CT scan of a patient with history of head injury shows a biconvex hyperdense lesion displacing the grey–white matter interface. The most likely diagnosis is
First, hyperdensity on CT usually indicates something dense, like blood. The shape is biconvex, which is classic for an epidural hematoma. Epidural hematomas are often lens-shaped or biconvex because they're located between the dura and the skull, and they can't spread into sulci or fissures. They're typically caused by arterial injury, most commonly the middle meningeal artery, which is why they're often located in the temporal region.
Now, let's look at the other options. Subdural hematomas are usually more crescent-shaped because they lie under the dural sinuses and can spread along the brain's surface. They might be hyperdense acutely but can become isodense or hypodense over time. Subarachnoid hemorrhage would show hyperdensity in the sulci and cisterns, not a biconvex lesion. Intracerebral hemorrhage is within the brain parenchyma and might not have the biconvex shape; it's more irregular.
The displacement of the grey-white matter interface suggests mass effect, which is common in epidural hematomas because they expand rapidly. The clinical pearl here is that epidural hematomas are often associated with a "lucid interval," where the patient initially loses consciousness, then regains it, followed by deterioration. This is a key point for exams like NEET PG or USMLE.
So, the correct answer is the one that's epidural hematoma. Let me make sure I didn't mix up the shapes with subdural. Yes, subdural is crescent, epidural is biconvex. The hyperdensity makes sense for both acute cases, but the shape is the differentiator. The displacement of the grey-white matter interface is a sign of expansion between the dura and skull, which fits with epidural.
**Core Concept**
This question tests recognition of CT imaging features of intracranial hemorrhage types. **Biconvex hyperdensity** on non-contrast CT is a hallmark of **epidural hematoma**, caused by arterial bleeding (e.g., middle meningeal artery) between the dura and skull.
**Why the Correct Answer is Right**
An epidural hematoma presents as a **lens-shaped (biconvex)** hyperdense lesion on CT due to acute arterial blood. It displaces the **grey-white matter interface** because it expands between the dura and calvarium, compressing the brain parenchyma. This is distinct from subdural hematomas (crescent-shaped) and intracerebral bleeds (irregular). The biconvex shape reflects the hematoma's confinement by the dural attachment at the suture lines.
**Why Each Wrong Option is Incorrect**
**Option A:** Subdural hematoma is **crescent-shaped**, not biconvex, and lies between the dura and arachnoid.
**Option B:** Subarachnoid hemorrhage shows **hyperdensity in sulci/cisterns