Monitoring of the Left Recurrent Laryngeal Nerve during Mediastinoscopy is Feasible and Safe

C l i n M e d International Library Citation: Karenovics W, Guigard S, Zenelaj B, Licker M, Triponez F (2014) Monitoring of the Left Recurrent Laryngeal Nerve during Mediastinoscopy is Feasible and Safe. Clin Med Rev Case Rep 1:012. doi.org/10.23937/2378-3656/1410012 Received: November 25, 2014: Accepted: December 26, 2014: Published: December 29, 2014 Copyright: © 2014 Karenovics W. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Karenovics et al. Clin Med Rev Case Rep 2014, 1:012


Introduction
Since the advent of EBUS and EUS the frequency of cervical mediastinoscopy has greatly diminished.It is, however, still an important tool in the staging for non small cell lung cancer (NSCLC) and in the diagnosis of mediastinal lymphadenopathies and other systematically in all patients undergoing a mediastinoscopy during the study period.Reasons for not using the neuromonitoring were unavailability of the neuromonitoring device or cases where there was no need to go in a region close to the left RLN.There were also 3 cases with bulky tumours, where dissection and visualisation of the left recurrent nerve was not possible.These were not included.

Results
Between October 2012 and October 2013 we prospectively included 12 patients on whom we performed a video-mediastinoscopy with intraoperative nerve monitoring.Median age was 60 years (range: 39 -78 years); 8 patients were males.Indications for mediastinoscopy were staging for NSCLC in 6 patients, suspected lymphoma in 3 patients, suspected sarcoidosis in 1 and mediastinal lymphadenopathies of unknown origin in 2 patients (Table 1).The left RLN could be clearly identified in the region of the 4L station.We obtained a good signal from the neuromonitor on the left RLN and the left vagus nerve at the end of the intervention in all patients.No abnormal position or trajectory was identified in this small group.The position of the left RLN was, in the contrary, very predictable and stable.We noted, however, that it could run above or below the more lateral station 4 nodes.The vagus nerve was identified and tested between left common carotid artery and left internal jugular vein at the height of the neck incision.This part of the procedure was challenging as the nerve is very deep and lateral and the incision small, sometimes making visualisation difficult.In all patients, biopsy or lymphadenectomy were performed at least in 3 lymph node stations, including 4L in all cases.There was no case of postoperative hoarseness or vocal cord palsy.Histology showed no mediastinal nodal metastasis in 3 cases, presence of mediastinal involvement in 3 cases, granulomatous inflammation in three patients, lymphoma in one patient, tuberculosis in one patient and reactive lymph nodes in one patient.

Discussion
Cervical mediastinoscopy is the gold standard for diagnosis and staging of mediastinal metastases in patients with NSCLC.It is also an important tool for the diagnosis of non-NSCLC mediastinal lymphadenopathies and tumours.It has a false negative rate between 2 and 9%; sensitivity and specificity are 78 to 94 and 100% respectively [2] for the staging of lung cancer.Since its beginnings in 1959, the complication rate has reportedly been low, generally less than 3 % [3][4][5][6][7][8].Complications include bleeding from central greater vessels (azygos vein, superior vena cava, innominate vein and artery, pulmonary artery, aorta) tracheal and oesophageal lesions, infection, pneumothorax and vocal cord palsy [9,10].This latter complication is in most series less than 1% in some, even large series, even 0%.It is probably underreported or under diagnosed.If specifically looked for with a postoperative laryngoscopy, incidence of vocal cord palsy may increase to 6 % [11].A recent report by Walles et al showed a similar rate of vocal cord palsy or hoarseness of about 6.5 % [12].Approximately the same rate, i.e. 5.5% of prolonged hoarseness of the voice, was confirmed by Chabowski et al in their series of 54 consecutive patients [13].
The reported occurrence of recurrent laryngeal nerve palsy in thyroid surgery is 2 to 3 times higher when this complication is specifically looked for, either by routine post-operative laryngoscopy or by systematic use of neuromonitoring of the RLN [1].The main reason for this is that the dysphonia can be very subtle or even absent in many patients with vocal cord palsy if the paralysed vocal cord is in a median or paramedian position.Paralysis of the RLN can lead to dysphonia which can greatly affect professional or recreational activities.However and perhaps more importantly in thoracic surgical patients, it can lead to bronchoaspiration and to inefficient cough.The vocal cords do not close properly during deglutition and do not protect the airways.In these patients, Valsalva manoeuvre is not possible and the efficacy of the cough to clear the airways is reduced.Prevention of this underrecognized complication is therefore important.
In our small series, none of the patients developed postoperative hoarseness or vocal cord palsy.This was, however, not verified by laryngoscopy.In the presence of a good nerve signal on the vagus nerve at the end of the operation, this did not seem necessary or useful.It has been shown that the neuromonitoring reliably predicts postoperative function [14,15] and the risk of postoperative RLN palsy is less than 0.1% -1% [1,[16][17][18] if there is a good signal.On the other hand, not in all cases of loss or marked diminution of the signal will there be a RLN palsy.It is, however, extremely important to follow a standardized and validated protocol to avoid potential errors in the utilization of the neuromonitoring system leading to erroneous results [19].Errors may result from surgical technique (quality of nerve exposure etc.), problems related to technical  aspects of the neuromonitor (strength of current, event threshold, electrode placement etc.), equipment malfunction, as well as from problems on the anesthesia front, like tube size and placement, type of anaesthesia, secretions around the electrodes etc. Communication with the anesthesiologist is therefore crucial.Intravenous anaesthesia and mechanical ventilation without additional myorelaxant agents facilitated the operating conditions and allowed us to apply correctly the nerve monitoring.Technically the most challenging part was the stimulation of the vagus nerve through the low and small neck incision.Clear visual identification of the vagus nerve was not always possible.A good signal could still be obtained by stimulating deeply between left common carotid artery and internal jugular vein after gentle dissection.
The use of mediastinoscopy has been decreasing steadily over the last few years [20].This is due mainly to the increased use of endoscopic ultra-sound guided fine needle aspiration (EBUS and EUS).These techniques are highly reliable with sensitivities and specificities of about 92% and 100% respectively [21].They also compare favourably with respect to invasiveness, patient comfort and morbidity [22].It therefore seems highly likely that they will gain further territory and mediastinoscopy become even less frequent.For young surgeons, it is thus becoming more and more difficult to learn the technique of mediastinoscopy and to feel comfortable with a rarely performed procedure.On the other hand, for the time being, mediastinoscopy is still necessary in order to clarify the status of lymph nodes in lung cancer if there is discordance between PET and EBUS [2,23] as well as in the diagnosis of lymphoma [22], where cytology is often not sufficient and in the diagnosis of other mediastinal lesions.The neuromonitoring helps to clearly identify the left recurrent nerve and to ascertain its functional integrity thus facilitating confident removal or biopsy of lymph nodes in its proximity.Obviously this helps to prevent direct injury to the nerve but would not prevent damage by other mechanisms like traction as described by Roberts et al. [6].We did not encounter this problem in our small series, however, and obtained a good signal on the vagus nerve at the end of the procedure in all cases.We also feel that the nerve in this region is very free and mobile unless it is encased by tumour, making it less prone to traction injury than closer to its entry in the larynx where it is relatively fixed, as in thyroid surgery.We also regularly observe during thyroid surgery that, for instance, cephalad traction on the thyroid while working on its inferior poles generates increased activity on the neuromonitor and may cause coughing.This seems to be related to patient arousal (no muscle relaxation) in response to the increased stimulation caused by this traction and is by no means predictive of recurrent laryngeal nerve injury.That said, it is possible that blunt finger dissection may cause harm to the left RLN especially when pushing the aorta forward [24].
Many institutions currently use a neuromonitoring system for thyroid procedures, so the device and know-how is available.The cost of disposable material (endotracheal tube and stimulation probe) is variable from one country to another and from one institution to another.In a study by Dionigi et al. on thyroid surgery in Italy, the added cost of neuromonitoring was evaluated at 215.5 Euros in institutions with a high volume and 278.8 Euros in institutions with low volume.The cost of the non-disposable equipment is also included in this analysis [25].
In conclusion, we demonstrate in this preliminary data that it is feasible and safe to identify the left recurrent laryngeal nerve intraoperatively.Further studies are needed to examine whether the use of neuromonitoring of the recurrent laryngeal nerve during mediastinoscopy reduces the rate of recurrent laryngeal nerve palsy.