Azygos anterior cerebral artery

Last revised by Francis Deng on 26 Feb 2023

An azygos anterior cerebral artery (sometimes spelled azygous) is a 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, a congenitally abnormal wall, or both. The reported incidence varies widely at 13-71% 1.

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

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