Laryngeal Video Stroboscopy Introduction

BERNARD TAWFIK, MD ♦ IDEL MOISA, MD Diplomates, American Board of Otolaryngology

LongIslandENTDoctors.com Specializing in Adult and Pediatric Disorders of the Ears, Nose, Throat and Neck ■ Sinus Infections Endoscopic Sinus Surgery Computer Image Guided Surgery Balloon Sinuplasty ■ Nasal / Sinus Allergies ■ Sleep Apnea ■ Snoring ■ Head & Neck Surgery Thyroid Gland Parathyroid Glands Salivary Glands Oral Cavity Larynx Esophagus ■ Acid Reflux Disease ■ Pediatric ENT ■ Hearing and Balance ■ Voice and Swallowing FEESST Trans-Nasal Esophagoscopy Laryngeal Video Stroboscopy ■ Affiliations New York University School of Medicine Glen Cove Hospital Winthrop University Hospital ProHealth Ambulatory Surgery Center DayOp Center of Mineola

The vocal cords are unique structures that exhibit two different types of motion – repetitive medial-to-lateral motion and high frequency oscillations. More appropriately termed the true vocal folds, each of these paired structures are composed of the vocalis muscle, elastic tissue, Reinke’s space, and overlying mucosa (Figure 1). Their posterior attachment to the arytenoid cartilages allows repetitive motion in a medial-to-lateral direction during voice production. Traditionally, we evaluate this motion under direct visualization using a dental mirror, a flexible fiberoptic laryngoscope, or a rigid endoscope. With “normal vocal fold motion,” there is full medial-to-lateral motion; the absence of such movement is known as “vocal fold paralysis.” High frequency oscillations of the vocal folds cannot be appreciated by the unaided eye and is evaluated using stroboscopy. Phonation results from a cyclic interaction between exhaled air and these rapid vocal fold oscillations of the glottic cycle. Proper evaluation of these vocal fold oscillations is therefore necessary in describing vocal function and in evaluating voice disorders.

Principles of Stroboscopy

Since the vocal folds vibrate at rates of 75 to 1,000 cycles/second, even the slowest vibratory patterns cannot be visualized without assistance. Stroboscopy is thus necessary to evaluate the vibratory patterns of the vocal folds that occur too rapidly to be visualized by the unaided human eye. During stroboscopy the larynx is visualized with a pulsed Xenon light source that allows rapid on-and-off bursts. In this manner, the larynx is visualized for only brief periods in the range of 1/1,000 of a second. Stroboscopy thus creates an illusion of continuous, slow-motion mucosal oscillation. This generates a series of still images of the vocal folds at slightly 1

different points across several glottal cycles, which are fused into an apparently fluid and continuous sequence by the examiner's eye. In modern stroboscopic equipment, the rate of laryngeal vibration is sensed by a microphone and used to control the rate of Xenon light firing. Video recording is important for documentation and improves accuracy in the diagnosis of vocal problems. Review of the stroboscopy, both at normal and reduced speeds, can reveal aspects of pathology not seen on initial examination. In addition to providing information regarding vibratory status, video recordings can be reviewed for comparison with previous examinations. Recorded laryngeal stroboscopic examinations can be used to follow changes in the glottal vibratory pattern over days, weeks, and years. This helps determine the effects of behavioral, medical, and surgical interventions on the larynx. Interpretation of laryngeal video stroboscopy requires knowledge of the stroboscopic appearance of the healthy larynx phonating at various frequencies and intensities. Evaluation criteria include symmetry, amplitude, periodicity, mucosal wave propagation, and glottal closure.

Indications for Laryngeal Video Stroboscopy

Laryngeal Video Stroboscopy is very useful in the following situations: • Assessing alteration of the mucosal waves due to vocal fold fibrosis or scarring as a result of previous trauma, intubation injury, surgery or inflammatory disease • Assessing vocal fold mobility and tone after paralysis • Demonstrating decreased vocal fold tone associated with vocal fold atrophy • Demonstrating recovery of vocal fold function after vocal fold surgery or laryngoplastic phonosurgery • Diagnosing superior laryngeal nerve paresis or paralysis • Identifying individuals potentially at risk for significant intubation injury • Evaluating the functional significance of mucosal and submucosal vocal fold pathology such as vascular lesions, varices, nodules and papillomas • Identifying early vocal fold carcinomas • Evaluating the thickness and depth of invasion of neoplastic lesions, such as leukoplakia or early carcinoma. Stroboscopy is not useful in assessing invasion of early carcinoma that involves the anterior commissure or arytenoids.

Summary

Vocal fold oscillations induced by exhaled air creates cyclic changes in air pressure. This is perceived as sound. Mirror, flexible or rigid laryngoscopy permits evaluation of the repetitive medial-to-lateral motion of each vocal fold in its entirety. Laryngeal Video Stroboscopy is the only technique that allows clinical imaging of vocal fold oscillations, which is not possible with still-light examination. It is the single strongest diagnostic instrument in most cases of dysphonia, especially for those disorders related to disturbances of mucosal vibration. In addition, Laryngeal Video Stroboscopy is helpful in identifying early vocal fold neoplasms, as well as evaluating their thickness and depth of invasion. In summary, Laryngeal Video Stroboscopy is the only practical way of imaging mucosal oscillation and the optimal way of identifying abnormalities in mucosal pliability secondary to an underlying neurologic process, trauma, surgery, early benign neoplasms, or early malignancies. Review of the videotaped stroboscopic examination in normal and slow motion greatly increases the accuracy of the voice evaluation.

Figure 1. Cross section of the true vocal fold.

This newsletter is provided in the interest of general medical education and is not intended as specific medical advice. For specific advice, please consult your physician.

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