A Heat Map of Superior Cervical Ganglion Location Relative to the Common Carotid Artery Bifurcation

Abstract

BACKGROUND: 

Determining the superior cervical ganglion's precise anatomical location for local anesthetic block, when stellate block is not feasible or is contraindicated, is difficult.

METHODS: 

We dissected the superior cervical ganglion in 60 embalmed cadaveric specimens. Multiple regressions determined whether subject characteristics predicted the distance between the superior cervical ganglion and common carotid artery bifurcation and the superior cervical ganglion dimensional width and area. Based on these regressions, we mapped the ganglion and common carotid artery bifurcation using a pseudocolor statistical heat map.

RESULTS: 

The statistical model significantly predicted the superior cervical ganglion–common carotid artery bifurcation distance (P = 0.01), and the superior cervical ganglion dimensional width (P = 0.02).

CONCLUSION: 

This study determined that the common carotid artery bifurcation is a good landmark for localizing the superior cervical ganglion for anesthetic block.

In Brief

Published ahead of print November 21, 2011

Vasospasm of the cerebral arteries is the leading cause of death and disability in patients recovering from aneurysmal subarachnoid hemorrhage.^1–3 Various pharmacological therapies to minimize or prevent vasospasm are being developed and have been attempted for clinical use, but with mixed results.^1,4,5 Another strategy for minimizing or preventing vasospasm is to temporarily interrupt the sympathetic innervation to the cerebral blood vessels by using a sympathetic ganglion block.^6,7 The cerebral blood vessels are highly innervated by sympathetic fibers originating from the superior cervical and stellate ganglia.⁸ These ganglia are classically localized to vertebral levels, but across individuals are variably positioned.^9,10 Because all cervical sympathetic fibers pass through the stellate ganglion and enter the head either via the vertebral artery or via the internal carotid artery from the superior cervical ganglion, the stellate ganglion has been the preferred choice for complete sympathetic block to the head.^6,7,11 However, stellate ganglion block can result in minor or serious complications.¹²

As an alternative to stellate ganglion block, Treggiari et al.² performed superior cervical ganglion blocks to improve cerebral perfusion in patients with cerebral vasospasm after aneurysmal subarachnoid hemorrhage. The present study builds on the work of Treggiari et al. by systematically determining the location of the superior cervical ganglion relative to the common carotid artery bifurcation, a landmark that is easily identifiable using ultrasound imaging.¹³

METHODS

Subject Demographics

This study involved an opportunity sample of human cadaveric material obtained from the UCLA (University of California, Los Angeles) Donated Body Program (DBP) that was previously used for educational purposes. The DBP provided demographic statistics (age, gender, weight, race) to the investigators of the study; personal information of the donors is held confidentially and securely by the DBP. Consistent with university IRB policy on biological specimens, IRB approval was not necessary. Subject demographics and group statistics (mean [SE]) included 15 males and 15 females; age: 79.1 (2.6) years; height: 1.7 (0.02) m; weight: 70.5 (3.2) kg; and race: Caucasian (27), Latino (1), African American (1), and Asian/Pacific Islander (1).

Measurements and Statistical Analysis

Removal of soft tissue structures surrounding the carotid triangle exposed the fascial layers associated with the neurovascular structures in the parapharyngeal spaces of both sides of the neck in all 30 subjects. We defined the extent of the superior cervical ganglion physically by palpation (differentiating it by its swelling) and by visual inspection (defined as being discernibly wider than the nonganglion part of the sympathetic cervical chain). We measured the distance of the inferior pole of the superior cervical ganglion to the common carotid artery bifurcation (operationally defined as the point where the external and internal carotid arteries could be distinguished from the carotid sinus) (Fig. 1). We also measured the ganglion's length, area, maximum width, and center width on each side.

Figure 1: Schematic (lateral view) (a) and example of a dissected specimen (anterolateral view) (b) from the right side. The common carotid artery bifurcation in (b) was pulled laterally from the superior cervical ganglion after the alar fascia was dissected to free the superior cervical ganglion from its position against the common carotid artery bifurcation. In all specimens, the superior cervical ganglion was located on the medial surface of the carotid vessels. We measured the length, maximum width, and center width of the superior cervical ganglion, and the distance (d) from its inferior pole to the common carotid artery bifurcation. Red pinheads indicate the approximate C6 reference plane between the transverse process (posterior) and the superior margin of the cricoid cartilage (anterior). SCG = superior cervical ganglion; ipSCG = inferior pole of the superior cervical ganglion; CCA = common carotid artery; CCAB = common carotid artery bifurcation; ICA = internal carotid artery; ECA = external carotid artery; TC = thyroid cartilage.

Statistical analysis was performed using the software package Stata 10.1 (StataCorp, College Station, TX). For principal components analyses, we performed a factor analysis that determined the patterns of the variables in the model. We then rotated the factor loadings to determine which variables within the factor loadings were highly correlated. Finally, we performed the predict function in Stata that explicitly determined which variables could be reduced to the specific factors. The factors were used for further analysis to find relationships between subject physical characteristics and the location and dimensions of the superior cervical ganglion using ordinary least-squares multiple regression. In this statistical model, for the variable of gender, males were coded as “0” and females were coded as “1.” The Pearson test was used for all correlation analyses. An α-significance value of 0.05 was used to determine P values for all statistical calculations.

Subject height and weight were significantly correlated (R = 0.56, P < 0.001). We performed principal components analysis with rotation on all the predictor variables associated with subject physical characteristics and found that height and weight could indeed be reduced to 1 factor, which we herein call physique.

Ganglion length and area were significantly correlated (R = 0.76, P < 0.001), as were maximum width and center width (R = 0.71, P < 0.001). We performed a principal components analysis with rotation on the superior cervical ganglion measurements and found that these 4 variables could be reduced to 2 factors, which we herein call dimensional width (maximum width and center width) and dimensional area (area and length).

We performed ordinary least-squares multiple regression to determine whether a model of age, gender, physique, and side predicted the (1) distance between the inferior pole of the superior cervical ganglion and the common carotid artery bifurcation, (2) dimensional width of the superior cervical ganglion, or (3) dimensional area of the superior cervical ganglion.

Heat Map

Photographs of the ganglia were acquired in situ and ex vivo. We masked the superior cervical ganglion from photographs using Adobe Photoshop CS5 (Adobe Systems, Inc., San Jose, CA). The superior cervical ganglion grayscale masks were linearly registered relative to the common carotid artery bifurcation and the linear superior-inferior axis of the neck. The opacity of the shapes was reduced to 50% and the image was flattened, resulting in a pseudodensity grayscale map of the superior cervical ganglion. The map was finally pseudocolorized into a heat map according to the grayscale intensity.

RESULTS

Dissections demonstrated and confirmed that the alar fascia thickens and compartmentalizes the superior cervical ganglion against the outside of the carotid sheath, thereby making the ganglion accessible to anesthetic but isolated from the vagus nerve.

The overall model of ordinary least-squares multiple regression for age, gender, physique, and side significantly predicted the distance between the inferior pole of the superior cervical ganglion and common carotid artery bifurcation (F[4,55] = 3.47, R² = 0.20, P = 0.01). Gender (β coefficient = −1.21, P = 0.002) and physique (β coefficient = −1.33, P = 0.001) contributed significantly to the variance in this model. The distance between the inferior pole of the superior cervical ganglion and the common carotid artery bifurcation was correlated independently with length (R = −0.47, P < 0.001), area (R = −0.37, P = 0.004), and center width (R = 0.31, P = 0.01) of the ganglion.

The statistical model for age, gender, physique, and side significantly predicted the dimensional width (F[4,53] = 3.16, R² = 0.19, P = 0.02), but not the dimensional area (F[4,53] = 1.67, R² = 0.11, P = 0.17). Gender (β coefficient = −0.75, P = 0.06) was the predictor that contributed the most to the variance in this model (Table 1).

Table 1: Measurements of the Superior Cervical Ganglion Between Males and Females

Post hoc statistical analysis using 1-way analysis of variance showed significant differences in area (P = 0.006), maximum width (P = 0.007), and center width (P = 0.005), but not length (P = 0.26), between males and females when these metrics were analyzed individually. Distance by itself was not significant between males and females, highlighting the important interaction of physique.

The pseudodensity heat map of the superior cervical ganglion is shown in Figure 2. The color red indicates the region where 100% of the ganglia from all 30 specimens, for each side, overlap. The color magenta indicates where 0% of the ganglia are located.

Figure 2: Heat maps depicting the localization of the entire superior cervical ganglion in females and males relative to the common carotid artery bifurcation (dashed line). On either extreme, the color red indicates the portion of the superior cervical ganglia that overlaps in all subjects; the color magenta indicates where none of the ganglia overlaps. Colors in between red and magenta on the heat index bar correspond to the percentage of ganglia overlap among subjects.

DISCUSSION

In this study, we measured the dimensions of the superior cervical ganglion and represented its location relative to the common carotid artery bifurcation using a pseudodensity heat map (Fig. 2). One limitation of our results is that embalmed specimens are more dehydrated than unembalmed specimens. Therefore, the measurements presented herein may underestimate true biological values. In addition, we found statistically significant differences in superior cervical ganglion–common carotid artery bifurcation distance and superior cervical ganglion morphometry, but it remains to be seen whether these differences are truly clinically relevant when the volume of injected anesthetic would be orders greater than the statistically measured differences.

Ultrasound-guided regional anesthesia is now a prevalent methodology for locating peripheral nerves for targeted block.^14,15 The very close proximity of the superior cervical ganglion and the common carotid artery bifurcation makes this artery a good landmark for the ganglion's localization for targeted block to relieve or prevent cerebral vasospasm when a stellate ganglion block is contraindicated. We propose an injection path indicated by the yellow dashed line (Fig. 3) in an ultrasound image with Doppler that we recently acquired to access the superior cervical ganglion for targeted blockade. Testing this hypothesis is the necessary next step of this research.

Figure 3: Coronal computed tomography of the neck at the level of the common carotid artery bifurcation (a) and ultrasound with Doppler that we recently acquired at approximately the same level (b). The external carotid artery (a, black arrow) is just starting to branch off the common carotid artery (*) near the superior horn of the thyroid cartilage. The proposed location and angle of the ultrasound transducer on the neck is represented overlying the common carotid artery bifurcation. The blue box indicates the view of the ultrasound image with Doppler that we acquired (b). Red indicates internal (left) and external (right) carotid arteries and blue indicates internal jugular vein. Based on our data, the superior cervical ganglion would be located at the tip of the white arrow. The dashed yellow line is our proposed path for the needle to introduce anesthetic to the superior cervical ganglion.

DISCLOSURES

Name: Jonathan J. Wisco, PhD.

Contribution: Study design, conduct of study, data analysis, manuscript preparation.

Name: M. Elena Stark, MD, PhD.

Contribution: Study design, conduct of study, manuscript preparation.

Name: Ilan Safir.

Contribution: Data analysis, manuscript preparation.

Name: Siamak Rahman, MD.

Contribution: Study design, conduct of study, manuscript preparation.

This manuscript was handled by: Terese T. Horlocker, MD.

ACKNOWLEDGMENTS

We thank our donors to the Donated Body Program at the University of California at Los Angeles as well as the staff including Dean Fisher, Elizabeth Megelin, and Travis Siems. We thank Ashley Salin and Megan Salin for their assistance with ganglia dimension measurements. Finally, we thank the University of California at Los Angeles, Academic Technology Services, Statistical Consulting Group, for their assistance with performing and interpreting the statistical results of the study.