accessory middle cerebral artery

Common and

uncommon intracranial arterial anatomic variations in multi-detector computed tomography angiography (MDCTA). What radiologists should be aware of. a Axial CT image at the level of the cavernous carotids shows occlusion of the left ICA (red arrow) due to atherosclerotic disease. b Coronal reconstruction at the level of the cavernous carotids verifies the occlusion of the left ICA (red arrow) as well as atherosclerotic disease. c CTA (VRT 3D reconstructions) shows the accessory MCA as a vessel coming from the A2 segment of the ipsilateral anterior cerebral artery (red arrow). d Axial MIP image shows the course of the AccMCA (black arrowheads), the anastomotic network (moyamoya type) at the level of the left mid M1 segment (red arrow) as well as the patent peripheral left MCA (black arrow). e CTA (VRT 3D reconstructions) reveals the same configuration and patent peripheral MCA (red arrow)

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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).

Epidemiology

The prevalence of accessory MCA is ~2%.

Gross anatomy

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.

Embryology

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.

Related pathology

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.