Segments and Branches
The ACA is classified into 5 segments with the smaller branches from the ACA "callosal" arteries (supracallosal) considered as the A4 and A5 segments:
- A1: this segment originates from the internal carotid artery and extends to the anterior communicating artery (AComm). The anteromedial central (medial lenticulostriate) arteries arise from this segment as well as the AComm, which irrigate the caudate nucleus and the anterior limb of the internal capsule
- A2: this segment extends from the AComm to the bifurcation forming the pericallosal and callosomarginal arteries. The recurrent artery of Heubner (distal medial striate artery), which irrigate the internal capsule, usually arises at the beginning of this segment near the AComm. 4 branches arise from this segment, the:
- Orbitofrontal artery (medial frontal basal): Arises first a small distance away from the AComm
- Frontopolar artery (polar frontal): Arises after the orbitofrontal close to when A2 curves posteriorly over the corpus callosum. Could also originate from the callosal marginal.
- A3: Also termed the pericallosal artery this is one of (or the only) the main terminal branches of the ACA, which extends posteriorly in the pericallosal sulcus to form the internal parietal arteries (superior, inferior) and the precuneal artery. This artery may form an anastomosis with the posterior cerebral artery.
- Callosal marginal artery: A commonly present terminal branch of the ACA, which bifurcates from the pericallosal artery. This artery in turn branches into the medial frontal arteries (Anterior, Intermediate, Posterior), and the paracentral artery, with the cingulate branches arising throughout its length. Depending on anatomical variation, the callosal marginal artery may be none discrete or not be visible. In the latter case, the branches mentioned will originate from the pericallosal artery. In a study of 76 hemispheres, the artery was present in only 60% of the cases. Angiography studies cite that the vessel can be seen 67% or 50% of the time.
Read more about this topic: Anterior Cerebral Artery
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