Which imaging feature best distinguishes epidural hematoma from subdural hematoma on CT scan?

Explanation

## Distinguishing Epidural from Subdural Hematoma ### Morphology and Anatomical Boundaries **Key Point:** The critical discriminator is the relationship of the hematoma to the dural attachments and suture lines. | Feature | Epidural Hematoma | Subdural Hematoma | |---------|-------------------|-------------------| | **Shape** | Lens-shaped (biconvex) | Crescent-shaped (concave) | | **Crosses suture lines** | NO — stops at suture lines | YES — crosses freely | | **Crosses midline** | NO — confined by falx | Rarely (unless massive) | | **Location** | Between skull and dura | Between dura and arachnoid | | **Typical source** | Meningeal artery (arterial bleed) | Bridging veins (venous bleed) | ### Why the Lens Shape Matters **High-Yield:** Epidural hematomas are bounded by the dural attachments at the suture lines. The dura is firmly adherent to the inner table of the skull along the sutures, so blood cannot cross these lines. This creates the characteristic **lens-shaped or biconvex** appearance. Subdural hematomas, by contrast, lie between the dura and brain surface. The dura is not attached to the arachnoid, so blood spreads freely and crosses suture lines, creating a **crescent shape** that conforms to the brain contour. ### Clinical Pearl **Clinical Pearl:** Epidural hematomas are typically arterial (middle meningeal artery injury) and present acutely with rapid deterioration. Subdural hematomas are venous (bridging vein injury) and may present insidiously, especially in elderly or anticoagulated patients. ### Mnemonic **Mnemonic:** **BLED** = **B**iconvex = **E**pidural; **C**rescent = **S**ubdural (or "**C**rescent = **C**erebral surface"). [cite:Harrison 21e Ch 445]