弥散张量成像在胶质瘤术前评估中的应用

目的探讨磁共振弥散张量成像在胶质瘤术前评估中的价值。方法对19例经病理证实胶质瘤的患者术前进行弥散张量成像，观察白质纤维束与肿瘤的关系，测量肿瘤实质区和周边水肿区的FA值。结果颅内胶质瘤所致白质纤维异常有三种基本改变：移位、浸润和破坏。19例中10例移位伴破坏，5例单纯浸润，4例浸润伴破坏；肿瘤的实质区和周边水肿区的FA值与对侧大脑白质FA值相比较存在显著差异（P〈0．05）。肿瘤的实质区和周边水肿区FA值之间无统计学显著差异（P〉0．05）。结论弥散张量成像技术可以显示胶质瘤与周围白质纤维束的关系，FA值不能区分肿瘤实质与周边水肿区。     

慢性炎症性脱髓鞘性多神经病的轴索损害

目的探讨慢性炎症性脱髓鞘性多神经病（CIDP）的轴索病理改变。方法对18例CIDP患者进行电生理和腓肠神经的病理检查，分析不同患者的腓肠神经病理改变特点，并对病理改变不同的两组进行临床、电生理及病理比较。结果5例以脱髓鞘改变为主者，主要出现薄髓鞘神经纤维和有髓神经纤维的洋葱球样结构，其中3例出现轴索损害。8例以轴索损害为主者，主要出现有髓神经纤维的Wallerian变性和再生簇结构。3例出现有髓神经纤维的髓鞘和轴索混合性损害。2例轻微病理改变。脱髓鞘损害为主者和轴索损害为主者的单核细胞浸润程度无明显差异，且两者可同时存在脱髓鞘和轴索损害的电生理改变特点。结论轴索损害是CIDP比较常见的病理改变，不应当作为该病的绝对排除标准。单核细胞的浸润是一种普遍改变。     

三维弥散张量成像在脑胶质瘤术前评价及术中神经导航中的应用

目的本文探讨以磁共振三维弥散张量成像(DTI)评价术前神经传导纤维情况及其在导航手术中的应用价值。方法对6例磁共振提示脑胶质瘤的病人进行两方面研究:1、术前对每例病人均以DTI评价神经传导纤维的完整性;2、DTI与神经导航序列影像融合进行术中导航。结果1、术前DTI提示2例神经纤维以推移为主、4例有不同程度神经纤维的破坏。2、本组术后弥散张量影像复查神经传导束未见进一步损伤,临床症状无加重。结论(1)DTI可以帮助医师在术前评价神经纤维损伤程度,借以估价预后。(2)DTI融合影像神经导航有助于术者设计合理的手术入路及指导手术的神经保护。     

多模态影像联合电生理监测在脑功能区胶质瘤手术中的应用研究

目的研究多模态影像联合电生理监测技术在脑功能区胶质瘤手术中的保护脑功能的应用价值。方法回顾性分析5例语言区和55例运动区胶质瘤患者的临床资料。术前行功能磁共振定位功能区,弥散张量成像显示重要传导束,融合多模态影像构建功能神经导航,术中采用皮层体感诱发电位定位中央沟,并运用皮层-皮层下电刺激技术监测语言区、运动区和皮层下重要神经传导束,在保护功能前提下尽可能切除病灶。术后评价肿瘤切除程度和神经功能。结果 5例语言区胶质瘤和30例病变毗邻运动皮层胶质瘤患者术前功能磁共振成功定位功能区,通过弥散张量成像3例语言区胶质瘤和42例运动区胶质瘤患者分别重建出弓状束和锥体束。术中电刺激语言区和运动区检出率分比为100%和92.7%;92.7%的运动区肿瘤患者可通过皮层体感诱发电位技术定位中央沟。术中神经导航对手术具有指导作用。肿瘤影像全切率86.7%,术后功能保留率91.7%。结论运用多模态影像技术有助于术前定位脑功能区,功能神经导航有助于术前规划、术中引导病灶切除,但需注意影像漂移。术中电生理监测技术是定位和保护脑功能结构的主要手段。     

弥散张量成像技术在脑肿瘤手术中的应用(附78例分析)

目的评估磁共振弥散张量成像（DTI）技术在脑肿瘤微侵袭手术治疗中的应用价值。方法对78例脑肿瘤采用DTI成像技术，在手术前获得脑白质纤维束图像，了解脑肿瘤与白质纤维束的关系，制定手术计划。其中脑胶质瘤56例，脑膜瘤15例，脑转移瘤5例，恶性淋巴瘤2例。均行显微外科手术，53例实施术中神经导航，其中13例行MR＋DTI影像融合导航。结果DTI显示脑白质纤维束受脑肿瘤占位效应、浸润和瘤周水肿等影响，而表现为移位、融合和破坏三种形式，可合并两种或三种形式存在。本组脑肿瘤累及白质纤维束受累区域为胼胝体区42例（单纯移位16例，融合15例，破坏11例）；锥体束27例（单纯移位14例，融合8例，破坏5例）；视放射9例（均为单纯移位）。脑白质纤维束受累体征术后改善或转阴性31例，无改变28例，新增或加重19例（其中脑肿瘤大部切除后伴发瘤周显著水肿12例，瘤床渗血7例）。无死亡病例。结论评定脑肿瘤与DTI之间关系对术前设计手术入路，术中决定切除范围和指导手术操作具有指导意义。神经导航为脑肿瘤手术中保护脑白质纤维束提供了可靠保证。     

白质纤维束的弥散张量成像在脑胶质瘤外科的应用

目的:探讨MRI弥散张量成像(DTI)显示脑白质纤维束在脑胶质瘤外科的意义。方法:2003年9月至2004年12月,30例脑内肿瘤患者接受术前常规头颅MRI序列检查的同时,进行DTI序列扫描,经后处理得到各向异性分数(FA)图显示脑白质纤维束结构,并进行FA值、图像信号强度及对比度的分析研究。结果:所有病例均成功实现包括DTI序列扫描以及FA图像生成。脑白质纤维束显示为显著的高信号结构;灰质显示为等信号;脑脊液显示为低信号;脑内肿瘤呈类圆形等、低信号灶;肿瘤周围间质水肿区白质纤维束仍能在DTI的FA图上显像。DTI的FA图像对于脑白质纤维束显影的信号对比度明显优于常规的T1W图像。结论:DTI影像可以清晰显示脑白质纤维束的形态结构。结合其他序列的MRI应用于脑胶质瘤的术前诊断,可以准确判别肿瘤和周围脑白质纤维束的毗邻关系,对脑胶质瘤手术方案设计以及术后神经功能障碍的预测与预防具有重要意义。     

功能影像构筑的研究在涉及运动区胶质瘤手术中的应用

目的通过研究脑磁图、功能磁共振皮层运动区、神经传导束影像构筑特点,探讨涉及大脑半球运动区胶质瘤病人的微创手术,最大程度的保护运动功能。方法采用脑磁图、功能磁共振完成14例涉及运动区胶质瘤术前评估,评价运动区及锥体束的完整性及与肿瘤的位置关系;在磁源影像（MSI）神经导航指导下,采用穿硬脑膜栅栏定位法分离瘤一运动区的界面后实施肿瘤手术。结果6例患侧脑功能区移位,8例锥体束走行移位,10例神经纤维束形态完好、4例纤维束弥散。肿瘤全切11例、部分切除3例。术后肌力恢复正常4例、减弱2例,其余病例术前后肌力均正常。结论运动区胶质瘤的手术应综合评价运动区分布和锥体束的影像构筑特点,这对设计和指导手术具有重要意义;功能性神经导航指导下的经硬膜栅栏法肿瘤切除有助于运动功能的保护。     

MRI弥散张量成像在脑胶质瘤诊断分级中的研究进展

脑胶质瘤是中枢神经系统常见肿瘤,因其生长具有高度侵袭性而常与正常脑组织分界不清,为临床准确诊断分级带来困难。弥散张量成像可微观监测水分子弥散运动并进行定性、定量分析从而反映脑组织微观结构的病理性变化、无创性显示脑白质纤维束。本文就弥散张量成像利用定量研究参数、脑白质纤维束显示等手段进行脑胶质瘤诊断分级的研究进展作一综述。     

额叶胶质瘤相关癫患者白质纤维网络改变研究

目的探讨额叶胶质瘤相关癫(FGRE)患者白质纤维束网络变化特点。方法前瞻性收集2014年1月至2017年12月共13例额叶胶质瘤相关癫患者和13例正常对照者,行MRI常规扫描和扩散张量成像(DTI),采用基于纤维束示踪的空间统计学方法(TBSS)观察全脑白质纤维束网络改变。结果与正常对照组相比,FGRE组患者全脑平均扩散率(MD)值显著升高,在3个区块13条白质纤维束中存在显著变化(FWE校正,均P 0.05);部分各向异性(FA)值变化区域与MD值大致相同,但是差异未达到统计学意义(FWE校正,P 0.05)。结论额叶胶质瘤相关癫的发生与肿瘤外区域特定白质纤维束网络改变相关。通过DTI参数和TBSS分析可初步揭示额叶胶质瘤相关癫患者早期白质纤维束网络的改变,尤其是MD值可以成为预测癫风险的影像学指标。     

腊肠体样周围神经病的临床和病理

报告４例经腓肠神经活检病理证实的腊肠体样周围神经病，以提高该病的临床认识和诊断能力。方法局麻下做腓肠神经活检，活检标本分别做ＨＥ和Ｍａｓｓｏｎ染色；髓鞘染色；剥离单神经；半薄和超薄切片，分别在光镜或电镜下观察。结果４例均为男性，１３～２１岁发病，其中３例有家族史，临床特征为反复发生的轻微机械性压迫或牵拉后单神经麻痹。电生理检查显示广泛性周围神经损害，传导速度明显减慢。临床符合遗传性压迫易感性麻痹神经病和痛性臂丛神经病。腓肠神经活检可见少数明显增粗的有髓纤维，直径达２０～２８μｍ，髓鞘增厚，而轴索正常，还可见到薄髓纤维。剥离单神经纤维可见局灶性髓鞘增厚，形似腊肠样。电镜下见到髓鞘板层层数增多，无轴索变性，雪旺细胞和无髓纤维未见明显异常。结论腊肠体样周围神经病有周围神经髓鞘发育缺陷，使周围神经易于损伤，是多发性单神经病的病因之一。     

A quantitative electron microscopic study of myelination in the pyramidal tract of rat

The ultrastructure of fibers during myelin formation in the pyramidal tract of rats is described. The distribution of fiber classes based on counts of myelin lamellae was determined for newborn, young and mature rats. In newborn rats (2–12 days), growth of the axon was extremely rapid in fibers undergoing early myelination, resulting in greater variation in the relation between axon circumference and sheath thickness and, also, in the presence of myelin sheaths that were unusually thin in relation to the size of the axons. In young rats (12 days to 8 weeks), the numbers of myelin lamellae present in the sheaths increased in proportion to the increase in axon circumference. In adult rats, the numbers of myelin lamellae present in the sheaths was in linear relation to axon circumference for all sizes of myelinated fibers. Approximately 20% of the fibers were nonmyelinated. The number of glia cells per axon at the onset of myelination was approximately 20% of the adult ratio. During growth, myelination gliosis resulted in a steady increase in the number of glia cells per axon until adult levels were ultimately achieved. Our observations suggest that formation of myelin lamellae by oligodendroglia cells may be controlled by the caliber of the axon.     

脑出血大鼠锥体束显微和超微结构改变

目的研究脑出血大鼠锥体束病理变化规律及特点。方法使用Ⅳ型胶原酶．肝素诱导大鼠基底节脑出血,采用劳克坚牢蓝（LFB）染色、神经丝蛋白（NF）免疫组化和电镜对内囊后肢进行观察。结果Ⅳ型胶原酶-肝素能成功建立具有典型神经功能缺损的大鼠脑出血模型。光镜发现锥体束髓鞘损伤在脑出血1～3d逐渐加重,7d开始再生修复,1～7d轴突损伤持续加重,14d轴突光度值（0．09±0．01）有所增加,但与7d（0．10±0．02）相比无显著性差异（P〉0．05）。电镜显示脑出血1d锥体束髓鞘松解,轴突水肿,部分无髓轴突崩解坏死消失,3d髓鞘松解、空泡样变性,局部髓鞘消失、厚薄不均,轴突水肿严重,甚至坏死崩解。结论大鼠脑出血后1w内锥体束损伤呈进行性加重,提示应早期和超早期予以干预治疗以减轻损伤和促进修复。     

Development of myelinated nerve fibers in the sixth cranial nerve of the rat: a quantitative electron microscope study

Myelination was studied quantitatively in the sixth cranial nerves of rats by counting and measuring all myelinated fibers during the first three postnatal weeks. In transverse semithin and thin sections cut serially at a well-defined anatomical site in the midsphenoid region, only a few axons (mean 12) were myelinated at birth. On days 2, 4, and 8, counts of myelinated fibers were respectively 5 times (mean 57), 20 times (mean 230), and 24 times (mean 273) the number seen at birth. During the second postnatal week, the number of myelinated fibers remained constant, whereas growth of axons and their myelin sheaths continued. By 15 days these fibers were large and relatively uniform in size; they had compact, circular myelin sheaths. During the third postnatal week, myelination of previously unmyelinated, smaller axons began. The number of myelinated fibers increased again and the size distribution of myelinated fibers became bimodal. Axon diameters, fiber diameters, and myelin sheath dimensions for all fibers were calculated from measurements made on electron micrographs. The transverse length of the myelin membrane increased exponentially with time. The growth increased rapidly during the formation of the first 20 spiral layers and remained relatively constant during the subsequent enlargement of the compact sheath. The association of axon diameter and myelin sheath thickness was poor at young ages, but it improved progressively with maturation of the sheath. The results show that myelination begins around axons that have a wide range of diameters. Also, the first axons to be myelinated become the large myelinated fibers of the sixth nerve. The small myelinated fibers originate from axons that do not become myelinated until the third postnatal week. Myelination, though differing in onset by 2 weeks, appeared to be similar in both populations as judged by similarity of sheath morphology and growth rates. It is of interest that at the level studied, the sixth nerve also contains a fascicle of unmyelinated cranial sympathetic fibers.     

Relation between the number of myelin lamellae and axon circumference in fibers of vagus and sciatic nerves of mice

Nerve fiber populations of the vagus and sciatic nerves of mice were classified according to the number of myelin lamellae present in the sheaths. This method for classifying fiber populations was superior to others used previously since it provided a more sensitive procedure for the analysis of individual fibers and better control over the technical factors involved in tissue processing. The relationship of the number of myelin lamellae in the sheath to axon circumference was found to be linear. In fresh tissue there was one myelin lamella for every 0.24 μ increase in axon circumference above da value of 2.32 μ (the mean circumference of an average-sized nonmyelinated fiber). A formula was proposed which may be useful for understanding how axons control myelin development and interpreting developmental stages, as well as for evaluating pathologic conditions affecting the peripheral nervous system. The critical diameter above which fibers were found to be myelinated was about 0.8 μ for fixed nerve and 1.1 μ for fresh nerve. The ratio of axon diameter to fiber diameter ranged between 0.5 and 0.9 and was not related to fiber size.     

Fiber analysis of the pyramidal tract of the laboratory rat

Light and electron microscopic study of the pyramidal tract of the laboratory rat at a midbulbar level revealed the total number of myelinated fibers on one side to be about 200,000. They ranged from 0.2 micron to more than 5 microns, but clustered strongly in the neighborhood of 1.0 micron (mode of 0.9 micron and mean of 1.2 micron), forming the highly skewed fiber spectrum so familiar for mammalian pyramidal tracts and other central fiber pathways. Numerous small clusters of unmyelinated axons were found scattered throughout the tract, adding another 100,000 axons to the estimated number. Not only were the fibers exceedingly small, but also the degree of myelination relative to axon diameter varied widely, suggesting that conduction speed within the tract is not optimal for all fibers. In fact, about half of the fibers in the pyramidal tract would, in theory, conduct faster if they had no myelin wrapping.     

Novel organization and development of copepod myelin. i. ontogeny

Nerve impulse conduction is greatly increased by myelin, a multilayered membranous sheath surrounding axons. Best known from and most extensively investigated among vertebrates, a few invertebrates, including some superfamilies of copepod, have functionally and structurally similar myelin-like sheaths surrounding their axons. We examined the development of myelin ultrastructure in Bestiolina similis, a paracalanoid copepod. Development occurred in a novel way: initial myelination always appeared first as a partial layer, which in later stages came to encircle an axon completely. This partial myelin first appeared in a single pair of reidentifiable fibers, at the second naupliar stage. Two additional pairs of reidentifiable fibers also became partially myelinated by the third naupliar stage. The number of myelin layers in this trio of axon pairs increased with development, but, at any one stage, each axon had the same number of layers along its entire length. These axons disappeared after the copepodite metamorphosis. After metamorphosis, the fiber that took over as largest in the nerve cord became the most heavily myelinated and was identified as the lateral dorsal giant fiber. The rate of myelination was also characterized in the antennular nerve as a representative of the peripheral nervous system. As axons became larger, they were more likely to be partially, and then completely, myelinated, the latter having a lower ratio of axon core to fiber diameter than the former. Copepod myelin is an instructive example of convergent evolution, with far-reaching consequences for nervous system functioning and the behavior that nervous systems subserve.     

A new approach toward analyzing peripheral nerve fiber populations. I. Variance in sheath thickness corresponds to different geometric proportions of the internodes

The thickness of the myelin sheath is known to increase with axon caliber, but there is also a superimposed, slight variation in sheath thickness depending on whether a fiber of a given caliber has very long or very short internodes. This relationship between myelin sheath thickness and the geometric proportion of the internode has been shown in subserial sections of isolated nerve fibers. It allows a prediction of sheath thickness from the quotient internode length/axon caliber, or conversely, a prediction of internode foreshortening from sheath thickness. We applied this new approach to the analysis of sciatic fiber populations of frogs, mice, rats and cats. The geometric proportions of these fibers were defined by the quotient internode length/fiber caliber. This quotient was compared with minor variation in sheath thickness as determined with a computer-assisted technique measuring large numbers of fibers in low-power electron micrographs. The method also calculated fiber shrinkage and recalculated all data for circular fiber profiles. The data obtained confirmed previous electron microscopic measurements showing that there is a slight reduction in sheath thickness when a fiber of a given caliber has relatively short internodes, and vice versa. A population of very thin, thinly myelinated fibers was also revealed. Sheath thickness and the geometric proportions of internodes in frogs differed markedly from those in mammals.     

Development of the pyramidal tract in the hamster. II. An electron microscopic study

We undertook a qualitative and quantitative electron microscopic study of the growth and development of the pyramidal tract in the hamster to investigate the mode of growth of the axons, the possibility of fiber degeneration during development, and the process of myelination. By calculating the total fiber number as the product of axon density and tract area for several postnatal ages, we found that the pyramidal tract grows through the medulla as a compact bundle containing nearly twice the number of fibers as the mature tract. During the second postnatal week there is a substantial loss of axons followed in the third and fourth weeks by a more gradual loss such that by 34 days after birth the total number of axons reaches the adult value. Myelination in the hamster pyramidal tract begins at 7 days and continues at a very slow rate until the third postnatal week, when a dramatic increase in myelin formation occurs. By 34 days after birth the number of myelinated axons is approximately 80% that of the adult. As has been reported for other CNS tracts, there does not seem to be a “critical diameter” of an axon that absolutely determines the presence or absence of myelin on a fiber. However, all axons above 0.5 μm in diameter are myelinated at approximately the same rate, while those under this diameter are myelinated much more slowly and even in the adult make up only a small percentage of the total myelinated fibers.     

Development of myelination in optic tract of the cat.

The postnatal development of myelin in the optic nerve and tract of normal and dark reared cats has been studied quantitatively with light and electron microscopy. In the newborn cat few myelinated fibers (3% of the population) are seen in the optic tract. Until the end of the second postnatal week, the total number of myelinated axons in the tract remains low (23%). At this time, however, there is an explosive increase in the rate of myelination and by the end of the fourth postnatal week 80% of the optic tract axons have acquired a myelin sheath. Thereafter, the number of myelinated axons increases gradually, reaching adult levels (100%) at 12 weeks. During the initial period of myelination, the average axon diameter is 0.6 mu for unmyelinated fibers and a.2 mu for myelinated fibers. Both of these means remain substantially unchanged until myelination is completed, suggesting that initial myelination of an axon is not a continuous process but rather proceeds in a step-wise manner. Dark rearing appears to have no effect on the initiation of myelination.