Gadolinium enhancement on MRI indicates active inflammation in MS by indicating breakdown of the blood-brain barrier.

• A. Chronic, inactive plaques.
• B. Active inflammation due to breakdown of the blood-brain barrier.
• C. Normal aging changes.
• D. Peripheral nerve lesions.

Answer: (B)

Gadolinium enhancement on MRI signifies active inflammation because gadolinium is an extracellular contrast agent that can only enter brain tissue if the blood-brain barrier is disrupted. In active MS lesions, inflammatory processes weaken and open the tight junctions of the BBB, allowing gadolinium to leak into the interstitial space. This leakage shortens T1 relaxation and shows up as bright enhancement on post-contrast T1-weighted images, marking an actively inflamed plaque.

This helps distinguish active, new demyelinating activity from chronic, inactive plaques, which typically don’t enhance once the BBB has largely repaired and there’s gliosis rather than ongoing inflammation. Normal aging changes don’t produce this pattern of BBB disruption, and peripheral nerve lesions wouldn’t manifest as brain gadolinium enhancement.