Study of the cervical plexus innervation of the trapezius muscle

A detailed review of the spinal accessory nerve and its anatomical variations with cadaveric illustration

The spinal accessory nerve, considered part of the eleventh cranial nerve, provides motor innervation to sternocleidomastoid and trapezius. A comprehensive literature review and two cadaveric dissections were undertaken. The spinal accessory nerve originates from the spinal accessory nucleus. Its rootlets unite and ascend between the denticulate ligament and dorsal spinal rootlets. Thereafter, it can anastomose with spinal roots, such as the McKenzie branch, and/or cranial roots. The spinal accessory nerve courses intracranially via foramen magnum and exits via jugular foramen, within which it usually lies anteriorly. Extracranially, it usually crosses anterior to the internal jugular vein and lies lateral to internal jugular vein deep to posterior belly of digastric. The spinal accessory nerve innervates sternocleidomastoid, receives numerous contributions in the posterior triangle and terminates within trapezius. Its posterior triangle course approximates a perpendicular bisection of the mastoid-mandibular angle line. The spinal accessory nerve contains sensory nociceptive fibres. Its cranial nerve classification is debated due to occasional non-fusion with the cranial root. Surgeons should familiarize themselves with the variable course of the spinal accessory nerve to minimize risk of injury. Patients with spinal accessory nerve injuries might require specialist pain management.

Transcutaneous cervical vagus nerve stimulation improves sensory performance in humans: a randomized controlled crossover pilot study

Accurate senses depend on high-fidelity encoding by sensory receptors and error-free processing in the brain. Progress has been made towards restoring damaged sensory receptors. However, methods for on-demand treatment of impaired central sensory processing are scarce. Prior invasive studies demonstrated that continuous vagus nerve stimulation (VNS) in rodents can activate the locus coeruleus-norepinephrine system to rapidly improve central sensory processing. Here, we investigated whether transcutaneous VNS improves sensory performance in humans. We conducted three sham-controlled experiments, each with 12 neurotypical adults, that measured the effects of transcutaneous VNS on metrics of auditory and visual performance, and heart rate variability (HRV). Continuous stimulation was delivered to cervical (tcVNS) or auricular (taVNS) branches of the vagus nerve while participants performed psychophysics tasks or passively viewed a display. Relative to sham stimulation, tcVNS improved auditory performance by 37% (p = 0.00052) and visual performance by 23% (p = 0.038). Participants with lower performance during sham conditions experienced larger tcVNS-evoked improvements (p = 0.0040). Lastly, tcVNS increased HRV during passive viewing, corroborating vagal engagement. No evidence for an effect of taVNS was observed. These findings validate the effectiveness of tcVNS in humans and position it as a method for on-demand interventions of impairments associated with central sensory processing dysfunction.

Functional and morphological evaluation of the trapezius muscle after spinal accessory nerve transfer to brachial plexus nerves

INTRODUCTION

The main innervation of the trapezius muscle is provided by the spinal accessory nerve. Several studies describe the contributions of cervical plexus roots to the trapezius muscle innervation, either directly or through connections with the spinal accessory nerve. There is no adequate understanding of how the trapezius muscle is affected after using the spinal accessory nerve in nerve transfer procedures with the usual technique, preserving at least 1 branch for the upper trapezius.

METHODS

We evaluated 20 patients with sequelae of traumatic brachial plexus injury who underwent surgical procedures for brachial plexus repair or free muscle transfer, which included the spinal accessory nerve transfer technique and were followed for a minimum of 1 year. The three portions trapezius muscle were evaluated by physical examination, magnetic resonance imaging (analysis of fatty degeneration) and electromyography.

RESULTS

In all evaluation methods, the middle and lower portions of the trapezius muscle showed more significant morphological and/or functional impairment than the upper portion, in most cases. There was a statistically significant difference in all the complementary exams results, between the affected side (with sacrifice of the nerve) versus the normal side, in the middle and lower portions of the trapezius muscle.

CONCLUSIONS

Physical examination alone is not sufficient to determine the residual functionality of the trapezius muscle. Magnetic resonance imaging and electromyography are useful tools to assess both morphological involvement of the trapezius muscle and nerve conduction impairment of the trapezius muscle, respectively. The results suggest that the middle and lower portions of the trapezius muscle are affected by previous SAN transfer and should be considered with caution for further muscle transfer procedures.

Anatomic Variability of the Accessory Nerve: Implications for Dissection of Level IIB

OBJECTIVES

During neck dissection, level IIB lymphadenectomy necessitates manipulation of the spinal accessory nerve that might be avoided and might cause postoperative disability. Current literature does not describe the effect of variation in the spinal accessory nerve in the upper neck. We sought to measure the effect of the dimensions of level IIB on nodal yield in level IIB and on patient reported neck symptoms.

METHODS

We measured the boundaries of level IIB of 150 patients undergoing neck dissection. Level II was dissected and separated into levels IIA and IIB intraoperatively. Patient-reported symptoms were assessed in 50 patients using the Neck Dissection Impairment Inventory. We computed descriptive statistics, and sought to identify correlation with the number and proportion of level IIB nodes and the number of metastatic nodes. Level IIB dimensions were analyzed as predictors of postoperative symptoms.

RESULTS

We measured 184 sides, with 37.7% of level II nodes found in level IIB. Mean accessory nerve length across level II was 2.5 cm. Every additional 1 cm in accessory nerve length was associated with two more level IIB nodes. At all accessory nerve lengths, meaningful numbers of nodes were present in level IIB. Accessory nerve length and other factors did not correlate with NDII scores.

CONCLUSIONS

Longer lengths of accessory nerve across level IIB correlated with greater nodal yield. However, data did not point to an accessory nerve length cutoff below which level IIB dissection could be avoided. In addition, the dimensions of level IIB did not correlate with postoperative neck symptoms.

LEVEL OF EVIDENCE

2 Laryngoscope, 134:154-159, 2024.

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.

Untrapped: bilateral hypoplasia of the trapezius muscle

Agenesis or congenital hypoplasia of skeletal muscles occurs infrequently but may occur with specific conditions such as Poland syndrome. The trapezius muscle can vary in the extent of its bony attachments or may have additional slips, however congenital absence or hypoplasia is extremely rare. There are only a few reports of partial or complete absence of the trapezius muscle. Two cases of bilateral absence of the trapezius were both in males and were accompanied by the absence of additional muscle in the pectoral girdle. Herein, we describe a case of a 56-year-old male cadaver with bilateral hypoplasia of the trapezius. The muscle was largely represented by atrophied muscle fibers with an abundance of fibrotic or fatty connective tissue. This subject had very minor hypoplasia of the left pectoralis major muscle, but the remaining muscles of the pectoral girdle were normal. The spinal accessory nerve terminated in the sternocleidomastoid muscle on both sides, failing to reach the trapezius. We interpret these findings to be consistent with a minor variant of Poland syndrome.

Transferência nervosa da raiz de C4 para C5 em lesões do plexo braquial. Estudo anatômico e descrição de técnica cirúrgica

Objective  This is an anatomical study of C4 and C5 roots for nerve transfers in upper brachial plexus injuries, with surgical technique demonstration.

Methods  Fifteen brachial plexuses from both male and female cadavers were dissected. Morphological features of C4 and C5 roots were recorded and analyzed, followed by a neurotization simulation.

Results  In all dissections, C4 and C5 roots morphological features allowed their mobilization and neurotization with no need for a nerve graft. The surgical technique spared important regional nerve branches.

Conclusion  Based on these data, we conclude that C4-C5 nerve transfers are feasible and result in no additional neurological deficit in upper brachial plexus injuries.

Trapezius Motor Evoked Potentials From Transcranial Electrical Stimulation and Transcranial Magnetic Stimulation: Reference Data, Characteristic Differences and Intradural Motor Velocities in Horses

Reason for Performing Study

So far, only transcranial motor evoked potentials (MEP) of the extensor carpi radialis and tibialis cranialis have been documented for diagnostic evaluation in horses. These allow for differentiating whether lesions are located in either the thoraco-lumbar region or in the cervical myelum and/or brain. Transcranial trapezius MEPs further enable to distinguish between spinal and supraspinal located lesions. No normative data are available. It is unclear whether transcranial electrical stimulation (TES) and transcranial magnetic stimulation (TMS) are interchangeable modalities.

Objectives

To provide normative data for trapezius MEP parameters in horses for TES and TMS and to discern direct and indirect conduction routes by neurophysiological models that use anatomical geometric characteristics to relate latency times with peripheral (PCV) and central conduction velocities (CCV).

Methods

Transcranial electrical stimulation-induced trapezius MEPs were obtained from twelve horses. TES and TMS-MEPs (subgroup 5 horses) were compared intra-individually. Trapezius MEPs were measured bilaterally twice at 5 intensity steps. Motoneurons were localized using nerve conduction models of the cervical and spinal accessory nerves (SAN). Predicted CCVs were verified by multifidus MEP data from two horses referred for neurophysiological assessment.

Results

Mean MEP latencies revealed for TES: 13.5 (11.1–16.0)ms and TMS: 19.7 (12–29.5)ms, comprising ∼100% direct routes and for TMS mixed direct/indirect routes of L:23/50; R:14/50. Left/right latency decreases over 10 > 50 V for TES were: –1.4/–1.8 ms and over 10 > 50% for TMS: –1.7/–3.5 ms. Direct route TMS-TES latency differences were 1.88–4.30 ms. 95% MEP amplitudes ranges for TES were: L:0.26–22 mV; R:0.5–15 mV and TMS: L:0.9 – 9.1 mV; R:1.1–7.9 mV.

Conclusion

This is the first study to report normative data characterizing TES and TMS induced- trapezius MEPs in horses. The complex trapezius innervation leaves TES as the only reliable stimulation modality. Differences in latency times along the SAN route permit for estimation of the location of active motoneurons, which is of importance for clinical diagnostic purpose. SAN route lengths and latency times are governed by anatomical locations of motoneurons across C2-C5 segments. TES intensity-dependent reductions of trapezius MEP latencies are similar to limb muscles while MEP amplitudes between sides and between TES and TMS are not different. CCVs may reach 180 m/s.

Cutaneous Branch of the Spinal Accessory Nerve: Case Report With Potential Relevance to Occipital Neuralgia

We describe a case in which a cutaneous branch was found arising from the spinal accessory nerve, a nerve typically characterized as a purely motor nerve. Although reported anatomical variations of the lesser occipital and spinal accessory nerves are uncommon, rare variants have been reported. Such anatomy might result in unexpected patient presentations or rare complications following spinal accessory nerve injury.

Anatomical aspects of the selective infraspinatus muscle neurotization by spinal accessory nerve

The suprascapular nerve (SSN) is commonly reconstructed by spinal accessory nerve (SAN) transfer. However, reinnervation of its branch to the infraspinatus muscle (IB-SSN) is poor. Reconstruction of the SSN in cases of scapular fractures is frequently neglected in clinical practice. The morphological study was performed on 25 adult human cadavers. The course and the length of SSN of minimal diameter of 2 mm within the trapezius muscle, the length of the distal stump of IB-SSN to its branching point and the length of the SSN available for reconstructive procedure were measured. The feasibility study of the SAN - IB-SSN neurotization performed by using a bony canal under the spine of scapula was performed. The mean distance of the SAN from the spine was 8.5 cm (±0.88) at the point where it perforates the trapezius muscle and 4.49 cm (±0.72) at the most distal part of the nerve. The mean length of the intramuscular portion of the nerve was 14.74 cm (±1.99). It ran under a mean latero-medial angle of 15.54^° (±2.51). The mean distance between the medial end of the scapular spine and the SAN was 2.44 cm (± 0.64). The mean length of the IB-SSN was 3.6 cm (± 0.67). The mean length of the SAN stump which was mobilized from its original course and transferred to the infraspinous fossa to reach distal stump of the IB-SSN was 8.09 cm (±1.6). Direct SAN to IB-SSN transfer is anatomically feasible in the adult population.

Spinal accessory neuropathy in patients with chronic trapezius myofascial pain syndrome

Background

Myofascial pain syndrome is a common musculoskeletal problem affecting the trapezius muscle. The aim was to assess the presence of spinal accessory neuropathy in patients with unilateral chronic trapezius myofascial pain syndrome.

Results

The study included 25 patients with unilateral chronic trapezius myofascial pain syndrome and 20 apparently healthy volunteers as the control group. There was a significantly delayed spinal accessory nerve latency on the symptomatic side in comparison to either asymptomatic side (P = 0.014) and control group (P = 0.001). Compound muscle action potential amplitude did not significantly differ between the symptomatic side versus the asymptomatic side and control group. Delayed spinal accessory nerve latency was present in seven patients (28%) and reduced compound muscle action potential amplitude in one of them (4%). The needle electromyography of the upper trapezius muscle revealed neuropathic motor units and incomplete interference pattern in the patient who showed reduced compound muscle action potential amplitude. Abnormal rest potentials were absent in all patients. Individually, seven patients (28%) had electrophysiological evidence of spinal accessory neuropathy, but only one (4%) of them had clinical evidence of spinal accessory neuropathy. Patients with abnormal electrophysiological findings had longer duration of complaint and more severe pain.

Conclusions

Spinal accessory neuropathy is common among patients with chronic trapezius myofascial pain syndrome. It could contribute to increased pain severity of myofascial pain syndrome. Electrodiagnosis is a good modality for identifying subclinical spinal accessory neuropathy.

ANALYSIS OF FATTY DEGENERATION OF THE TRAPEZIUS MUSCLE AFTER USE OF ACCESSORY NERVE

Objective:

To investigate, through magnetic resonance imaging, the occurrence of fatty degeneration of the trapezius in adult patients undergoing nerve transfer procedure, using the spinal accessory nerve.

Methods:

A total of 13 patients meeting the criteria of unilateral brachial plexus injury and more than one year of postoperative care after nerve transfer surgery underwent an MRI scan of the trapezius. A T1-weighted 3D sequence was used, with the IDEAL technique using 8.0 mm cut thickness, 8.0 mm cut spacing, TR of 100 ms, TE of 3.45 ms, flip angle of 10 degrees, 20 cuts, on the sagittal plane. The images of the upper, transverse and lower parts of the trapezius muscle were then classified according to the degree of fatty degeneration, compared with the contralateral side, using the Goutallier score.

Results:

For the upper trapezius there was a change of the degeneration state in 23% (p = 0.083), for the transverse section there was a change in 84.6% (p = 0.003), for the lower one there was a change in 92.3% (p = 0.002).

Conclusion:

The upper trapezius did not undergo significant degeneration after transfer. The lower and transverse trapezius suffered fatty degeneration in most patients, indicating severe functional impairment. Level of Evidence IV, Case series.

Preoperative Evaluation of Iatrogenic Spinal Accessory Nerve Palsy: What Is the Place for Electrophysiological Testing?

PURPOSE

Electrophysiological testing has been used for the early diagnosis of iatrogenic spinal accessory nerve palsy in clinical practice. However, the presence of low-amplitude compound action potential in 70% to 90% of the patients suffering from iatrogenic nerve transection was reported in several studies. We have encountered the same issue and made minor modifications to the methods of electrophysiological testing. The purpose of this study was to retrospectively evaluate the reliability of our modified electrophysiological testing as preoperative examination in patients receiving surgical revision.

METHODS

In this study, we compared preoperative electrophysiological testing results with intraoperative diagnosis in the 24 patients with iatrogenic spinal accessory nerve palsy who were referred to our hospital from 2009 to 2018.

RESULTS

During operation, 20 patients were diagnosed with neurotmesis and the remaining 4 patients were found axonotmesis depending on the results of surgical exploration and intraoperative electrophysiological examination. Six of the 20 patients with neurotmesis demonstrated a low-amplitude compound muscle action potential of the upper trapezius during preoperative electrophysiological testing. Needle electromyography revealed voluntary motor unit potentials in 8 of the 20 patients. Meanwhile, concomitant great auricular nerve or dorsal scapular nerve injuries were preoperatively revealed in 7 of 24 patients.

CONCLUSIONS

The rate of low-amplitude compound muscle action potentials in these patients suffering from spinal accessory nerve neurotmesis was about 30% with our modified electrophysiological testing. We should be aware of this pitfall before surgical nerve repair. Furthermore, electrophysiological testing is an informative preoperative examination revealing the concomitant nerve injuries.

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.

New Rhizotomy Procedure for Primary Spasmodic Torticollis

OBJECTIVE

Spasmodic torticollis (ST) is an idiopathic neurologic disorder affecting the muscles of the neck. Surgery is a preferred treatment, when conservative treatments or Botulinum neurotoxin injections fail to relieve the symptoms. Our objective here is to report the outcome of a new surgical method for treating ST patients in our department.

METHODS

The new procedure consists of rhizotomy of the spinal accessory nerve (SAN) and C1-C2 nerve roots, coagulation of the distal end of SAN (Group A). The results of this procedure were compared with a group of patients who underwent only rhizotomy of the SAN and anterior C1-C2 nerve roots (Group B). Clinical data were retrospectively collected from 39 patients with laterocollis and rotatory torticollis subtypes of ST from Jun 1, 2014 to Jun 1, 2015. The effect of the surgery was evaluated by the reduction in the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) total scores preoperatively and postoperatively. The mean duration of the postoperative follow-up period was 2.57 years, ranging from 2 to 3 years.

RESULTS

The mean preoperative TWSTRS score was 65.89 ± 3.55 and 65.80 ± 3.45 in Groups A and B, respectively. Six months after the surgery, the TWSTRS scores decreased to 40.00 ± 12.14 and 26.04 ± 11.77, respectively. There was a statistically significant improvement preoperatively and postoperatively in both groups (P < 0.05). The decrease in TWSTRS score of Group B was more significant than that of Group A (P < 0.05). The main complications included shoulder numbness, shoulder weakness, and hoarseness.

CONCLUSIONS

The procedure in this study provides a new and effective surgical method for patients with ST. This procedure should be recommended if conservative therapy does not offer satisfactory relief of symptoms.

Oncologic safety of cervical nerve preservation in neck dissection for head and neck cancer

BACKGROUND

Although the functional merits of preserving cervical nerves in neck dissection for head and neck cancer have been reported, the oncologic safety has not yet been determined. Therefore, the purpose of this study was to evaluate the safety of cervical nerve preservation.

METHODS

A retrospective chart review was performed on patients with head and neck cancer who had been treated by neck dissection between 2009 and 2014 at Kyoto Medical Center. Management of cervical nerves and clinical results were analyzed.

RESULTS

A total of 335 sides of neck dissection had been performed in 222 patients. Cervical nerves were preserved in 175 neck sides and resected in 160 sides. The 5-year overall survival (OS) rate calculated by the Kaplan-Meier method was 71%. The 5-year neck control rate was 95% in cervical nerve preserved sides and 89% in cervical nerve resected sides.

CONCLUSION

Preserving cervical nerves in neck dissection is oncologically safe in selected cases.

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.

The innervation of the soft palate muscles involved in cleft palate: a review of the literature

OBJECTIVE

Surgical techniques to obtain adequate soft palate repair in cleft palate patients elaborate on the muscle repair; however, there is little available information regarding the innervation of muscles. Improved insights into the innervation of the musculature will likely allow improvements in the repair of the cleft palate and subsequently decrease the incidence of velopharyngeal insufficiency. We performed a literature review focusing on recent advances in the understanding of soft palate muscle innervation.

MATERIAL AND METHODS

The Medline and Embase databases were searched for anatomical studies concerning the innervation of the soft palate.

RESULTS

Our literature review highlights the lack of accurate information about the innervation of the levator veli palatini and palatopharyngeus muscles. It is probable that the lesser palatine nerve and the pharyngeal plexus dually innervate the levator veli palatini and palatopharyngeus muscles. Nerves of the superior-extravelar part of the levator veli palatini and palatopharyngeus muscles enter the muscle form the lateral side. Subsequently, the lesser palatine nerve enters from the lateral side of the inferior-velar part of the levator veli palatini muscle. This knowledge could aid surgeons during reconstruction of the cleft musculature. The innervation of the tensor veli palatini muscle by a small branch of the mandibular nerve was confirmed in all studies.

CONCLUSION

Both the levator veli palatini and palatopharyngeus muscles receive motor fibres from the accessory nerve (through the vagus nerve and the glossopharyngeal nerve) and also the lesser palatine nerve. A small branch of the mandibular nerve innervates the tensor veli palatini muscle.

CLINICAL RELEVANCE

Knowledge about these nerves could aid the cleft surgeon to perform a more careful dissection of the lateral side of the musculature.

Role of Sonography in Surgical Decision Making for Iatrogenic Spinal Accessory Nerve Injuries: A Paradigm Shift

The spinal accessory nerve (SAN) is susceptible to iatrogenic injury in the posterior cervical triangle. Early diagnosis and management of suspected SAN transection injuries are crucial in the restoration of shoulder stability and function. Although neurologic examination and electrodiagnostic testing can assess SAN function, they cannot assess nerve continuity. We report the use of sonography to prospectively evaluate the SAN in 6 patients with suspected iatrogenic SAN injury. Sonography directly visualized SAN transection in 4 cases, whereas sonographic findings were reported as "probable" transection in the fifth case and was nondiagnostic in the sixth case in the setting of extensive scarring.

Selective peripheral denervation for cervical dystonia: long-term follow-up

OBJECTIVE

61 procedures with selective peripheral denervation for cervical dystonia were retrospectively analysed concerning surgical results, pain, quality of life (QoL) and recurrences.

METHODS

The patients were assessed with the Tsui torticollis scale, Visual Analogue Scale (VAS) for pain and Fugl-Meyer scale for QoL. Evaluations were performed preoperatively, early postoperatively, at 6 months, then at a mean of 42 (13-165) months. All patients underwent electromyogram at baseline, which was repeated in cases who presented with recurrence of symptoms after surgery.

RESULTS

Six months of follow-up was available for 55 (90%) of the procedures and late follow-up for 34 (56%). The mean score of the Tsui scale was 10 preoperatively. It improved to 4.5 (p<0.001) at 6 months, and 5.3 (p<0.001) at late follow-up. VAS for pain improved from 6.5 preoperatively to 4.2 (p<0.001) at 6 months and 4 (p<0.01) at late follow-up. The Fugl-Meyer score for QoL improved from 43.3 to 46.6 (p<0.05) at 6 months, and to 51.1 (p<0.05) at late follow-up. Major reinnervation and/or change in the dystonic pattern occurred following 29% of the procedures, and led in 26% of patients to reoperation with either additional denervation or pallidal stimulation.

CONCLUSIONS

Selective peripheral denervation remains a surgical option in the treatment of cervical dystonia when conservative measures fail. Although the majority of patients experience a significant relief of symptoms, there is a substantial risk of reinnervation and/or change in the pattern of the cervical dystonia.

Quantification of Trapezius Muscle Innervation During Neck Dissections: Cervical Plexus Versus the Spinal Accessory Nerve

OBJECTIVES

Despite increasing use of selective, nerve-sparing surgical techniques during neck dissections, the reported rate of postoperative paralysis of the trapezius muscle is still high. The aim of the study is to measure and compare motor inflow to the trapezius muscle, in order to better understand the peripheral neuroanatomy.

METHODS

Intraoperative nerve monitoring (electroneurography) in patients undergoing routine neck dissection (n=18). The innervation of the 3 functional parts of the trapezius muscle was mapped and quantified through compound muscle action potentials.

RESULTS

In 18/18 (100%) of the patients, the spinal accessory nerve (SAN) innervated all parts of the trapezius muscle. In 7/18 (39%) of the patients, an active motor branch from the cervical plexus was detected, equally distributed to all functional parts of the trapezius muscle, at levels comparable to the SAN.

CONCLUSIONS

Compared to the SAN, branches from cervical plexus provide a significant amount of neural input to all parts of the trapezius muscle. Intraoperative nerve monitoring can be used in routine neck dissections to detect these branches, which may be important following surgical injury to the SAN.

Division of the spinal accessory nerve in the anterior triangle: a prospective clinical study

The anatomical relation between the spinal accessory nerve and internal jugular vein is well documented, but other variants of the nerve, including the contributions of the cervical plexus to supply motor fibres to the trapezius, are less well known. We have previously described an anatomical variant in which the spinal accessory nerve divided before entering the sternocleidomastoid, and the inferior trunk passed directly under it to supply the trapezius. We now present a prospective study of 133 neck dissections (excluding radical dissections) in which a meticulous search was made for the variant in the anterior triangle of the neck during operation. We found it in 3 necks (2%). One of the 3 patients had a bilateral neck dissection but it was found on one side only, and in 2 cases it communicated with the cervical plexus. In all 3, stimulation of the inferior division resulted in contraction of the trapezius while the upper division was found to supply the sternocleidomastoid only. The finding of this variant, which was more common than first thought, highlights the need for meticulous dissection of the nerve before it enters the sternocleidomastoid to ensure that, when present, the inferior branch is preserved to minimise potential postoperative shoulder dysfunction. Further research including a cadaveric study is needed to understand this important variant more fully.

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.

Intracisternal cranial root accessory nerve schwannoma associated with recurrent laryngeal neuropathy

Intracisternal accessory nerve schwannomas are very rare; only 18 cases have been reported in the literature. In the majority of cases, the tumor origin was the spinal root of the accessory nerve and the tumors usually presented with symptoms and signs of intracranial hypertension, cerebellar ataxia, and myelopathy. Here, we report a unique case of an intracisternal schwannoma arising from the cranial root of the accessory nerve in a 58-year-old woman. The patient presented with the atypical symptom of hoarseness associated with recurrent laryngeal neuropathy which is noted by needle electromyography, and mild hypesthesia on the left side of her body. The tumor was completely removed with sacrifice of the originating nerve rootlet, but no additional neurological deficits. In this report, we describe the anatomical basis for the patient's unusual clinical symptoms and discuss the feasibility and safety of sacrificing the cranial rootlet of the accessory nerve in an effort to achieve total tumor resection. To our knowledge, this is the first case of schwannoma originating from the cranial root of the accessory nerve that has been associated with the symptoms of recurrent laryngeal neuropathy.

Histologic confirmation of neuronal cell bodies along the spinal accessory nerve

INTRODUCTION

Most sources conclude that the spinal accessory nerve (SAN) is a purely motor nerve. There are some reports that suggest a sensory component, although the exact nature of such sensory fibers has yet to be elucidated. With such discrepancies in the literature and with well-established pain syndromes of unknown etiology following SAN injury, the authors performed the present study to better clarify this anatomy.

MATERIALS AND METHODS

The entire accessory nerve was harvested from 10 adult cadavers. Samples were then submitted for immunohistochemical analyses.

RESULTS

Occasional microganglia cells were identified along the SAN in all specimens. These ganglia were most numerous along the intracranial segment of the SAN, but none was found along the cranial rootlets of the accessory nerve.

CONCLUSIONS

Neuronal cell bodies were identified along the course of the SAN in human cadavers. Although the function is not certain, such cells have been found in other animals to be nocioceptive in nature. Pending further study, these cells may be found to be involved in enigmatic pain syndromes thought to arise in the sternocleidomastoid and trapezius muscles.

Measurement of the trapezius muscle volume: A new assessment strategy of shoulder dysfunction after neck dissection for the treatment of head and neck cancers

BACKGROUND

The purpose of this study was to determine the actual degree of shoulder muscle change and its relation to symptoms after neck dissection for head and neck cancers.

METHODS

Forty-two patients who underwent unilateral neck dissection were selected. Data obtained from each subject were trapezius muscle volume ratio and a Shoulder Disability Questionnaire (SDQ) score. Patients who had undergone neck dissection with spinal accessory nerve (SAN) preservation were compared with those who had received radical neck dissection. The preservation group was further separated into subgroups by the extent of neck dissection.

RESULTS

Trapezius muscle volume ratio was higher and SDQ score was significantly lower in the SAN preservation group compared to the radical neck dissection group. However, the SAN preservation subgroups did not differ from each other. In addition, a good correlation between the muscle volume ratio and SDQ score was observed.

CONCLUSION

With trapezius muscle volume ratio, clinicians may be able to diagnose shoulder dysfunction after neck dissection. Further research on the subject is warranted. This suggests a novel strategy for assessing the degree of shoulder dysfunction.

Motor innervation of the trapezius muscle: Intraoperative motor conduction study during neck dissection

OBJECTIVES

To evaluate the motor input from the spinal accessory nerve (SAN) and the branches of the cervical plexus in an intraoperative motor nerve conduction study measuring motor action potentials by direct stimulation of the exposed nerve during neck dissection.

METHODS

The entire length of the SAN and the contributions from the upper cervical plexus were preserved. Compound muscle action potentials were measured for each part of the trapezius muscle on stimulation of the SAN, C2, C3, and C4 nerves.

RESULTS

With stimulation of the spinal nerve, evoked responses were obtained from all 24 patients in the descending, transverse, and ascending trapezius muscle. C2 contributions were noted in 2 out of 24 patients; however, no patient revealed responses in all three parts of the muscle. C3 contributions were seen in 11 out of 24 patients, supplying all three parts of the muscle in 8 patients, and C4 contributions were noted in 20 out of 24 patients, supplying all three parts of the muscle in 16 of them.

CONCLUSIONS

The SAN provided the most consistent motor input to the trapezius muscle. The C2, C3, and C4 nerves also provided motor input to the trapezius muscle; however, they were either inconsistently present or, when present, irregularly innervated the three parts of the trapezius muscle.

A comprehensive review with potential significance during skull base and neck operations, Part II: glossopharyngeal, vagus, accessory, and hypoglossal nerves and cervical spinal nerves 1-4

Knowledge of the possible neural interconnections found between the lower cranial and upper cervical nerves may prove useful to surgeons who operate on the skull base and upper neck regions in order to avoid inadvertent traction or transection. We review the literature regarding the anatomy, function, and clinical implications of the complex neural networks formed by interconnections between the lower cranial and upper cervical nerves. A review of germane anatomic and clinical literature was performed. The review is organized into two parts. Part I discusses the anastomoses between the trigeminal, facial, and vestibulocochlear nerves or their branches and other nerve trunks or branches in the vicinity. Part II deals with the anastomoses between the glossopharyngeal, vagus, accessory and hypoglossal nerves and their branches or between these nerves and the first four cervical spinal nerves; the contribution of the autonomic nervous system to these neural plexuses is also briefly reviewed. Part II is presented in this article. Extensive and variable neural anastomoses exist between the lower cranial nerves and between the upper cervical nerves in such a way that these nerves with their extra-axial communications can be collectively considered a plexus.

Electrodiagnosis in persons with amyotrophic lateral sclerosis

Electrophysiology remains an important tool in the evaluation of patients presenting with signs and symptoms of motor neuron disease. The electrodiagnostic study should include peripheral nerve conduction studies and needle electromyography to both exclude treatable disease and gather evidence regarding a diagnosis of amyotrophic lateral sclerosis (ALS). The recent changes in the revised El Escorial criteria, recommended by the Awaji-shima consensus group, have increased the diagnostic significance of fasciculation potentials to equal that of fibrillation and positive sharp-wave potentials in the needle electromyography examination of patients suspected of having ALS. In addition, electrophysiologic evidence is now considered equivalent to clinical signs and symptoms in reaching a diagnostic certainty of ALS. These changes, strategies for the design, and implementation of an effective electrodiagnostic evaluation, in addition to electrophysiologic techniques and their relationship to the evaluation of a patient with ALS, are reviewed and discussed.

Ultrasound visualization of the spinal accessory nerve in vivo

BACKGROUND

Inadvertent injury of the spinal accessory nerve during surgical procedures is a cause of significant morbidity with medicolegal repercussions. Surface anatomy is an unreliable guide to the nerve's location. We suggest that ultrasound can be used to map the course of the nerve in the posterior triangle of the neck.

MATERIALS AND METHODS

Fifty healthy subjects (28 females, mean age 37 y) were scanned using a VF13-5 linear probe and a Siemens Sonoline Antares ultrasound machine (Siemens Medical Solutions USA Inc., Malvern, PA). The caliber, course, and distribution of the nerve in the posterior triangle of the neck were recorded.

RESULTS

The nerve was visualized bilaterally in all subjects, running superficially across the posterior triangle with either a straight (56%) or tortuous (44%) course at a depth of about 3 mm beneath the skin surface. It had a mean caliber of 0.76 ± 0.12 mm. It exited the posterior border of sternocleidomastoid at a mean of 6.7 (4.0-9.4) cm below the mastoid process and 1.1 (0.1-2.1) cm above the great auricular point and penetrated the anterior border of trapezius 5.4 (2.1-9.2) cm above the clavicle. Importantly, 58% of nerves divided into 2-4 branches before penetrating trapezius; the nerve branched on at least one side in 49 of 50 individuals.

CONCLUSIONS

The spinal accessory nerve and its anatomical variants can be consistently and reliably demonstrated by ultrasound in normal individuals. Surface anatomical landmarks are not a reliable guide to the position and course of the nerve in the posterior triangle. Preoperative mapping of the nerve with ultrasound may reduce the risk of iatrogenic injury.