Interest in this subject was aroused about 5 years ago during routine pre-and post-thyroidectomy check up of the vocal cords. In our department it is customary to do a complete E.N.T. investigation on every patient due for a thyroidectorny and follow this up 1 month post-operatively. At first this was considered to be sufficient, but as our interest in the progress of the operated thyroid gland increased, spontaneous complaints of the patients as regards the voice assumed some sort of parttern. Patients volunteered, when questioned some months post-operatively, almost unanimously without any leading questions being asked, that their singing ability had been severely handicapped by this operation. A line of thought developed from this and we found it increasingly interesting to determine something more in these patients than just the state of wellbeing of the recurrent laryngeal nerve. The usual story was one of being unable to sing in the church or bathroom, although it turned out later that these people were very reluctant to sing anywhere else, especialty when asked to do so. This is, of course, of primary importance, the fact that our patients cannot by any standards be regarded as accomplised vocalists. It makes the examination all the more difficult when you cannot rely on the subjects' voice control, eg. keeping tune repeating a note of specific frequency, controlling the height of the larynx on phonation, etc. It strikes one every time how unmusical we really are when people are so tone deaf that they cannot repeat an ordinary scale after one. To start of with, we applied rough screening by making a tape recording of the singing voice and comparing tile pre- and post-operative results. As we progressed, more and more pitfals came up, eg. the tune had to begin on the same note every time and it is incredible how it takes hours of patience and encouragement with the majority of people to have them accomplish this. At the moment we feel that we have a fairly comprehensive check list in which we list interalia a full history note taking including previous operations, vocal pitch range, vocal tone, tone power, voice exhaustion and quality. Indirect mirror laryngoscopy is supplemented by laryngeal tomography, stroboscopic, examination and sound spectrum analysis. We have found it astonishing to hear various surgeons views on possible causes for the post-operative change in voice, ranging from scar tissue around the larynx to sutures being put into the cricothyroid muscle by accident. You are all aware of the difference of opinion that exists on the question of identifying the laryngeal nerves during the operation. I do not wish to lay myself open to criticism as regards the technique of operation.

Our Thyroidectomy report specifically includes the following:

INCISION
e.g. Height above manubrium
Lenght
Relation to Sterno cleido mastoid muscle
Depth.

STRAP MUSCLES
Sterno hyoid Left & right Were they cut
Stemo thyroid Left & right
Omo hyoid Left & right

ANSA HYPOGLOSSI
Was it cut or not?

PEDICLES AND VESSELS

NERVES
Recurrens Identified partially
or wholly
or not at all
Damaged
External laryngeal nerve
-Identified
-Damaged

CRICOTHYROID MUSCLE
Damaged, Diathermy

PARATHYROIDS
Identified
Removed

THYROID STUMP LEFT BEHIND
Approximate weight

OOZING
Amount

DRAINAGE

The great volume of material on thyroid surgery and injury to the laryngeal innervation deals with the recurrent laryngeal nerves. Frequently the superior laryngeal nerves are mentioned and a warning is given to avoid injuring them during dissection of the superior pole of the thyroid gland.

The signs of paralysis of the superior laryngeal nerve may be subtle and often overlooked because any change in voice other than total hoarseness after thyroidectomy has usually been thought due to laryngeal oedema and tracheitis, particularly if injury of the recurrent laryngeal nerve is not evident. However, these changes can be due to trauma or division of the external branch of the superior laryngeal nerve. If the nerve has been severed, the voice becomes easily fatigued, is lower pitched, has a decreased range and is often coarse or husky. These changes are often transient, but can be permanent and disastrous to the person relying greatly upon the use of his voice. During Thyroidectomy the superior thyroid vessels are located and their course and branches noted. The external branch of the superior laryngeal nerve is followed from its posterior situation above the hyoid bone, anteriorly and inferiorly, to its insertion into the thyro pharyngeal and cricothyroid muscles. Special attention is given to the relation between the external branch of the superior laryngeal nerve and the superior thyroid artery and their location with respect to the superior pole of the thyroid gland. We found that the external branch in approximately 80% of specimens lay immediately adjacent to the vascular pedicle of the superior pole of the thyroid gland. It is here that the nerve passes deep to the superior thyroid vesseis and could easily be included in a careless ligature passed around both vessels and their adjacent areolar tissue. Because this nerve lies within its own compartment in the visceral or deep layer of pretracheal fascia, and because the superior thyroid vesseis are incorporated into the outer layer pf pretracheal fascia, the nerve should not be injured if the vessels are individually ligated with care. Deliberate exposure of the external branch of superior laryngeal nerves at the superior pole of the thyroid should be routine even if the surgeon is aware of its intimate relation to the superior thyroid vesseis at this point and he should take the precaution of careful dissection and individual ligation of the superior thyroid artery and vein. That the nerve will often be visible in this location without search cannot be doubted. Our project is limited to those cases in which no obvious post-operative lesions can be found with the ordinary routine screening, in other words the common cord paralysis is excluded. With X-ray tomography we have found no significant data as yet. There is just as much upward movement of the larynx pre as post-operatively. We are not dogmatic about this though, seeing that we attach great importance to whether any of the strap muscles have been cut. We examine our patients with the stroboscope because the vibrations of the vocal cords durino ohonation are much too rapid to be followed by indirect laryngoscopy, but with the stroboscope an effect of slowing down can be achieved, enabling them to be followed and analysed by the naked eye. This apparent slowing down is brought about by the use, during indirect laryngoscopy, of an interrupted source of light. If, when the patient phonates, the frequency of the note uttered corresponds exactly with the frequency of the flashes of interrupted light, the same phase of the vocal cord movement will be illuminated by each flash, and the cords will appear to be motionless. If, however, the speed of the disc be so altered that there is a difference of one second between the frequency of the note and the light flashes, a slightly different phase of the vocal cord vibration will be illuminated by each flash, with the original phase re-appearing at the end of one second. It will appear, therefore, as though only one excursion of the vocal cords is taking place each second and the cords can be examined as regards behaviour and their margins in that position at rest. So one can determine whether one cord abducts faster than the other, whether they have the same amount of lateral excursion and also compare them as they move back towards their medial position. With this one can evaluate the thickness of the cords and also the attachment and mobility of the mucous membrane in the marginal area. It can also be of great significance to see whether the margins are touching each other (in chest register) along the whole length of the glottis or not; this may be important for determining with certainty the degree of vocalis pareses, or for locating in the earliest stage growths or a slight cord oedema which may exist subglottal and not be visible with normal laryngoscopes. With these examinations it is better to let the patient sing with a soft voice because then the influence of those pathologic changes on the cords upon their vibratory action is much greater and can be seen more easily. The Spectogram gives a visible picture of the spectral analysis of sound. In the case of speech the spectrogram portrays the frequency areas that are reinforced in the vocal tract. The narrow band presentation shows all harmonics of the vocal pitch that are passed by the process of resonance in the vocal tract. These harmonics with frequencies closest to the natural frequencies of the resonant cavities are more prominent than the others. The wide band presentation tends to integrate the high intensity frequency areas into wide formant bands so that individual harmonics are no longer visible. In the speech process the quality of the glottal tone is modified by the vocal tract in such a way that speech sound quality results. Ali components of speech sounds owe their existance in the first place to components in the glottal tone and in the second place to the resonce cavities. Any change in the quality of a particula speech sound, can only be attributed to change in the glottal tone. Comparing speech quality before and after thyroidectomies, means comparing glottal quality before and after the operation. The present pilot investigation aims to determine whether the thyroidectomy operation modifies glottal tone quality, and whether such a change, if present, can be measured. We found that cutting the strap muscles can lower the tone by as much as 75 cycles per second. This is probably due to the formation of scar tissue with contraction. Furthermore, failure to demonstrate and preserve the superior laryngeal nerve in 90% of cases affected the voice as can be seen from the spectrograph slides. Our preliminary findings therefore suggest that damage to the strap muscles and failure to demonstrate the superior laryngeal nerve are responsible for the post operative vocal changes following thyroidectomy.

NOTE: Slides will be shown to demonstrate the spectrograph recordings, anatomical considerations and stroboscope.

The Timbre and Pitch Range Variations Following Thyroidectomy.

Summary:

A research project is currently being conducted by our department of Otorhinolaryngology at the University of Pretoria into the possible causes of the timbre and pitch range, variations that may follow thyroidectomy. This investigation was promted by complaints of thyroidectomized patients that their singing ability had been severely handicapped by this operation. To date 140 cases have been evaluated in an effort to determine whether the operating technique does in effect influence the voice of the patient. Examinations include pre- and post-operative laryngoscopic, stroboscopic, sonographic and pitch range determinations as well as the routine notetaking and laryngeal tomography. During the operation particular attention is paid to any trauma of the strap muscles. Identification of the external branch of N. laryngeus superior, the N. laryngeus inferior and any possible damage to the M. cricothyroideus and external laryngeal muscles is noted. Our methods of examination are described, the results of the observations discussed and a possible explanation for this phenomenon is offered.

AUTOR: DR. JOHAN REYNERE
PRETORIA - SOUTH ÁFRICA