Sonographic characteristics of the facial nerve in healthy volunteers

Peripheral nerve ultrasound has become an effective imaging technique. However, imaging of cranial nerves, especially in healthy volunteers, has received minimal attention. The objectives of this study were to describe the sonographic characteristics of the facial nerve and to establish average values of its diameter.The extra-cranial part of the facial nerve was scanned bilaterally along its longitudinal axis inside the parotid gland using a 13-MHz probe in 50 healthy adults. The diameter was measured at the nerve's thickest region.The facial nerve appeared as a thin, tubular, hypoechoic structure inside the parotid gland. The mean facial nerve diameter was 0.5 ± 0.1 mm, and the mean side-to-side difference in diameter was 0.1 ± 0.1 mm.The average facial nerve diameter values may provide help with identification of nerve abnormalities using ultrasound.