Imaging of White Matter Lesions

Abstract

Magnetic resonance imaging (MRI) is very sensitive for the detection of white matter lesions (WML), which occur even in normal ageing. Intrinsic WML should be separated from physiological changes in the ageing brain, such as periventricular caps and bands, and from dilated Virchow-Robin spaces. Genuine WML are best seen with T2-weighted sequences such as long TR dual-echo spin-echo or FLAIR (fluid-attenuated inversion recovery); the latter has the advantage of easily separating WML from CSF-like lesions. Abnormal T2 signal in MRI is not specific, and can accompany any change in tissue composition. In the work-up of WML in small vessel disease, magnetic resonance angiography can be used to rule out (concomitant) large vessel disease, and diffusion-weighted MRI to identify new ischaemic lesions (amidst pre-existing old WML). The differential diagnosis of WML includes hereditary leukodystrophies and acquired disorders. The leukodystrophies that can present in adult age include metachromatic leukodystrophy, globoid cell leukodystrophy, adrenomyeloneuropathy, mitochondrial disorders, vanishing white matter, and cerebrotendinous xanthomatosis. These metabolic disorders typically present with symmetrical abnormalities that can be very diffuse, often with involvement of brainstem and cerebellum. Only the mitochondrial disorders tend to be more asymmetric and frequently involve the grey matter preferentially. Among the acquired white matter disorders, hypoxic-ischaemic causes are by far the most prevalent and without further clinical clues there is no need to even consider the next most common disorder, i.e. multiple sclerosis (MS). Among the nonischaemic disorders, MS is far more common than vasculitis, infection, intoxication and trauma. While vasculitis can mimic small vessel disease, MS has distinctive features with preferential involvement of the subcortical U-fibres, the corpus callosum, temporal lobes and the brainstem/cerebellum. Spinal cord lesions are very common in MS, but do not occur in normal ageing nor in small vessel disease.

Assessment of the Virchow-Robin Spaces in Alzheimer Disease, Mild Cognitive Impairment, and Normal Aging, Using High-Field MR Imaging

“…Even so, leukoaraiosis was more prominent for VRSs than other factors such as global atrophy, consistent in the present and other studies. 19,29,30 Indeed, the VRSs and leukoaraiosis have similar pathogenesis; both are triggered by the slow occlusion of interstitial fluid due to the deposition of ␤-amyloid in the cortical and leptomeningeal arteries in AD. 24,31 It is known that the prevalence of VRSs increases with advanced age, 3,4 and our data verify this.…”

MR Imaging of Brain Volumes: Evaluation of a Fully Automatic Software

“…12 We believe FLAIR images should be used because they seem to have a higher specificity and accuracy compared with T2 images, especially in the periventricular region. 24,25 As to ICV and BTV, the limits of agreement between automatic and manual were larger compared with inter-/intraobserver limits of agreement.…”

Neuroimaging - Clinical Applications

“…Bilateral and symmetric white-matter lesions are other important features against the diagnosis of multiple sclerosis. Although adult forms of leucodystrophies, such as adrenoleucodystrophy, metachromatic leucodystrophy, and Krabbe disease may have a MRI pattern resembling that of MS, whitematter lesions tend to be bilateral and symmetric (Barkhof & Scheltens, 2002). Diffuse and confluent symmetrical T2-weighted hyperintensities in the deep and periventricular white matter with characteristic involvement of the external capsules and temporal poles are considered highly specific for cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) and may distinguish it from MS (Andreadou et al, 2008;Singhal et al, 2005).…”

“…Furthermore, the presence of multiple microhaemorrhagic foci, which can be seen on gradient-echo images, is another characteristic feature of CADASIL (Dichgans et al, 2002). Another feature pointing against the diagnosis of MS is significant asymmetry of the white-matter abnormalities, which is usually suggestive of ipsilateral carotid disease (Andreadou et al, 2010;Barkhof & Scheltens, 2002 (Lycklama et al, 2003;Agosta and Filippi, 2007), spinal cord abnormalities are not observed in patients with hypoxic-ischemic disease and are rarely reported in other immune-mediated disorders (Bot et al, 2002), and progressive multifocal leucoencephalopathy . Another characteristic pointing against the diagnosis of MS is the complete disappearance of spinal cord lesions in systemic immune-mediated diseases after steroid or immunosuppressive treatment .…”