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Anterior cerebral artery (A2 Segment)

The anterior cerebral artery (ACA) is divided into several segments, with the A2 segment extending from the junction with the anterior communicating artery (AComA) to the origin of the callosomarginal artery. The A2 segment courses anteriorly and superiorly over the corpus callosum (pericallosal region), running within the interhemispheric fissure.

It supplies the medial aspects of the frontal lobe and parietal lobe, including the supplementary motor area, medial primary motor cortex, medial primary sensory cortex, and cingulate gyrus. This segment is clinically significant because occlusion leads to contralateral leg weakness and sensory loss due to involvement of medial motor and sensory cortices. The A2 segment often gives rise to perforating branches (medial lenticulostriate arteries) and communicates with the pericallosal and callosomarginal arteries.

Synonyms

  • Pericallosal segment of ACA

  • Post-communicating segment of ACA

  • A2 portion of anterior cerebral artery

Function

  • Supplies blood to the medial frontal lobe, paracentral lobule, and anterior cingulate cortex

  • Provides collateral circulation through callosomarginal and pericallosal branches

  • Nourishes motor and sensory areas controlling contralateral lower limb

  • Supports executive functions and attention networks via cingulate cortex perfusion

MRI Appearance

T1-weighted images (non-contrast):

  • Appears as a flow void (signal loss) coursing within the interhemispheric fissure above the corpus callosum

  • Difficult to delineate lumen without vascular sequences

T2-weighted images:

  • Also seen as flow voids, surrounded by CSF of the interhemispheric fissure

  • Adjacent cortical hyperintensity may indicate ischemia

MRA (Magnetic Resonance Angiography):

  • Time-of-flight (TOF) or contrast-enhanced MRA clearly demonstrates the A2 origin from AComA, its course, and distal branches

  • Normal lumen appears as a bright, continuous enhancing signal

  • MRA is crucial for detecting stenosis, occlusion, aneurysms at the AComA/A2 junction, or vascular malformations

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Vessel lumen shows intense enhancement

  • Useful for confirming patency or evaluating small cortical branches and aneurysms when combined with MRA

CT Appearance

Non-contrast CT:

  • Vessel not directly seen unless thrombosed, when it may appear as a hyperdense ACA sign

  • Infarcts in the ACA territory present as hypodense changes in medial frontal and parietal cortex

CT Angiography (CTA):

  • Accurately depicts the A2 segment course above the corpus callosum and its cortical branches

  • Contrast opacifies lumen for evaluation of stenosis, occlusion, aneurysm, or AVM

  • CTA is the gold standard for stroke mapping, surgical planning, and aneurysm evaluation

MRI images

Anterior cerebral artery (A2 Segment) mri axial image

MRI images

Anterior cerebral artery (A2 Segment) mri sagittal image -img-00000-00000