## Imaging Characteristics: Epidural vs Subdural Hematoma **Key Point:** The shape and distribution of blood on CT is the primary distinguishing feature between these two extra-axial collections. ### Epidural Hematoma - **Shape:** Lens-shaped or biconvex (convex on both sides) - **Distribution:** Does NOT cross the midline or suture lines - **Reason:** Blood is confined between dura and inner table of skull; dural attachments at sutures prevent spread - **Location:** Typically over convexities, commonly temporal region ### Subdural Hematoma - **Shape:** Crescent-shaped (concave inward toward brain) - **Distribution:** CAN cross the midline and suture lines - **Reason:** Blood strips dura from inner table; no anatomical barriers prevent spread along brain surface - **Location:** Follows brain contour; often bilateral in elderly ### Comparative Table | Feature | Epidural | Subdural | | --- | --- | --- | | **Shape on CT** | Lens/biconvex | Crescent | | **Crosses midline** | No | Yes | | **Crosses sutures** | No | Yes | | **Location** | Between dura & skull | Between dura & brain | | **Typical location** | Temporal (middle meningeal artery) | Convexities, interhemispheric | | **Age group** | Younger (head trauma) | Elderly, chronic alcoholics | | **Lucid interval** | Common | Rare | **High-Yield:** The lens shape that respects dural attachments is pathognomonic for epidural hematoma and is a high-yield imaging sign in NEET PG. **Clinical Pearl:** Epidural hematomas are neurosurgical emergencies because they expand rapidly and cause mass effect; subdural hematomas progress more slowly, especially chronic subdurals in elderly patients. 
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