Selective Laryngeal Denervation and Reinnervation for Adductor Spasmodic Dysphonia
The purpose of the operation is to improve voice function in those with predominantly adductor type spasmodic dysphonia (AdSD). The operation is designed to reduce laryngeal adductory closing forces by selectively eliminating nerve supply from the recurrent laryngeal nerve (RLN) to the thyroarytenoid (TA) and lateral cricoarytenoid (LCA) muscles and to replace the nerve supply to the TA with innervation from the ansa cervicalis. Native innervation to the interarytenoid (IA) and posterior cricoarytenoid (PCA) muscles are preserved. The procedure is typically performed bilaterally during the same operation.
Indications/Contraindications
AdSD or laryngeal dystonia dominated by adductory hyperfunction.
Although not a specific contraindication, vocal tremor is generally not improved with this procedure. Patients with tremor and AdSD should be appropriately counseled. Those whose disease is dominated by tremor should not be offered this operation.
Because this operation is specifically designed to alter or reduce laryngeal closing forces, those with a mixed laryngeal dystonia or primarily with abductor spasmodic dysphonia (AbSD) should not be considered for this operation.
This operation represents an alternative to other accepted treatments for AdSD, including botulinum toxin injections.
In the Clinical Setting
Key Points
The TA and the LCA muscles are selectively denervated by direct lysis of their nerves.
The nerve branch to the LCA is typically not seen until after lysis and lifting of the TA branch. The IA muscle and nerve are not specifically seen or addressed in this operation.
The PCA and its nerve are specifically not seen nor manipulated. Preservation of the laryngeal abductory function is paramount. Preservation of the cricothyroid joint and a posterior strut of thyroid cartilage both maintains laryngeal superstructure and protects the posterior abductor branch of the RLN from trauma.
Only selective reinnervation of the TA is performed, as the nerve to the LCA is too small for a reliable anastomosis to the ansa cervicalis. Because of this limitation, the LCA muscle is partially divided and a partial LCA myotomy is additionally performed.
Small fibers emanating from the superior laryngeal nerve (SLN) can sometimes be seen entering the paraglottic space along with the insertion of the cricothyroid muscle (CT). If noted, these should be lysed.
Pitfalls
There is a small vascular bundle that travels with the intralaryngeal RLN. Careful bipolar cautery will help maintain a blood-free operative field during dissection of the paraglottic space.
Aggressive resection of the LCA may lead to instability and lateralization of the arytenoid, especially in the male larynx, and should be avoided.
From a Technical Perspective
Key Point
Intralaryngeal dissection should be carefully performed under louposcopic or microscopic magnification. The procedure is traditionally described and typically performed bilaterally.
Pitfalls
Especially in the female larynx, the apex of the laryngeal ventricle can be quite close to the underlying thyroid cartilage perichondrium. During creation of the cartilage window, one should carefully avoid passing point and entering the laryngeal lumen.
Do not divide the donor branch of the ansa cervicalis until ready for anastomosis toward the end of the procedure. To avoid tension on the anastomosis, use the longer sternothyroid branch and divide this as distally as possible.
Stepwise Procedure
Mount a cadaveric larynx for open dissection.
OR Pearl: The procedure is performed with the patient intubated and under general anesthesia. Electromyographic (EMG) monitoring of the laryngeal nerves can be helpful in identification and dissection of the intralaryngeal anatomy.
OR Pearl: A horizontal incision is made at approximately the top of the cricoid cartilage and extended laterally to the belly of the sternocleidomastoid (SCM). This is carried down to the superficial layer of the deep cervical fascia and standard subplatysmal flaps are developed. Exposure should extend from the top of thyroid cartilage to the cricoid cartilage. Flaps are retracted to drapes.
OR Pearl: The ansa cervicalis is dissected by approaching the carotid sheath. The crotch formed by the SCM and omohyoid muscles is lifted toward the ceiling with an Army-Navy retractor. Once the muscles are retracted, the exposed space overlying the carotid sheath is composed of loose areolar fascia and dissected easily with a Kittner sponge. The ansa cervicalis should be seen overlying the carotid sheath with branches extending toward the underside of the various strap muscles.
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