Ultrasound-Guided Glossopharyngeal Nerve Block: A Cadaver and a Volunteer Sonoanatomy Study

Abstract

Background and objectives: Glossopharyngeal nerve (GPN) blocks are usually performed by topical, intraoral, or peristyloid approaches, which carry significant complication risks due to the proximity of important neurovascular structures. This study presents a proof of concept for a new ultrasound (US)-guided technique, which would block the GPN distally, in the parapharyngeal space, away from the immediate vicinity of high-risk collateral structures.

Methods: Five cadaver heads were dissected, and the location of the GPN was explored bilaterally. In 40 healthy volunteers (20 men and 20 women; median age, 35.5 years [range, 24-69 years]) parapharyngeal sonograms were obtained, saved, and analyzed. To assess the technical feasibility of a distal GPN block in the parapharyngeal space, unilateral US-guided dye injections were performed in 3 fresh cadavers, followed by dissections.

Results: The GPN was consistently identified between the stylopharyngeal and middle pharyngeal constrictor muscles in all cadaver specimens. The median distance between the GPN and the ipsilateral greater horn of the hyoid bone was 2.4 cm (range, 2.3-2.7 cm) on the right and 2.6 cm (range, 2.3-2.9 cm) on the left. The mean skin-to pharyngeal wall distances in the volunteers were 2.03 (SD, 0.41) cm on the right and 2.02 (SD, 0.45) cm on the left. The mean hyoid bone-to-pharyngeal wall distances were 2.04 (SD, 0.35) cm (right) and 2.07 (SD, 0.35) cm (left). The fresh cadaver dissections demonstrated dye deposition adjacent to the GPN in the parapharyngeal space in all specimens.

Conclusions: Based on our anatomical results in cadavers and healthy volunteers, we submit that successful and safe blockade of the distal GPN at the pharyngeal wall level is technically feasible under US guidance.