El nervio laríngeo superior en la cirugía del tiroides: estudio experimental en el perro / The laryngeal superior nerve in thyroid surgery: experimental study in dog

Las lesiones de la rama externa del nervio laríngeo superior durante la realización de cirugía de la glándula tiroides pueden ocasionar serias consecuencias. La estrategia intraoperatoria para la identificación y preservación de la rama externa del nervio fue evaluada en un modelo experimental (30 caninos) mestizos de ambos sexos, sanos desparasitados con peso promedio entre 12 y 15 kg, procedentes del bioterio del Instituto de Cirugía Experimental de la Universidad Central de Venezuela. El 20 por ciento de las ramas transitaban distalmente a través del músculo constrictor de la faringe, requeriendo de la disección intramuscular para lograr su correcta identificación alrededor del polo superior del lóbulo tiroideo. En el 23 por ciento se logró identificar el nervio sin desección. Su curso parcialmente lateral a la arteria tiroidea superior y sus ramas implicó el riesgo definitivo de lesionar la rama externa durante la división de los vasos de polo superior (arterias-venas). El 72 por ciento de los nervios fueron reconocidos sin necesidad de realizar la disección intramuscular, y 19 por ciento de estos pasaban parcialmente lateral a la arteria tiroidea superior. Solamente en un animal se lesionó la rama probablemente por la diatermia durante la hemostasia de los vasos. La identificación intraoperatoria de la rama externa con disección entre el músculo constrictor de la faringe implicó ser inviable, pero la identificación (visualización) de su curso es importante por su alta vulnerabilidad durante la ligadura de los vasos del polo superior y sus ramas.

Injury to external branch of superior laryngeal nerve during thyroid surgery can have serious consequences. A strategy for perioperative identification and preservation of the superior laryngeal nerve was evaluated by experimental study in 30 adult mongrel dogs model weighing 45 to 55 pounds were used after approval by the animal studies committee at the Central University School of Medicine. These showed that 20 % of external branch of the superior laryngeal nerve run distally through the pharyngeal constrictor muscle, which necessitates intramuscular dissection for identification in the area around the superior thyroid pole. In 23 % of external branch of the superior laryngeal nerve identifiable without intramuscular dissection, a course partly lateral to the superior thyroid artery its branches implied definitive risk of injury during division of the superior pole vessels. 72 % of the external branch of the superior laryngeal nerve was identifiable without intramuscular dissection, and 19 % of these were lateral partly to the superior thyroid artery. Only one patient had signs of external branch of the superior laryngeal nerve injury postoperatively, probably caused by diathermy to an adjacent vessel. Perioperative identification of external branch of the superior laryngeal nerve with dissection into the pharyngeal constrictor muscle appears to be inadvisable, but identification of external branch of the superior laryngeal nerve with other courses is important, as around 20 % are highly vulnerable during division of the superior thyroid artery and its branches.

Laryngeal vocal and endoscopic alterations after thyroidectomy under local anesthesia and hypnosedation / Alterações vocais e endoscópicas da laringe após tireoidectomia com anestesia local e hipnossedação

Vocal alterations after thyroidectomy are generally related to laryngeal nerve injury or laryngotracheal mobility disorders caused by postoperative fibrosis or strap muscle lesion. AIM: this study aims to evaluate the frequency of vocal and rima glottidis disorders after thyroidectomy. MATERIALS AND METHOD: This is a prospective study based on 35 patients submitted to thyroidectomy under local anesthesia and hypnosedation. All patients underwent voice auditory perception evaluation, voice acoustic tests and videolaryngostroboscopy preoperatively, and at one week and at 30 days postoperatively. Bilateral cricothyroid muscle electromyography was performed on the thirtieth day after surgery to confirm the presence of injury in the external branch of the superior laryngeal nerve. RESULTS: 14.3 percent of the patients presented posterior glottis deviation before surgery and normal electromyography findings. Transient and permanent vocal alteration occurred in 25.7 percent and 14.2 percent of the patients respectively. CONCLUSION: voice disorders evaluated after voice auditory perceptive evaluation and voice acoustic tests were more intense in the group with superior laryngeal nerve external branch injury than in the injury-free dysphonic patient group. Oblique glottis can be present in normal patients; however its onset after thyroidectomy is indicative of superior laryngeal nerve external branch lesion.

Alterações vocais após tireoidectomia estão geralmente relacionadas a lesão de nervos laríngeos ou alteração na mobilidade laringotraqueal causada pela fibrose pós-operatória ou lesão da musculatura pré tireoidiana. OBJETIVO: Avaliar a frequência de alterações vocais e da rima glótica após tireoidectomia. MATERIAL E MÉTODO: Estudo prospectivo baseado em 35 pacientes submetidos à tireoidectomia com anestesia local e hipnossedação.Todos os pacientes foram submetidos à avaliação perceptiva auditiva da voz, avaliação acústica da voz e videolaringoestroboscopia nos períodos pré-operatório e pós-operatório uma semana e 30 dias após a cirurgia. Eletromiografia do músculo cricotireoideo bilateralmente foi realizada no trigésimo dia do período pós-operatório para confirmação de lesão do ramo externo do nervo laríngeo superior. RESULTADOS: 14,3 por cento dos pacientes apresentaram desvio posterior da glote no período pré-operatório com eletromiografia normal. Alteração vocal temporária e permanente ocorreu em 25,7 por cento e 14,2 por cento dos pacientes, respectivamente. CONCLUSÃO: Alteração vocal avaliada após análise perceptiva auditiva e acústica da voz foi mais intensa no grupo com lesão do ramo externo do nervo laríngeo superior do que no grupo de pacientes disfônicos sem lesão. Glote oblíqua pode estar presente em pacientes normais, porém o seu aparecimento após tireoidectomia é indicativo de lesão do ramo externo do nervo laríngeo superior.

The external laryngeal nerve in thyroid surgery: the 'no more neglected' nerve.

AIMS: To describe a novel surgical technique of 'lateralization' of superior pole to identify and save external branch of superior laryngeal nerve (EBSLN) during thyroidectomy. SETTINGS AND DESIGN: Prospective, nonrandomized at a tertiary care hospital in a specialized unit. MATERIAL AND METHODS: Over 30 months, 46 patients underwent thyroidectomy using technique of 1) 'Lateralization' of upper pole and dissection of avascular cricothyroid space 2) identification of EBSLN 3) skeletonization and individual ligation of superior thyroid vessels. Identified nerves were classified according to Cernea's classification. Outcomes were number of nerves identified, number of 'at risk' nerves' bilateral asymmetry and incidence of injury assessed by subjective interview and indirect laryngoscopy. RESULTS: Of the 78 dissected superior poles, nerves could be identified in 72 (92.31%). There were 22 (28.2%) type I, 42 (53.54%) IIa and 8 (10.25%) IIb 'at risk' nerves. In 32 patients with bilateral dissections, asymmetry of nerve was noted in 15%. Injury to nerve was not recorded in any of the patients. Average weight of glands was 69.59 g. Thyroidectomy was performed for benign disease in 28, malignancy in 4 and thyrotoxicosis in 14 patients. CONCLUSIONS: With technique of 'lateralization' and 'skeletonization and individual ligation of the superior vessels,' EBSLN identification increases and injury can be prevented. These results relate to the utilization of specific surgical technique and it is reasonable to expect that most surgeons, once familiar with the technique, should be able to achieve similar outcomes.

Complicaciones de la cirugía tiroidea / Postoperative complications of thyroidectomy

En este artículo se revisan las complicaciones de la cirugía tiroidea con especial énfasis en la lesión de nervio recurrente, hipoparatiroidismo transitorio y permanente, sangrado post operatorio y la lesión de nervio laringeo superior. Se mencionan los factores de riesgo que predisponen a complicaciones quirúrgicas insistiendo en la necesidad de una técnica operatoria cuidadosa que extreme los cuidados en la hemostasia, realice una exacta localización y preservación de los nervios recurrentes y una correcta identificación del mayor número posible de glándulas paratiroides ejerciendo una manipulación depurada y cuidadosa de estas estructuras. El uso de drenajes en el lecho operatorio de la tiroidectomía es controvertido, razón por la cual se comentan los pro y contras del uso rutinario. Se concluye que la experiencia del cirujano y una técnica quirúrgica meticulosa son los factores más determinantes de la morbilidad de esta cirugía.

Precautions to avoid injuring the superior laryngeal nerve [SLN] and its external and internal branches during thyroidectomy

The aim of this study is to find out the best operative measures and precautions to be undertaken to avoid injury and to safeguard the superior laryngeal nerve and its branches particularly its external laryngeal branch which is near and intimate to vascular pedicle of the superior pole of the thyroid gland during the operation of Thyroidectomy. This is in order to minimize the incidence of the serious disabilities associated with their injury particularly those of voice changes after Thyroidectomy. 30 patients with definite indications for Thyroidectomy were included into this study. From the operative findings of this series, it has been found that [the best operative precautions to be taken in consideration are either to identify the external laryngeal nerve which is most desirable but not always easy and sometimes time consuming or to dissect carefully the individual branches and tributaries of the distal 1.5cm to 2 cm of the superior thyroid pedicle and to tie and divide them right on the surface of the upper pole, and to avoid altogether the traditional method of mass clamping and ligation whether high or low of the superior thyroid pedicle during thyroidectomy since according to the operative findings in this study mass ligature is not without danger to the external laryngeal nerve, and to the superior laryngeal nerve if high ligature is adopted]. Lekacos et al 1987 [20] reported three cases of superior laryngeal nerve injury after 54 classical high ligations of the superior thyroid artery [STA]

study of topographic patterns of the external branch of superior laryngeal nerve [EBSLN] in conventional neck surgery: cadaveric and surgical dissection

Based on a cadaveric and surgical dissection of 38 superior thyroid poles [19 fresh cadavers] and 20 superior thyroid poles [15 patients for thyroidectomy and total thyroid lobectomy], a topographic categorization of external branch of the superior laryngeal nerve [EBSLN] was planned considering the hazard during thyroidectomy. This study correlated between the cadavers and the surgical dissection and presented a simple and easy classification to the relation of the EBSLN and superior thyroid artery with the upper pole of the thyroid lobe and also compared between them. Only one patient had a sign of the EBSLN injury postoperatively, probably caused by dissection or during ligation of superior thyroid pedicle in high risk dissection area behind the thyroid pole. The topographic description pattern of variable course of the EBSLN may help to decrease the risk of iatrogenic lesion of this imperative nerve