Anatomy of the superior laryngeal nerve space: Cadaveric evaluation and its clinical implication for regional anesthesia in the airway management

Abstract This present study was designed to visualize the superior laryngeal nerve (SLN) space and investigate the spreading patterns of the agent in the SLN space using three-dimensional (3D) micro-computed tomography (CT), histologic study, and cadaveric evaluation. Thirteen non-embalmed human cadavers were used in this study. Micro-CT images of the larynx and the surrounding structures were obtained, and 3D images were reconstructed. The structure of the SLN space was verified via histological examination and manual dissection. To evaluate anatomical findings, 1 and 3 mL of dye were injected into the SLN space with unilateral or midline approach under ultrasound guidance, and the dye spreading patterns were investigated. Micro-CT and histological findings revealed that the SLN space was delimited between the infrahyoid muscle groups anteriorly and the thyroid membrane attached closely to the pretracheal fascia posteriorly. The ipsilateral internal branch of the SLN was fully stained by injecting 1 mL of dye unilaterally and furthermore, the ipsilateral external branch and recurrent laryngeal nerve were also frequently involved when 3 mL of the dye was used. A single injection of 3 mL dye through the midline approach was sufficient to involve internal branches of the SLN of both sides. The SLN space should be an anatomical target for the internal branch of the SLN block. In addition, this space provides potential pathways for the spread of injectate to the adjacent nerves that innervate the airway.