Cendes Fernando
Departamento de Neurologia, FCM, UNICAMP, Campinas, SP 13083-880, Brazil.
Continuum (Minneap Minn). 2013 Jun;19(3 Epilepsy):623-42. doi: 10.1212/01.CON.0000431379.29065.d3.
This review discusses the MRI and functional imaging findings in patients with focal seizures, practical ways to improve the detection of subtle lesions, and limitations and pitfalls of the various imaging techniques in this context.
A proper MRI investigation of patients with focal epilepsy requires the use of specific protocols, selected based on identification of the region of onset by clinical and EEG information. For practical purposes, the focal epilepsies are divided here into mesial temporal lobe epilepsies and neocortical epilepsies. The majority of patients with mesial temporal lobe epilepsies associated with hippocampal sclerosis undergoing presurgical evaluation will have a clear-cut unilateral atrophic hippocampus with increased T2 signal and a normal-appearing contralateral hippocampus. Among the several types of neocortical lesions, focal cortical dysplasias deserve especial attention because these lesions are often missed on routine MRIs. The focal cortical dysplasias include a gradient of morphologic changes from dysplastic lesions that can be easily identified by conventional MRI techniques to minor structural abnormalities with small areas of discrete cortical thickening and blurring of the gray/white matter interface that often go unrecognized.
The use of MRI protocols targeted for the study of patients with epilepsy allows the diagnosis of the etiology of epilepsy in most patients with focal seizures. However, in a considerable number of patients with epilepsy, MRI results are considered normal. Although the etiology remains unclear in these cases, the malformations of cortical development (mainly focal cortical dysplasias) have been identified as most likely pathologic substrates. The effort involved in trying to increase the detection of these "invisible" lesions involves the improvement of structural imaging techniques and the combination of metabolic and functional studies, including 18F-fluorodeoxyglucose-positron emission tomography (18F-FDG-PET), ictal single-photon emission computed tomography (SPECT), diffusion MRI, and magnetic resonance spectroscopy (MRS). The methods used to enhance the detection of subtle cortical abnormalities by improving the structural images have addressed two basic aspects of the examination by MRI: signal acquisition and imaging postprocessing.
本综述讨论局灶性癫痫患者的MRI及功能成像结果、提高细微病变检测的实用方法以及在此背景下各种成像技术的局限性和陷阱。
对局灶性癫痫患者进行恰当的MRI检查需要使用基于临床和脑电图信息确定发作起始区域而选择的特定方案。出于实际目的，此处将局灶性癫痫分为内侧颞叶癫痫和新皮质癫痫。大多数接受术前评估的内侧颞叶癫痫伴海马硬化患者会有明确的单侧海马萎缩，T2信号增加，对侧海马外观正常。在几种类型的新皮质病变中，局灶性皮质发育异常值得特别关注，因为这些病变在常规MRI上常被漏诊。局灶性皮质发育异常包括一系列形态学改变，从可通过传统MRI技术轻松识别的发育异常病变到具有离散皮质增厚小区域和灰白质界面模糊的微小结构异常，这些异常往往未被识别。
使用针对癫痫患者研究的MRI方案可在大多数局灶性癫痫发作患者中诊断癫痫病因。然而，相当数量的癫痫患者MRI结果被认为正常。尽管这些病例的病因仍不清楚，但皮质发育畸形（主要是局灶性皮质发育异常）已被确定为最可能的病理基础。试图增加对这些“隐匿”病变检测的努力包括改进结构成像技术以及代谢和功能研究的结合，包括18F-氟脱氧葡萄糖正电子发射断层扫描（18F-FDG-PET）、发作期单光子发射计算机断层扫描（SPECT）、扩散MRI和磁共振波谱（MRS）。通过改进结构图像来增强细微皮质异常检测的方法涉及MRI检查的两个基本方面：信号采集和成像后处理。
