**Core Concept**
Epidural hematoma is a type of traumatic brain injury characterized by the accumulation of blood between the skull and the dura mater, leading to increased intracranial pressure and potential brain herniation. The diagnosis of epidural hematoma on CT scan relies on the identification of specific radiological features.

**Why the Correct Answer is Right**
The correct answer is typically characterized by a biconvex or "lens-shaped" appearance on CT scan, which is due to the collection of blood within the epidural space. This is in contrast to a subdural hematoma, which typically has a crescentic or "crescent moon" shape. The biconvex shape is caused by the blood being compressed against the skull by the dura mater, resulting in a more rounded appearance.

**Why Each Wrong Option is Incorrect**
* **Option A:** A biconvex shape is not typically associated with subdural hematomas, which usually have a crescentic shape.
* **Option B:** A lentiform shape can be seen in epidural hematomas, but it is not the most characteristic or specific appearance.
* **Option C:** A biconvex shape is not typically associated with subarachnoid hemorrhage, which usually appears as a diffuse hyperdensity along the surface of the brain.

**Clinical Pearl / High-Yield Fact**
It is essential to carefully evaluate the CT scan for signs of increased intracranial pressure, such as midline shift, effacement of the sulci, and compression of the ventricles. A biconvex epidural hematoma can rapidly progress to a life-threatening condition if not promptly treated.

**Correct Answer:** C.