Is Thyroidectomy Safe After Identificating Recurrent Laryngeal Nerve Biology Essay

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Injury to recurrent laryngeal nerve remains a common complication of thyroid surgery. It is argued whether routine dissection leads to increase risk of palsy or otherwise.

Objectives: To assess recurrent laryngeal nerve injury risk during thyroidectomy with and without routine identification of the recurrent laryngeal nerve during surgery.

Settings and study design: Department of Surgery, Liaquat University of Medical & Health Sciences, Jamshoro/Hyderabad over 3 years.

Patients and Methods: The frequency of recurrent laryngeal nerve injury following surgery for benign, nontoxic thyroid disease was studied in consecutive patients undergoing hemithyroidectomy, subtotal thyroidectomy or near total thyroidectomy. Patients with benign and non toxic goitre were included in the study while those with toxic goitre and malignancy were excluded.

Results: A total of 88 patients were included in the study. They were divided into two groups, group A included patients in whom dissection of recurrent laryngeal nerve was done as standard procedure while in group B, the nerve was not exposed. There were 34 unilateral and 54 bilateral explorations. The mean age of patients in the two groups was almost same, with preponderance of females (M:F ratio 1:17). The incidence of recurrent laryngeal nerve injury was not significant in both groups (p=0.502), but the incidence of nerve injury in patients who underwent near total thyroidectomy was 17.6% compared to 0.17% in patients who had hemithyroidectomy, indicating that it is not the exploration but the extent of thyroid resection that is a risk factor for recurrent laryngeal nerve injury.

Conclusions: Dissection of nerve does not significantly reduce the risk of recurrent laryngeal nerve injury therefore, routine exploration of the nerve during thyroid surgery is not recommended in an expert hand.

Key words: Recurrent laryngeal nerve palsy, non toxic goitre, thyroidectomy.

Introduction

The recurrent laryngeal nerve was first described by Galen1 but Kocher identified its importance in thyroidectomy. Injury to recurrent laryngeal nerve is the commonest complication in thyroid surgery2, with an incidence of injury as high as 12.5 per cent3. The nerve is vulnerable to damage due to its variable position, course and relationship to key anatomical structures in the neck. It rarely lies precisely in the trachea-oesophageal groove.

Corresponding Author:

Fazila Hashmi

Department of Surgery

Liquat University Hospital

Jamshoro/ Hyderabad.

Email: fazilahashmi@hotmail.com The essential prerequisite for avoiding permanent damage to the recurrent laryngeal nerve is a good knowledge of normal anatomy of the nerve and its variations by the surgeon. Opinions regarding routine identification of the recurrent laryngeal nerve during thyroidectomy vary. Prioleau4 and others5 considered it unsafe to expose the nerve while others advocate routine exploration of the nerve along its entire course in order to avoid injury6. Yet some find the entire debate futile and postulate no significant risk of hoarseness with or without routine identification of the nerve7 and therefore the debate continues. This study was conducted to assess the risk of recurrent laryngeal nerve injury during thyroidectomy with and without routine identification of the recurrent laryngeal nerve during operation for thyroid disease.

Patients and Methods

This simple random study was carried out at the department of Surgery, Liaquat University Hospital, Jamshoro/Hyderabad. All patients coming for benign, nontoxic thyroid disease from June 2006 to May 2009 were included in the study. Patients with documented evidence of sub-clinical derangement of thyroid hormones or cytology suggestive of malignancy were excluded. Total or subtotal thyroidectomy was done depending upon the need.

Patients were divided into two groups with 44 patients in each group through lottery method. In group A, dissection of recurrent laryngeal nerve was done as a standard procedure, exposing one or both recurrent laryngeal nerves depending upon the surgical procedure. In group B, the nerve was not exposed. The surgical procedures carried out included hemi-thyroidectomy, subtotal thyroidectomy or near total thyroidectomy as the situation warranted. Postoperatively, alteration in the tone, timbre, or intensity of voice was considered as signs of recurrent laryngeal nerve injury and this was confirmed by vocal cord paralysis during indirect laryngoscopy. Voice change was considered permanent, where hoarseness persisted for more than six months. All the patients were reviewed at 1, 3 and 6 months postoperatively.

Data were analyzed using SPSS version 11.0. Mean, mode and standard deviation were calculated for variables like age, gender and clinical variety of goitre. The association of recurrent laryngeal nerve with or without routine exploration was measured using chi-square test. The same test was also applied to assess the relevance between the operative procedure performed and the nerve palsy. The association was considered significant if the calculated p-values were less than 0.05.

Results

A total of 88 patients were operated with 44 patients in group A and 44 in group B. Thirty four nerves were at risk on unilateral exploration and, 54 on bilateral exploration in both the groups. The mean age of patients in both groups was more or less same with a slight difference in range and standard deviation (Group A; range 14-60 yrs, mean age 33.75, SD±13.13 and Group B; range 14-58 yrs, mean age33.5, SD±13.93). There was female preponderance in both groups with male and female ratio of 1:17. Most patients presented with multinodular goitre (23(52%) and 25(57%) in group A and B respectively).

The characteristics of the patients are shown in Table-1. Patients in each group underwent either of the three procedures, as the situation warranted, and all parameters showed insignificant p-values.

Ten patients showed evidence of nerve injury giving an incidence of permanent damage in 3.4% and temporary palsy in 7.9% cases. In group A, 3(6.8%) patients developed temporary hoarseness of voice and 1(2.2%) had permanent voice change while in group B, 2 patients (4.5%) developed permanent and 4(9%) temporary hoarseness (not significant (p<0.768). The nerve palsy was not related to the number of unilateral versus bilateral nerve explorations. The type of surgery, however, was an independent risk factor for the nerve injury and near total thyroidectomy had significantly higher frequency of nerve damage (Table-2). No patient developed respiratory tract obstruction warranting tracheostomy in the post-operative period.

Table 1: Characteristics of patients in two groups.

Study Variable

Group A

Group B

p-value

n=44

(%)

n=44

(%)

Age in years

(mean age)

33.75

34.5

0.505

Gender distribution

Male

Female

03

41

7

93

02

42

5.5

94.5

0.645

Clinical variety of goitre

Diffuse

Multinodular

Solitary Nodule

3

23

18

7

52

41

3

25

16

7

57

36

0.905

Procedure performed

Hemithyroidectomy

Subtotal thyroidectomy

Near-total thyroidectomy

18

11

15

41

25

34

16

9

19

36

20

43

0.674

Nerves at risk

Unilateral

Bilateral

28

26

63.4

36.3

16

18

36

40

0.661

Number of paralysed nerves

4

9

6

14

0.502

Type of recurrent laryngeal nerve palsy

Temporary

Permanent

3

1

6.8

2.2

4

2

9

4.5

0.768

Table 2: Relation of recurrent laryngeal nerve injury with type of goitre and procedure performed.

Clinical Variety

Recurrent laryngeal nerve-Injury Group A Group B Total

n= 44 n=44 n=88

p-value

Diffuse

Multinodular

Solitary Nodule

0 0 0

3(6.8)* 5(11) 8 (18)

1(2) 1(2) 2 (4)

0.364

0.86

0.199

Procedure Performed

Hemithyroidectomy

Subtotal Thyroidectomy

Near total Thyroidectomy

1(2) 1(2) 2(4)

1(2) 1(2) 2 (4)

2(4.5) 4(9) 6 (13)

0.199

0.827

0.141

* Values in brackets are percentages.

Discussion

The present study showed association of nerve damage with the type of surgery but did not show any benefit of nerve exploration in reducing risk of nerve injury. Paralytic dysphonia and dysphasia resulting from recurrent laryngeal nerve injury during thyroid surgery results in significant morbidity8. The nerve injury not only diminishes the quality of life due to poor voice quality and increased vocal effort9 but may cause fatal aspiration pneumonia, especially in old patients or patients with impaired pulmonary function10. The incidence of recurrent laryngeal nerve palsy ranges from 5-8%11-15 with incidence as high as 12.5% reported in some series3. The average incidence of temporary and permanent recurrent laryngeal nerve palsy is 9.8 and 2.3% respectively16.

Surgical technique is one of the important factors affecting the outcome of thyroidectomy vis-à-vis recurrent laryngeal nerve injury. In past, most surgeons avoided dissections in the close proximity to the recurrent laryngeal nerve to avoid its damage. Now identification and preservation of recurrent laryngeal nerve is deemed necessary to avoid its injury17. Canbaz et al6 reported a significant increase in recurrent laryngeal nerve injury when the nerve was not identified. Matting et al18 showed similar observations and reported that routine identification of the recurrent laryngeal nerve decreased its permanent injury rate from 5.9-0.88% and similar reduction in nerve injury from 1.2% temporary and 0.6% permanent palsy was reported by Pimpl et al19. Non-recurrence and variations in the ascending course of the nerve makes it essential to identify the nerve to avoid its damage. In a study of 292 recurrent laryngeal nerves exposed during thyroidectomy, Jiang et al20 found only 134 nerves in the tracheosophageal groove with 158 deviating from it; great variation was also observed in the relationship of the nerve with the inferior thyroid artery and its branches. Extra laryngeal bifurcation of recurrent laryngeal nerve, seen in 23% cases is a common anatomical variation requiring great care to ensure that there is no unidentified anterior branch which contains all the motor fibres21.

Despite these excellent studies, the merit of routine dissection of recurrent laryngeal nerve has been questioned by others. Koch et al5 reported a similar incidence of temporary recurrent laryngeal nerve palsy in 800 subtotal unilateral resections of thyroid, irrespective of whether recurrent laryngeal nerve was identified or not and same was reported by Bergamaschi et al22. The demand for obligatory intra-operative identification of recurrent nerve, therefore, remains unsettled.

Present study showed that the incidence of nerve injury was proportional to the extent of thyroid resection in both groups, but near-total thyroidectomy carried a disproportionate incidence of nerve injury. Same was reported by others23. The incidence of nerve injury in patients who underwent near total thyroidectomy was 17.6% compared to 0.17% in patients who had hemithyroidectomy, indicating that it is not the exploration but the extent of thyroid resection that is a risk factor for recurrent laryngeal nerve injury. Although many studies strongly recommend an unambiguous identification of the nerve24, but our results show that identification of recurrent laryngeal nerve does not prevent the nerve palsy, however, extent of surgery does play a role in reducing nerve damage.

Larger studies with longer follow up are required to see the short term and long term of nerve exploration in patients undergoing thyroid surgery.

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