A 68-year-old man with hypertension presents to the emergency department with a 3-day history of progressive headache, confusion, and left-sided weakness. His son reports a fall from stairs 4 days ago, which the patient initially dismissed. On examination, he is drowsy, with a left hemiparesis and dilated right pupil. CT head shows a crescent-shaped hyperdense collection along the right cerebral convexity that does not cross the midline. What is the most likely diagnosis?

Explanation

## Clinical Presentation & Imaging Correlation This patient presents with a **delayed presentation** (3 days post-injury) with progressive neurological deterioration, which is the hallmark of acute subdural hematoma (aSDH). ### Key Radiological Features | Feature | Subdural Hematoma | Epidural Hematoma | |---------|-------------------|-------------------| | **Shape** | Crescent (concave) | Lens-shaped (convex) | | **Crosses suture lines** | Yes | No (respects dural attachments) | | **Crosses midline** | No | No | | **Location** | Between dura and brain surface | Between skull and dura | | **Typical interval** | Hours to days (progressive) | Minutes to hours (rapid) | | **Mechanism** | Tearing of bridging veins | Tearing of middle meningeal artery | **Key Point:** The **crescent-shaped** hyperdense collection that does NOT cross the midline is pathognomonic for acute subdural hematoma. ### Pathophysiology of Delayed Presentation 1. Tearing of **bridging veins** (low-pressure system) during head trauma 2. Slow venous bleeding into subdural space 3. Progressive mass effect over 24–72 hours 4. Uncal herniation → ipsilateral pupillary dilation (Hutchinson pupil) 5. Contralateral hemiparesis from brainstem compression **Clinical Pearl:** The **3-day delay** before symptom onset is typical for aSDH. In contrast, epidural hematomas present acutely (within hours) with the classic "talk-and-die" syndrome—lucid interval followed by rapid deterioration. **High-Yield:** The **dilated right pupil** (ipsilateral to the hematoma) indicates uncal herniation from mass effect, confirming a space-occupying lesion requiring urgent neurosurgical evacuation. ### Why the Crescent Shape Matters The dura is adherent to the inner table of the skull along suture lines and at the falx/tentorium. Subdural bleeding strips the dura away from the brain surface, creating a **concave (crescent) margin** that conforms to the brain's convexity. Epidural bleeding, by contrast, is confined between dura and skull, creating a **convex (lens) shape** that respects suture lines.