A 35-year-old man is brought to the emergency department after a high-speed motor vehicle collision. Non-contrast CT head shows a biconvex hyperdense collection in the right frontoparietal region with mass effect. Which of the following is NOT consistent with a diagnosis of extradural hematoma?

Explanation

## Extradural Hematoma: Imaging and Clinical Features ### Pathophysiology and Source **Key Point:** Extradural (epidural) hematoma results from **arterial bleeding** — typically from the middle meningeal artery or its branches — between the dura mater and the inner table of the skull. This is a high-pressure arterial bleed. **High-Yield:** The dura is firmly attached to the inner table of the skull at the sutures and at the falx cerebri and tentorium cerebelli. These attachments prevent the hematoma from crossing sutures or the midline, creating a characteristic **lens-shaped (biconvex)** collection. ### CT Imaging Features of Extradural Hematoma | Feature | Extradural | Subdural | |---------|-----------|----------| | **Shape** | Lens-shaped (biconvex) | Crescent-shaped (concave) | | **Crosses sutures?** | No | Yes | | **Crosses midline?** | No | Yes | | **Density (acute)** | Hyperdense | Hyperdense | | **Extent** | Confined to one compartment | Extends across lobes | | **Mass effect** | Often marked despite smaller volume | Variable | **Clinical Pearl:** The **biconvex lens shape** is the hallmark of extradural hematoma on CT. It is bounded by the skull laterally and dural attachments medially, creating a smooth, convex inner margin. ### Why Option 4 Is Incorrect **Warning:** The statement "the hematoma appears crescent-shaped and extends across multiple gyri" is **NOT consistent** with extradural hematoma. This description fits **subdural hematoma**, not extradural. - **Crescent-shaped** = subdural (concave inner margin) - **Extends across multiple gyri/lobes** = subdural (not limited by sutures or midline) - **Biconvex/lens-shaped** = extradural (the correct shape) ### Classic Clinical Presentation: The Lucid Interval **High-Yield:** Extradural hematoma is famous for the **"lucid interval"** — the patient loses consciousness at impact, then regains consciousness and appears well, only to deteriorate rapidly over hours as the arterial bleed accumulates. This occurs because: 1. Initial trauma causes brief unconsciousness 2. Patient awakens and seems fine (lucid interval) 3. Arterial bleeding continues under high pressure 4. Mass effect and increased ICP develop 5. Rapid deterioration, herniation, death if untreated **Mnemonic:** **LENS** for Extradural — **L**ens-shaped, **E**pidural location, **N**o crossing of sutures, **S**evere arterial bleeding. **Mnemonic:** **CRESCENT** for Subdural — **C**rescent shape, **R**ecurrent (chronic form), **E**lderly/alcoholics, **S**low venous bleed, **C**rosses sutures, **E**xtends across lobes, **N**o lucid interval (usually), **T**rivia causes it. ### Comparison Table: Extradural vs Subdural | Criterion | Extradural | Subdural | |-----------|-----------|----------| | **Vessel** | Middle meningeal artery (arterial) | Bridging veins (venous) | | **Pressure** | High (arterial) | Low (venous) | | **Shape** | Biconvex/lens | Crescent | | **Crosses midline** | No | Yes | | **Crosses sutures** | No | Yes | | **Lucid interval** | Common (classic) | Rare | | **Onset** | Acute (hours) | Acute, subacute, chronic | | **Age group** | Young (dura adherent) | Elderly (dura loose) | | **Trauma severity** | Usually severe | Can be trivial | **Clinical Pearl:** In young patients, the dura is firmly adherent to the skull, making extradural hematoma more common. In elderly patients, dural adherence is loose, predisposing to subdural hematoma.