Anterior cerebral artery

The anterior cerebral artery (ACA) is one of the two terminal branches of the internal carotid artery. It supplies mainly the medial surfaces of the frontal and parietal lobes, including the cortical areas concerned with motor and sensory function of the contralateral lower limb.

Origin and course

• The anterior cerebral artery arises from the internal carotid artery near the medial end of the lateral sulcus.

• It passes anteromedially above the optic nerve and optic chiasm towards the longitudinal cerebral fissure.

• The right and left ACAs are connected by the short anterior communicating artery, forming the anterior part of the Circle of Willis.

• Beyond the anterior communicating artery, the ACA enters the longitudinal cerebral fissure and curves around the genu of the corpus callosum.

• It then continues posteriorly along the superior surface of the corpus callosum, principally as the pericallosal artery.

Segments

The anterior cerebral artery (ACA) is commonly divided into anatomical/angiographic segments:

• A1 – precommunicating segment: extends from the internal carotid artery to the anterior communicating artery.

• A2 – postcommunicating segment: extends from the anterior communicating artery towards the region of the genu of the corpus callosum.

• More distal portions may be designated A3–A5, corresponding broadly to the artery as it curves around and then courses along the corpus callosum.

Branches

The ACA gives off both central (perforating) and cortical branches.

1. Central branches

Central branches arise particularly from the proximal ACA and anterior communicating region and supply deep structures of the basal forebrain. An important vessel is the recurrent artery of Heubner, which usually arises near the A1–A2 junction and supplies portions of the head of the caudate nucleus, anterior putamen, globus pallidus and anterior limb of the internal capsule.

2. Cortical branches

Important cortical branches include the:

• Pericallosal artery – the principal continuation of the ACA along the corpus callosum.

• Callosomarginal artery – courses within or close to the cingulate sulcus and supplies medial frontal and parietal cortex.

• Additional frontal and parietal branches supply the medial cerebral hemisphere.

Distribution

The ACA supplies:

• most of the medial surface of the frontal lobe;

• medial surface of the parietal lobe as far posteriorly as approximately the parieto-occipital region;

• a narrow strip of cortex along the superomedial border extending onto the superolateral surface;

• much of the cingulate gyrus;

• a substantial portion of the corpus callosum through its pericallosal branches; and

• deep structures through its perforating branches.

Importantly, its cortical territory contains the medial portions of the primary motor and primary somatosensory cortices, where the lower limb and perineum are represented.

Clinical correlates

1. Motor and sensory homunculi

ACA occlusion classically produces contralateral weakness and sensory impairment predominantly affecting the lower limb. Depending on the site and extent of the lesion, patients may also develop abulia, impaired executive or behavioural function, urinary incontinence and gait disturbance due to involvement of medial frontal structures.

2. Intracranial aneurysms and subarachnoid haemorrhage

The anterior communicating artery–ACA complex is also an important site for intracranial aneurysms. Their rupture can cause subarachnoid haemorrhage.