A lateral infarct is an ischemic stroke where the blood supply to the outer surface, or lateral aspect, of the brain’s cerebral hemispheres is suddenly blocked. This blockage deprives brain tissue of the oxygen and glucose required to function. The infarct refers to the location of tissue death, typically supplied by branches of the Middle Cerebral Artery (MCA). This lack of blood flow rapidly kills brain cells, causing neurological deficits dependent on the affected region.
Understanding the Anatomy of an Infarct
The word “infarct” describes tissue that has died due to a prolonged lack of blood supply, a process known as ischemia. This is a form of ischemic stroke and accounts for the majority of all stroke cases. When blood flow stops, brain cells are deprived of oxygen and glucose, leading to irreversible damage within minutes.
The term “lateral” refers to the side or outer surface of the cerebrum. The primary blood vessel supplying this large territory is the Middle Cerebral Artery (MCA). The MCA spreads its branches over the lateral surface of the frontal, parietal, and temporal lobes, making it the most frequently affected artery in cerebral infarction.
The lateral cerebral cortex controls high-level functions, including sensation, movement, and language. An infarct here can involve the outer cortical tissue and deeper structures, such as the basal ganglia and internal capsule, supplied by the MCA’s penetrating branches. The extensive area supplied by the MCA means a blockage often results in severe neurological impairment.
Primary Vascular Causes and Risk Factors
A lateral infarct is caused by an obstruction in an artery supplying the lateral cerebral hemisphere. The two main mechanisms are thrombosis and embolism. Thrombosis occurs when a blood clot forms directly within a cerebral artery, often at a site narrowed by atherosclerosis (fatty plaque buildup).
Embolism involves a clot traveling from a different location until it lodges in a smaller brain artery. The heart is a frequent source, especially in conditions like atrial fibrillation, where an irregular heartbeat allows clots to form. This is known as a cardioembolic stroke, and the MCA is a common destination for these emboli.
Several systemic conditions increase the risk of developing the vascular disease that leads to an infarct. Uncontrolled high blood pressure (hypertension) damages vessel walls, promoting atherosclerosis. Other major risk factors include diabetes mellitus, high cholesterol levels, and pre-existing heart conditions that predispose to clot formation, such as coronary artery disease.
Specific Neurological Manifestations
Symptoms of a lateral infarct are sudden and reflect the functions controlled by the damaged lateral cortex. A common manifestation is weakness or paralysis (hemiparesis or hemiplegia) affecting the side of the body opposite the infarct. Because the MCA supplies the face and arm areas of the motor cortex, these regions are often more severely affected than the leg.
Speech and language difficulties are prominent if the infarct occurs in the dominant hemisphere (the left side for most people). Damage to language centers in the lateral frontal and temporal lobes causes aphasia, impairing the ability to produce or understand language. Symptoms may also include sensory loss, causing numbness or diminished ability to feel touch on the opposite side of the body.
Damage to the non-dominant hemisphere (typically the right side) can lead to spatial neglect, where the person ignores objects or events on the opposite side of their body. Another potential consequence is visual field loss, or homonymous hemianopsia, causing blindness in the corresponding half of the visual field in both eyes.
Confirmation and Acute Medical Intervention
Rapid identification of a lateral infarct is paramount, operating on the principle that “time is brain.” Immediate brain imaging, typically a non-contrast Computed Tomography (CT) scan, is required when stroke is suspected. This scan primarily rules out a hemorrhagic stroke (bleeding in the brain) before clot-dissolving treatment is considered.
If imaging confirms an ischemic stroke, the first-line acute treatment is often an intravenous injection of a thrombolytic agent, such as tissue plasminogen activator (tPA). This medication dissolves the blood clot and must be administered within a narrow time window, ideally within four and a half hours of symptom onset.
For blockages in a large artery, such as the main trunk of the MCA, mechanical thrombectomy may be performed. This involves a surgeon threading a catheter to the brain to physically remove the clot. This endovascular procedure can be performed for a longer duration than tPA and is highly effective in restoring blood flow and reducing long-term disability.