Vocal cord paresis (VCP) caused by injury to the recurrent laryngeal nerve (RLN) is a well-known complication of thyroid surgery and has been widely documented in the literature. However, a systematic review by Jeannon et al. demonstrated wide variation in PCV detection methods and rates among previously published studies.
Rates for temporary PCV range from 1.4% to 38.4% (mean 9.8%), and from 0% to 18.6% (mean 2.3%) for permanent PCV [1]. The incidence of PCV may be underestimated unless routine vocal cord evaluation is performed.
In a study involving 26 Scandinavian hospitals with 3660 recorded thyroid operations, institutions that performed routine postoperative laryngoscopy reported almost twice the rates of PCV than those that did not [2].
Postoperative injury to the RLN is considered permanent if immobility or complete dysfunction of the vocal cord lasts more than 1 year [3].
Permanent injuries have been documented in up to 1.4%, and transient injuries in 5.2–12.6% of patients, according to studies using routine postoperative vocal cord examination [4, 5].
Reported risk factors for intraoperative RLN injury include advanced age, intrathoracic goiter, thyrotoxicosis, thyroid malignancy, prior thyroidectomy, reoperation for bleeding, extensive surgery, low or medium hospital case volume, and low surgeon case volume. [2.5-8].
The primary objective of this study was to prospectively evaluate the prevalence of preoperative incidental vocal cord paresis and the incidence rate of perioperative RLN injury, using routine laryngoscopic screening, before and after thyroid surgery.
Secondary objectives were to identify risk factors for RLN injury and analyze the outcome of postoperative PCV during a 12-month follow-up.
| Material and methods |
> Study patients
This was a single-institution observational study based on prospectively collected data. The local ethics committee approved this study and informed consent was not required from the patients.
All consecutive patients who underwent new or repeat thyroid surgery, between January 2011 and December 2016, were prospectively recorded in an electronic database, as part of a surgical quality initiative, in an effort to improve care. of the patient.
Follow-up data for the final analysis were collected retrospectively up to 12 months postoperatively.
All patients referred for elective surgical evaluation underwent clinical examination, thyroid ultrasound, and fine-needle aspiration biopsy (FNAB), when appropriate. Indications for surgery were recorded as; primary goiter, recurrent goiter (previous thyroid surgery), suspicious thyroid nodule, malignant thyroid nodule, completion of thyroidectomy, hyperthyroidism, or other indication.
“Suspected thyroid nodule” was defined as follicular neoplasia, or clinical suspicion of malignancy (based on size, appearance, or growth rate on ultrasound imaging), when an FNAB was inconclusive [9].
Patients with suspicious thyroid nodule underwent hemithyroidectomy. Thyroidectomy was completed in a second stage if it was proven that the removed nodule was malignant.
The indication for surgery was defined as “malignant thyroid nodule” when the preoperative FNAB was clearly malignant, according to the Bethesda system [10].
Postoperative hypocalcemia was defined as ionized serum calcium below 1.16 mmol/L for more than 2 postoperative days, requiring medication and/or prolongation of hospital stay. A low-volume surgeon was defined as one who performed fewer than 20 procedures per year.
> Vocal cord evaluation and follow-up
All patients underwent independent evaluation of vocal cord function by otolaryngologists who were not involved in the surgical procedure.
Indirect laryngoscopy and/or fibrolaryngoscopy was routinely performed before and after surgery. Fibrolaryngoscopy was used in cases where visibility on indirect laryngoscopy was inadequate or suboptimal.
Postoperative laryngoscopy was performed before discharge. A “new PCV” was defined as a new-onset PCV diagnosed postoperatively, which had not been detected in the preoperative examination.
Patients with PCV were scheduled for a 1-month follow-up, and then followed for approximately 1 year postoperatively, or until spontaneous recovery of vocal fold function. “Complete recovery” from postoperative PCV was determined by complete recovery of normal vocal cord function, documented on laryngoscopic examination.
A “near complete recovery” from PCV was defined as the return of vocal fold function after paralysis, without symptoms, with only minimal residual dysfunction on laryngoscopic examination. In case of insufficient follow-up data, the natural outcome of PCV was defined as uncertain, unless a major RLN injury had been verified intraoperatively.
> Statistical analysis
All statistical analyzes were carried out using SPSS Statistics 24.0 (IBM Corp, Armonk, NY). Continuous variables were expressed as mean ± standard deviation (SD). Fisher’s exact test or Pearson’s Chi-square test were used to compare nominal data.
Univariate and multivariate analyzes were performed on the independent variables to identify risk factors for postoperative PCV, using logistic and stepwise regression models with variable elimination. Odds ratio (OR) with 95% confidence interval (CI) was used to reflect the probability of a new postoperative PCV.
The Kaplan-Meier method was used to estimate the PCV recovery rate during the 12-month follow-up. Values of P < 0.05 were considered statistically significant.
| Results |
During the 6-year study period, 920 thyroid operations were performed on 866 patients (mean age 55 ± 16 years, 82% women), with 1296 nerves at risk.
Pre- and postoperative laryngoscopy was performed in 95% and 98% of cases, respectively. Preoperatively, 24 patients (2.8%) had a PCV prior to the primary operation; 14 were symptomatic.
Six had had a previous ipsilateral thyroid operation, which was the probable cause of the injury. Eight patients with preoperative PCV had a malignant thyroid nodule on the same side as the paresis, while 10 patients had no known cause for preoperative incidental PCV, thus considered idiopathic. Nineteen of the preoperative PCVs persisted and 5 resolved during follow-up after surgery.
Postoperatively, a new unilateral PCV was detected after 51 operations. Two patients had a new bilateral PCV after surgery; One operation had been performed due to a recurrent goiter and in the other the indication was hyperthyroidism.
Two of the 51 patients with a new PCV had a preoperative contralateral PCV and therefore had a postoperative bilateral PCV. Rates for new PCV were 5.8% ( n =53/920) for operations, and 4.2% ( n =55/1296) for nerves at risk.
The rates of new PCV and permanent PCV were 5.2% and 2.9% for primary goiter, 22.5% and 15.0% for recurrent goiter, 3.7% and 1.8% for operations performed for a suspicious thyroid nodule, 20.5% and 12.8% for operations with malignancy confirmed by FNAB, and 4.1% and 0.8% for thyroidectomies due to hyperthyroidism, respectively. Malignant histology was found in 172 (19%) of all 920 surgical specimens sent to pathology.
An unexpected malignant disease was found in 39/383 (10%) of operations performed for symptomatic goiter. Malignant neoplasms were confirmed in 73/271 (27%) cases operated on for suspicious or indeterminate thyroid nodule.
Furthermore, 17 additional malignancies were found in 56 complete thyroidectomies (30% incidence rate for complete resection procedures). When FNAB revealed a high suspicion of malignancy, postoperative histological examination confirmed carcinoma in 97% of cases (one proved to be a follicular adenoma).
> Risk factors for postoperative PCV
Univariate analysis of risk factors for new PCV showed that recurrent goiter and FNAB verifying a malignant thyroid nodule were prominent preoperative predictors of RLN injury during surgery. Other operation-related risk factors for RLN injury were total thyroidectomy, concomitant lymph node dissection, and sternotomy.
In relation to postoperative variables, hypocalcemia, malignant histology and, especially, T3-T4 invasive disease, were associated with lesions.
During the operation, the surgeon identified 722 (56%) of the 1296 nerves at risk. If the RLN was identified as intact, it was negatively correlated with risk of injury, whereas reporting a possible injury was strongly correlated with PCV.
One fifth of the procedures were performed by surgeons with low case volume, with experience of less than 20 cases per year (ranging from 1 to 10 cases per year). High-volume surgeons perform 20–35 operations per year. However, there was no statistically significant difference in PCV rates between low- and high-volume surgeons: 7.1% vs. 5.4% ( P = 0.387).
In multivariate analysis, significant risk factors for PCV were total thyroidectomy, recurrent goiter, drain use, and malignant histology at final pathologic examination.
Eighteen patients (34%) with a new PCV had a known risk factor for RLN injury before undergoing surgery (such as previous neck surgery, substernal goiter, or extended surgery requiring sternotomy or thoracotomy).
The RLN was deliberately sacrificed in 3 cases to ensure radical dissection of a malignant tumor, and the RLN was dissected from a tumor in 6 cases with a new PCV.
> Natural result of postoperative PCV
Of the 53 patients with a new postoperative PCV (mean age 61 ± 15 years), 42 (79%) were women. Forty-six patients (87%) with a new PCV were initially symptomatic.
Complete recovery of the PVC was documented with laryngoscopic examination in 14 of 53 patients during follow-up. Almost complete recovery was clinically and visually documented in 4 patients. Additionally, 4 patients canceled their follow-up visit because they were completely asymptomatic and were also defined as “almost complete recovery.”
PCV was definitively determined to be permanent in 29 patients and 30 nerves at risk; one patient had a new bilateral PCV.
Two patients were lost to follow-up at 6 months and therefore their recovery status was uncertain. For this reason, the number of permanent PCVs was estimated between 29 and 31 (3.2–3.4%) in 920 thyroid operations, and between 30 and 32 (2.3–2.5%) in 1296 nerves at risk. .
Consequently, the estimated rate of complete recovery at 12 months was 34 ± 8%, and 47 ± 8%, when almost complete recoveries were included.
Most recoveries occurred during the first 4 months and no improvement occurred after 12 months. Two-thirds of all patients with a new PCV received active voice therapy. Three patients underwent laryngoplasty with calcium hydroxyapatite injection.
| Discussion |
Although well recognized and widely reported in the literature, the incidence of PCV before and after thyroid surgery is exceptionally variable. An important feature of the present study was that the decision to detect PVC did not rest on the judgment of the patient or the surgeon.
Instead, virtually all cases were independently examined by third-party investigators (otolaryngologists) with laryngoscopic screening coverage of 95% preoperatively and 98% postoperatively.
Lang et al. argued against preoperative laryngoscopic examination based on their findings in 302 patients undergoing evaluation of nerve function before and after thyroid surgery [11].
In their cases, the prevalence of preoperative PCV was 2.3% and only one of the patients (0.4%) had not undergone prior thyroid surgery. Similarly in the present study, the preoperative PCV rate was 2.8%; However, in 10 cases (1.1% of all patients), the etiology was idiopathic.
In the practice of the authors of this work, the reasons for performing preoperative laryngoscopy are:
(1) To record, in case of postoperative PCV, whether it was in fact new and caused by the primary procedure
(2) In the case of preoperative PCV, be aware of the risk of bilateral PCV after surgery. There were 2 patients with previous unilateral PCV who presented with bilateral PCV after surgery.
In both cases, the indication for the procedure was recurrent goiter and the preoperative PCV was due to the primary procedure. Fortunately, in both cases, the new PCVs were transient.
According to these results, the incidence of new PCV was 53 in 920 operations (5.8%), and 55 in 1296 nerves at risk (4.2%).
Compared with the results of previous studies using routine laryngoscopy [4,5], the complication rate was lower (5.8% vs 7.6–13.9%). On the other hand, a much higher rate of permanent PCV was observed than had been demonstrated in those previous studies (3.2–3.4% vs. 0.9–1.4%).
In this study, less than half of the PCVs were transient, compared with approximately 80%–90% in the other studies [4,5]. These notable differences need to be analyzed by focusing, for example, on patient characteristics, diagnoses, extent of surgical procedures, reported standards, and volume of hospital and surgeon cases.
In hospitals that reported lower rates of permanent PCV, operations were generally performed by an experienced surgical team. The institution where the authors of this work work is a university teaching hospital and, consequently, many operations are performed by surgeons in training.
It is very important for any institution performing thyroid surgery to reliably recognize its RLN injury rate, and institutional risk should be discussed with the patient when weighing between surgery and surveillance.
Patients need to be well informed of the institution’s complication rates, rather than provided only vague risk estimates based on the literature.
Although only a small proportion of patients with PCV were asymptomatic in this study (13%), postoperative PCV can be easily missed unless routine vocal cord examination is implemented in the surgical quality control regimen. [2].
Routine visualization of the RLN is considered the gold standard for the prevention of its injury [12]. In the present study, the identification rate of the NLR was only 56%.
Interestingly, no difference was found in the PCV rate in cases in which the RLN was visualized, compared to cases in which it was not. Still, visualization of an intact RLN during surgery was correlated with normal vocal fold function postoperatively.
Evidence for routine visualization of the RLN is supported by case series, such as the recent publication by Dhillon et al., from John Hopkins Hospital , which included 2527 nerves at risk, with routine evaluation of the RLN by the attending surgeon in all cases. cases; The reported rates of temporary (2.9%) and permanent (0.4%) PCV for nerves at risk were significantly lower than those in the present study [13].
However, their study had a mixed cohort, including parathyroid procedures, while repeat procedures were not included; The postoperative rate of PCV was 72/2153 nerves at risk (3.3%) in primary thyroid procedures, compared with 55/1296 (4.2%) in this study, with both primary and repeat procedures.
Likewise, Dhillon’s study represents the vast experience of a single high-volume surgeon at one of the world’s most renowned hospitals, while the present study is a “real world” representation of outcomes at a small hospital. .
During the study period, intraoperative neuromonitoring was not used . Although it is widely recommended in special situations, such as repeat surgery, according to 2 meta-analyses with 23,500 and 9000 patients pooled, the routine use of neuromonitoring did not show a decrease in PCV rates [12,14].
Considering the high rate of permanent PCV in the present study, the authors modified their technique after the study to include neuromonitoring and recommend routine identification of the RLN.
The present study confirmed that recurrent goiter is one of the most significant risk factors for postoperative PCV, with a risk almost nine times higher than all other indicators combined.
Previously, patients with recurrent benign goiter were found to have a 4.7-fold increased risk of permanent PCV in a multi-institutional study of 16,448 procedures [6]. While this risk is well identified in the literature, it may still be underestimated in clinical work. The benefits of repeat surgery must be carefully weighed against the risk of RLN injury.
Other risk factors for RLN injury in this study were total thyroidectomy, sternotomy, lymph node dissection, hypocalcemia, and drain use. In total thyroidectomy, both RLNs were at risk and therefore the risk was at least two-fold higher compared with hemithyroidectomy.
Sternotomy, lymph node dissection, hypocalcemia, and drain use (in only 6% of operations) were all associated with extensive surgery and therefore an increased risk of RLN injury. Drain use itself has not been identified as a risk factor for PCV in a meta-analysis with 1927 patients [15].
In the present study, drainage was used more liberally, in 51% of patients. This work was performed at a time when the use of energy devices (i.e., electronic sealing instruments) had been adapted to routine practice (used in 99% of cases).
The effect of energy devices on the RLN injury rate could not be evaluated, because there were not enough cases for a control group; Only a few patients were operated without the vessel sealing instrument.
Almost identically to a previous meta-analysis of 1798 patients, two-thirds of the PCV patients in the present study received vocal therapy, while only 5.7% underwent injection laryngoplasty [16]. Early voice therapy in patients with unilateral VCP has been associated with better outcomes than late rehabilitation in an 11-year retrospective study of 171 patients [17].
Routine postoperative laryngoscopy allows early diagnosis and, consequently, initiation of vocal therapy without delay, which is also important for the prevention of aspiration-related problems.
Additionally, routine vocal fold screening provides direct feedback to the surgeon and may help prevent RLN injuries in the future.
> Limitations of the study
Although this observational study was carried out prospectively, follow-up was not structured and data were extracted retrospectively. A few patients with PCV declined follow-up to 12 months, and therefore the Kaplan-Meier method with data caesura was used to estimate the recovery rate.
It was not clearly defined whether the RLN was identified before or after removal of the thyroid lobe. Consequently, the results related to the identification of the NLR should be interpreted with caution.
Conclusions
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