Kraus Marilyn F, Susmaras Teresa, Caughlin Benjamin P, Walker Corey J, Sweeney John A, Little Deborah M
Department of Psychiatry, University of Illinois at Chicago Medical Center, Chicago, IL, USA.
Brain. 2007 Oct;130(Pt 10):2508-19. doi: 10.1093/brain/awm216. Epub 2007 Sep 14.
Traumatic brain injury (TBI) is a serious public health problem. Even injuries classified as mild, the most common, can result in persistent neurobehavioural impairment. Diffuse axonal injury is a common finding after TBI, and is presumed to contribute to outcomes, but may not always be apparent using standard neuroimaging. Diffusion tensor imaging (DTI) is a more recent method of assessing axonal integrity in vivo. The primary objective of the current investigation was to characterize white matter integrity utilizing DTI across the spectrum of chronic TBI of all severities. A secondary objective was to examine the relationship between white matter integrity and cognition. Twenty mild, 17 moderate to severe TBI and 18 controls underwent DTI and neuropsychological testing. Fractional anisotropy, axial diffusivity and radial diffusivity were calculated from the DTI data. Fractional anisotropy was the primary measure of white matter integrity. Region of interest analysis included anterior and posterior corona radiata, cortico-spinal tracts, cingulum fibre bundles, external capsule, forceps minor and major, genu, body and splenium of the corpus callosum, inferior fronto-occipital fasciculus, superior longitudinal fasciculus and sagittal stratum. Cognitive domain scores were calculated from executive, attention and memory testing. Decreased fractional anisotropy was found in all 13 regions of interest for the moderate to severe TBI group, but only in the cortico-spinal tract, sagittal stratum and superior longitudinal fasciculus for the mild TBI group. White Matter Load (a measure of the total number of regions with reduced FA) was negatively correlated with all cognitive domains. Analysis of radial and axial diffusivity values suggested that all severities of TBI can result in a degree of axonal damage, while irreversible myelin damage was only apparent for moderate to severe TBI. The present data emphasize that white matter changes exist on a spectrum, including mild TBI. An index of global white matter neuropathology (White Matter Load) was related to cognitive function, such that greater white matter pathology predicted greater cognitive deficits. Mechanistically, mild TBI white matter changes may be primarily due to axonal damage as opposed to myelin damage. The more severe injuries impact both. DTI provides an objective means for determining the relationship of cognitive deficits to TBI, even in cases where the injury was sustained years prior to the evaluation.
创伤性脑损伤（TBI）是一个严重的公共卫生问题。即使是分类为轻度的损伤（最常见的），也可能导致持续性神经行为障碍。弥漫性轴索损伤是TBI后的常见表现，被认为与预后有关，但使用标准神经影像学检查时可能并不总是明显。扩散张量成像（DTI）是一种更新的在体评估轴索完整性的方法。本研究的主要目的是利用DTI对所有严重程度的慢性TBI患者的白质完整性进行特征描述。次要目的是研究白质完整性与认知之间的关系。20名轻度、17名中度至重度TBI患者和18名对照者接受了DTI和神经心理学测试。从DTI数据中计算出分数各向异性、轴向扩散率和径向扩散率。分数各向异性是白质完整性的主要测量指标。感兴趣区域分析包括放射冠前后部、皮质脊髓束、扣带纤维束、外囊、小钳和大钳、胼胝体膝部、体部和压部、额枕下束、上纵束和矢状层。认知领域得分由执行、注意力和记忆测试计算得出。在中度至重度TBI组的所有13个感兴趣区域均发现分数各向异性降低，但在轻度TBI组仅在皮质脊髓束、矢状层和上纵束中发现。白质负荷（一种衡量分数各向异性降低区域总数的指标）与所有认知领域呈负相关。对径向和轴向扩散率值的分析表明，所有严重程度的TBI均可导致一定程度的轴索损伤，而不可逆的髓鞘损伤仅在中度至重度TBI中明显。目前的数据强调，包括轻度TBI在内，白质变化存在一个连续谱。一种整体白质神经病理学指标（白质负荷）与认知功能相关，即白质病理学越严重，认知缺陷越严重。从机制上讲，轻度TBI白质变化可能主要是由于轴索损伤而非髓鞘损伤。更严重的损伤则两者均有影响。DTI为确定认知缺陷与TBI之间的关系提供了一种客观方法，即使在损伤发生于评估前数年的情况下也是如此。
