Magnetic resonance imaging (MRI) is a primary tool for evaluating the central nervous system, particularly when diagnosing conditions like multiple sclerosis (MS). MS is a condition where the immune system mistakenly attacks the protective myelin sheath surrounding nerve fibers. While contrast provides specific insights into disease activity, non-contrast MRI scans can reveal significant information about MS.
How MRI Visualizes MS
An MRI machine uses strong magnetic fields and radio waves to create detailed images of organs and soft tissues within the body. This technology measures the water content in tissues, which helps differentiate various structures. In the context of multiple sclerosis, MRI is used to identify lesions, which are areas of damage to the myelin or nerve fibers in the brain and spinal cord.
These lesions appear as distinct bright or dark spots on different types of MRI sequences, such as T2-weighted and FLAIR (Fluid Attenuated Inversion Recovery) images. T2-weighted sequences are effective at highlighting areas of demyelination, which show up as bright white spots. FLAIR sequences further improve lesion detection by suppressing signals from cerebrospinal fluid, making lesions more apparent.
Identifying MS Lesions Without Contrast
Many MS lesions are clearly visible on standard, non-contrast MRI sequences. These include older or inactive lesions that do not show active inflammation. On T2-weighted and FLAIR images, these lesions typically appear as bright spots, often with an oval or ovoid shape. Their presence and specific distribution patterns are important diagnostic indicators for MS.
Lesions commonly appear in certain characteristic regions of the central nervous system. These locations include:
- The periventricular white matter, close to the brain’s fluid-filled ventricles.
- Juxtacortical areas, located just beneath the brain’s outer surface.
- The infratentorial region, encompassing the brainstem and cerebellum.
- The spinal cord.
Additionally, non-contrast MRI can assess brain atrophy, which is brain shrinkage that can occur in MS.
The Role of Contrast in MS Imaging
Despite the utility of non-contrast MRI, a contrast agent, typically gadolinium, is often used to gain additional information about MS activity. Gadolinium is injected intravenously and helps to highlight areas where the blood-brain barrier (BBB) is disrupted. The BBB normally prevents substances from the bloodstream from entering the brain and spinal cord.
In active MS lesions, inflammation causes the blood-brain barrier to become temporarily leaky, allowing the gadolinium contrast to enter the tissue. These “enhancing lesions” appear as bright areas on T1-weighted MRI sequences and indicate acute inflammation or new disease activity. Contrast enhancement helps distinguish new, active lesions from older, inactive ones, which do not typically enhance. This distinction is valuable for monitoring disease progression and assessing the effectiveness of treatments.
A Complete MS Diagnosis
Diagnosing multiple sclerosis involves more than just MRI findings; it is a clinical process that integrates various pieces of information. A thorough neurological examination is an important initial step, where a neurologist assesses a person’s reflexes, coordination, balance, and other neurological functions to identify symptoms and signs of MS.
Other diagnostic tools complement MRI results. A lumbar puncture, also known as a spinal tap, involves collecting cerebrospinal fluid (CSF) to test for specific antibodies, such as oligoclonal bands or an elevated IgG index, which can indicate an immune system response in the central nervous system. Evoked potentials tests measure the electrical signals in the brain in response to sensory stimuli, like visual patterns or electrical impulses, to detect slowed nerve conduction caused by demyelination. Ultimately, a neurologist considers all these findings, including a person’s symptoms, medical history, and the results from MRI, CSF analysis, and evoked potentials, to make a definitive diagnosis based on established criteria.