Department of Ear, Nose and Throat, Hospital of Besancon, France and *Private Practice, Lausanne, Switzerland
Summary: The history and principles of stroboscopy are reviewed, and stro- boscopic findings during videolaryngoscopy are evaluated in relationship to the rest of the laryngological clinical evaluation to arrive at the bases for a stro- boscopic semiology. Key Words: Diagnosis--Videostrobolaryngoscopy-- Stroboscopy---Tumor.
Stroboscopy is as useful to the clinician as indi- rect laryngoscopy or laryngeal endoscopy because it allows evaluation of the dynamic aspects of vocal fold vibrations. Stroboscopic examination of the vocal folds provides information for a quick and precise phoniatric diagnosis that is useful for med- ical, functional, or surgical treatment, as well as for follow-up. Stroboscopy is of use to the phoniatrist, the ear, nose, and throat surgeon, the speech pa- thologist and, when used in conjunction with a video tape recorder, to the patient.
Quite often phoniatric consultation is sought by professional voice users who have noticed slight breathiness, hoarseness, intensity difficulties, or changes of timbre within their phonatory range. Granted that many quality changes may have their origin in the vocal tract resonatory system or alter- ations in the laryngopharyngeal mucosa, clinical ex- perience teaches that most difficulties are attribut- able to anomalies of the mucosal wave of the vocal folds. Stroboscopic examination permits assess- ment of the flexibility of the vocal fold (perfect, moderate, uni- or bilateral, total or partial). Stro- boscopy may demonstrate suspicious phenomena suggestive of organic pathology that could be an obstacle to a professional career. We believe that stroboscopy is of great value to both the clinician and the professional voice user.
Address correspondence and reprint requests to Marie-Agnes Faure, 32 Rue Coquilli6re, 75001 Paris, France.
HISTORICAL BACKGROUND
In Greek, strobos means whirling and scopein signifies watching or observing. Perello has de- scribed stroboscopy as "un metodo creado para observar un organo que se mueve con un rno- vimiento regular." The principle of stroboscopy was simultaneously discovered by Plateau in Brus- sels and yon Stampfer in Vienna in 1833. It was first applied to laryngeal examination by Toepler in 1866; by 1878, Oertel had extended its use to laryn- gology.
The eye cannot discriminate separate images that last <1/5 second because of the interaction between the length of the stimulus image and the persistence of the image on the retina. This explains why, to the unaided eye, the vibrating vocal folds seem to be stationary except for some low-frequency move- ments under certain conditions. The problem of re- solving the too-rapid motion is solved by illuminat- ing the larynx with brief flashes of light at a fre- quency just slightly less than their vibratory rate. Perello provides the example of a patient phonating at musical ut2, which is 128 Hz. Light flashes with a frequency of 127 Hz will slow the apparent vibra- tory rate to one glottal cycle per second, which pro- vides a good slow-motion view of the glottic wave. According to Kitzing, the difference between the phonatory frequency and the rate of light flashes should be -1.5 Hz.
The first mechanical stroboscope, called strobo-
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rama, was constructed by Sequin-Tarneaud; the first electronic stroboscope was built by Cary and Guillet in Paris in 1931. Commercialization of the instrument was accomplished by Timcke in 1956 (1). The first major publication on stroboscopy, Schoenharl's Die Stroboskopie in der praktischen laryngologie, appeared in 1960 (2). There have been many articles on the subject in medical journals, but the second overall review of the area has been pre- pared by Hirano and Bless (3).
Present-day stroboscopes usually indicate the frequency of the phonatory signal and, occasion- ally, its intensity. With phase variability the dy- namic aspect of the vocal folds can be assessed. It is common to couple the instrument to video re- cording systems to store results for research, teach- ing, and treatment. Speech pathologists, phonia- trists, and surgeons may also generate hard-copy prints of the video images to augment clinical records.
Stroboscopy through a fibroscope is also possi- ble. It allows the analysis of vowels less closed than / i /and/e/ , but the image obtained is frequently too small and too blurred for careful analysis of mu- cosal wave patterns. Some researchers (4-7) have used a microscope to magnify the stroboscopic im- age. Wendler proposed telemicrostroboscopy in 1973 (8). In 1977 Kittel reported using color tele- videostroboscopy (9). Computerized manipulation of the stroboscopic image also holds considerable promise.
GLOTTIC WAVE AND STROBOSCOPY
Figure 1, modified from Hirano (10), illustrates the stroboscopic representation of the vertical mo- tion of the mucosal wave, first suspected by Schon- had (11) and Smith (12). The glottic wave tells us about the status of the tissue situated between the superficial mucosa of the vocal fold (the cover), and the vocal muscle (the body). The deep and interme- diate layers of the lamina propria connect the body and cover and serve as a transition between the two. The free motion represented by this wave may be diminished by all kinds of adhesions between the superficial mucosa and ligament resulting from sev- eral different primary and secondary pathologies (such as chronic inflammation). The adhesions in- crease the stiffness of the fold and limit its move- ment. In clinical consultation we try to observe the transverse movement of the muscular body of the
FIG. 1. Schematic presentation of vocal fold vibration. Left col- umn: frontal section; right column: view from above. (Repro- duced with permission (120).)
vocal fold and the vertical wave motion of the mu- cosal cover.
STROBOSCOPIC SEMIOLOGY
This semiology has benefitted enormously from the very specialized work of Drs. Cornut and Bouchayer (13) of Lyon. Conditions for successful evaluation of the glottic wave include comfortable phonatory intensity; fundamental frequencies that provide an optimal view of the vocal folds; the vowel / i / fo r low frequency phonations; use of the
S T R O B O S C O P Y 141
patient's habitual speaking Fo. (High frequencies and head voice are associated with low vibratory amplitude and therefore should be avoided.)
Characteristic phenomena to be observed include the vibratory amplitude of the glottic wave, which provides insight into the flexibility of the mucosa and its freedom from the underlying body of the vocal fold. Mucosal flexibility is associated with a clear voice and rich resonance. Specific aspects of importance are amplitude of the opening phase; am- plitude of the closing phase; bilateral symmetry of these amplitudes; diminution of the opening phase; diminution of the closing phase; variability with phonatory frequency or intensity; and phase delay of wave activity when comparing the two folds.
Abnormal stiffness of the glottic wave is also im- portant, and may present in several ways: complete and permanent stiffness on the whole length of the fold (unilateral or bilateral); permanent stiffness on part of the vocal fold (one-third or two-thirds of the
FIG. 2. Bilat. sulcus-vergeture in a 44-year-old man.
FIG. 3. Bilat, epidermoid cysts in a M-year-old woman.
fold unilateral or bilateral); and vibratory "escape" on a localized part on the opening phase or the clos- ing phase. The permanence of the "escape" may vary with frequency or intensity.
Differential Diagnosis The differential diagnosis rests on four criteria:
flexibility of the glottic wave; glottic shape; acous- tic qualities of the voice; and history of the dyspho- nia.
Stroboscopic Findings Clinicians using the stroboscope must be able to
relate the vibratory pattern to the anatomical con- figuration and to the pathophysiology of the disor- der. This requires interpreting the stroboscopic re- cordings relative to normal expectations. The fol- lowing details the major stroboscopic findings.
Static vocal fold concavity, unilateral or bilateral, may be apparent with diminished closing phase; oval glottic shape; slight veiled timbre, absence of richness; slightly diminished intensity; and occa- sionally difficulties maintaining a sufficiently wide
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vocal scale, correct timbre, or intensity appropriate to the setting. Note that this concavity suggests ei- ther a bilateral or unilateral glottic sulcus of the open cyst type, whose pathogenesis is congenital. There may eventually be a localized or extended vergeture or mini-vergeture (stria) (33, Fig. 2).
A localized bulge may be well delimited at the upper part of the free border of the vocal fold. It may have more or less transparency than the sur- rounding tissue. The bulge may be accompanied by diffuse inflammation; arborescent capillary dilation or longitudinal dilatation; stroboscopic manifesta- tions of stiffness or significant decrease of vibratory amplitude or decrease of the opening phase of a small localized segment (e.g., adynamic segment); permanent wheezy or hoarse timbre with bitonality; decreased vocal frequency range; strong or weak vocal intensity; and a long history of vocal difficulty (perhaps hereditary problems), which argues more for an intracordal epidermoid cyst (Fig. 3). In con- trast, recent infection with sudden and persistent acoustic and resonance changes implies a submu- cosal cyst with less vascularization. Note that, ac- cording to Cornut and Bouchayer, retentional mu- cous cysts are often anterior or more subglottic. Furthermore, several aspects of the disorder termed monocorditis often mask a congenital ipsi- lateral or contralateral subjacent lesion, although dysfunction may be associated with a particular ef- fort. This clinical term should be replaced by one based on the associated pathology.
Bulging of the free margin of the vocal fold may be associated with stroboscopic evidence of flexi- bility and a complete disappearance of the bulge during the opening phase; a glottal hourglass shape during phonation; and variations of timbre for cer- tain pitches and intensities. Note that total disap- pearance of the bulge during the opening phase sug- gests a fusiform edema, or nodules. A more trans- lucent bulge that does not completely disappear during opening phase suggests a pseudocyst. If the bulge is sufficiently voluminous, it may diminish the stroboscopic amplitude, as in the case of large pol- yps.
A blunt anterior commissure with radiating vas- cularization associated with slight glottic gap on phonation, other pathologies (including, according to Cornut and Bouchayer, nodules and pseudo- cysts), diminished stroboscopic flexibility of the an- terior-most quarter of the vocal fold. This should arouse suspicion of an anterior or subcommissural microcongenital web. The web may provide some
explanation for the hyperfunctional laryngeal ten- sion.
In pseudomyxoma and Reinke's edema, the myx- oid material generates a massive inertia. Surgical intervention is rarely an urgent issue in any of the nonmalignant pathologies described previously.
Malignant tumors often show superficial inflam- matory changes or hyperplasia with keratosis or moderate to severe dysplasia. In these cases stro- boscopy shows a major and localized mucosal stiff- ness, which is an urgent signal for biopsy and his- tological evaluation before radiotherapy or surgery.
Laryngeal paresis (flaccid) results in a loss of muscle tone of the affected side. This implies de- creased stiffness of the vocal fold body, which makes the entire vocal fold operate mechanically as a single structure because the body is as flaccid as the cover. The vibratory pattern of such a relaxed vocal fold is characterized by wide undulating mo- tions (like the fluttering of a flag) and, as Kitzing has noted, by marked reduction or absence of the mu- cosal wave. After successful vocal fold augmenta- tion there is generally acoustic and functional indi- cation of improvement in the glottic closure, even if the stroboscopic evidence does not suggest com- plete recovery.
Vascular or capillary ectasia that seem to be isoo lated call for an examination to show possible sub- jacent pathology (intracordal cyst, nodule, mi- croweb). Occasionally these isolated ectasia show substantial change in the stroboscopic movement pattern. They may be part of the class of constitu- tional vascular fragility and may respond to medical or behavioral phoniatric treatment.
Follow-up stroboscopic examination allows pre- cise evaluation of the healing of the mucosa, partic- ularly in its depiction of the freedom of the mucosal wave. However, inflammation that follows surgical procedures, even after 7-8 days of complete vocal rest, restricts glottic flexibility as observed strobo- scopically. Recovery of the glottic wave may not be apparent until as late as the third postoperative month.
Many phoniatrists note a failure of glottic wave recovery, or diminished vibratory amplitude after laser procedures. This may also be the case after excessive surgical removal of lesions, which leaves a tissue defect that may extend as far as the vocal ligament.
Ventricular fold phonation may present with a distinct stroboscopic picture. The ventricular folds may be seen to approximate but not actually vi-
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S T R O B O S C O P Y 143
brate; they may be seen to approximate and to vi- brate; and they may be seen to adduct and though not approximated show clear signs of vibration; and occasionally they may be seen to adduct and inter- act to produce sound, as in some cases of so-called hyperphonia. In some cases the ventricular folds are the primary sound source.
Isolated small stroboscopic asymmetries that co- incide with partial changes in vocal register or that occur at specific frequencies within the vocal range disappear after a few sessions of functional therapy. The effect is produced by relaxation of the laryngeal suspensory musculature, which modifies the forces on the larynx and the mass of the vocal folds, per- mitting better acoustic functioning that can be visu- alized stroboscopically.
We have abandoned the terms hyperfunctional and hypofunctional in describing voice disorders. We believe that they frequently represent cordal pathology (often congenital) or compensation for an isolated difficulty that can be rehabilitated. Strobo- scopic study of the vowe l s / i / and /e / a t several fre- quencies produced in ascending and descending scales and at different intensities may confirm or eliminate suspicions of vocal pathology.
FUTURE CLINICAL POSSIBILITIES
Laryngeal stroboscopy has come a long way in the past 100 years (1-255), yet there are still many desirable improvements. In the near future we could imagine the following improvements and de- velopments for stroboscopic generators:
1. Standardization of intensity level, frequency level, and phase indications. These data will also appear on the screen of any associated video system.
2. Greater light intensity to allow better use of flexible fiberscopes.
3. Standardization of video systems (maintaining color fidelity during stroboscopy; having high fidelity audio recording and reproduction; and having colored video printing of specific se- quences such as inspiration and one cycle of vibration at normal pitch and loudness).
4. Providing the possibility of obtaining precise millimetric measures from the video screen or video print.
5. Simultaneous stroboscopy and kymography (Gross and Schultz-Coulon) so as to obtain more precise quantitative measures.
6. Coupling of stroboscopy to inexpensive sound spectrographic analysis; electroglottography; and frequency and intensity analysis with pa- per printout for clinical records.
7. Higher video frame rate recordings.
Having achieved these enhancements, stroboscopy may well be considered the best all-around clinical laryngological diagnostic procedure.
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