Common Causes of Subarachnoid Hemorrhage: A Comprehensive Overview

Understanding Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) refers to the leakage of blood into the subarachnoid space—the area between the brain and the thin tissues that cover it. This condition is a serious medical emergency, often resulting in severe neurological complications or even death if not promptly diagnosed and treated. While SAH can arise from various causes, its most frequent origin lies in ruptured intracranial aneurysms.

The Leading Cause: Ruptured Cerebral Aneurysms

Ruptured cerebral aneurysms account for approximately 80% of spontaneous subarachnoid hemorrhages. An aneurysm is a weak spot in the wall of a brain artery that bulges outward and fills with blood. Over time, increased pressure or other stressors can cause this weakened vessel to burst, spilling blood into the surrounding subarachnoid space. These aneurysms are commonly located at branching points in the Circle of Willis, a critical arterial network at the base of the brain.

Other Vascular Abnormalities Contributing to SAH

Besides aneurysms, several other vascular disorders may lead to subarachnoid bleeding. Arteriovenous malformations (AVMs), which are tangles of abnormal blood vessels connecting arteries and veins, can rupture and cause hemorrhage. Similarly, Moyamoya disease, a rare cerebrovascular disorder characterized by progressive narrowing of the arteries in the brain, increases the risk of SAH due to fragile collateral vessel formation. Additionally, dural arteriovenous fistulas (dAVFs)—abnormal connections between arteries and veins in the dura mater—can also result in bleeding into the subarachnoid space, especially when high-flow shunts develop.

Non-Aneurysmal Subarachnoid Hemorrhage: A Milder Variant

Not all cases of SAH stem from aneurysms. Non-aneurysmal subarachnoid hemorrhage, often localized to the perimesencephalic region, tends to have a more favorable prognosis. The exact cause of this type remains unclear, but it's believed to involve small venous bleeds or capillary-level ruptures. Patients with this form typically experience fewer complications and have lower rates of rebleeding compared to those with aneurysm-related SAH.

Contributing Factors and Risk Elements

Certain physiological and pathological factors significantly influence the likelihood of developing SAH. Sudden spikes in blood pressure, such as those caused by intense physical exertion, emotional stress, or hypertensive crises, can trigger vessel rupture. Moreover, structural damage to blood vessel walls—due to aging, smoking, chronic hypertension, or genetic connective tissue disorders like Ehlers-Danlos syndrome—further elevates the risk. Trauma, although less common in spontaneous SAH, can also lead to bleeding in the subarachnoid space.

Why Early Detection Matters

Given the life-threatening nature of subarachnoid hemorrhage, recognizing symptoms early—such as a sudden, severe headache ("thunderclap headache"), neck stiffness, nausea, and altered consciousness—is crucial. Rapid imaging, including non-contrast CT scans and lumbar puncture when needed, helps confirm the diagnosis. Identifying the underlying cause through angiography allows for targeted interventions, improving patient outcomes and reducing long-term disability.