Ultrasound imaging of the phrenic nerve at the scalene muscle level

The aim of this study is to utilize ultrasound to evaluate the normal cross-sectional area (CSA) of the phrenic nerve (PN), at the level of the anterior scalene muscle. The study included 62 PNs in 31 healthy subjects (13 men, 18 women); mean age, 36.6 years; mean height, 161.1 cm; mean weight, 69.6 kg; and mean body mass index 25.8 kg/m2. High-resolution ultrasound images of the bilateral PNs were obtained by a radiologist with 15 years of experience in neuromusculoskeletal ultrasound. Three separate CSA measurements for the bilateral PNs bilaterally were obtained. Images were also reviewed by an experienced neurologist to evaluate for inter-rater variability. The mean CSA of the right PN was 0.54 mm2 ± 0.16. The mean CSA of the left PN was 0.53 mm2 ± 0.18. We believe that the reference values for the normal CSA of the PNs obtained in our study could help in the sonographic evaluation of PN enlargement, as it relates to the diagnosis of various diseases affecting the PN. Furthermore, knowledge of its location and size, at the level of the scalene muscle, could help prevent PN-related complications during interventional procedures in that area. Additionally, for each participant, demographic information of age and gender as well as body mass index, weight, and height were documented.