Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Alzheimers Dement. 2012;8(2):105-13. doi: 10.1016/j.jalz.2011.05.2416.
The fornix is the predominant outflow tract of the hippocampus, a brain region known to be affected early in the course of Alzheimer's disease (AD). The aims of the present study were to: (1) examine the cross-sectional relationship between fornix diffusion tensor imaging (DTI) measurements (fractional anisotropy [FA], mean diffusivity [MD], axial diffusivity, and radial diffusivity), hippocampal volume, and memory performance, and (2) compare fornix DTI measures with hippocampal volumes as predictors of progression and transition from amnestic mild cognitive impairment to AD dementia.
Twenty-three mild cognitive impairment participants for whom hippocampal volumetry and DTI were conducted at baseline received detailed evaluations at baseline; 3, 6, and 12 months; and 2.5 years. Six participants converted to AD over the follow-up period. Fornix and posterior cingulum DTI measurements and hippocampal volumes were ascertained using manual measures. Random effects models assessed each of the neuroimaging measures as predictors of decline on the Mini-Mental State Examination, Clinical Dementia Rating-sum of boxes, and memory z scores; receiver operating characteristic analyses examined the predictive value for conversion to AD.
There was a significant correlation between fornix FA and hippocampal volumes. However, only the fornix measurements (FA, MD, radial diffusivity, and axial diffusivity) were cross-sectionally correlated with memory z scores. Both fornix FA and hippocampal volumes were predictive of memory decline. Individually, fornix FA and MD and hippocampal volumes were very good predictors of progression, with likelihood ratios >83, and better than 90% accuracy.
Fornix FA both cross-sectionally correlated with and longitudinally predicted memory decline and progression to AD. Manually drawn region of interest within the fornix shows promise comparable with hippocampal volume as a predictive biomarker of progression, and this finding warrants replication in a larger study.
穹窿是海马体的主要流出道，海马体是阿尔茨海默病（AD）早期受影响的大脑区域。本研究的目的是：（1）检查穹窿弥散张量成像（DTI）测量值（各向异性分数[FA]、平均弥散度[MD]、轴向弥散度和径向弥散度）、海马体体积与记忆表现之间的横断面关系，（2）比较穹窿 DTI 测量值与海马体体积作为向 AD 痴呆进展和转变的预测因子。
23 名轻度认知障碍参与者在基线时进行了海马体体积和 DTI 检查，在基线时、3、6 和 12 个月以及 2.5 年后接受了详细评估。在随访期间，有 6 名参与者转为 AD。使用手动测量法确定穹窿和后扣带回的 DTI 测量值和海马体体积。随机效应模型评估了每种神经影像学测量值作为 Mini-Mental State Examination、临床痴呆评定总和箱和记忆 z 评分下降的预测因子；接受者操作特征分析检查了对向 AD 转换的预测价值。
穹窿 FA 与海马体体积之间存在显著相关性。然而，只有穹窿测量值（FA、MD、径向弥散度和轴向弥散度）与记忆 z 评分呈横断面相关。穹窿 FA 和海马体体积均能预测记忆下降。单独来看，穹窿 FA 和 MD 以及海马体体积是进展的极好预测因子，似然比>83，准确率优于 90%。
穹窿 FA 与记忆下降和向 AD 进展均呈横断面相关，并具有预测性。在穹窿内手动绘制感兴趣区，作为进展的预测生物标志物，具有与海马体体积相当的潜力，这一发现需要在更大的研究中得到复制。
