A 68-year-old man with chronic alcoholism presents to the emergency department with a 2-week history of progressive headache, confusion, and gait disturbance following a minor head trauma he barely remembers. CT head (non-contrast) shows a crescent-shaped hypodensity over the frontal convexity that does not cross the midline. What is the investigation of choice to confirm the diagnosis and guide management?

Explanation

## Clinical Presentation & Imaging Findings The patient presents with a **subacute subdural hematoma** — the classic triad of: - Delayed presentation (2 weeks post-trauma) - Chronic alcoholism (brain atrophy → bridging vein stretching) - Crescent-shaped hypodensity that respects the dural attachment (does not cross midline) ### Why MRI with SWI is the Investigation of Choice **Key Point:** MRI with susceptibility-weighted imaging (SWI) is superior to CT for: 1. **Detection of blood products at all stages** — SWI is exquisitely sensitive to hemosiderin and deoxyhemoglobin, detecting even small or chronic bleeds missed on CT 2. **Differentiation of subdural from epidural** — subdural collections are typically crescent-shaped and cross sutures (but not midline), while epidural are lens-shaped and do not cross sutures 3. **Assessment of chronic/subacute hematomas** — SWI shows characteristic low signal (blooming artifact) from hemosiderin, confirming old blood 4. **Treatment planning** — MRI helps determine if the hematoma is loculated, multiloculated, or organizing, which guides whether burr holes or needle aspiration is needed **High-Yield:** In subacute subdural hematoma (7–20 days), CT may show isodensity (same density as brain), making it **occult on CT**. MRI-SWI will always demonstrate it. ### Why Non-Contrast CT is Insufficient Here While non-contrast CT was appropriate for **acute** epidural/subdural (hyperacute bleeding), this patient has a **2-week-old collection** that may be isodense on CT. The clinical suspicion is high, and MRI-SWI provides definitive confirmation. **Clinical Pearl:** Chronic subdural hematomas in elderly/alcoholic patients are a classic presentation because brain atrophy creates subdural space, and anticoagulation/coagulopathy from liver disease increases bleeding risk from minor trauma. ## Comparison: Epidural vs Subdural Hematoma | Feature | Epidural | Subdural | |---------|----------|----------| | **Location** | Between skull and dura | Between dura and arachnoid | | **Shape on CT/MRI** | Lens-shaped (biconvex) | Crescent-shaped (concave) | | **Crosses sutures?** | No (stopped by dural attachments) | Yes (does not respect sutures) | | **Crosses midline?** | No | No (respects falx) | | **Typical mechanism** | High-impact trauma (young) | Minor trauma (elderly/alcoholic) | | **Onset** | Acute (hours) | Acute, subacute, or chronic | | **Vessel involved** | Middle meningeal artery | Bridging veins | | **Best imaging** | Non-contrast CT (acute) | MRI-SWI (all stages, esp. subacute) | [cite:Neuroradiology: Imaging of Intracranial Hemorrhage, Osborn's Brain Imaging]