Middle cerebral artery

The middle cerebral artery (MCA) is one of the three major arteries that supply blood to the cerebral cortex, specifically the lateral aspects of the brain. It arises from the internal carotid artery and is the largest branch of the internal carotid system.

Location

The middle cerebral artery originates from the internal carotid artery, typically at the level of the Sylvian fissure (lateral sulcus), which separates the temporal lobe from the frontal and parietal lobes. It courses laterally and extends across the lateral fissure to reach the lateral surface of the cerebral hemisphere. The MCA runs within the Sylvian cistern, branching into several cortical and perforating arteries that supply large portions of the frontal, temporal, and parietal lobes. Its deep branches, known as lenticulostriate arteries, penetrate the brain to supply subcortical structures such as the basal ganglia and internal capsule.

Structure and Anatomy

The middle cerebral artery (MCA) is a key vessel that supplies blood to a significant portion of the cerebral cortex. It arises from the internal carotid artery and courses laterally across the brain, supplying both cortical and subcortical structures. Below is a detailed description of the anatomy of the MCA.

Origin

The middle cerebral artery arises from the internal carotid artery, one of the major arteries that supply blood to the brain. The MCA originates at the bifurcation of the internal carotid artery, where it divides into the anterior cerebral artery and the MCA. This bifurcation typically occurs near the base of the brain, at the level of the Sylvian fissure (lateral sulcus), which separates the temporal lobe from the frontal and parietal lobes.

Course

The MCA courses laterally from its origin at the internal carotid artery, traveling through the Sylvian fissure, also known as the lateral sulcus. It follows a winding path over the insular cortex and within the Sylvian cistern, where it is surrounded by cerebrospinal fluid. As it travels through the fissure, the MCA branches extensively to supply the lateral surfaces of the cerebral hemispheres.

The MCA can be divided into several segments based on its course:

• M1 Segment (Horizontal Segment): This is the initial part of the MCA that extends laterally from the internal carotid artery to the Sylvian fissure. The M1 segment runs horizontally and gives off deep penetrating branches, known as the lenticulostriate arteries, which supply the basal ganglia and internal capsule.
• M2 Segment (Insular Segment): As the MCA enters the Sylvian fissure, it reaches the insular cortex and is known as the M2 segment. This segment runs along the surface of the insula and supplies blood to the insular cortex. At this point, the MCA begins to divide into superior and inferior divisions.
• M3 Segment (Opercular Segment): This segment continues as the MCA exits the Sylvian fissure and courses over the operculum, which consists of the overlying portions of the frontal, parietal, and temporal lobes. The M3 segment gives rise to several smaller branches that supply the opercular regions.
• M4 Segment (Cortical Segment): The M4 segment represents the terminal branches of the MCA that emerge onto the lateral surface of the cerebral cortex. These branches fan out over the lateral aspects of the frontal, parietal, and temporal lobes, supplying blood to a broad region of the brain involved in motor, sensory, and language functions.

Branches

The middle cerebral artery gives rise to numerous branches that can be classified into two major categories: deep branches and cortical branches.

• Deep (Lenticulostriate) Branches:These small, penetrating arteries arise from the M1 segment of the MCA and are known as lenticulostriate arteries. They supply deep subcortical structures, including the basal ganglia, internal capsule, and parts of the thalamus. The lenticulostriate arteries are important for providing blood to areas that control motor functions and are often implicated in conditions such as strokes.
• Cortical Branches:The cortical branches of the MCA supply blood to the lateral surfaces of the cerebral cortex, covering a wide range of brain functions. These branches are divided into superior and inferior divisions:
• Superior Division: This division supplies the lateral surfaces of the frontal lobe and the parietal lobe. Key branches include:
• Orbitofrontal artery: Supplies the orbitofrontal cortex, a region involved in decision-making and emotional regulation.
• Precentral and Central arteries: Supply the primary motor cortex and premotor cortex, responsible for voluntary movement.
• Inferior Division: This division supplies the lateral surfaces of the temporal lobe and parts of the parietal lobe. Key branches include:
• Temporal arteries: Supply the superior and middle temporal gyri, involved in auditory processing and language comprehension.
• Angular artery: Supplies the angular gyrus, a region involved in language and mathematical processing.

Relations

• Anteriorly: The MCA is related to the anterior cerebral artery (ACA), which runs medially and anteriorly from the internal carotid artery. The MCA and ACA form the major branches of the internal carotid system.
• Medially: The MCA lies medial to the insular cortex and travels within the Sylvian fissure as it courses laterally toward the cortical surface. It runs adjacent to the lenticulostriate arteries, which penetrate deep into the brain to supply the basal ganglia and internal capsule.
• Laterally: The MCA branches extensively over the lateral surface of the cerebral cortex, including the frontal, parietal, and temporal lobes. Its cortical branches run near the middle cerebral vein and other venous structures.

Segments of the MCA

As mentioned earlier, the MCA is divided into four primary segments based on its course:

• M1 Segment (Horizontal Segment): The initial segment that extends laterally from the internal carotid artery.
• M2 Segment (Insular Segment): The portion that travels over the insular cortex.
• M3 Segment (Opercular Segment): The segment that runs over the operculum.
• M4 Segment (Cortical Segment): The terminal branches that fan out over the cortical surface.

Anastomoses

The MCA forms important anastomoses with other arteries in the brain, ensuring collateral blood flow:

• Anterior Cerebral Artery (ACA): The MCA anastomoses with the ACA through small branches along the medial surfaces of the brain.
• Posterior Cerebral Artery (PCA): The MCA anastomoses with the PCA through its posterior cortical branches, particularly in the temporal and occipital lobes. These connections are crucial for maintaining blood supply in cases of arterial occlusion or stroke.

Variations

Anatomical variations of the MCA are not uncommon. These variations may involve differences in the size, course, or branching patterns of the artery. In some cases, there may be additional accessory branches, or the MCA may have an atypical origin from the internal carotid artery. Variations in the lenticulostriate arteries may also be present, affecting the blood supply to the basal ganglia and internal capsule.

Function

The middle cerebral artery (MCA) is one of the most important arteries supplying the brain, providing oxygenated blood to vast regions responsible for essential functions such as motor control, sensory processing, language, and cognition. Below is a detailed explanation of the functions served by the MCA.

Blood Supply to the Lateral Cerebral Cortex

The MCA supplies the majority of the lateral surface of the cerebral cortex, including critical regions of the frontal, temporal, and parietal lobes. These regions are involved in a wide range of higher cognitive functions, including motor control, language, sensory processing, and memory. The cortical branches of the MCA are divided into superior and inferior divisions, each supplying specific functional areas:

Superior Division:

• Frontal Lobe: The superior branches of the MCA supply the primary motor cortex (located in the precentral gyrus), which controls voluntary movements of the face, upper limbs, and trunk. The premotor cortex and supplementary motor area are also supplied, supporting the planning and coordination of movements.
• Parietal Lobe: The superior branches also supply the primary somatosensory cortex (located in the postcentral gyrus), which is responsible for processing tactile information, such as touch, pressure, pain, and temperature from the opposite side of the body.

Inferior Division:

• Temporal Lobe: The inferior branches of the MCA supply parts of the superior and middle temporal gyri, areas responsible for auditory processing and language comprehension (Wernicke’s area). These regions play a crucial role in the ability to understand spoken and written language.
• Parietal Lobe: The inferior division also supplies the angular gyrus and supramarginal gyrus, which are involved in higher cognitive functions like language, mathematical processing, and the integration of sensory information from different modalities.

Blood Supply to the Motor and Sensory Areas

The MCA is the primary artery supplying blood to the regions of the brain involved in motor control and sensory processing, particularly those controlling the face, upper limbs, and trunk.

• Motor Functions: The precentral gyrus (primary motor cortex), supplied by the superior division of the MCA, is responsible for the voluntary movements of the opposite side of the body. The areas of the motor cortex that control the face, arm, and hand receive blood from the MCA, making it critical for fine motor skills and facial expressions.
• Sensory Functions: The postcentral gyrus (primary somatosensory cortex), also supplied by the MCA, processes sensory input from the face, arm, hand, and upper body. This region interprets signals related to touch, pressure, pain, and temperature from the opposite side of the body.

The MCA’s role in supplying these areas makes it essential for voluntary movement and the perception of sensory stimuli from the environment.

Blood Supply to the Language Centers

The MCA is critical for language function, supplying key areas in the brain involved in speech production and comprehension.

• Broca’s Area: Located in the inferior frontal gyrus of the left hemisphere, Broca’s area is supplied by the superior division of the MCA. This region is responsible for the motor aspects of speech production, including the coordination of muscles needed for speech. Damage to this area (due to an MCA stroke) can result in Broca’s aphasia, where the patient has difficulty forming complete sentences despite understanding language.
• Wernicke’s Area: Located in the superior temporal gyrus, Wernicke’s area is supplied by the inferior division of the MCA. This region is responsible for language comprehension. Damage to Wernicke’s area can result in Wernicke’s aphasia, characterized by fluent but nonsensical speech and difficulty understanding spoken language.

The MCA’s supply to these language centers, particularly in the dominant hemisphere (typically the left), makes it essential for normal speech and language function.

Blood Supply to Deep Subcortical Structures

The MCA also provides blood to important deep subcortical structures through its lenticulostriate arteries, which arise from the M1 segment.

• Basal Ganglia: The lenticulostriate arteries supply blood to the basal ganglia, a group of nuclei involved in the control of voluntary movements, motor learning, and emotion. The basal ganglia are critical for regulating movement patterns and ensuring smooth, coordinated motor actions.
• Internal Capsule: The internal capsule is a white matter structure that contains fibers connecting the cortex with the brainstem and spinal cord. It is involved in transmitting motor signals from the cortex to the spinal cord and sensory signals from the body to the brain. Damage to the internal capsule, often due to MCA stroke, can result in contralateral motor and sensory deficits.

These deep structures are crucial for motor control, coordination, and communication between different parts of the nervous system, and their proper function depends on the blood supply provided by the lenticulostriate arteries.

Regulation of Cognitive Functions

The MCA supplies regions of the parietal lobe involved in cognition, spatial awareness, and sensory integration. The MCA’s cortical branches nourish areas responsible for higher cognitive functions:

Angular Gyrus and Supramarginal Gyrus: These regions in the parietal lobe are responsible for the integration of sensory input, mathematical reasoning, and aspects of language processing, such as reading and writing. They are also involved in body awareness and understanding the spatial relationship of objects.

The MCA’s role in supplying these regions helps support advanced cognitive functions, making it integral to reasoning, problem-solving, and spatial orientation.

Support for Auditory Processing

The temporal lobe, specifically the superior temporal gyrus, is supplied by the inferior division of the MCA. This area contains the primary auditory cortex, responsible for processing auditory information. The MCA’s role in supplying this region is essential for:

• Auditory Perception: Interpreting sounds, including speech and environmental noises.
• Language Comprehension: The Wernicke’s area in the superior temporal gyrus, as mentioned, is crucial for understanding spoken language.

By supplying the superior temporal gyrus, the MCA ensures proper auditory processing and the comprehension of language.

Clinical Significance

The middle cerebral artery (MCA) is clinically significant due to its role in supplying blood to critical areas of the brain, including regions responsible for motor control, sensory processing, language, and cognition. The MCA is the most commonly affected artery in ischemic strokes, and occlusion or damage to the MCA can lead to severe neurological deficits.

An MCA stroke can result in contralateral hemiparesis (weakness on the opposite side of the body), sensory loss, and visual field deficits. If the dominant hemisphere (typically the left) is affected, it can lead to Broca’s aphasia (difficulty in speech production) or Wernicke’s aphasia (impaired language comprehension). Damage to the lenticulostriate branches of the MCA can cause significant impairment in motor function, as these branches supply the internal capsule and basal ganglia.

Given its extensive supply to both cortical and subcortical structures, the MCA is one of the most critical arteries in stroke pathology, and its involvement often results in profound functional impairments, including difficulties in movement, language, and sensory perception.