# Ultrasound-Guided Botulinum Neurotoxin Injection for Alleviating Cricopharyngeus Muscle Spasticity: A Cadaveric Feasibility Study with Nerve Ending Analysis

## TL;DR

This study shows that ultrasound-guided botulinum toxin injections can effectively target nerve-rich areas in the cricopharyngeus muscle to treat swallowing difficulties.

## Contribution

The study introduces a modified staining method and demonstrates the feasibility of ultrasound-guided botulinum toxin delivery to specific nerve-rich regions in the cricopharyngeus muscle.

## Key findings

- Nerve endings are most abundant in the posterolateral areas of the cricopharyngeus muscle.
- Ultrasound-guided injections successfully targeted these areas in 75% of cases.
- Injections did not spread to unintended muscles in most successful cases.

## Abstract

Botulinum neurotoxin (BNT) injection into the cricopharyngeus muscle (CPM) under ultrasound (US) guidance is a minimally invasive technique performed to relieve cricopharyngeal dysphagia by reducing CPM spasticity. This technique is basically accessible only to both lateral sides of the CPM. This cadaveric study aimed to evaluate whether US-guided injection could effectively deliver BNT to abundant areas of gross nerve endings within the CPM. We utilized a newly modified Sihler’s staining method to identify regions with abundant neural endings within the CPM while preserving the three-dimensional morphology of the muscle in 10 sides of 5 fresh cadavers. A mixture of 0.2 mL dye was injected into the 16 sides of CPM under US guidance in 8 cadavers. Nerve endings were abundant in posterolateral areas of the CPM; the injected dye was identified at the posterolateral area on 12 sides (12/16 side, 75%) without diffusion into the posterior cricoarytenoid muscle. The injection failed on four sides (two sides of the prevertebral fascia and two sides of the esophagus below the CPM). These results suggest that US-guided injection could be a feasible technique as it can deliver BNT to the most abundant nerve distribution areas within the CPM in most cases.