A 72-year-old woman on warfarin for atrial fibrillation develops acute onset severe occipital headache with ataxia and vertical gaze palsy. Non-contrast CT head is normal. What is the most appropriate next investigation to confirm the diagnosis of pontine hemorrhage?

## MRI as the Diagnostic Gold Standard for Occult Hemorrhage ### Clinical Scenario: Normal CT, Suspicious Hemorrhage This patient presents with a classic brainstem syndrome (ataxia, vertical gaze palsy, occipital headache) in a patient on anticoagulation. Non-contrast CT is **negative**, yet clinical suspicion for hemorrhage is high. This is a classic scenario where **MRI is superior to CT**. **Key Point:** MRI, particularly T2-weighted and gradient echo (GRE) sequences, is more sensitive than CT for detecting acute and subacute hemorrhage in the posterior fossa and brainstem. ### Why MRI Detects Hemorrhage CT Misses 1. **Posterior fossa sensitivity** — CT is limited by beam hardening artifact at the skull base; MRI has no such limitation 2. **Gradient echo (GRE) / susceptibility-weighted imaging (SWI)** — these sequences are exquisitely sensitive to hemoglobin iron, detecting even small microhemorrhages 3. **T2-weighted sequences** — show acute hemorrhage as hypointense (deoxyhemoglobin) and subacute as hyperintense (methemoglobin) 4. **No radiation** — important for repeat imaging if needed ### Comparison of Investigations | Investigation | Sensitivity for Acute ICH | Sensitivity for Posterior Fossa | Timing | Limitations | |---|---|---|---|---| | **Non-contrast CT** | 95% (supratentorial) | 60–70% (posterior fossa) | Immediate | Beam hardening artifact, less sensitive in brainstem | | **MRI with GRE/SWI** | >98% | >95% (posterior fossa) | 30–60 min | Contraindicated in unstable patients, pacemakers; takes longer | | **Lumbar puncture** | Indirect (xanthochromia) | Yes, but invasive | 30 min | Invasive, risk of herniation, not diagnostic (xanthochromia not specific) | | **Repeat CT at 24 hrs** | May improve visibility | Still limited by artifact | 24 hrs | Delays diagnosis, unnecessary radiation | | **Transcranial Doppler** | None (functional, not structural) | — | 15 min | Cannot diagnose hemorrhage; assesses flow only | **High-Yield:** In **posterior fossa hemorrhage** (especially brainstem), MRI is the investigation of choice when CT is normal or inconclusive. This is a high-yield NEET PG fact. **Clinical Pearl:** Warfarin-associated brainstem hemorrhage can present with isolated neurological signs before headache becomes prominent; MRI should be obtained urgently even if CT is normal. **Mnemonic: "GRIM"** — **G**radient echo, **R**apid (for acute hemorrhage), **I**ron-sensitive, **M**RI is best for posterior fossa. [cite:Harrison 21e Ch 296]