Rodríguez-Cruces Raúl, Concha Luis
Instituto de Neurobiología, Universidad Nacional Autónoma de México, Querétaro, México.
Quant Imaging Med Surg. 2015 Apr;5(2):264-78. doi: 10.3978/j.issn.2223-4292.2015.02.06.
Using magnetic resonance imaging, it is possible to measure the behavior of diffusing water molecules, and the metrics derived can be used as indirect markers of tissue micro-architectural properties. Numerous reports have demonstrated that patients with temporal lobe epilepsy (TLE) have water diffusion abnormalities in several white matter structures located within and beyond the epileptogenic temporal lobe, showing that TLE is not a focal disorder, but rather a brain network disease. Differences in severity and spatial extent between patients with or without mesial temporal sclerosis (MTS), as well as differences related to hemispheric seizure onset, are suggestive of different pathophysiological mechanisms behind different forms of TLE, which in turn result in specific cognitive disabilities. The biological interpretation of diffusion abnormalities is based on a wealth of information from animal models of white matter damage, and is supported by recent reports that directly correlate diffusion metrics with histological characteristics of surgical specimens of TLE patients. Thus, there is now more evidence showing that the increased mean diffusivity (MD) and concomitant reductions of diffusion anisotropy that are frequently observed in several white matter bundles in TLE patients reflect reduced axonal density (increased extra-axonal space) due to smaller-caliber axons, and abnormalities in the myelin sheaths of the remaining axons. Whether these histological and diffusion features are a predisposing factor for epilepsy or secondary to seizures is still uncertain; some reports suggest the latter. This article summarizes recent findings in this field and provides a synopsis of the histological features seen most frequently in post-surgical specimens of TLE patients in an effort to aid the interpretation of white matter diffusion abnormalities.
使用磁共振成像，可以测量水分子扩散的行为，所得到的指标可作为组织微观结构特性的间接标志物。大量报告表明，颞叶癫痫（TLE）患者在致痫颞叶内外的几个白质结构中存在水扩散异常，这表明TLE不是一种局灶性疾病，而是一种脑网络疾病。有或无内侧颞叶硬化（MTS）的患者在严重程度和空间范围上的差异，以及与半球性癫痫发作起始相关的差异，提示不同形式的TLE背后存在不同的病理生理机制，进而导致特定的认知障碍。扩散异常的生物学解释基于来自白质损伤动物模型的大量信息，并得到最近一些报告的支持，这些报告将扩散指标与TLE患者手术标本的组织学特征直接关联起来。因此，现在有更多证据表明，TLE患者多个白质束中经常观察到的平均扩散率（MD）增加和扩散各向异性同时降低，反映了由于轴突直径较小导致的轴突密度降低（轴突外空间增加），以及剩余轴突髓鞘的异常。这些组织学和扩散特征是癫痫的易感因素还是继发于癫痫发作仍不确定；一些报告表明是后者。本文总结了该领域的最新发现，并概述了TLE患者手术标本中最常见的组织学特征，以帮助解释白质扩散异常。
