Thyroidectomy is one of the most frequently performed surgeries in iodine-deficient regions. The most common complications during thyroidectomy are recurrent laryngeal nerve (RLN) injury and hypoparathyroidism1,2. While temporary nerve injury occurs in 1-10% of total thyroidectomies and 0.9-6% of subtotal thyroidectomies, the rate of permanent paralysis is 0-1.4% for both2-4. Similarly, the rate of permanent hypoparathyroidism is 1% or less in both surgeries.
In our country, subtotal thyroidectomy is still commonly performed for cases diagnosed with benign or suspicious malignancies4. Following subtotal resections, recurrence rates can reach as high as 3-30%1,3,4. In recurrent goiters, surgery is technically challenging due to adhesions and anatomical changes in the operation site, resulting in higher complication rates associated with RLN and parathyroid glands4,5.
Postoperative inflammation, scar tissue, bleeding, and edema following the first thyroid surgery can make it difficult to identify and dissect anatomical structures in secondary thyroid surgeries6. In reoperations, the complication rates for RLN and parathyroid glands increase by 4-8 times3-5. Many studies have shown that intraoperative nerve monitoring (IONM) reduces the risk of permanent nerve damage by aiding in the identification of the nerve.
This study aims to evaluate the success of nerve monitoring in preventing RLN injury and associated vocal cord paralysis in patients undergoing completion thyroidectomy after a prior limited thyroid surgery at our clinic or elsewhere.
Materials and Methods
This study retrospectively analyzed data from thyroid cancer patients who underwent secondary thyroid surgery for recurrent goiter or local recurrence after a limited resection (less than total lobectomy) between January 2005 and October 2010. Patients were divided into two groups: those who underwent nerve monitoring (group 1) and those who did not (group 2).
Preoperative and postoperative vocal cord examinations were performed on all patients. Vocal cord paralysis lasting six months or longer was considered permanent, while paralysis lasting less than six months was considered temporary7. The rates of temporary and permanent RLN paralysis were compared. In patients with RLN monitoring, the nerve was preserved by tracing its path from where it enters the thyroid lodge beneath the carotid artery to its entry into the larynx.
In group 1, intubation was performed without neuromuscular blockade. Endotracheal-based imaging systems (e.g., Medtronic NIM, Jacksonville, FL) were used to visualize bilateral thyroarytenoid muscles for real-time EMG activity. Neural stimulation was performed using a disposable probe set to a current of 1.5 mA. Before identifying the RLN, an initial EMG signal was obtained from the vagus nerve. Vagal stimulation was used to verify the correct placement of the tube before dissection near the RLN.
Stimulation was initially set at 1.5 mA, with a threshold of 100 μV. When the RLN was located in the tracheoesophageal groove, signals were obtained from the RLN, and the nerve was fully dissected and separated. If no signal was obtained at 2 mA, it was considered a failed placement. The vagus nerve was tested one final time after achieving complete hemostasis in the surgical field.
Postoperative outcomes were statistically analyzed using Pearson's chi-square and Mann-Whitney U tests.
Results
Among 23 patients (19 females, 4 males) with a mean age of 49.5±11.8 years, 6 were in group 1, and 17 were in group 2. In group 1, 4 patients underwent bilateral interventions, and 2 underwent unilateral interventions, involving a total of 10 at-risk nerves. Temporary paralysis of the left vocal cord was detected postoperatively in 1 patient (10%, per nerve).
In group 2, 29 at-risk nerves were involved: 12 in bilateral interventions and 5 in unilateral interventions due to local recurrence. Preoperatively, 2 patients had left vocal cord paralysis, and 1 had right vocal cord paralysis. Postoperatively, permanent vocal cord paralysis was detected in 2 patients (6.8%, per nerve). No significant statistical difference was found between the groups regarding temporary or permanent vocal cord paralysis (p>0.05 for both comparisons). The median time between the initial surgery and the secondary operation was 110 months (range: 3–240 months) (Table 1).
Discussion
Patients who have undergone surgeries other than total thyroidectomy for benign or malignant conditions retain a risk of recurrence or residual disease. Generally, any secondary intervention in such cases is referred to as completion thyroidectomy8-10. However, in patients who previously underwent unilateral lobectomy, removing the remaining lobe in a secondary surgery is termed completion thyroidectomy, whereas interventions targeting residual thyroid tissue after subtotal resection are referred to as "revision thyroidectomy"11.
Fibrosis-induced adhesions secondary to the initial surgery complicate the identification of anatomy during all revision thyroidectomy operations12,13. The most common complication following a secondary thyroid surgery is RLN injury, occurring at rates of 3–13%8-13. IONM is employed to improve RLN visibility amidst these anatomical changes and to reduce postoperative nerve complications.
Our findings align with the literature, demonstrating the potential role of IONM in aiding nerve identification during reoperative thyroid surgeries. Although our study found no significant difference in permanent RLN paralysis rates between groups, this may be attributed to the small sample size.
In conclusion, reoperation for recurrent or persistent thyroid cancer poses significant challenges for surgeons. While no statistically significant differences were observed, the absence of permanent nerve paralysis in the IONM group suggests that this method may contribute to reducing the risk of permanent nerve damage in reoperative thyroid surgeries. We believe nerve monitoring should be considered a preferred auxiliary technique in recurrent thyroid surgeries.
