Localization of the cricothyroid muscle under ultrasound guidance for vagal nerve mapping

• Ultrasound guidance can provide valuable information regarding precise location and depth of the cricothyroid muscle.
• A more distinct signal from the cricothyroid muscle can be recorded due to precise intramuscular needle placement guided by ultrasound.
• Another advantage of this approach is that the expense of 2 subdermal needles is considerably lower than that of a surface electrode that attaches to the endotracheal tube.

During surgical removal of tumors of the skull base or cerebellopontine angle with brainstem compression, the vagus nerve is at a high risk for injury that can result in permanent or transient swallowing and speech dysfunction. Intramuscular recording of cricothyroid muscle can be used for vagal nerve mapping during intraoperative neurophysiologic monitoring so as to prevent the above complications. However, it is a small muscle that lies beneath the strap muscles over the anterior neck and is not easily accessible by a blind approach. Here, we present a case in which cricothyroid muscle was identified for precise electrode placement under ultrasound guidance during preparation for intraoperative monitoring. We concluded that localization of the cricothyroid muscle by ultrasonography proved to be a feasible and easy technique, and the compound muscle action potential recorded by this approach is clearly recognizable during intraoperative vagal nerve mapping.