A 68-year-old man with hypertension and on aspirin for secondary stroke prevention presents to the emergency department with acute onset severe headache, confusion, and right-sided weakness. His wife reports he fell from standing height 3 days ago and hit his head on the corner of a table, but seemed fine immediately after. On examination, he is drowsy, with a right pupil dilated to 5 mm, and right hemiparesis. CT head (non-contrast) shows a crescent-shaped hyperdense collection that does not cross the midline, with mass effect and midline shift. What is the most likely diagnosis?

Explanation

## Clinical Presentation & Imaging Correlation **Key Point:** The crescent-shaped hyperdense collection that does NOT cross the midline on CT is pathognomonic for acute subdural hematoma (SDH). The delayed presentation (3 days post-trauma) with progressive neurological deterioration is classic for SDH, especially in elderly patients on antiplatelet agents. ## Distinguishing Extradural vs Subdural Hematoma | Feature | Epidural Hematoma | Subdural Hematoma | |---------|-------------------|-------------------| | **Shape on CT** | Lens-shaped (biconvex), bounded by suture lines | Crescent-shaped, crosses suture lines | | **Crosses midline** | No (confined by dura) | Yes (can cross midline) | | **Crosses suture lines** | No (stops at sutures) | Yes (crosses sutures) | | **Typical interval** | Immediate or within hours | Hours to days (or weeks in chronic) | | **Mechanism** | Tear of middle meningeal artery (usually) | Tearing of bridging veins | | **Age group** | Younger patients (dura adherent to bone) | Elderly, alcoholics, anticoagulated | | **Lucid interval** | Classic (loss → recovery → deterioration) | Less common; progressive decline | | **Prognosis** | Better if treated early | Worse; higher mortality | **High-Yield:** The crescent shape that CROSSES sutures and the delayed presentation in an elderly patient on aspirin are the key discriminators pointing to acute SDH. ## Pathophysiology Subdural hematomas result from tearing of bridging veins that traverse the subdural space. In elderly patients with brain atrophy, these veins are stretched and more prone to rupture even from minor head trauma. The patient's aspirin use increases bleeding risk and may accelerate hematoma expansion. ## Clinical Pearl **Dilated ipsilateral pupil (blown pupil)** indicates uncal herniation from mass effect—a neurosurgical emergency requiring urgent decompression. This patient requires immediate CT confirmation and likely burr holes or craniotomy. ## Why This Is Not Epidural Hematoma Epidural hematomas are lens-shaped and bounded by suture lines; they do not cross the midline. They typically present acutely (within hours) with a classic "lucid interval." The 3-day delay and crescent morphology exclude epidural hematoma.