# Intraoperative Identification and Stimulation of the Ansa Cervicalis Nerve Plexus

## TL;DR

This study examines the anatomy of the ansa cervicalis nerve and tests neurostimulation to control hyolaryngeal movement during neck surgery.

## Contribution

The study identifies the common sternothyroid trunk as a promising target for neurostimulation to achieve maximal hyolaryngeal descent.

## Key findings

- The ansa cervicalis nerve showed minor variability in diameter, supporting standardized electrode design.
- Neurostimulation of the common sternothyroid trunk produced the greatest hyolaryngeal descent.
- Stimulation amplitudes ranged from 0.35 ± 0.18 mA to 0.57 ± 0.40 mA.

## Abstract

Quantify the anatomic variation of the ansa cervicalis and evaluate neurostimulation of the infrahyoid musculature.

Intraoperative physiology study.

Tertiary referral center.

Adult patients undergoing lateral neck dissection including level IV for head and neck cancer were recruited. Ansa cervicalis plexus branches were documented during surgical dissection. In a subset of participants, an electrode was placed on branches of the common sternothyroid trunk innervating the sternothyroid and sternohyoid muscles. Hyolaryngeal excursion with neurostimulation was recorded.

Measurements were collected from 39 of 50 participants. Reasons for intraoperative exclusion included significant radiation fibrosis (n = 4), nodal disease burden (n = 3), and surgeon preference (n = 4). The mean lengths of the common sternothyroid trunk and sternothyroid branch were 37.6 ± 15.0 mm and 20.4 ± 8.1 mm, respectively. Their respective mean diameters were 2.1 ± 0.7 mm and 1.5 ± 0.5 mm. The distance from sternothyroid branch muscle insertion to the sternum varied substantially (12.8 ± 14.8 mm). Nine patients underwent neurostimulation of the common sternothyroid trunk. The amplitude of first observed muscle contraction was 0.35 ± 0.18 mA and maximal was 0.57 ± 0.40 mA, during which the hyolaryngeal complex descended by 13.6 ± 4.6 mm. In patients with anatomy amenable to neurostimulation of other nerve branches, stimulation of the common sternothyroid trunk produced the greatest hyolaryngeal descent (P < .05).

The minor variability observed in ansa cervicalis nerve diameter across patients and branches supports the feasibility of a standardized electrode design for an implantable neurostimulation device. Stimulation of the common sternothyroid trunk resulted in the greatest hyolaryngeal descent, highlighting its value as a potential neuromodulation target.