Laryngostroboscopy

Laryngostroboscopy is a specialized endoscopic technique for examining the larynx in detail. It allows precise evaluation of the vibratory function of the vocal folds during phonation. By using intermittent (stroboscopic) light, the technique creates the optical illusion of slowed vocal fold movement. This makes it possible to analyze their oscillatory patterns accurately.

This method is considered the gold standard for assessing voice disorders causing dysphonia. It provides invaluable information about vocal fold biomechanics that cannot be obtained with conventional laryngoscopy using continuous light.

Principle of the Method

Human vocal folds vibrate at very high frequencies, typically between 100 and 300 Hz in adults. Under continuous illumination, these rapid movements appear blurred. Stroboscopy overcomes this limitation by capturing successive phases of vocal fold vibration.

The procedure works as follows:

1. A microphone placed on the patient’s neck records the fundamental frequency of the voice (F₀).
2. A stroboscopic light source, attached to the endoscope, emits brief flashes of light.
3. The flash frequency is synchronized with the vocal fold vibration but slightly offset, usually by 1–2 Hz.

Each flash illuminates the vocal folds at a slightly different phase of their vibratory cycle. The human eye and video camera integrate these sequential “snapshots” into a continuous slow-motion view of the vocal folds in oscillation.

Technique and Evaluated Parameters

The examination is performed using either a rigid or flexible endoscope connected to a video camera and stroboscopic light source. The patient is asked to sustain a vowel sound, most often “ee”, at varying pitch and loudness.

Key parameters assessed include:

• Symmetry: The examiner evaluates whether the left and right vocal folds move in a mirror-like manner.
• Regularity (periodicity): Oscillatory movements are assessed for rhythm and consistency across cycles; aperiodic vibrations indicate pathology.
• Amplitude of vibration: The lateral displacement of the vocal folds from the midline is measured.
• Mucosal wave: The mucosal wave refers to the wave-like motion of the vocal fold mucosa. It is a key parameter reflecting the elasticity of the tissue. Reduced or absent waves indicate scarring, tissue infiltration, or stiffness.
• Glottic closure: The pattern of contact between the vocal folds during the closed phase of vibration is examined, which may be complete, incomplete, or hourglass-shaped.

Clinical Role

Laryngostroboscopy is an essential tool in phoniatrics and otolaryngology for evaluating hoarseness. It enables clinicians to distinguish functional voice disorders from organic pathology. The technique is particularly valuable for assessing vocal fold lesions. Nodules and polyps generally do not disrupt the mucosal wave, whereas cysts, scars, or malignant lesions abolish it in the affected region. Stroboscopy is also crucial for diagnosing vocal fold paresis and paralysis. Furthermore, it is widely used to assess vocal fold function before and after phonosurgical procedures.