**Core Concept**
The question is testing the ability to identify a characteristic imaging finding in the brain, specifically a hyperdense lesion in the 3rd ventricle. The underlying concept is the recognition of hemorrhagic lesions on non-contrast computed tomography (NC-CT) scans.

**Why the Correct Answer is Right**
On NC-CT scans, acute hemorrhage appears as a hyperdense (bright) lesion due to the high density of blood. The 3rd ventricle is a midline structure located between the two hemispheres of the brain, and a hyperdense lesion in this location is highly suggestive of a hemorrhagic stroke. The most common cause of hemorrhagic stroke is a rupture of an intracranial aneurysm, which can occur in the walls of blood vessels that supply the brain, including those in the vicinity of the 3rd ventricle.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a hyperdense lesion in the 3rd ventricle is not typically associated with a tumor, such as a glioma. While tumors can occur in the brain, they are not usually characterized by acute hyperdensity on NC-CT scans.

**Option B:** This option is incorrect because a hyperdense lesion in the 3rd ventricle is not typically associated with an infectious process, such as meningitis. While meningitis can cause changes in the brain, it is not usually characterized by a single hyperdense lesion on NC-CT scans.

**Option C:** This option is incorrect because a hyperdense lesion in the 3rd ventricle is not typically associated with a vascular malformation, such as an arteriovenous malformation (AVM). While AVMs can cause hemorrhage, they are not usually characterized by a single hyperdense lesion on NC-CT scans.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that acute hemorrhage on NC-CT scans typically appears as a hyperdense lesion, whereas ischemic stroke appears as a hypodense (dark) lesion. This distinction is crucial for making an accurate diagnosis and determining the appropriate treatment.

**Correct Answer:** C.