Causes of Subarachnoid Hemorrhage: Understanding the Primary Triggers and Risk Factors
What Is a Subarachnoid Hemorrhage?
A subarachnoid hemorrhage (SAH) refers to bleeding that occurs in the subarachnoid space—the area between the brain and the thin tissues that cover it. This region is filled with cerebrospinal fluid and houses critical blood vessels, including major arteries and veins. Think of the brain's structure as similar to a walnut, where each lobe is separated by small gaps. These gaps contain the subarachnoid space, which protects and cushions the brain while allowing vital circulation.
Main Cause: Ruptured Brain Aneurysms
Approximately 75% of all subarachnoid hemorrhages are caused by the rupture of a cerebral aneurysm. A brain aneurysm is a weak or bulging spot on a blood vessel in the brain that can burst under pressure, leading to sudden and potentially life-threatening bleeding into the subarachnoid space. When this happens, blood spills into the surrounding fluid-filled areas, increasing intracranial pressure and disrupting normal brain function.
Ruptured aneurysms often result in severe symptoms such as a sudden, intense headache—commonly described as "the worst headache of my life"—along with nausea, vomiting, neck stiffness, and sometimes loss of consciousness. Early diagnosis and treatment are crucial to improving outcomes and reducing the risk of complications like stroke or permanent neurological damage.
Other Contributing Causes
While brain aneurysms are the most common cause, other vascular abnormalities can also lead to subarachnoid hemorrhage. One notable example is cerebral arteriovenous malformation (AVM), a congenital condition where arteries and veins form abnormal tangles, bypassing the capillary system. These malformed vessels are prone to rupture, especially under stress or elevated blood pressure.
In some cases, trauma—such as a severe head injury from an accident—can cause bleeding into the subarachnoid space. Less commonly, conditions like bleeding disorders, tumors, or the use of anticoagulant medications may contribute to non-aneurysmal SAH.
Idiopathic Cases: When No Clear Cause Is Found
Despite advances in neuroimaging and diagnostic techniques, a small percentage of subarachnoid hemorrhage cases remain unexplained. These are classified as idiopathic, meaning no definitive source of bleeding—such as an aneurysm or AVM—is identified even after thorough testing, including CT angiography and lumbar puncture. Researchers continue to study these cases to better understand potential underlying mechanisms, including microvascular weaknesses or transient vascular events.
Why Understanding the Cause Matters
Identifying the root cause of a subarachnoid hemorrhage is essential for effective treatment and long-term management. For instance, patients with aneurysms may require surgical clipping or endovascular coiling to prevent rebleeding. Those with AVMs might benefit from embolization, radiosurgery, or surgical removal. Even in unclear cases, close monitoring and lifestyle modifications—such as controlling hypertension, avoiding smoking, and limiting alcohol intake—can significantly reduce future risks.
Early detection through regular health screenings, especially for individuals with a family history of aneurysms or vascular diseases, plays a key role in prevention. Public awareness and timely medical intervention remain the best defenses against this serious neurological emergency.