Anthropometric Measures, Recurrent Laryngeal Nerves Diameter, Electromyographic Responses and Vocal Cord Paralysis Risk

Objectives: To examine (1) the relationship between anthropometric measurements and recurrent laryngeal nerve (RLN) diameter; (2) whether thin RLNs have different baseline electromyographic (EMG) characteristics; (3) if thin or branched morphology is associated with increased risk of EMG adverse events, loss of signal (LOS) or vocal cord paresis/paralysis (VCP). Methods: In this prospective study, anthropometric data were collected, including weight, height, body mass index (BMI), neck circumference, shoulder diameter, and circumference of the right middle finger (RMF) or right ring finger (RRF). Results: We enrolled 216 patients who underwent surgery from 2016 to 2020 with 307 RLNs at risk. Thin nerves were defined as those ≤ 1.5 mm in diameter. The mean RLN diameter was 2 mm; the RLN was thinner in females and in patients with BMI < 20 kg/m2, body weight < 120 kg, height < 175 cm, neck circumference < 40 cm, shoulder diameter < 50 cm, and RMF or RRF < 7.6 cm (all p < 0.05). No statistically significant differences were detected in baseline EMG characteristics between thin and thick RLNs bilaterally (except for right RLN R2 latency). We had zero cases of LOS or VCP. In all branched nerves, motor fibers resided in the anterior branch. Conclusion: Multiple anthropometric factors were associated with RLN diameter. Most of the studied EMG signal characteristics did not statistically differ by RLN diameter. With zero events of LOS or VCP, our study is not powered to determine if thin diameter or branching are independent risk factors for RLN injury in a high-volume endocrine surgery practice utilizing IONM.