The MRI and MS Part II: Diagnosing MS
As I have said in previous posts, the diagnosis of MS requires demonstrated inflammation in different parts of the central nervous system (this is referred to as dissemination in space) and at different points of time (this is referred to as dissemination in time). Historically this relied primarily on a patient’s history and physical examination. While this is still primarily the case, recently doctors have begun to make more use the MRI in place of clinical symptoms and exam abnormalities allowing for the earlier diagnosis of MS. Formal criteria have been established so that the MRI can be used to show the dissemination in time or space, allowing doctors to diagnose MS in patients who may have had only one clinical event. These criteria are presented below:
Dissemination in Space:
- More than one lesion in at least two out of four areas of the central nervous system: periventicular, juxtacortical, infratentorial, or spinal cord. I will show examples of these confusing terms below.
Dissemination in Time:
- A single MRI showing both a lesion that enhances with contrast (indicating active inflammation) as well as non-enhancing lesions, indicating prior inflammation.
- A new lesion on any follow-up MRI done after the original MRI.
Let’s examine what this all means along with the different kinds of MRIs a neurologist might show a patient with MS. Probably the one sequence that neurologists turn to first, and patients are most familiar with, is called the FLAIR MRI. In this sequence, the lesions of MS appear as oval-shaped white spots that radiate away from the large holes in the center of the brain, called the ventricles. These lesions are called periventricular lesions. (Remember, the definition for MS requires there must be lesions in two out of four areas in the brain: periventicular, juxtacortical, infratentorial, and spinal cord). These periventricular lesions are shown in the MRIs below.
The lesions located closer to the gray matter are called juxtacortical lesions. The area in the red circle shows a lesion near the cortex of the brain, but still in the white matter.
Lesions in lower parts of the brain, including the brainstem and cerebellum are called infratentorial lesions. Such lesions are shown in the MRIs at left and right.
Finally, lesions can appear throughout the thoracic and cervical spine in patients with MS. Such an MRI is shown at left.
It is important to note that not all white spots mean MS. Although the MRI is an amazing piece of technology that shows the brain and spinal cord from multiple different angles, it only shows shades of black and white. Other illness, such migraines, vascular diseases, or prior brain infections can produce changes very similar to MS. Often, the findings in these illnesses, produce smaller lesions that look more like white dots than the round balls of MS.
Additionally, they are not typically located near the ventricles and do not enhance with contrast. Below are several MRI images from a patient with multiple risk factors for vascular disease. He was sent for an MS evaluation based on these MRIs. Often, it is not possible to determine whether a patient has MS based on solely on the appearance of the MRI. It is important for neurologists to take a thorough history and perform detailed neurological exam on all of their patients. In equivocal cases, a spinal tap may be necessary.
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