Research Article: A Closer Look at Laryngeal Nerves during Thyroid Surgery: A Descriptive Study of 584 Nerves

Date Published: June 12, 2012

Publisher: Hindawi Publishing Corporation

Author(s): P. V. Pradeep, B. Jayashree, Skandha S. Harshita.


Morbidity after thyroidectomy is related to injuries to the parathyroids, recurrent laryngeal (RLN) and external branch of superior laryngeal nerves (EBSLN). Mostly these are due to variations in the surgical anatomy. In this study we analyse the surgical anatomy of the laryngeal nerves in Indian patients undergoing thyroidectomy. Materials and Methods. Retrospective study (February 2008 to February 2010). Patients undergoing surgery for benign goitres, T1, T2 thyroid cancers without lymph node involvement were included. Data on EBSLN types, RLN course and its relation to the TZ & LOB were recorded. Results. 404 thyroid surgeries (180 total & 224 hemithyroidectomy) were performed. Data related to 584 EBSLN and RLN were included (324 right sided & 260 left sided). EBSLN patterns were Type 1 in 71.4%, Type IIA in 12.3%, and Type IIB in 7.36%. The nerve was not seen in 4.3% cases. RLN had one branch in 69.34%, two branches in 29.11% and three branches in 1.36%. 25% of the RLN was superficial to the inferior thyroid artery, 65% deep to it and 8.2% between the branches. TZ was Grade 1 in 65.2%, Grade II in 25.1% and Grade III in 9.5%. 31.16% of the RLN passes through the LOB. Conclusions. A thorough knowledge of the laryngeal nerves and anatomical variations is necessary for safe thyroid surgery.

Partial Text

Thyroid surgery was associated with high mortality rates in the early nineteenth century. The high mortality (20%) was attributed to the lack of meticulous dissection techniques and asepsis [1]. So much so, in the year 1850 the French Academy of Medicine banned thyroid surgery [2]. With the advent of antiseptic techniques and antibiotics the mortality due to sepsis has disappeared. So also, the refinement in surgical techniques, recognition of the presence of parathyroids, RLN, and need to protect the EBSLN resulted in lesser morbidity. Through understanding of the surgical anatomy has been crucial in decreasing the morbidity. Mostly the morbidity is due to technical failure to identify the vital structures and the variations in the surgical anatomy when the gland is pathologically enlarged. Several studies have been published revealing the anatomy of the laryngeal nerves as seen during thyroid surgery [1, 3–5]. Exposure of EBSLN and individual ligation of superior thyroid artery branches in the medial thyroid space was initially stressed to avoid injury to it [1, 6, 7]. Based on the course of the EBSLN; classifications were also put forward by Cernea et al. and Friedman et al. [4, 8]. EBSLN has several branches to pharynx and thyroid gland apart from the clinically important cricothyroidal branch [9]. The RLN is routinely exposed and traced during all thyroid surgeries. It has been realised that the RLN has extralaryngeal branching and this can be damaged if the individual branches are not taken care of by meticulous dissection [10, 11]. However, no such detailed study has been published from Indian subjects. In this study we analyse the surgical anatomy of the laryngeal nerves both RLN and EBSLN and its variations in Indian patients undergoing thyroid surgeries at a specialised endocrine surgical unit.

This descriptive study based on the retrospective data was conducted at a tertiary care centre in South India during the period February 2008 to 2010. Approval of the Institutional Ethics committee was obtained for publishing the study. All patients give informed consent prior to thyroid surgery. Patients who were operated for benign goitres including toxic goitres and early thyroid cancers (T1/T2 N0M0) were included. Patients undergoing surgery for recurrent goitres and advanced thyroid cancers were excluded. The surgical findings are recorded in predesigned “Operation notes” register. These were later entered in the SPSS software 13vs for the analysis.

A total of 404 patients who underwent thyroid surgery are included in this study. Among these 180 underwent total thyroidectomy (TT) and 224 patients had hemithyroidectomy (HT). There were 324 nerves on the right side and 260 nerves on the left side in this study. The male to female ratio was 1 : 8. The mean age was 37.52 ± 12.9 years and the mean duration of goitre was 39.49 ± 46.82 months. The indications of surgery included Graves disease, toxic multinodular goitre, early carcinoma thyroid, and non toxic benign goitres. A total of 584 EBSLN and RLN were dissected. Type 1 nerve was the commonest among the 324 right-side EBSLN and 260 EBSLN on the left. The different types of EBSLN are depicted in Table 1. 3.4% of the nerves on the left and 5.4% on the right side were not identified. Figure 1 shows type 1 and Figure 2 show type 2 EBSLN.

Thyroid surgery was limited to only life-threatening complications arising in the goitre in the early part of the nineteenth century [1, 2] due to the associated mortality. Apart from the introduction of general anaesthesia and antisepsis understanding of the thyroid anatomy and pathology decreased the mortality from thyroid surgeries. As the safety of thyroid surgery increased the complications of the procedure came to limelight and all surgeons concentrated on preventing this. Since the surgical anatomy is now well studied, the morbidity of thyroid surgery has decreased to less than 1%. In this study we describe the nerve course, types, and their variations in 584 laryngeal nerves in our patients undergoing thyroid surgery. Most of the studies on the laryngeal nerve anatomy are cadaveric studies [13]; however, this study demonstrates the anatomy as seen during live surgery in pathologically enlarged glands.




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