**Question:** T-sign is seen in

A. Acute Subarachnoid Hemorrhage (SAH)
B. Acute Ischemic Stroke
C. Subdural Hematoma
D. Encephalitis

**Correct Answer:** A. Acute Subarachnoid Hemorrhage (SAH)

**Core Concept:** T-sign is a radiological sign in neuroimaging studies, particularly computed tomography (CT) scans, which indicates the presence of subarachnoid hemorrhage (SAH). SAH is a type of stroke resulting from bleeding into the subarachnoid space, typically caused by a ruptured aneurysm.

**Why the Correct Answer is Right:** T-sign is a characteristic finding on CT scans in patients with acute SAH. It represents the presence of blood within the subarachnoid space, which can be seen as a hyperdense line or a signet ring-like appearance at the level of the third ventricle in the brain. This sign is a crucial clue for the diagnosis of SAH, as it is not seen in other conditions like acute ischemic stroke or subdural hematoma.

**Why Each Wrong Option is Incorrect:**

A. Acute Ischemic Stroke (AIS): In AIS, the CT findings typically include early ischemic changes, hemorrhagic conversion, or infarcts. T-sign is not seen in AIS.

B. Subdural Hematoma (SDH): T-sign is not specific to SDH, which would typically present with hyperdense or low-density subdural hematoma on CT scan.

C. Encephalitis: Encephalitis presents with various neurological symptoms and signs, rather than specific CT findings like T-sign.

**Clinical Pearl:** T-sign is a valuable imaging clue for the initial diagnosis of SAH, especially when combined with other imaging findings like the empty sella sign, widened fourth ventricle, or the "crazy paving" pattern. Early recognition of these signs aids in initiating prompt management, including neurosurgical intervention and neurovascular evaluation for aneurysm detection.