Videostroboscopy

Introduction

Over the past 3 decades, expanding knowledge of vocal fold anatomy and physiology has revolutionized the clinical and surgical practice of laryngology. Since Hirano's original description of the layered microstructure of the human vocal fold in the 1970s, ^[1] increasingly sophisticated diagnostic and surgical techniques have evolved to more precisely address and preserve vocal production. Innovative diagnostic modalities have grown out of an improved understanding of the critical importance of vocal-fold pliability to voice production. Videostroboscopy has evolved as the most practical and useful technique for the clinical evaluation of the visco-elastic properties of the phonatory mucosa. ^{[2, 3, 4, 5]}

Key considerations

Video documentation of laryngeal anatomy along with its mechanical function is a painless, office-based procedure done with topical anesthesia and is essential for state-of-the-art management of human voice disorders.

Stroboscopy is a special method used to visualize vocal fold vibration. ^[1] It uses a synchronized, flashing light passed through a flexible or rigid telescope. 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. The video below depicts videostroboscopic examination of the vocal folds of an adult male.

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. The information acquired from the stroboscopic examination of the vocal folds is essential for planning effective phonomicrosurgery (endoscopic surgery to enhance vocal function) ^[6] . Optimal human voice production is dependent on optimal vocal fold vibration. This requires aerodynamically competent closure of vocal folds along with pliable phonatory mucosa.

Indications

Videolaryngoscopy with stroboscopy is the essential diagnostic procedure for the evaluation of laryngeal mucosa, vocal fold motion biomechanics, and mucosal vibration. ^[7] These are the key elements for detecting and assessing pathology as well as determining the impact on voice and airway function. ^[8]

Videostroboscopy fulfills several important requirements of a complete office voice examination. It provides useful, real-time information concerning the nature of vibration, an image to detect vocal pathology, and a permanent video record of the examination. As important as any of these aspects, stroboscopy substantially improves the sensitivity of subtle laryngeal diagnoses over techniques with continuous nonstroboscopic light sources (eg, rigid or flexible transnasal laryngoscopy).

Contraindications

There are no absolute contraindications, but the patient needs to be able to open his mouth or have a patent nasal airway.

Prognosis

The success of videostroboscopy depends upon patient comfort. Clear communication between the surgeon and patient before each step of the procedure is crucial to obtain adequate local anesthesia, to provide reassurance, and to diminish anxiety. The ideal candidate has a patent nasal airway, minimal gag reflex with flexible/rigid laryngoscopy, and is able to remain still, upright, and poised in the exam chair throughout the procedure.

Anesthesia

For rigid strobolaryngoscopy, it is often helpful to apply topical anesthesia (typically, Cetacaine spray) to the posterior aspect of the anterior tongue as well as the posterior oropharynx.

For flexible strobolaryngoscopy, the nose and nasopharynx are typically anesthetized and decongested with a mixture of 0.25% phenylephrine and 2-3% lidocaine using an atomizer.

Equipment

A videostroboscopic unit consists of a stroboscopic light source and microphone, a video camera, an endoscope, and a video recorder. Stroboscopy can be performed by using either rigid or flexible endoscopes; each has its own benefits and drawbacks. See the images below.

Standard 70-degree rigid strobolaryngoscope.

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Camera attachment with mounted microphone.

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Laryngeal microphone.

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Although flexible endoscopy is ideal for observing unaltered laryngeal behavior from various angles and for viewing the glottis through a narrow supraglottic aperture, it suffers from the low intensity of light carried through the long fiberoptic bundle to the tip of the narrow endoscope. With standard endoscopes, the light bouncing off objects being observed must then travel the length of the endoscope back to a camera or the operator's eye to be detected.

The introduction of distal-chip technology to flexible endoscopes, in which the camera is placed at the distal end of the scope (see image below), effectively lessened the drawback profile of flexible laryngoscopes. The enhanced digital picture quality with improved illumination has greatly improved the quality and resolution of transnasal laryngeal stroboscopy.

Distal chip flexible laryngostroboscope.

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Rigid telescopic transoral endoscopy produces the optimal image to assess phonatory mucosal pliability because of its magnified bright image; however, it requires extracting the patient's tongue forward throughout the examination, which distorts the natural phonatory posture of the pharynx and larynx. Moreover, the patient must have suitable anatomy and the physical tolerance (gag reflex) to allow the clinician to visualize the entire glottis.

Rigid endoscopy additionally requires increased patient cooperation and amenable patient anatomy for successful visualization of the larynx. Recent research has suggested that the application of the Mallampati classification system, as shown below, is useful for predicting the adequacy of transoral rigid laryngoscopic exposure for stroboscopy.

Mallampati classification.

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Positioning

Videostrobolaryngoscopy begins by seating the patient in the examination chair at a height comfortable for the examiner. The patient leans forward with the neck flexed and the head extended at the atlo-occipital joint (Kirstein position).

Complication prevention

When performing videostrobolaryngoscopy, it is important to consider the patient's overall health status. Body weight/body mass index may play a role in the difficulty of examination. It is also important to consider cardiopulmonary comorbidities. The patient's mental health may play a role in the patient's cooperation for the examination. Patients with excessive anxiety or mental illness may not be good candidates for videostroboscopy. Anticoagulation is a relative contraindication; however, clinical experience has shown complications to be rare in these patients, even if unable to be taken off anticoagulation medications.

It is also vital to consider the amount of topical lidocaine that is used to ensure the procedure is not complicated by lidocaine toxicity.

Rigid strobolaryngoscopy

The technique for rigid strobolaryngoscopy is described as follows:

1. Once the patient is in the appropriate position, it is often helpful to apply topical anesthesia (typically, Cetacaine spray) to the posterior aspect of the anterior tongue as well as the posterior oropharynx. The examiner should ensure that the microphone is calibrated properly and have the patient hold the laryngeal diaphragm against the thyroid lamina. With mouth open and tongue protruded, the examiner retracts the tongue anteriorly and carefully inserts the rigid telescope. Optimal examination hinges on the examiner’s attention to achieving proper focus of the vocal folds. Proper focus demonstrates clear visualization of the subepithelial vasculature of the vocal fold. To avoid condensation on the scope, the tip of the telescope is dipped in hot water just prior to beginning the examination.

2. With the vocal folds in clear focus, the examiner can take the patient through a number of vocal tasks using the “ee” sound. This should be done at low, mid-range, and high frequency pitches as well as different volumes. Soft glottal onset and offset (low subglottal pressure), especially in high-pitch frequencies, may also be of use to help define some smaller lesions. The examiner is also able to comment on arytenoid and vocal fold mobility, glottic closure pattern, mucosal wave, and pliability. Ulcerative lesions or masses can also be observed.

The image and video below depict rigid strobolaryngoscopy.

Depiction of rigid strobolaryngoscopy.

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Flexible strobolaryngoscopy

The technique for flexible stroboscopy is described as follows:

1. The patient is positioned as above. The nose and nasopharynx are typically anesthetized and decongested with a mixture of 0.25% phenylephrine and 2-3% lidocaine using an atomizer.

2. After allowing adequate time for decongestion, the flexible scope is inserted through the nose and passed in to position above the larynx. The examination described above can then be performed.

Current recording capabilities of the videostroboscopic examination allow the physician and patient to review the diagnostic findings during their office visit. This will lend itself to the decision for surgical management versus non-surgical management.

Recording capabilities allow for storage of preoperative and postoperative exam findings for long-term follow-up.