Spinal accessory nerve anatomy in the posterior cervical triangle: A systematic review with meta-analysis.

This study aimed to investigate the anatomy of the spinal accessory nerve (SAN) in the posterior cervical triangle, especially in relation to adjacent anatomical landmarks, along with a systematic review of the current literature with a meta-analysis of the data. Overall, 22 cadaveric and three prospective intraoperative studies, with a total of 1346 heminecks, were included in the analysis. The major landmarks relevant to the entry of the SAN at the posterior border of the SCM muscle (PBSCM) were found to be the mastoid apex, the great auricular point (GAP), the nerve point (NP), and the point where the PBSCM meets the upper border of the clavicle. The SAN was reported to enter the posterior cervical triangle above GAP in 100% of cases and above NP in most cases (97.5%). The mean length of the SAN along its course from the entry point to its exit point from the posterior triangle of the neck was 4.07 ± 1.13 cm. The SAN mainly gave off 1 or 2 branches (32.5% and 31%, respectively) and received either no branches or one branch in most cases (58% and 23%, respectively) from the cervical plexus during its course in the posterior cervical triangle. The major landmarks relevant to the entry of the SAN at the anterior border of the TPZ muscle (ABTPZ) were found to be the point where the ABTPZ meets the upper border of the clavicle and the midpoint of the clavicle, along with the mastoid apex, the acromion, and the transverse distance of the SAN exit point to the PBSCM. The results of the present meta-analysis will be helpful to surgeons operating in the posterior cervical triangle, aiding the avoidance of the iatrogenic injury of the SAN.

Anatomical variations in the course of spinal accessory nerve in the neck triangles: A descriptive study.

BACKGROUND: Spinal Accessory Nerve (SAN), which innervates the sternocleidomastoid (SCM) and trapezius muscles, is closely related to the internal jugular vein (IJV) in the anterior triangle of the neck and passes superficially in the posterior triangle. Injury to SAN is a major complication of level II neck dissection, leading to shoulder syndrome. The present study aims to assess the course and its relation to the SCM muscle and IJV in the Tamil ethnolinguistic groups in South India. METHODS AND MATERIALS: The anterior and posterior triangles of the neck were dissected in 28 formalin-fixed adult cadavers. The course of the SAN and the entry and exit points of SAN along the SCM muscle were assessed using the mastoid process as the reference. Recorded data was analyzed using SPSS software. RESULTS: The SAN was anteriorly related to the IJV in 58.73%, posteriorly in 37.5%, and pierced through the IJV in 3.57% of the specimens. The entry and exit points of SAN from the mastoid process were 37.86±7.26mm and 48.55±8.22mm, respectively. In 86.67% of the cases, the SAN traversed through the SCM muscle, and in 13.33%, it was deep to the SCM. CONCLUSION: The present study reports that the SAN is variable in its course, and relation to SCM and IJV. Knowledge about the variant anatomy of the SAN in the triangles of the neck is important and it aids surgeons to prevent iatrogenic injuries to SAN or IJV and enhance surgical safety in neck procedures.

Lower cranial nerve syndromes: a review.

The purpose of this paper is to provide a comprehensive review encompassing the syndromes associated with the lower cranial nerves (LCNs). We will discuss the anatomy of some of these syndromes and the historical contributors after whom they were named. The LCNs can be affected individually or in combination, since the cranial nerves at this level share their courses through the jugular foramen and hypoglossal canal and the extracranial spaces. Numerous alterations affecting them have been described in the literature, but much remains to be discovered on this topic. This paper will highlight some of the subtle differences among these syndromes. Symptoms and signs that have localization value for LCN lesions include impaired speech, deglutition, sensory functions, alterations in taste, autonomic dysfunction, neuralgic pain, dysphagia, head or neck pain, cardiac or gastrointestinal compromise, and weakness of the tongue, trapezius, or sternocleidomastoid muscles. To assess the manifestations of LCN lesions correctly, precise knowledge of the anatomy and physiology of the area is required. Treatments currently used for these conditions will also be addressed here. Effective treatments are available in several such cases, but a precondition for complete recovery is a correct and swift diagnosis.

A contextual thematic analysis of the accessory nerve in Scottish historical medical collections of the Royal Colleges of Edinburgh and Glasgow.

INTRODUCTION: The classification of the accessory nerve (CN XI) remains a source of debate; its exact function has not been fully elucidated having also an atypical morphology for a cranial nerve. A better insight into its anatomical and physiological features is of clinical relevance. The aim was to conduct a review of 18th and 19th century books from the Royal Medical/Surgical Colleges in Scotland, United Kingdom. A contextual historical analysis of the depictions and descriptions of the accessory nerve could provide insight into the disparity in the current descriptions. MATERIALS AND METHODS: Online archive catalogues were systematically searched and, during site visits, resources were formally and contextually analyzed, with the information then thematically analyzed. The themes were discussed against a widely known reference textbook of the era. RESULTS: Based on the thematic analysis, the resources were categorized either as practical anatomy books or field-specific anatomy books including neuroanatomy atlases. This intended use, along with the target audience, influenced the scope and detail of information, typically with general anatomy for students in the practical resources, and specialist information in the field-specific resources. The authors' professional background also influenced the way the accessory nerve was described and/or depicted, with surgeons/physicians placing emphasis on the clinical aspects. Content variations could also be attributed to communication restrictions of the era, and associated purchasing costs. CONCLUSIONS: Although scientific advances are nowadays disseminated at a faster pace, actively bridging the gap between anatomical sciences and clinical research is still needed when considering the accessory nerve to further elucidate the mysteries of this structure.

Anatomic Danger Zones of the Head and Neck.

BACKGROUND: Dermatologic procedures require a detailed understanding of surface anatomy to avoid complications. The head and neck region has prominent danger zones including nerves and vasculature that may be at risk during cutaneous surgery. A thorough understanding of these danger zones can help avoid complications that may lead to functional or cosmetic impairment. METHODS: The anatomic literature regarding the course of high-risk structures of the head and neck was reviewed. Structures deemed at risk during dermatologic procedures were included in the analysis. The final analysis focused on branches of the facial nerve, parotid duct, spinal accessory nerve, trigeminal nerve, and the lacrimal system. Anatomical information was compiled regarding each high-risk structure to develop a "danger zone" at which each respective structure is at risk. RESULTS: The danger zone for each structure was compiled based on the review of the literature and depicted in the figures. CONCLUSION: With careful attention to anatomy and the meticulous surgical technique, there is great potential for reduction in surgical injury to danger zones of the head and neck.

Effective botulinum toxin injection guide for treatment of cervical dystonia.

The aim of this study was to elucidate the distribution of the accessory nerve within the sternocleidomastoid muscle (SCM) to aid identifying the optimum sites for botulinum neurotoxin (BoNT) injections and applying chemical neurolysis. Thirty SCM specimens from 15 Korean cadavers were used in this study. Sihler's staining was applied to 10 of the SCM specimens. Transverse lines were drawn in 20 sections to divide the SCM into 10 divisions vertically, and a vertical line was drawn into the medial and lateral halves from the mastoid process to the sternoclavicular joint. The most densely innervated areas were 5/10-6/10 and 6/10-7/10 along the lateral and medial parts of the muscle, respectively. We suggest injecting BoNT in the medial region 6/10-7/10 along the SCM prior to injecting in the lateral region 5/10-6/10 along the muscle to ensure safe and effective treatment. Clin. Anat. 33:192-198, 2020. © 2019 Wiley Periodicals, Inc.

Surgical "Safe Zone": Rapid Anatomical Identification of the Lesser Occipital Nerve.

BACKGROUND: Surgical intervention has established a vital role in the management of chronic headaches. The lesser occipital nerve (LON) is a common target in patients suffering from occipital neuralgia and is often resected as a first-line option. We endeavored to define the relationships of the LON in the posterolateral neck to facilitate its safe and rapid intraoperative identification. METHODS: Seven fresh cadavers (14 nerves) were dissected, and their relationships to the mastoid prominence and nearby spinal accessory nerve (SAN) and greater auricular nerve were noted. RESULTS: The distance from the mastoid to the emergence of the LON along the posterior sternocleidomastoid ranged from 36 to 51 mm (mean: 45.2 mm), with relative symmetry between the two nerves in the same cadaver. The SAN emerged an average of 54 mm from the mastoid prominence. CONCLUSION: Exploration for the LON should begin at a point 40 mm from the mastoid prominence along the posterior border of the sternocleidomastoid muscle. If the point of exit of the LON is not identified within 10 mm of this exposure, our dissection continues cranially along the posterior border of the sternocleidomastoid, anterior to the trapezius. In rare cases the nerve may pierce the fibers of the muscle and ascend directly on top of the muscle belly. By limiting the caudal extend of the dissection, we can avoid exposure of the SAN and minimize the risk of iatrogenic nerve injury.

Accessory nerve distribution for aesthetic botulinum toxin injections into the upper trapezius muscle: anatomical study and clinical trial : Reproducible BoNT injection sites for upper trapezius.

PURPOSE: The descending part of the trapezius muscle is clinically associated with neck pain and aesthetic applications. The innervation of the trapezius muscle is not well described in the medical literature for clinicians. The aim of study was to analyze the perforating branch pattern of the accessory nerve in the descending part of the trapezius muscle with the aim of describing the most efficient and reproducible BoNT injection sites for aesthetic treatment of shoulder contouring. METHODS: Twenty-six specimens (five male and eight female) from embalmed Korean cadavers were used in this study. The trapezius muscle was dissected scrupulously and then reflected to enable examination of the locations of the perforating points. The thickness of trapezius muscle was measured in 13 volunteers using a diagnostic ultrasonography system. BoNT was injected into the trapezius muscle bilaterally. Injections were performed at 6 points separated by 2 cm. The muscle thicknesses were measured three times using ultrasonography: before the injection and at 4 and 12 weeks after the injection. RESULTS: The dense arborization of the perforating accessory nerve branches was confined mostly to section b (66.7%, 54/81) and section c (33.3%, 27/81). The mean muscle thickness at 4 and 12 weeks consistently decreased 0.68-0.63 cm  in conventional method and 0.65-0.61 cm in new method (NDM) respectively (right and left). CONCLUSION: To optimize the outcome of BoNT injection, we recommended injecting into six points separated by 2 cm in sections b and c of the upper trapezius muscle. It is significant that it is easier to apply to anyone than to apply unstructured techniques.

Variations of the accessory nerve: anatomical study including previously undocumented findings-expanding our misunderstanding of this nerve.

INTRODUCTION: The anatomy of the accessory nerve has been well described but continued new clinical and anatomical findings exemplify our lack of a full understanding of the course of this nerve. Therefore, this study aimed to expand on our knowledge of the course of the 11th cranial nerve via anatomical dissections. METHODS: Fifty-six cadavers (112 sides) underwent dissection of the accessory nerve from its cranial and spinal origins to its emergence into the posterior cervical triangle. Immunohistochemistry was performed when appropriate. RESULTS: Our findings included two cases (1.8%) where the nerve was duplicated, one intracranially and one extracranially. One accessory nerve (0.9%) was found to enter its own dural compartment within the jugular foramen. The majority of sides (80%) were found to have a cranial root of the accessory nerve. Thirty-one sides (28%) had connections to cervical dorsal roots medially and three sides (2.7%) laterally. Medial connections were most common with the C1 nerve. Medial components of these dorsal root connections were all sensory in nature. However, lateral components were motor on two sides (1.8%). Nerves traveled anterior to the internal jugular vein on 88% of sides. One (0.9%) left side nerve joined an interneural anastomosis between the dorsal rootlets. Macroganglia were found on the spinal part of the intracranial nerve on 13% of sides. The lesser occipital nerve arose directly from the accessory nerve on two sides (1.8%) and communicated with the accessory nerve on 5.4% of sides. One side (0.9%) was found to communicate with the facial nerve with both nerves innervating the sternocleidomastoid muscle. CONCLUSIONS: Additional anatomical knowledge of the variants of the accessory nerve may benefit patient care when this nerve is pathologically involved.

Topographic anatomy of the great auricular point: landmarks for its localization and classification.

PURPOSE: The great auricular point (GAP) marks the exit of the great auricular nerve at the posterior border of the sternocleidomastoid muscle (SCM). It is a key landmark for the identification of the spinal accessory nerve, and its intraoperative localization is vital to avoid neurological sequelae. This study delineates the topography and surface anatomy landmarks that used to localize the GAP. METHODS: Thirty cadaveric heminecks were dissected on a layer-by-layer approach. The topography of the GAP was examined relative to the insertion point of the SCM at the clavicle, tip of the mastoid process, and angle of the mandible. The GAP and its relation to the SCM were determined as a ratio of the total length of the SCM. RESULTS: The GAP was demonstrated to be in a predictable location. The mean length of the SCM was 131.4 ± 22 mm, and the mean distance between the GAP and the mastoid process was found to be 60.4 ± 13.76 mm. The ratio of the GAP location to the total SCM length ranged between 0.33-0.57. The mean distance between the angle of the mandible and the GAP was determined to be 57 ± 22.2 mm. Based on the midpoint of the SCM, the GAP was above it in 66.7 % of subjects and classified to Type A, and below it in 33.3 % of subjects appointed to Type B. CONCLUSIONS: The anatomical landmarks utilized in this study are helpful in predicting the location of the GAP relative to the midpoint of the SCM and can reduce neural injuries within the posterior triangle of the neck.

Sternocleidomastoid innervation from an aberrant nerve arising from the hypoglossal nerve: a prospective study of 160 neck dissections.

BACKGROUND: Anatomical variants of the spinal root of the accessory nerve and cervical plexus are well known but other variants are exceptionally rare. METHODS: A prospective study of 160 selective neck dissections was undertaken following an index case, where a presumed C1 nerve (travelling with the hypoglossal nerve) was found to innervate sternocleidomastoid (SCM). A search was subsequently made for this variant while not compromising the neck dissection surgery itself. Eight cases could not be included due to metastatic disease precluding safe dissection in this area. A nerve stimulator was used to confirm the motor supply to SCM. RESULTS: This nerve variant was found in 4/160 necks (2.5 %). In all cases, it originated directly from the hypoglossal nerve and stimulation resulted in isolated SCM contraction. No accessory nerve anomalies were found. CONCLUSION: This finding adds to the knowledge of variants in this area. Meticulous dissection and preservation of all nerves, where possible, is important for optimising functional outcomes following surgery.

Internal Jugular Vein Duplication: Anatomic Relationship With the Spinal Accessory Nerve.

Level II neck dissection is a commonly performed procedure in head and neck surgery. It carries the risk of injury to the spinal accessory nerve (SAN) and the internal jugular vein (IJV). Injury to any of these structures leads to increased intraoperative and postoperative complications and morbidity. Knowledge of the anatomic relation and possible variations from the norm is vital to decrease the morbidity of this frequently practiced procedure. This report describes 2 rare variations of the relation of the SAN to the IJV: 1) the IJV splitting with SAN passage through the IJV window and 2) the IJV splitting without SAN passage through the IJV window. Preoperative imaging and the pertinent literature regarding the variability in the relations of these structures are reviewed.

The Spinal Accessory Nerve for Functional Muscle Innervation in Facial Reanimation Surgery: An Anatomical and Histomorphometric Study.

INTRODUCTION: Facial reanimation surgery is performed in severe cases of facial palsy to restore facial function. In a 1-stage procedure, the spinal accessory nerve can be used as a donor nerve to power a free gracilis muscle transplant for the reanimation of the mouth. The aim of this study was to describe the surgical anatomy of the spinal accessory nerve, provide a guide for reliable donor nerve dissection, and analyze the available donor axon counts. METHODS: Dissections were performed on 10 nonembalmed cadavers (measurements of 20 nerves). Surgical anatomy of the spinal accessory nerve was described and distances to important landmarks were measured. Nerve biopsies were obtained of the main nerve trunk distal to the skull base, caudoposterior to the sternocleidomastoid muscle, proximal to the trapezius muscle and at the level of donor nerve harvest to analyze the myelinated axon count throughout the course of the spinal accessory nerve. The donor nerve length and available donor nerve axon count were the primary outcome parameters in this study. RESULTS: The mean donor nerve length was 11.6 cm. The spinal accessory nerve was transferred to the mandibular angle without tension for ideal coaptation to the free muscle transplant. After retraction of the trapezius muscle, a small distal nerve branch that leaves the main nerve trunk at a 90-degree angle medially was used as a landmark to indicate the level of donor nerve transection. On average, 1400 myelinated donor axons were available for innervation of the gracilis muscle transplant. CONCLUSIONS: This study gives a practical guide for spinal accessory nerve dissection for its application in facial reanimation as a motor source for the innervation of a free muscle transplant.

Topographical and functional anatomy of trapezius muscle innervation by spinal accessory nerve and C2 to C4 nerves of cervical plexus.

The aim of this study was to determine the existence and the frequency of communicating branches between the spinal accessory nerve (SAN) and the C2, C3 and C4 roots of the cervical plexus. The present study also aimed to elucidate whether these branches contain motor fibers or not. Dissection of the cervical region was performed on twelve adult cadavers. A powered operating microscope was necessary to dissect the SAN and its branches and also to dissect C2, C3 and C4 nerve branches. In a second step, data from 13 patients who underwent 25 modified neck dissections under trapezius muscle's monitoring were collected. At the end of surgery, intraoperative stimulation on the SAN, C2, C3 and C4 nerve branches was performed. Registered potentials in the three parts of the trapezius muscle, using the NIM Medtronic system, were analyzed. During cadaver dissection, 18 (78 %) communicating branches were identified between the SAN and C2, 11 (48 %) between the SAN and C3, 12 (52 %) between the SAN and C4. Intraoperative stimulation of the SAN and its branch for the trapezius muscle provided a significant electroneurographic response in the three parts of the trapezius muscle in all subjects. Intraoperative stimulation of C3 led to recordable contractions of the trapezius muscle in 5 (20 %) modified neck surgeries, stimulation of C4 led to recordable contractions during 5 (20 %) modified neck dissections. One case of contraction was recorded after intraoperative stimulation of C2 (7 %). Although we were able to identify at least one communicating branch between the SAN and the roots of the cervical plexus in each cadaver dissection, the cervical plexus is not always involved in trapezius motor innervation. Intraoperative electroneurography demonstrated that a motor input from the cervical plexus to the trapezius muscle was provided in only 32 % of cases. Therefore, SAN trunk and C3-C4 roots should be carefully preserved during modified neck dissection to protect trapezius and shoulder functions.

Image-guided, microsurgical topographic anatomy of the endolymphatic sac and vestibular aqueduct via a suboccipital retrosigmoid approach.

The endolymphatic sac (ES) and the vestibular aqueduct (VA) are often in the surgical field when posterior fossa lesions are targeted using retrosigmoid approaches. The purpose of this work is to validate neuronavigator accuracy in predicting VA location as well as to give guidelines to preserve the ES and VA. A retrosigmoid approach was performed bilaterally in six specimens in the semisitting position. Preoperatively, we registered in the CT scans the position of the VA genu (virtual genu). After the approach execution, ES and VA genu topographic relationships with evident posterolateral cranial base structures were measured using neuronavigation. Next, we exposed the VA genu: its position coincided with the virtual VA genu in all the specimens. On the average, the ES was 17.93 mm posterosuperolateral to the XI nerve in the jugular foramen, 12.26 mm posterolateral to the internal acoustic meatus, 20.13 mm anteromedial to the petro-sigmoid intersection at a point 13.30 mm inferior to the petrous ridge. The VA genu was located 7.23 mm posterolateral to the internal acoustic meatus, 18.11 mm superolateral to the XI nerve in the jugular foramen, 10.27 mm inferior to the petrous ridge, and 6.28 mm anterolateral to the endolymphatic ledge at a depth of 3.46 mm from the posterior pyramidal wall. Our study demonstrates that is possible to use neuronavigation to reliably predict the location of the VA genu. In addition, neuronavigation may be effectively used to create a topographical framework that may help maintaining the integrity of the ES/VA during retrosigmoid approaches.

An anatomic-based approach to the iatrogenic spinal accessory nerve injury in the posterior cervical triangle: How to avoid and treat it.

Iatrogenic injury of the spinal accessory nerve (SAN) is a significant reducible risk with any invasive procedure involving the posterior cervical triangle. Most commonly associated with cervical lymph node biopsy, it affects 3-6% of patients and serves as a major cause of avoidable medical malpractice litigation. Medical malpractice cases not only affect the primary surgeon but also may include the repairing surgeon through a shift of blame. For this reason, we discuss the strategies all clinicians may utilize in approaching iatrogenic SAN injuries. By taking basic precautionary measures based on simple application of anatomy in the management of these patients, clinicians may protect themselves from needless malpractice litigation. A thorough knowledge of the anatomy and application in preventative strategies may provide guidance for clinicians in reducing the incidence of iatrogenic injuries, providing effective postinjury management, and ensuring the salvaging surgeon is not at fault if litigation is pursued.

Expanding what is known of the anatomy of the spinal accessory nerve.

The spinal accessory nerve (SAN) is classically considered a motor nerve innervating the sternocleidomastoid and trapezius muscles. Its anatomical relevance derives from the high prevalence of lesions following head and neck surgeries. As expected, trapezius weakness and atrophy are the most common findings; however, it is also commonly accompanied by pain and other sensory deficits that have no clear explanation, suggesting other functions. We have recently seen two patients presenting with an unrecognized sign, that is, subclavicular/pectoral asymmetry secondary to the SAN lesion. Retrospectively, we reviewed other patients with similar findings in our case series and in the literature. We discuss the anatomical connections of the SAN with the superficial cervical plexus and propose an explanation for this finding. Of the 41 patients in our series, we identified this sign in all who had preoperative photographs. New insights on the anatomy and connections of the SAN may account for the diversity of symptoms and signs presented following an operative intervention as well as the variability of its severity.

ANATOMICAL STUDY OF CRANIAL NERVE EMERGENCE AND SKULL FORAMINA IN THE HORSE USING MAGNETIC RESONANCE IMAGING AND COMPUTED TOMOGRAPHY.

For accurate interpretation of magnetic resonance (MR) images of the equine brain, knowledge of the normal cross-sectional anatomy of the brain and associated structures (such as the cranial nerves) is essential. The purpose of this prospective cadaver study was to describe and compare MRI and computed tomography (CT) anatomy of cranial nerves' origins and associated skull foramina in a sample of five horses. All horses were presented for euthanasia for reasons unrelated to the head. Heads were collected posteuthanasia and T2-weighted MR images were obtained in the transverse, sagittal, and dorsal planes. Thin-slice MR sequences were also acquired using transverse 3D-CISS sequences that allowed mutliplanar reformatting. Transverse thin-slice CT images were acquired and multiplanar reformatting was used to create comparative images. Magnetic resonance imaging consistently allowed visualization of cranial nerves II, V, VII, VIII, and XII in all horses. The cranial nerves III, IV, and VI were identifiable as a group despite difficulties in identification of individual nerves. The group of cranial nerves IX, X, and XI were identified in 4/5 horses although the region where they exited the skull was identified in all cases. The course of nerves II and V could be followed on several slices and the main divisions of cranial nerve V could be distinguished in all cases. In conclusion, CT allowed clear visualization of the skull foramina and occasionally the nerves themselves, facilitating identification of the nerves for comparison with MRI images.

Cranial roots of the accessory nerve exist in the majority of adult humans.

The inclusion of a cranial root as a component of the accessory nerve is controversial with at least one recent study claiming that intracranial rootlets do not exist in humans. In response to this debate, the present study aimed to clarify this anatomy in a large cadaveric sample. In this study, 43 adult cadavers (86 sides) were dissected via a posterior approach to the craniocervical junction. Observations were made for the presence or absence of cranial roots of the accessory nerve, and when present, their lengths and diameters were measured. Relationships of these rootlets were documented. A cranial root of the accessory nerve was identified in 76% of sides. When identified, 1-6 cranial rootlets (mean 4.5) of the accessory nerve were observed. They ranged in diameter from 0.1 to 1.1 mm (mean 0.7 mm). The length of these nerves ranged from 8 to 24 mm with a mean of 17 mm. In general, the more superior rootlets were shorter and the more inferior rootlets were longer. Although there was a slight tendency for the cranial roots to be more numerous and larger on right sides and in males, this did not reach statistical significance. We believe this to be the largest study to date documenting the presence of a cranial root of the accessory nerve. Based on our findings, a cranial root exists in the majority of specimens. Neurosurgical procedures or high quality imaging of this area should enable the physician to see these structures.