Talk:Circle of Willis

message: If any one of the arteries in the circle become blocked or narrowed (stenosed) or one of the arteries supplying the circle is blocked or narrowed, blood flow from the other blood vessels is usually insufficient to maintain cerebral perfusion.
although there is are anastamosis, it is insufficient to maintain blood flow to the brain.
:AFAIK, the above assertion is not true in the clinical context.  In carotid stenosis the cerebral arterial circle often perserves flow. See the following -- Hendrikse J, Eikelboom BC, van der Grond J. Magnetic resonance angiography of collateral compensation in asymptomatic and symptomatic internal carotid artery stenosis. J Vasc Surg. 2002 Oct;36(4):799-805.  and de Boorder MJ, van der Grond J, van Dongen AJ, Klijn CJ, Jaap Kappelle L, Van Rijk PP, Hendrikse J. Spect measurements of regional cerebral perfusion and carbondioxide reactivity: Correlation with cerebral collaterals in internal carotid artery occlusive disease. J Neurol. 2006 Oct 24; [Epub ahead of print] .  Please modify if you believe I'm incorrect but provide us with a reference to bolster your case.  I changed the article to reflect that fact that people have measured differences with magnetic resonance.  That said, many people with a carotid artery occulsion are asymptomatic.  Nephron  T|C 23:18, 26 October 2006 (UTC)
replies: text: The wording was ambiguous.  I've changed the wording to clarify that a blockage or stenosis in the section that forms the circle (itself) are of little consequence (if the circle is complete).  It appears you read the section as pertaining to the section of the cerebral vessels distal to the arterial circle.  I agree these blockages/stenoses are significant.  That said, a blockage of, for example, one A1 segment of the anterior cerebral artery that develops over time (due to atherosclerosis) is unlikely to clinical be significant. Also, a block of an ICA is not significant if it develops over time and does not shed a thrombus and cause an ischemic stroke in the process of occluding. Feel free to tweak some more... if you think it needs further clarification. Nephron  T|C 00:19, 31 October 2006 (UTC)
thread_title: Physiologic significance

message: The Basilar artery is part of the vertebral-basilar system and is not part of the circle of Willis. The vertebral-basilar system, also know as the posterior circulation to the brain includes the vertebral artery, the posterior inferior artery, the basilar artery, and the spinal arteries.  The anterior circulation to the brain is supplied by a ring of blood vessels called the circle of Willis which is located at the base of the brain. The circle of Willis is composed of the posterior cerebral arteries, the posterior communicating arteries, the interior and middle cerebral arteries, anterior communicating branches, and the internal carotid arteries.  ^ Silvestri, L. A., MSN, RN. (2008). Comprehensive review NCLEX-RN examination, 4th ed., Canada: Saunders --Aplexy (talk) 01:19, 3 April 2012 (UTC)
thread_title:  = Anatomy: Components = 

message: The following text has been moved from the main article as it seems to be more appropriately placed here:
"(The author of the above information was wrong, the MIDDLE CEREBRAL arteries are the continuation of the Internal Carotid arteries. Which means he/she is also wrong that the Middle Cerebral arteries DO indeed contribute to the circle. The Anterior Cerebral and Posterior Communicating arteries branch off the Middle Cerebral).
(I'm also is of opinion that middle cerebral artery should not be considered part of  circle of Willis. The simple reason being that middle cerebral artery, with direction of blood flow through it, cannot contribute to the blood supply of the circle in case of occlusion in one of arteries of circle. Moreover ICA trifurcates rather than MCA)."
I believe the original text they are commenting on (The posterior communicating artery is given off ...  middle cerebral artery does not contribute to the circle.) is accurate as far as I understand the circle of Willis, but I am no expert on the subject.
GadBeebe (talk) 17:05, 5 May 2012 (UTC)
thread_title:  Commentary removed from main text