The carotid arteries are a pair of major blood vessels located on either side of the neck, functioning as the primary conduits for delivering oxygen-rich blood to the head and brain. The Left Internal Carotid Artery (LICA) is the main vessel on the left side responsible for this supply. These vessels originate in the chest and ascend through the neck, making them a significant focus in vascular and neurological medicine.
Location and Role in Brain Blood Supply
The LICA begins where the left common carotid artery divides, a point known as the carotid bifurcation, usually at the level of the fourth cervical vertebra. Unlike its counterpart, the LICA has no branches in the neck. It enters the cranium by passing through a bony tunnel called the carotid canal, which classifies it as an “internal” artery.
Once inside the skull, the LICA follows a complex course before terminating by splitting into the anterior and middle cerebral arteries. This network supplies the anterior two-thirds of the left cerebral hemisphere. This region controls functions like speech, motor control for the right side of the body, and sensation.
A specific branch of the LICA, the ophthalmic artery, supplies blood to the left eye. The continuous flow through the LICA is necessary for maintaining vision and proper motor and sensory function.
Internal Versus External Carotid Arteries
The common carotid artery on each side bifurcates into two distinct vessels: the Internal Carotid Artery (ICA) and the External Carotid Artery (ECA). The ICA, which includes the LICA, travels inward toward the brain and the eyes, delivering blood to these intracranial structures.
The ECA, by contrast, supplies the extracranial structures, meaning those outside the skull, including the face, scalp, neck, and part of the skull. The ECA is easily distinguished because it gives off multiple branches in the neck, while the ICA typically does not branch until it enters the skull.
The functional difference is significant: the ICA supports the low-resistance vascular bed of the brain, requiring a high and continuous flow. The ECA supplies a high-resistance bed, resulting in a more pulsatile flow pattern. Issues affecting the internal artery, like the LICA, pose a direct threat to brain function, whereas external artery issues generally affect surface tissues.
Primary Health Concerns Associated with the LICA
The most common health issue affecting the LICA is atherosclerosis, where fatty deposits (plaque) build up inside the artery walls. This buildup causes the artery to narrow (carotid stenosis), restricting blood flow to the left side of the brain. The plaque can also crack or rupture, triggering a blood clot that further obstructs the vessel.
A blockage in the LICA significantly elevates the risk of an ischemic stroke, which occurs when blood flow to the brain is severely reduced or cut off. If plaque or a blood clot breaks away, it can travel downstream and lodge in a smaller artery, instantly depriving that area of oxygen. Because the LICA supplies the left cerebral hemisphere, a stroke resulting from its blockage typically causes neurological symptoms on the right side of the body (contralateral effect).
Another concern is carotid artery dissection, which involves a tear in the inner lining of the LICA wall. Blood enters and separates the layers of the artery wall, forming a clot or causing the vessel to bulge, which blocks blood flow. Dissections can occur spontaneously or after minor trauma, and are a leading cause of stroke in younger individuals.
Recognizing Signs of Carotid Artery Issues
Issues with the LICA often manifest as a Transient Ischemic Attack (TIA), sometimes called a “mini-stroke,” which is a temporary interruption of blood flow to the brain. A TIA is often a warning sign that a full-blown stroke may be imminent. Symptoms are sudden in onset and typically affect the side of the body opposite the blocked artery.
A person may experience sudden weakness or numbness in the face, arm, or leg on the right side of the body. Difficulty speaking or understanding speech (aphasia) is also a common sign if the stroke affects the dominant left hemisphere. Vision changes may occur, specifically temporary, painless vision loss in the left eye, a condition called amaurosis fugax.
Because brain cells begin to die within minutes of oxygen deprivation, these symptoms require immediate medical attention. Any sudden onset of unilateral weakness, speech difficulty, or vision loss should be treated as a medical emergency. Acting quickly when these signs appear can reduce the chance of long-term disability.