An occlusion of the Middle Cerebral Artery (MCA) is an ischemic stroke that occurs when a blood clot blocks blood flow through this large vessel in the brain. This event is a serious medical emergency because the deprived brain tissue rapidly begins to die, a process known as infarction. MCA occlusions are the most common type of ischemic stroke, frequently resulting in extensive neurological deficits due to the broad area of the brain the artery supplies. Immediate recognition of symptoms and rapid transport to a hospital are crucial, as effective treatment depends heavily on the time elapsed since the blockage occurred.
The Middle Cerebral Artery’s Role
The Middle Cerebral Artery is the largest of the three major arteries that channel oxygenated blood to the cerebrum, arising as a branch of the internal carotid artery. It supplies the majority of the brain’s lateral surface, including large portions of the frontal, temporal, and parietal lobes. This territory includes regions that govern movement, sensation, and language processing.
The artery’s deep branches, known as the lenticulostriate arteries, perfuse subcortical structures like the basal ganglia and the internal capsule. Damage to these areas severely disrupts the pathways for motor and sensory function throughout the body.
Recognizing the Symptoms
Symptoms of an MCA occlusion appear abruptly and are directly related to the functions of the affected brain regions. A common sign is contralateral hemiparesis, or weakness or paralysis affecting the opposite side of the body from the blocked artery. This weakness is typically more pronounced in the face and arm compared to the leg, reflecting the organization of the motor cortex supplied by the MCA.
Patients often experience sensory loss, or hemisensory deficit, on the same side of the body as the motor weakness. If the occlusion affects the dominant hemisphere (the left side for most people), aphasia, or difficulty with language, is a defining symptom. This can manifest as trouble producing speech (Broca’s aphasia) or difficulty understanding spoken language (Wernicke’s aphasia).
A blockage can also cause a visual field defect known as homonymous hemianopia, where the person cannot see the visual field on the side opposite the stroke. If the non-dominant hemisphere (usually the right side) is affected, patients may exhibit profound neglect. This is a failure to notice or respond to stimuli on the opposite side of space and the body.
Confirming the Diagnosis
The diagnostic process must be rapid to determine the nature and location of the stroke and to exclude other conditions. The first imaging test performed is a non-contrast Computed Tomography (CT) scan of the head. This is done immediately to rule out an intracranial hemorrhage (bleeding in the brain), which would disqualify the patient from receiving clot-busting medications.
Following the initial scan, a CT Angiography (CTA) is performed, using an injected contrast dye to visualize the blood vessels. This test confirms the presence and precise location of the arterial occlusion, such as whether it is in the proximal M1 segment or a more distal M2 segment of the MCA. The severity of the neurological deficit is quickly quantified using the National Institutes of Health Stroke Scale (NIHSS), a standardized assessment measuring functions like consciousness, vision, sensation, and movement.
The NIHSS score, combined with imaging results, helps guide treatment decisions. Advanced imaging techniques, such as CT perfusion (CTP) or Magnetic Resonance Imaging (MRI), may also be used. These identify the core area of irreversible damage versus the surrounding salvageable tissue, known as the penumbra.
Acute Treatment Strategies
Acute treatment for MCA occlusion is highly time-sensitive, emphasizing that minutes lost mean millions of neurons lost. The primary pharmaceutical intervention is Intravenous Thrombolysis (IVT), which involves administering a clot-busting medication such as tissue plasminogen activator (tPA). This drug dissolves the clot and restores blood flow, but it must be administered within a specific window, typically 4.5 hours from the last time the patient was known to be well.
For patients with a confirmed large vessel occlusion in the MCA, Mechanical Thrombectomy (MT) is the preferred treatment, often performed in addition to IVT. This endovascular procedure involves threading a catheter through an artery up to the blocked artery in the brain. The clot is then physically removed using a stent retriever or aspiration device. Mechanical thrombectomy is recommended for eligible patients presenting within six hours of symptom onset.
The window for thrombectomy has expanded significantly beyond six hours for select patients who meet specific imaging criteria. Using advanced imaging to identify a favorable ratio of salvageable brain tissue (penumbra) to dead tissue (infarct core), treatment can be extended up to 24 hours after the last known well time. This extended time frame allows physicians to treat patients who wake up with stroke symptoms or present late, maximizing the opportunity for functional recovery.