Ansa Cervicalis–Recurrent Laryngeal Nerve Laryngeal Reinnervation for Unilateral Vocal Fold Motion Impairment
This procedure is designed to provide new innervation to a denervated hemilarynx following loss of appropriate innervation from the recurrent laryngeal nerve. With a new nerve supply, the paralyzed vocal fold often achieves a median position, tension similar to the non-impaired vocal fold and three-dimensional bulk similar to the other side. This combination of features allows the vocal folds to meet during phonation and to have sufficient symmetry to prevent irregular oscillation during most phonatory tasks. Swallowing function and the efficiency of cough are also usually improved. Return of motion of the affected vocal fold in abduction and adduction is not achieved.
Indications/Contraindications
Unilateral vocal fold motion impairment (VFMI) resulting from recurrent laryngeal nerve (RLN) injury
Adductor spasmodic dysphonia (selected cases)
This operation generally can be done at any time following unilateral RLN injury, but it is generally preferred to wait 9 months or longer, so as not to preclude recovery via spontaneous RLN regeneration (unless a known RLN transaction has occurred).
It is sometimes useful, but not mandatory, that such patients are followed with laryngeal electro-myography (LEMG) to confirm that denervation (fibrillation potentials) is present in one (generally thyroarytenoid [TA]) or more of the intrinsic muscles. However, excellent results may be obtained with this operation in the face of LEMG polyphasic or even normal motor action potentials, as long as clinically the vocal fold does not show return of abductor/adductor phasic motion, and the voice is sub-optimal. That is to say, in such patients with poor vocal quality in association with laryngeal synkinesis, this operation can restore excellent vocal/phonatory results, by restoring quiet resting tone (favorable synkinesis) to all four intrinsic muscles (TA, lateral cricoarytenoid [LCA], interarytenoid [IA], and posterior cricoarytenoid [PCA]).
The goal, then, of this procedure is to restore quiet resting muscle tone to the four intrinsic muscles and also, importantly, to restore relatively normal anatomic positioning of the arytenoid cartilage, its vocal process, and accordingly the posterior vocal fold.
Prior irradiation is not an absolute contraindication, but the patient should be advised that results may not be as good as in unirradiated patients.
It is known that older patients regenerate nerves at a slower rate, and hence it will take longer for the reinnervation to take place.
If an older patient has a comorbidity, such as diabetes, which might conceivably also affect nerve regeneration adversely, one might consider a different technique, such as medialization thyroplasty.
In the Clinical Setting
Key Points
The operation is generally best performed using loupes, as they aid and expedite identification and dissection of both ansa cervicalis and recurrent laryngeal nerves. The actual nerve anastomosis can be done with loupes, although the author prefers the operating microscope and either 8–0 or 9–0 monofilament nylon.
There is no necessity in this procedure for intralaryngeal RLN branch dissection. In fact, the author feels that the well-documented success of this process is because all four of the intrinsic muscles receive ansa cervicalis-derived reinnervation. (The PCA muscle reinnervation is key to helping relocate the normal position of the vocal process, which generally moves to an inferior-superior position matching the contralateral normal vocal process. It is known that the PCA, although generally thought of as the all-important sole abductor muscle, is important during phonation, especially high-pitched phonation, and hence its reinnervation is critical to the results of this procedure.)
The author frequently finds it useful to divide the strap muscles horizontally at the level of the lower border of the thyroid cartilage. (This frequently expedites and facilitates the nerve anastomosis, and the denervated strap muscles are subsequently sutured with 3–0 Monocryl suture at the end of the case.)
Occasionally, an enlarged thyroid lobe will make it difficult to find and identify the distal RLN. In these cases the thyroid gland′s superior pole can be mobilized inferiorly.
Pitfalls
It is important to consider the vitality, and even the existence, of the ipsilateral ansa cervicalis nerve. Following thyroidectomy, neck dissection, or anterior cervical spine orthopedic/neurosurgical procedures, there have been instances when the author has been unable to find any remnants of the ipsilateral ansa cervicalis. In such instances, reinnervation can be achieved by using the contralateral ansa cervicalis, but in these instances the surgeon must be prepared to generate longer length of both contralateral ansa and recipient RLN, or be prepared to use an interposition nerve graft.
Length of time since RLN injury: In general, the procedure should probably be best performed in the first 18 months following RLN injury. As a general rule, LEMG is performed for many cases 9 months or longer after injury, and if no fibrillation or other action potentials are generated from either TA or LCA muscles, it is advisable to perform another operative procedure, such as medialization laryngoplasty.
Irradiation makes nerve identification and mobilization more difficult. Radiation also reduces both the magnitude and rate of nerve regeneration through the nerve anastomosis.
In general we do not perform this operation in individuals over 65 years of age. As with irradiation, age is not an absolute contraindication.
A tension-free anastomosis is critical. Remember to take into account, when completing the anastomosis, that the larynx ascends superiorly in the neck up to one inch with each swallow. Accordingly, there must be additional length and “slack” in the two nerves to prevent disruption of the nerve anastomosis during postoperative swallowing.
Postoperative “bucking” during emergence from anesthesia, or cervical hyperextension, can also disrupt the anastomosis.
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