58 Superior Laryngeal Nerve Block

The superior laryngeal nerve is a branch of the vagus nerve (cranial nerve X). At some variable point in the neck, it divides into internal and external branches. The internal branch provides sensory innervation of the larynx above the vocal cords. The external branch innervates the cricothyroid muscle, which is an adductor tensor of the vocal cords.

The superior laryngeal nerve lies close to the superior laryngeal artery. The internal branch of the superior laryngeal nerve lies on average 2.4 mm inferior to the greater horn of the hyoid bone.¹ The hyoid bone is U shaped in transverse scans of the neck. The superior laryngeal nerve enters the larynx through an aperture (ostium) in the thyrohyoid membrane together with the superior laryngeal artery and vein.

Block of the superior laryngeal nerve is sometimes used to facilitate awake fiberoptic intubation or transesophageal echocardiography.

Suggested Technique

A hockey-stick transducer with a small footprint can be used for imaging. A 27-gauge, 1.25-inch hypodermic needle can be used for the block. The patient is instructed not to swallow because this causes movement of the hyoid bone. The nerve is superficial, so an out-of-plane approach can be used to guide infiltration adjacent to the hyoid bone.

Acoustic standoff can be used to improve imaging of the superficial nerve. It addition, the conforming gel dissipates the transducer pressure over a larger area. This improves patient tolerance of transducer placement over a sensitive area of the neck.

Clinical Pearls

• The external branch of the superior laryngeal nerve lies near the superior pole of the thyroid gland. It can be difficult to identify, even with direct dissection and nerve stimulation.²

• The internal branch of the superior laryngeal nerve lies immediately inferior and deep to the greater cornu of the hyoid bone.³

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