Multiple sclerosis (MS) is a neurological condition characterized by damage to the brain and spinal cord. This damage often appears as areas of inflammation and demyelination, known as lesions. Magnetic Resonance Imaging (MRI) is a powerful tool for visualizing these lesions within the central nervous system, making it fundamental in understanding and assessing MS.
Active Versus Inactive Lesions on MRI
The visibility of MS lesions on an MRI scan largely depends on their activity level. Lesions that are actively inflamed involve a compromised blood-brain barrier, which is a protective layer of cells surrounding the brain and spinal cord. This breakdown allows a contrast agent called gadolinium to leak into the affected tissue.
When gadolinium is injected, active lesions appear as bright spots on T1-weighted MRI scans. This enhancement indicates the lesion is relatively new, typically lasting a few weeks, though it can persist for up to two months. In contrast, inactive or older lesions do not show this enhancement because their blood-brain barrier has healed or the inflammation has subsided. These lesions remain visible on other MRI sequences, such as T2-weighted or FLAIR scans, but without the bright signal from the contrast agent.
How Lesions Change Over Time
MS lesions change over time, affecting their long-term visibility on MRI. Some lesions may undergo a process of healing, where the inflammation resolves and the damaged myelin is repaired. These lesions might eventually disappear from subsequent MRI scans, indicating a degree of recovery in the affected brain or spinal cord tissue.
Other lesions, however, do not fully heal and can persist, undergoing continuous changes. These persistent lesions may be categorized as “chronic active lesions” or “smouldering lesions,” characterized by ongoing, low-level inflammation at their edges. These lesions can slowly expand over time, indicating a continuous process of tissue injury and myelin breakdown. A subset of chronic lesions may appear as “black holes” on T1-weighted MRI scans. These dark areas signify permanent nerve damage and significant tissue loss within the brain, often reflecting irreversible axonal damage and associated with increased neurological disability.
Using MRI for MS Management
MRI plays a central role in MS management, from initial diagnosis to ongoing monitoring. It is a tool for confirming a suspected MS diagnosis, providing detailed images of lesions in the brain and spinal cord. This initial scan establishes a baseline for assessing disease burden and helps rule out other conditions.
Regular follow-up MRI scans are often recommended, typically every six months to two years, to track changes in lesion activity and overall brain volume. These scans help identify new or enlarging lesions, which indicate ongoing disease activity, even if symptoms are not present. Monitoring brain atrophy, or the shrinkage of brain tissue, is also an important aspect of these follow-up scans, as it can correlate with disease progression and cognitive decline. The information gathered from serial MRIs helps healthcare providers assess the effectiveness of MS treatments and make informed decisions about adjusting therapy.