Demyelinating disorders of the central nervous system may be divided into primary (cause unknown, eg, multiple sclerosis (MS)) and secondary (eg, infective, hypoxic–ischaemic, metabolic, toxic) processes. The underlying cause damages the myelin sheath and/or oligodendrocyte. MRI is the imaging modality of choice because of its high spatial and contrast resolution, but imaging features are often non-specific.
The most common causes of multifocal white matter lesions are perivascular spaces, ischaemia (small vessel disease) and MS.⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓
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Imaging red flags—? MS- consider alternate diagnosis*
T2W axial MRI of a neurologically normal 45-year-old shows small ill-defined foci of high T2 signal in the frontal subcortical white matter. These are almost certainly age-related changes of no significance.
T2W axial (A) and axial apparent diffusion coefficient MRIs (B) in a 63-year-old man with sudden onset right hemiparesis, showing multiple small peripheral, poorly defined foci of high T2 signal in the frontal lobes and adjacent to the trigones of both lateral ventricles—more numerous than in the patient in figure 1. He is a smoker. The cause of his right hemiparesis is an ischaemic stroke in the deep white matter: the result of small vessel disease. This appears as an area of decreased diffusion on the apparent diffusion coefficient map (B).
Axial T2W MRIs in a 70-year-old man with diabetes mellitus and hypertension, showing diffuse high T2 signal in the deep white matter bilaterally, resulting from white matter hypoperfusion due to vascular disease. There are areas of ischaemic damage in the basal ganglia and pons.
Two patients with multiple sclerosis (MS) (A,B) and (C,D). T2W axial MRIs (A–C) and FLAIR coronal (D) MRI show the typical appearance of MS plaques: multiple, …