A 22-year-old man is brought to the emergency department following a motor vehicle collision with loss of consciousness at the scene. He regains consciousness within 5 minutes and appears alert. However, 30 minutes later, he becomes increasingly drowsy, develops a fixed dilated right pupil, and has a left-sided hemiparesis. Urgent non-contrast CT head shows a lens-shaped hyperdensity in the right temporal region that does not cross the midline and respects the suture lines. What is the most likely diagnosis?

Explanation

## Classic Presentation of Epidural Hematoma **Key Point:** The **lucid interval** (period of consciousness between initial loss of consciousness and deterioration) is the hallmark of epidural hematoma. This patient lost consciousness, regained it, then deteriorated 30 minutes later—a textbook lucid interval. **High-Yield:** Epidural hematoma is a **neurosurgical emergency** requiring immediate evacuation. The lens-shaped (convex) hyperdensity that respects suture lines and does not cross the midline is pathognomonic. The fixed dilated pupil and contralateral hemiparesis indicate uncal herniation from mass effect. ## Pathophysiology Epidural hematoma results from **tearing of the middle meningeal artery** (or its branches) that run in grooves along the inner table of the skull. Arterial bleeding accumulates between the dura and inner skull table, creating a high-pressure hematoma that rapidly increases intracranial pressure. The classic presentation occurs in younger patients with significant head trauma because the dura is less adherent to the skull in younger individuals. ## Imaging & Clinical Features: Epidural Hematoma | Feature | Details | |---------|----------| | **Shape** | Lens-shaped (convex/biconvex) | | **Location** | Between dura and inner table of skull | | **Crosses midline** | No (limited by dural attachments at falx/tentorium) | | **Crosses suture lines** | No (stops at suture lines where dura is firmly attached) | | **Vessel injured** | Middle meningeal artery (most common) | | **Typical age** | Younger patients (20–40 years) | | **Trauma severity** | Usually significant | | **Lucid interval** | Characteristic (70–80% of cases) | | **Onset** | Acute (minutes to hours) | | **Prognosis** | Excellent if evacuated promptly; poor if herniation occurs | **Clinical Pearl:** The fixed dilated pupil (blown pupil) on the **same side** as the hematoma indicates ipsilateral uncal herniation, compressing CN III. The contralateral hemiparesis results from compression of the contralateral cerebral peduncle (Kernohan's notch phenomenon). ## Why This Is Epidural, Not Subdural | Criterion | This Case | Epidural | Subdural | |-----------|-----------|----------|----------| | **Age** | 22 years | Younger patients | Elderly | | **Trauma severity** | Significant (MVC) | Significant | Minor/trivial | | **Lucid interval** | Yes (5 min → 30 min) | Characteristic | Delayed but not lucid | | **Imaging shape** | Lens-shaped | Lens-shaped ✓ | Crescent | | **Crosses midline** | No | No ✓ | Yes | | **Respects sutures** | Yes | Yes ✓ | No | | **Onset** | Acute (30 min) | Acute ✓ | Progressive (hours–days) | **Mnemonic:** **EPIDURAL = Early presentation, Presyncope/lucid interval, Injury to meningeal artery, Dura-skull space, Urgent evacuation, Respects sutures, Arterial bleeding, Lens-shaped** ## Uncal Herniation Signs 1. **Fixed dilated pupil** (ipsilateral) — CN III compression 2. **Contralateral hemiparesis** — cerebral peduncle compression 3. **Altered consciousness** — midbrain compression 4. **Posturing** — brainstem involvement ```mermaid flowchart TD A[Acute head trauma]:::outcome --> B{Age & mechanism?}:::decision B -->|Young, significant trauma| C[Arterial bleeding<br/>Middle meningeal artery]:::outcome B -->|Elderly, minor trauma| D[Venous bleeding<br/>Bridging veins]:::outcome C --> E[Rapid accumulation<br/>High pressure]:::outcome D --> F[Slow accumulation<br/>Low pressure]:::outcome E --> G[Lucid interval common]:::outcome F --> G2[Delayed presentation]:::outcome G --> H[Acute deterioration<br/>minutes to hours]:::outcome G2 --> H2[Progressive symptoms<br/>hours to days]:::outcome H --> I[Lens-shaped<br/>respects sutures]:::outcome H2 --> J[Crescent-shaped<br/>crosses midline]:::outcome I --> K[Epidural hematoma<br/>NEUROSURGICAL EMERGENCY]:::urgent J --> L[Subdural hematoma]:::action K --> M[Immediate CT + neurosurgery consult]:::action ```