An aneurysm represents an abnormal bulge or ballooning that develops in the wall of a blood vessel, typically an artery. This weakening allows the vessel wall to expand outward, similar to a weak spot on an overinflated balloon or a bulge in a garden hose. The constant force of blood flow through the weakened area can cause it to enlarge over time. This localized dilation can occur in any artery throughout the body, though some locations are more commonly affected.
Anatomy of an Aneurysm
A healthy blood vessel wall consists of three distinct layers: the tunica intima, tunica media, and tunica adventitia. The innermost layer, the tunica intima, provides a smooth surface for blood flow and helps regulate blood pressure. The middle layer, the tunica media, contains elastic fibers and smooth muscle cells that allow the vessel to expand and contract, maintaining blood flow. The outermost layer, the tunica adventitia, provides structural support and contains nerves and small blood vessels.
An aneurysm forms when the structural integrity of these layers, particularly the tunica media, becomes compromised. As the vessel wall weakens, the consistent pressure of blood pushing against it causes a localized outpouching. This abnormal expansion can take on different shapes. A saccular aneurysm appears as a berry-like sac attached to one side of the vessel, often connected by a narrow neck. This type is frequently observed in brain arteries.
In contrast, a fusiform aneurysm presents as a spindle-shaped bulge that encompasses the entire circumference of the blood vessel. These aneurysms involve a longer segment of the artery compared to saccular types.
Common Aneurysm Locations
Aneurysms can develop in various arteries throughout the body, with certain areas being more susceptible due to anatomical factors or high blood pressure. The brain is a common site for aneurysms, known as cerebral aneurysms, often forming at the junctions where arteries branch.
The aorta, the body’s largest artery carrying blood from the heart, is another common location for aneurysm formation. Aortic aneurysms can occur in the chest, known as thoracic aortic aneurysms, or in the abdomen, termed abdominal aortic aneurysms (AAAs). The abdominal aorta is the most frequent site for aortic aneurysms. Other less common locations include arteries behind the knees (popliteal aneurysms), in the intestines (mesenteric artery aneurysms), or near the spleen (splenic artery aneurysms).
Visualizing an Aneurysm Rupture
The primary concern with an aneurysm is its potential to rupture, a serious medical emergency. A rupture occurs when the pressure of blood inside the vessel becomes too great for the weakened aneurysm wall to contain, leading to a tear. When this happens, blood leaks out from the vessel into the surrounding tissues.
For a cerebral aneurysm, a rupture releases blood into the subarachnoid space, the area around the brain filled with cerebrospinal fluid. This bleeding can irritate brain tissue and lead to a sudden, severe headache, often described as the “worst headache of one’s life”. In other body locations, such as the aorta, a rupture can cause internal bleeding into the abdominal or chest cavity. This leakage of blood is a life-threatening event, potentially leading to complications like stroke, brain damage, or even death.