Precision-Targeted Injection Laryngoplasty and Longitudinal Biomaterial Effects Evaluation Using High-resolution Ultrasonography in a Rat Model

OBJECTIVE

Current laryngeal injection models rely on the transoral route and are suboptimal due to limited view, narrowed working space, and the need to sacrifice animals for investigation of the injectables. In the present study, a novel surgical model for laryngeal intervention therapy utilizing an ultra-high frequency ultrasound imaging system was proposed. Based on this system, we developed a systemic evaluation approach, from guidance of the injection process, documentation of the injection site of the material, to in vivo longitudinal follow-up on the augmentation and medialization effect by analyzing the ultrasonography data.

STUDY DESIGN

In vivo animal study.

SETTING

Academic institution.

METHODS

Injection laryngoplasty with hyaluronic acid under ultrasonography guidance was performed on Sprague-Dawley rats one week after induced unilateral vocal paralysis. Ultrasonography was performed at preinjection, immediately postinjection, on Day 2, Day 7 and then weekly for 4 weeks to obtain measurements, including the glottic area, angle between bilateral folds, and vocal fold width ratio. Laryngoscopic and histologic studies were also performed.

RESULTS

Unilateral injections to the paralyzed fold were successfully performed as demonstrated by ultrasonographic, laryngoscopic, and histologic studies. The width ratio was significantly increased after injection for 4 weeks, while the glottic airway area was unchanged.

CONCLUSION

Here, a novel surgical model for laryngeal injection utilizing ultrasonography in rats was established. In addition to providing visual guidance for precise localization of the injection, robust documentation of the treatment effect was also demonstrated. This methodology could be beneficial for screening therapeutic agents for treatment of glottic insufficiency.

Rabbit model with vocal fold hyperadduction

OBJECTIVE

Adductor spasmodic dysphonia (AdSD) is caused by hyperadduction of the vocal folds during phonation, resulting in a strained voice. Animal models are not yet used to elucidate this intractable disease because AdSD has a difficult pathology without a definitive origin. For the first step, we established an animal model with vocal fold hyperadduction and evaluated its validity by assessing laryngeal function.

METHODS

In this experimental animal study, three adult Japanese 20-week-old rabbits were used. The models were created using a combination of cricothyroid approximation, forced airflow, and electrical stimulation of the recurrent laryngeal nerves (RLNs). Cricothyroid approximation was added to produce a glottal slit. Thereafter, both RLNs were electrically stimulated to induce vocal fold hyperadduction. Finally, the left RLN was transected to relieve hyperadduction. The sound, endoscopic images, and subglottal pressure were recorded, and acoustic analysis was performed.

RESULTS

Subglottal pressure increased significantly, and the strained sound was produced after the electrical stimulation of the RLNs. After transecting the left RLN, the subglottal pressure decreased significantly, and the strained sound decreased. Acoustic analysis revealed an elevation of the standard deviation of F0 (SDF0) and degree of voice breaks (DVB) through stimulation of the RLNs, and degradation of SDF0 and DVB through RLN transection. Formant bands in the sound spectrogram were interrupted by the stimulation and appeared again after the RLN section.

CONCLUSION

This study developed a rabbit model with vocal fold hyperadduction . The subglottal pressure and acoustic analysis of this model resembled the characteristics of patients with AdSD. This model could be helpful to elucidate the pathology of the larynx caused by hyperadduction, and evaluate and compare the treatments for strained phonation.

Characterizing Vocal Fold Injury Recovery in a Rabbit Model With Three-Dimensional Virtual Histology

OBJECTIVES/HYPOTHESIS

In animal studies of vocal fold scarring and treatment, imaging-based evaluation is most often conducted by tissue slicing and histological staining. Given variation in anatomy, injury type, severity, and sacrifice timepoints, planar histological sections provide limited spatiotemporal details of tissue repair. Three-dimensional (3D) virtual histology may provide additional contextual spatial information, enhancing objective interpretation. The study's aim was to evaluate the suitability of magnetic resonance imaging (MRI), microscale computed tomography (CT), and nonlinear laser-scanning microscopy (NM) as virtual histology approaches for rabbit studies of vocal fold scarring.

METHODS

A unilateral injury was created using microcup forceps in the left vocal fold of three New Zealand White rabbits. Animals were sacrificed at 3, 10, and 39 days postinjury. ex vivo imaging of excised larynges was performed with MRI, CT, and NM modalities.

RESULTS

The MRI modality allowed visualization of injury location and morphological internal features with 100-μm spatial resolution. The CT modality provided a view of the injury defect surface with 12-μm spatial resolution. The NM modality with optical clearing resolved second-harmonic generation signal of collagen fibers and two-photon autofluorescence in vocal fold lamina propria, muscle, and surrounding cartilage structures at submicrometer spatial scales.

CONCLUSIONS

Features of vocal fold injury and wound healing were observed with MRI, CT, and NM. The MRI and CT modalities provided contextual spatial information and dissection guidance, whereas NM resolved extracellular matrix structure. The results serve as a proof of concept to motivate incorporation of 3D virtual histology techniques in future vocal fold injury animal studies.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:1578-1587, 2021.

The Role of Cytokines in Modulating Vocal Fold Fibrosis: A Contemporary Review

OBJECTIVES

Vocal fold (VF) scarring and laryngeal stenosis are a significant clinical challenge. Excessive scar formation causes low voice quality or even life-threatening obstructions. Cytokines are thought to modulate multiple steps of the establishment of VF fibrosis, but there is no systematic report regarding their role in modulating VF fibrosis. This review aims to investigate the role of cytokines in modulating vocal fold fibrosis.

STUDY DESIGN

Literature review.

METHODS

This review searched for all relevant peer publications in English for the period 2009 to 2019 in the PubMed database using search terms: "laryngeal stenosis," "vocal fold scarring," and "cytokines." A thorough investigation of the methods and results of the reviewed studies was performed.

RESULTS

Comprehensive research in various studies, including analyses of prostaglandin E2 (PGE2), granulocyte-macrophage colony-stimulating factor (GM-CSF), hepatocyte growth factor (HGF), basic fibroblast growth factor (bFGF), transforming growth factor-β3 (TGF-β3), and interleukin-10 (IL-10), supports cytokine therapy for VF scarring and laryngeal stenosis to some extent. A few clinical studies on this topic support the conclusion that HGF and bFGF can be selected as effective drugs, and no serious side effects were found.

CONCLUSIONS

This review describes the potential of cytokines for modulating the process of VF fibrogenesis, although cytokines are still an unproven treatment method. As no ideal drugs exist, cytokines may be considered the candidate treatment for preventing VF fibrogenesis. Laryngoscope, 131:139-145, 2021.

Effect of pirfenidone injection on ferret vocal fold scars: A preliminary in vivo study

OBJECTIVES

This study examined the antifibrotic effect of pirfenidone (PFD), which has received regulatory approval in the United States and Japan for treatment of idiopathic pulmonary fibrosis, on the scarred ferret vocal fold (VF) in vivo.

METHODS

Eight male ferrets were divided into two groups: saline and PFD. All animals underwent unilateral scarring under anesthesia. The right VF was electrocauterized with ablation of the entire lamina propria. PFD (1.0 mg/mL) or saline injections into right-side scarred VFs were performed (under an operating microscope) 4 weeks later. After an additional 4 weeks, the larynges were harvested for histological analysis. Prior to harvesting, the ferrets were re-anesthetized, and the VFs were observed and recorded using a rigid video laryngoscope. We immunohistochemically evaluated the expression of collagen types I and III, alpha-smooth muscle actin (α-SMA), and fibronectin in the entire lamina propria. We compared the affected areas (calculated using ImageJ software) between the treated (right) and untreated (left) sides within the same animals and between groups.

RESULTS

Collagen type I (P = 0.0021) and α-SMA (P = 0.0021) expression levels were lower in the PFD group, but the collagen type III and fibronectin levels did not differ significantly between the two groups.

CONCLUSION

PFD injection into the scarred VF is a potentially promising novel antifibrotic treatment.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:726-731, 2020.

Pathophysiology of Fibrosis in the Vocal Fold: Current Research, Future Treatment Strategies, and Obstacles to Restoring Vocal Fold Pliability

Communication by voice depends on symmetrical vibrations within the vocal folds (VFs) and is indispensable for various occupations. VF scarring is one of the main reasons for permanent dysphonia and results from injury to the unique layered structure of the VFs. The increased collagen and decreased hyaluronic acid within VF scars lead to a loss of pliability of the VFs and significantly decreases their capacity to vibrate. As there is currently no definitive treatment for VF scarring, regenerative medicine and tissue engineering have become increasingly important research areas within otolaryngology. Several recent reviews have described the problem of VF scarring and various possible solutions, including tissue engineered cells and tissues, biomaterial implants, stem cells, growth factors, anti-inflammatory cytokines antifibrotic agents. Despite considerable research progress, these technical advances have not been established as routine clinical procedures. This review focuses on emerging techniques for restoring VF pliability using various approaches. We discuss our studies on interactions among adipose-derived stem/stromal cells, antifibrotic agents, and VF fibroblasts using an in vitro model. We also identify some obstacles to advances in research.