Sagittal Flair MRI image of a 39-year-old female patient with known Multiple Sclerosis. Multiple Sclerosis on MRI scanning is characterized by white matter lesions, or plaques, that are a result of old scar tissue due to the inflammatory process. It is important to note that the presence of white matter lesions on MRI does not necessarily always correlate with a diagnosis of Multiple Sclerosis. Multiple Sclerosis does have a typical pattern of white matter lesions however, which involve the corpus callosum, U-fibres, temporal lobes, brainstem, cerebellum and spinal cord.(1) The scan in image 1 illustrates multiple oval-shaped, hyperintense (or white) lesions at the callosal-septal interface with the longest axis perpendicular to the corpus callosum. This finding is known as ‘Dawson’s fingers’ and represents areas of demyelination that show as white matter inflammatory changes, typically seen in Multiple Sclerosis, along the periventricular medullary veins.
Multiple Sclerosis (MS) is the most common disease to affect the central nervous system (CNS). The central nervous system consists of two main structures, the brain and the spinal cord. Although Multiple Sclerosis is often described as an ‘autoimmune’ disease this continues to be debated due to the lack of an identifiable antigen and it is therefore often described as an ‘immune-mediated disease’. ‘An immune-mediated inflammatory disease (IMID) is characterized by common inflammatory pathways leading to inflammation which may result from, or be triggered by, a dysregulation of the normal immune response’.(2) Multiple Sclerosis affects the central nervous system; the immune system attacks and damages the myelin, (which is the insulating sheath that protects nerve fibres), the underlying nerve fibres and the myelin-producing cells called ‘oligodendrocytes’ with resulting formation of lesions, or plaques, and inflammation. The resulting nerve damage affects the communication of the body’s nervous system and results in a diverse range of signs and symptoms.
The McDonald Criteria for diagnosis of Multiple Sclerosis was established in 2001 by an international panel of neurologists in America, it was updated in 2005 and more recently in 2010. The use of MRI imaging plays a crucial role in this diagnostic criteria which is based on the presence of central nervous system lesions or plaques that are ‘disseminated in time and space’. Basically MRI scan can show multiple lesions (dissemination in space) and new lesions (dissemination in time) by follow up scans or by ageing of the older lesions.
MRI of a patient with known Multiple Sclerosis. A good example of the McDonald criteria indicating dissemination in space, that is showing multiple lesions in key areas of the brain associated with Multiple Sclerosis. Lesions in the deep white matter, indicated by arrow 1, can be seen in a variety of diseases and are therefore non-specific to Multiple Sclerosis. Arrows 2, 3 and 4 are more typical findings in cases of Multiple Sclerosis. Arrow 2 indicates the lesions or plaques present in the corpus callosum. Arrow 3 highlights temporal lobe involvement and arrow 4 shows juxtacortical lesions. An understanding of the definition of juxtacortical is important to the Mcdonald criteria and does not mean ‘near to, or around the cortex, ‘ but refers to lesions which abut (touch, join or lean on) the cortex and therefore involve the subcortical U-Fibres. These fibres are known as short association fibers and are found within the brain cortex in the outer parts of the subcortical white matter. An alternative term to juxtacortical which is perhaps more easily understood is leukocortical i.e. involving both cortex and juxtacortical white matter.(3) Also visible are multiple lesions adjacent to the ventricles.
3. Dr Frank Gaillard ‘Juxtacortical may not mean what you think it means’ Royal Melbourne Hospital, Melbourne, Australia, http://radiopaedia.org/blog/juxtacortical-may-not-mean-what-you-think-it-means