Comparison of ultrasound frequency in laryngeal ultrasound for vocal cord evaluation.

BACKGROUND: Laryngeal ultrasound is a new method of vocal cord evaluation in patients at risk for vocal cord palsy. However, the previously described laryngeal ultrasound reportedly has a high failure rate of vocal cord visualization in male patients. We compared 2 ultrasound frequencies in laryngeal ultrasound to improve on the limitations of this method.

METHOD: A total of 301 (55 male, 246 female) consecutive laryngeal ultrasound and direct laryngoscopy exams were performed for patients with thyroidectomy and other neck operations. High-frequency transducer (12-5 MHz broad band spectrum) and low-frequency transducer (9-3 MHz broad band spectrum) were used for all laryngeal ultrasound. Findings were independently cross-validated with direct laryngoscopy.

RESULTS: High-frequency and low-frequency laryngeal ultrasound had 88.4% and 97.7% visualization rates, respectively. In addition, low-frequency laryngeal ultrasound showed improved sensitivity of 97.6% and specificity of 96.5%, compared with a sensitivity of 92.9% and specificity of 86.5% for high-frequency laryngeal ultrasound in vocal cord evaluation.

CONCLUSION: The low-frequency laryngeal ultrasound method significantly enhances the visualization of vocal cords, especially in patients who have diffuse thyroid cartilage calcification interrupting laryngeal ultrasound, and therefore enhances the overall efficacy of laryngeal ultrasound as a perioperative diagnostic tool for vocal cord palsy. Hence, we recommend using a low-frequency transducer (about 9-3 MHz) for laryngeal ultrasound if it is available.