Accessory middle cerebral artery
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The accessory middle cerebral artery is a variant of the middle cerebral artery (MCA) that arises from the anterior cerebral artery (ACA). It is different from a duplicated middle cerebral artery, in which the duplicated vessel originates also from the distal end of the internal carotid artery (ICA).
The prevalence of accessory MCA is ~2%.
It runs parallel to the course of the MCA and supplies some of the MCA territory. The accessory MCA typically supplies anterior frontal lobe.
Accessory MCA may arise from either the proximal or distal portion of the A1 segment of the ACA. There are classification systems (Teal and Manelfe) which reflect this.
Other common embryological variants of the MCA include duplicated middle cerebral artery (vessel arising from the ICA bifurcation, and typically supplying the anterior temporal lobe), and fenestrated middle cerebral artery.
Accessory MCA may be present due to the persistence of two perforators. Early suggestions that the anomaly arises from a hypertrophied recurrent artery of Heubner (RAH) are now thought unlikely, as RAH often coexists, and the territory of supply is different. The vessel may be an anomalous early branch of the MCA.
There is an association between MCA variants and intracranial aneurysms. It is important to accurately document MCA anomalies as they have implications for operative or endovascular management.
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