正常颅神经在稳态课件

正常颅神经在稳态自由进动正常颅神经在稳态自由进动MRMR成像中的表现成像中的表现 引言稳态自由进动序列(steady-state free precession，SSFP)优点：1）具有亚毫米的空间分辨率，并且它可以进行多维重建；2）脑脊液和实质结构之间的高对比度，对于显示颅神经的脑池段非常有帮助。3）SSFP序列的总的采集时间较传统的MR成像脉冲序列短，这有助于减少脑脊液搏动伪影 缺点：降低了不同软组织之间的对比度分辨率，另外，由于采用亚毫米的层厚，对于解剖结构整体的界限的显示就不太理想。引言这一序列已成为评估桥小脑角及内耳病变的主要方法。可以更精确的区分颜面部及前庭窝神经的分支，更准确的发现桥小脑角及内耳道内的小结节病灶，更详细的显示内耳的内淋巴及外淋巴。为了更好的利用这种成像方法，放射科医师必须了解并熟悉12对颅神经在SSFP成像上的表现。1.嗅神经（Olfactory Nerve）嗅神经含白质束，并且没有被神经鞘细胞包绕。嗅觉的感觉细胞存在于沿鼻腔顶部的嗅上皮内。嗅神经细胞的轴突穿过筛骨的筛板扩展进入嗅神经前方末端的嗅球内。然后在嗅沟内穿过颅前窝（Fig 1），之后嗅神经脑池段走行于眶回和内侧的直回之间的下方（Fig 2）。嗅神经的轴突终止于颞中下回、颞下沟及内嗅皮质。Fig 1：Axial(a)and coronal(b)0.8-mm-thick SSFP MR images show the olfactory nerve(white arrow)within the CSF-filled olfactory groove and the optic nerve(black arrow in b)ringed by high-signal-intensity CSF within the dural sheath.嗅神经（Olfactory Nerve）Fig 2：Coronal 1.0-mm-thick SSFP MR image shows the cisternal segment of the olfactory nerve(arrow),which is located inferior to and between the gyrus rectus 直回(r)and the medial orbital gyrus 眶会(o).2.视神经（Optic Nerve）与嗅神经相似，视神经也是一条没有施万细胞环绕的白质束。全程可分为四个解剖学节段（Fig 3）：1）视网膜段：视网膜节细胞的轴突，在视神经盘处聚集，穿过巩膜筛板后形成视神经；2）眼眶段：被硬脑膜鞘包绕，其内含有脑脊液（CSF），神经穿行于被脂肪填充的眶腔的中心；3）视神经管段：指神经位于视神经管内的部分，位于眼动脉的下方，这一节段在影像上常容易被忽略掉，因此当看有视觉障碍患者的影像时要特别注意寻找并观察这一段；4）脑池段：在鞍上池内可以直观的看到，它向后内走行至垂体的前方连于视交叉。视神经（Optic Nerve）Fig 3：Axial oblique 0.8-mm-thick SSFP MR image shows three of four segments of the optic nerve:the retinal(black arrow),orbital(black arrowheads),and canalicular(white arrowhead)segments.The infundibulum of the pituitary gland（垂体漏斗部）(white arrow)also is seen.The fourth(cisternal)segment of the optic nerve would be visible on more superior images.视神经（Optic Nerve）鞍上池内的典型解剖标志包括：垂体的漏斗部（花柄状）、大脑前动脉和后面的视交叉，乳头体（神经）。（Fig 4）视神经终止于视交叉，此处，两侧的视神经汇合、交叉并形成视神经束。视神经束沿大脑脚的周围走形，之后其大部分神经轴突进入丘脑的外侧膝状体（loop around the inferior horns of the lateral ventricles(Meyer loop),进入枕叶的视皮质。（Fig 5）视神经（Optic Nerve）Fig 4：Axial MR image obtained with a T2-weighted fast spin-echo sequence and a section thickness of 3 mm provides better depiction of global anatomic relationships than do images obtained with SSFP sequences.The cisternal segment of the optic nerve(white arrow)leads to the chiasm,which resembles the Greek letter in this plane.The optic tract(white arrowheads)leads backward from the chiasm to the thalamus（丘脑）.Important anatomic landmarks include the mamillary bodies(black arrowhead)and the anterior cerebral artery（大脑前动脉）(black arrow).视神经（Optic Nerve）Figure 5：Residual tumor near the optic chiasm in an 18-year-old woman after resection of a pituitary adenoma.Axial oblique 0.8-mm-thick SSFP MR image shows a thin layer of cerebrospinal fluid(arrow)between the residual tumor(t)and the left optic nerve and chiasm,a finding suggestive of resectability.The residual tumor was removed successfully with an expanded endonasal approach鼻内进路.3.动眼神经（Oculomotor Nerve）动眼神经起始于中脑水管腹侧上丘深部的核团，邻近松果体，然后从中脑的后方到前方横过中脑走行。动眼神经根进入脚间池，在神经根进入脚间池的区域是在轴位SSFP图像上辨别动眼神经的一个好方法（Fig 6）。在桥前池，动眼神经走行于小脑上动脉和大脑后动脉之间，这使得在冠状位SSFP图像上较容易辨别出动眼神经（Fig 7）。动眼神经海绵窦段沿海绵窦外侧壁上部走行，之后通过眶上裂进入眶腔，分成上、下两支。这一解剖特点可以帮助我们辨别出神经异常的精确部位(Fig 8)动眼神经（Oculomotor Nerve）Figures 6,7.Oculomotor nerve.(6)Axial oblique 0.8-mm-thick SSFP MR image shows the nerve(small arrows)where it emerges from the interpeduncular cistern(large arrow),which lies medial to the cerebellar peduncle(p).(7)Coronal 0.8-mm-thick SSFP MR image shows the oculomotor nerve(white arrow)in cross section between the posterior cerebral artery(white arrowhead)and the superior cerebellar artery(black arrowhead),which are distal branches of the basilar artery(black arrow).动眼神经（Oculomotor Nerve）Figure 8：Oculomotor nerve compression in an 82-year-old woman with ptosis of the right eye.Axial 0.8-mm-thick SSFP MR image shows displacement and compression of the right oculomotor nerve in the root entry zone(long arrow)by the distal basilar artery(short arrow).The left oculomotor nerve(arrowhead),in comparison,appears normal.4.滑车神经（Trochlear Nerve）滑车神经是唯一神经根起源于中脑背侧的神经。滑车神经经过脑桥的外侧，弯曲绕到小脑角上部的前方，然后横靠大脑前动脉和大脑后动脉之间的动眼神经走行。之后穿过硬脑膜进入enter the cisterna basalis。结束脑池段后，滑车神经在动眼神经的下方穿过海绵窦的外侧壁，通过眶上裂进入眼眶支配上斜肌。这条细小神经的脑池段在脑干的后外侧是最容易识别的（Fig 9）。滑车神经的部分颅内段是位于硬脑膜内的，这一段在影像上很难显示出来。对于可疑滑车神经麻痹的患者，要特别注意tentorium的前方。滑车神经（Trochlear Nerve）Figure 9:Trochlear nerve.Axial 0.8-mm-thick SSFP MR image shows both trochlear nerves(arrows)where they emerge from the dorsal midbrain to cross the ambient cisterns（环池）.The characteristic course of the trochlear nerves allows their differentiation from the nearby superior cerebellar artery(arrowheads).5.三叉神经（Trigeminal Nerve）三叉神经是最粗大的脑神经，含躯体感觉和内脏运动纤维。神经根起始于中脑的外侧,穿过桥前池至前方的美克尔腔（the Meckel(trigeminal)cave，颅中窝内一个被脑脊液包绕的囊）（Fig 10）。在Meckel cave，三叉神经形成一个网状结构，在高分辨率图像上可以直观的看到（Fig 11）。在美克尔腔的前方，三叉神经形成形成三叉神经节，后分出三个亚分支。V1分支（眼神经）和V2分支（上颌神经）从内侧进入海绵窦外侧壁，经眶上裂及圆孔出颅。V3分支（下颌神经）是经卵圆孔出颅。三叉神经（Trigeminal Nerve）Figure 10.Trigeminal nerve.Axial 0.8-mm-thick SSFP MR image shows the sensory(arrowhead)and motor(large arrow)roots of the trigeminal nerve where they cross the prepontine cistern and enter the Meckel cave(small arrows).三叉神经（Trigeminal Nerve）Figure 11.Trigeminal nerve.Coronal 0.8-mm-thick SSFP MR image at the level of the Meckel cave shows the complex web of trigeminal nerve branches(arrows),which coalesce anteriorly to form the gasserian ganglion.The temporal horn of the lateral ventricle(arrowhead)is also shown.6.外展神经（Abducens Nerve）外展神经起始于第四脑室前脑桥的展神经核，之后向前走行，经脑桥、脑桥延髓交界处进入桥前池内（Fig 12）。从后往前穿过桥前池后，外展神经垂直的沿斜坡的后方走行，其内有一个纤维鞘成为Doreello canal（Fig 13）。外展神经之后再越过内侧的岩骨尖和海绵窦，经眶上裂进入眼眶，支配外直肌。外展神经斜坡段走行的全程是很重要的，放射科医师在诊断外展神经麻痹时一定要尤其注意观察斜坡及岩骨尖处。尽管外展神经临近其前下方的小脑动脉，但是由于他们是成直角分布的，所以较容易识别（Fig 13）。外展神经（Abducens Nerve）Figure 12.Abducens nerve.Axial 0.8-mm-thick SSFP MR image at the level of the pontomedullary junction shows both abducens nerves(arrows)where they traverse the prepontine cistern.The bottom of the pons(p)and the top of the medulla(m)are visible in this section,and the cerebellopontine angle(CPA)桥小脑角and basilar artery(arrowhead)are important anatomic landmarks.外展神经（Abducens Nerve）Figure 13.Abducens nerve.Axial 0.8-mm-thick SSFP MR image shows the abducens nerve where it enters the Dorello canal(arrow)along the posterior aspect of the clivus斜坡.Vascular landmarks include the basilar artery(black arrowhead)and the anterior inferior cerebellar artery(white arrowhead).7，8：颜面神经和前庭蜗神经面神经和前庭蜗神经在脑池段和小管段走行相似(Fig14）。他们均起始于脑桥下缘的外侧，并以一个倾斜的角度穿过脑桥小脑脚和桥前池。接下来，这两条神经穿过耳门（即脑桥小脑脚池和内耳道的开口，也可称为内听道）并经过内耳道全长。精确显示出肿块与内听道关系的影像有助于外科手术计划的制定（Fig 15）。在内耳道，前庭蜗神经分为三部分（耳蜗、前庭上及前庭下）。前庭蜗神经的三条分支与面神经一起，在倾斜的矢状切面SSFP图像上有一个特征性的表现（Fig 16）。这一切面的图像常用来显示前庭窝神经的耳蜗神经的发育不全。颜面神经和前庭蜗神经Figure 14.Axial 0.8-mm-thick SSFP MR image shows the parallel courses of the facial(black arrowheads)and superior vestibular(white arrowheads)nerves as they cross the cerebellopontine angle to enter the internal auditory canal through the porus acusticus(double arrow).颜面神经和前庭蜗神经Figure 15.Cerebellopontine angle meningioma(脑膜瘤)in a 52-year-old woman with left sensorineural hearing loss.(a)Axial 0.8-mm-thick SSFP MR image shows a tumor that fills the in-ternal auditory canal(arrow)and ex-tends into the cerebellopontine angle cistern.The relation of the tumor to the facial and vestibulocochlear nerves is not clearly shown.(b)Coronal oblique 0.8-mm-thick SSFP MR image shows direct involvement of the facial nerve(arrowhead),a contraindication against surgical resection.The tumor was treated instead with stereotactic radiosurgery.Figure 16.Cochlear nerve aplasia（耳蜗神经发育不全）in a 4-year-old girl with congenital hearing loss who was under consideration for cochlear implantation（耳蜗植入）.Sagittal oblique 1.0-mm-thick SSFP images,obtained in planes perpendicular to the left(a)and right(b)internal auditory canals,show the main branches of the facial and vestibulocochlear nerves in cross section.The anterior(A),posterior(P),superior(S),and inferior(I)aspects of the canals are labeled for ease of orientation.In both a and b,the facial(white arrow),superior vestibular(white arrowhead),and inferior vestibular(black arrowhead)nerves are depicted;however,the cochlear nerve(black arrow in a)is absent in b,and that fnding is a contraindication禁忌症 against cochlear implantation for the right ear.Incomplete separation of the superior and inferior vestibular nerves,also shown in b,is a normal variant颜面神经和前庭蜗神经面神经从内耳道出来后在Bill bar的前方，经fallopian aqueduct（法娄皮欧氏管）进入面神经管。之后经颞骨岩部内一段复杂的走行后，面神经通过茎乳孔出颅进入腮腺实质内。在单纯轴位SSFP图像上，这四支神常仅有2支可以较明显的显示出来。如果看到一支神经进入耳蜗的蜗轴，那么明显显示的那两条神经就是耳蜗神经或下方的前庭神经。如果中央耳蜗的蜗轴在图像上不能看到，则显示出来的那两条神经是颜面神经和上方的前庭神经。在SSFP图像上如果看到膜迷路内的充盈缺损，则可能代表面神经或前庭窝神经的某一分支的异常。9.舌咽神经（Glossopharyngeal Nerve）舌咽神经起源于延髓侧面的髓质后进入小脑延髓池的侧面，与面神经在同一水平，且位于迷走神经的上方。在小脑延髓池的侧面，舌咽神经是与小脑的绒球伴随出现的（Fig 17)。小脑绒球是小脑的一个分叶，且与舌咽神经紧邻，诊断时不要误诊为异常。舌咽神经从小脑延髓池的侧面进入颈静脉窝，后经颈静脉孔出颅。在颈静脉孔处，舌咽神经位于迷走神经和副神经的前方，并且被自身的硬脑膜鞘包绕。舌咽神经（Glossopharyngeal Nerve）Figure 17.Coronal oblique 0.8-mm-thick SSFP MR image through the cerebellopontine angle shows the glossopharyngeal nerve(arrow)just beneath the flocculus(f)of the cerebellum.The two roots of the vagus nerve(arrowheads)are visible in the same plane,and the superior and inferior vestibular前庭 nerves can be seen above the focculus.10.迷走神经（Vagus Nerve）迷走神经包含两条神经根，分别起源于延髓的侧面和后外侧沟。离开延髓后，神经根紧邻舌咽神经进入小脑延髓池的外侧，并与舌咽神经平行走行穿过脑池。由于迷走神经跟舌咽神经在脑池段是平行走行的，因此在轴位SSFP图像上较难辨别他们。冠状位或沿着神经走行方向倾斜的冠状位图像是观察神经最好的方法（Fig 17）。倾斜的穿过小脑延髓池（Fig 18），迷走神经进入颈静脉窝，之后在舌咽神经和副神经之间经颈静脉孔出颅。在颈部，迷走神经走行于颈动脉鞘内，且颈内静脉和颈总动脉之间的后方。迷走神经（Vagus Nerve）Figure 17.Coronal oblique 0.8-mm-thick SSFP MR image through the cerebellopontine angle shows the glossopharyngeal nerve(arrow)just beneath the flocculus(f)of the cerebellum.The two roots of the vagus nerve(arrowheads)are visible in the same plane,and the superior and inferior vestibular nerves can be seen above the focculus.迷走神经（Vagus Nerve）Figure 18.Axial oblique 0.8-mm-thick SSFP MR image shows the vagus nerve(arrow)where it crosses the lateral cerebellomedullary cistern(LCM)小脑延髓池 and approaches the jugular foramen（颈静脉孔）.The vagus and glossopharyngeal nerves,which are diffcult to distinguish in this plane,are clearly distinguishable in the coronal oblique plane(see Fig 17).11.副神经（Accessory Nerve）副神经是由脑根和脊髓根组成。脑根在迷走神经的下方进入小脑延髓池的外侧（Fig 19）。脊髓根起始于脊髓的上颈段（Fig 20）。离开脊髓后，脊髓根在椎管内上行，穿过枕骨大孔进入小脑延髓池，走行于椎动脉的后方，并在小脑延髓池的外侧与脑根汇合。之后在舌咽神经和迷走神经的后方经颈静脉孔出颅。副神经（Accessory Nerve）Figure 19.Axial 0.8 mm-thick SSFP MR image at the level of the cervicomedullary junction(CMJ)shows the cranial rootlets脑根(arrowheads)of the accessory nerve.副神经（Accessory Nerve）Figure 20.Coronal oblique 0.8-mm-thick SSFP MR image shows the spinal rootlets(arrows)of the accessory nerve arising from the upper spinal cord to cross the foramen magnum（枕骨大孔）and join the cranial rootlets.12.舌下神经（Hypoglossal Nerve）舌下神经起始于第四脑室前方延髓内的舌下神经核，是以若干神经根丝形式自延髓的前外侧沟发出的，后延伸到小脑延髓池的侧面（Fig 21）。汇合的神经根穿过小脑延髓池，此段舌下神经被前方的椎动脉和后方的小脑后下动脉包绕（Fig 22）。舌下神经通过舌下神经管出颅，且在轴平面上是倾斜走行的，与冠状面和矢状面之间呈45度的夹角。出颅后，舌下神经走行于舌咽神经、迷走神经和副神经之间，并深入二腹肌，环绕舌骨，支配舌的大部分。舌下神经（Hypoglossal Nerve）Figure 21.Coronal oblique 0.8-mm-thick SSFP MR image shows multiple hypoglossal nerve roots(arrows)converging toward the hypoglossal foramen 舌下神经孔(arrowhead).The nerve roots are immediately posterior to the vertebral artery椎动脉(V).舌下神经（Hypoglossal Nerve）Figure 22.Axial 0.8-mm-thick SSFP MR image shows the oblique course of the hypoglossal nerve(black arrowhead)as it crosses the lateral cerebellomedullary cistern 小脑延髓池 toward the hypoglossal canal舌下神经管(white arrowheads).The vertebral arteries(white arrows)are anterior to the nerve,and the posterior inferior cerebellar artery(black arrow)is posterior to the nerve.结论运用传统的MR成像脉冲序列，要评价颅神经的脑池段是困难的。因为颅神经的脑池段直径非常小并且临近其他的一些解剖结构。SSFP序列可以显示这些神经段的一些细节，并且可以提供一些关于颅神经与病理学过程的关系的重要信息。为了更好的利用这些信息，放射学医师必须熟悉这些颅神经的解剖及相关的解剖标志。研究生：李逢芳