Causes of Subarachnoid Hemorrhage: Understanding the Risk Factors Behind a Life-Threatening Condition

Subarachnoid hemorrhage (SAH) is a critical medical emergency characterized by bleeding into the space between the brain and the surrounding membrane, known as the subarachnoid space. This condition can lead to severe neurological damage or even death if not promptly diagnosed and treated. Identifying the underlying causes of SAH is essential for both prevention and effective management.

Primary Cause: Ruptured Intracranial Aneurysms

Intracranial aneurysms are the most common cause of subarachnoid hemorrhage, accounting for approximately 50% to 80% of all cases. These aneurysms are weak, bulging spots on the walls of brain arteries that can rupture under pressure. The risk is significantly increased in individuals with chronic hypertension or atherosclerosis, which weaken blood vessel integrity over time. In some instances, aneurysms may develop due to infections, leading to what is known as fungal (mycotic) aneurysms. These are less common but equally dangerous, often arising from bacterial endocarditis or other systemic infections that spread to cerebral vessels.

Vascular Malformations: A Significant Contributor

Another major cause of SAH is cerebrovascular malformations, responsible for about 10% of cases. Among these, arteriovenous malformations (AVMs) make up nearly 80% of vascular abnormalities linked to hemorrhagic events. AVMs are tangles of abnormal blood vessels that disrupt normal blood flow and are prone to rupture. They are typically present from birth and are more frequently diagnosed in younger adults and adolescents. Over 90% of these malformations are located in the supratentorial region of the brain, particularly within the territory supplied by the middle cerebral artery, making them a key focus in neurovascular assessments.

Less Common but Important Causes

Moyamoya disease is a rare cerebrovascular disorder that plays a notable role in pediatric SAH, contributing to around 20% of cases in children. It involves the progressive narrowing of the internal carotid arteries, leading to the formation of fragile collateral vessels that are highly susceptible to bleeding.

Other potential triggers include brain tumors, which may erode blood vessels or increase intracranial pressure, and pituitary apoplexy, a sudden hemorrhage into the pituitary gland. Additionally, hematological disorders such as leukemia or clotting deficiencies can predispose individuals to spontaneous bleeding in the subarachnoid space.

Conditions like cerebral venous sinus thrombosis — where blood clots form in the brain's venous system — and complications from anticoagulant therapy (such as warfarin or heparin use) also elevate the risk of SAH, especially in patients with pre-existing vascular vulnerabilities.

Idiopathic Cases: When No Clear Cause Is Found

Despite advances in diagnostic imaging and clinical evaluation, approximately 10% of subarachnoid hemorrhage cases remain cryptogenic, meaning no definitive cause can be identified. These idiopathic cases underscore the complexity of cerebrovascular health and highlight the need for ongoing research and vigilant monitoring in at-risk populations.

Early detection, lifestyle modifications, and proper management of conditions like high blood pressure and vascular abnormalities are crucial steps in reducing the incidence of SAH. Public awareness and timely medical intervention can significantly improve outcomes for individuals facing this serious neurological event.