MAGNETIC-RESONANCE-IMAGING IN VASCULAR DE MENTIA

The heterogeneity of vascular dementia depends on the cause, size, loc ation and nature of the vascular lesions (36, 62). Magne tic resonance imaging (MRI) techniques are of major interest to detect the vascular origin of dementia : the lack of focal lesions or leukoencephalopathy excludes the vascular origin of dementia (36). Occlusions of large ex tra-cerebral arteries usually lead to cortical or large subcortical in farcts or both (28). Dementia may be due to multiple infarcts or to a single infarct located in a strategic area (47). Lacunar infarcts are due to the occlusion of one single deep perforator with a thickening o f the arterial wall due to lipohyalinosis (25), usually in a patient w ith arterial hypertension; lacunes are located in a territory supplied by the deep perforators. They appear as hyperintense in T2-weighted s equences and hypo-intense in T1-weighted sequences. Old small hemorrha ges have the same appearence than infarcts on CT-scans but their cente r appears hypo-intense in T2-weighted sequences. In normal subjects, a ge and arterial hypertension are risk factors for hemispheric while ma tter hyperintensities (59, 60). Their vascular origin is likely becaus e of the evidence of lesions of the wall of deep perforators (17, 21), their association with lacunes (17, 21, 30, 37) or deep hemorrhages ( 30, 32, 37), and their frequency in amyloid angiopathy (26). Their pre valence is higher in vascular dementia than in Alzheimer's disease (59 ). They sometimes fulfill criteria for Binswanger's disease (5). Even after exclusion of predisposing factors they remain frequent in health y subjects over 50 years (39, 56); however, whether they herald subseq uent dementia remains unsettled. The acronym CADASIL (for Cerebral Aut osomal Dominant Arteriopathy with Subcortical Infarcts and Leukoenceph alopathy) has been introduced to define an hereditary autosomal domina nt disease of the small deep perforators; the gene is located on chrom osome 19; CADASIL usually leads to multiple recurrent lacunes and deme ntia(66); MRI is always abnormal(10, 14): it reveals (i) lacunar infar cts in the basal ganglia and (ii) a severe leukoencephalopathy even in 50% of asymptomatic members of the family over 40 who have the gene. Therefore, MRI is crucial for a diagnosis of vascular dementia because of its ability to reveal multiple small vascular lesions and leukoenc ephalopathy (J Mal Vasc 1995; 20 : pages 194-208).