Morphological characteristics of the cranial root of the accessory nerve

There has been the controversy surrounding the cranial root (CR) of the accessory nerve. This study was performed to clarify the morphological characteristics of the CR in the cranial cavity. Fifty sides of 25 adult cadaver heads were used. The accessory nerve was easily distinguished from the vagus nerve by the dura mater in the jugular foramen in 80% of 50 specimens. The trunk of the accessory nerve from the spinal cord penetrated the dura mater at various distances before entering the jugular foramen. In 20% of the specimens there was no dural boundary. In these cases, the uppermost cranial rootlet of the accessory nerve could be identified by removing the dura mater around the jugular foramen where it joined to the trunk of the accessory nerve at the superior vagal ganglion. The cranial rootlet was formed by union of two to four short filaments emerging from the medulla oblongata (66%) and emerged single, without filament (34%), and usually joined the trunk of the accessory nerve directly before the jugular foramen. The mean number of rootlets of the CR was 4.9 (range 2–9) above the cervicomedullary junction. The CR of the accessory nerve was composed of two to nine rootlets, which were formed by the union of two to four short filaments and joined the spinal root of the accessory nerve. The CR is morphologically distinct from the vagus nerve, confirming its existence. Clin. Anat. 27:1167–1173, 2014. © 2014 Wiley Periodicals, Inc.     

Is the cranial accessory nerve really a portion of the accessory nerve? Anatomy of the cranial nerves in the jugular foramen

The accessory nerve is traditionally described as having both spinal and cranial roots, with the spinal root originating from the upper cervical segments of the spinal cord and the cranial root originating from the dorsolateral surface of the medulla oblongata. The spinal rootlets and cranial rootlets converge either before entering the jugular foramen or within it. In a recent report, this conventional view has been challenged by finding no cranial contribution to the accessory nerve. The present study was undertaken to re-examine the accessory and vagus nerves within the cranium and jugular foramen, with particular emphasis on the components of the accessory nerve. These nerves were traced from their rootlets attaching to the spinal cord and the medulla and then through the jugular foramen. The jugular foramen was exposed by removing the dural covering and surrounding bone. A surgical dissecting microscope was used to trace the roots of the glossopharyngeal nerve (CN IX), vagus nerve (CN X) and accessory nerve (CN XI) before they entered the jugular foramen and during their travel through it. The present study demonstrates that the accessory nerve exists in two forms within the cranial cavity. In the majority of cases (11 of 12), CN XI originated from the spinal cord with no distinct contribution from the medulla. However, in one of 12 cases, a small but distinct connection was seen between the vagus and the spinal accessory nerves within the jugular foramen.     

Neurons of origin of the internal ramus of the rabbit accessory nerve: localization in the dorsal nucleus of the vagus nerve and the nucleus retroambigualis

The neurons of origin of the internal ramus of the rabbit accessory nerve were identified in the dorsal nucleus of the vagus nerve, using bilateral injections of horseradish peroxidase into the inferior vagal ganglion, soft palate, and pharynx, which were preceded by different combinations of the unilateral intracranial severings of the rootlets of the vagus and glossopharyngeal nerves, those of the cranial root of the accessory nerve, and the trunk of its spinal root. The neurons of origin occupied the caudal four-fifths of the dorsal vagal nucleus extending from about 1.0 mm rostral to the obex as far caudally as the second cervical spinal segment, with their number being about half the total number of neurons of the nucleus. Although considerably fewer, they were also located in the nucleus retroambigualis of the caudal half of the first cervical spinal segment and the second segment. Axons of most internal ramus neurons traversed the rootlets of the cranial accessory root. Axons of the few neurons located more caudally than about 1.0 mm caudal to the obex emerged from the upper cervical spinal cord to run along the trunk of the spinal accessory root before finally joining the internal ramus; caudal to the midlevel of the first cervical segment, the dorsal vagal nucleus and the nucleus retroambigualis contained neurons whose axons followed only that course.     

The relationship of the posterior inferior cerebellar artery to cranial nerves VII-XII

The posterior inferior cerebellar artery (PICA) is the largest branch of the vertebral artery. It usually arises at the anterolateral margin of the medulla oblongata close to the lower cranial nerves. The PICA had the most complex relationship to the cranial nerves of any artery and it is frequently exposed in approaches directed to the fourth ventricle. The aim of this article is to describe the anatomical relationship of the PICA to the lower cranial nerves. In this study, 12.5% of PICAs passed between the glossopharyngeal and vagus nerves, 20% between the vagus and accessory nerves, and 65% through the rootlets of the accessory nerve. The lateral medullary segment of the PICA showed a lateral loop which in 20% specimens pressed against the inferior surfaces of the facial and vestibulocochlear nerves. The lateral medullary segment of the PICA in 20% specimens passed superior to the hypoglossal nerve, in 47.5% through the rootlets of the hypoglossal nerve, and in 30% inferior to the hypoglossal nerve. The findings on the relationship of the PICA to the lower cranial nerves could be helpful in microsurgery of this region.     

颅后窝三角显微解剖及临床意义

目的：研究颅后窝三角的显微特征，为颅后窝手术提供快速辨认神经、血管的方法。方法：旁正中切口、乙状窦后入路，逐层开颅并切开硬脑膜，显微观察12具成人头部标本硬脑膜形成的三角。结果：颅后窝硬脑膜皱襞反光形成一个三角形：外上顶点即“光点”，位于横窦与乙状窦移行处的前方；内上顶点恰是岩静脉注入岩上窦的位置；颈静脉孔构成颅后窝三角内下顶点。结论：手术显微镜下，颅后窝硬脑膜形成的标志性三角，可以帮助迅速辨认三叉神经、岩静脉，经过内耳门的面神经、前庭蜗神经以及经过颈静脉孔的舌咽神经、迷走神经、副神经。     

Vagal baro‐ and chemoreceptors in middle internal carotid artery and carotid body in rat

The glossopharyngeal nerve, via the carotid sinus nerve (CSN), presents baroreceptors from the internal carotid artery (ICA) and chemoreceptors from the carotid body. Although neurons in the nodose ganglion were labelled after injecting tracer into the carotid body, the vagal pathway to these baro‐ and chemoreceptors has not been identified. Neither has the glossopharyngeal intracranial afferent/sensory pathway that connects to the brainstem been defined. We investigated both of these issues in male Sprague–Dawley rats (n = 40) by injecting neural tracer wheat germ agglutinin‐horseradish peroxidase into: (i) the peripheral glossopharyngeal or vagal nerve trunk with or without the intracranial glossopharyngeal rootlet being rhizotomized; or (ii) the nucleus of the solitary tract right after dorsal and ventral intracranial glossopharyngeal rootlets were dissected. By examining whole‐mount tissues and brainstem sections, we verified that only the most rostral rootlet connects to the glossopharyngeal nerve and usually four caudal rootlets connect to the vagus nerve. Furthermore, vagal branches may: (i) join the CSN originating from the pharyngeal nerve base, caudal nodose ganglion, and rostral or caudal superior laryngeal nerve; or (ii) connect directly to nerve endings in the middle segment of the ICA or to chemoreceptors in the carotid body. The aortic depressor nerve always presents and bifurcates from either the rostral or the caudal part of the superior laryngeal nerve. The vagus nerve seemingly provides redundant carotid baro‐ and chemoreceptors to work with the glossopharyngeal nerve. These innervations confer more extensive roles on the vagus nerve in regulating body energy that is supplied by the cardiovascular, pulmonary and digestive systems.     

面神经和位听神经在脑桥小脑角及内耳道的显微外科解剖

用手术显微镜观察了成年头颅标本33个(66侧)面神经的运动根、感觉根(中间神经)和位听神经。1.面神经和位听神经自脑干至内耳道底平均长20.52mm。2.面神经运动根丝1根55侧、2根8侧、3根3侧。运动根自发出点至与中间神经联合点平均长14.86mm。3.中间神经近侧段、中间段、远侧段平均长分别为4.95、9.36、6.45mm。中间神经中间段1根束30侧、2根束28侧、3根束6侧,4根束2侧。中间神经可分为A、B、C、D、E、F 6型。4.位听神经根据分出蜗神经和前庭神经顺序,可分为A、B、C、D 4型。本文联系中间神经切除术,讨论了中间神经的分型、经过、根数和交通支的临床应用意义。     

Morphological study on the rootlets comprising the root of the intermediate nerve

The number and arising sites of the rootlet comprising the intermediate nerve root were investigated in 100 sides of human brains. The arising sites of the rootlets were the pons halfway between the facial and vestibulocochlear nerves (31.9%), the arising portion of the vestibulocochlear nerve on the pons (28.8%) and the stem of the vestibulocochlear nerve (15.9%). The number of roots varied from one to five, with the most common being one root (58%). The number of rootlets per root also varied from one to five. Most of the roots had one rootlet (63%), while 2% of the roots had five rootlets. The variation of the arising sites of the intermediate nerve rootlets and its clinical significance were also discussed.     

Landmarks for the greater petrosal nerve

The anatomy of the greater petrosal nerve while within the middle cranial fossa is lacking in the English literature and must be well understood by the surgeon who operates in this area. Twenty-two sides from six female and five male cadavers were examined. Measurements were made between the greater petrosal nerve as it coursed through the middle cranial fossa and surrounding structures such as the arcuate eminence and lateral wall of the middle cranial fossa. Mean distances from the arcuate eminence to the hiatus of the greater petrosal nerve into the middle cranial fossa measured 17.5 mm (SD = 2.2). The length of this nerve within the middle fossa was approximately 10 mm (SD = 2). From the lateral wall of the middle fossa to a midpoint of the greater petrosal nerve mean distances measured 39 mm (SD = 2.4). The mean distance from the foramen spinosum to the exit of this nerve inferior to the trigeminal ganglion measured 7 mm (SD = 1.8). These measurements will hopefully aid the surgeon who wishes to expose or avoid the greater petrosal nerve within the middle cranial fossa.     

颞骨岩部入路颅底手术有关的应用解剖

目的:为经岩部入路颅底手术提供解剖学参数.方法:观测成人的100例干燥整颅、20例颅底标本、15例尸头及36侧正常颅底CT资料;观测项目为与经岩部入路颅底手术有关的颞骨表面标志与岩部内重要结构的位置及其间距.结果:整颅及颅底内面各项测量结果左右侧比较U均<1.96,P均>0.05,颞骨内重要结构间及与表面标志间距离测量结果多数项目男女性间比较U均>1.96或>2.58,P<0.05或<0.01;颅中窝入路可以弓状隆起作标志寻认上骨半规管以确认内耳道,也可以岩大神经管裂孔为标志暴露面神经膝状神经节与迷路段确认内耳道底;磨除岩尖部骨质时可以颈动脉管后壁与内耳门内侧缘的连线作为界线.结论:颞骨表面标志点间距及颞骨岩部内重要结构间的位置关系可为经岩部入路颅底手术提供重要参考,有利于术中岩部重要结构的定位与保护.     

舌咽神经、迷走神经和副神经断层解剖与MRI

目的：探讨舌咽神经、迷走神经和副神经的走行和毗邻关系,为影像学诊断及临床开展该区手术提供形态学依据。方法：利用36例成尸头部连续横断层标本和15例成尸头部连续冠状断层标本,并与10例志愿者的3D—CISS序列MR图像进行对照,观察舌咽神经、迷走神经和副神经在颅内的走行规律及其与周围结构的位置关系。结果：舌咽、迷走和副神经由上而下从延髓的橄榄后沟发出,跨过延池,穿颈静脉孔出颅。根据走行,可分其为延髓内段、脑池段和颈静脉孔段。在脑池段,舌咽神经走行在上方,迷走神经和副神经在下方且结合紧密;在颈静脉孔段,这3对脑神经及其与颈内静脉和颈内动脉的关系是：颈内动脉位于最前方,颈内静脉位于最外侧,舌咽神经走行在前内上方,有单独的硬脊膜包绕,迷走神经和副神经位于其后外下方,形成迷走、副神经复合体。结论：在标本的连续断面和对应的MR图像上能够清楚地显示舌咽、迷走和副神经的走行和毗邻关系。     

Bony eminence on the middle cranial fossa corresponding to the temporomandibular joint

We report a nameless bony eminence over the temporomandibular joint (TMJ) and its possible clinical significance. Forty-two half heads of 21 UK Caucasian cadavers (61-95 years old, mean 84.3 +/- 8.2 years, male:female = 11:10) were used to investigate the surface of the middle cranial fossa (MCF) over the TMJ. The thickness of the bony roof of the glenoid fossa was also measured. A bony eminence over the glenoid fossa was observed in half of the specimens. Some showed a complete oval bulge, which completely reflected the contour of the glenoid fossa. The others showed a bony bulge, which partially reflected that contour. The mean (+/-SD) thickness of the bone in the roof of glenoid fossa was 1.5 +/- 1.2 mm. The mean bony thickness of specimens showing the eminence was 0.8 +/- 0.5 mm, whereas it was 2.3 +/- 1.2 mm in specimens without an eminence. These differences were statistically significant (P < 0.01). The osteological features we describe may be relevant to certain clinical problems. Traumatic dislocation of mandibular condyle, for example, might relate to a weakness of the glenoid fossa.     

Carotid endarterectomy: Importance of cranial nerve anatomy

A retrospective study of 100 consecutive cases of carotid endarterectomy was performed. Special attention was given to the incidence, clinical significance, and prevention of cranial nerve injury. The operative mortality was 1%, and there were no perioperative strokes. There was clinical evidence of 22 cranial nerve injuries. Nineteen injuries were temporary, resulting in a 3% incidence of permanent cranial nerve deficit. The clinical anatomy of cranial nerves encountered during carotid endarterectomy is reviewed. Technical suggestions to minimize cranial nerve injury based on a thorough knowledge of this anatomy are provided. The relationship of laryngeal physiology and vagus nerve anatomy indicates that unilateral vocal cord dysfunction may be asymptomatic. Bilateral nerve injury can cause potentially fatal airway obstruction, which may be unrecognized until after the second operation. Preoperative laryngoscopy prior to carotid endarterectomy is suggested in patients with a history of prior cardiac or neck surgery and those scheduled for the second of staged bilateral carotid procedures.     

The Accessory Nerve: A Comprehensive Review of its Anatomy,Development, Variations,Landmarks and Clinical Considerations

Introduction: The eleventh cranial nerve, the accessory nerve, has a complex and unique anatomy and has been the subject of much debate. Herein, we review the morphology, embryology, surgical anatomy, and clinical manifestations of the accessory nerve. Included in this review, we mention variant anatomy, molecular development, histology, and imaging of the accessory nerve. Conclusions: The accessory nerve continues to be a topic of much discussion regarding its exact function and in particular to its cranial roots. Recently, various surgical procedures have been devised that repurpose the accessory nerve (e.g., lengthening procedures, contralateral neurotization procedures). Currently, we continue to learn and have much to learn about this lower cranial nerve. Anat Rec, 302:620–629, 2019. © 2018 Wiley Periodicals, Inc.     

大鼠迷走神经和膈神经的解剖相关性实验研究

目的 为大鼠迷走神经移位膈神经重建高位颈髓损伤大鼠的膈肌功能提供显微解剖学依据。 方法　10只健康雌性SD大鼠在10倍手术显微镜下解剖双侧膈神经、迷走神经及其分支。用数显卡尺测量迷走神经与膈神经在“膈神经主干起始平面”、“锁骨上平面”、“入膈肌平面”的相对距离,用读数显微镜测量各平面迷走神经和膈神经的直径。 结果　在颈部,迷走神经直径为（0.3284±0.0247）mm,膈神经直径为（0.2267±0.0164）mm,二者的相对距离很接近,无论是在“膈神经主干起始平面”还是“锁骨上平面”,平均都不超过2.5 mm;在“入膈肌平面”平面,迷走神经直径为（0.2912±0.0326）mm,膈神经直径为（0.2794±0.0282）mm,二者的相对距离较颈部远,左侧为（8.71±0.804）mm,右侧为（6.203±0.952） mm。 结论　(1)在颈部,迷走神经与膈神经的直径相差不大,相对距离很接近,二者可直接无张力缝合。(2)在入膈肌平面,迷走神经与膈神经的直径大致相同,相对距离稍远,但将膈神经和迷走神经向上游离一段距离后仍可实现二者的直接无张力缝合。     

Intradural anastomoses between the accessory nerve and the posterior roots of cervical nerves: their clinical significance.

This study was performed to identify the anastomoses between the accessory nerve and the posterior roots of cervical nerves below the level of C1 segment, and to evaluate their clinical significance. One hundred spinal cord sides of Koreans were studied under the surgical microscope. In order to trace the posterior root of a cervical nerve after anastomosis with the accessory nerve, or the bridging fibers between the accessory nerve and the cervical posterior roots, the accessory nerves with the posterior roots and the bridging fibers were stained with osmium tetroxide. The anastomosis was classified into five types, according to whether the accessory nerve and the cervical posterior root crossed each other, and also according to the site of the bridging fiber between them. The bridging fibers in the most common type of anastomoses were observed to connect the posterior roots of a cervical nerve with the spinal rootlet of the accessory nerve. The possibility that the motor fibers of accessory nerve from the spinal cord may innervate the trapezius muscle through the cervical nerve, was discussed.     

Distribution of Neuron Cell Bodies in the Intraspinal Portion of the Spinal Accessory Nerve in Humans

The spinal accessory nerve is often identified as a purely motor nerve innervating the trapezius and sternocleidomastoid muscles. Although it may contain proprioceptive neurons found in cervical spinal levels C2–C4, limited research has focused on the histology of the spinal accessory nerve. The objective of the present study was to examine the spinal accessory nerve to determine if there are neuronal cell bodies within the spinal accessory nerve in humans. Cervical spinal cords were dissected from eight cadavers that had previously been used for dissection in other body regions. The segmental rootlets were removed to quantify the neuron cell bodies present at each spinal level. Samples were embedded in paraffin; sectioned; stained with hematoxylin and eosin; and examined using a microscope at 4×, 10×, and 40× magnification. Digital photography was used to image the samples. Neuronal cell bodies were found in 100% of the specimens examined, with non‐grossly visible ganglia found at spinal levels C1–C4. The C1 spinal level of the spinal accessory nerve had the highest number of neuron cell bodies. Anat Rec, 299:98–102, 2016. © 2015 Wiley Periodicals, Inc.