A 28-year-old female presents with relapsing-remitting neurological deficits. MRI brain shows multiple periventricular ovoid T2 hyperintense lesions oriented perpendicular to the lateral ventricles. These lesions are described as 'Dawson's fingers'. Gadolinium-enhancing lesions are present along with non-enhancing lesions. The dissemination in space and time criterion is met. What does enhancement in MS lesions specifically indicate?

• A Axonal loss and gliosis (irreversible damage)
• B Remyelination in progress
• C Wallerian degeneration of white matter tracts
• D Active demyelination with breakdown of the blood-brain barrier ✓

Explanation

Enhancement in multiple sclerosis lesions on gadolinium-enhanced MRI indicates acute active demyelination with blood-brain barrier (BBB) disruption — leakage of gadolinium into the extravascular space of the plaque. Enhancement typically lasts 4–6 weeks and marks the active/inflammatory phase. Non-enhancing T2 lesions represent old, inactive plaques with gliosis. Axonal loss correlates with T1 black holes (permanent hypointensity).

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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