A patient presented with thunder clap headache followed by unconsciousness and progressive III cranial nerve palsy. Which of the following is the most likely diagnosis:

Answer is B (Aneurysmal subarachnoid hemorrhage): Thunderclap Headache (sudden onset severe headache reaching maximum intensity < 1 min) together with third cranial nerve palsy and unconsciousness suggest a diagnosis of aneurysmal subarachnoid hemorrhage Thunderclap Headache is defined as high intensity headache of abrupt onset that reaches maximum intensity in less than 1 minute. Subarachnoid hemorrhage is the most common secondary cause of thunderclap headache although it may be seen with several other conditions including migraine (Thunder clap migraine). The diagnosis is suggested by clues in the history and physical examination. The presence of an associated third nerve palsy (subarachnoid aneurysm) and unconsciousness following the sudden severe headache suggests a diagnosis of SAH in the above question.