加齢性白質病変（leukoaraiosis）update

Age-related White Matter Lesions (Leukoaraiosis): An Update

はじめに

　高齢者の脳の磁気共鳴画像（magnetic resonance imaging：MRI）のT₂強調画像やFLAIR（fluid-attenuated inversion recovery）画像では，高頻度に大脳白質に高信号領域が観察される。脳のMRI検査において，最も頻繁に目にする病変である¹⁾。最近では，脳小血管病（cerebral small vessel disease）としても注目され，多くの前向き研究により，脳卒中や認知症などの重要なリスクファクターの1つであることが明らかになってきている^2-8)。以前は，何を見ているかよくわかっていなかったことから，UBO（unidentified bright object）とも呼ばれたことがあるが，現在では，多くの，画像と病理との対比研究により，「何を見ているか」がわかってきた。本稿では，高齢者における大脳白質病変について，最近の知見を含め，概説する。

Abstract

　Leukoaraiosis (age-related white matter hyperintensities) is the most frequently seen lesion on brain magnetic resonance (MR) images. This lesion is a subject of much current interest, because a number of multicenter studies have revealed that it is associated with various disturbances and poor prognoses. Leukoaraiosis corresponds to various pathologies, including demyelination, apoptosis, edema, dilated perivascular spaces, axonal damage, gliosis, and infarcts. Also noted in leukoaraiosis are changes in small vessels, such as fibrohyalinosis and venous collagenosis. The main cause of leukoaraiosis is thought to be chronic ischemia; other causes include edema and breakdown of the blood-brain barrier. Major risk factors for leukoaraiosis are age and hypertension. Disturbances that are related to leukoaraiosis include stroke, dementia, cognitive impairment, gait disturbance, fall, and depression. Leukoaraiosis is also a risk factor for death. Technologies, such as automatic volumetry, tissue segmentation, diffusion tensor imaging, magnetization tensor imaging, diffusion kurtosis imaging, and ultra-high field MR imaging may provide further insights into leukoaraiosis.