Middle cerebral artery

Introduction

The middle cerebral artery (MCA) is one of the major cerebral arteries, playing a crucial role in supplying blood to large portions of the lateral cerebral cortex and subcortical structures. It is of particular clinical importance due to its involvement in ischemic strokes and aneurysmal disease. Understanding its anatomy and vascular territories is essential for accurate diagnosis and management of cerebrovascular disorders.

Anatomy of the Middle Cerebral Artery

Origin and Course

The MCA originates from the internal carotid artery after its bifurcation into the anterior cerebral artery. It courses laterally through the Sylvian fissure, giving rise to multiple branches that supply the lateral aspects of the cerebral hemispheres. Along its path, the artery maintains close relationships with cortical and subcortical structures, providing critical blood flow to functionally important areas of the brain.

• Origin: Lateral branch of the internal carotid artery
• Course: Travels through the Sylvian fissure toward the lateral surface of the cerebral hemisphere
• Relations: Adjacent to frontal, parietal, and temporal lobes, basal ganglia, and internal capsule

Segments of the MCA

The MCA is anatomically divided into four main segments, each with distinct features and clinical relevance.

• M1 (horizontal segment): Extends from origin to the bifurcation or trifurcation, giving rise to lenticulostriate arteries
• M2 (insular segment): Courses over the insula within the Sylvian fissure
• M3 (opercular segment): Passes over the opercular regions of the frontal, parietal, and temporal lobes
• M4 (cortical branches): Terminal branches spreading over the lateral cortical surface

Branches

The MCA gives rise to several important branches that supply both cortical and subcortical structures.

• Lenticulostriate arteries: Penetrating arteries supplying basal ganglia and internal capsule
• Cortical branches: Supply lateral surfaces of the frontal, parietal, and temporal lobes

Vascular Territories

The middle cerebral artery supplies a wide range of cortical and subcortical regions, each with specific functional significance. Knowledge of these territories is important for understanding the clinical presentation of MCA strokes.

• Frontal lobe territory: Lateral convexity including primary motor and premotor areas, affecting voluntary movement and executive functions
• Parietal lobe territory: Somatosensory cortex, responsible for sensation, spatial awareness, and visuomotor coordination
• Temporal lobe territory: Superior and lateral temporal gyri, including areas critical for language comprehension and auditory processing
• Subcortical structures: Basal ganglia and internal capsule supplied via lenticulostriate arteries, important for motor control and coordination

Physiology and Hemodynamics

The MCA plays a central role in cerebral circulation and is a key determinant of cerebral perfusion in its territories. Its physiological characteristics ensure adequate oxygen and nutrient delivery to critical brain regions.

• Role in cerebral blood flow: Supplies approximately 80% of the lateral cerebral hemisphere, providing high metabolic demand areas with continuous perfusion
• Autoregulation mechanisms: Maintains relatively constant blood flow despite fluctuations in systemic blood pressure through vasodilation and vasoconstriction
• Collateral circulation: Communicates with anterior and posterior cerebral arteries via the Circle of Willis, providing alternative pathways in case of partial occlusion

Development and Anatomical Variations

Embryological Development

The middle cerebral artery develops from the distal portion of the internal carotid artery during early embryogenesis. Proper formation of the MCA is essential for establishing lateral cerebral perfusion and integrating with the Circle of Willis.

• Originates from the primitive internal carotid artery
• Formation of M1 to M4 segments occurs as the cerebral hemispheres expand
• Lenticulostriate arteries develop to supply deep subcortical structures

Common Anatomical Variations

Anatomical variations of the MCA can influence susceptibility to vascular events and affect surgical or endovascular approaches.

• Accessory MCA: an additional branch arising from the internal carotid artery
• Duplicated MCA: two parallel arteries supplying overlapping territories
• Variation in branching patterns, such as early bifurcation or trifurcation of M1

Pathology of the Middle Cerebral Artery

Occlusive Disorders

The MCA is frequently involved in ischemic strokes due to thrombotic or embolic occlusions.

• Thrombotic stroke: Local arterial clot formation, often at a site of atherosclerosis
• Embolic stroke: Occlusion by a clot or plaque fragment originating from the heart or proximal arteries
• Lacunar infarcts: Small vessel occlusions via lenticulostriate arteries affecting subcortical structures

Aneurysms

The MCA can develop aneurysms, which carry a risk of rupture and subarachnoid hemorrhage.

• Common sites: Bifurcation points of M1 segment
• Clinical presentation: Sudden headache, neurological deficits, or loss of consciousness
• Rupture risk influenced by aneurysm size, shape, and hemodynamic stress

Other Vascular Disorders

Additional pathological conditions affecting the MCA include arteriovenous malformations and vasculitis.

• Arteriovenous malformations: Abnormal direct connections between arteries and veins causing high-flow shunts
• Vasculitis: Inflammatory involvement of MCA branches leading to stenosis or occlusion

Clinical Significance

Stroke Syndromes

The middle cerebral artery is the most commonly affected artery in ischemic stroke, leading to characteristic neurological deficits based on the affected hemisphere and territory.

• Contralateral hemiplegia and hemianesthesia affecting face, arm, and sometimes leg
• Hemineglect and spatial awareness deficits, typically with right hemisphere involvement
• Aphasia (Broca’s or Wernicke’s) when the dominant hemisphere is affected
• Visual field deficits, including homonymous hemianopia

Diagnostic Evaluation

Accurate assessment of MCA pathology relies on both imaging and clinical evaluation.

• Computed tomography (CT) and magnetic resonance imaging (MRI) for infarct detection
• CT angiography (CTA) and MR angiography (MRA) for visualizing vessel patency and aneurysms
• Digital subtraction angiography (DSA) as the gold standard for detailed vascular mapping

Therapeutic Interventions

Management of MCA disorders depends on the underlying pathology and may include medical, endovascular, or surgical approaches.

• Thrombolysis and mechanical thrombectomy for acute ischemic stroke
• Surgical clipping or endovascular coiling for aneurysms
• Medical management of risk factors including hypertension, diabetes, and hyperlipidemia
• Rehabilitation therapies for functional recovery following stroke

References

1. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer; 2018.
2. Standring S, ed. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020.
3. Netter FH. Atlas of Human Anatomy. 7th ed. Philadelphia: Elsevier; 2019.
4. Hurst RW, et al. Middle Cerebral Artery Stroke: Clinical and Imaging Correlation. Stroke. 2017;48(6):1505-1512.
5. Kulkarni P, et al. Anatomy and Variations of the Middle Cerebral Artery: Implications for Neurosurgery. J Neurosurg. 2018;129(4):1047-1055.
6. Albers GW, et al. Thrombectomy for Stroke in the MCA Territory. N Engl J Med. 2018;378(1):11-21.
7. Rhoton AL Jr. Cerebral Arteries: Microsurgical Anatomy and Relevance. Neurosurgery. 2019;85(3S):S3-S34.