The term “basilar” refers to the base of a structure. The basilar artery is a large vessel located at the base of the brain. It forms the central part of the brain’s posterior circulation system and delivers oxygenated blood to structures that regulate basic survival functions. A disruption in blood flow through this vessel has profound health implications.
The Basilar Artery: Location and Role
The basilar artery is a single, midline vessel that runs along the front surface of the brainstem, specifically resting against the pons. It is formed by the union of the two vertebral arteries, which ascend through the neck and join together at the junction between the medulla oblongata and the pons.
The artery and its branches are responsible for supplying blood to three highly sensitive areas of the central nervous system. These areas include the brainstem, which controls functions like breathing, consciousness, and heart rate. It also supplies the cerebellum, which manages balance, coordination, and voluntary movements. The basilar artery terminates by dividing into the posterior cerebral arteries, which supply the posterior cerebrum, including the occipital lobes responsible for visual processing.
Basilar Artery Occlusion (Stroke)
A Basilar Artery Occlusion (BAO) is a type of ischemic stroke where a blockage, typically a blood clot, suddenly cuts off blood flow in the basilar artery. This event is a form of posterior circulation stroke, which affects the back portion of the brain. While BAO is relatively uncommon, accounting for only 1% to 4% of all ischemic strokes, it carries a high rate of severe disability or death due to the structures it supplies.
The immediate danger of a BAO stems from the resulting ischemia, or lack of oxygen, to the brainstem. Since the brainstem regulates essential functions like heart rate and breathing, occlusion can quickly lead to coma, respiratory failure, and death. Without treatment, the fatality rate for a complete basilar artery occlusion is estimated to be greater than 80%.
The most frequent causes of BAO are similar to those of other strokes, including local vessel narrowing and blockage due to atherosclerosis. Another significant cause is an embolism, where a clot travels from a different location, such as the heart or the vertebral arteries, and lodges in the basilar artery. Atherosclerosis tends to affect the proximal and middle segments of the artery, while embolic events more often block the distal segment.
Recognizing Symptoms and Warning Signs
The symptoms of a basilar artery stroke can be highly varied and often confusing, which can delay diagnosis. Prodromal symptoms, or warning signs that occur before a full stroke, can include transient ischemic attacks (TIAs) in the posterior circulation territory. These temporary episodes may feature vertigo, nausea, and headache, sometimes preceding the main event by days or weeks.
When the artery becomes fully occluded, the resulting syndrome often involves a combination of neurological deficits. Patients may experience double vision (diplopia), difficulty speaking (dysarthria), and problems swallowing (dysphagia). Motor function is frequently impaired, resulting in weakness on one side of the body (hemiparesis) or paralysis on both sides (quadriparesis).
One of the most severe outcomes of a mid-basilar occlusion is “locked-in syndrome,” where a patient is fully conscious but completely paralyzed, unable to move anything except for limited vertical eye movements. This condition results from ischemia in the pons, leaving the parts of the brain controlling consciousness intact but disconnecting them from the body’s motor control systems. The presence of any of these symptoms, especially when combined with vertigo and nausea, requires immediate emergency medical attention to maximize the chance of a favorable outcome.
Diagnosis and Acute Treatment
When a patient presents with symptoms suggestive of a basilar artery occlusion, medical teams must move quickly to confirm the diagnosis and visualize the blockage. Initial imaging often involves a non-contrast Computed Tomography (CT) scan to rule out a hemorrhagic stroke, as clot-busting medication would be unsafe. The preferred immediate diagnostic tool is CT angiography (CTA), which uses contrast dye to clearly visualize the blood vessels and identify the exact location of the occlusion.
Magnetic Resonance Angiography (MRA) is also effective for identifying the occlusion and assessing the extent of brain injury, though it may not be as rapidly available as CTA. Once a basilar artery occlusion is confirmed, the medical team initiates acute treatment to restore blood flow.
The first line of treatment may include intravenous thrombolysis, a medication administered through a vein to dissolve the blood clot. For eligible patients, the most aggressive and effective intervention is mechanical thrombectomy. This is a procedure where a specialized device is guided through the blood vessels to the site of the blockage to physically remove the clot. Thrombectomy is frequently performed in combination with thrombolysis to improve patient outcomes.