Abstract
Objective
In certain cases, the recurrent laryngeal nerve (RLN) has to be sacrificed. This often results in an inadequate length of residual RLN to be used in a reinnervation procedure. We investigated the length of the distal stump of the RLN from the inferior border of the inferior pharyngeal constrictor muscle (IPCM), where it is frequently compromised, to its entrance into the larynx. Our objective was to determine whether this residual nerve stock was sufficient for margin clearance and neurorrhaphy.
Study design
Cadaveric study
Methods
Recurrent laryngeal nerves were identified in fresh frozen cadavers. The IPCM was divided, revealing the distal stump of the RLN, which was measured.
Results
Dissection was performed in 20 cadavers (40 nerves). The average length of the right RLN and the left RLN from the IPCM until it entered the larynx was 15 mm and 14 mm, respectively. All residual RLN remnants were of sufficient length for neurorrhaphy.
Conclusion
Concomitant RLN reinnervation procedures in the setting of nerve sacrifice are not well described. A barrier to reinnervation in this setting may be insufficient residual nerve length for a neurorrhaphy. Often, when the RLN is sacrificed intraoperatively either iatrogenically or due to tumor invasion, it is close to the cricoarytenoid joint, at the inferior border of the IPCM. This study demonstrates that by splitting the IPCM, sufficient length can be obtained for neurorrhaphy.
1
Introduction
Injury to the recurrent laryngeal nerve (RLN) is one of the most frequent causes of unilateral vocal fold paralysis (UVFP) . This can occur from inadvertent iatrogenic injury, for example, during thyroid surgery or from intentional nerve sacrifice due to tumor infiltration. Regardless of the etiology, vocal fold paralysis from RLN injury leads to incomplete glottic closure, resulting in dysphonia, vocal fatigue, aspiration, and a significant decrease in quality of life.
Management of unilateral vocal fold paralysis can be accomplished in a variety of ways — including thyroplasty, vocal fold injections, arytenoid adductions, or laryngeal reinnervation . Laryngeal reinnervation refers to any method that seeks to reconstitute neural pathways to the vocal fold. Various nerve strategies for reinnervation have been described. The methods include nerve–muscle pedicle, muscle–nerve–muscle pedicle, and donor nerve–RLN anastomosis . The approach has been divided into selective reinnervation, which targets specific laryngeal adductor and abductor muscles, and unselective reinnervation . It has been previously described that the ansa cervicalis (AC)-to-RLN anastomosis should be strongly considered as the initial and best treatment for the patient suffering from a UVFP, as this technique results in an excellent, and often a normal voice . In scenarios when it is known that the nerve is injured intraoperatively or when it needs to be sacrificed, it would be ideal to perform this procedure concomitantly as it prevents the patient from undergoing a staged procedure that may be compromised by postsurgical anatomic obfuscation from scar.
The AC-to-RLN anastomosis is well described and is usually accomplished without difficulty as there is typically enough length of the RLN to anastomose with the AC. However, in cases where the nerve needs to be sacrificed due to invasive thyroid malignancy, there may not be enough residual distal RLN length to use for a reinnervation procedure. This can further be complicated by concerns for tumor margin control if normal appearing nerve cannot be appreciated at the superior resection margin.
The objectives of this study therefore were two-fold—first, to provide normative descriptive data regarding the length of the distal stump of RLN from the inferior border of the inferior pharyngeal constrictor muscle (IPCM), where it is typically sacrificed, to its entrance into the larynx; and second, to determine whether this stump would be long enough for potential margin clearance and neurorrhaphy with the AC.
2
Materials and methods
This was an anatomic, adult cadaveric study to determine proof of concept and normative values to ascertain whether there is sufficient nerve stock for neurorrhaphy in the setting of RLN sacrifice. The necks of 20 human adult fresh, nonfixed frozen cadavers were dissected and the RLNs were identified bilaterally. Exclusion criteria included prior neck surgery.
In all 20 cadavers, the thyroid gland was dissected in a lateral-to-medial direction, allowing for identification of the RLN in the tracheoesophageal groove. The RLN was then dissected anterograde to the IPCM. A 7-0 Prolene suture was placed through the RLN at the junction of where it passes underneath the IPCM ( Fig. 1 ) giving a fixed location to measure at the point from where the IPCM was split. The IPCM was then divided along the lateral edge of the thyroid cartilage, revealing the distal stump of the RLN. This stump was mobilized and then measured to its point of entrance into the larynx ( Fig. 2 ). This is further illustrated in Fig. 3 , which represents a schematic of the distal stump of the RLN and its relation to the thyroid cartilage and IPCM. In situations where there was extralaryngeal branching, the distal measurement was taken from the IPCM to the first extralaryngeal branch, as this would be the clinically relevant location for a neurorrhaphy. Significant large caliber nerve branching proximal to the inferior border of the IPCM was not appreciated.
Continuous variables were compared using the t-test. Values of p < 0.05 were considered statistically significant. Data analysis was performed using JMP software (SAS Institute, Inc., Cary, NC).
2
Materials and methods
This was an anatomic, adult cadaveric study to determine proof of concept and normative values to ascertain whether there is sufficient nerve stock for neurorrhaphy in the setting of RLN sacrifice. The necks of 20 human adult fresh, nonfixed frozen cadavers were dissected and the RLNs were identified bilaterally. Exclusion criteria included prior neck surgery.
In all 20 cadavers, the thyroid gland was dissected in a lateral-to-medial direction, allowing for identification of the RLN in the tracheoesophageal groove. The RLN was then dissected anterograde to the IPCM. A 7-0 Prolene suture was placed through the RLN at the junction of where it passes underneath the IPCM ( Fig. 1 ) giving a fixed location to measure at the point from where the IPCM was split. The IPCM was then divided along the lateral edge of the thyroid cartilage, revealing the distal stump of the RLN. This stump was mobilized and then measured to its point of entrance into the larynx ( Fig. 2 ). This is further illustrated in Fig. 3 , which represents a schematic of the distal stump of the RLN and its relation to the thyroid cartilage and IPCM. In situations where there was extralaryngeal branching, the distal measurement was taken from the IPCM to the first extralaryngeal branch, as this would be the clinically relevant location for a neurorrhaphy. Significant large caliber nerve branching proximal to the inferior border of the IPCM was not appreciated.
