Nerve to Thyrohyoid

nervus musculi thyreohyoidei

The nerve to thyrohyoid is a branch from the hypoglossal nerve (CN XII) arising in the carotid triangle, but it carries fibres from the C1 anterior ramus (not true hypoglossal fibres). It descends along the thyroid cartilage to enter the thyrohyoid muscle from its deep surface. Like the nerve to geniohyoid, it represents C1 motor fibres hitchhiking in the CN XII nerve trunk.

Region: Neck

Clinical Relevance

Clinical Notes

The nerve to thyrohyoid is relevant in laryngeal and neck surgery where the hypoglossal nerve is identified and protected. Division of CN XII in the carotid triangle also sacrifices this nerve, paralysing the thyrohyoid and preventing the laryngeal elevation during swallowing that normally pulls the thyroid cartilage toward the hyoid. This laryngeal fixation deficit contributes to aspiration in patients with combined CN XII and thyrohyoid nerve injury. Understanding that this is a C1-derived nerve explains its occasional preservation in some patterns of skull base CN XII injury.

Pathology

Common Injuries & Conditions

Thyrohyoid Palsy in Laryngeal Surgery

Division of the hypoglossal nerve or its thyrohyoid branch during thyroid, parathyroid, or laryngeal surgery impairs laryngeal elevation, reducing the superior hyoid movement that closes the laryngeal vestibule during swallowing and contributes to aspiration of liquids.