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Laryngeal Video
Stroboscopy
Introduction
BERNARD TAWFIK, MD ♦ IDEL MOISA, MD
Diplomates, American Board of Otolaryngology
LongIslandENTDoctors.com
Specializing in
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Larynx
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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
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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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