Characteristics of the Middle Cervical Sympathetic Ganglion: A Systematic Review and Meta-Analysis

BACKGROUND: Understanding the characteristics of the middle cervical sympathetic ganglion (MCSG) may minimize procedure-related complications and maximize efficacy during surgery or ultrasound (US)-guided procedures. The location and detection rate of the MCSG were variable in small population studies. Therefore, a large population study or meta-analysis could give more information about the MCSG. OBJECTIVES: We aim to review the published literature and evaluate the anatomical features of the MCSG, including the detection rate, location, size, and a normal variation, and to review the clinical relevance of MCSG for procedures including, US-guided ganglion block, ethanol ablation (EA), or radiofrequency ablation (RFA). STUDY DESIGN: A systematic review and meta-analysis. The Ovid-MEDLINE and EMBASE databases were searched to find the detection rate, location, and other characteristics of the MCSG. SETTING: The pooled proportions for the detection rate of the MCSG were assessed using the DerSimonian-Laird random-effects model. METHODS: Heterogeneity among the studies was determined using a chi-square analysis for the pooled estimates and inconsistency index (I²). In order to reduce the heterogeneity, sensitivity analyses were performed. RESULTS: A review of 542 studies identified 8 eligible studies, with 273 MCSGs included in the meta-analysis. The pooled proportion for the detection rate of the MCSG was 50.4% (95% confidence interval [CI], 34.5 - 66.4%). Considerable heterogeneity among the studies was observed (I² = 94.9%). In the sensitivity analysis, when excluding one study, heterogeneity was reduced with a recalculated pooled proportion of 44.2% (95% CI, 32.1 - 56.2%; I² = 86.0%). The location of the MCSG is usually posterior to the carotid sheath and anterior to the longus colli muscle at the level of the C3 - C7 vertebrae. There was a variant where the cervical sympathetic trunk was located at the posterior wall of the carotid sheath and was adherent to the sheath. The size of the MCSG is as follows: the width, length, and height ranges were 3.8 - 6.3 mm, 6.3 - 10.5 mm, and 1.7 - 2.1 mm, respectively. A specific type of MCSG, referred to as the "double middle cervical ganglion", consisting of 2 ganglia, was demonstrated in 3 studies with a detection rate of 2.9 - 10%. LIMITATIONS: This meta-analysis included a relatively small number of studies. Significant heterogeneity was also present in the detection rate of MCSG in these studies. There was a lack of concentrated information about the MCSG, because the majority of the included studies focused on the entire cervical sympathetic chain, not only MCSG primarily. Improving complication rates might be limited due to the approximate 50% detection rate. CONCLUSION: Understanding the characteristics and variations of the MCSG could minimize complications and maximize efficacy during surgery and US-guided procedures. KEY WORDS: Middle cervical sympathetic ganglion, cervical sympathetic trunk, cervical sympathetic chain, ultrasound, nerve block, ethanol ablation, radiofrequency ablation, thyroid, Horner syndrome, meta-analysis.