ORIGINAL ARTICLE Superior Laryngeal Nerve Identification and Preservation in Thyroidectomy Michael Friedman, MD; Phillip LoSavio, BS; Hani Ibrahim, MD Background: Injury to the external branch of the su- recorded and compared on an annual basis for both be- perior laryngeal nerve (EBSLN) can result in detrimen- nign and malignant disease. Overall results were also com- tal voice changes, the severity of which varies according pared with those found in previous series identified to the voice demands of the patient. Variations in its ana- through a 50-year literature review. tomic patterns and in the rates of identification re- ported in the literature have discouraged thyroid sur- Results: The 3 anatomic variations of the distal aspect geons from routine exploration and identification of this of the EBSLN as it enters the cricothyroid were encoun- nerve. Inconsistent with the surgical principle of pres- tered and are described. The total identification rate over ervation of critical structures through identification, mod- the 20-year period was 900 (85.1%) of 1057 nerves. Op- ern-day thyroidectomy surgeons still avoid the EBSLN erations performed for benign disease were associated rather than identifying and preserving it. with higher identification rates (599 [86.1%] of 696) as opposed to those performed for malignant disease Objectives: To describe the anatomic variations of the (301 [83.4%] of 361). Operations performed in recent EBSLN, particularly at the junction of the inferior con- years have a higher identification rate (over 90%). strictor and cricothyroid muscles; to propose a system- atic approach to identification and preservation of this Conclusions: Understanding the 3 anatomic variations nerve; and to define the identification rate of this nerve of the distal portion of the EBSLN and its relation to the during thyroidectomy. inferior constrictor muscle allows for high rates of iden- tification of this nerve. The EBSLN should be explored Materials and Methods: A retrospective review of thy- during thyroid surgery and identification is possible in roid lobectomies and total thyroidectomies performed be- most cases. Preservation of the EBSLN maintains opti- tween 1978 and 1997 was carried out. A total of 884 pa- mal function of the larynx. tients were included, with 1057 EBSLNs explored. Intraoperative findings of identification of the EBSLN were Arch Otolaryngol Head Neck Surg. 2002;128:296-303 HE CLINICAL significance of Most of these articles focus on the ana- the superior laryngeal nerve tomic relationship of the SLN to the su- (SLN) has been clearly over- perior thyroid artery. They discuss the like- shadowed by emphasis on lihood of the SLN being at risk for injury therecurrentlaryngealnerve. and the probability of identifying the SLN TThe principles of head and neck surgery during surgery; they suggest that the SLN are based on identification and preserva- often cannot be identified. Very little has tion as opposed to avoidance of impor- been written on the anatomy of the distal tant structures. These principles would set portion of the SLN as it enters the crico- identification and preservation of the thyroid muscle.3 From the Department of SLN as standard in all thyroid surgery. This study was undertaken to review Otolaryngology and The nerve is clearly at risk, and injury is the experience of the senior surgeon (M.F.) Bronchoesophagology, clearly detrimental to the patient. De- with the SLN in more than 1000 thyroid lo- Rush-Presbyterian-St Luke’s spite these facts, the SLN is not routinely bectomies over a 20-year period. The study Medical Center (Drs Friedman identified by most surgeons, and some reviews the anatomy of the distal end of the and Ibrahim and Mr LoSavio), and the Division of physicians have presented studies to jus- SLN as it relates to the practical aspect of Otolaryngology, Advocate tify this apparent inconsistency in opti- surgical identification. It also reviews the 1-3 Illinois Masonic Medical Center mal surgery. percentage of cases in which the SLN was (Drs Friedman and Ibrahim), Many articles deal with the variable actually identified. It presents a reliable Chicago, Ill. anatomy of the superior laryngeal nerve.3-11 technique for practical identification and (REPRINTED) ARCH OTOLARYNGOL HEAD NECK SURG/ VOL 128, MAR 2002 WWW.ARCHOTO.COM 296 ©2002 American Medical Association. All rights reserved. Downloaded From: http://archotol.jamanetwork.com/ by a Rush University User on 10/02/2015 MATERIALS AND METHODS The muscle response of the stimulated nerve is quite dif- ferent than the response of direct muscle stimulation. Ab- sence of identification by stimulation should direct the sur- This nonrandomized retrospective study reviews a 20- geon back to the region of the vessels to search for a missed year experience of thyroid lobectomies from the year 1978 type 1 nerve. to 1997. The charts of all patients who underwent thyroid- This classification is based on the terminal aspect of ectomy and/or lobectomy were reviewed to assess if the ex- the EBSLN and is provided as a practical guide for identi- ternal branch of the SLN (EBSLN) was identified and pre- fication. It does not replace previously described classifi- served or not identified at surgery. Cases were categorized cations by Kierner et al4 and Cernea et al5 that focus on the into benign or malignant as determined by pathology re- EBSLN and the superior thyroid vessels’ relationship. The ports at the time of surgery, and the percent identification percentage of patients with anatomy corresponding to 1 of was compared for each calendar year. Overall, 884 patient these 3 types has not been studied in detail by us or by other cases were reviewed with a total of 1057 EBSLNs put at risk investigators. Lennquist et al3 studied the percentage of their (696 nerves [65.8%] in cases with benign tumors and 361 patients with type 3 distribution and found it to be 20%. nerves [34.2%] with malignant tumors). A full literature Although the retrospective review of the data was not de- search was performed on the OVIDWEB-MEDLINE data- tailed enough in that study to identify which type was pres- base looking for all relevant articles since 1950 that com- ent in every case, all 3 types were frequently identified. ment on the identification, preservation, anatomy, surgi- cal technique, and injury rate to the EBSLN. SURGICAL TECHNIQUE SURGICAL ANATOMY A previously described systematic approach14 was used consistently in all of our cases. After raising subplatysmal The SLN is classically described as originating from the flaps, care was taken to maintain meticulous hemostasis middle of the nodose ganglion. In addition, it receives as the sternohyoid and sternothyroid muscles were indi- contributions from the superior cervical sympathetic gan- vidually elevated laterally (Figure 4 and Figure 5). The glion. Its path of descent initially begins posteriorly and sternohyoid muscle was elevated laterally up to the hyoid proceeds medially to the internal carotid artery where it to allow visualization of the sternothyroid muscle inser- bifurcates into an internal (sensory and autonomic) and tion into the oblique line of the thyroid cartilage. The external laryngeal branch (motor).12,13 The internal sternothyroid muscle was then elevated laterally until the branch proceeds to pierce the thyrohyoid membrane with lateral edge of the thyroid gland was reached. The medial the superior laryngeal artery and subsequently divides edge of the superior attachment of the sternothyroid into an upper and lower branch. The external branch con- muscle was transected with a bipolar cautery for a dis- tinues to travel inferiorly, passing superficially to the infe- tance of 5 mm (Figure 6), which provided better expo- rior constrictor and then piercing it to finally reach the sure of the inferior constrictor–cricothyroid junction. The cricothryoid muscle.12 While this level of description can horizontal and oblique bellies of the cricothyroid muscle suffice for the nonsurgical observer, more detailed were identified as was the anterior edge of the inferior descriptions have helped to elucidate the variations in the constrictor. anatomy of the EBSLN to aid the surgeon operating in A disposable nerve stimulator (set on 2 mA) was used this area.3-11 to identify the terminal branches of the EBSLN as they en- This study focused on the anatomy of the EBSLN at ter the cricothyroid bellies. The stimulator was first used its insertion into the cricothyroid muscle. Terminal directly on the cricothyroid muscle to assess the response branches of the EBSLN penetrate the horizontal and of direct muscle stimulation. This helps differentiate muscle oblique bellies of the cricothyroid muscle as well as the stimulation from nerve stimulation. If the EBSLN was iden- inferior constrictor. However, 3 variations have been tified over the inferior constrictor (type 1, Figure 1), it was described for the main trunk of the EBSLN prior to its ter- followed in a retrograde direction. Identification of the nerve minal branching. In the type 1 variation, it runs its whole in this location allows for preservation of the nerve. This course superficially or laterally to the inferior constrictor, anatomic variant is usually associated with an EBSLN that descending with the superior thyroid vessels until it termi- crosses the superior thyroid artery at or below the supe- nates in the cricothyroid muscle (Figure 1). In the type 2 rior thyroid pole. This scenario places the nerve at risk not variation, the EBSLN penetrates the inferior constrictor in only during ligation of the superior thyroid vessels but dur- the lower portion of the muscle (Figure 2). In this case it ing dissection of the loose areolar tissue adjacent to the su- is only partially protected by the inferior constrictor. And perior pole. Routinely, the superior pole vessels and the loose finally, the type 3 nerve dives under the superiormost areolar tissue surrounding them are not dissected until the fibers of the inferior constrictor, remaining covered by this EBSLN is explored.