Introduction
The stellate ganglion (SG) in sympathetic chain is the result of fusion of the 8th cervical and first thoracic ganglia.1 The first rib and subclavian artery serve as important anatomical landmarks to locate the SG.2 It is a particularly attractive nexus point for targeting sympathetic outflow to the heart given that preganglionic to postganglionic neurotransmission occurs predominantly here.3 The correlation between the sympathetic nervous system (SNS) and arrhythmogenesis has long been studied in animal models4 and in humans.5 For arrhythmia control Cardiac sympathetic denervation, involving removal of lower half of the stellate ganglion, and the 2nd through 4th segment (T2-T4) of the sympathetic chain was used as treatment modality for almost a century; however, its efficacy was challenged time to time and still requires further investigation.6, 7
In clinical practice Stellate ganglion block (SGB) is frequently used for the treatment of various medical conditions by injecting a local anesthetic around stellate ganglion (SG). It influences both the central and peripheral nervous system. In central nervous system it influences the hypothalamus, known for regulating the systemic autonomic nervous, immune, and endocrine systems and to maintain homeostasis and normal cardiovascular function.8 Physiologically Peripheral nervous system regulates vascular dilatation and constriction, muscular movement, bronchial smooth muscle relaxation and contraction, and pain conduction.9 Clinically this procedure is adopted for modulating sympathetically mediated pain affecting the head, neck and upper limbs as a routine protocol.10, 11 Stellate ganglion block (SGB) has inhibitory control over sympathetic innervation and can be used for treatment of reflex sympathetic dystrophy as well.
Ultra-sonography (US) guided procedures are advocated for their safety and efficacy by direct visualization of the soft tissues, bony surfaces, and dynamic tracing of the needle path and the spread/ absorption of drugs. SGB under US guidance is considered more accurate and greatly reduces complications than the blind technique.12, 13
As Stellate (cervicothoracic) ganglion block (SGB) can be associated with serious complications, such as esophageal and vascular injury, the sonological anatomy of the neck and relevant structures for the SGB at the sixth (C6) and seventh (C7) cervical vertebral levels is crucial. Therefore, for determining the intervening course of blood vessels and esophagus in the simulated path of needle insertion ultrasound-guided approaches can be preferred over in the conventional to perform a SGB.14
Anterior cervical surgery for the treatment of cervical vertebral body lesions, including tumor infection and trauma is complex, which increases surgical difficulty and risk. Sympathetic nerve injury, a complication of the surgery, has been studied and commonly associated with Horner's syndrome.15, 16
Materials and Methods
Cadaveric part
Both the right and left stellate ganglia were identified in 15 formaldehyde embalmed adult cadavers (Male-9, Female -6) lying anterior to the C7 transverse process or neck of the first rib on each side, and identification of the course of subclavian artery, vertebral artery was done meticulously. Ganglia were dissected and removed completely.
After cleaning Ganglia were a placed on a towel for examination. The measured morphologic details include weight, the length of the ganglia in the superior-inferior axis and Volume (in milliliter, mL) which was measured by water displacement.
Ultra-sonographic (US) part
After approval By Ethical Committee study was conducted on total 50 adult patients (14 men and 36 women), with an average age of 25.22 ± 5.46 years (range 21–46 years). The inclusion criteria were age ≥18 years, with no history of neck irradiation and neck surgery or trauma.
All US examinations were performed by a trained sonologist using an 18 MHz linear-array transducer (Toshiba Aplio 500, Japan). Examination performed in the supine position with slightly turned their necks to the opposite side. The participants were asked to lie while relaxing their necks. Initially, the ultrasound transducer was placed on the neck in transverse plane and scanned from up to down, up to the C7 transverse process, and down to the supraclavicular fossa. SG was located between the carotid sheath and the Longus Coli Muscle.
Thus under US guidance Length, shape, echogenicity, margin, the inferior pole of SG, the relationship between the superior pole of SG and the transverse process of C7, and the relationship between the superior pole of SG and the inferior thyroid artery were evaluated. In addition, the relationships between SG and other surrounding tissues, such as thyroid gland, scalenus anterior muscle, and vagus nerve, were also evaluated.
The degree of deviation of the esophagus relative to the larynx/trachea as well as the likelihood of encountering a vessel in the simulated path of needle insertion in C7 approach to SGB; the incidence of the vertebral artery being situated outside the foramen transversarium at the C6 level; and the distance of the simulated path of needle insertion in the anterior and lateral approaches to SGB at the C7 level was assessed.
Results
Cadaveric part
A total of 30 left and right stellate ganglia from 15 cadavers (Male-9, Female -6) were examined with mean age was 72.6 ± 13.6 years, causes of death included coronary artery disease, congestive heart failure and cardiopulmonary arrest.
Morphologically, the 30 stellate ganglia, independent of laterality, could be sorted into three gross categories: fusiform-rounded, fusiform-elongated, and bi-lobed. In fusiform ganglia, there is complete fusion of C8 and T1, such that the two ganglia are indistinguishable. However, as the names indicate, rounded ganglia have a spherical appearance while elongated ganglia appear finger-like. Bi-lobed SG are identified as two adjacent ganglia (superior-inferior) connected by a stalk.
Results
Table 3
Morphometry and relations of RSG on Ultra-Sonography
Table 4
Morphometry and relations of LSG on ultra-sonography
Discussion
Anatomy of SG- findings of cadaveric studies
The cervical sympathetic chain has always been the subject of investigation for researchers due to its therapeutic uses, and susceptibility to injury during surgical dissections in the neck. Multiple anatomical studies on the cervicothoracic/stellate ganglion have identified such a ganglion in 37-100% of cadavers studied,17 however whether significant difference exist between sides is not well understood.
Yin et al. in their study compared the appearance of LSG and RSG (and cervical sympathetic chain) in Chinese cadavers, recording significant lateral asymmetry, although morphologic characteristics of the ganglia (length, width, and thickness) were similar.18 Zhang et al. In examining the anatomic variations of the upper thoracic sympathetic chain (including the SG), found bilateral symmetry in only 16% of cases.19 A study from Marcer et al, shows significant morphological heterogeneity (five different shapes identified), although histologic confirmation of neuronal somata was not performed.20 Although these studies have demonstrated anatomic dissimilarity between LSG and RSG, study by Known et al6 simultaneously mapped the adult SG morphologically and identify the distribution of neuronal somata within the ganglia histologically. The superior-inferior length of the ganglia in their study is consistent with findings from prior studies in adults like Pather et al., Marcer et al., and Yin et al.18
Anatomy of sg- comparative analysis of ultrasonographic studies
Studies by Civlek et al and Won et al showed that the cervical sympathetic chain, including SG, is usually located posteromedial to the carotid sheath and anterior to the Longus Colli Muscle (LCM), between the C7 transverse process and the first rib.21, 22
In present study encountered Ultrasound limitations in identifying the first rib from the second rib. While the first rib was identified easily being adjacent to the supraclavicular fossa. Therefore, we chose the supraclavicular fossa as the landmark on US images.
This study demonstrated that the inferior poles of 15% SGs were not clearly visible, which may be due to the fact that the inferior poles of some SGs were obscured by the bone tissue, so it was difficult to note accurately with US. When we analyzed the relationship between the superior pole of SG and the inferior thyroid artery, we found that most of the superior pole of SGs were located under the inferior thyroid artery. This finding may be beneficial to localize the position of SG in the clinical practice. The location of the SG was found variable. Therefore, we divided subjects depending upon the position of SG into two types, at the C7 transverse process level and behind the C7 transverse process level. In addition, the superior poles of 73% SGs was located to the C7 transverse process level, and the superior poles of 27% SGs was located to behind the C7 transverse process level. The result was in line with finding in a cadaver study by Kiray et al, 23 which showed that the upper pole of the SG was located at the C7 transverse process level in 63.2% of specimens, and the remaining 36.8% of specimens were located between the first rib and the C7 transverse process. However, another cadaver study by Saylam et al. has shown some differences, revealing that 40% SG/inferior ganglion were located at the level of C7, 25% at the level of C7-Th1 disc, and 35% at the level of T1.24 Different study samples might be the reason for this relevant discrepancy.
The major limitation of the study was that the verification of histology concerning SG was not performed. Finally to reduce the possibility of misdiagnosis on US examination, SG was needed to satisfy the following conditions: (1) the nodular structure; (2) between the carotid sheath and the LCM; (3) between the the supraclavicular fossa and C7 transverse process (4) can be seen on the transverse section and the longitudinal section. The efficacy of US-guided SGB by identifying and monitoring SG itself should be further evaluated in future clinical practice. 11
Surgical considerations
Stellate ganglion block (SGB) inhibits sympathetic innervation and is a common modality of treatment for reflex sympathetic dystrophy.25 As Cardiac electrophysiology is under regulatory control of the autonomic nervous system (ANS), SGB has its definitive role in treatment of arrhythmia.
Cervical Sympathetic Trunk (CST) injury is most commonly caused by excessive exposure of the outer surface of the bone in front of the lower cervical vertebral body. Cutting off the CST in operation is known while stripping or excessively stretching the LCM. Among the reasons recorded, excessive exposure of the cervical anterior lateral part or the transverse foramen and consequent excessive stretching of the LCM were the main reasons that the CST was injured.26 Lu et al concluded that any injury of the CST in front of the lower cervical spine could cause Horner syndrome.27 Therefore, during anterior lower cervical operations, hooks should not be placed above the LCM, and there is no need to expose the sympathetic trunk; a little blunt dissection below the inner edge of the LCM, placing the retractor under the LCM and pulling carefully for the sake of avoiding sympathetic trunk injury may serve the purpose. Sometimes, the position of the middle cervical ganglion must be identified during surgery.18
Significance of present study
The findings of the present study suggest that the variable morphology of the SG is deciding factor for surgical outcome. Knowledge of the ganglia’s morphology may allow greater precision and accuracy in the transection or block the SG during stellate ganglionectomy/block towards treatment of arrhythmias, potentially improving both the safety and efficacy of the procedure.
Most US findings were similar to cadaver studies in our research which need to be backed up with histological examination. Our preliminary study demonstrates that US imaging provides the capability of precisely detecting SG. This may be helpful in reducing complications and improving the accuracy of US-guided SGB.
Familiarity with the adjacent anatomical characteristics of the LCM and CST could contribute to identifying the sympathetic trunk correctly during surgery and reducing the occurrence of surgical complications.
Conclusion
SG appear in three major forms and contain varying distributions of somata. Larger studies are warranted to define the relationship between gross anatomy and distribution of neuronal somata to improve the efficacy of Clinical procedures. Ultrasonographic guided SGB may improve safety and allows the visualization of the local anesthetic depot. Studying the local anesthetic spread might allow the avoidance of side effects as well as typical complications of SGB.
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