Unilateral True Vocal Cord Paralysis

Our patient today is a 60-year-old gentleman who presented to the VA Clinic at the otolaryngology complaining of hoarseness. He had this hoarseness for about three months and he noticed that he had been coughing a little more, and having to work a little harder to breathe. He noted that it had all began following a thoracotomy that he had three months earlier for the excision of a mediastinal mass. When we examined him, we found that his maximum phonation time was limited to five seconds. He did indeed have a very weak cough along with a decrease in his vocal range and in his projection. This is a video here of what was seen on laryngoscopy and you notice a couple of different things. You notice that he had a left true vocal cord that was fixed in a paramedian position. There was a minimal amount of bowing. There was about a 3-4 mm glottic gap and there was some pooling of secretions. This led us to a diagnosis of a likely recurrent laryngeal nerve injury during his thoracic operation leading to a true vocal cord paralysis. He was treated with a thyroplasty and he has done very well postoperatively, but it did lead me to think more about thyroplasty and I wanted to learn more about it.

Now, the history of laryngology is where treatment of voice disorders all began. It began with the invention of the mirror laryngoscope by Manuel Garcia back in 1855. Mr. Garcia was actually an opera teacher. His technique was modified by Drs. Czermak and Turck in 1858 to be used for actual clinical laryngology. Then in the post civil war era, laryngeal surgery really took off. Dr. Solis-Cohen, who had been a general surgeon for the Union Army, actually performed the first successful treatment of laryngeal tumor using excision through a mirror laryngoscopy. Then in the late 1880s, Dr. Dwyer began to do routine cannulation of the larynx. When you combine that with a laryngoscope invented by Kirsten in 1895, you end up with a routine ETT intubation for airway control, which revolutionized surgery. With the onset of endotracheal intubation, we then could do more general anesthetic, longer procedures, achieve better control of the airway, and along with intubation and better surgery came more recurrent nerve paralysis. An injection laryngoplasty was first used in 1911 by Dr. Buening to treat cord paralysis. The problem that he had with this, however, was that he was using mostly bone paste and it was absorbed very quickly, and so this fell out of favor because he was not getting very good long-term results. Dr. Arnold, in 1955, re-popularized the idea. Then in 1974, Dr. Isshiki published a paper describing the first medialization thyroplasty and the arytenoid adduction procedure in 1978. Dr. Jamie Koufman began to popularize these techniques in the United States and medialization laryngoplasty in 1986 brought together, in one term, arytenoid reduction and type I thyroplasties.

To understand thyroplasty, a detailed understanding of laryngeal anatomy is obviously important. The larynx is basically a tube for passage of air that is controlled by a very intricate valve. There are false folds and true folds. The true folds are, of course, the phonatory organs that control the airflow. Histology is very important in understanding how they work. They are composed of an epithelium, which is only eight cell layers thick. Beneath that is a lamina propria composed of a superficial, middle, and deep layer with varying amounts of elastin versus collagen as you move from superficial to deep. Beneath these layers is the vocalis muscle, which is the medial most portion of the thyroarytenoid muscle. These layers can be further classified in to: the cover, which is the epithelium and the superficial lamina propria; the vocal ligament, which is the middle and deep lamina propria; and, the body of the core, composed of the thyroarytenoid muscle. It is important because the epithelium and the lamina propria are able to slide over the vocal ligament and create the fine vibrations that give us our voice and our fine control of air passage. This is controlled by a very intricate series of muscles. Conventionally, we only have one abductor at the posterior cricoarytenoid. The other muscles are considered adductors. There is also, in recent literature, a compartmentalized theory of how these muscles work. This theory states that even these intrinsic muscles are further divided into subcompartments, each to receive their own sub-innervations. Although this has been supported by sophisticated biochemical and neurophysiological studies involving fibrotic grouping, it is of questionable functional and clinical significance. Bringing all this together gives us the normal anatomy of the larynx that we see.

The innervation of the larynx comes entirely from the vagus nerve. There is a superior laryngeal nerve that has an internal branch that supplies sensation to our glottis and supraglottis, an external branch that provides movement for the cricothyroid muscle, and the recurrent laryngeal nerve that provides sensation to the subglottis and motor innervation to the intrinsic muscles of the larynx outside of cricothyroid.

Understanding the anatomy of the recurrent laryngeal nerve vital to appreciating how injury can occur. The right recurrent laryngeal nerve follows the carotid artery down to the neck. At the level of the innominate artery, it loops underneath the subclavian and comes back up into the neck in a tracheoesophageal route. The right recurrent laryngeal nerve is much shorter than the left nerve; it is only about 6 cm in length. Also, it takes a more lateral course as it comes through the neck. It enters the tracheoesophageal close to the cricothyroid membrane, coming laterally across the neck from the subclavian artery up into the groove during most of its course, and has a variable relationship with the inferior thyroid arteries, which are the majority of its blood supply. The left recurrent laryngeal nerve is different. Like the right, it runs with the carotid artery through the neck; however, it does not loop underneath until it gets to the arch of the aorta, at the level the ligamentum arteriosum it does loop and stays much more medial in the neck. It enters the tracheoesophageal groove much earlier and then stays medial in this groove until it enters the larynx of the cricothyroid membrane. It is also much longer, twice as long, leading to a much higher likelihood of injury during its course.

The neurophysiology of how vocal fold paralysis happens in the setting of recurrent laryngeal nerve injury is also very interesting. Complete denervationthrough nerve ligation can happen, but it is typically very rare. More often there is a dysfunctional reinnervation, which can be either inadequate or inappropriate, depending on the particular mechanism of injury. Dysfunctional reinnervation accounts for anywhere from 70%-85% of all vocal cord paralyses. Vein nerves repair themselves during regeneration. This is an example of a single axon regenerating itself after an injury. The myelin sheath forms a sort of a pathway and the axon travels down this highway until it gets back to its original motor endplate. Nerves are composed of enormous piles of axons composing a fascicle that is wrapped in the perineurium and the numerous fascicles are wrapped in epineurium. In inadequate reinnervation, only a limited number of these fascicles return to the original motor units and so while some of the muscle is reinnervated, some is not. That portionof muscle which is not reinnervated atrophies and becomes dysfunctional resulting in motor unit dysfunction and a larynx that just does not work correctly. An inappropriate reinnervation can be characterized as such: you end up with the same nerve that has been cut, same group of fascicles that are going to go back to their target destinations, but they do not go back to their original locations. Now let us take, for example, the red, innervated and adductor and the blue innervated and abductor. You know how the nerve had originally innervated and adducting muscle giving information to an abducting muscle. This ends up with what is called synkinesis, where you have abductor and adductor antagonists acting together on discoordination. You think you want your larynx to close and it opens and it ends up with a very discoordinated motion in the larynx, often with abductors and adductors acting together at the same time. The vocal folds simply cannot close or open correctly when this happens. This is fairly well documented in both human and animal models.

The etiology of recurrent laryngeal nerve injury is that the vast majority of them are neoplasms and trauma. There are some idiopathic causes along with some inflammatory causes and CNS etiologies like the Guillain-Barré syndrome and cerebrovascular disease. But neoplasms and trauma are what we are going to focus on today. In terms of neoplasms, it is important to remember that lesions that can cause recurrent laryngeal nerve injury can occur anywhere from the skull base down to the upper thorax, given especially, on the left side, the long course of the recurrent laryngeal nerve. It also has a much poorer prognosis than in surgical injuries. There have been a numbers of studies documenting that there is a fairly high rate of recovery in most traumatic injuries, but a very low rate of recovery in many cases of neoplastic infiltration of the nerve.

The most common cause of a neoplastic injury to the nerve is thyroid cancer. This is an MRI showing a patient that had papillary thyroid carcinoma who had a recurrent nerve paralysis at the time of presentation. It can be very impressive when it happens. In terms of trauma, it is important to distinguish surgical injury such as Bovie injury, stretch compression, and ligation versus injury that can happen from endotracheal intubation. Nearly 10% of all recurrent laryngeal nerve injuries actually can be attributed to intubation injury. The mechanism of the injury is that the endotracheal tube compresses the intralaryngeal segment of the anterior branch of the recurrent laryngeal nerve, the thyroid cartilage and the arytenoid cartilage causing compression of the nerve and a compression injury with demyelination and injury to the nerve. In terms of surgical injury, thyroid surgery is by far the most common cause. Anywhere from 0.5% to 2.4% of these can be permanent. Slightly more of them can be temporary and the vast majority does recover spontaneously. In terms of thyroid surgery and the recurrent laryngeal nerve, the main thing to be considered is whether or not to use the monitor, and usually this depends on the surgeon’s preference.

There are various studies documenting this choice, but the general consensus is that it can be very useful, especially for recurrent goiters, revision surgery, and for patients with a known malignancy, but it is still boils down to surgeon’s preference. But it is important to remember that thyroid surgery is by far the most common etiology of an iatrogenic recurrent laryngeal nerve injury, although intubation injury can still be the cause even in a patient recovering from thyroid surgery. Anterior approaches to the cervical spine can also have about a 2%-6% incidence of recurrent laryngeal nerve injury. We are unsure about how the mechanism occurs with either stretch or compression. One thing that was interesting is that there has been an association with right-sided approaches. There have been three studies documenting this: the most recent by Dr. Morpeth and Williams in 2000, one study by Dr. Netterville and one study by Dr. Robinson. This we have studied as a catalog 500 patients who had had anterior cervical spine surgery. Of these, 41 of them had had injuries to the recurrent laryngeal nerves, and of those 41, 39 of them had approaches from the right side as opposed to the left side. They are unsure of the mechanism, but it may have something to do with the more lateral course of the right recurrent laryngeal nerve. Another thing important to remember: a lot of times in an anterior approach of the cervical spine, recurrent laryngeal nerve is not identified and the retractors that are placed, putting a great deal of pressure on the recurrent laryngeal nerve, which can add to the likelihood that the nerve is going to be pinched between the tracheal tube and the walls of the larynx. It is therefore important to think about this when a patient present asking us to evaluate them for hoarseness.

Thoracic surgery can also be an etiology of recurrent laryngeal nerve injury and these lesions are going to have a fairly high rate of preoperative nerve paralysis to begin with based on aneurysms, thoracic tumors, and pancreas tumors. The left nerve is at much increased risk in thoracic surgery because it is the one that dips down into the mediastinum, but the rate of nerve paralysis is hardly procedure dependent. Open heart operations, as you can see, have a fairly low incidence of injury whereas lung surgery, esophageal surgery, and then, of course, thoracic aortic aneurysm surgeries have much higher rates of nerve injury. It is also important to be aware that with thoracic surgeries, the nerve injury can be a known and deliberate complication. The nerve might be in the way of tumor resection or the aneurysm repair and the surgeon will even document that the nerve injury is known and happened. For the endarterectomy, it is also certainly considered when looking at the surgical causes of nerve injury. The incidence is about the same as it is for anterior cervical spine surgery and the mechanism is also, likewise, unknown. However, one thing that is proposed is that the vagal fibers that are eventually going to produce the recurrent laryngeal nerve are slightly more vulnerable at the level of a carotid bulb where they are doing the operation. At this level, the recurrent laryngeal nerve fibers are actually running very medially in the vagus nerve and you can see from the strand that the nerve is running just lateral to the carotid artery. So, during this process, any manipulation of the nerve at the level of the carotid bulb is most likely to impinge on the recurrent laryngal nerve fibers first and therefore cause potential recurrent laryngeal injury.

So, a patient now presents to your office complaining of hoarseness. You suspect nerve injury. How are you going to evaluate them? The first thing is to take a very focused history. There is also a vocal capability battery and upper airway endoscopy. There are a few key components of the history to think about. One is that is there is a temporal relationship with surgery. Has the patient had anterior cervical spine surgery, or thyroid surgery recently? Do they have any other neurological symptoms, especially the contralateral symptoms that might raise the likelihood of a stroke or Guillain-Barré syndrome or some other central nervous system pathology? Was the onset gradual, suggesting tumor infiltration, or was it sudden, suggesting traumatic injury? More importantly, does the patient have dysphagia, which can be very important in deciding on treatment options? It the patient is complaining about their voice, we are going to be very concerned about the airway, about dysphagia, and about aspiration.

Patients who have mild hoarseness and thin liquid dysphagia probably have an isolated nerve injury and probably tolerate it for a while and wait to see what happens. If is were a more severe dysphagia with nasal regurgitation, an increased likelihood of higher vagal injury necessitates more urgent repair. In someone who has hoarseness with the hypopharyngeal outlet obstruction that cannot get any down, thin about the possibly of an esophageal malignancy or etiology. The center of that complaint is that there is going to be very high pitch to their voice, sometimes called the paralytic false air. They are going to have impaired yelling projection. They cannot close their glottis. They cannot generate the force necessary to yell and project their voice. They are going to have what is called the air-wasting phenomenon. Basically what happens in this condition is that because they cannot completely close the glottis, they cannot contain tight regulation of airflow. So they cannot keep their alveoli open as long as they normally would during expiration, and cannot use air in their lungs as efficiently. They can become winded more easily, and are going to be more tired at the end of the day because they are wasting a lot of the air that they bring into their lungs. They simply cannot use it very efficiently. They have impaired airway protection, and are going to have loss of their ability to perform Valsalva maneuvers.

In terms of the vocal capability test, ask the patient to read aloud, usually the Rainbow Passage in the English language, listening to them for voice luffing or a raspy, sloppy sound of the voice that they try to project. In fact, their vocal range is going to be decreased especially at the higher frequencies. Listen to them cough. If they are not able to, we are sure to listen to maximum phonation time. Have the patient count as high as they can or hold a single sound as long as they can. In a normal patient, it is going to be 10 seconds or longer. In patients with nerve paralysis, it is going to be shorter, usually in the neighborhood of 5 or 6 seconds. This is an example of the patient with a nerve paralysis reading that passage. It is very gruff sounding and he cannot project. Endoscopy, usually videostroboscopy, but sometimes flexible laryngoscopy is performed. You find the larynx at rest and during phonation. Look at its position. Look at symmetry of vocal cord closure and how well the vocal cord is lined up. Look at soft palate elevation and the way the pharyngeal fore closure. This is an example of what you would you like to see: nice symmetric elevation of the soft palate suggesting that the vagus nerve is fully intact. You also evaluate the oropharynx and hypopharynx and try to evaluate, if you can, laryngeal sensation. This can be done with a flexible laryngoscope. Doing all those maneuvers can help you establish if this is a high vagal lesion or an isolated recurrent laryngeal nerve injury. Based on these findings, you can perform other imaging studies. Usually a CT scan with contrast or MRI with contrast can be helpful, keeping in mind to go from the skull base all the way down to the mediastinum to be sure and get the course of recurrent laryngeal nerve. If you think that the patient might have an esophageal problem, esophagoscopy and esophagograms can always be performed. A neurology consultation can be useful if you have suspect a central nervous system pathology.

Now I would also like to go over some other treatment modalities used for unilateral recurrent nerve paralysis. The main goals of treatment, of course, are to improve glottic competence. The patients are going to be more satisfied if they get their voices back. We, as clinicians, are going to be most happy because they recover their ability to close their glottis and protect their airway. Your goals are to improve their hoarseness, improve their dysphagia, and prevent aspiration. The modalities that we can use include voice therapy and medialization procedure, either injection or open, and then the potential for laryngeal reinnervation based on some fairly contemporary work. One of the most important things are to consider is the timing of the treatment, which is determined by a number of factors. One is the location of injury, which impacts the severity of their dysphagia and aspiration., and even how likely they are to recover. If you believe that the patient has a higher vagal injury that is not likely to recover, and they are going to have problems with dysphagia and aspiration, you may be more inclined to perform a procedure earlier rather than later. This may provide them with more ability to protect their airway and hopefully prevent pneumonia or other severe complications. Even if the patient has a highly likelihood of recovery, based on, for example, ENG potentials that show that the nerve is starting to regenerate, you might want to do consider doing something more temporary, like an injection, to try and buy them some time while the nerve recovers.

The first modality that can be used is voice therapy. The main goal here is to strengthen the larynx and teach the patient compensatory mechanisms: forced adduction, glottic attack, and things like that. Many times these patients will report some subjective improvement in their voice. This also may help to improve their dysphagia. This can be helpful until a more definitive repair is made and can be very helpful when the patient is recovering from a laryngoplasty procedure, in terms of maximizing the effectiveness and the use of the thyroplasty either as an open implant or injection.

In terms of injection laryngoplasty, there are two places you can put the injection. You can either go lateral into the thyroarytenoid muscle or in the perichondrium of the thyroid cartilage or you can go medially into the vocal ligament itself. This is based on what you are trying to accomplish and what material you are going to use. You have a bowed paralyzed cord here, over on the left side. After the injection you feel especially the anterior and middle portion of the cord and, hopefully, the goal is to restore glottic competence. Materials that are ideal for lateral injection include Teflon. Substances that are thicker have more body to them, and require higher gauge needles to inject them. Teflon, adipose, autologous fascia and hyaluronic acid have been used a lot for these purposes. The one thing to keep in mind if you are going to use Teflon, is that it can form granulomas. Teflon is more often used in patients who are older because this can be an eventual complication down the road. Items that are used for medial injection to the vocal medial ligament include Gelfoan, collagen/Cymetra, which is cadaveric collagen, and hyaluronic acid. These are materials that are more viscous and are designed to provide more physiological return of function to the vibratory surface of the vocal fold.

Then there is open thyroplasty. This was first described by Dr. Isshiki in 1974. The basic principle was to create a window in a thyroid cartilage to provide you some access to the larynx. You then insert an implant that permanently medializes the cord. This can be augmented with either arytenoid adductions or posterior flange to address a more posterior glottic gap. When it is performed, you measure a window in the thyroid cartilage. It is going to hopefully approximate to the point at which you want to enter to access thorax. Usually this is going to be about 5-8mm behind the midline. The dimensions of the window can easily be around 5-6mm in the vertical dimension and about 13-14mm in the horizontal dimension. Once you determine the one, you drill it out. You then elevate the perichondrium off the internal surface of the cartilage and use a particular instrument to measure how much adduction is necessary. Once this has been accomplished, you carve your implant and insert it. This is what you end up with preop and postop, with a nice permanent medialization of the paralyzed cord, which provides glottic competence. There are some variations on the thyroplasty technique. There are lots of different thoughts on where to put the window, how big to make the window, and potentials for minifenestration procedures. There are a lot of people, Dr. Netterville for example, who would like to use pre-carved implants versus implants that you carve yourself. Then there is the potential for usage of other posterior or lateral flanges. On the left you see a lateral flange, which is used to help hold the implant in place. Some people pass sutures through the lateral flanges. There is also the pastier flange, shown on the right, which can help provide closure of a posterior glottic gap since these implants are usually much better at providing anterior and middle approximation than providing closure of the posterior glottic gaps.

There are also multiple different materials that can be used. Silastic and Gortex are the two most common, and they are probably easiest to deal with, especially after the revision. You form a nice fibrous capsule around the mix and it is fairly easy to revise and put a new one in. Hydroxyapatite tends to become integrated into the cartilage and can be difficult to deal with in the setting of a revision thyroplasty.

You can also perform a concomitant arytenoid adduction if you are concerned about a posterior glottic gap. This has been most ardently advocated by Dr. Netterville. Treatment adduction is used to close the posterior glottic gap. The basic idea is to hopefully rotate the vocal process anterior and medially. This is actually done by placing a stitch to rotate the muscular process anteriorly and laterally, which provides a medial and anterior rotation of the vocal process. It is important to note that if you do perform an arytenoid reduction, there is a much higher surgical risk: it is much more posterior, much deeper dissection into the larynx, with much more manipulation of the larynx with a higher risk of edema, bleeding or complications that can be referred as severe at times. This can be done concomitantly with thyroplasty and if you have to revise them, you are most likely going to have to separate the cricoarytenoid joint and perform a more formal repositioning and fixation of the arytenoid cartilage. As you rotate the muscular process out, you can end up with an inferior dislocation of the vocal process and then, when the patient tries to voice, the arytenoid cartilages do not line up correctly the patient ends up with the same problem: glottic incompetence. This can be addressed by placing what is called a PCA simulating suture or posterior cricoarytenoid simulating suture between the vocal process and inferior horn of the thyroid that provides some fixation of the arytenoid cartilage and prevents a migration of it in the vertical plane and helps prevent this problem. One of the problems that can occur with thyroplasty is because it is a static operation done for a very dynamic organ. The organ will continue to change over time after these injuries. It can continue to atrophy and this can lead to gradual deterioration of the voice. An implant is placed for a larynx that is one size but later you have a larynx of a different size and revision may be required. So, although this is a problem that can occur, normally thyroplasty is a very successful operation with very good results.

The last thing that can be talked about it is the potential for laryngeal reinnervation. This is not normally done for vocal cord paralysis, but it is described in literature. One is the hypoglossal to recurrent laryngeal nerve transfer, advocated by Dr. Paniello from Washington University, who has performed this operation with some success to return mostly body and bulk to the cord rather than the ability of the cord to move. You do still have the same problems with synkinesis during the denervation and reinnervation. This remains fairly experimental, but it is an area of potential research.

The key points to take home from this talk: A left recurrent laryngeal nerve graft is at increased risk for injury due to its increased length and its longer course down into the mediastinum. Dysfunctional reinnervation as opposed to complete denervation is much more common and a much more likely pathophysiology of cord paralysis in the setting of nerve injury. Neoplasms and surgical trauma are the most common etiologies of paralyses. Neoplasms cannot be forgotten during the evaluation of these paralyses and they must be thoroughly looked for. Lesions can be located anywhere between the skull base and the mediastinum and these should be imaged appropriately. Last, treatment modality can be tailored to each situation in terms of permanent versus temporary fixes, and injections versus open implants. They can be tailored both to the patient needs and to the surgeon’s preference and experience.