An aneurysm and a stroke are not the same medical condition, though they are fundamentally related through the body’s vascular system. An aneurysm is a structural weakness in a blood vessel wall, essentially a balloon-like bulge, most commonly occurring in the brain or aorta. A stroke, by contrast, is a medical emergency that happens when blood flow to the brain is interrupted, causing brain cells to die from a lack of oxygen and nutrients. A ruptured aneurysm in the brain is a direct cause of a specific, life-threatening type of stroke.
Understanding Aneurysms
An aneurysm is a localized, abnormal bulging in the wall of a blood vessel, caused by a weakening of the vessel’s structure. While aneurysms can appear in any artery, they are most frequently found in the aorta, the body’s largest artery, and the arteries supplying the brain, known as cerebral aneurysms. The constant force of blood pressure pushes against the weakened section, causing the vessel to stretch outward.
Aneurysms are classified by their shape, with the two main types being saccular and fusiform. A saccular aneurysm, often called a berry aneurysm in the brain, bulges out on only one side of the artery wall. The fusiform type involves a uniform dilation that bulges out on all sides of the vessel. Risk factors contributing to this weakening include long-term high blood pressure, smoking, and certain genetic conditions.
Most aneurysms are small and do not cause noticeable symptoms, often discovered incidentally during imaging for an unrelated condition. However, a larger, unruptured brain aneurysm can cause symptoms if it presses on nearby nerves or brain tissue. These signs can include pain above or behind one eye, a dilated pupil, changes in vision, or numbness on one side of the face. These symptoms result from physical pressure on surrounding structures, not a disruption of blood flow.
Understanding Strokes
A stroke is a time-sensitive event where the brain is deprived of blood flow, rapidly leading to the death of brain cells. This interruption occurs in two primary ways, differentiating the main categories of stroke: ischemic and hemorrhagic. The effects of a stroke depend on which part of the brain is damaged and the extent of that damage.
The vast majority of strokes, approximately 87%, are ischemic strokes, caused by a blockage in a blood vessel supplying the brain. This blockage is often a blood clot. If the clot forms directly in the brain’s arteries, it is a thrombotic stroke. If the clot travels from another part of the body and becomes lodged in a brain artery, it is an embolic stroke. Atherosclerosis, the buildup of fatty plaque, is a common underlying factor leading to clot formation.
The less common type is a hemorrhagic stroke, accounting for about 13% of all cases, which involves bleeding into or around the brain. This occurs when a blood vessel ruptures, causing blood to accumulate and compress surrounding brain tissue. High blood pressure is a major cause, as it damages and weakens small blood vessels over time. Hemorrhagic strokes are classified based on the location of the bleeding: intracerebral (within the brain tissue) or subarachnoid (in the space surrounding the brain).
When Aneurysms Lead to Strokes
While an aneurysm is a structural defect and a stroke is a resulting brain injury, a ruptured aneurysm directly causes a specific stroke type. When a cerebral aneurysm bursts, it causes an immediate and catastrophic brain bleed. This event is a form of hemorrhagic stroke, specifically a subarachnoid hemorrhage (SAH), accounting for about 85% of SAH cases.
The rupture releases blood into the subarachnoid space, the area surrounding the brain. The sudden influx of blood causes a rapid and severe increase in pressure inside the skull, which damages brain cells. This bleeding and subsequent pressure constitute the hemorrhagic stroke event. Symptoms of this rupture, like a sudden, excruciating headache often described as the “worst headache of one’s life,” are immediate signs of a hemorrhagic stroke.
It is important to understand that not all hemorrhagic strokes are caused by a ruptured aneurysm, even though all ruptured cerebral aneurysms lead to a hemorrhagic stroke. Other factors, like uncontrolled high blood pressure or arteriovenous malformations, can also cause blood vessels to rupture and result in bleeding within the brain. Thus, an aneurysm is a dangerous pre-existing condition that, upon rupture, triggers a life-threatening type of stroke.