CLINICAL TECHNIQUE |
https://doi.org/10.5005/jp-journals-10023-1242 |
Transcutaneous Laryngeal Ultrasonography: A Reliable and Noninvasive Alternative to Laryngoscopy in Diagnosing Vocal Fold Palsy
1,3,5Department of ENT and Head & Neck Surgery, Lokmanya Tilak Municipal General Hospital and Lokmanya Tilak Municipal Medical College, Mumbai, Maharashtra, India
2,4Department of Radiology, Lokmanya Tilak Municipal General Hospital and Lokmanya Tilak Municipal Medical College, Mumbai, Maharashtra, India
Corresponding Author: Anagha A Joshi, Department of ENT and Head & Neck Surgery, Lokmanya Tilak Municipal General Hospital and Lokmanya Tilak Municipal Medical College, Mumbai, Maharashtra, India, Phone: +91 2224081090 e-mail: anagha_5@rediffmail.com
Received on: 17 September 2021; Accepted on: 15 January 2023; Published on: 30 June 2023
ABSTRACT
Aim: The aim of this study is to validate the usefulness of laryngeal ultrasonography as a screening tool for vocal fold palsy by correlating it with laryngoscopy findings.
Methods: The study includes 60 patients in a tertiary care center over a period of 1 year. Based on the findings of Hopkins 70° rigid laryngoscopy, the patients were categorized into two groups, group I with normal vocal fold mobility and group II with vocal fold palsy. Laryngeal ultrasonography was then done on all the patients by a team of well-trained ultrasonologists, blinded from the laryngoscopy results. These results were then correlated.
Result: The vocal folds were appreciated in laryngeal ultrasonography, and the mobility was assessed successfully in 56 of these patients, and results were found to be correlating with the laryngoscopy findings in all these patients. In four patients, the vocal folds could not be visualized by ultrasonography due to severe calcification of the thyroid cartilage. In our study, we noted that as a screening tool, laryngeal ultrasonography has a sensitivity of 90% and a specificity of 96.67%.
Conclusion: Laryngeal ultrasonography is a simple, easy, cheap, non-invasive, and easily available tool in diagnosing vocal fold palsy, where laryngoscopy is not possible. Laryngoscopy is an aerosol-generating procedure, hence carries a risk of spread of coronavirus disease 2019 (COVID-19) infection or other similar communicable diseases. Laryngeal ultrasonography circumvents this problem and can be used as a primary diagnostic tool in suspected cases of vocal fold palsy. The utility may be limited to some extent in elderly male patients when the thyroid cartilage is severely calcified.
How to cite this article: Subramaniasamy G, Joshi AR, Joshi AA, et al. Transcutaneous Laryngeal Ultrasonography: A Reliable and Noninvasive Alternative to Laryngoscopy in Diagnosing Vocal Fold Palsy. Int J Phonosurg Laryngol 2023;13(1):9-13.
Source of support: Nil
Conflict of interest: None
Keywords: Echolaryngography, Laryngoscopy, Laryngeal ultrasonography, Screening tool, Vocal fold palsy.
INTRODUCTION
Ultrasonography imaging is a widely used and very effective diagnostic tool for the head and neck.1 Vocal fold movements during phonation can be visualized in real-time using ultrasonography.2 Laryngoscopy and stroboscopy are the basic tools for diagnosing vocal fold pathologies, but the availability of these diagnostic tools in remote areas, the high cost of the equipment, and the difficulty of performing these diagnostic tests in uncooperative patients and children are limiting factors. Laryngoscopy is an aerosol-generating procedure; hence, there is a greater risk of spread of COVID-19 infection. In such scenarios, ultrasonography is deemed highly accurate, reliable, radiation-free, and better tolerated by patients for assessment of vocal fold mobility.3 The purpose of this study is to validate the usefulness of Laryngeal ultrasonography as a screening tool for diagnosing vocal fold palsy by correlating with laryngoscopy findings.
There have been studies where ultrasonography has been used to evaluate vocal folds.4,5 It is a useful Supplementary video to the flexible laryngoscopy to assess pediatric benign vocal fold lesions.6,7
In this study, we have correlated the ultrasonography assessment of vocal fold mobility with laryngoscopy findings by including patients of different age groups to analyze the accuracy of diagnosis.
MATERIALS AND METHODS
A prospective pilot study was carried out over a period of 1 year at our institute. A total of 60 patients were included in the study and categorized into two groups based on the findings of Hopkin’s 70° rigid laryngoscopy. Group I was patients with bilateral normal vocal fold mobility who were undergoing thyroidectomy, intrathoracic surgery, or any other surgery with a risk of causing vocal fold paralysis. Group II was patients who had unilateral or bilateral vocal fold palsy due to any cause. A total of 30 patients were included in each of the two groups. Laryngeal ultrasonography was then done by a team of well-trained ultrasonologists for all the patients. The findings of the laryngoscopy were blinded by the ultrasonologists.
The ultrasonography was done using an ultrasound system of model RS-80A (Samsung Medison, Republic of Korea). The imaging was done in B mode using a linear probe at a frequency of 3–16 MHz. A bolster or pillow was placed below the shoulder with the patient in the supine position to give neck extension (Fig. 1). A linear probe was placed over the thyroid cartilage at different angulations to visualize the vocal folds in the transverse plane. Real-time imaging of the vocal folds was assessed. The vocal folds were identified during quiet respiration, and then the mobility of the vocal folds was assessed with the patient phonating a sustained constant vowel “e.” The mobility was confirmed in the sagittal plane also. The laryngeal ultrasonography image in the axial plane, as seen at the level of vocal folds, is shown in Figure 2.
Fig. 1: Position for transcutaneous laryngeal ultrasonography for vocal fold mobility assessment
Fig. 2: Laryngeal ultrasonography image in B mode. A, arythenoid; PGS, paraglottic space; GS, glottic space; red line denotes medial border of the vocal cords
The thyroid cartilage is first identified. When highly calcified, the thyroid cartilage can cause acoustic shadowing. However, this can be bypassed by proper angulation of the probe at the thyroid notch through a window at the site of the least calcification. The internal laryngeal structures were identified in most patients by this technique.
The vocal folds are seen as triangular hypoechoic structures, with the apex lying behind the reentrant area of the thyroid lamina and the base at the hyperechoic arytenoid vocal process. Hypoechogenicity is due to the muscular part of the vocal folds. Once the vocal folds are appreciated, the movement of the vocal folds is noted when the patient phonates a sustained constant vowel “e.” The findings are then documented and correlated with the laryngoscopy findings.
RESULTS AND ANALYSIS
Laryngeal ultrasonography was done in all 60 patients in the study. The vocal folds were appreciated, and the mobility was assessed successfully in 56 of these patients, and results were found to be correlating with the laryngoscopy findings in all these patients (Fig. 3). In four patients (one patient in group I and three patients in group II), the vocal folds could not be visualized by ultrasonography. This was due to severe calcification of the thyroid cartilage, which made no acoustic window possible for the sonography waves to pass from any angulations of the probe.
Figs 3A and B: Correlating laryngeal ultrasonography with laryngoscopy in right vocal fold palsy; (A) During inspiration—bilateral vocal folds are seen in the abduction position; (B) On phonation—the left vocal fold is seen adducting to midline with the immobile right vocal fold in a cadaveric position
Male to female sex ratio of the study population was almost equal in both groups, with 33 males and 27 females. Vocal fold assessment was possible in all females. Whereas out of the 33 males, vocal visualization was not possible in four males who were above 40 years of age with calcified thyroid cartilage.
Vocal fold assessment and mobility results had a 100% correlation in children and adults of age <40 years. The incidence of thyroid cartilage calcification was found to be high in patients >40 years of age. There were 17 patients with ages >40 years in our study, and in 13 of these patients (76.5%), vocal fold assessment was possible in spite of calcified thyroid cartilage by the angulation technique described earlier.
The results of laryngeal ultrasonography in groups I and II are represented graphically according to age distribution in Figures 4 and 5, respectively.
Fig. 4: Group I—normal mobility
Fig. 5: Group II—vocal fold palsy
The results obtained in the study were analyzed with indicators for a screening test
| Normal mobility diagnosed with laryngoscopy (group I—30 patients) | Vocal cord palsy diagnosed with laryngoscopy (group II—30 patients) | |
|---|---|---|
| Findings confirmed with ultrasonography | 29 | 27 |
| Findings not appreciated in ultrasonography | 1 | 3 |
Sensitivity for ultrasonography to diagnose vocal fold palsy = 27/30 × 100 = 90%; and specificity = 29/30 × 100 = 96.67%.
DISCUSSION
The interior of the larynx was first visualized when Manuel Garcia saw his own vocal folds with a dental mirror in 1854.8 The fiberoptic laryngoscope was introduced in 1976 and, since then, has undergone multiple advancements in optics and illumination.9 Today, stroboscopy and flexible laryngoscopy are the clinical gold standard to assess the structure and phonatory functions of the glottis.10 However, the procedure has its disadvantages, such as; the cost factor and the difficulty of doing the procedure in children and adults with an excessive gag reflex.2 Laryngoscopy and stroboscopy are aerosol-generating procedures and hence carry an increased risk of the spread of COVID-19 infection from an unsuspected carrier. In these cases, laryngeal ultrasonography is a viable and useful tool in such situations. Immediate postoperative on-table evaluation of vocal folds is possible with ultrasonography. The vocal folds can be assessed at the same time during thyroid ultrasonography, translating into an effective cost-saving screening tool.11,12 A further useful application of this tool would be to document vocal fold movements before head and neck, and thoracic surgeries.
Ultrasonic imaging depends on the reflection of sound from tissues of varying acoustic properties back into the transducer.13 Laryngeal ultrasonography has been useful in diagnosing laryngeal lesions since 1960.14 Tamura et al. were the first in 1973 to discover differential echoes from the free margins of the vocal folds.15 The larynx was visualized completely using ultrasonography by Noyek and Zizmor in 1977.16 By the late 1980s, ultrasound was used effectively to diagnose vocal fold lesions and analyze vocal fold mobility.4,17 Huang et al. reported that a probe frequency of 10–30 MHz is more effective in the diagnosis of vocal fold disorders.18 Vats et al. specified the use of laryngeal ultrasound in children to diagnose vocal fold paralysis as it is a noninvasive technique.19
Properly tuned ultrasound frequency can be used to visualize a slow-motion montage of vocal fold vibration.20 Vocal folds are seen as triangular, hypoechoic structures with their apex lying behind the reentrant area of the thyroid lamina with the base on the hyperechoic arytenoid vocal process. The hypogenicity of the vocal folds is due to its muscular part. The false folds are hyperechoic due to their fatty content and mucous glands.17 Raghavendra et al. demonstrated in ultrasonography that the vocal fold movements were visible in “real-time” during phonation and representative of normal respiration.17 Hino reported on the use of B mode in laryngeal ultrasonography to visualize the vocal folds.21
Ultrasonography is used as a routine efficient diagnostic tool for the head and neck. However, its use in the diagnosis of laryngeal disorders is still not well explored. This could be due to the acoustic extinction caused by the calcification of laryngeal cartilage. Recent studies on laryngeal ultrasonography show that when the probe is used in an oblique transverse plane bisecting the epiglottis and posterior-most part of the folds, the acoustic block by ossified thyroid cartilage can be bypassed.22 Further modifications, such as using a concave ultrasound probe, would improve visualization and, thus, the diagnosis.22 Bozzato et al. have noted that despite acoustic interference due to ossified thyroid cartilage that hindered the visualization of vocal folds in 16% of cases, the ultrasound depiction of laryngeal anatomy is still adequate.23
Many studies in the past have evaluated the efficacy of laryngeal ultrasonography as a diagnostic tool for benign vocal fold lesions in small populations. In a study by Vats et al.,19 there was 81% concordance between ultrasonic and endoscopic findings in vocal folds. Amis et al. reported that laryngeal ultrasound to assess vocal fold mobility might be a better modality for ruling out vocal fold paresis (specificity 89%) than for screening vocal fold paresis (sensitivity 71%).22 Matta et al.2 also reported a sensitivity of 92%. In a study by Wong et al. on postthyroidectomy patients, the sensitivity and specificity were 85.3 and 94.7%, respectively.24 A recent study by Nasser et al. recommends considering laryngeal ultrasound as the initial method of screening for structural or mobility pathology of the vocal folds.25
The results of our study show a sensitivity of 90% and a specificity of 96.67%. The prediction of the status of vocal fold mobility was 100% accurate when vocal fold visualization was not obscured. This accuracy was seen in 56 out of the 60 patients in our study. Children and young adults had 100% sensitivity in vocal fold assessment. Assessment of elderly males of age more than 40 years is a challenge in assessment. The latest linear probes with proper angulations can help to overcome this challenge. A total of 13 of 17 patients (76.5%) of the old age population were also successfully assessed in our study.
Laryngeal ultrasonography is a very effective tool to assess vocal fold mobility when a flexible or rigid laryngoscopy is not available. However, laryngeal ultrasonography has its limitations. It is a reliable tool to diagnose vocal fold palsy with challenges when the thyroid cartilage is severely calcified. The finer aspects of mobility, especially paretic motion, can only be effectively assessed by flexible laryngoscopy and not by ultrasonography.
We propose that laryngeal ultrasonography can be used to diagnose vocal fold palsy in the following situations:
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During the COVID-19 pandemic, as a routine screening tool for assessing vocal fold movement before any head-neck or thoracic surgery.
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To rule out vocal fold palsy as a reason for hoarseness in cases of communicable respiratory infections.
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For diagnostic examination in the pediatric age group not cooperating for flexible laryngoscopy.
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For preoperative documentation of vocal fold mobility as part of a thyroid scan.
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To screen for vocal fold mobility for patients requiring continuous intensive unit care when a facility for laryngoscopy is unavailable.
CONCLUSION
Transcutaneous laryngeal ultrasonography is a cost-effective, noninvasive, and easily available tool causing no radiation exposure in diagnosing vocal fold immobility. It is not an aerosol-generating invasive procedure like laryngoscopy; hence with proper precautions, it minimizes the risk of transmission of respiratory infections and thus can be effectively used during the COVID or any respiratory disease pandemic. This tool could be optimally utilized when patients cannot undergo laryngoscopy or when the required setup is not available. We acknowledge that the use of this tool may be difficult to some extent in elderly males due to severe calcification of the thyroid cartilage. Its use is limited to assessing just the mobility of the vocal cords and not in assessing the finer pathologies of the vocal cords.
COMPLIANCE WITH ETHICAL STANDARDS
Written, informed, and valid consent was taken from the patients.
SUPPLEMENTARY MATERIAL
Supplementary material has been provided on the website www.ijopl.com
ORCID
Anagha R Joshi https://orcid.org/0000-0002-2494-8512
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