The next step is to identify the RLN. In cases where there has been previous neck surgery, the nerve is most reliably found adjacent to the cricothyroid joint. The larynx must be rotated by applying upward traction on a skin hook carefully placed on the posterior border of the thyroid cartilage. The constrictor muscles are dissected off the cartilage and the nerve revealed lying just deep to them. The nerve is then followed in a retrograde direction and a sling is passed around the nerve.
Once the nerves have been identified it is possible to judge the lengths required to form a tension free anastomosis between them. The ascending movement of the larynx on swallowing must also be taken into account.
The nerves are then transected and the axons that subsequently protrude beyond the epineurium are trimmed so that they are flush to the epineurium. A 9/0 suture is used to perform an end-to-end anastomosis of the epi/perineurium and a small amount of tissue glue applied to support it. Haemostasis is secured and the wound closed in layers. It is usually not necessary to insert a drain and the procedure can be carried out as a day case.
It is unlikely that there will be any improvement before 4 months and so a short-acting injection augmentation with fat, collagen or hyaluronic acid should be considered, particularly if there is an immediate aspiration risk.
In a series of 20 patients reinnervated with this technique, Crumley et al. [12, 15, 17, 19] report excellent to normal phonatory quality with excellent medialisation of the cord and correction of the arytenoid malposition. Other authors have achieved similar results [20, 21].
Paniello et al. [22] performed a comparative trial of ansa-RLN reinnervation versus thyroplasty with 12 patients in each arm. They showed an improved outcome with reinnervation in those patients less than 52 years of age.
Wang et al. [23] reported a series of 237 patients receiving ansa-RLN reinnervation with a mean follow-up of 5.2 years. They found no significant difference in the voice outcome compared to that of the healthy control group.
Jean-Paul Marie [24, 25] has a 10-year experience with this technique. He has found that with appropriate selection of patients, including LEMG, the short-term and long-term results are excellent with normal voice. He has not experienced a worse outcome in the over 52 age group.
15.2.3.2 Combination Technique
In cases where there is incomplete closure of the posterior glottis, some authors advocate performing a simultaneous arytenoid adduction procedure at the time of reinnervation [26]. Tucker [27, 28] demonstrated poor long-term results following thyroplasty due to muscle atrophy and proposed performing reinnervation at the time of thyroplasty to augment and preserve results. Equally, we have seen good results from reinnervation in cases with inadequate improvement following thyroplasty where the implant is left in situ but also following extrusion of the implant.
15.2.3.3 Unilateral Reinnervation in Children
In the paediatric population, reinnervation offers several advantages over the alternatives of injection medialisation or framework surgery. It provides a permanent result without disruption of the growing larynx. It is well recognised that the patient should be awake and able to vocalise on command to achieve the best voice outcome with thyroplasty. As this is not possible in children, reinnervation under general anaesthetic is favourable.
15.2.3.4 Superior Laryngeal Nerve Injury
Paralysis of the cricothyroid muscle may occur due to damage of the main trunk of the vagus or SLN or due to damage of the external branch of the SLN only as this branch supplies the muscle. The clinical consequence is mild dysphonia, poor pitch control and loss of the higher register. Before considering surgery, it is important to await the results of speech therapy and spontaneous recovery. The traditional surgical approach is a cricothyroid approximation but this increases the tension in the vocal cords at all times and risks feminisation of a male voice and loss of the low register. Reinnervation is a viable alternative that has been used with some success. El Kashlan et al. [31] used a muscle-nerve-muscle technique, also described in cats by Hogikyan et al. [32]. It involves a nerve implanted at one end in the donor muscle and at the other in the recipient denervated muscle. An alternative is reinnervation with the ansa to distal stump of the external branch of the SLN if it can be identified.
When there is transection of the vagus, there is a high risk of aspiration. Sensory rehabilitation by reinnervation of the SLN may be considered. Based on our animal experiments, we have developed a new approach to this problem by anastomosing the SLN to a branch of the superficial cervical plexus [33].
15.3 Conclusion
Unilateral non-selective reinnervation has been shown to be a highly successful alternative to type 1 thyroplasty. Insertion of an implant in thyroplasty carries a risk of infection and extrusion, has cost implications and must be taken into consideration in future intubations due to its position in the airway. Overall, reinnervation seems to have better long-term results by preventing muscle atrophy, avoids glottic scarring and does not require an implant. It is suitable for paediatric patients in whom the larynx is still growing and if not successful a thyroplasty can always be performed.
However, laryngeal reinnervation has not been widely adopted. This is possibly due to a lack of surgical confidence with microsurgical techniques.
15.4 Bilateral Vocal Cord Palsy: Selective Reinnervation
The ultimate aim of selective reinnervation is the restoration of vocal cord trophicity and mobility coordinate with respiration and phonation.
It is observed that in bilateral palsy the vocal cords usually lie in the paramedian position resulting in dyspnea but good voice quality. The main issue therefore is the recovery of abduction on inspiration.
The key is to apply an inspiratory trigger to the sole abductor muscles, the posterior cricoarytenoids (PCA). To this end, after decades of animal experiments, two techniques went into trial in humans. The nerve-muscle pedicle with ansa hypoglossi technique pioneered by Tucker [34–38] and the phrenic nerve reinnervation of the PCA as championed by Crumley, van Lith-Bijl et al. and Marie et al.
Tucker used the ansa hypoglossi with an island of strap muscle attached distally and swung this across to be imbedded into the PCA. He reported 214 patients with bilateral palsy of which 202 had at least 2 years follow-up with 74% success [38]. He reports deterioration in 17% of these 2–5 years later, which he attributes to cricoarytenoid ankylosis. However, other surgeons failed to achieve similar results with this technique and it is not performed today. In conclusion it was felt that any improvement of the glottic airway was static and due to contractile scarring of the PCAs. No active arytenoid abduction was achieved. On closer consideration of the ansa it is apparent that whilst it is active on deep inspiration, this is not the case in quiet breathing. This limits it usefulness as a donor nerve in this clinical scenario. The other possible drawback of this technique is that the RLNs are not actively cut at the time of the procedure and so there is no re-denervation and thus the muscles are not in a state of actively seeking innervation, although some double innervation may be possible.
15.4.1 Selective Reinnervation Using the Phrenic Nerve
We demonstrated in animal models that the phrenic nerve, unlike the ansa, is active in quiet breathing [39]. This makes it a far more physiologically appropriate donor nerve if the goal is inspiratory activity of the recipient abductor muscles. However, unlike the ansa, the phrenic nerve serves a central role in respiration. The challenge was to utilise the phrenic without negatively impacting on respiratory function. Thus techniques were developed to preserve adequate nerve supply to the diaphragm.
- 1.
Crumley et al. [40–42] used a split phrenic graft, first in animals and then in humans (Fig. 15.2). The main trunk of the RLN was transected to remove the residual innervation of the larynx and to stimulate the muscles to accept the new innervation. The phrenic nerve graft was anastomosed onto the diminutive abductor branch of the RLN inside the larynx.
Good results were obtained in animals but the first human results [42], presented in 1983, showed some improvement in glottis diameter but no active arytenoid abduction.
- 2.
Variations of this technique have been described by Rice [43], Mahieu et al. [44] and van Lith-Bijl [45, 46]. They performed an extra-laryngeal anastomosis onto the more robust, main trunk of the RLN. They then sectioned the adductor branch inside the larynx and implanted its proximal stump also into the RLN to direct all the donor fibres to the PCAs.
- 3.
Zheng et al. [50] performed a hybrid technique on humans using the phrenic nerve, as above, to reinnervate one side and the ansa nerve-muscle pedicle technique on the other side. Inspiratory abduction of the arytenoids was only noted on the side reinnervated by the phrenic.
- 4.
Bilateral Selective Motor Reinnervation of adductor and abductor muscles of the larynx (Fig. 15.3).
Fig. 15.3
Schematic view of total motor reinnervation of the larynx: both PCA reinnervation by the upper root of one phrenic nerve; both adductors muscles reinnervation by thyrohyoid branches of both hypoglossal nerves [2, 49, 53–62]. The free interposition nerve graft (green) is now replaced by a Y shaped lengthening nerve graft (red), implanted in both PCA
Having obtained successful results in dogs with unilateral reinnervation of both the adductor and abductor muscles using the ansa and phrenic nerves, respectively [2, 3, 49], we endeavored to develop these techniques for use in humans.
We studied the effects of partial phrenic nerve resection on the respiration of dogs and rabbits, observing that the resection of the upper phrenic nerve root had only a slight and temporary impact on respiration [3, 7, 8, 39].
In order to optimise glottic opening it was clearly desirable to achieve bilateral inspiratory abduction of the arytenoids. However utilising the phrenic nerve on both sides carried the risk of significant respiratory morbidity. In exploring these possibilities it became apparent that the arytenoid abduction achieved was in fact better if the PCA received fewer axons from the donor phrenic nerve [2]. This awakened us to the potential of using one phrenic root to supply both PCAs.
For the simultaneous reinnervation of the adductors, the nerve to the thyrohyoid (a branch of the hypoglossal) emerged as the best candidate [53]. This nerve is the only nerve to the strap muscles that fires during phonation and swallowing. As such it can provide appropriate supply to the adductors in phonation and protection of the airway on swallowing [54].
As this technique involves re-denervation of the larynx (by transecting the RLNs), it can be done at any stage after the initial injury as any established synkinesis is removed and so cannot work against the donor nerve supply.
Having formulated and trialed this technique in animals, we obtained approval for a prospective trial in humans. Today, more than 50 patients have undergone the procedure [55–59]. Here we describe the technique and present the results (Fig. 15.3). We are confident that this procedure can offer these patients a significant improvement in quality of life. It is a single surgical procedure requiring no expensive implants or on-going medical involvement. It can free a patient of their uncomfortable, unsightly, time-consuming, and expensive tracheostomy whilst preserving voice.
On the basis of these positive results we have extended the remit of the procedure to include those patients with previous cordotomy. This is on the condition that the cricoarytenoid joints are mobile and that the patient appreciates that there may be the need for secondary medialisation to improve voice.
15.4.2 Technique (Fig. 15.3)
- 1.
Tracheostomy: This is performed if the patient does not already have a tracheostomy. It should be low in the neck to avoid the unsterile tracheostomy site becoming in continuity with the operative site.
- 2.
Surgical Incision: A skin crease incision is made at the level of the cricothyroid membrane.
- 3.
Harvesting the free graft from the Great Auricular Nerve: This is a convenient stage to harvest a section of the right great auricular nerve. This may be done by extension of the original incision or through a small additional skin crease incision overlying the upper third of the sternocleidomastoid. A Y shaped graft of about 10 cm in length is acquired by following the nerve superiorly into the parotid gland where it branches.
- 4.
Phrenic nerve exploration: For the right-handed surgeon it is convenient to utilise the right phrenic nerve. Having identified the main trunk, it is followed in a retrograde direct to its roots as they emerge from the spinal foramina. The upper nerve root is isolated and a vascular sling passed around it for ease of identification later in the procedure. It is important to remember that this root may be only 2 cm in length. The root is tested with a nerve stimulator (with prior warning to the anaesthetist) and a hand place on the patient’s abdomen to feel for contractions of the diaphragm. The other roots and accessory phrenic (if present) are also tested to ensure that the diaphragm will receive adequate innervation once the upper root is transected.
- 5.
Identification of the Nerve to thyrohyoid: This is performed bilaterally. It is a small branch of the hypoglossal nerve that comes off anterior to the descendens hypoglossi, crossing the hyoid bone to lie on the superficial aspect thyrohyoid muscle, which it enters in the superior part of the muscle. Vascular slings are placed around the nerves, which are not at this stage transected.
- 6.
Intralaryngeal dissection of the RLNs: The larynx is rotated to the contralateral side by applying traction to a skin hook placed behind the posterior border of the thyroid cartilage. The inferior constrictors are dissected off the cartilage and the RLN is seen lying between the just posterior to the cricothyroid joint. Sometimes it is possible to identify and the small branch to the PCA. This is performed bilaterally and vascular slings placed for ease of location of the nerves.
- 7.
Retrolaryngeal dissection: A tunnel is created posterior to the cricoid cartilage, superficial to the PCAs. This dissection must be minimised to avoid significant disruption to the retropharyngeal plexus.
- 8.
Reinnervation of the adductors: The adductors are reinnervated by transecting the main trunks of the RLNs as low as the previous nerve lesions allow. The distal stumps of the RLNs are swung upwards and a free nerve graft is interposed between the stump and ipsilateral nerve to thyrohyoid on each side.
- 9.
Reinnervation of the PCAS with the phrenic nerve: The y-shaped, free nerve graft is passed from left to right (single end first) through the retrocricoid tunnel such that the single end is ready to be attached to the previously identified root of the right phrenic. The double ends of the y then come to lie each one adjacent to its ipsilateral PCA. The double ends of the y graft are then implanted one into each PCA. This is done by inserting the end of the graft into a small pocket, which is created in the muscle. A 9/0 suture is used to secure the nerve in place and some tissue glue applied. The single end of the graft is anastomosed onto the root of the phrenic using a 9/0 epi-perineural suture and tissue glue. It is essential to ensure there is no tension on these anastomoses and it may be prudent to pass the graft through a tunnel between the jugular vein and the carotid artery to shorten the distance.
In the situation where the PCA branch of the RLN has been identified, it is possible to make the anastomosis of the phrenic root, via a graft, to the main trunk of the RLN. The adductor branch is then transected and the proximal stump anastomosed to another free cable graft (harvested from the ansa), which is passed through the retrocricoid tunnel to reach the contralateral side where it is anastomosed onto the PCA branch of the RLN. The distal stump of the adductor branch is then anastomosed via a free nerve graft to the nerve to thyrohyoid on both sides.
15.4.3 Post-Operative Instructions
In fact, the act of severing both RLNs removes the paradoxical adduction during phonation and usually reduces laryngeal resistance with improvement of the airway. However, it is strongly advisable to leave the tracheostomy in situ for 5 days. Aspiration can occur in the immediate post-operative period and so the patient is initially fed by nasogastric tube, which is also removed at 5 days.
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