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Date of last update: 10/04/2017.

Forum Name: Neurology Topics

Question: MRA Circle of Willis ... what does it show?

 tiffairy - Tue Sep 15, 2009 12:20 pm

I was sent for an MRA of my brain to rule out Aneurysm (Symptoms of localized headache lasting weeks, localized pulsating sensation in same spot, pain behind eye) and the report says "MRA of the Circle of Willis region" was normal. But I am aware that this region is not the entire brain but a group of arteries at the base of the skull which does not include, for instance, the basilar artery. So my question is, does this test view all possible aneurysm locations or not? My doctor said this ruled out aneurysm anywhere in my brain but how could it if it is only viewing those arteries in the circle of willis?

Lastly, I did also have an accompanying MRI with/without contrast. How good is this test for detection of brain aneurysm? Thank you.
 Dr.M.Aroon kamath - Thu Dec 03, 2009 12:48 am

User avatar Hi,

Approximately 85% of cerebral aneurysms develop in the anterior part of the Circle of Willis ((Anterior circulation aneurysms ).

About 10% of all intracranial aneurysms arise on the posterior (vertebrobasilar or Posterior circulation) circulation. About 7% arise from the basilar artery bifurcation, and the remaining 3% arise at the origin of the posterior inferior cerebellar artery (PICA) where it comes off of the vertebral artery.

Computed tomographic angiography (CTA) and magnetic resonance angiography (MRA), are used in the investigation of aneurysms.

CTA is said to be better(by some experts) than MRA in detection and characterization of of the intra-cranial aneurysms.

The 'circle of willis' is formed by the two internal carotid arteries (Anterior circulation) and the two vertebral arteries(Posterior circulation).This 'circle' is situated in a fairly small area and thus there should not be much difficulty in identifying basilar artery aneurysms (as most of them are the so-called 'Basilar Tip' aneurysms, arising at the bifurcation of the basilar artery).
Best wishes!

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