|Year : 2021 | Volume
| Issue : 1 | Page : 25-29
A Study of Brachial Plexus Sheath and Dye Spread Through the Sheath in Single- and Multi-Directional Injections in Cadaver
Subhramoy Chaudhury1, Anasuya Ghosh2
1 Associate Professor, Department of Anatomy, Medical University of the Americas, Charlestown, Nevis, West Indies
2 Assistant Professor, Department of Anatomy, All India Institute of Medical Sciences, Kalyani, West Bengal, India
|Date of Submission||28-Aug-2020|
|Date of Decision||11-Oct-2020|
|Date of Acceptance||18-Dec-2020|
|Date of Web Publication||27-Jan-2021|
Department of Anatomy, All India Institute of Medical Sciences, NH-34 Connector, Basantapur, Saguna Kalyani, Kalyani - 741 245, West Bengal
Source of Support: None, Conflict of Interest: None
Background: The in-depth understanding of the anatomy of brachial plexus (BP) sheath is very important for the successful application of BP block. The flow dynamics of injectable anesthetic might vary depending on the site and mode of injection. The objectives of this study were to explore and document the detailed anatomy of BP sheath and to compare the dye spread by injections given in single direction and multi-directional approaches in formalin-fixed cadavers. Materials and Methods: This study is a descriptive, observational, and cross-sectional study based on findings on cadaver dissection and injecting dye in cadavers. Twenty-four sides of 12 well-embalmed cadavers were utilized for injecting dye solution into the intact brachial sheath by single-direction and multi-direction injection approaches at the axillary level. All the cadavers were dissected to compare the spread of dye in two approaches. In addition, one more cadaver was utilized for a detailed dissection of the infraclavicular part of BP sheath and its contents without injecting dye. Microsoft Excel software was used for statistical analysis. Results: We observed BP sheath was a fibrous connective tissue sheath-containing multiple neurovascular structures, all of which had individual delicate connective tissue wrapping around them. More uniform dye spread was observed in multi-direction approaches and the musculocutaneous nerve was stained more frequently in multi-direction approach. Conclusions: The presence of delicate porous connective tissue wrapping gives a tunnel-like appearance of the infraclavicular part of BP sheath. Multi-directional injections resulted in dye staining of the larger area involving more structures than single-direction injections.
Keywords: Brachial plexus block, brachial sheath, dye spread in brachial sheath
|How to cite this article:|
Chaudhury S, Ghosh A. A Study of Brachial Plexus Sheath and Dye Spread Through the Sheath in Single- and Multi-Directional Injections in Cadaver. Natl J Clin Anat 2021;10:25-9
|How to cite this URL:|
Chaudhury S, Ghosh A. A Study of Brachial Plexus Sheath and Dye Spread Through the Sheath in Single- and Multi-Directional Injections in Cadaver. Natl J Clin Anat [serial online] 2021 [cited 2021 Feb 25];10:25-9. Available from: http://www.njca.info/text.asp?2021/10/1/25/308113
| Introduction|| |
The brachial plexus (BP) sheath can be described as a fibrous connective tissue sheath around the BP structures and adjacent vessels. Good understanding of BP sheath anatomy plays an instrumental role during administering a regional BP block for the perioperative anaesthesia and surgical excision of neural sheath schwannomas and neurofibromas affecting the BP structures.,,,, The published literature has conflicting and debatable theories regarding the BP sheath if it is a dense tubular single tunnel-like structure,, or a multi-compartment tunnel-like structure with delicate septa around each nerve.,,,
The functional anatomy of BP sheath still needs further exploration. The aim of this study is to explore and understand the anatomy of the infraclavicular part of BP sheath and compare the spread of injectable dye solution in single-direction and multi-direction approaches through the brachial sheath in cadaver.
| Materials and Methods|| |
The study was conducted at the anatomy dissection lab of our institution after approval from the Institutional Ethics committee (dated - 17.12.18). It was an observational, cross-sectional, descriptive study.
Formalin embalmed cadaveric upper limbs were dissected for exposure of infra-clavicular part of BP sheath over a period of 9 months. Seven male and 6 female cadavers (total 13 cadavers) were selected for this study, aged between 79 and 87 years and without any obvious pathology in the upper arm and neck region. 12 cadavers were used for injecting dye directly into the brachial sheath and one cadaver was utilized to explore the brachial sheath anatomy without injecting dye. The standard dissection method for the upper limb was followed to reflect the skin of the pectoral region and arm. Subcutaneous tissue was removed to expose the pectoralis major muscles, the muscle was reflected along its clavicular attachment, to expose the pectoralis minor muscle deep to which lies infraclavicular part of BP sheath. The loose connective and fatty tissue around the BP sheath was cleaned with great care to keep the sheath as intact as possible [Figure 1]. The thickness of the brachial sheath was observed with the naked eye and was felt with fingers. Some part of it which appeared tough and opaque was considered as thick area and the part of it appearing as transparent delicate membrane-like was considered as thin area.
|Figure 1: Intact brachial sheath. BPS: brachial plexus sheath, BB: Biceps brachii muscle, PM: Pectoralis minor muscle|
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All the arms were minimally abducted to prevent tearing of formalin-fixed muscle, the elbow was kept extended for the same reason. An 18G needle was used to inject the dye into the intact BP sheath from the medial aspect. Methylene blue dye was dissolved in gelatin solution and was injected in the BP sheath under direct vision by single direction (12 sides) and multi-direction approaches (12 sides). The needle was inserted at the lower border of teres major muscle and the tip of the needle was placed medially towards superficial aspect of the brachial artery in single direction injection. For the multi-direction approach, the needle tip was placed at the lower border of teres major muscle and the tip was directed at following directions-toward tip of the coracoid process, toward the superficial aspect and deeper aspect of the brachial artery. We chose this landmark following the axillary BP block technique for this study and placed the needle at the lower border of teres major as it is a fixed anatomical landmark and easily approachable in a dissected cadaver without any need of ultrasonic aid/nerve stimulator. In 12 cadavers, all the right upper limbs (12 sides) were utilized for single-direction technique and all the left upper limbs (12 sides) were utilized for multi-direction technique. In all cases, 10 ml dye solution was injected very slowly for 1 min for both approaches.
After the injection was applied, the arms were left undisturbed for 30 min. After 30 min, the BP sheaths were incised and the cords were exposed to observe the spread of dye in single and multi-direction approaches. The spread of dye in the surrounding soft-tissue proximal and distal to the injection site was noted too.
In addition, we dissected both upper limbs of one male cadaver to observe the anatomy of BP sheath in details without injecting any dye.
During the whole process, photographs were taken at different stages.
| Results|| |
We observed the BP sheath enclosing the infraclavicular part of BP was located on the medial aspect of the biceps brachii muscle in the arm. The BP sheath was a well visible deep facial sheath wrapping around the BP structures and axillary and brachial artery. We observed the thickness of BP sheath varied in different regions. The thickness of the sheath was more on the proximal part of the arm and the posterior wall of the sheath was thicker than anterior or medial aspects and beyond mid-arm the sheath became thinner and thinner. We noticed the sheath was externally covered with variable amounts of fats blending with loose connective tissues of the axilla. The sheath was pierced by blood vessels at different levels.
We observed the spread of dye varied around different cords and branches and some differences were noticed, between single and multi-direction injection approaches [Figure 2].
|Figure 2: BP cord staining achieved in multi-shot versus single shot approach. Dark grey bars-multi shot approach, light grey bars-single shot approach|
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In single-direction approach, maximum dye concentration was noticed around the lateral cords in all 12 cases and in 6 cases the dye concentrated around all three cords. In only 2 cases, the dye stained the musculocutaneous nerve.
In multi-direction approach, the lateral cord was deeply stained in all 12 cases. All lateral, medial, and posterior cords were stained in 8 cases, though in 6 cases all the cords were stained uniformly and in two cases the lateral cord was deeply stained than the medial and posterior cord. The musculocutaneous nerve was noticed to be faintly stained in 6 cases.
In a single direction approach, we saw the spread of dye proximally extending up to the tip of the coracoid process and distally spread noted till midshaft of the humerus. In multi-direction approach, the proximal extension was up to the root of the neck above the clavicle and retrograde stain spread was noted beyond the mid-arm.
Tissue leakage of dye was noted in the arm (around brachialis muscle) and posterior wall of the axilla (subscapularis muscle) in single shot, whereas in multiple shot dye stain was noted at the root of the neck besides the arm and axilla [Figure 3].
|Figure 3: Tissue spread of dye in multi shot versus single shot approach. Light grey line-multi-shot approach, dark grey line-single shot approach|
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In naked eye observation, we found the BP sheath wrapped around the cords and branches of the BP and brachial or axillary artery blends with superficial fascia of axilla covering around the axillary veins and lymphatics. With careful dissection, we could separate the BP sheath from the superficial fascia around the axillary vein keeping the BP sheath intact.
On gross dissection of BP sheath, we tried to separate the nerves within the BP sheath keeping the sheath intact as much as possible to explore if the internal compartments exist within the BP sheath or not. In our case, we successfully separated the axillary vein, musculocutaneous nerve, median nerve out of the BP sheath keeping the rest of it, and the contents in place [Figure 4]. While separating we noticed very thin lacelike membranes mixed with variable amount of fat wrapping around individual BP nerves and kept them separate within the BP sheath.
|Figure 4: Separated axillary vein, musculocutaneous nerve and median nerve from rest of brachial sheath. MN: Median nerve, MC: Medial cord, LC: Lateral cord, MCN: Musculocutaneous nerve, BPS: Brachial plexus sheath, AV: Axillary vein with fascial sheath, CB: Coracobrachialis muscle, BB: Biceps brachii muscle|
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| Discussion|| |
In the current study, we explored the anatomy of BP sheath. We observed the dye spread within BP sheath after single and multi-directional injections following the axillary approach of BP block in formalin-fixed cadavers.
Configuration of BP sheath
BP sheath was first narrated by Burnham et al. and other researchers including Franco et al. reconfirmed it., The BP sheath was thought to be the continuation of the prevertebral layer of deep cervical fascia, although Feigl and Marhofer opined it is formed by epineural sheath which is a continuation of duramater and the number of septa between neurovascular contents increased distally. According to Thompson and Rorie, the BP sheath is a multi-compartment entity where connective tissue septa run from inner layers of the sheath to BP structures, the compartments around cords of BP are distally continuous with the median and ulnar nerves, and there are possible routes of drug exchange between compartments. On the contrary, an article by Brenner et al. claimed inconsistent existence of the fascial layer within the BP sheath. We could not find any solid physical septa separating the BP branches or cords from each other, but we found that all contents within the BP sheath had individual very delicate connective tissue membranes around them. Our study observation supports the explanation provided by Partridge et al. [Table 1].
|Table 1: Summary of findings related to configuration of brachial sheath|
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Spread of dye and nerve staining
In the present study, we observed a differential spread of dye following single or multi-direction injections within the BP sheath [Figure 5] and [Figure 6], whereas Cornish and Leaper used continuous catheter system for dye spread. We noticed the dye concentration was highest around the lateral cords in all the cases. We also observed the dye spread comparably around the lateral, medial, and posterior cords both in single and multiple directions inject and the difference was not very prominent. However, more uniform and all around spread of dye was noted with multi-directional injections. Lahori et al. demonstrated more or less similar grade of nerve block with the axillary and infra-clavicular approach by multiple and single injection, respectively, in a clinical study. Flohr-Madsen et al. achieved satisfactory nerve block by injecting 19 ml drug in a single shot in living and their findings have similarity with current study though their study subjects and methodology was different.
|Figure 5: Spread of dye in a single direction injection. BB: Biceps Brachii, PC: Posterior cord, LC: Lateral cord, MC: Medial cord, MCN: Musculocutaneous nerve|
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|Figure 6: Spread of dye in multi-direction injection. BS: BP sheath, MC: Medial cord, PC: Posterior cord, LC: Lateral cord, MN: Median nerve, A: Axillary artery|
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We noticed the musculocutaneous nerve (MCN) got the dye stains more frequently (50%) when the injection was applied in multi-direction approach [Figure 7]. However, Partridge et al. observed single injection was sufficient to stain most nerves immediately in the axillary approach. Karpal et al. and Fleischmann et al. considered the infraclavicular approach as a better one to block a greater number of nerves including MCN, [Table 2].
|Figure 7: Musculocutaneous nerve staining achieved in multi shot versus single injections. Light grey bar-multi shot, Dark grey bar-single shot|
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Spillage of dye in surrounding tissue
We observed the dye spilled out into surrounding tissues which possibly explains the BP sheath is most likely porous in nature and the dye can leak out with time and pressure. Similar observations were noted by Partridge et al. The nature of dye spread in the current study probably explains the possible complications like unwanted phrenic nerve block and impaired diaphragmatic movement observed by Rettig et al. although the study methodology was different. In living, several factors including surgery, movements of the chest wall and joint, and blood flow might expedite the tissue permeation of injected material.
The main limitation of this study is it was performed on formalin embalmed cadavers which are never the ideal one to compare the spread of anesthetic with a living body. We compared the spread of dye in single direction versus multi-direction approach in the same formalin-fixed cadavers. We did not exactly recreate the technique of injecting anesthetic during axillary or infraclavicular BP block what is done in real life due to some technical issues. The other limitation of our study is our findings were based on cadaver only and no experimentation was done on living in the real clinical setting. Future studies should include freshly frozen or soft embalmed cadavers and microanatomy observations should be included to bring out more accurate conclusions about BP sheath configuration.
| Conclusions|| |
The present study supports the existence of very delicate individual membranous sheaths around each content of the infraclavicular part of the BP sheath. A more uniform distribution of injected drug can be expected in multi-directional approaches in comparison to single direction injection. MCN block is more likely to be achieved with multi-direction technique although this procedure has higher chances of unwanted nerve blocks.
The authors like to express their sincere gratitude towards those who donated their bodies to the department of Human body structure-function for medical science and education; without their generosity and kindness, this work could not have been done.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2]