A 68-year-old man presents with a 3-week history of progressive headache, confusion, and gait disturbance following a minor head trauma he barely remembers. CT head shows a crescent-shaped collection over the cerebral convexity with mixed density (acute and chronic blood). Which of the following is NOT a typical feature of subdural hematoma?

Explanation

## Distinguishing Extradural from Subdural Hematoma ### Key Anatomical Difference **Key Point:** Subdural hematomas are **crescent-shaped** collections that follow the brain contour and cross the midline, while **extradural (epidural) hematomas are lens-shaped** and do NOT cross suture lines. ### Comparison Table | Feature | Subdural Hematoma | Extradural Hematoma | | --- | --- | --- | | **Shape on CT/MRI** | Crescent (follows brain surface) | Lens-shaped (biconvex) | | **Crosses midline?** | Yes, commonly | No, stops at suture lines | | **Crosses falx/tentorium?** | Yes | No | | **Vascular source** | Bridging veins (cortical veins) | Meningeal artery (usually middle meningeal) | | **Dura relationship** | Between dura and arachnoid | Between skull and dura | | **Onset** | Insidious (especially chronic/elderly) | Acute, lucid interval common | | **Age group** | Elderly, alcoholics, anticoagulated | Young, high-impact trauma | ### Why the Correct Answer is Wrong **High-Yield:** A **lens-shaped collection** is the hallmark of **extradural hematoma**, NOT subdural. Subdural hematomas are **crescent-shaped** because they spread along the brain surface between the dura and arachnoid membrane. ### Clinical Pearl The crescent shape of subdural hematoma is so characteristic that it is pathognomonic. The collection conforms to the curvature of the cerebral hemispheres and commonly crosses the midline (involving both frontal or both parietal regions), unlike the lens-shaped extradural hematoma which respects suture lines. ### Mnemonic: SUBDURAL FEATURES **S** – **S**preads across midline (crescent) **U** – **U**nder dura (between dura and arachnoid) **B** – **B**ridging veins torn **D** – **D**ural sinuses may be involved **U** – **U**sually insidious in elderly **R** – **R**ecurrent bleeds (chronic subdural) **A** – **A**cross falx/tentorium common **L** – **L**ow-impact trauma sufficient ### Why Each Option is Correct (Except One) 1. **Crosses midline** ✓ — Subdural hematomas commonly cross the midline and involve both hemispheres because they spread freely under the dura. 2. **Bridging veins torn** ✓ — The classic mechanism; cortical bridging veins tear as they cross the subdural space. 3. **Insidious onset in elderly** ✓ — Chronic subdural hematomas present weeks to months later with subtle symptoms; elderly patients are at high risk due to brain atrophy and fragile vessels. 4. **Lens-shaped collection** ✗ — This is the defining shape of extradural hematoma, not subdural. [cite:Robbins 10e Ch 28]