Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: Kitty on 02/03/2004 17:55:06
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Hi,
I wondered if any of the naked scientists would have an answer about the Circle of Willis. ( If you answer with your clothes on that is still acceptable)!
My friend who is 50 has had an MRI/MRA done and has been told that she has no posterior communicating arteries in the Circle of Willis. They are both absent. The scan was ordered because she was experiencing memory loss, had some sudden hearing loss in the left ear and also has spells of weakness with slurring of her speech. My first question is could the findings on the scan ( which was otherwise largely normal) related to her symptoms and how? This was never clearly expained. My other questions are: How important are these communicating arteries and why do some people have them and not others? How would you know from looking at the scan, if the arteries are diseased ( and blocked) or simply absent altogether? What part of the brain do they normally supply with blood? If they are missing how is the bloody supply replaced and can done anything medically be done to help do this? Kitty
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Does she not have posterior communicating arteries because she has an anomalous brain, or are they occluded?
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It was never explained in the scan report whether the arteries were absent or diseased/occluded. I am interested in knowing how you would know the difference from looking at the MRA. Or if it is possible to know the difference. Perhaps there is a neuradiologist who can answer that question. It is also not clear if this could be progressive in nature, ie other arteries may become involved or whether this is something a person is born with. If it is the latter then how is the collaterol circulation compensated within the brain and can anything be done to improve it?
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There are variations in the cerebral blood supply between individuals. I think this is more likely to be the case because obliteration of the post. communicating artery on both sides by disease, without overt disease (which would be visible on the scan) in other proximal (larger) vessels does not seem that likely.
As I say, variations between individuals do crop up. I know a guy who volunteered for a research study. When he hopped into the MRI scanner he turned out not to have any temporal lobes in his brain (temporal lobe agenesis). As he was also a successful neuroscientist it clearly was not affecting his cognition terribly much !
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Here's a diagram of the Circle of Willis (after Thomas Willis, 17th century anatomist).
Blood reaches the brain via 2 major arterial systems - the carotid arteries (which enter at the front) and the vertebral arteries (which enter from the back). These arterial inputs are linked together in a circle so that blood can be shunted from left to right and front to back and vice versa keeping the flow steady. The ability of this system to compensate for vascualr disease means that it is not uncommon to see patients with a carotid artery that is completely blocked on one side. The brain on that side is receiving blood shunted across the Circle of Willis from the carotid on the other side, and from the vertebral arteries behind.
The posterior communicating arteries are part of this circle, but their absence, in the absence of any other disease, is not harmful.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.bartleby.com%2F107%2FImages%2Flarge%2Fimage519.gif&hash=1e4a1e0b1ba2f815f632bf84677876dd)
(From Henry Gray (1825–1861). Anatomy of the Human Body. 1918)
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Thanks for your helpful input. I came across a study of 2,362 brains which revealed that both Posterior Communicating Arteries were absent in only 0.3% of the time. It seemed far more common to have only one absent from the circle of Willis.
I also was reading more about the areas of the brain these arteries normally supply with blood. The Newletter of the Memory Disorders Project of Rutgers-Newark states:
"The posterior communicating artery is a small blood vessel which lies near the base of the brain and bridges the larger posterior cerebral arteries. These arteries, together with the anterior cerebral arteries and anterior communicating artery, form a ring of blood vessels called the Circle of Willis.
The PCoA supplies much of the blood to the hippocampus and nearby structures in the medial temporal lobe. A stroke or aneurysm which impedes blood flow through this artery can deprive and damage these regions, which are critical for the formation of new memory. The result can be anterograde amnesia: the inability to form new memories. If the damage is relatively limited to the hippocampus and nearby structures, there may be little or no effect on intelligence, attention, judgment or personality; only memory is seriously impaired. "
My question is - how and from what arterial source are the areas of the brain supplied with blood when these arteries are missing?
Many thanks,
Kitty
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Tissues guide their own blood supply provision, meaning that the congenital absence of an artery usually means that blood will reach the dependent tissues via an alternative route.
Blood vessels are very dynamic things and variations from the 'norm' are relatively common.
THe absence of the posterior communicating arteries (which are very small vessels) means that blood cannot be shunted from front to back or back to front across the circle of willis. But in health this is not a problem.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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[:o)]
I have read the previous discussion. I am 51 years old and a MRA shows that I was born without a posteria cerebral artery on the left side. This was after several tests and a couple of events similar to TIA'S. Other than the missing artery, all tests were normal. I am now experiencing problems with language. I often substitute words and have difficulties writing. I also am biting my tongue at night and have body jerks. I started having headaches and am having several vision problems. My question is are these symptoms related to the missing artery? Is this something that gets worse with time? My doctors have told me that I have some kind of neurolgia on the left side of my face, but I have no pain just left sided weakness. Is this a common situatin.
Lb
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[:o)]
I have read the previous discussion. I am 51 years old and a MRA shows that I was born without a posteria cerebral artery on the left side. This was after several tests and a couple of events similar to TIA'S. Other than the missing artery, all tests were normal. I am now experiencing problems with language. I often substitute words and have difficulties writing. I also am biting my tongue at night and have body jerks. I started having headaches and am having several vision problems. My question is are these symptoms related to the missing artery? Is this something that gets worse with time? My doctors have told me that I have some kind of neurolgia on the left side of my face, but I have no pain just left sided weakness. Is this a common situatin.
Lb