Topographic anatomy of the internal laryngeal nerve: surgical considerations.

Background: This study is focused on the topographic features of the internal branch of the superior laryngeal nerve (ibSLN) at the thyrohyoid membrane area using as anatomic landmarks the posterior border of the thyrohyoid muscle and the superior border of the thyroid cartilage.

Methods: Thirty-six fresh adult cadavers were dissected to determine the topography and branching pattern of the ibSLN and the superior laryngeal artery.

Results: The ibSLN prior to thyrohyoid membrane's penetration was divided into 3 or 2 branches, in 72.22% and 27.78% of cases. The trifurcated ibSLN was more common than the bifurcated in both sexes and in both sides of the neck. In over 80% of cases the ibSLN penetrated the thyrohyoid membrane 0.1 to 0.9 cm far from the posterior border of the thyrohyoid muscle and 0.1 to 1.2 cm far from the superior border of the thyroid cartilage.

Conclusions: We provide a schematic overview of the ibSLN penetration zone at the thyrohyoid membrane, the so-called danger zone, to avoid ibSLN damage.