The Utility of Stroboscopy in Evaluating Patients with Benign Vocal Fold Lesions

Abstract

Purpose: The present study aims to provide a comprehensive analysis of the use of stroboscopy as an assessment tool for patients with benign lesions of the vocal folds.

Methods: The current study was based on an extensive review of the international bibliography regarding the evaluation of voice in patients with benign lesions of the vocal cords using videostroboscopy.

Results: Stroboscopy is a convenient technique used by otolaryngologists that has been established as a valuable diagnostic tool for assessing patients with dysphonia and benign vocal cords lesions.

Conclusions: Stroboscopy is recommended in the literature as the preferred method for assessing vocal cord vibratory function. The future poses challenges in standardizing guidelines and quantifying measurements of stroboscopic findings.

Keywords:stroboscopy, benign vocal folds lesions, stroboscopic evaluation, videolaryngostroboscopy.

INTRODUCTION

In 1855, Manuel Garcia first reported the use of a continuous light source in vocal tract imaging (1, 2). Over time, laryngeal photography has been progressively improved, leading to enhanced diagnostic accuracy, documentation and educational benefits (3). Later, in 1895, Oertel made the initial observation of a living human larynx using a periodically interrupted light produced by a rotating disc. Using this method, he observed the vibration of the vocal folds (1). In 1898, Musehold created the first stroboscopic photographs in Berlin (4, 5). In 1932, Kallen used a stroboscope with a contemporary flash tube for the first time (6).

Stroboscopic analysis of vocal fold function is crucial in making therapeutic and surgical decisions for patients with voice disorders (7-10). Videolaryngostroboscopy (VLS) enables clinicians to assess detailed aspects of vocal folds and identify specific types of lesions (9, 11). Specific visual parameters used to assess and report findings seen in videostroboscopy during phonation such as mucosal wave, amplitude, vibratory behavior, phase closure, etc. These laryngeal properties are very special for each voice disorder and can reveal clinical information that clearly establish the diagnosis (1, 11-14). Many rating forms and optimized protocols have been used as evaluating tools of stroboscopic examination (11, 15-21). The European Laryngeal Society recommends the use of stroboscopy as the primary diagnostic test for dysphonia (16). However, the lack of a standardized and validated assessment protocol may explain why stroboscopy is used rarely (13).

The aim of this study is to provide a detailed analysis of the role of sroboscopy in evaluating patients with benign vocal fold lesions (BVFL).

METHODS

A comprehensive electronic search was performed to identify articles pertaining to the assessment of benign lesions of the vocal folds using videostroboscopy. The review was limited to published articles using PubMed, Google Scholar and Scopus Library. We employed a range of English keywords, including “stroboscopy”, “laryngeal stroboscopy”, “videostroboscopy”, “laryngostroboscopy”, “videolaryngostroboscopy”, “stroboscopic parameters”, “stroboscopic evaluation” “stroboscopic method”, “role of stroboscopy”, “stroboscopic examination”, “benign vocal fold lesions”, “stroboscopic evaluation of benign lesions of the vocal folds”, “diagnosis of benign vocal lesions using stroboscopy”. The authors removed duplicates and selected articles related to the topic.

RESULTS

There is a growing number of reports on the usefulness of stroboscopy in clinical decision-making for laryngeal pathology. These reports have described various aspects of vocal fold vibration that were visualized using stroboscopic techniques (22-25). As voice disorders are common (26) and dysphonia affects an individual’s quality of life (27, 28), the need for personalized treatment in patients with dysphonia is imperative. Over half of patients with voice complaints exhibit benign vocal fold disorders (29-32).

Clinicians commonly use traditional methods such as mirror examination or fiberoptic laryngoscope examination due to their ease of application and interpretation (33). Stroboscopy has been established as a valuable diagnostic tool for assessing patients with dysphonia and is an integral component of phoniatrics in Europe and Japan (33). The use of this technique in the evaluation of professional voice and its disorders has been priorly discussed by many researchers (34-39).

There are several signs that can be visualized through stroboscopy during vocal fold vibration. These signs include the glottal configuration, glottal closure (the shape of the glottis at closure), phase closure (the amount of opening/closing time), phase symmetry (the rating of vibratory phase symmetry), regularity (rating of periodicity), amplitude (the extend of the lateral displacement of the vocal fold), mucosal wave propagation, vibratory behavior (presence or absence), supraglottic activity, edge (ratings of smoothness and straightness) and vertical level (7, 40, 41).

Benign vocal cord lesions, including vocal nodules, polyps and cysts, significantly impair vocal fold vibratory function, leading to dysphonia (42). Benign vocal fold lesions develop in the layer of superficial lamina propria located between the epithelium and the intermediate lamina propria, commonly referred to as “Reinke’s space”. So, BVFL disrupt the flexibility and subsequently reduce or eliminate the passive mucosal wave that occurs at the glottis when the vocal folds are brought together during phonation (31). The dysphonic patient due to BVFL often experiences hoarseness, increased vocal effort, fatigue, strain, even dyspnea during phonation, in cases of large lesions (31).

Stroboscopy plays a crucial role in serial examinations of patients with benign lesions of the vocal folds undergoing treatment. Stroboscopy can be utilized to assess the progress of voice therapy in reducing vocal nodules. Stroboscopy can also be used to document improved vibratory behavior and increased mucosal wave propagation when medical treatment is employed to enhance hydration and reduce inflammation. Finally, this technique can enhance diagnostic accuracy and prevent unwarranted surgical expectations in patients undergoing evaluation for surgery (3, 33). Videolaryngostroboscopy examination results can identify patients who may require additional microlaryngoscopy (3).

Special stroboscopic findings observed in BVFL are as follows: vocal cord nodules are usually bilateral and symmetric and cause hourglass shaped glottic closure, symmetry of the vocal folds and normal or slightly decreased mucosal wave (22, 43, 44). Vocal cord scars cause complete glottic closure. Vocal fold polyps and cysts cause asymmetry of vocal cord as they appear unilaterally and rough vocal edge, periodicity of vocal fold and normal amplitude of vocal cord (44). Vocal folds with small polyps have intact mucosal wave and larger polyps can show decreased mucosal wave. Decreased or absent mucosal wave can be observed on a vocal fold with cyst (44, 45).

Although stroboscopic examination provides a visually captivating display of the vibratory patterns of the vocal folds during phonation, the interpretation of these findings remains subjective (33).

DISCUSSION

Comparison of VLS with other diagnostic methods for the evaluation of the vocal fold vibration

The intricate movement of the vibratory edge of the vocal folds is crucial to produce a typical voice. Due to the rapid opening and closing of the vocal folds, which occurs at a frequency of approximately 60 to 1,500 times per second depending on the pitch, it is not feasible to conduct a thorough physical examination of the vibratory edge using continuous light and a laryngeal mirror (22). High speed photography permits the detailed examination of vocal fold vibration in slow motion. However, it is a complex process which only permits the evaluation of phonation samples that are relatively short. High speed video used in videokymatography has a limited availability (31, 33). Researchers at Pusan National University in South Korea have successfully developed a conceptually proven 2D scanning videokymography technique. These advancements are expected to have a significant impact on voice disorder research soon, with potential implications for clinical applications (46, 47). The fiberoptic laryngoscopy cannot provide the required sharpness to capture the vibration behavior of the vocal cords in detail (25). However, stroboscopy is a more time-intensive procedure compared to standard indirect laryngoscopy (33). There is a limitation applicable to both laryngoscopy and stroboscopy. The use of rigid endoscopes modifies phonatory mechanisms, yet the captured images are of higher quality compared to fiberoptic recordings (17, 48). Newer laryngeal imaging techniques, including optical coherence tomography, depthkymography and high-resolution laryngeal magnetic resonance, offer clinicians improved quantification of phonation (7). Optical coherence tomography (OCT) is an emerging non-invasive imaging technique that offers high-resolution cross-sectional views of the vibrating vocal folds. However, its application in clinical laryngology is still in the early stages of development (49). In a recent study, Sebastian Dippold et al concluded that the combined use of narrow band imaging (NBI) and white light endoscopy yielded a higher probability of detecting benign vocal fold lesions compared to using white light endoscopy alone. But NBI was not compared with stroboscopy (50). Ultrasound has traditionally been a cost-effective imaging technique for the neck, but its usefulness in laryngeal imaging has been limited (31).

Strobovideolaryngoscopy is the most convenient technique for otolaryngologists to assess the vibratory function of the vocal fold during phonation in detail (22).

The value of VLS in clinical practice and research

The convenience, ease of use, availability and commercial nature of stroboscopy equipment may account for its growing utilization in clinical practice (7, 51, 52).

Recent studies recommend the use of laryngeal stroboscopic assessment for diagnosing general hoarseness (53, 54). In a prospective study of hoarse patients assessed by VLS, Woo P. et al concluded that 15 cases needed to change the diagnosis made by referring otolaryngologists. Specifically, six patients avoided surgery and nine patients were referred to surgery instead of voice and medical therapy (33). In a series of 486 examinations, Sataloff et al found that stroboscopy was beneficial in diagnosing and treating around one-third of the professional voice users in their practice (33). Bouchayer et al (24) conducted a study involving 157 cases of sulci, mucosal bridges and vocal cord cysts. Their study emphasized the significance of stroboscopy in distinguishing these lesions from other conditions by observing the vibratory pattern of the vocal folds. In a survey conducted among 273 members of the American Academy of Otolaryngology— Head & Neck Surgery (AAOHNS), most respondents (84%) indicated their practice of videostroboscopy. A classification system for benign vocal fold lesions was developed by Rosen C. et al by using stroboscopy among multiple criteria (55). In their prospective study, Welham N.V. et al used videostroboscopy as a diagnostic tool for the evaluation of surgical treatments for vocal fold scar and pathologic sulcus vocalis (56).

The primary benefit of laryngostroboscopy lies in its ability to facilitate detailed visualization and analysis of vocal fold and epithelial movement. Through the process of analyzing a strobe video, it is possible to generate a strobe frame. A stroboscopic photo frame is in fact a compilation of stroboscopic images acquired from consecutive places within many glottal cycles. There are specific stroboscopic findings for each voice disorder involving the vibratory function of the vocal cords (13) (Figure 1).

Quantification of stroboscopic imaging and the need for a standardized approach: a challenge for the future

Several authors have reported on the quantification of stroboscopic images. Perceptual criteria previously outlined by Kitzing and Bless have been used to analyze laryngostroboscopic images. Glottic closure has been classified by Bless into seven separate groups (17, 57). Watanabe H. et al proposed a computer-analyzing system where the glottal area was displayed as a function of time (58). More recently, to analyze stroboscopic images on 16-mm motion picture film, Koike and Imaizumi employed a data reductionbased (57). Sercarz J. et al used a video monitor, a telescope, a 50 mm lens and a diopter lens, a handheld stethoscope to put into operation a system for objective measurement of videostroboscopic images (57). Omori et al measured the glottal gap and the amplitude of vibration in patients undergoing thyroplasty type 1 using digitized laryngostroboscopy (59). Kuo CJ et al created a brand-new laser projection marking module and mounted it on the laryngeal video stroboscope to convert the physiological parameters of the glottis and give scale conversion reference parameters for glottal imaging (60). Noordzij J. P. et al analyzed quantitatively videostroboscopic images using the glottal area waveform(GAW), a plot of glottal area versus time (61).

To date, there is a growing number of rating forms used to measure stroboscopic findings. Woo et al used the stroboscopic rating forms proposed by Hirano and selected parameters before and after microlaryngeal surgery (42). Poburka B. J. et al proposed the Stroboscopy Examination Rating Form (SERF) to address issues that the Stroboscopic Assessment of Voice (SAV) form-based stroboscopy rating study had identified (15). Later, Poburka B. J. et al developed the Voice-Vibratory Assessment with Laryngeal Imaging (VALI) rating form, the first rating form that was created a priori and contains visual-perceptual ratings of stroboscopy (19). Rosen C. A. et al used a rating form including six common described stroboscopic parameters (62). In a systematic review performed by Bonihla et al came to the conclusion that VALI was a promising option for a commonly used stroboscopy rating assessment tool (11).

Despite the number of protocols that have been used, the infrequent use of stroboscopy as a therapeutic outcome measure may be due to the absence of a widely accepted, standardized, validated and trustworthy approach to evaluate laryngeal architecture and physiology (11).

CONCLUSION

Stroboscopy is highly regarded for its exceptional capacity to assess the structure and function of the glottis during phonation. This diagnostic method offers unique information not found in any other methods. Clinicians through stroboscopy can assess the larynx during various phonatory tasks that simulate normal speaking or singing. It can be repeated an recorded, and it is also a cost-effective approach. Improving our understanding of the diagnostic value of stroboscopy for patients with benign laryngeal pathologies can inform more efficient patient referrals and regulation of access to specialized voice care. Stroboscopic examination is beneficial for patients with benign lesions on the vocal fold edge that cannot be seen through indirect laryngoscopy, dysphonic patients with normal indirect laryngoscopy results and professional voice users. The future presents challenges in establishing common guidelines and quantifying measurements of the stroboscopic findings.

Conflict of interests: none declared.

Financial support: none declared.

FIGURE 1.

Photo frame of stroboscopic images in a patient with bilateral vocal cord paralysis, two months after total thyroidectomy, with the following findings being observed: incomplete glottis closure, similar vertical plane between vocal folds, decreased mucosal wave bilaterally, intermittently asymmetric vocal folds and absence of vocal fold muscle tone