Normal anatomy, variants and factors associated with the cervical vagus nerve topography: a high-resolution ultrasound study.

Purpose: To describe the cervical vagus nerve (CVN) topography at the thyroid lobe (TL) level using high-resolution ultrasound and to investigate the possible association with anthropometric data, TL size, and thyroid disease.

Methods: We prospectively examined 550 CVNs in 275 (205 female, 70 male) individuals with normal thyroid (53/275, 19.3%), multinodular disease (167/275, 60.7%), and Hashimoto thyroiditis (55/275, 20%). The CVN location relative to the common carotid artery was recorded as typical (lateral position) and atypical (anterior, medial, and posterior position). The shortest distance between CVN and TL margin, the TL dimensions, and volume were measured.

Results: Normal thyroid subjects had lateral-positioned right CVNs in 100% and lateral/anterior/medial left CVNs in 81.1%, 15.1%, and 3.8%, respectively. CVN types did not differ significantly bilaterally between study groups. Asymmetry in CVN topography in all subjects was found in 22.2%, of which anterior CVN was the most common atypical position (64%), especially on the left side (82%). Significant gender, age, body mass, and BMI differences among CVN types were observed on the left side only. Among CVN types, no difference in TL dimensions, volume, and CVN-TL distance was found in all study groups. A weak negative correlation was recorded between CVN-thyroid distance and TL volume only on the left side (r = - 0.147, p = 0.01).

Conclusion: Asymmetry in CVN topography is mainly due to the increased incidence of the anterior location of CVN on the left side. Age and anthropometric parameters are different on the left side possibly due to the increased prevalence of left CVN variants.