A 35-year-old man is brought to the emergency department 2 hours after a motor vehicle collision. He was unconscious at the scene for approximately 30 seconds, then regained consciousness and was alert during transport. Now he complains of severe headache and is becoming increasingly drowsy. On examination, his left pupil is dilated and sluggish. CT head (non-contrast) shows a lens-shaped hyperdense collection in the left frontoparietal region, tightly bounded by the coronal and sagittal sutures, with no midline crossing. What is the most likely diagnosis?

Explanation

## Clinical Presentation & Imaging Hallmarks **Key Point:** The lens-shaped (biconvex) hyperdense collection bounded by suture lines, combined with the classic "lucid interval" (loss of consciousness → recovery → deterioration), is pathognomonic for acute epidural hematoma (EDH). ## Epidural vs Subdural: Quick Discriminators | Feature | Epidural Hematoma | Subdural Hematoma | |---------|-------------------|-------------------| | **Shape** | Lens-shaped (biconvex) | Crescent-shaped | | **Suture boundary** | Stops at sutures (confined by dura) | Crosses sutures freely | | **Midline crossing** | No | Yes | | **Lucid interval** | Classic (70% of cases) | Rare | | **Arterial source** | Middle meningeal artery (90%) | Bridging veins | | **Time to presentation** | Minutes to hours | Hours to days | | **Age group** | Younger (dura adherent to bone) | Elderly, anticoagulated | | **Prognosis** | Good with early intervention | Worse; higher mortality | **High-Yield:** The lucid interval is the most clinically important distinguishing feature—it occurs in ~70% of epidural hematomas but is rare in subdural hematoma. ## Mechanism & Pathophysiology 1. Blunt head trauma → fracture of temporal bone (often) 2. Laceration of middle meningeal artery (or its branches) 3. Arterial bleeding accumulates between dura and inner surface of skull 4. Dura is firmly adherent to bone → hematoma confined within suture lines 5. Lens shape results from dura's anatomical attachments at sutures ## Clinical Pearl **The lucid interval** is the patient's window of opportunity for survival. Early recognition and emergent burr holes or craniotomy can be lifesaving. The dilated left pupil indicates ipsilateral uncal herniation—a neurosurgical emergency requiring immediate decompression. ## Mnemonic **LENS = Lucid interval, Epidural, Neuro-surgery, Suture-bounded** Remember: Epidural = **Lens** shape, bounded by **sutures**, with a **lucid interval**. ## Why This Is Not Subdural Hematoma Subdural hematomas are crescent-shaped, cross suture lines and the midline, and present with progressive neurological decline (no lucid interval). The 3-day delay is more typical of SDH than the acute presentation here.