Okay, let's tackle this question about the shape of an extradural hematoma on a non-contrast CT scan. The user wants a detailed explanation following specific sections. First, I need to recall the core concept here.

The core concept is the anatomy and imaging characteristics of extradural hematomas. Extradural hematomas occur between the skull and the dura mater, often due to arterial injury, typically the middle meningeal artery. The shape is a key differentiator from subdural hematomas.

Now, the correct answer should be a lens-shaped or biconvex appearance. Why? Because the dura is adherent to the skull, so the hematoma can't cross suture lines, leading to that shape. Subdural hematomas, in contrast, are more crescent-shaped as they follow the contour of the brain and can cross sutures.

For the wrong options: if the options included crescent (which is subdural), triangular (maybe epidural?), or other shapes, I need to explain why they're incorrect. Each distractor would be labeled and addressed briefly.

Clinical pearl: Remembering that "lens shape" is epidural, "crescent" is subdural. This is crucial for differentiating on imaging. Also, epidural hematomas are often due to arterial injury, while subdural are venous.

Finally, the correct answer line. Need to make sure all sections are covered concisely without exceeding the character limit. Check formatting for markdown and ensure all key terms are bolded correctly.

**Core Concept**
Extradural (epidural) hematomas result from arterial bleeding (e.g., middle meningeal artery) between the skull and dura mater. Their **biconvex (lens-shaped)** appearance on non-contrast CT distinguishes them from subdural hematomas, which are crescent-shaped due to dural mobility.

**Why the Correct Answer is Right**
Extradural hematomas are **lens-shaped (biconvex)** because the dura is tightly adherent to the skull and cannot expand beyond the cranial sutures. This creates a convex margin against the skull and a concave interface with the brain, forming a lens shape. The rigid adherence to suture lines and arterial bleeding pattern are key imaging features.

**Why Each Wrong Option is Incorrect**
**Option A:** Crescent-shaped is incorrect—this describes subdural hematomas, which follow the dura’s contour and span suture lines.
**Option B:** Triangular is incorrect—no such classification exists for extradural hematomas.
**Option C:** Irregular is incorrect—extradural hematomas have a distinct, regular lens shape due to anatomical constraints.

**Clinical Pearl / High-Yield Fact**
"**Lens = Epidural, Crescent = Subdural**"—this is a critical imaging differentiator. Remember that epidural hematomas are often arterial (high density on CT) and classically caused by temporal bone fractures.

**Correct Answer: C. Lens-shaped**

✓ Correct Answer: B. Lens shaped