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Old 08-03-2011
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Default watershed infarction

Watershed area has double blood supplies, but why is it tend to infarct in ischemia, e.g. spenic flexure in ishcemia bowel disease? Can someone explain its pathophysiology?
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Old 05-21-2014
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I think firstly you need to consider what would happen to the watershed area under two different circumstances:
(1) atherosclerosis
(2) systemic hypoperfusion

The term "watershed" refers to those areas that receive dual blood supply from the *branching ends of two large arteries that do not anastomose.

In case (1), you're correct. The watershed regions are generally spared from ischemia by nature of their dual blood supply.

However in case (2), such as during DIC or heart failure, the watershed area is MOST susceptible to infarction because it's supplied by the most distal part of their arteries, and are therefore less likely to receive enough blood. The analogy is often made of comparing this blood supply to an "irrigation system". Blood flow to distal artery territories of the brain is like delivering water to the "last field on a farm", which is the area with the *least supply of water and therefore most vulnerable to any reduction in flow.

In the brain, the area between the *ACA and *MCA is usually at greatest risk. If a watershed infarct occurred, it'd be evidence by contraction band necrosis.

Key words in question/answers:
*Splenic flexure (end of SMA, beginning of IMA)
*Hippocampus (pyramidal cells)
*Cerebellum (purkinje cells)

Hope that helps
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