A patient presented with thunder clap headache followed by unconsciousness with pregressive III ranial nerve palsy. Likely diagnosis is
**Core Concept**
The patient's presentation suggests a diagnosis related to a sudden, severe headache, often associated with non-contrast CT findings of subarachnoid hemorrhage (SAH). This is likely due to the rupture of an intracranial aneurysm, which leads to bleeding into the subarachnoid space.
**Why the Correct Answer is Right**
The patient's symptoms, particularly the thunderclap headache followed by unconsciousness, are classic for a SAH. The progressive IIIrd cranial nerve palsy is likely due to the compression or stretching of the oculomotor nerve (IIIrd cranial nerve) by the expanding aneurysm or blood clot. This is a result of the aneurysm's location, which may be near the base of the brain, close to the oculomotor nerve.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, but it is essential to address the distractors explicitly. If an option was listed, it could be a condition like a meningioma or an arteriovenous malformation (AVM), which might cause SAH but doesn't directly explain the IIIrd cranial nerve palsy.
* **Option B:** A pituitary apoplexy could cause sudden headache and IIIrd cranial nerve palsy due to compression of the nerve by an expanding pituitary adenoma. However, it typically presents with endocrine dysfunction and would not typically cause SAH.
* **Option C:** A cerebral vasculitis could cause SAH and IIIrd cranial nerve palsy due to inflammation and damage to blood vessels. However, it is less likely to present as an acute, isolated event and would often be associated with systemic symptoms and other vascular findings.
* **Option D:** A posterior communicating artery aneurysm could cause IIIrd cranial nerve palsy due to compression of the nerve by the aneurysm. However, it would not typically present with the thunderclap headache and SAH seen in this patient.
**Clinical Pearl / High-Yield Fact**
The "doughnut sign" on non-contrast CT is a classic finding in SAH, representing a ring of high density surrounding a central area of low density due to blood in the subarachnoid space. This sign is often associated with aneurysmal SAH.
**Correct Answer:** C.