Abstract
Objective
This study was aimed at analyzing the frequency of the newly reported variation and the frequency of postoperative palsy associated with three different kinds of known variations.
Methods
We conducted a retrospective study on the data of 2068 consecutive Chinese patients who underwent thyroidectomy. The study included 1362 left and 1507 right (2869 in total) RLNs.
Results
Among all the RLNs, 548 were found to have variations at the laryngeal entry of the RLN. The most frequent variation was extralaryngeal branching (n = 322), followed by the fan-shaped branching (n = 201). Our newly identified variation was also noted in 25 of our patients. In these cases, the RLN entered the larynx from sites that were distant from the posterior cricothyroid joint. The distance from the entry of the RLN to the back of cricothyroid joints was over 5 mm. Compared to the rates reported from other countries, the rate of the first type of variation is lower, while that of the second type is higher. The frequency of the new variation has not been reported in other populations, but it is consistent with our previous finding. The incidence of postoperative palsy was greater for RLNs with the first and third types of variations than in the normal RLNs.
Conclusion
We confirmed that the incidence of patients with the new type of variation of the RLN at the entry of the larynx was about 1% in Chinese. Awareness among surgeons regarding this variation is important to avoid postoperative palsy.
1
Introduction
The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve arising at the level of the arch of aorta . In humans, the RLNs of the right and left sides have different courses. The left RLN traverses underneath and behind the arch of aorta; ascends into a groove at the tracheoesophageal junction behind the posterior, middle part of the outer lobes of the thyroid gland; and enters the larynx below the inferior constrictor muscle. The left RLN is longer than the right one because the former traverses under the arch of the aorta at the ligamentum arteriosum, while the latter crosses at the right subclavian artery . The RLNs supply all the intrinsic muscles of the larynx except for the cricothyroid muscles, controlling the opening and closure of the vocal cords and carrying sensory inputs from the laryngeal mucous membranes below the lower surface of the vocal fold . Therefore, injury to RLNs can result in the weakening (hoarseness) or loss (aphonia) of voice and respiratory difficulty. This makes the RLN an important structure to be considered during thyroid surgery .
While its course is the same in a majority of the population, the RLN shows some anatomical variations that can potentially compromise the safety of thyroid surgery . Therefore, thorough knowledge of the RLN anatomy, including all of its variations, is mandatory for all thyroid surgeons. At the site of entry into the larynx, RLNs have been reported to have two kinds of variations, namely, extralaryngeal branching variation and fan-shaped branching . We have recently reported a new variation of RLN at the entry of larynx, namely branching posterior to the cricothyroid joint ; the prevalence of this variation has not been documented in the Chinese population or other populations. To evaluate the distribution of this variation in the Chinese population, we undertook a retrospective study of 2404 consecutive patients who underwent thyroidectomy.
2
Materials and methods
2.1
Study protocol
This study was designed as a retrospective investigation of 2068 patients who underwent thyroid surgery at our hospital between January 2009 and December 2013 and provided written informed consent to participate in the study. The documentation about each recurrent laryngeal nerve was carefully recorded and majority of recurrent laryngeal nerve were imaged if variation exists. All the procedure was performed by the same doctor. The study protocol was approved by the review board of Ruijin Hospital, Shanghai Jiaotong University School of Medicine, China.
2.2
Study population
The following were the inclusion criteria of the study: (1) evidence of malignancy on fine-needle aspiration biopsy (FNAB); (2) ultrasonography findings suggestive of malignancy of the thyroid nodules; (3) presence of single or multiple solid thyroid nodules with efficient blood supply and maximum diameter of > 3 cm; (4) diagnosis of Hashimoto’s thyroiditis with grade III enlargement of the thyroid, resulting in tracheal compression; (5) hyperthyroidism with grade III enlargement of the thyroid, causing tracheal compression; and (6) detection of retrosternal goiter. Among the patients, 1894 and 510 were female and male, respectively, with a median age of 45.01 years (range: 14–80 years). The total number of isolated RLNs investigated in this study was 3275, including 1576 left RLNs and 1699 right RLNs.
In all, 791 patients underwent bilateral total or near-total thyroidectomy or central lymph node dissection. Unilateral thyroid surgery was performed in 1277 patients, including unilateral total or near-total thyroidectomy, unilateral central lymph node dissection, and unilateral total or near-total thyroidectomy combined with contralateral subtotal resection. Among the 791 patients with bilateral dissection, 534 patients are papillary thyroid carcinoma or minimal papillary thyroid carcinoma, 7 patients are thyroid follicular carcinoma, 12 patients are medullary thyroid carcinoma, 1 patient is parathyroid carcinoma, 200 patients are nodular goiter, 26 patients are Hashimoto’s thyroiditis and 11 patients are hyperthyroidism. Among the 1277 patients with unilateral dissection, 442 patients are papillary thyroid carcinoma or minimal papillary thyroid carcinoma, 563 patients are nodular goiter, 251 patients are thyroid adenoma, 17 patients are Hashimoto’s thyroiditis and 4 patients are hyperthyroidism.
2.3
Surgery procedure
The left RLN enters the cervical tracheoesophageal groove. Therefore, generally, the left RLN can be easily identified under the middle and lower areas of the thyroid. The right RLN travels behind the carotid artery and crosses into the right side near the oblique tracheoesophageal groove, and then ascends, whereby the right RLN can be easily located at the middle portion of the thyroid. After the removal of the thyroid, the downstream course of the RLN from the thyroid was further exposed until the clavicle. The upstream course of the RLN from the thyroid was exposed until the site of entry into the larynx. The recurrent laryngeal nerve was not monitored by RLN monitor during operation.
2.4
Identification of RLN injury and follow-up
If patients showed postoperative hoarseness, laryngoscopy was performed to check for RLN palsy. Patients who did have nerve palsy were administered neurotrophic medication and underwent follow-up laryngoscopy at postoperative months 1, 3, and 6 to examine the status of the vocal cords. If the functioning of the nerve was not restored within this 6-month period, the RLN injury was deemed to be permanent.
2.5
Statistics
All statistical analyses were performed using the SPSS Inc. Released 2007, SPSS Windows, Version 16.0 (SPSS Inc., Chicago, IL). Fisher’s exact test, χ 2 test, or stratified chi-square test was used for the comparison of patient groups. The results were considered significant when the P value was < 0.05.
2
Materials and methods
2.1
Study protocol
This study was designed as a retrospective investigation of 2068 patients who underwent thyroid surgery at our hospital between January 2009 and December 2013 and provided written informed consent to participate in the study. The documentation about each recurrent laryngeal nerve was carefully recorded and majority of recurrent laryngeal nerve were imaged if variation exists. All the procedure was performed by the same doctor. The study protocol was approved by the review board of Ruijin Hospital, Shanghai Jiaotong University School of Medicine, China.
2.2
Study population
The following were the inclusion criteria of the study: (1) evidence of malignancy on fine-needle aspiration biopsy (FNAB); (2) ultrasonography findings suggestive of malignancy of the thyroid nodules; (3) presence of single or multiple solid thyroid nodules with efficient blood supply and maximum diameter of > 3 cm; (4) diagnosis of Hashimoto’s thyroiditis with grade III enlargement of the thyroid, resulting in tracheal compression; (5) hyperthyroidism with grade III enlargement of the thyroid, causing tracheal compression; and (6) detection of retrosternal goiter. Among the patients, 1894 and 510 were female and male, respectively, with a median age of 45.01 years (range: 14–80 years). The total number of isolated RLNs investigated in this study was 3275, including 1576 left RLNs and 1699 right RLNs.
In all, 791 patients underwent bilateral total or near-total thyroidectomy or central lymph node dissection. Unilateral thyroid surgery was performed in 1277 patients, including unilateral total or near-total thyroidectomy, unilateral central lymph node dissection, and unilateral total or near-total thyroidectomy combined with contralateral subtotal resection. Among the 791 patients with bilateral dissection, 534 patients are papillary thyroid carcinoma or minimal papillary thyroid carcinoma, 7 patients are thyroid follicular carcinoma, 12 patients are medullary thyroid carcinoma, 1 patient is parathyroid carcinoma, 200 patients are nodular goiter, 26 patients are Hashimoto’s thyroiditis and 11 patients are hyperthyroidism. Among the 1277 patients with unilateral dissection, 442 patients are papillary thyroid carcinoma or minimal papillary thyroid carcinoma, 563 patients are nodular goiter, 251 patients are thyroid adenoma, 17 patients are Hashimoto’s thyroiditis and 4 patients are hyperthyroidism.
2.3
Surgery procedure
The left RLN enters the cervical tracheoesophageal groove. Therefore, generally, the left RLN can be easily identified under the middle and lower areas of the thyroid. The right RLN travels behind the carotid artery and crosses into the right side near the oblique tracheoesophageal groove, and then ascends, whereby the right RLN can be easily located at the middle portion of the thyroid. After the removal of the thyroid, the downstream course of the RLN from the thyroid was further exposed until the clavicle. The upstream course of the RLN from the thyroid was exposed until the site of entry into the larynx. The recurrent laryngeal nerve was not monitored by RLN monitor during operation.
2.4
Identification of RLN injury and follow-up
If patients showed postoperative hoarseness, laryngoscopy was performed to check for RLN palsy. Patients who did have nerve palsy were administered neurotrophic medication and underwent follow-up laryngoscopy at postoperative months 1, 3, and 6 to examine the status of the vocal cords. If the functioning of the nerve was not restored within this 6-month period, the RLN injury was deemed to be permanent.
2.5
Statistics
All statistical analyses were performed using the SPSS Inc. Released 2007, SPSS Windows, Version 16.0 (SPSS Inc., Chicago, IL). Fisher’s exact test, χ 2 test, or stratified chi-square test was used for the comparison of patient groups. The results were considered significant when the P value was < 0.05.
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