A 68-year-old woman with chronic alcoholism presents with progressive headache and confusion over 3 weeks. MRI brain shows a crescent-shaped hematoma that crosses the midline. Which feature most reliably distinguishes this subdural hematoma from an acute extradural hematoma in terms of vascular source?

Explanation

## Vascular Source: Key Discriminator Between Extradural and Subdural Hematoma ### Bleeding Source and Clinical Presentation **Key Point:** The vascular source determines the rate of accumulation and clinical presentation. Extradural hematomas bleed from arterial sources (rapid), while subdural hematomas bleed from venous sources (slow). ### Comparison Table | Parameter | Extradural Hematoma | Subdural Hematoma | | --- | --- | --- | | **Vascular source** | Middle meningeal artery (arterial) | Cortical bridging veins (venous) | | **Bleeding rate** | Rapid (high pressure) | Slow (low pressure) | | **Time to symptoms** | Hours (acute presentation) | Days to weeks (chronic/subacute) | | **Lucid interval** | Common (70–80% of cases) | Rare | | **Age predilection** | Young adults (dura adherent to skull) | Elderly, alcoholics (brain atrophy) | | **Trauma severity** | Often high-energy | Often minor or trivial | | **Prognosis** | Better if evacuated early | Worse if chronic (brain herniation risk) | ### Pathophysiological Basis **High-Yield:** - **Extradural:** Middle meningeal artery runs in grooves on inner table of skull. Temporal bone fractures tear this artery → arterial bleeding → rapid accumulation → acute presentation with lucid interval. - **Subdural:** Cortical bridging veins cross subdural space from brain to dural sinuses. Tearing of these veins → venous bleeding → slow accumulation → insidious presentation, especially in elderly with brain atrophy (more subdural space). ### Clinical Pearl **Clinical Pearl:** Chronic subdural hematoma (>20 days) is common in elderly and chronic alcoholics because: 1. Brain atrophy creates more subdural space 2. Fragile bridging veins tear easily with minor trauma 3. Slow venous bleeding allows time for organization and encapsulation 4. Patients often do not recall the initial injury **Mnemonic:** **AVED** = Arterial (Extradural), Venous (subdural) — **A**rterial = **A**cute, **V**enous = **V**ague/slow onset. ```mermaid flowchart TD A[Head Trauma]:::outcome --> B{Vessel injured?}:::decision B -->|Middle meningeal artery| C[Extradural Hematoma]:::outcome B -->|Cortical bridging veins| D[Subdural Hematoma]:::outcome C --> E[Rapid arterial bleeding]:::action D --> F[Slow venous bleeding]:::action E --> G[Acute presentation, lucid interval]:::outcome F --> G2[Insidious presentation, chronic course]:::outcome G --> H[Emergency evacuation needed]:::urgent G2 --> I[May present weeks later]:::action ``` [cite:Harrison 21e Ch 434]