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

The role of intraoperative neuromonitoring in preventing lesions of the spinal accessory nerve during functional neck dissection

Intraoperative neuromonitoring (IONM) in thyroid surgery offers a valid aid to the operator in identifying the recurrent laryngeal nerve and preserving its function. Recently, IONM has also been used in other surgeries, such as spinal accessory nerve dissection, during lymphectomy of the II, III, IV, and V laterocervical lymph nodes. The goal is the preservation of the spinal accessory nerve, whose macroscopic integrity does not always indicate its functionality. A further difficulty is the anatomical variability of its course at the cervical level. The aim of our study is to assess whether the use of the IONM helps to reduce the incidence of transient and permanent paralysis of the spinal accessory nerve, compared to "de visu" identification by the surgeon alone. In our case series, the use of the IONM reduced the incidence of transient paralysis, and no permanent paralysis was recorded. In addition, if the IONM registers a reduction in nerve potential, compared to the baseline value during surgery, it could indicate the need for early rehabilitation treatment, increasing the patients' chances of regaining function and reducing the costs of prolonged physiotherapy treatment.

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.

Restoration of Neck Extension after Severe Oncological Surgery of the Posterior Cervical Trunk

Reconstruction of posterior cervical trunk defects secondary to tumor resection carries significant morbidity when vertebral hardware or the spinal cord is exposed, and neck extension is interrupted. Complete reconstruction includes the coverage and obliteration of dead spaces, but functional outcomes are necessary to prevent the head dropping. This report documents the first known technique, using a free latissimus dorsi neurovascular flap to provide neck extension after ablative oncological surgery affecting trapezium and paraspinal muscles of the neck. The author explains the method by using a branch of the accessory nerve as the donor nerve. While keeping the head in a neutral position, the tendinous part of the neurovascular flap was firmly attached to the occipital periosteum and to the cephalad remnants of the trapezius, splenius capitis, and semispinalis muscles. At the caudal portion of the defect, cardinal notches were used to set the muscle at rest, avoiding excessive fiber tension. The maximal length of the muscle at rest was measured before flap elevation, calculated via the anatomical 3D print model. The thoracodorsal nerve was stimulated until the muscle shortened its length to 50%. Head extension was tested several times via neurostimulation and electromyographic control. The described procedure may provide neck extension and circumvent the problem with donor nerve providing synergy to the desired function.

The Role of IONM in Reducing the Occurrence of Shoulder Syndrome Following Lateral Neck Dissection for Thyroid Cancer

Lateral neck dissection (LND) leads to a significant morbidity involving accessory nerve injury. Modified radical neck dissection (MRND) aims at preservation of the accessory nerve, but patients often present with negative functional outcomes after surgery. The role of neuromonitoring (IONM) in the prevention of shoulder syndrome has not yet been defined in comparison to nerve visualization only. We retrospectively analyzed 56 thyroid cancer patients who underwent MRND over a period of six years (2015–2020) in a high-volume institution. Demographic variables, type of surgical procedure, removed lymph nodes and the metastatic node ratio, pathology, adoption of IONM and shoulder functional outcome were investigated. The mean number of lymph nodes removed was 15.61, with a metastatic node ratio of 0.2745. IONM was used in 41.07% of patients, with a prevalence of 68% in the period 2017–2020. IONM adoption showed an effect on post-operative shoulder function. There were no effects in 89.29% of cases, and temporary and permanent effects in 8.93% and 1.79%, respectively. Confidence intervals and two-sample tests for equality of proportions were used when applicable. Expertise in high-volume centres and IONM during MRND seem to be correlated with a reduced prevalence of accessory nerve lesions and limited functional impairments. These results need to be confirmed by larger prospective randomized controlled trials.

Trapezius muscle branch of the spinal accessory nerve without penetrating the sternocleidomastoid muscle as a pitfall in neck dissection: prevalence in a Japanese institution and a protocol for the prevention of iatrogenic injury

BACKGROUND

The spinal accessory nerve (SAN) has several anatomical variations, which may be a pitfall in neck dissection (ND). These include the trapezius muscle branch (TB), which stems from the common trunk before entering the sternocleidomastoid muscle (SCM).

AIMS/OBJECTIVES

To investigate the prevalence of this variation and suggest a protocol for preventing unexpected injury of the TB in ND.

MATERIALS AND METHODS

We conducted a retrospective cohort study for 93 patients who had undergone neck dissection (117 sides) without resection of the SCM nor SAN. We recorded the division of the TB after and before penetration of the SCM by the common trunk (penetrating type TB [PTB]) and non-penetrating type TB [NPTB], respectively).

RESULTS

Among NDs, PTB and NPTB were observed in 61 (52%) and 56 (48%) sides, respectively. In the subgroup of 24 cases with bilateral ND, PTB/PTB, NPTB/NPTB, and NPTB/PTB were observed in eight (33%), nine (38%), and seven (29%) cases, respectively. The prevalence of PTB/NPTB did not differ according to age, sex, or laterality.

CONCLUSIONS AND SIGNIFICANCE

NPTB is a common anatomical variation. The presence or absence of a branch from the common trunk must be initially checked to avoid unexpected damage to the TB.

Management of the Neck in Well-Differentiated Thyroid Cancer

PURPOSE OF REVIEW

In this narrative review, we discuss the indications for elective and therapeutic neck dissections and the postoperative surveillance and treatment options for recurrent nodal disease in patients with well-differentiated thyroid cancer.

RECENT FINDINGS

Increased availability of advanced imaging modalities has led to an increased detection rate of previously occult nodal disease in thyroid cancer. Nodal metastases are more common in young patients, large primary tumors, specific genotypes, and certain histological types. While clinically evident nodal disease in the lateral neck compartments has a significant oncological impact, particularly in the older age group, microscopic metastases to the central or the lateral neck in well-differentiated thyroid cancer do not significantly affect outcome. As patients with clinically evident nodal disease are associated with worse outcomes, they should be treated surgically in order to reduce rates of regional recurrence and improve survival. The benefit of elective neck dissection remains unverified as the impact of microscopic disease on outcomes is not significant.

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.

Optimal Trapezius Electrophysiological Recording Site

BACKGROUND

Various active recording electrode positions for the trapezius motor nerve conduction study have been suggested.

OBJECTIVE

To determine the optimal recording site of the trapezius muscles in a spinal accessory nerve conduction study.

DESIGN

Retrospective descriptive study.

SETTING

Department of physical medicine and rehabilitation in a tertiary clinic center.

PARTICIPANTS

Thirty-four patients between 33 and 82 years of age with preoperative head and neck cancer (68 upper and middle trapezius muscles).

INTERVENTIONS

Analysis of compound muscle action potentials (CMAPs) of upper and middle trapezius.

MAIN OUTCOME MEASUREMENTS

CMAP latency and amplitudes were obtained at five and four recording points with constant intervals on the horizontal line of the upper and middle trapezius, respectively.

RESULTS

The maximum CMAP amplitude of the upper trapezius was (mean ± SD) 8.5 ± 1.4 mV with the recording at the midpoint between the C7 spinous process and the lateral margin of the acromion. The maximum CMAP amplitude of the middle trapezius was 4.2 ± 1.4 mV, recorded on the horizontal line at the junction of the middle and lateral thirds between the root of the scapular spine and the vertebral spinous process.

CONCLUSION

The optimal recording site in motor nerve conduction study of the trapezius is the midpoint between the C7 spinous process and the acromion for the upper trapezius, and the junction of middle and lateral thirds of the line between the root of scapular spine and the vertebral spine for the middle trapezius.

Elective neck dissection in oral squamous cell carcinoma: Past, present and future

In 1994 a decision analysis, based on the literature and utility ratings for outcome by a panel of experienced head and neck physicians, was presented which showed a threshold probability of occult metastases of 20% to recommend elective treatment of the neck. It was stated that recommendations for the management of the cN0 neck are not immutable and should be reconfigured to determine the optimal management based on different sets of underlying assumptions. Although much has changed and is published in the almost 25 years after its publication, up to date this figure is still mentioned in the context of decisions on treatment of the clinically negative (cN0) neck. Therefore, we critically reviewed the developments in diagnostics and therapy and modeling approaches in the context of decisions on treatment of the cN0 neck. However, the results of studies on treatment of the cN0 neck cannot be translated to other settings due to significant differences in relevant variables such as population, culture, diagnostic work-up, follow-up, costs, institutional preferences and other factors. Moreover, patients may have personal preferences and may weigh oncologic outcomes versus morbidity and quality of life differently. Therefore, instead of trying to establish "the" best strategy for the cN0 neck or "the" optimal cut-off point for elective neck treatment, the approach to optimize the management of the cN0 neck would be to develop and implement models and decision support systems that can serve to optimize choices depending on individual, institutional, population and other relevant variables.

[Dissection and observation of a large unnamed nerve in the posterior cervical triangle]

OBJECTIVE

To characterize the anatomical features of a large unnamed nerve in the posterior cervical triangle and clarify its relationship with the lesser occipital nerve.

METHODS

We dissected 31 adult formalin-fixed cadaver head and neck specimens (62 sides). The lateral cervical region, the anterior cervical region, the sternocleidomastoid region, and the occipital region were dissected to define the anatomical features of the unnamed nerve.

RESULTS

This unnamed nerve was identified in the posterior cervical triangle in 96.8% of the specimens. The main trunk of the nerve had a diameter of about 3 mm with a length of around 10 cm. The nerve arose from the anterior branch of the second cervical nerve (C2, C2-3), entered the posterior cervical triangle at 1-3 cm above the accessory nerve, and continued to ascend along or in parallel with the posterior border of the sternocleidomastoid muscle. It passed between the attachments of the sternocleidomastoid and the trapezius to the occiput and divided into 3-5 branches, which innervated the skin area between the lesser and greater occipital nerves.

CONCLUSIONS

We identified a large unnamed nerve in the posterior cervical triangle, for which we coined the name "long occipital nerve" based on its unique anatomical features. The discovery of this nerve can be important for local surgery and for diagnosis and treatment of related diseases.

Spinal accessory nerve preservation in modified neck dissections: surgical and functional outcomes

The spinal accessory nerve (SAN) or XI cranial nerve is frequently encountered during neck surgery, and as such is at risk of iatrogenic injury, resulting in "shoulder syndrome". Modified neck dissection (MND) with preservation of the SAN is based on desire to minimise the functional deformity associated with section of the eleventh nerve. The aim of this study was to analyse the intra-operative variations of the spinal accessory nerve pathway and to evaluate shoulder dysfunction postoperatively. The cross-sectional demonstration analysis was created through the medical records retrospectively of 165 consecutive patients who underwent neck dissections at our institution in the past 5 years with attention to ultrasound and MRI preoperative findings, type of neck dissection, type of identification and dissection of SAN, postoperative morbidity and survival rate. The safest identification of SAN is in the posterior neck triangle where it may be recognised exiting from the posterior border of the sternocleidomastoid muscle (SCM) at Erb's point. For exact preoperative planning, ultrasound and MRI are superior to determine the position of the eleventh nerve. The mean distance between the greater auricular point and the SAN was 0.90 cm. Average length of the trunk from Erb's point until the penetration in the trapezius muscle was around 5.1 cm, ranging from 4.8 to 5.4 cm. The diversity in the course from the posterior border of the SCM and posterior neck triangle was confirmed in 9 cases (15%), predominantly at the level of entering the posterior neck triangle. The frequency of postoperative morbidity of SAN was 46.7% for radical neck dissections, 42.5% for selective neck dissections and 25% for MND. For each separate type of dissection, different subtypes were included. Identification of the SAN over established landmarks is unconditionally reliant on the exact preoperative mapping of the nerve with imaging diagnostics. MND has similar regional control rates to more comprehensive operations in appropriately selected patients and significantly reduces the risk of functional disability.

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.

Decremental responses in patients with motor neuron disease

OBJECTIVE

Involvement of the neuromuscular junction (NMJ) in amyotrophic lateral sclerosis (ALS) has been reported and is increasingly recognized as an important pathophysiological aspect. The relationship between decrement and clinical measures for possible application as a biomarker has not been comprehensively explored.

METHODS

We performed routine repetitive nerve stimulation (RNS) of three nerves on patients with ALS. We captured measures of muscle strength, grip strength, fatigability, and calculated slow vital capacity (SVC) rates of change assessing for associations.

RESULTS

In 42 subjects, 210 muscles were studied. Negative correlation was found between the percentage of decrement and compound muscle action potential (CMAP) amplitude. Approximately half of the patients with hand weakness did not have decrement. There was no significant correlation between decrement and handgrip fatigue, SVC < 80% predicted, or more rapid worsening of SVC over time.

CONCLUSIONS

Abnormal decremental responses are well described in ALS. We report that the degree of decremental response does not correlate with the degree of weakness. Abnormal decrement is only rarely present in nerve-muscle pairs with normal motor power. Our findings did not support a correlation between abnormal decrement and clinical measures suggesting that RNS may not be useful as a biomarker to monitor ALS progression.

Fracture of the Clavicle following Radical Neck Dissection and Reconstruction Using Pectoralis Major Myocutaneous Flap Accompanied by Postoperative Radiotherapy

Fracture of the clavicle following radical neck dissection (RND) and/or radiotherapy is a rare complication. Several causes of fracture of the clavicle after treatment of head and neck cancer were postulated in previous reports. We present a case of fracture of the clavicle after treatment of squamous cell carcinoma of the tongue. An 81-year-old Japanese woman underwent RND, subtotal glossectomy, reconstruction using a pectoralis major myocutaneous flap (PMMCF), and postoperative radiotherapy (50.4 Gy). One month after the primary treatment, fracture of the clavicle occurred. It was thought that muscular dynamic factor and reduction of blood supply in the clavicle associated with RND and PMMCF were the causes of the fracture. We have to recognize the occurrence of this complication and try to reduce the factors related to the complication.

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.

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.