Cerebral small vessel disease (SVD) is a common cause of vascular cognitive impairment. A number of disease features can be assessed on MRI including lacunar infarcts, T2 lesion volume, brain atrophy, and cerebral microbleeds. In addition, diffusion tensor imaging (DTI) is sensitive to disruption of white matter ultrastructure, and recently it has been suggested that additional information on the pattern of damage may be obtained from axial diffusivity, a proposed marker of axonal damage, and radial diffusivity, an indicator of demyelination. We determined the contribution of these whole brain MRI markers to cognitive impairment in SVD. Consecutive patients with lacunar stroke and confluent leukoaraiosis were recruited into the ongoing SCANS study of cognitive impairment in SVD (n = 115), and underwent neuropsychological assessment and multimodal MRI. SVD subjects displayed poor performance on tests of executive function and processing speed. In the SVD group brain volume was lower, white matter hyperintensity volume higher and all diffusion characteristics differed significantly from control subjects (n = 50). On multi-predictor analysis independent predictors of executive function in SVD were lacunar infarct count and diffusivity of normal appearing white matter on DTI. Independent predictors of processing speed were lacunar infarct count and brain atrophy. Radial diffusivity was a stronger DTI predictor than axial diffusivity, suggesting ischaemic demyelination, seen neuropathologically in SVD, may be an important predictor of cognitive impairment in SVD. Our study provides information on the mechanism of cognitive impairment in SVD.

In this Review, we aim to provide up-to-date and evidence-based answers to common questions regarding the diagnosis and prognosis of prenatally detected agenesis of the corpus callosum (ACC).

The clinical phenotype in cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL), an autosomal dominant cerebral arteriopathy, is variable, but the reasons for this remain uncertain. Possible factors include the mutation site and the influence of additional modulating factors, which could include both epistatic interactions and interactions with cardiovascular risk factors known to cause sporadic small vessel disease. In a large prospectively recruited cohort of CADASIL subjects we determined relationships between phenotype and mutation site, the apoE genotype and cardiovascular risk factors. In addition to clinical features, disease severity was assessed by MRI lesion volume, measured both semiquantitatively (Scheltens scale) and quantitatively. One hundred and twenty-seven CADASIL cases from 65 families with 17 different mutations were studied. Site of mutation was not associated with the presence or age of onset of stroke, migraine, dementia, dependency or MRI lesion load. There was no evidence of intrafamilial clustering of particular phenotypes. Amongst subjects with stroke/transient ischaemic attack, smoking at the time of the event was independently associated with earlier age of onset (P = 0.01). There were no associations between age of onset or presence of stroke and other cardiovascular risk factors, including homocysteine. Homocysteine levels were higher in migraineurs [mean (SD) 12.8 (5.6) versus 9.8 (3.4) micromol/l, P = 0.02)] and elevated homocysteine was independently associated with an earlier age of onset of migraine (P = 0.01). No relationship was found between MRI lesion volume and risk factors, or between apoE genotype and phenotype. Our results show no notch 3 genotype-phenotype correlations. This implies that modulating factors influence phenotype. Smoking appears to increase the risk of stroke, while high homocysteine levels are associated with an increased risk of migraine.