Azygos anterior cerebral artery

Last revised by Dr Daniel J Bell on 30 Aug 2022

An azygos anterior cerebral artery is an uncommon to rare variant of the circle of Willis where the two A1 segments of the anterior cerebral artery (ACA) join to form a single trunk. As a result, there is no anterior communicating artery. This organization is similar to that seen in lower primates 2.

They are present in approximately 0.4-1% of the population 1.

An azygos anterior cerebral artery is associated with numerous abnormalities, including 1:

Berry aneurysms are often seen at the eventual bifurcation of the single vessel, due to either altered hemodynamics or congenitally abnormal wall, or both. The reported incidence varies widely, from 13 to 71% 1.

As there is frequent hypoplasia of the anterior communicating artery and supply of the medial surface of the hemispheres by contralateral ACA branches, confirmation of an azygos ACA can be difficult on angiography 2.
Cross compression views can be helpful.

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Cases and figures

  • Figure 1: azygos ACA
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  • Case 1
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  • Figure 2: conventional ACA anatomy
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  • Case 2: septooptic dysplasia
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  • Case 3: with corpus callosal dysgenesis and lipoma
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  • Case 4: with syntelencephaly
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  • Case 5
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  • Case 6
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  • Case 7
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  • Case 8
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  • Case 9: with pericallosal lipoma
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