Fazekas F, Schmidt R, Scheltens P
Department of Neurology, Karl Franzens University, Graz, Austria.
Dement Geriatr Cogn Disord. 1998 Jul;9 Suppl 1:2-5. doi: 10.1159/000051182.
Magnetic resonance imaging (MRI) has dramatically enhanced our capability of detecting age-related changes of the brain even before they become clinically apparent. Among those are preferentially alterations of the white matter in periventricular, deep and subcortical locations which display high signal intensity on both proton density- and T2-weighted images. Correlative histopathologic findings show hyperintense periventricular capping of the frontal horns to reflect predominantly a specific anatomic situation characterized by loosely arranged fine-fiber tracts with low myelin and high extracellular fluid content. A smooth halo of periventricular hyperintensity has been linked to disruption of the ependymal lining with subependymal gliosis and concomitant loss of myelin. In contrast, punctate, early confluent and confluent hyperintensities in the deep and subcortical white matter as well as irregular periventricular hyperintensity appear to be of vascular origin. Punctate lesions tend to correspond to a perivascular reduction in myelin content with atrophy of the neuropil and seem to constitute a negligible extent of tissue damage from low permeability through thickened arteriolar walls. Early confluent and confluent hyperintensities, however, indicate more extensive ischemic damage consistent with advanced microangiopathy.
磁共振成像（MRI）极大地增强了我们在脑部与年龄相关的变化出现临床症状之前就进行检测的能力。其中，脑室周围、深部和皮质下白质的变化尤为明显，在质子密度加权像和T2加权像上均显示高信号强度。相关组织病理学结果显示，额叶角脑室周围的高强度帽状影主要反映了一种特定的解剖学情况，其特征是细纤维束排列松散，髓鞘含量低，细胞外液含量高。脑室周围高强度的光滑晕环与室管膜内衬破坏伴室管膜下胶质增生及髓鞘同时丢失有关。相比之下，深部和皮质下白质中的点状、早期融合和融合性高强度以及不规则的脑室周围高强度似乎起源于血管。点状病变往往对应于血管周围髓鞘含量减少和神经纤维网萎缩，似乎是由于通过增厚的小动脉壁的低渗透性导致的可忽略不计的组织损伤程度。然而，早期融合和融合性高强度表明存在与晚期微血管病变一致的更广泛的缺血性损伤。
