Question

The most common cause of spontaneous subarachnoid hemorrhage is

• A. Rupture of an arterio-venous malformation
• B. Saccular aneurysm
• C. Extension from intracerebral hemorrhage
• D. Head injury

Hint:

Remember the question asks about non-traumatic bleeding only.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
This question asks for the leading cause of subarachnoid hemorrhage (SAH) that occurs spontaneously, that is, without a traumatic trigger. Distinguishing "spontaneous" from "traumatic" SAH is the key to answering correctly.

Step 2: Key Concept or Approach:
Head injury is actually the single most common cause of SAH overall, but the question specifically excludes trauma by asking about spontaneous hemorrhage. Among non-traumatic causes, rupture of a saccular (berry) aneurysm at the circle of Willis accounts for the large majority of cases, followed at a distance by arteriovenous malformations and by bleeds that extend into the subarachnoid space from an underlying intracerebral hematoma.

Step 3: Working Through the Options:
Rupture of an arterio-venous malformation does cause spontaneous SAH but is far less common than aneurysm rupture, and AVMs tend to present at a younger age. Saccular aneurysm rupture, typically at branch points such as the anterior communicating artery or the posterior communicating artery origin, is responsible for roughly 75-80 percent of spontaneous SAH and is the classic answer for this question. Extension from intracerebral hemorrhage can produce blood in the subarachnoid space, but this is a secondary phenomenon, not the primary or most common cause. Head injury is excluded by the word "spontaneous" in the question, even though it is the leading cause of SAH when trauma is included.

Step 4: Conclusion:
The correct answer is saccular aneurysm, the classic cause of non-traumatic subarachnoid hemorrhage.