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1、DTT在听神经瘤诊治中的应用进展浙江大学医学院附属邵逸夫医院神经外科郭洪彬DTT 成像的基本原理（DIFFUSION TENSOR TRACTOGRAPHY，DTT）以往有关大脑白质纤维束（white matter fiber ，WMF）的研究主要依赖于活体动物的大脑组织或尸体解剖研究。常规的磁共振成像如 T2WI、FLAIR、MT (magnetization transfer imaging )图像虽然可以显示大脑白质和灰质之间的差别，但这些成像方法不能显示大脑白质纤维的走行方向，因此也就不能提供完全的白质纤维的解剖信息。DTI反映了 WMF 中水分子弥散的方向依赖特性，其 FA 图像可以
2、显示大脑白质纤维的结构和各向异性特征，如显示内囊、胼胝体、外囊等结构。但 DTI 不能提供相邻体素之间白质纤维是如何连接的。随着计算机软件的不断开发和利用，人们利用 DTI 所获得的数据进行大脑白质纤维成像，此即为弥散张量纤维束成像（diffusion tensor tractography，DTT），DTT 是 DTI 技术的进一步发展，它可以辨认大脑内的特殊纤维通道及其相互之间的连接。由于 DTT 是新近应用的磁共振弥散成像技术，其名称尚欠统一，例如有称为纤维跟踪技术（fiber tracking）或白质纤维束成像（tractography）等。ABSTRACTMethods We inv
3、estigated 11 patients with VS who underwent tumor resection. Visualized tracts were compared with loca- tions of the facial and cochlear nerves as identified by intra- operative electrophysiological monitoring.作者研究了11例的听神经瘤的病例，并进行了手术切除。所获得的DTT成像与术中的神经电生理所示的面神经和耳蜗神经的位置比较。Conclusions We visualized fac
4、ial or vestibulocochlear nerves in nine of 11 patients (81.8 %). For the first time, DTT proved able to visualize not only the facial nerve but also the vestibulocochlear nerve in VS patients. 面神经和前庭耳蜗神经的可视率达81.8 %，DTT第一次被证明可用于可视化前庭耳蜗神经。ABBREVIATIONS平均扩散率(mean diffusivity，MD)与各向异性分数(fractional aniso
5、tropy, FA)是最常用的DTI导出量,MD反映水分子扩散的剧烈程度，FA反映水分子扩散的各向异性程度。INTRODUCTIONMost recently, preoperative prediction of the locations of the nerves using diffusion tensor tractography (DTT) has been adopted as an aid to improving preservation rates for facial nerve function。术前应用DTT预测神经纤维束的所在，被采用以提高听瘤手术的面神经功能保留率
6、。MATERIALS AND METHODSMRI was performed using a 3.0-T system (Signa 3.0 T; GE, Milwaukee, WI, USA) equipped with an eight-channel phased-array head coil.MRI采用的是3.0T的。Fig. 1 Method for setting the seed region of interest (ROI). In the proposed method, the porus of the internal auditory canal is viewe
7、d from a direction parallel to the courses of the nerves inside the internal auditory canal (a arrow), and the seed ROI is placed at the porus of the internal auditory canal in a plane perpendicular to the courses of the nerves (b red circle)From among the visualized fiber tracts, we verified as tru
8、e fiber tracts those that ran on the surface or inside of the tumor and reached the brainstem and were identified as nerves based on electrophysiological testing performed during the operation.在那些被显示的纤维束中，作者认定那些走行在肿瘤表面或中间，且到达脑干的可视的纤维束为true纤维束。然后根据术中的神经电生理检测认定为神经纤维束。Identifying the vestibular nerve e
9、lectrophysiologi- cally during surgery is not currently possible. We therefore judged visualized fiber tracts that coincided with the cochlear nerve identified during surgery as the vestibulocochlear nerve.因为术中电生理目前还不能辨识前庭神经。所以术中根据走形判定，与耳蜗神经汇合的为前庭耳蜗神经。With regard to the cochlear nerve, since we inve
10、nted electric stimuli-elicited dorsal cochlear nucleus ac- tion potential (ESE-DNAP) monitoring 5, 9, we could iden- tify the specific direct connection of the specific nerve fascicle with the dorsal cochlear nucleus by intraoperative electrical stimulation around 0.20.4 mA.辨识耳蜗神经也很困难。辨识耳蜗神经。依据作者的一个
11、发明。electric stimuli-elicited dorsal cochlear nucleus ac- tion potential (ESE-DNAP) monitoring RESULTSfacial nerve function according to House & Brackmann Classification(House-Brackmann 面神经瘫痪面神经瘫痪分级分级,1级正常，级正常，6级全瘫级全瘫)hearing function was graded using the Gardner-Robertson ClassificationRESULTS平均扩散率(
12、mean diffusivity，MD)与各向异性分数(fractional anisotropy, FA)是最常用的DTI导出量,MD反映水分子扩散的剧烈程度，FA反映水分子扩散的各向异性程度。Fig. 2 Case 2. Contrast-enhanced fast imaging employing steady-state acquisition imaging shows left cerebellopontine angle vestibular schwannoma in the (a) axial view. b Axial view of diffusion tensor t
13、ractography (DTT). c Sagittal view of DTT. d Oblique view of DTT. DTT when using the upper limit of the FA threshold visualizes the fiber tract running in the posterior middle one-third to the tumor. e, fIntraoperative view. Electrophysiological diagnosis performed during the surgery confirms that t
14、he cochlear nerve passes in the posterior middle one-third to the tumor (f asterisk). Positive wave of elicited dorsal cochlear nucleus action potential (ESE-DNAP) represents the presence of the cochlear nerve (e arrowhead)Case 2,术前把FA值设定在上限时可显示一个模糊的DTT影在肿瘤的中后部。术中电生理证实耳蜗神经穿行在肿瘤的中后三分之一。ESEDNAP显示阳性波，显
15、示为耳蜗神经。In this patient, we intended to preserve hearing function, and there- fore only performed a biopsy at that time, since resection of the tumor without injury to the cochlear nerve using a lateral suboccipital approach seemed very difficult. We subsequently performed complete resection of the t
16、umor using an extended middle cranial fossa approach.此病例，作者试图保留听力，所以只做了活检，因为手术采用的是枕下外侧入路，作者认为这个入路极有可能损伤到听神经。所以下次采用中颅窝入路全切肿瘤，术后听力为1级。Fig. 3 Case 8. DTT when using the upper limit of the fractional anisotropy threshold visualizes the fiber tract running in the anterior superior one-third to the tumor.
17、 d Intraoperative view. Electrophysiological diag- nosis performed during the sur- gery confirms that the facial nerve runs in the anterior superior one- third to the tumor (asterisk) a图显示曾强MR一个大型听瘤。采用FA上限设定，DTT显示一个纤维束穿行在肿瘤的前上三分之一。术中神经电生理监测在为面神经。DISCUSSION追根溯源（）第一步，设定兴趣点a。第二步，非选择性重建。第三步，根据内听道内发出的纤维走
18、向，重建。病例4,70岁女性。磁共振脑池成像不能辨别面神经，DTT发现面神经被肿瘤挤压向前移位。病例2,55岁女性。A增强MR，bMR脑池造影，c和d 立体显像， e透明叠加显像。DTT显示面神经束被挤向后上。F，术中证实。病例4,63岁女性，b图中箭头所示的线样影像好像是面神经，但是应用DTT未能发现在此处的纤维束。病例5，34岁男性，MR提示一个囊性的听神经瘤。术中发现一个神经束被压向前下，而DTT显示一个神经纤维束穿过了肿瘤，肿瘤内有横隔样结构。DISCUSSIONIn this report, we indicated for the first time that DTT allow
19、s visualization of not only the facial nerve but also the vestibulocochlear nerve in VS patients.此报道第一次阐述了，DTT不仅能显示面神经，而且能显示前庭耳蜗神经。In fact, we were uncertain whether the fiber tract visualized on DTT represented facial nerve, vestibulocochlear nerve, or mere noise in case 2, because the visualized f
20、iber tract followed a course that the facial and vestibulocochlear nerves were considered unlikely to take对于case2，作者术前不能确定DTT图像显示的是面神经还是前庭耳蜗神经，因为作者认为这样的走形，面神经和前庭耳蜗神经都不大可能出现。FA values of the nerve fiber tract visualized as the vestibulocochlear nerve were higher than those of the facial nerve, leadin
21、g to a higher rate of vestibulocochlear nerve vi- sualization by DTT.能够显示前庭耳蜗神经的神经纤维束的FA值比面神经的高，导致前庭耳蜗神经比面神经在DTT图像上更容易被分辨出来。Application of DTT to VS was first reported by Taoka et al. 14, and in a later study the preoperative visualization rate for the facial nerve was increased to 90.9 % 3. On the
22、other hand, visualization of the vestibulocochlear nerve was either not mentioned 1, 10 or was reported as impossible 3. The present results are thus very different .DDT应用于听神经瘤的诊治首先是2006年由Taoka et al使用。后来，DTT于术前显示面神经的比率增加到90.9%。但DTT显示前庭耳蜗神经却没有被提及，或者被报道为不可能。With regard to interpretation, as shown in
23、this study, completely eliminating false tracts is difficult, and even if only nerve fiber tracts can be visualized, distinguishing whether a depicted fiber represents facial or vestibulocochlear nerve or noise is also problematic.此技术，就像在此研究中提到的，完全消除错误的神经束的是很困难的。即使看到了神经束，也不能确定它代表的是面神经还是前庭耳蜗神经或者是nois
24、e。even though fibers other than the facial nerve may have been visualized, previous reports have judged the visualized fiber as representing the facial nerve, thus increasing the visualization rate for the facial nerve.正是因为不是面神经纤维束的纤维束可能被显影，以前的报道判断实际上增加了面神经的显示率。Despite our findings, good methods for distinguishing whether a visualized nerve tract represents facial nerve, vestibulocochlear nerve, or only noise remain unavailable. Close attention should therefore be paid to the interpretation of visualized fibers.不足之处，或者有待进一步发展的地方。小结：DTT技术可以较好的于术前显示面神经和前庭耳蜗神经，为保留面神经功能或听力提供帮助。需与神经电生理监测技术配合使用。
