Neuroradiology
Core Concepts
Neuroradiology covers imaging of the brain, spine, and head and neck. You must understand the strengths of CT and MRI: CT is fast and sensitive for acute hemorrhage and fractures; MRI is superior for soft tissue, ischemia, and demyelination. Know the classic appearances of stroke (early signs on CT: loss of insular ribbon, hyperdense MCA), hemorrhage (hyperdense on CT), and tumors (ring-enhancing lesions). Also, be familiar with spine imaging: disc herniation, spinal stenosis, and cord compression. Pediatric and neonatal neuroimaging (e.g., intraventricular hemorrhage, hypoxic-ischemic encephalopathy) is also fair game.
Common Traps
A frequent trap is the timing of imaging in acute stroke: non-contrast CT is the first test to exclude hemorrhage, but it may be normal in early ischemia. MRI with diffusion-weighted imaging (DWI) is most sensitive for acute infarction. Another trap is confusing the appearance of blood on MRI by age (acute: deoxyhemoglobin, intracellular; subacute: methemoglobin, extracellular). Also, beware of “lumbar puncture first” in suspected subarachnoid hemorrhage-CT is first-line if within 6 hours.
Worked Example
A 70-year-old woman with sudden severe headache. Non-contrast CT shows hyperdensity in the basal cisterns, consistent with subarachnoid hemorrhage. The next step is CT angiography to identify an aneurysm. Rule of thumb: hyperdense on CT = acute blood.
Key Points
- Non-contrast CT is first-line for acute stroke to rule out hemorrhage.
- DWI is most sensitive for acute infarction.
- Hyperdense MCA sign indicates acute thrombus.
- Subarachnoid hemorrhage: CT first, then CTA.
- MRI signal of hemorrhage evolves with age.