Neural monitoring during ultrasound-guided radiofrequency ablation of thyroid nodules

Figures & data

Figure 1. Consort flow diagram of the study.

Table 1. Characteristics of the patients and nodules at baseline.

Patients	n = 16
Age (years)	42.8 ± 15.9 [17–74]
Sex
Male	3 (19)
Female	13 (91)
Symptoms
Neck discomfort or pain	4 (25)
Foreign body sensation	5 (31)
Compressive symptoms	3 (19)
Cosmetic problems	4 (25)
Nodules	n = 20
Cytology
Benign	20 (100)
Malignant	0
Location
Left	8 (40)
Right	4 (20)
Bilateral	4 (20)
Ventral side	5 (25)
Dorsal side	15 (75)
Size
Length (cm)	2.5 ± 0.7
Width (cm)	1.9 ± 0.8
Thickness (cm)	1.7 ± 0.6
Composition
Solid	9 (45)
Cystic	2 (10)
Mixed	9 (45)

Values are presented as mean ± standard deviations (range min–max) or n (%).

Figure 2. Establishment of neural monitoring system (a) A pair of cutaneous, surface-electrodes were attached to the neck skin of the left and right lamina of the thyroid cartilage (b) Another pair cutaneous surface electrodes were attached to the upper arm of the patient (c) Ambu® Neuroline 715 single patient surface electrodes (d) Nerve stimulation needle was connected to a saline syringe as a stimulating electrode (e) All electrodes were connected an interface-connector box.

Figure 3. Procedure of neural monitoring during radiofrequency ablation of thyroid nodules (a) An ultrasoundguided puncture with the nerve-stimulation needle was performed between the lateral common carotid artery (CCA) and the medial internal jugular vein (IJV) and the vagus nerve (VN) was identified (b) EMG amplitudes were measured by NIM® Nerve Monitoring System 3⋅0 (Medtronic) (c) The needle was used to inject saline and continuously detect the recurrent laryngeal nerve with 3.0 mA current (d) A ‘liquid isolation zone’ was formed with a width of approximately 5 mm on the dorsal side of thyroid gland (e) The radiofrequency electrodes were placed into the nodule, and ablation was performed (f) After ablation, a final vagus electromyography (V2) was induced using 3.0 mA stimulus current and fibro laryngoscopies were performed on the first day following the procedure.

Figure 4. Simulation diagram of main steps (a) Initial Vagal Stimulation (b) Detection of RLN and Hydrodissection Technology (c) US-Guided RF Ablation (d) End of RFA Neural Testing.

Table 2. Neural monitoring data during ultrasound-guided thyroid nodule ablation.

Nerve no.	Location of the vagus nerve	Amplitude (μV)		Latency (ms)
		V1 (3 mA)	V2 (3 mA)	V1 (3 mA)	V2 (3 mA)
1	Right	730	701	5.1	5.1
2	Left	650	663	7.5	7.4
3	Right	882	817	5.2	5.2
4	Left	619	630	7.1	7.0
5	Right	801	783	5.5	5.5
6	Left	763	772	7.6	7.6
7	Left	601	500	7.1	7.2
8	Left	505	486	8.0	8.0
9	Left	528	509	7.3	7.3
10	Left	475	463	7.0	7.1
11	Left	676	661	7.1	7.1
12	Right	725	711	5.6	5.6
13	Left	641	623	7.2	7.2
14	Left	513	498	7.0	7.0
15	Left	416	422	7.1	7.1
16	Right	435	410	5.0	5.0
17	Right	517	498	5.2	5.2
18	Left	702	671	7.0	7.0
19	Right	620	587	5.3	5.3
20	Right	455	448	5.1	5.1
Mean ± standard deviation		612.7 ± 130.4	592.7 ± 127.3 (p < 0.05)	6.4 ± 1.0	6.5 ± 1.0 (p > 0.05)

Table 3. Correlation of electrophysiologic events with RLN function.

Variable	Number of VNs stimulated	Normal RLN function based on EMG signal	Normal vocal cord activity on laryngoscopy
Normative EMG	20	20 (100)	20 (100)
Impending adverse EMG or LOS	0	0	0

Values are presented as n (% of the total).

RLN: recurrent laryngeal nerve; VNs: vagus nerves; EMG: electromyogram; LOS: loss of signal.