Most common cause of subarachnoid hemorrhage is:
**Core Concept**
Rupture of an aneurysm in the cerebral blood vessels leads to bleeding into the subarachnoid space, causing a subarachnoid hemorrhage. This condition is often life-threatening and requires prompt medical attention.
**Why the Correct Answer is Right**
The most common cause of subarachnoid hemorrhage is the rupture of an aneurysm, typically located in the anterior communicating artery complex or the middle cerebral artery bifurcation. When an aneurysm ruptures, it releases blood into the subarachnoid space, which surrounds the brain and spinal cord. This can lead to increased intracranial pressure, vasospasm, and potentially life-threatening complications.
**Why Each Wrong Option is Incorrect**
* **Option A:** Atherosclerotic disease is a common cause of ischemic strokes, but it is not typically associated with subarachnoid hemorrhage.
* **Option B:** Hypertension is a risk factor for aneurysm formation, but it is not the direct cause of subarachnoid hemorrhage.
* **Option C:** Infection or inflammation of the blood vessels (vasculitis) can cause bleeding into the subarachnoid space, but it is a less common cause compared to aneurysm rupture.
**Clinical Pearl / High-Yield Fact**
When evaluating a patient with a subarachnoid hemorrhage, it is essential to promptly diagnose and treat the underlying aneurysm to prevent further complications. A non-contrast CT scan is often used as an initial imaging modality to identify the hemorrhage and guide further management.
**Correct Answer: C. Aneurysmal rupture.**