An internal carotid artery (ICA) stroke is an ischemic stroke that occurs when blood flow to a portion of the brain is blocked. The ICA is a pair of large vessels in the neck that supply the majority of the brain’s blood, making its occlusion a serious event. A blockage in the ICA results in a widespread lack of oxygen and nutrients to a large section of the cerebral hemisphere. Recognizing the mechanisms and resulting symptoms is important for rapid medical response.
Understanding the Internal Carotid Artery and Stroke Mechanism
The ICA begins in the neck, where the common carotid artery divides, and travels upward without branching until it enters the skull base. Once inside the skull, it gives rise to several major branches that form the anterior circulation, which supplies the frontal, parietal, and temporal lobes of the brain. These areas are responsible for higher-level functions, including movement, sensation, and language.
The ICA branches into the Middle Cerebral Artery (MCA) and the Anterior Cerebral Artery (ACA). Since the MCA is often a direct continuation of the ICA, a blockage frequently causes a large-territory stroke affecting the entire MCA distribution. The primary mechanism of an ICA stroke is typically thromboembolism, where a clot or plaque fragment breaks off the ICA wall and travels downstream to lodge in a smaller artery, such as the MCA.
This event results in sudden and severe ischemia to the affected brain tissue. In some cases, the ICA itself can become completely occluded, leading to widespread brain damage. This damage occurs unless collateral blood vessels from the posterior circulation are able to reroute blood flow to the deprived areas.
Primary Causes and Specific Risk Factors
The most frequent cause of an ICA stroke is severe narrowing, or stenosis, usually due to atherosclerosis. This process involves the buildup of fatty deposits, cholesterol, and calcium, which hardens and narrows the inner channel of the artery. This plaque can become unstable, rupture, and form a blood clot that either blocks the artery locally or travels to the brain as an embolus.
Another specific cause, more common in younger stroke patients, is carotid artery dissection. This involves a tear in the inner lining of the artery wall, allowing blood to enter and split the wall layers apart. The resulting hematoma, or collection of clotted blood within the wall, can narrow the artery and impede blood flow. Dissections can occur spontaneously or after minor neck trauma, such as a sudden head turn or whiplash.
Specific medical conditions that contribute to atherosclerosis are the primary risk factors for an ICA stroke. These include:
- Uncontrolled high blood pressure
- Elevated cholesterol levels
- Diabetes mellitus
- Cigarette smoking, which damages arterial walls
- Advanced age
Recognizing the Unique Warning Signs and Symptoms
Because the ICA supplies a large territory of one cerebral hemisphere, the resulting stroke symptoms involve one side of the body. Common signs include sudden, profound weakness or paralysis on the side of the body opposite the blocked ICA, known as hemiparesis or hemiplegia. Patients may also experience a loss of sensation, like numbness or tingling, on the same side of the body.
If the blockage occurs on the dominant side of the brain (usually the left hemisphere), the patient may experience aphasia, which is difficulty understanding or expressing language. Conversely, a stroke on the non-dominant side of the brain may result in neglect, where the patient is unaware of the opposite side of their body or their environment. These hemispheric signs are characteristic of a large vessel occlusion in the anterior circulation.
A unique warning symptom directly related to ICA blockage is amaurosis fugax. This temporary symptom is often described as a curtain or shade descending over one eye. It occurs because a tiny embolus breaks off the ICA plaque and temporarily blocks the ophthalmic artery, a direct branch of the ICA that supplies the retina of the eye.
Emergency Diagnosis and Acute Intervention Strategies
The urgent diagnosis of an ICA stroke begins with rapid imaging to confirm ischemia and identify the blockage location. A Computed Tomography (CT) scan is the first test, used to rule out a hemorrhagic stroke, which would contraindicate certain treatments. Following this, CT Angiography (CTA) or Magnetic Resonance Angiography (MRA) visualizes the neck and brain vessels, confirming ICA occlusion or severe stenosis. A non-invasive Carotid Duplex Ultrasound may also be used to assess blood flow and the degree of narrowing in the ICA in the neck.
Acute intervention focuses on rapidly restoring blood flow to the brain. For eligible patients presenting within a short time window, Intravenous Thrombolysis (IV tPA) may be administered to dissolve the clot. However, mechanical thrombectomy is often necessary for a large vessel occlusion, such as an ICA or proximal MCA blockage.
Mechanical thrombectomy is an endovascular procedure where a specialized catheter is threaded through the arteries to physically retrieve or remove the clot. After the acute stroke is managed, procedures address the underlying ICA problem to prevent recurrence. These include Carotid Endarterectomy (CEA), which surgically removes plaque, or Carotid Artery Stenting (CAS), where a mesh tube holds the artery open.