Real-Time Light-Guided Vocal Fold Injection: An In Vivo Feasibility Study in a Canine Model

Abstract

Objectives: The transcutaneous approach is a good option for office-based vocal fold injection (VFI). However, precise localization requires extensive experience because the needle tip is invisible in small and complex laryngeal spaces. Recently, real-time light-guided VFI (RL-VFI) was proposed as a new technique that allows simultaneous injection under precise needle localization by light guidance. Herein, we aimed to verify the feasibility of RL-VFI in an in vivo canine model and explored its clinical usefulness.

Methods: The device for RL-VFI comprised a light source (light-emitting diode modules [10 W] of red color [650 nm]) and injectors (1.5 inches, 23 gauge). An adult male beagle was used for the experiment. After tracheostomy, a rigid laryngoscope was inserted and suspended to expose the larynx. A flexible naso-laryngoscopy system was used to visualize the vocal folds.

Results: RL-VFI was performed using various transcutaneous approaches, including the cricothyroid, transthyroid, and transhyoid approaches. Light guidance helped identify the path of the needle and prevent inadvertent penetration. The location of the needle tip was accurately indicated by the light. The illuminated needle could be easily placed at the intended points in the vocal fold with real-time visual-motor feedback. Hyaluronic acid could be simultaneously injected lateral to the vocal process under light guidance without manipulation of the device.

Conclusion: RL-VFI was found to be safe and feasible in an in vivo canine model, providing precise localization and visualmotor feedback. The clinical application of RL-VFI is expected to improve the safety and precision of VFI.

Keywords: In Vivo Animal Study; Real-Time Light-Guided Vocal Fold Injection; Transcutaneous Approach; Vocal Fold Injection; Vocal Fold Palsy.

Fig. 1.

(A) The device for real-time light-guided vocal fold injection (RL-VFI). (B) The injector of the RL-VFI device. (C) The experimental setting. A flexible laryngoscope was inserted via a rigid laryngoscope to visualize the vocal folds, mimicking office-based transcutaneous VFI. (D) The injector of the RL-VFI device was inserted through the cervical skin.

Fig. 2.

Various transcutaneous approaches of the real-time light-guided vocal fold injection device in an in vivo canine model. (A) The cricothyroid approach, (B) the transthyroid approach, and (C) the transhyoid membrane approach.

Fig. 3.

Identification of the needle tip in the cricothyroid (CT) approach using the real-time light-guided vocal fold injection device. The location of the needle tip can be identified by the red light: (A) before the needle insertion, (B) on the CT membrane, (C) in the paraglottic space, (D) lateral to the vocal process, (E) on the mucosa on the superior surface of the vocal fold, and (F) on the medial surface of the vocal fold. The scattering and intensity of the light can inform the depth of the needle in the vocal fold.

Fig. 4.

Identification of the needle tip in the transthyroid approach using real-time light-guided vocal fold injection. The location of the needle tip can be identified by the red light: (A) before the needle insertion, (B) around the vocal fold and the laryngeal ventricle, (C) lateral to the vocal process, (D) around the vocal process, (E) on the posterior mucosa, and (F) on the anterior vocal fold mucosa.

Fig. 5.

Identification of the needle tip in the transhyoid approach using real-time light-guided vocal fold injection. The location and the route of the needle tip can be identified by the red light: (A) before the needle insertion, (B) in the pre-epiglottic space, (C, D) on the mucosa of the petiole, (E) during the penetration of the mucosa, and (F) during the insertion of the needle into the vocal fold.

Fig. 6.

Real-time light-guided vocal fold injection with hyaluronic acid (HA) in the cricothyroid approach: (A) before the needle insertion, (B) placement of the illuminated needle in the deep thyroarytenoid muscle, and (C-E) during injection of HA into the muscle. HA has a higher light transmittance than muscle and mucosa; therefore, the illuminated needle in the material shows stronger dispersion, which can provide information on the extent of the injectate. (F) After removal of the needle, it could be confirmed that the vocal folds was sufficiently medialized.

Fig. 7.

H&E-stained section of the extracted vocal folds showed that hyaluronic acid (asterisk) had been properly injected into the thyroarytenoid muscle of the left vocal fold. There were no histological findings related to thermal damage on the tissue around the materials in the left vocal fold. L, left; R, right.