Scalene muscles and the brachial plexus: anatomical variations and their clinical significance

Anatomical variations of the brachial plexus in adult cadavers: A descriptive study and clinical significance

BACKGROUND

Brachial plexus injury is recognized as one of the most severe clinical challenges due to the complex anatomical configuration of the brachial plexus and its propensity for variation, which complicates safe clinical interventions. This study aimed to ascertain the prevalence and characterize the types of brachial plexus variations, and to elucidate their clinical implications.

MATERIALS AND METHODS

We conducted meticulous dissections of 60 formalin-fixed cadavers' upper arm, axilla and lower neck to reveal and assess the roots, trunks, divisions, cords, and branches of the brachial plexus. The pattern of branching was noted by groups of dissecting medical students and confirmed by the senior anatomists. The variations discovered were record and photographed using a digital camera for further analysis.

RESULTS

Variations in the brachial plexus were identified in 40 of the 60 cadavers, yielding a prevalence rate of 66.7%. These variations were classified into root anomalies (2.1%), trunk anomalies (8.5%), division anomalies (2.1%), and cord anomalies (4.3%). Notably, anomalies in communicating branches were observed in 39 cadavers (83.0%): 14 with bilateral anomalies, 14 with anomalies on the left side, and 11 on the right side. These communicating branches formed connections between the roots and other segments, including trunks, cords, and terminal nerves, and involved the median, musculocutaneous, and ulnar nerves.

CONCLUSION

The frequency and diversity of brachial plexus variations, particularly in communicating branches, are significant in cadavers. It is imperative that these variations are carefully considered during the diagnostic process, treatment planning, and prior to procedures such as supraclavicular brachial plexus blocks and nerve transfers, to mitigate the risk of iatrogenic complications.

Predisposing Anatomy for Thoracic Outlet Syndrome and Functional Outcomes after Supraclavicular Thoracic Outlet Decompression in Athletes

Purpose

This study aims to examine predisposing anatomic factors and subsequent post-decompression functional outcomes among high-intensity athletes with thoracic outlet syndrome (TOS).

Materials and Methods

A single-institution retrospective review was performed on a prospective database of patients with TOS from 2018 to 2023 who had undergone operative decompression for TOS. Demographics, TOS characteristics, predisposing anatomy, operative details, and postoperative outcomes were examined. The primary outcome was postoperative return to sport. Secondary outcomes included vascular patency.

Results

A total of 13 patients who were engaged in high-demand athletic activity at the time of their diagnosis were included. Diagnoses included 8 (62%) patients with venous TOS, 4 (31%) patients with neurogenic TOS, and 1 (8%) patient with arterial TOS. Mixed vascular and neurogenic TOS was observed in 3 (23%) patients. The mean age of the cohort was 30 years. Abnormal scalene structure was observed in 12 (92%) patients, and abnormal bone structures were noted in 4 (27%) patients; 2 (15%) with cervical ribs and 3 (23%) patients with clavicular abnormalities. Prior ipsilateral upper extremity trauma was reported in 4 (27%) patients. Significant joint hypermobility was observed in 8 (62%) patients with a median Beighton score of 6. Supraclavicular cervical and/or first rib resection with scalenectomy was performed in all patients. One case of postoperative pneumothorax was treated non-operatively. Ten (77%) patients returned to sport. Duplex ultrasonography showed subclavian vein patency in all 8 patients with venous TOS and wide patency with no drop in perfusion indices in the patient with arterial TOS.

Conclusion

Athletes with TOS who required operative intervention had a high incidence of musculoskeletal aberrations and joint hypermobility. Supraclavicular decompression was associated with a high success rate, with overall good functional outcomes and good likelihood of patients returning to preoperative high-intensity athletics.

Continuous Interscalene Brachial Plexus Blocks: An Anatomical Challenge between Scylla and Charybdis?

Brachial plexus blocks at the interscalene level are frequently chosen by physicians and recommended by textbooks for providing regional anesthesia and analgesia to patients scheduled for shoulder surgery. Published data concerning interscalene single-injection or continuous brachial plexus blocks report good analgesic effects. The principle of interscalene catheters is to extend analgesia beyond the duration of the local anesthetic's effect through continuous infusion, as opposed to a single injection. However, in addition to the recognized beneficial effects of interscalene blocks, whether administered as a single injection or through a catheter, there have been reports of consequences ranging from minor side effects to severe, life-threatening complications. Both can be simply explained by direct mispuncture, as well as undesired local anesthetic spread or misplaced catheters. In particular, catheters pose a high risk when advanced or placed uncontrollably, a fact confirmed by reports of fatal outcomes. Secondary catheter dislocations explain side effects or loss of effectiveness that may occur hours or days after the initial correct function has been observed. From an anatomical and physiological perspective, this appears logical: the catheter tip must be placed near the plexus in an anatomically tight and confined space. Thus, the catheter's position may be altered with the movement of the neck or shoulder, e.g., during physiotherapy. The safe use of interscalene catheters is therefore a balance between high analgesia quality and the control of side effects and complications, much like the passage between Scylla and Charybdis. We are convinced that the anatomical basis crucial for the brachial plexus block procedure at the interscalene level is not sufficiently depicted in the common regional anesthesia literature or textbooks. We would like to provide a comprehensive anatomical survey of the lateral neck, with special attention paid to the safe placement of interscalene catheters.

Anatomical Study of the Ventral Upper Arm Muscles with a Case Report of the Accessory Coracobrachialis Muscle

Background and Objectives: The muscles in the upper arm are categorized into two groups: ventral muscles, which include the biceps brachii, coracobrachialis, and brachialis, and dorsal muscles comprising the triceps brachii and anconeus. These muscles are positioned in a way that they contribute to movements at the shoulder and elbow joints. Given the importance of the upper arm muscles for various reasons, they need to be well-known by medical professionals. Ventral upper arm muscles exhibit various topographical and morphological variations. Understanding these variations is critical from both anatomical and clinical standpoints. Therefore, our aim was to conduct an anatomical study focusing on these muscles and potentially identify ventral upper arm muscle variations that could contribute to the broader understanding of this area. For this anatomical study, 32 upper limbs obtained from 16 adult cadavers were dissected. Case report: During our anatomical survey, an accessory coracobrachialis muscle in the left upper extremity of one cadaver was discovered. This additional muscle was located anterior to the classical coracobrachialis muscle and measured 162 mm in length. It originated from the distal anterior surface of the coracoid process and was inserted into the middle third of the humeral shaft. The accessory muscle was supplied by the musculocutaneous nerve. No apparent anatomic variations were observed in the other upper arm muscles in any of the cadavers. Conclusions: Gaining insight into the ventral upper arm muscle variations holds vital significance in both anatomy and clinical practice, as they can influence surgical approaches, rehabilitation strategies, and the interpretation of imaging studies. Based on the morphological characteristics of the accessory coracobrachialis muscle discovered in our case, we hypothesize that it could have caused an atypical palpable mass in the medial brachial area, adjacent to the short head of the biceps brachii.

A Procedure for Measuring Anterior Scalene Morphology and Quality with Ultrasound Imaging: An Intra- and Inter-rater Reliability Study

OBJECTIVE

Ultrasound (US) imaging is an essential tool for clinicians because of its cost-effectiveness and accessibility for assessing multiple muscle metrics including muscle quality, size and shape. Although previous studies highlighted the importance of the anterior scalene muscle (AS) in patients with neck pain, studies analyzing the reliability of US measurements for this muscle are lacking. This study aimed to develop a protocol for assessing AS muscle shape and quality measured with US and investigating its intra- and inter-examiner reliability.

METHODS

Through use of a linear transducer, B-mode images of the anterolateral neck region at the C7 level were acquired in 28 healthy volunteers by two examiners (one experienced and one novel). Cross-sectional area, perimeter, shape descriptors and mean echo-intensity were measured twice by each examiner in randomized order. Intra-class correlation coefficients (ICCs), standard errors of measurement and minimal detectable changes were calculated.

RESULTS

Results indicated no muscle side-to-side asymmetries (p > 0.05). Gender differences were found for muscle size (p < 0.01), but muscle shape and brightness were comparable (p > 0.05). Intra-examiner reliability was good to excellent for all metrics for the experienced and (ICC >0.846) and novel (ICC >780) examiners. Although inter-examiner reliability was good for most of the metrics (ICC >0.709), the estimates for assessing solidity and circularity were unacceptable (ICC <0.70).

CONCLUSION

This study found that the described ultrasound procedure for locating and measuring anterior scalene muscle morphology and quality is highly reliable in asymptomatic individuals.

Management of the brachial plexus in head and neck cancer

PURPOSE OF REVIEW

The brachial plexus is an important anatomical structure that is regularly encountered by head and neck surgeons and radiation oncologists. Surgical or radiation-induced brachial plexus injury have great impact on arm function and quality of life. Anatomical variations and management of the brachial plexus in head and neck cancer treatment are discussed.

RECENT FINDINGS

The brachial plexus consists of spinal roots from C5-C8 and T1. The most prevalent anatomical variations in brachial plexus anatomy include the prefixed brachial plexus (additional contribution from C4) in 11%, the roots of C5 and C6 piercing the belly of the anterior scalene muscle in 6.8%, and presence of the scalenus minimus muscle in 4.1-46%. Due to its location, the brachial plexus is at risk of inadvertent division or neuropraxia during surgical procedures such as neck dissection or robot-assisted transaxillary thyroid surgery (RATS). In case of inadvertent division, nerve reconstruction surgery is warranted and may lead to improved function. The risk of radiation-induced brachial plexus injury is dose-dependent and occurs in approximately 12-22%. Currently, no successful treatment options exist for radiation-induced injury.

SUMMARY

Knowledge of anatomical variations is important for head and neck surgeons to minimize the risk of brachial plexus injury. Limiting radiation therapy dose to the brachial plexus is desirable to decrease the risk of brachial plexus injury.

Anterior Scalene Anomaly in a Patient With Arterial and Neurogenic Thoracic Outlet Syndrome

Compression of the neurovascular structures of the upper extremity as they pass through the thoracic outlet result in thoracic outlet syndrome. The myriad of symptoms associated with the syndrome vary based on the structure(s) compressed: the subclavian artery/vein or the inferior trunk of the brachial plexus. This is a common site of compression especially in the presence of upper extremity injury, overuse or anatomical abnormalities. Majority of patients present with neurogenic pain and weakness; herein, we present the case of a patient with symptoms of both arterial and neurogenic compression caused by aberrant anterior scalene anatomy. These patients are excellent surgical candidates for first rib resection and anterior scalenectomy. A transaxillary approach offers the clinician an adequate window to identify anatomical abnormalities intraoperatively and safely excise the first rib and anterior scalene muscle.

A new anatomical brachial plexus variation during interscalene block

We aimed to present our anesthetic management for an ultrasound-guided (USG) interscalene block in the presence of a new brachial plexus variation in a 59-year-old male patient underwent shoulder arthroscopy. An accessory muscle between the anterior scalene (ASM) and middle scalene muscle (MSM) was viewed via ultrasound. When four roots that the accessory muscle separated into two groups, which should be normally present between the ASM and MSM were displayed, we decided to use nerve stimulator to perform block. The contraction response from the deltoid muscle group from both root groups was regarded as a possible new brachial plexus variation in the C5 nerve root. For interscalene block, 30 ml of 0.375% bupivacaine was used via multi-injection. We confirmed this new brachial plexus variation with magnetic resonance neurography for the first time in a patient. Interscalene block should be definitely performed under USG and when a new anatomical variation is suspected, roots should be separated with a nerve stimulator to increase the success of the block.

Clinically Relevant Anatomical Variations in the Brachial Plexus

Anatomical variation in the brachial plexus may result in a variety of clinically relevant patterns, including various neuralgias of the upper extremity and differing nerve territories. Some conditions can be debilitating in symptomatic patients, resulting in paresthesia, anesthesia, or weakness of the upper extremity. Others may simply result in cutaneous nerve territories that deviate from a traditional dermatome map. This study evaluated the frequency and anatomical presentations of a large number of clinically relevant brachial plexus nerve variations in a sample of human body donors. We identified a high frequency of various branching variants, of which clinicians, especially surgeons, should be aware. The medial pectoral nerves in 30% of the sample were found to originate from either the lateral cord, or both the medial and lateral cords of the brachial plexus rather than exclusively from the medial cord. The dual cord innervation pattern greatly increases the number of spinal cord levels traditionally believed to innervate the pectoralis minor muscle. The thoracodorsal nerve arose as a branch of the axillary nerve 17% of the time. The musculocutaneous nerve sent branches to the median nerve in 5% of specimens. The medial antebrachial cutaneous nerve shared a common trunk with the medial brachial cutaneous nerve in 5% of individuals and derived from the ulnar nerve in 3% of specimens.

Supraclavius muscle observed during anterior scalenectomy for thoracic outlet syndrome: A report of two cases and review of the literature

Background

Thoracic outlet syndrome (TOS) is a clinical diagnosis caused by compression of neurovascular structures in the thoracic outlet. There are a variety of structures that cause compression implicated in TOS. TOS patients frequently require surgical decompression. Various structural anomalies encountered during decompression have been reported in the literature.

Case Description

We present two females (ages 42 and 45) that each underwent anterior scalenectomy for thoracic outlet decompression through a supraclavicular approach. A supraclavius muscle anomaly was observed in both patients. Analogous to the two reports previously described in the literature, the muscle inserted, along the medial superior undersurface of the clavicle and originated dorsally along the trapezius muscle. This is not to be confused with the subclavius posticus muscle, which originates from the first rib and inserts on the upper border of the scapula.

Conclusion

These two cases represent just the third and fourth ever descriptions of a supraclavius muscle anomaly encountered during TOS surgery. Due to the wide variety of anatomical variations encountered during TOS surgery, it is not only crucial for continued reporting of such anatomical variations to be reported in the literature but equally important for clinicians that treat TOS to be aware of such variations.

Botulinum Toxin A, a Better Choice for Skeletal Muscle Block in a Comparative Study With Lidocaine in Rats

A positive response to scalene muscle block (SMB) is an important indication for the diagnosis of thoracic outlet syndrome. Lidocaine injection is commonly used in clinical practice in SMB, although there have been some cases of misdiagnosis. Botulinum toxin A (BTX-A) is one of the therapeutic agents in SMB, but whether it is also indicated for SMB diagnosis is controversial. To evaluate the muscle block efficiency of these two drugs, the contraction strength was repeatedly recorded on tibialis anterior muscle in rats. It was found that at a safe dosage, 2% lidocaine performed best at 40 μL, but it still exhibits an unsatisfactory partial blocking efficiency. Moreover, neither lidocaine injection in combination with epinephrine or dexamethasone nor multiple locations injection could improve the blocking efficiency. On the other hand, injections of 3, 6, and 12 U/kg BTX-A all showed almost complete muscle block. Gait analysis showed that antagonistic gastrocnemius muscle, responsible for heel rising, was paralyzed for nonspecific blockage in the 12 U/kg BTX-A group, but not in the 3 U/kg or 6 U/kg BTX-A group. Cleaved synaptosomal associated protein 25 (c-SNAP 25) was stained to test the transportation of BTX-A, and was additionally observed in the peripheral muscles in 6 and 12 U/kg groups. c-SNAP 25, however, was barely detectable in the spinal cord after BTX-A administration. Therefore, our results suggest that low dosage of BTX-A may be a promising option for the diagnostic SMB of thoracic outlet syndrome. SIGNIFICANCE STATEMENT: Muscle block is important for the diagnosis and treatment of thoracic outlet syndrome and commonly performed with lidocaine. However, misdiagnosis was observed sometimes. Here, we found that intramuscular injection of optimal dosage lidocaine only partially blocked the muscle contraction in rats, whereas low-dosage botulinum toxin, barely used in diagnostic block, showed almost complete block without affecting the central nervous system. This study suggests that botulinum toxin might be more suitable for muscle block than lidocaine in clinical practice.

Unexpected Anatomical Variation While Performing an Ultrasound-Guided Interscalene Block for Shoulder Surgery

Anatomical variations of the brachial plexus are very common. Knowledge of the possible anatomical variations encountered in ultrasound imaging is crucial for the safe and effective practice of regional anesthesia. The interscalene block (ISB) targets the brachial plexus roots in the interscalene groove, between the anterior and middle scalene muscles (MSM), at the level of the sixth cervical vertebra. Blockade of the brachial plexus roots anesthetizes the shoulder region, making the ISB one of the preferred regional anesthesia options in shoulder surgeries. Abnormalities of the muscular structures surrounding the brachial plexus roots can pose a challenge while performing an ultrasound-guided ISB. We present a case of an unanticipated anatomical variation of the anterior scalene muscle (ASM) encountered on ultrasound imaging when performing an ISB. Our patient was found to have a small redundant ASM, which necessitated an alternative scanning approach and the use of a nerve stimulator to properly identify the brachial plexus roots. Based on our findings, we recommend placing the ultrasound probe parallel to the clavicle in the supraclavicular area and scanning in a cranial direction, tracing the brachial plexus back to the roots, and then confirming the needle placement by using a traditional nerve stimulator before local anesthetic deposition.

Imaging of non-specific complaints of the arm, neck, and/or shoulder (CANS): role of the scalene muscles and piercing variants in neurogenic thoracic outlet syndrome

Complaints of the arm, neck and/or shoulder (CANS) are common in the general population (40%) and workers (30%) and have significant economic impact. Twenty-three conditions have been designated as specific CANS. Cases where no cause is identified are reported as non-specific CANS; these cases make up the majority of CANS. Non-specific CANS presentations overlap with clinical entities including cervicobrachial and scalene myofascial syndromes that are associated with neurogenic thoracic outlet syndrome (NTOS). The scalene muscles have been identified as the commonest site of NTOS, although this has been reported to be functional and in conjunction with cervicothoracic junction variants that compromise the brachial plexus lower trunk. Anatomical variants in relation to both the scalene muscles and brachial plexus are not widely recognised in the clinical and imaging literature; however, pass-through and pass-over (or "piercing") variants of the brachial plexus upper trunk and scalene muscles have been well described in the anatomical and anaesthetic literature. In this review, we demonstrate the presence and describe the imaging of scalene muscle pathology and variant muscle-brachial plexus anatomy affecting the upper trunk that are underdiagnosed causes of non-specific CANS presentations and NTOS.

A consensus statement on the use of botulinum toxin in pediatric patients

Botulinum toxin has been used in medicine for the past 30 years. However, there continues to be controversy about the appropriate uses and dosing, especially in the pediatric population. A panel of nine pediatric physiatrists from different regions and previous training programs in the United States were nominated based on institutional reputation and botulinum toxin (BoNT) experience. Based on a review of the current literature, the goal was to provide the rationale for recommendations on the administration of BoNT in the pediatric population. The goal was not only to review safety, dosing, and injection techniques but also to develop a consensus on the appropriate uses in the pediatric population. In addition to upper and lower limb spasticity, the consensus also provides recommendations for congenital muscular torticollis, cervical dystonia, sialorrhea, and brachial plexus palsies.

Neurobiological tensegrity: The basis for understanding inter-individual variations in task performance?

Bernstein's (1996) levels of movement organization includes tonus, the muscular-contraction level that primes individual movement systems for (re)organizing coordination patterns. The hypothesis advanced is that the tonus architecture is a multi-fractal tensegrity system, deeply reliant on haptic perception for regulating movement of an individual actor in a specific environment. Further arguments have been proposed that the tensegrity-haptic system is implied in all neurobiological perception and -action. In this position statement we consider whether the musculoskeletal system can be conceptualized as a neurobiological tensegrity system, supporting each individual in co-adapting to many varied contexts of dynamic performance. Evidence for this position, revealed in investigations of judgments of object properties, perceived during manual hefting, is based on each participant's tensegrity. The implication is that the background organizational state of every individual is unique, given that no neurobiological architecture (musculo-skeletal components) is identical. The unique tensegrity of every organism is intimately related to individual differences, channeling individualized adaptations to constraints (task, environment, organismic), which change over different timescales. This neurobiological property assists transitions from one stable state of coordination to another which is needed in skill adaptation during performance. We conclude by discussing how tensegrity changes over time according to skill acquisition and learning.

Feasibility and Safety of the Craniocaudal Approach for Superior Sulcus Lesions of the Thorax

Purpose

To evaluate the feasibility and safety of the craniocaudal approach for superior sulcus lesions of the thorax.

Material and Methods

Between October 2010 and December 2020, the data from 22 consecutive patients who underwent drainage or biopsy using a craniocaudal trajectory were retrospectively reviewed. The craniocaudal approach was applied for patients in which the fluid collection or tumor was limited to the superior thoracic sulcus lesion or otherwise inaccessible owing to intervening structures such as pleural dissemination. The indications for this procedure were drainage in 20 patients and biopsy in 2 patients. Technical success, procedure time, complications, and clinical success were evaluated.

Results

Technical and clinical success were achieved in all patients, and no major complications were found. The median procedure time was 25 min (range 15–40 min). This procedure was performed with fluoroscopic guidance in 11 patients and ultrasound guidance in 11 patients. The routes of needle passage were the first intercostal space (n = 16), the second intercostal space (n = 5), and between the clavicle and the first rib (n = 1).

Conclusion

The craniocaudal approach for superior sulcus lesions might be a safe and feasible option for patients in which the conventional intercostal approach is difficult.

Level of Evidence

Retrospective cohort study. Level 4.

A meta-analysis on the anatomical variability of the brachial plexus: Part I - Roots, trunks, divisions and cords

INTRODUCTION

The brachial plexus is a complex anatomical structure that gives rise to all the nerves of the upper limb. Its variability is frequently observed and represents a challenge for interventions in the lower neck and axilla. The aim of this study was to present a comprehensive and evidence-based review with meta-analytic techniques on the variability of roots, trunks, divisions and cords of the brachial plexus.

MATERIALS AND METHODS

Major medical databases were searched to identify all anatomical studies investigating the variability in the formation of the brachial plexus. Data extracted consisted of demographic information, morphometric parameters, the arrangement of the brachial plexus at the level of the roots, trunks, divisions and cords and the relationship of the brachial plexus to the axillary artery and scalene muscles. The different configurations of the brachial plexus were put into a new classification, and the pooled prevalence of each case was calculated using a random effects model. A sub-analysis on age and geographical location was also performed.

RESULTS

A total of 40 studies (3055 upper limbs) were included in the meta-analysis. The regular arrangement of roots forming trunks was identified in 84% (95% CI 79-89%) of cases. The overall prevalence of the prefixed and postfixed brachial plexus was 11% (95% CI 6-17%) and 1% (95% CI 0-1%), respectively and in less than 0.1% of cases the brachial plexus received a branch from both C4 and T2. For divisions forming cords, the regular arrangement was observed in 96% (95% CI 93-98%) of cases. Additional communicating branches between the components of the brachial plexus appeared in 5% (95% CI 3-7%) of cases. The relationship of the brachial plexus to the axillary artery and scalene muscles was considered regular in 96% (95% CI 89-100%) and 86% (95% CI 66-98%) of cases, respectively. Analysis of the morphometric parameters revealed the proportional consistency between the components forming the plexus during aging.

CONCLUSIONS

Knowledge of anatomical variations of the brachial plexus is important for examinations and interventions in the lower neck and axilla. The variability was observed especially in the roots forming trunks, while divisions forming cords showed quite stable appearance. The results of this evidence-based review and meta-analysis can be applied in many different medical disciplines.

Coexistence of Brachial Plexus-Anterior Scalene and Sciatic Nerve-Piriformis Variants

The trunks of the brachial plexus typically pass through the interscalene triangle, between the anterior and middle scalene muscles and superior to the first rib. Likewise, the two components of the sciatic nerve, tibial and common fibular nerves, usually join and pass together inferior to the piriformis muscle. We present a cadaver with anatomic variations of both the right brachial plexus-interscalene triangle relationship and the sciatic nerve-piriformis relationship. The right brachial plexus C5 and C6 roots formed the superior trunk as they passed through a bifurcated anterior scalene muscle, while the C7, C8, and T1 roots passed posterior to the anterior scalene. After passing through the left greater sciatic foramen, the sciatic nerve branched into the common fibular and tibial nerves, which passed through and inferior to the piriformis muscle, respectively. The presence of these anatomic variations may predispose individuals to symptomatic nerve entrapments such as thoracic outlet syndrome and piriformis syndrome. This finding is relevant to clinicians performing invasive procedures and diagnosing neurological conditions. 

Scalenus Minimus Muscle: Overestimated or Not? An Anatomical Study

The wide range of scalenus minimus muscle incidence reported in the literature along with the plethora of fibromuscular structures that may appear in the interscalene triangle, having various terminologies, were the reasons to conduct the present study questioning the reported high incidence of this supernumerary scalene muscle. Seventy-three Greek cadavers were dissected and examined for the presence of a scalenus minimus muscle. It was found unilaterally in three of 73 (4.11%) cadavers studied. The literature review, concerning its incidence, revealed a wide range between 7.8 and 71.7 per cent, which cannot be attributed only to racial variation. Thus, there is a matter whether other variations of the scalene muscles are considered as a true scalenus minimus muscle. Recognition of this muscle is important not only for anatomists, but also has clinical significance for the diagnosis of the thoracic outlet syndrome. Surgeons performing scalenectomy and anesthesiologists during interscalene brachial plexus block should keep in mind the anatomical variations of this region.

High definition ultrasound imaging of the individual elements of the brachial plexus above the clavicle

Background and objectives

Ultrasonography of the brachial plexus (BP) has been described but there are limited data on visualization of the T1 ventral ramus and the inferior trunk. This prospective observational study aimed to evaluate a high definition ultrasound imaging technique to systematically identify the individual elements of the BP above the clavicle.

Methods

Five healthy young volunteers underwent high definition ultrasound imaging of the BP above the clavicle. The ultrasound scan sequence (transverse oblique scan) commenced at the supraclavicular fossa after which the transducer was slowly swept cranially to the upper part of the interscalene groove and then in the reverse direction to the supraclavicular fossa. The unique sonomorphology of the C7 transverse process was used as the key anatomic landmark to identify the individual elements of the BP in the recorded sonograms.

Results

The neural elements of the BP that were identified in all volunteers included the ventral rami of C5–T1, the three trunks, divisions of the superior trunk, and formation of the inferior trunk (C8–T1). The C6 ventral ramus exhibited echogenic internal septation with a split (bifid) appearance in four of the five volunteers. In three of the four volunteers with a bifid C6 ventral ramus, the C7 ventral ramus was also bifid.

Conclusion

We have demonstrated that it is feasible to accurately identify majority of the main components of the BP above the clavicle, including the T1 ventral ramus and the formation of the inferior trunk, using high definition ultrasound imaging.

Trial registration number

ChiCTR1900021749.

Anatomical entrapment of the dorsal scapular and long thoracic nerves, secondary to brachial plexus piercing variation

Circumscapular pain is a frequent complaint in clinical practice. The dorsal scapular and long thoracic nerves course through the neck, where they may become entrapped between or within adjacent scalene muscles. Additionally, a high frequency of brachial plexus "piercing" variants have recently been documented, and it is unclear how they influence branching patterns distally along the brachial plexus. In the project reported here we strived to identify and quantify variations in dorsal scapular nerve and long thoracic nerve secondary to brachial plexus piercing variation. Ninety brachial plexuses from human cadavers (45 female/45 male) were evaluated to identify nerve branching patterns, specifically piercing versus non-piercing variants in the brachial plexus roots and nerves. Anatomical entrapment of the dorsal scapular nerve and long thoracic nerve was found in high frequencies (60.8% and 44.6%, respectively). Anomalous brachial plexus piercing variants were associated with higher frequencies of distal nerve branches also coursing through the scalene musculature, and there was a statistically significant correlation between brachial plexus and long thoracic nerve piercings (p = 0.027). Anatomical entrapment of nerves within scalene musculature is common and may be causative factors for idiopathic circumscapular pain, dorsalgia, and dysfunction of scapulohumeral rhythm. This study revealed a link between anatomical arrangement of the brachial plexus and occurrence of long thoracic nerve entrapment, which may lead to a series of cascading neurologic effects in which affected individuals may suffer from increased incidence of thoracic outlet syndrome and long thoracic nerve entrapment resulting in additional symptoms of interscapular pain and compromised shoulder mobility.

Triangles of the neck: a review with clinical/surgical applications

The neck is a geometric region that can be studied and operated using anatomical triangles. There are many triangles of the neck, which can be useful landmarks for the surgeon. A better understanding of these triangles make surgery more efficient and avoid intraoperative complications. Herein, we provide a comprehensive review of the triangles of the neck and their clinical and surgical applications.

The importance of costoclavicular space on possible compression of the subclavian artery in the thoracic outlet region: a radio-anatomical study

OBJECTIVES

The purposes of this study were to identify possible compression points along the transit route of the subclavian artery and to provide a detailed anatomical analysis of areas that are involved in the surgical management of the thoracic outlet syndrome (TOS). The results of the current study are based on measurements from cadavers, computed tomography (CT) scans and dry adult first ribs.

METHODS

The width and length of the interscalene space and the width of the costoclavicular passage were measured on 18 cervical dissections in 9 cadavers, on 50 dry first ribs and on CT angiography sections from 15 patients whose conditions were not related to TOS.

RESULTS

The average width and length of the interscalene space in cadavers were 15.28 ± 1.94 mm and 15.98 ± 2.13 mm, respectively. The widths of the costoclavicular passage (12.42 ± 1.43 mm) were significantly narrower than the widths and lengths of the interscalene space in cadavers (P < 0.05). The average width and length of the interscalene space (groove for the subclavian artery) in 50 dry ribs were 15.53 ± 2.12 mm and 16.12 ± 1.95 mm, respectively. In CT images, the widths of the costoclavicular passage were also significantly narrower than those of the interscalene space (P < 0.05). The measurements from cadavers, dry first ribs and CT images were not significantly different (P > 0.05).

CONCLUSIONS

Our results showed that the costoclavicular width was the narrowest space along the passage route of the subclavian artery. When considering the surgical decompression of the subclavian artery for TOS, this narrowest area should always be kept in mind. Since measurements from CT images and cadavers were significantly similar, CT measurements may be used to evaluate the thoracic outlet region in patients with TOS.

Sonographic Guide for Botulinum Toxin Injections of the Neck Muscles in Cervical Dystonia

Intramuscular botulinum toxin (BoTX) injection is the first-line treatment of cervical dystonia. Poor treatment outcomes and some side effects, however, have been reported after BoTX applications. One of the most important reasons is incorrect localization of the needle during toxin injections. Without imaging, it is impossible to verify precise needle positioning in the proper muscle. Ultrasound has been recommended because of its high capability in illustrating most of the neck muscles. This review article discusses how ultrasound imaging can be used to scan/access neck muscles, mainly from the perspective of BoTX injections.

Effort thrombosis of the subclavian artery as a consequence of a unique anomaly

Congenital anatomic anomalies and variations are frequent in the thoracic outlet and may be associated with clinical symptoms. Arterial thoracic outlet syndrome (TOS) is characterized by subclavian artery compression and vascular pathology, almost always in the presence of a bony abnormality. We describe here a patient with arterial thromboembolism following a fall on the outstretched arm, who was found to have subclavian artery stenosis and post-stenotic dilatation in the absence of a bony abnormality. Surgical exploration revealed a previously undescribed anomaly in which the subclavian artery passed through the costoclavicular space in front of the anterior scalene muscle, where it was subject to bony compression between the first rib and clavicle. Successful treatment was achieved by scalenectomy, first rib resection and interposition bypass graft reconstruction of the affected subclavian artery. This newly acknowledged anatomical variant adds to our understanding of the diverse factors that may contribute to development of TOS.

Variations of Cords of Brachial Plexus and Branching Pattern of Nerves Emanating From Them

Brachial plexus is complex network of nerves, formed by joining and splitting of ventral rami of spinal nerves C5, C6, C7, C8, and T1 forming trunks, divisions, and cords. The nerves emerging from trunks and cords innervate the upper limb and to some extent pectoral region. Scanty literature describes the variations in the formation of cords and nerves emanating from them. Moreover, the variations of cords of brachial plexus and nerves emanating from them have iatrogenic implications in the upper limb and pectoral region. Hence study has been carried out. Twenty-eight upper limbs and posterior triangles from 14 cadavers fixed in formalin were dissected and rare and new variations of cords were observed. Most common variation consisted of formation of posterior cord by fusion of posterior division of upper and middle trunk and lower trunk continued as medial cord followed by originating of 2 pectoral nerves from anterior divisions of upper and middle trunk. Other variations include anterior division of upper trunk continued as lateral cord and pierced the coracobrachialis, upper and middle trunk fused to form common cord which divided into lateral and posterior cords, upper trunk gave suprascapular nerve and abnormal lateral pectoral nerve and formation of median nerve by 3 roots. These variations were analyzed for diagnostic and clinical significance making the study relevant for surgeons, radiologists in arresting failure patients and anatomists academically in medical education.

Ultrasonographic Diagnosis of Thoracic Outlet Syndrome Secondary to Brachial Plexus Piercing Variation

Structural variations of the thoracic outlet create a unique risk for neurogenic thoracic outlet syndrome (nTOS) that is difficult to diagnose clinically. Common anatomical variations in brachial plexus (BP) branching were recently discovered in which portions of the proximal plexus pierce the anterior scalene. This results in possible impingement of BP nerves within the muscle belly and, therefore, predisposition for nTOS. We hypothesized that some cases of disputed nTOS result from these BP branching variants. We tested the association between BP piercing and nTOS symptoms, and evaluated the capability of ultrasonographic identification of patients with clinically relevant variations. Eighty-two cadaveric necks were first dissected to assess BP variation frequency. In 62.1%, C5, superior trunk, or superior + middle trunks pierced the anterior scalene. Subsequently, 22 student subjects underwent screening with detailed questionnaires, provocative tests, and BP ultrasonography. Twenty-one percent demonstrated atypical BP branching anatomy on ultrasound; of these, 50% reported symptoms consistent with nTOS, significantly higher than subjects with classic BP anatomy (14%). This group, categorized as a typical TOS, would be missed by provocative testing alone. The addition of ultrasonography to nTOS diagnosis, especially for patients with BP branching variation, would allow clinicians to visualize and identify atypical patient anatomy.

Anatomical variations in the brachial plexus roots: implications for diagnosis of neurogenic thoracic outlet syndrome

Neurogenic thoracic outlet syndrome (NTOS) is the most common type of TOS. Typically it results from impingement of the neurovasculature as it passes between the anterior and middle scalene muscles; this classic anatomical relationship being the foundation of clinical diagnosis. Positional testing relies on vascular compromise occurring when the subclavian artery is compressed in this space. This study describes several anatomical variations observed in this relationship. Sixty-five cadavers (35m/30f) were assessed to determine the frequency and extent of brachial plexus branching variants. A total of thirty-one variations from "classic" anatomy were observed (47.7%). In two specimens (3.1%), the entire superior trunk coursed completely anterior to the anterior scalene in a position of relative vulnerability. In 27 instances, a portion of or the entire superior trunk pierced the anterior scalene muscle, and in two, the middle trunk also pierced the muscle belly. Interestingly, while two bilateral branching variations were observed, the majority occurred unilaterally, and almost exclusively on the left side. There were no sex differences in frequency. The high frequency of these variations and their potential to predispose patients to neurogenic TOS suggest that current diagnostic methods may be insufficient in clinical diagnosis. Due to lack of vascular compromise, patients with the piercing variant would not display positive signs on the traditional positional tests. The use of ultrasound to determine the route of the brachial plexus could determine whether this variation is present in patients who suffer from TOS symptoms but lack a diagnosis based on traditional positional testing.

Aberrant Dual Origin of the Dorsal Scapular Nerve and Its Communication with Long Thoracic Nerve: An Unusual Variation of the Brachial Plexus

Pre and post-fixed variations at roots of the brachial plexus have been well documented, however little is known about the variations that exist in the branches which arise from the brachial plexus. In this paper, we describe about one such rare variation related to the dorsal scapular and the long thoracic nerve, which are the branches arising from the roots of the brachial plexus. The variation was found during routine dissection. The dorsal scapular nerve, which routinely arises from the fifth cervical nerve root (C5), was seen to receive contributions from C5 as well as sixth cervical nerve (C6), while the long thoracic nerve arose from C6 and seventh cervical nerves (C7) only. Furthermore along with variations in origin of the dorsal scapular and long thoracic nerves, the brachial plexus was seen to exist as a prefixed plexus receiving a contribution from C4 nerve root. An aberrant communicating branch between the dorsal scapular and long thoracic nerve was also identified. Knowledge about the course and anatomy of such variations can be vital for understanding the aetiology of various conditions such as winging of scapula, interscapular pain, administration of cervical nerve blocks, surgeries and for effective management of regions and muscles supplied by dorsal scapular and long thoracic nerve.

The supraclavius muscle is a novel muscular anomaly observed in two cases of thoracic outlet syndrome

Various anomalous muscles and fibrofascial structures have been described in relation to the anatomy of thoracic outlet syndrome. We describe two patients with a previously undescribed muscle anomaly, which originated laterally near the trapezius muscle, coursed across the supraclavicular space deep to the scalene fat pad, and attached obliquely to the superior undersurface of the medial clavicle, which we have termed the “supraclavius” muscle. The significance of the supraclavius muscle is unknown, but its occurrence in patients with thoracic outlet syndrome indicates that it can be associated with narrowing of the anatomic space adjacent to the neurovascular structures.

Thoracic outlet syndrome in a patient with absent scalenus anterior muscle

This case report describes the rare anomaly of an absent right anterior scalene muscle presenting with the symptoms and signs of the thoracic outlet syndrome. The thoracic outlet syndrome in our patient can be attributed to the absence of the right anterior scalene muscle, which resulted in the brachial plexus being in proximity to the subclavian vein and artery in a narrowed and abnormal interscalene space. In addition, the absence of the anterior scalene muscle resulted in the neurovascular structures being compressed onto the first rib in the costoclavicular space. The most likely cause of the presentation is, however, the possibility of the presence of aberrant muscle slips, which would cause compression of the structures in the anterior (venous) and posterior (neurological) sections of the thoracic outlet.

Ultrasound guided therapeutic injections of the cervical spine and brachial plexus

Introduction: Recent applications in ultrasound imaging include ultrasound assessment and ultrasound guided therapeutic injections of the spine and brachial plexus. Discussion: Ultrasound is an ideal modality for these regions as it allows accurate safe and quick injection of single or multiple sites. It has the added advantages of lack of ionising radiation, and can be done without requiring large expensive radiology equipment. Conclusion: Brachial plexus pathology may be present in patients presenting for shoulder symptoms where very little is found at imaging the shoulder. It is important to understand the anatomy and normal variants that may exist to be able to recognise when pathology is present. When pathology is demonstrated it is easy to do a trial of therapy with ultrasound guided injection of steroid around the nerve lesion. This review will outline the normal anatomy and variants and common pathology, which can be amenable to ultrasound guided injection of steroid.

Brachial plexus anesthesia: A review of the relevant anatomy, complications, and anatomical variations

The trend towards regional anesthesia began in the late 1800s when William Halsted and Richard Hall experimented with cocaine as a local anesthetic for upper and lower limb procedures. Regional anesthesia of the upper limb can be achieved by blocking the brachial plexus at varying stages along the course of the trunks, divisions, cords and terminal branches. The four most common techniques used in the clinical setting are the interscalene block, the supraclavicular block, the infraclavicular block, and the axillary block. Each approach has its own unique set of advantages and indications for use. The supraclavicular block is most effective for anesthesia of the mid-humerus and below. Infraclavicular blocks are useful for procedures requiring continuous anesthesia. Axillary blocks provide effective anesthesia distal to the elbow, and interscalene blocks are best suited for the shoulder and proximal upper limb. The two most common methods for localizing the appropriate nerves for brachial plexus blocks are nerve stimulation and ultrasound guidance. Recent literature on brachial plexus blocks has largely focused on these two techniques to determine which method has greater efficacy. Ultrasound guidance has allowed the operator to visualize the needle position within the musculature and has proven especially useful in patients with anatomical variations. The aim of this study is to provide a review of the literature on the different approaches to brachial plexus blocks, including the indications, techniques, and relevant anatomical variations associated with the nerves involved.

Standard approaches for upper extremity nerve blocks with an emphasis on outpatient surgery

PURPOSE OF REVIEW

Currently, no standards exist with regard to the techniques and administration of ultrasound-guided peripheral nerve blocks. Consequently, the techniques and teaching substantially vary among practitioners and institutions. The purpose of this review is to propose a set of standard US-guided techniques for upper extremity nerve blocks.

RECENT FINDINGS

On the basis of the synthesis of information in available literature and the consensus of an internationally recognized collaborative panel of regional anaesthesia experts, the review recommends a standardized approach to common upper extremity nerve blocks using ultrasound guidance.

SUMMARY

A set of structured recommendations and approaches are suggested to help standardize clinical practice and teaching of ultrasound-guided upper extremity nerve blocks. Additional emphasis is placed on the discussion of nerve blocks in outpatient surgery.

Thoracic outlet syndrome: a neurological and vascular disorder

Thoracic outlet syndrome (TOS) is a condition arising from compression of the subclavian vessels and/or brachial plexus as the structures travel from the thoracic outlet to the axilla. Despite the significant pathology associated with TOS, there remains some general disagreement among experts on the specific anatomy, etiology, and pathophysiology of the condition, presumably because of the wide variation in symptoms that manifest in presenting patients, and because of lack of a definitive gold standard for diagnosis. Symptoms associated with TOS have traditionally been divided into vascular and neurogenic categories, a distinction based on the underlying structure(s) implicated. Of the two, neurogenic TOS (nTOS) is more common, and typically presents as compression of the brachial plexus; primarily, but not exclusively, involving its lower trunk. Vascular TOS (vTOS) usually involves compression of the vessel, most commonly the subclavian artery or vein, or is secondary to thrombus formation in the venous vasculature. Any anatomical anomaly in the thoracic outlet has the potential to predispose a patient to TOS. Common anomalies include variations in the insertion of the anterior scalene muscle (ASM) or scalenus minimus muscle, the presence of a cervical rib or of fibrous and muscular bands, variations in insertion of pectoralis minor, and the presence of neurovascular structures, which follow an atypical course. A common diagnostic technique for vTOS is duplex imaging, which has generally replaced more invasive angiographic techniques. In cases of suspected nTOS, electrophysiological nerve studies and ASM blocks provide guidance when screening for patients likely to benefit from surgical decompression of TOS. Surgeons generally agree that the transaxillary approach allows the greatest field of view for first rib excision to relieve compressed vessels. Alternatively, a supraclavicular approach is favored for scalenotomies when the ASM impinges on surrounding structures. A combined supraclavicular and infraclavicular approach is preferred when a larger field of view is required. The future of TOS management must emphasize the improvement of available diagnostic and treatment techniques, and the development of a consensus gold standard for diagnosis. Helical computed tomography offers a three-dimensional view of the thoracic outlet, and may be valuable in the detection of anatomical variations, which may predispose patients to TOS. This review summarizes the history of TOS, the pertinent clinical and anatomical presentations of TOS, and the commonly used diagnostic and treatment techniques for the condition.

High-resolution sonography detects extraforaminal nerve pathology in patients initially diagnosed with cervical disc disease: a case series

In patients presenting with neck and upper limb complaints, MRI changes suggestive of cervical disc disease do not exclude concomitant extraforaminal pathology, as shown in the series of three cases presented here. High-resolution ultrasound of the brachial plexus and peripheral nerves may be useful in identifying an extraforaminal pathology when (1) symptoms and signs are disproportionate to MRI findings of cervical disc disease; (2) there is obvious discordance between MRI and nerve conduction findings; (3) an entrapment neuropathy is suspected but the site of nerve lesion is unidentifiable on the basis of available investigations and clinical findings.

MRI findings in thoracic outlet syndrome

We discuss MRI findings in patients with thoracic outlet syndrome (TOS). A total of 100 neurovascular bundles were evaluated in the interscalene triangle (IS), costoclavicular (CC), and retropectoralis minor (RPM) spaces. To exclude neurogenic abnormality, MRIs of the cervical spine and brachial plexus (BPL) were obtained in neutral. To exclude compression on neurovascular bundles, sagittal T1W images were obtained vertical to the longitudinal axis of BPL from spinal cord to the medial part of the humerus, in abduction and neutral. To exclude vascular TOS, MR angiography (MRA) and venography (MRV) of the subclavian artery (SA) and vein (SV) in abduction were obtained. If there is compression on the vessels, MRA and MRV of the subclavian vessels were repeated in neutral. Seventy-one neurovascular bundles were found to be abnormal: 16 arterial-venous-neurogenic, 20 neurogenic, 1 arterial, 15 venous, 8 arterial-venous, 3 arterial-neurogenic, and 8 venous-neurogenic TOS. Overall, neurogenic TOS was noted in 69%, venous TOS in 66%, and arterial TOS in 39%. The neurovascular bundle was most commonly compressed in the CC, mostly secondary to position, and very rarely compressed in the RPM. The cause of TOS was congenital bone variations in 36%, congenital fibromuscular anomalies in 11%, and position in 53%. In 5%, there was unilateral brachial plexitis in addition to compression of the neurovascular bundle. Severe cervical spondylosis was noted in 14%, contributing to TOS symptoms. For evaluation of patients with TOS, visualization of the brachial plexus and cervical spine and dynamic evaluation of neurovascular bundles in the cervicothoracobrachial region are mandatory.

Thoracic outlet syndrome: a controversial clinical condition. Part 1: anatomy, and clinical examination/diagnosis

Thoracic outlet syndrome (TOS) is a frequently overlooked peripheral nerve compression or tension event that creates difficulties for the clinician regarding diagnosis and management. Investigators have categorized this condition as vascular versus neurogenic, where vascular TOS can be subcategorized as either arterial or venous and neurogenic TOS can subcategorized as either true or disputed. The thoracic outlet anatomical container presents with several key regional components, each capable of compromising the neurovascular structures coursing within. Bony and soft tissue abnormalities, along with mechanical dysfunctions, may contribute to neurovascular compromise. Diagnosing TOS can be challenging because the symptoms vary greatly amongst patients with the disorder, thus lending to other conditions including a double crush syndrome. A careful history and thorough clinical examination are the most important components in establishing the diagnosis of TOS. Specific clinical tests, whose accuracy has been documented, can be used to support a clinical diagnosis, especially when a cluster of positive tests are witnessed.