Anatomical study applied to anesthetic block technique of the superior laryngeal nerve

The topography of the internal branch of the superior laryngeal nerve (ibSLN) was prospectively studied to evaluate the greater horn of the hyoid bone (ghHB) and the incisura of the thyroid cartilage (iTC) as anatomical repairs in laryngeal anesthetic block. Factors such as gender, ethnicity and side of the neck were also analyzed concerning their influence in the ibSLN position.

One hundred neck dissections were performed in 50 human cadavers bilaterally identifying the ibSLN, the ghHB and iTC. The distance between the ghHB and ibSLN in the cranio-caudal direction (dHB), and the distance between the iTC and the ipsilateral thyrohyoid membrane ostium (dTC) were measured. Furthermore, the results were statistically analyzed according to ethnicity, gender and side of the neck.

The ibSLN was juxtaposed to the apex ghBH in 31 out of 100 dissections. The mean dHB was 2.4 mm, and mean dTC was 33.4 mm. The statistical analysis did not identify any significant difference regarding those distances between the groups in terms of ethnicity, gender and side of the neck.

The ibSLN was often dissected very close to the ghHB, and this result was not influenced by any factor studied. Therefore, the ghHB can be considered a good anatomical repair to localize the ibSLN in the local block of the larynx. Furthermore, the dTC could frequently be reached by routinely used nerve block needle. However, a few anatomical variations may occur, resulting in a low failure rate of this anesthetic procedure.