Understanding Laryngeal Stroboscopy

Key Glossary Terms

Rigid Laryngoscopy
An examination of the voice box in which a rigid telescope is used; this examination provides the clearest magnified detail of the voice box, but the patient is unable to speak or sing during the exam

Flexible Laryngoscopy
An examination of the voice box in which a flexible fiberoptic scope is used; this examination allows the physician to view the voice box in action (i.e., while the patient is producing sound)

Stroboscopy
An examination in which a strobe light is combined with rigid or flexible laryngoscopy, allowing an examination of vocal fold vibration and vocal fold closure

Glossary

• Vocal folds vibrate so fast during sound production that this vibration is impossible to see with the naked eye, similar to the wings of a hummingbird.
• Stroboscopy is a special method used to visualize vocal fold vibration. It uses a synchronized, flashing light passed through a flexible or rigid telescope to visualize vocal fold vibration. The flashes of light from the stroboscope are synchronized to the vocal fold vibration at a slightly slower speed, allowing the examiner to observe vocal fold vibration during sound production in what appears to be slow motion. This "slow motion picture" is an illusion, as the speed of actual vocal fold vibration is not changed by stroboscopy.
• This special viewing allows the voice care team to evaluate each vocal fold's vibration properties during the different phases of the vocal fold's vibration cycle. Because vocal fold vibration is so fast, the "slow motion" view is actually derived from many successive vibration cycles. (For more information, see Anatomy & Physiology of Voice Production.)
• Stroboscopy also provides detailed information regarding the pattern and duration of vocal fold closure during sound production.
• The stroboscopy light can be used with a flexible laryngoscope or a rigid laryngoscope.

Stroboscopy provides key information needed in the investigation of voice disorders. It allows the examiner to evaluate two key components of sound production.

1. Vocal fold vibration: Stroboscopy provides detailed and often essential information on the nature, degree, and quality of vocal fold vibration.
   • How regular is it? Normal vocal fold vibration is regular and periodic.
   • How wide do the vocal folds open during vibration?
   • Are the left and right vocal folds "balanced" during vibration? Normal vocal folds are "balanced" or symmetrical.
   • How pliable are the vocal folds? Normal vocal folds are pliable (i.e., not stiff) hence demonstrate a normal "mucosal wave."
   Key Information

   Mucosal Wave

   Stroboscopy allows the examiner to assess the mucosal wave. The "mucosal wave" is the term used to refer to the pattern of light traveling on the top surface of the vocal folds during vibration – seen on stroboscopy.

   Mucosal wave is the wave-like movement of the vocal fold cover (epithelium + superficial lamina propria) over the vocal fold body (vocalis muscle).

   How Assessing Mucosal Wave Helps in Diagnosis of Voice Disorders

   • How dynamic this mucosal wave is reflects how pliable the vocal fold covering is, hence how efficiently the folds vibrate.
   • Decreased mucosal wave reflects stiffness of vocal fold which can be caused by swelling, scarring, etc.
   • Areas or spots with mucosal wave abnormality signal where lesions on or within the vocal fold most likely are.

2. Vocal fold closure: Stroboscopy provides information about the nature, degree and quality of vocal fold closure.
   • How well do the vocal folds close? Normal vocal folds can achieve complete closure during the vibratory cycle.

Vocal fold vibration and closure are essential for normal sound production. Even minor abnormalities of vocal fold vibration or closure can account for significant voice problems. Changes in vocal fold vibration detected by stroboscopy provide important clues to the cause or causes of the voice problem.

• Stroboscopy is essential when a voice disorder is due to abnormalities that affect vocal fold vibration. These abnormalities span a spectrum of disorders, such as:
  • Vocal fold scarring
  • A mass (e.g., cyst, polyp, nodule)
  • Incomplete closure of vocal folds
  • Abnormal vocal fold vibration
• Stroboscopy is often required to identify the causes of voice disorders. It can pinpoint the underlying problem or problems with vocal fold vibration so treatment can be directed appropriately.

• Stroboscopy can only be used when the patient's voice is fairly stable. Thus stroboscopy is not possible for patients with severe voice loss or hoarseness.
• Stroboscopy provides a view of vocal fold vibration from the top (a two-dimensional image). Although this view is clearly informative, it cannot evaluate the region of the vibrating vocal folds below (a three-dimensional image).
• Investigation of certain voice disorders (e.g., vocal fold scarring, sulcus vocalis, etc.) needs to include both three-dimensional views of the vocal folds and tactile assessment of the vocal folds, as can be done using microlaryngoscopy.

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