A 68-year-old man on warfarin for atrial fibrillation presents with insidious onset headache and progressive confusion over 3 weeks. CT head shows a crescent-shaped hypodensity along the cerebral convexity. Which investigation is most appropriate to confirm the diagnosis and guide management?

## Clinical Presentation & Imaging Findings The patient presents with a **subacute subdural hematoma** — characterized by insidious onset (weeks), anticoagulation history, and crescent-shaped hypodensity on CT that follows the brain contour. ## Why MRI with GRE/SWI is the Investigation of Choice **Key Point:** MRI with gradient echo and susceptibility-weighted imaging sequences is superior for detecting and characterizing subdural hematomas, particularly in the subacute and chronic phases. ### Advantages of MRI over CT: | Feature | MRI (GRE/SWI) | CT | |---------|---------------|----| | **Sensitivity for subdural hematoma** | Excellent (detects blood at all stages) | Good for acute; poor for chronic | | **Hemoglobin breakdown products** | Visualizes deoxyhemoglobin, methemoglobin, hemosiderin | Cannot differentiate blood stages | | **Subdural membrane visualization** | Clearly shows organizing membranes | Limited soft tissue contrast | | **Posterior fossa lesions** | No artifact; excellent visualization | Beam hardening artifact | | **Age of hematoma** | Can estimate based on signal intensity | Cannot reliably date hematoma | **High-Yield:** GRE and SWI sequences are exquisitely sensitive to blood products due to their susceptibility to magnetic field inhomogeneities caused by iron in hemoglobin. This makes them the gold standard for detecting and characterizing subdural hematomas. **Clinical Pearl:** In a patient on anticoagulation with subacute presentation, MRI helps confirm the diagnosis, assess for recurrent bleeding, and evaluate for organizing membranes that may require surgical evacuation. ## Mermaid: Imaging Algorithm for Suspected Subdural Hematoma ```mermaid flowchart TD A[Suspected intracranial hematoma]:::outcome --> B{Acute presentation?}:::decision B -->|Yes, within 24-48 hrs| C[Non-contrast CT head]:::action B -->|No, subacute/chronic| D[MRI with GRE/SWI]:::action C --> E{Hematoma confirmed?}:::decision E -->|Yes, acute SDH| F[Assess for mass effect]:::action E -->|Negative but high suspicion| G[MRI for better sensitivity]:::action D --> H[Characterize age & membranes]:::outcome H --> I{Surgical evacuation needed?}:::decision I -->|Yes| J[Burr hole drainage]:::action I -->|No| K[Medical management + anticoagulation reversal]:::action ``` **Reasoning:** MRI with GRE/SWI is the most sensitive and specific test for subdural hematoma, especially in the subacute phase where CT may appear isodense or hypodense. It also characterizes the age of the hematoma and visualizes organizing membranes, directly informing surgical decision-making.