An aneurysm is a cerebrovascular disorder characterized by a localized ballooning or bulging of a blood vessel wall within the brain. When this weakening affects the basilar artery, it poses a particular risk due to its location.
The basilar artery is a single, large vessel formed by the joining of the two vertebral arteries at the base of the skull. It is a fundamental component of the posterior circulation, supplying oxygen-rich blood to the brainstem and cerebellum, which regulate life-sustaining functions such as consciousness, breathing, and heart rate. Aneurysms in this location are infrequent, accounting for approximately five percent of all intracranial aneurysms, yet their proximity to these vital structures makes them highly consequential.
Causes and Risk Factors for Aneurysm Formation
The underlying cause of a basilar artery aneurysm is a structural weakness in the vessel wall, which can develop from a combination of inherited and acquired factors. Genetic predisposition plays a role, often involving conditions that affect connective tissue, such as Ehlers-Danlos syndrome or Autosomal Dominant Polycystic Kidney Disease. A family history of cerebral aneurysms also suggests a congenital vulnerability in the arterial structure.
Acquired risk factors degrade the integrity of the artery wall over time. High blood pressure (hypertension) is a significant, modifiable factor, as the constant force of elevated pressure stresses the vessel walls and contributes to the development of microaneurysms.
Smoking is another major acquired factor, as chemicals in tobacco smoke weaken the arterial lining. Atherosclerosis (the hardening and narrowing of arteries due to plaque buildup) can also be implicated, particularly in fusiform aneurysms of the basilar trunk.
Recognizing Symptoms of Basilar Artery Pressure
Symptoms of a basilar artery aneurysm vary dramatically depending on whether the aneurysm is unruptured or has burst, causing a hemorrhage. An unruptured aneurysm may grow large enough to press on nearby cranial nerves or the brainstem, leading to specific neurological signs. Because the brainstem controls many movements, patients might experience double vision (diplopia) or a drooping eyelid.
Facial weakness, facial numbness, or difficulty with balance and coordination, known as ataxia, are also common symptoms resulting from brainstem compression. Some individuals may notice dizziness or vertigo, along with difficulty swallowing or speaking (dysarthria).
Rupture leads to a life-threatening subarachnoid hemorrhage, where blood leaks into the space surrounding the brain. The hallmark is the sudden onset of an extremely severe headache, often described as the “worst headache of my life.” This is accompanied by nausea, vomiting, a stiff neck, and a rapid decrease in consciousness.
Advanced Imaging Techniques for Diagnosis
The diagnosis of a basilar artery aneurysm relies on specialized medical imaging techniques that visualize the blood vessels in the brain. A non-contrast Computed Tomography (CT) scan is often the first test performed in an emergency setting to quickly detect blood surrounding the brain, which confirms a rupture. If the initial CT scan is negative for blood but a rupture is still suspected, a lumbar puncture may be performed to check the cerebrospinal fluid for red blood cells.
For a detailed view of the vasculature, non-invasive methods like Computed Tomography Angiography (CTA) or Magnetic Resonance Angiography (MRA) are used. CTA involves injecting a contrast dye to create a three-dimensional model of the arteries and the aneurysm’s shape. Contrast-enhanced MRA is also effective, providing excellent visualization of the posterior circulation and the aneurysm’s relationship to surrounding structures.
The most definitive and detailed diagnostic tool is Digital Subtraction Angiography (DSA), considered the gold standard for mapping the aneurysm. DSA is an invasive procedure where a catheter is threaded from an artery in the groin or wrist up to the cerebral arteries. Contrast dye is injected directly, offering high-resolution, real-time images crucial for treatment planning.
Treatment Modalities for Basilar Artery Aneurysms
Treatment decisions for a basilar artery aneurysm depend on its size, shape, location, and whether it has ruptured, with observation being an option for small, asymptomatic aneurysms. Due to the deep and delicate location of the basilar artery, endovascular techniques are frequently favored as a less invasive approach to repair the vessel. These procedures are performed by navigating a catheter through the body’s arterial system to the aneurysm site in the brain.
One common endovascular technique is coiling, which involves deploying tiny platinum coils into the aneurysm sac to induce clotting. The coils fill the aneurysm, effectively blocking blood flow into the weakened area.
Another advanced endovascular strategy is flow diversion, where a specialized mesh stent is placed across the neck of the aneurysm. This stent diverts blood flow away from the sac, promoting long-term healing.
Surgical clipping is an alternative treatment option requiring an open procedure called a craniotomy to access the aneurysm. A neurosurgeon places a small metal clip across the neck of the aneurysm, permanently excluding it from the circulation. However, clipping the basilar artery is technically challenging and carries higher risk due to the artery’s deep location and its proximity to the brainstem and critical perforating vessels.