Abstract
Aims and Background:
Ultrasound (US) is useful for imaging the head and neck, including laryngeal disorders. The gold standard for diagnosing laryngeal abnormalities is flexible laryngoscopy; however, because US does not interfere with vocal cord vibrations and is useful in assessing vocal cord mobility issues, it is especially helpful for individuals who have an enhanced gag reflex.
Materials and Methods:
Eighty-six participants in prospective observational research were gathered in a tertiary care hospital between June 2022 and June 2024. Following informed consent, the patients were selected for the study based on inclusion and exclusion criteria. Using US grading, they underwent video-laryngoscopy and US neck to detect vocal cord palsy, and the data were tabulated and statistically analysed.
Results:
US can be used to assess vocal cord palsy, and various grading systems have been proposed to classify the severity of vocal cord dysfunction based on US findings. One commonly used grading system is the Aston Grade or Aston Classification, which categorises vocal cord palsy into four grades. Causes of cord palsy can be identified noninvasively like vocal cord polyps and neoplasms, and correlated with gold standard video-laryngoscopy.
Conclusion:
While US is a valuable tool for evaluating vocal cord function, assessing its specificity in diagnosing vocal cord palsy requires careful consideration of various factors, including operator expertise, equipment quality and patient characteristics. Despite challenges in specificity assessment, US remains an important adjunctive imaging modality in the diagnostic evaluation of vocal cord dysfunction.
Introduction
Vocal cord paralysis (VCP) can result from any condition that disrupts the normal functioning of the vagal or recurrent laryngeal nerves. It may serve as an initial indicator of a broader and more serious underlying pathology.[1]
The vocal cords are essential for phonation, and the muscles controlling their movement are primarily innervated by the recurrent laryngeal nerves. These nerves are branches of the vagal nerves. Because of the extensive anatomical pathways of the vagal and recurrent laryngeal nerves, numerous disease processes can lead to VCP. Various factors such as malignancy, surgery, infection, trauma and inflammation can all contribute to the development of VCP.[1]
Radiologists need to recognise the imaging features and potential mimics of VCP. Lesions affecting the vagal and recurrent laryngeal nerves can lead to VCP.[1]
Approximately 40% of unilateral VCP and 50% of bilateral VCP are attributed to surgical injury. Thyroid surgery is more frequently the cause of bilateral VCP, whereas unilateral VCP is more commonly associated with other surgeries such as carotid endarterectomy, anterior cervical spine approaches and surgeries involving the heart or great vessels.[1,2]
Ultrasound (US) offers a straightforward, efficient and noninvasive approach to diagnosing vocal cord palsy with real-time, dynamic two-dimensional (2D) or three-dimensional (3D) imaging. Despite the widespread availability of US in medical practice, its application in laryngeal disorders remains limited.[3]
US proves valuable in head and neck imaging, including laryngeal conditions. Although flexible laryngoscopy is the gold standard for diagnosing laryngeal disorders, US is particularly beneficial for patients with an increased gag reflex, as it does not disrupt vocal cord vibrations and is effective in evaluating vocal cord mobility disorders.[3]
The incidence of VCP was 0.42%, or 42 per 10,000 new patents. Most cases (77.2%) occurred in patients in their 50s and 60s. Hoarseness of voice was the predominant symptom, reported in 83.6% of cases. In 60% of instances, the onset of symptoms was gradual. The left vocal cord was affected nearly twice as often (61.9%) as the right vocal cord (38.1%).[3]
The vocal cords consist of mucous membrane infoldings that extend horizontally across the middle of the laryngeal cavity. They attached anteriorly at the angle on the interior surface of the thyroid cartilage and project posteriorly to the arytenoid cartilages on either side.[3]
Use of US in vocal cord palsy reveals a growing body of evidence supporting its efficacy and utility in both diagnosis and management. US, traditionally employed in various medical fields, has emerged as a valuable tool for evaluating vocal cord function due to its noninvasiveness, cost-effectiveness and real-time imaging capabilities.
Diagnostic Accuracy
Numerous studies have highlighted the high diagnostic accuracy of US in identifying vocal cord palsy. US enables clinicians to visualise vocal cord movements dynamically, aiding in the identification of asymmetry, reduced mobility and other characteristic features associated with palsy. Comparative studies with traditional imaging modalities, such as laryngoscopy, have demonstrated the sensitivity and specificity of US in diagnosing vocal cord palsy.
Dynamic Assessment
Unlike static imaging techniques, US provides real-time, dynamic assessments of vocal cord function. This dynamic visualisation is crucial for capturing subtle abnormalities in vocal cord movement and assessing the impact on phonation. Clinicians can observe vocal cord dynamics during various vocal tasks, offering a more comprehensive understanding of the extent and nature of the impairment.
Guidance for Interventional Procedures
US serves as a valuable guide for clinicians performing interventions related to vocal cord palsy. Needle electromyography (EMG) and botulinum toxin injections, commonly used in the management of vocal cord palsy, can benefit from US guidance. Real-time visualisation allows for precise needle placement, improving the accuracy and efficacy of these procedures while minimising the risk of complications.
Monitoring Treatment Response
Longitudinal studies have demonstrated the utility of US in monitoring treatment response. By tracking changes in vocal cord mobility and function over time, clinicians can objectively assess the effectiveness of therapeutic interventions. This capability is particularly valuable in tailoring individualised treatment plans and optimising patient outcomes.
Paediatric Applications
Research in paediatric populations suggests that US is a well-tolerated and informative tool for assessing vocal cord function in children with congenital or acquired palsy. Its noninvasive nature makes it particularly suitable for repeated assessments in paediatric patients, contributing to the comprehensive management of vocal cord disorders in this population.
Challenges and Limitations
While the literature generally supports the use of US in vocal cord palsy, some studies acknowledge certain limitations, such as operator dependence and challenges in obtaining optimal imaging in certain patient populations.[4] Standardisation of techniques and training for clinicians may address these issues and further enhance the reliability of US in this context.
Materials and Methods
The study’s design is prospective observational. There are 86 patients in the cohort who had both vocal cord palsy symptoms and risk factors for the condition. The study was carried out at Apollo Main Hospital’s Radiology and Imaging Sciences Department on Greams Road in Chennai, Tamil Nadu, India.
Population under study were 86 patients of both sexes make up the study population. All of the patients taking part in the trial gave their written consent after the Institutional Ethical and Scientific Committee gave its approval. Study group included patients with vocal cord palsy symptoms, such as hoarseness, loss of pitch, choking when swallowing food, drink or saliva, vocal fatigue and noisy breathing, as well as those with cord palsy risk factors listed in the inclusion criteria. Study excluded people not undergoing laryngoscopy for comparison and intubated patients.
Methodology
Patients referred for vocal cord sonography who met the inclusion criteria were initially screened for a history of thyroidectomy surgery and informed consent was obtained from all participants.
The study employed the Philips high-resolution US scanner with a linear transducer with frequency bandwidth of 7–12 MHz was used and US system equipped with dynamic imaging. B-mode was used to record the images throughout.
Patient was positioned in supine with neck extended. The thyroid cartilage is to be identified by palpation and the probe to be moved superiorly and inferiorly till different laryngeal structures are visualised.
The glottis was visualised at or near the midpoint of the distance between the thyroid notch and inferior border of the thyroid cartilage.
The US will be done in two phases:
Normal position of vocal cords during quiet breathing—both cords are adducted in median position
Statistical Analysis
The mean (±) standard deviation (SD) was used to represent all continuous variables. Percentages were used to express each classified variable. The independent sample t-test was used to compare continuous variables. The ideal cutoff value for vocal cord palsy will be determined by comparing categorical variables using the chi-squared test or Fisher’s receiver operating characteristic (ROC) in order to identify the best sensitivity and specificity. A precise test that takes into account the quantity of observations. Specificity and sensitivity will be calculated. The MS-Excel spreadsheet was used to enter the data. IBM SPSS version 28.0 was used to validate and analyse the data. P values less than .05 were all regarded as statistically significant.
Observations and Results
Statistical Analysis
There were 92 cases collected in total during our study duration, out of which 6 were excluded on the basis of our exclusion criteria. Four patients did not undergo laryngoscopy correlation, and two patients were intubated. Eighty-six patients were recruited for the diagnostic accuracy study. All the patients underwent high-resolution B mode US imaging and a confirmatory diagnostic video-laryngoscopy. Out of 86 cases, 56 cases were having unilateral palsy, and 30 cases were having bilateral palsy.
Descriptive statistics were provided using frequency (percentage) for categorical variables and Mean (±) SD for continuous variables. Median (interquartile range [IQR]) was presented while the data was skewed. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated to determine the accuracy between laryngoscopy and side vocal cord palsy findings. All statistical analysis was carried out by using SPSS (IBM, 28.0)
Demographic Factors
We found that the overall mean age of the patients in our study was 46.84 (±) 12.99. The minimum age among the patients was 22 years, and the maximum was 82 years (P value = .183); hence, no statistically significant relationship was found between age groups and vocal cord palsy [Table 1].
Age in years
Overall, out of the 86 patients, 56 (65.1) were male, and the remaining 30 (34.9) were female (P value = –.077). No significant relation between gender and diagnosis of vocal cord palsy was observed in our study [Table 2].
Gender distribution
Imaging and Laryngoscopy Characteristics
Overall, out of the 86 patients, 56 (65.1) were unilateral cord palsy, and the remaining 30 (34.9) were bilateral cord palsy [Table 3] on US [Figure 2].
Side of vocal cord palsy
Bar graph for accuracy between laryngoscopy and side of vocal cord palsy
Overall, out of the 86 patients, 53 (61.6) were having grade II cord palsy, and 16 (18.6) were having grade I cord palsy, 15 (17.4) were having grade III cord palsy and remaining 2 (2.3) were having grade IV cord palsy [Table 4; Figure 3].
Grading of cord palsy on US
Pie chart for grading of cord palsy on high-resolution B mode sonography
Overall, out of the 86 patients, 68 (79.1) presented with hoarseness of voice and the remaining 18 (20.9) were having presentation due to other causes [Table 5].
Clinical presentation
Overall, out of the 86 patients, 55 (64) had surgical causes and the remaining 31 (36) were due to other causes [Table 6].
Causes
Overall, out of the 86 patients, 56 (65.1) were unilateral cord palsy, and the remaining 30 (34.9) were bilateral cord palsy [Table 7] on laryngoscopy.
Laryngoscopy findings
The sensitivity of US in detecting vocal cord palsy can vary depending on several factors, including the experience of the operator, the quality of the equipment used and the specific characteristics of the patient’s anatomy and pathology.[5]
However, studies have generally shown US to be a sensitive imaging modality for diagnosing vocal cord palsy [Table 8] and diagnostic accuracy between laryngoscopy findings and side vocal cord palsy [Table 9].
Sensitivity and specificity
Diagnostic accuracy between laryngoscopy findings and side vocal cord palsy
Sensitivity (95% CI): 90 (73.5–97.9); Specificity (95% CI): 94.6 (85.1–98.9)
PPV (95% CI): 90 (74.8–96.5)
NPV (95% CI): 94.6 (85.8–98.1)
Discussion
US can be used to assess vocal cord palsy, and various grading systems have been proposed to classify the severity of vocal cord dysfunction based on US findings. One commonly used grading system is the Aston Grade or Aston Classification, which categorises vocal cord palsy into four grades:
In Grade I, there is partial immobility of the affected vocal cord. The affected cord may demonstrate reduced mobility or incomplete abduction/adduction during phonation or quiet respiration. This grade indicates relatively mild impairment of vocal cord function
Grade II involves significant immobility of the affected vocal cord. The affected cord typically demonstrates limited or absent movement during phonation or respiration. While some mobility may be present, it is notably reduced compared to Grade I.
In Grade III, there is complete immobility of the affected vocal cord. The affected cord remains fixed in a paramedian or lateral position, with no discernible movement during phonation or respiration. This grade indicates a severe impairment of vocal cord function, potentially leading to significant voice and respiratory difficulties.
Grade IV represents total immobility of the affected vocal cord. The affected cord remains fixed in a paramedian or lateral position, with no movement observed during dynamic US examination. This grade indicates the most severe form of vocal cord palsy, resulting in profound voice and respiratory impairment.
The Aston Grade system provides a standardised approach to assess vocal cord palsy using US, facilitating communication among clinicians and researchers regarding the severity of the condition.
However, it is essential to note that other grading systems may exist, and the choice of classification may vary depending on institutional preferences or specific research objectives. Additionally, US findings should be interpreted in conjunction with clinical history, laryngoscopy and other diagnostic modalities for comprehensive evaluation and management of vocal cord dysfunction.
The sensitivity of US in detecting vocal cord palsy can vary depending on several factors, including the experience of the operator, the quality of the equipment used and the specific characteristics of the patient’s anatomy and pathology. However, studies have generally shown US to be a sensitive imaging modality for diagnosing vocal cord palsy.
High Sensitivity in Detecting Structural Abnormalities: US is particularly sensitive in detecting structural abnormalities associated with vocal cord palsy, such as reduced mobility, asymmetry and abnormal positioning of the affected vocal cord [Figure 4]. The real-time imaging capabilities of US allow for the dynamic evaluation movement of vocal cords during various tasks, enhancing sensitivity in identifying subtle abnormalities.[6]
Comparison with Laryngoscopy: Several studies have compared the sensitivity of US with flexible laryngoscopy, which is considered the gold standard for diagnosing vocal cord palsy. While laryngoscopy provides direct visualisation of the vocal cords, US has shown comparable sensitivity in detecting vocal cord palsy, particularly when performed by experienced operators.[7]
Dynamic Evaluation: US offers the advantage of dynamic evaluation of vocal cord function, allowing clinicians to assess the range of motion and coordination of the vocal cords during phonation, respiration and swallowing. This dynamic assessment improves sensitivity in detecting subtle abnormalities that may not be evident on static imaging modalities.[8]
Paediatric Population: Studies have also demonstrated the sensitivity of US in detecting vocal cord palsy in paediatric populations, where traditional laryngoscopy may be challenging or less tolerated. US is well-tolerated and can provide accurate assessment of vocal cord function in children with congenital or acquired palsy.
Limitations and Challenges: Despite its high sensitivity, US may have limitations in certain clinical scenarios, such as cases where the acoustic window is limited due to patient factors or anatomical variations. Additionally, operator-dependent factors, such as skill and experience in performing and interpreting US examinations, can influence sensitivity.
b) Left adductor palsy on video-laryngoscopy
In summary, US is generally considered a sensitive imaging modality for detecting vocal cord palsy, offering real-time visualisation and dynamic assessment of vocal cord function. While it may have limitations and challenges, particularly in certain patient populations or clinical scenarios, US remains a valuable tool in the diagnostic evaluation of vocal cord dysfunction. The specificity of US in diagnosing vocal cord palsy refers to its ability to accurately identify cases where vocal cord dysfunction is present and rule out cases where it is not present. While US is a valuable imaging modality for evaluating vocal cord function, its specificity can vary depending on several factors, including operator expertise, equipment quality and patient characteristics.
Here is an overview:
Differentiating Normal from Abnormal Function: US can distinguish between normal and abnormal vocal cord function by visualising their positioning and movements during various tasks, such as phonation, respiration and swallowing. Specificity is enhanced when abnormalities, such as reduced mobility or asymmetry, are clearly identified and correlated with clinical symptoms. Comparative Studies with Gold Standard: Assessing the specificity of US often involves comparing its findings with those of the gold standard for diagnosing vocal cord palsy, typically flexible laryngoscopy. Studies have shown that US can achieve high specificity when performed by experienced operators and interpreted in conjunction with clinical history and other diagnostic tests. Challenges in Specificity Assessment: Determining the specificity of US in vocal cord palsy can be challenging due to the lack of a universally accepted reference standard for comparison. While flexible laryngoscopy is commonly used as the gold standard, discrepancies in findings between the two modalities can occur, leading to uncertainty in specificity estimates. False Positive and False Negative Results: False positive results, where US incorrectly identifies vocal cord dysfunction, and false negative results, where it fails to detect existing pathology, can impact specificity. Factors contributing to false positives may include misinterpretation of normal variations or artifacts as pathology. False negatives may occur due to technical limitations or inadequate visualisation of the vocal cords. Operator Expertise and Experience: Operator expertise plays a crucial role in achieving high specificity with US. Experienced operators are better able to distinguish normal variations from pathological findings, reducing the likelihood of false positive results and improving overall specificity. Patient Factors and Anatomical Variations: Specificity may also be influenced by patient factors, such as body habitus, anatomical variations and the presence of comorbid conditions. Certain anatomical variations, such as neck position or thyroid cartilage abnormalities, can affect the interpretation of US images and potentially impact specificity.[9]
Grading Systems on Video-laryngoscopy
Grade I: Normal mobility.
Grade II: Reduced mobility with normal glottis closure.
Grade III: Paradoxical motion (incomplete closure).
Grade IV: Fixed position (no movement).
Mild, moderate and severe classifications. Clinical Evaluation:
Methods used by ENT specialists to assess vocal cord function.
Importance of laryngoscopy and other diagnostic tools.
Voice changes (hoarseness, breathiness). Swallowing difficulties. Potential respiratory issues (especially in severe cases).
b) Video-laryngoscopy confirms bilateral adductor palsy
Ultrasound imaging of neck of a 54-year-old male presenting with hoarseness of voice showing
Lobulated heteroechoic lesion with internal vascularity, wider than taller nodule in left lobe of thyroid with extra-thyroid extension into strap muscles anteriorly and left side recurrent laryngeal nerve
Left abductor palsy—left side vocal cord is in medial position during phonation and quiet breathing
Ultrasound imaging of neck of a 49-year-old male presenting with hoarseness of voice showing
Left abductor palsy—grade I in patient with hoarseness of voice
Video-laryngoscopy confirming left abductor palsy
Results of US in Vocal Cord Palsy
US can provide several valuable results in the evaluation of vocal cord palsy, although its primary role is typically in initial assessment rather than definitive diagnosis or prognosis. Here are the key results that US can contribute:
Visualisation of vocal cord position: US can visualise the anatomical position of the vocal cords at rest[11]. It helps identify if there is any asymmetry or abnormal positioning of the vocal cords, which may suggest unilateral vocal cord palsy or paralysis.
Detection of Structural Abnormalities
US can detect structural abnormalities such as vocal cord nodules, polyps, cysts or masses that may contribute to vocal cord dysfunction [Figure 8]. These findings can guide further diagnostic and treatment decisions.
Ultrasound imaging of neck of a 43-year-old female presenting with hoarseness of voice showing
Right vocal nodule—well-defined hypoechoic lesion with posterior acoustic enhancement
Video-laryngoscopy shows right vocal cord nodule
Assessment of Vocal Cord Mobility
While not as comprehensive as dynamic assessment methods like laryngoscopy, US can sometimes detect reduced or absent movement of a vocal cord during phonation or breathing. This observation can support the diagnosis of vocal cord palsy or paralysis [Figure 9].
b) Video-laryngoscopy showing phonatory gap
Evaluation of Surrounding Structures
US can assess the adjacent structures such as the thyroid gland, trachea and lymph nodes. This can help identify potential causes or associated conditions contributing to vocal cord palsy, such as thyroid disorders or tumours.
Monitoring Changes Over Time and Prognosis
US can be used to monitor changes in vocal cord position or size over time, which may be relevant for assessing response to treatment or progression of the underlying condition.
However, it is important to note that US has limitations in providing a comprehensive assessment of vocal cord function and may need to be complemented by other imaging modalities (like laryngoscopy, computed tomography (CT) or magnetic resonance imaging (MRI)) and functional tests for a thorough evaluation of vocal cord palsy.
Conclusion
In conclusion, while US is a valuable tool for evaluating vocal cord function, assessing its specificity in diagnosing vocal cord palsy requires careful consideration of various factors, including operator expertise, equipment quality and patient characteristics. Despite challenges in specificity assessment, US remains an important adjunctive imaging modality in the diagnostic evaluation of vocal cord dysfunction.
Footnotes
Acknowledgements
Thanks to the research department, Apollo Main Hospital, Chennai, Tamil Nadu.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship and/or publication of this article.
Institutional ethical committee approval number
Institutional ethical approval has been obtained (2005–2022).
Informed consent
Informed consent has been obtained from all patients who met eligible criteria.
Credit author statement
MR participated in conceptualization, data analysis, literature search, investigations, draft preparation, and review.
SK and MKK participated in conceptualization, investigation, supervision, data analysis, and manuscript editing.
All the authors reviewed and approved the manuscript.
Data availability statement
Data supporting the findings of the study is available with the corresponding author.
Use of artificial intelligence
No AI tools were utilized.