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Identification of the External Branch of the Superior Laryngeal Nerve During Thyroidectomy

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Identification of the External Branch of the Superior Laryngeal Nerve During Thyroidectomy ORIGINAL ARTICLE Identification of the External Branch of the Superior Laryngeal Nerve During Thyroidectomy Nitin A. Pagedar, MD; Jeremy L. Freeman, MD, FRCSC Objectives: To determine the feasibility of identifica- sition according to Cernea classification and correlation tion of the external branch of the superior laryngeal nerve with patient and gland characteristics. (EBSLN) during routine thyroidectomy and to describe the EBSLN position according to the Cernea classifica- Results: Three of 178 EBSLNs (1.7%) could not be iden- tion system. tified using the routine technique. The EBSLN was found in the highest-risk position (Cernea type 2b, crossing the Design: Prospective case series. superior vascular pedicle below the upper border of the gland) in 48.3% of cases, and in the lowest-risk position Setting: Academic tertiary care center. (Cernea type 1, crossing more than 1 cm above the up- per border) in 7.3%. Specimens larger in weight and in Patients: One hundred twelve consecutive patients un- dimension were correlated with type 2b nerves. dergoing hemithyroidectomy or total thyroidectomy by the senior author between August 15 and December 31, Conclusions: The EBSLN can be routinely identified dur- 2007. ing thyroidectomy. Moreover, many EBSLNs are in po- sition to be at high risk of injury during ligation of the Interventions: None. superior vascular pedicle. Main Outcome Measure: Proportion of EBSLNs iden- tified. Secondary outcome measures included EBSLN po- Arch Otolaryngol Head Neck Surg. 2009;135(4):360-362 TUDIES HAVE SHOWN THAT SUB- identified than in cases in which no search jective voice disturbance after was performed. thyroidectomy is very com- Anatomic studies have sought to delin- mon,1,2 even without injury to eate the course of the nerve near the supe- the recurrent laryngeal nerves. rior pole and to identify patterns. Cernea et SOne possible cause for postoperative dys- al5 created a 3-way system according to the phonia is injury to the external branch of level at which the nerve crosses behind the the superior laryngeal nerve (EBSLN). The artery: type 1 nerves cross more than 1 cm EBSLN supplies the cricothyroid muscle, above the upper border of the thyroid gland; which acts to lengthen the vocal folds dur- type 2a nerves cross within 1 cm of the up- ing phonation. The external branch courses per border of the thyroid; and type 2b nerves deep to the superior thyroid artery and vein cross below the upper border of the gland. from superolateral to inferomedial and in- Their study showed that 37% of cadaveric serts at the cricothyroid muscle medial to nerves were found in a position as to be vul- the superior pole of the thyroid gland. The nerableduringthyroidectomy;amorerecent Author Affiliations: nerve is vulnerable to injury during thy- clinical study using the same classification Department of roidectomy as the surgeon dissects and system found 64% of nerves to be at risk.6 In- Otolaryngology−Head and Neck ligates the superior thyroid vascular pedi- terestingly, Hurtado-Lopez et al7 found that Surgery, Mount Sinai Hospital cle. Injury to the superior laryngeal nerve increasing thyroid nodule size did not pre- and University of Toronto, leads to objective alterations in voice qual- dict postoperative cricothyroid dysfunction, Toronto, Ontario, Canada. 3 4 8 Dr Pagedar is now at the ity, even in nonsingers. Cernea et al re- although Cernea et al found an increased in- Department of ported that an experienced thyroid sur- cidence of high-risk nerves in patients with Otolaryngology−Head and Neck geon had a lower incidence of postoperative very large goiters. In this study, we report our Surgery, University of Iowa, cricothyroid muscle dysfunction in cases experience of EBSLN identification in a se- Iowa City. in which the nerve was searched for and ries of consecutive thyroidectomies. (REPRINTED) ARCH OTOLARYNGOL HEAD NECK SURG/ VOL 135 (NO. 4), APR 2009 WWW.ARCHOTO.COM 360 ©2009 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/23/2021 METHODS Table. Cernea Classifications of the 175 Identified Nerves The Research Ethics Board of Mount Sinai Hospital approved No. (%) of this study. We retrospectively reviewed the medical charts of Cernea Classa Superior Poles 112 consecutive patients who underwent thyroidectomy per- 1 13 (7.3) formed by the senior author (J.L.F.) at our tertiary care center 2a 76 (42.7) between August 15 and December 31, 2007. 2b 86 (48.3) We used a standardized approach for each superior pole. The sternohyoid muscle was retracted laterally and the ster- a See introductory paragraphs for definitions of the Cernea classes. nothyroid muscle was divided at its midpoint. The gland was retracted inferolaterally while the sternothyroid muscle was bluntly dissected upward, after which the avascular space be- finding the EBSLN in a high-risk position. Fifty-two lobes tween the larynx and the superior thyroid pole was opened larger than 5.5 cm in the superior-inferior dimension were bluntly. During this dissection, the lateral surface of the crico- found; type 2b EBSLNs were discovered in 62% of cases thyroid muscle was exposed and the EBSLN was identified. Its (OR, 2.13; 95% CI, 1.10-4.13; P=.02). There were 19 lobes course was traced laterally to the point where it crossed the su- larger than 3.5 cm in the anteroposterior dimension; 79% perior thyroid vessels. No sharp dissection or electrocautery of these were associated with type 2b EBSLNs (OR, 4.65; was used at the superior pole prior to identification of this point. 95% CI, 1.48-14.63; P=.005). We did not use a nerve stimulator or other laryngeal nerve moni- tor. We then proceeded to dissect the remainder of the attach- ments of the thyroid gland. COMMENT For each patient, we recorded the laterality of the proce- dure and whether relevant nerves were identified and their Cer- The EBSLN is commonly associated intimately with the nea classifications. We also noted the dimensions and weight superior thyroid pole, as we confirm in this study. Our of the thyroidectomy specimen and the patient’s body mass in- data demonstrate that the technique of ligation of the su- dex. Risk factors were analyzed by ␹2 test. Statistical analysis was performed with EpiInfo software (Centers for Disease Con- perior polar vessels flush with the thyroid gland would trol and Prevention, Atlanta, Georgia). still result in a high risk of injury in almost half of the superior poles. We conclude that, just as in the case of the recurrent laryngeal nerve, every superior polar dis- RESULTS section should include a search for the EBSLN. Our results confirm the high proportion of patients We studied 112 patients in whom 178 superior poles were in whom the EBSLN is found after only limited dissec- dissected. There were 91 right sides and 87 left sides. Using tion. Mishra et al6 described not encountering the EBSLN the standard procedure, 175 nerves were identified in only 8 of 78 superior poles. Friedman et al9 reported (98.3%). Two of the remaining 3 nerves were located, finding the EBSLN, using a different technique, in 85% but only after the division of the superior vascular pedicle; of 1057 superior poles. the third was in a patient with an atrophic right thyroid The proportion of EBSLNs found to be in the type 2b lobe in whom no superior pole was present. The posi- position was 48%, which is higher than reported previ- tions of the 175 identified nerves are shown in the Table. ously. Cernea et al5 found 20% of 30 cadaveric nerves in The 2 patients in whom we were unable to find the the type 2b position, whereas Ozlugedik et al10 found 18% EBSLN with our standard dissection had firm nodules of 40 cadaveric nerves in the type 2b position. Surgical or inflamed thyroid parenchyma, which prevented lat- series by Mishra et al6 and Bellantone et al11 identified eral retraction of the superior pole and thus prohibited only 10% in the type 2b position. One possible explana- our usual blunt dissection technique. tion is the manner in which the superior pole is ex- There were 23 obese patients (body mass index [cal- posed. The cadaveric dissections of the superior pole may culated as weight in kilograms divided by height in me- result in a perspective of the nerve that varies from that ters squared] Ͼ30), with 37 nerves dissected. The odds obtained by surgical exposure, especially the technique ratio (OR) for finding a type 2b nerve was 1.34 (95% con- used in the present series of dissecting from inferior to fidence interval [CI], 0.65-2.76; P=.43). Among these dis- superior underneath the divided sternothyroid muscle. sections, 2 type 1 nerves were identified. There were 66 It is difficult to explain the differences between our re- total thyroidectomies. In this group, in 37 patients (56%), sults and those of Mishra et al6; neither study incorpo- the right and left EBSLNs were found in the same posi- rated the use of a nerve stimulator or monitor to con- tion. Of the 71 nerves found in the Cernea type 2b po- firm the identity of the nerve. sition, 68 of the contralateral nerves were found in either We have identified factors associated with the finding the type 2a or 2b position. of type 2 nerves, including the weight of the thyroidec- We studied the relationship between EBSLN posi- tomy specimen and the dimensions of the lobe. Specimens tion and the size of the thyroidectomy specimen. For 4 were weighed in their entirety, so we were unable to evalu- patients, specimen mass was not recorded. For the re- ate a correlation between lobe weight and nerve position, maining 108 specimens, the median mass was 21.5 g.
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