embolizing rectal branches off of the superior hemorrhoidal branch of the IMA, one must remember the rich collateral network around the rectum with middle hemorrhoidal branches arising from the internal iliac arteries. The internal iliac arteries should be studied after embolizing a rectal branch to exclude the possibility of collateral flow to the bleeding site. 

Differences in segmental arterial supply probably also impact on the risk of infarction. The rectum is likely to tolerate embolization better than other regions since it has a dual blood supply with the superior hemorrhoidal artery off of the inferior mesenteric artery and middle hemorrhoidal arteries arising from the internal iliac circulation. This translates into increased potential for collateral blood flow and thus decreased risk of ischemia. The cecum may be more prone to ischemia since there is not a well developed arcade along the mesenteric border of the cecum and instead there are separate anterior and posterior cecal branches. The tissue supplied by these individual branches may be more susceptible to ischemia and in fact infarction of the cecum (even after microcatheter embolization) has been reported [13]. 

The uterine artery arises from the anterior division of the internal iliac artery usually close to, or in common with the middle hemorrhoidal or vaginal artery. There are several configurations for the origin of the uterine artery. It can be the first... 

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