What is the most frequent cause of subarachnoid hemorrhage?

• A. Hypertensive bleed
• B. Berry aneurysms
• C. Arteriovenous malformation
• D. Trauma

Answer: (B)

Rupture of a saccular (berry) aneurysm is the most common cause of subarachnoid hemorrhage. These aneurysms occur at arterial bifurcations in the circle of Willis where the vessel wall is inherently weak, and when they rupture, blood floods the subarachnoid space, producing a sudden, severe headache and signs of meningismus. Hypertensive hemorrhage tends to bleed into the brain parenchyma itself (intraparanchymal hemorrhage) rather than into the subarachnoid space, so it is not the typical source of SAH. Arteriovenous malformations can cause SAH but are less frequent than berry aneurysm rupture. Trauma can also cause SAH, especially in the setting of head injury, but among spontaneous causes, berry aneurysm rupture remains the most frequent.