Recurrent laryngeal nerve injury after thyroidectomy

Discussion

In the present study, RLN injury after thyroid surgery was observed in only 5 (1.1%) patients, which is in line with previously published studies.^2,5 Table 3 depicts the incidence among different centers in Saudi Arabia.^6-16 Although all 5 patients were female, our data revealed no statistically significant relation between gender, age, and the risk of nerve injury, which is also consistent with previous studies.^1,9,12

Injuries can be transient or permanent, unilateral, or bilateral. The incidence of transient injuries have been reported to be 4-7% and permanent injuries have been reported to be 1-4%.⁵ However, another study found that the incidence of transient injuries ranged from 1-30%, while that of permanent injuries ranged from 0.5-5%.² According to Oertli et al,¹⁷ the risk of transient injury was 3.5-5.2% and 0.5-2.4% of permanent injury. In contrast, Reeve et al¹⁸ emphasized that the risk of injury was less than 1%. In our study, 4 (0.9%) patients had transient injuries, while one (0.2%) had a permanent injury.

The most common clinical manifestations of unilateral RLN injury are voice weakness and hoarseness. Conversely, dyspnea and glottal obstruction are common in bilateral RLN injury.¹⁶ All our patients with RLN injury developed hoarseness. Four of the patients subsequently recovered and regained their normal vocal qualities. The fifth patient had permanent bilateral RLN injury. Despite that, she did not require a tracheostomy.

There are several mechanisms of RLN injury. These include ischemia, traction, stretching, entrapment, thermal injury, contusion, hematoma, compression, transection, irritation without actual damage, and endotracheal cuff compression.⁵ In the latter (due to vocal fold edema), the voice changes usually resolve in a few days. In rare occasions, RLN transection may occur or be required during thyroid surgeries. Therefore, re-anastomosis should be carried out with the aim to restore vocalis muscular tone. In contrast, transient RLN dysfunction could develop if the RLN is stretched during surgery and in such cases, calcium channel blockers are helpful in recovery.¹⁹

Graves’ disease, huge multinodular goiter, thyroid malignancy, the extent of surgery, central lymph node dissection, redo surgeries, and the inexperience of surgeons are all precipitating factors for RLN injury.^1,2,16 In our study, patient one had a malignant pathology with retrosternal and extrathyroidal extensions and required central neck dissection. Patient 2 had Graves’ disease, while patient 3 had retrosternal extension. Additionally, patient 4 had only adhesions, and lastly, patient 5 had a large left lobe with adhesions and fibrosis.

Compared with other conservative procedures, total thyroidectomy has been reported to have a higher risk of nerve injury.^6,16 However, our data showed no significant relationship between the extent of thyroidectomy and the risk of RLN injury. Karamanakos et al¹ also found no relationship between the extent of thyroidectomy and the risk of RLN injury in their univariate analysis only. However, their multivariate analysis identified pathology type (malignancy, recurrent goiter, and thyroiditis) as an independent risk factor for transient RLN injury, which contradicts our findings.¹ In addition to these factors, anatomical distortions and variations may increase the risk of RLN injury.²⁰

Although RLN injury cannot be totally prevented, careful intraoperative inspection and understanding of its anatomical course, along with its variations, should significantly reduce the risk.^2,18 Anatomically, the left RLN has a straightforward course in the neck, whereas the right RLN follows a variable course. The right RLN is slightly more lateral than the left RLN. Additionally, it is important to know the different relationships between the inferior thyroid artery and the RLN. The artery may be in front or behind the RLN. It may also pass between the nerve and its branches or split before reaching the nerve.²⁰ Some experienced surgeons do not routinely expose the nerve but are still able to avoid RLN injury. However, visualization is still recommended, at least during a portion of the procedure.¹⁸ This is also a routine practice at our institution. According to Dralle et al,²¹ visual nerve identification is the gold standard strategy for thyroid surgery. Furthermore, in a meta-analysis, systematic nerve visualization was found to be the best step for avoiding RLN injury.²²

There is still controversy regarding recurrent nerve dissection and whether it increases the risk of RLN injury. Several studies have concluded that recurrent nerve dissection was unnecessary in subtotal thyroidectomy; however, it is beneficial in complicated cases, such as thyroid malignancy.^6,16 Echternach et al²³ found that recurrent nerve dissection did not increase the risk of both temporary and permanent RLN injuries. Surprisingly, they reported that the risk of permanent RLN injury was reduced, implying that recurrent nerve dissection is advised.^23,24

The use of neuromonitoring is similarly controversial. Some authors have advocated for nerve monitoring to reduce the incidence of RLN injury, while others have found no statistically significant evidence to support its use.¹⁶ Furthermore, it did not aid in the anatomical dissection of the RLN.^2,16 The risk of injury has been reported to be 3.1% in cases of nerve visualization; 3.5% when a nerve stimulator was used.²² Some authors have also argued that nerve monitoring should be used only in redo surgeries, huge goiters, malignant cases, and widespread metastatic lymph node invasion.³

Different treatment approaches for RLN injuries have been proposed, including voice therapy, vocal exercises, medialization, injection laryngoplasty, and arytenoid adduction.^2,25 Tracheostomy is indicated in permanent bilateral RLN injuries associated with severe dyspnea.³