Preoperative Visualized Ultrasound Assessment of the Recurrent Laryngeal Nerve in Thyroid Cancer Surgery: Reliability and Risk Features by Imaging

Figures & data

Figure 1 Ultrasound visualization of the recurrent laryngeal nerve (RLN), preoperative (A–C) and intraoperative (D–F).

Figure 2 Confirmation of preoperative ultrasound assessment of the recurrent laryngeal nerve (RLN) based on intraoperative detection of adjacent lymph nodes marked with carbon nanoparticles (arrow, RLN; triangle, lymph node; pentagon, injection needle).

Table 1 Inter-Observer Reliability of the Measurements of Recurrent Laryngeal Nerve (RLN) Parameters

Variable	Mean±SD		ICC	P	R^2
	Observer A	Observer B
CSA (R)	3.760±0.972	4.440±0.763	0.648	0.001	0.4454
CSA (L)	4.085±1.188	4.675±1.027	0.824	<0.001	0.6925
Width (R)	2.370±0.382	2.510±0.325	0.707	<0.001	0.5124
Width (L)	2.355±0.363	2.460±0.422	0.792	<0.001	0.6407
Thickness (R)	2.190±0.284	2.210±0.269	0.495	0.011	0.2460
Thickness (L)	2.305±0.351	2.315±0.345	0.675	<0.001	0.4563

Notes: CSA values are expressed in mm². The other values are expressed in mm.

Abbreviations: SD, standard deviation; ICC, intraclass correlation coefficient; CSA, cross-sectional area; R, right RLN; L, left RLN.

Table 2 Intra-Observer Reliability of the Measurements of Recurrent Laryngeal Nerve (RLN) Parameters

Variable	Mean±SD		ICC	P	R^2
	First Measurement	Second Measurement
CSA (R)	4.100±0.903	3.860±0.661	0.603	0.002	0.4009
CSA (L)	3.870±0.746	3.920±0.654	0.820	<0.001	0.6845
Width (R)	2.165±0.225	2.260±0.308	0.629	0.001	0.4356
Width (L)	2.140±0.289	2.135±0.223	0.807	<0.001	0.6957
Thickness (R)	1.975±0.188	2.010±0.210	0.587	0.003	0.3488
Thickness (L)	2.060±0.277	2.045±0.218	0.787	<0.001	0.6562

Notes: CSA values are expressed in mm². The other values are expressed in mm.

Abbreviations: SD, standard deviation; ICC, intraclass correlation coefficient; R, right RLN; L, left RLN; CSA, cross-sectional area.

Figure 3 Comparison of pre- and intra-operative ultrasound measurement of recurrent laryngeal nerve (RLN).

Table 3 Normal Recurrent Laryngeal Nerve (RLN) Parameters, Stratified by Age, Sex, and Body Mass Index

Variable	Age, Yr		P	Sex		P	BMI, kg/m^2		P	Average Value
	>50	≤50		Male	Female		≥ 24	< 24
CSA (R)	4.253±1.003	4.389±0.949	0.647	4.660±0.864	4.219±0.970	0.068	4.624±1.012	4.220±0.898	0.089	4.364±0.953
CSA (L)	4.300±1.206	4.371±0.860	0.802	4.634±0.961	4.225±0.819	0.080	4.612±1.025	4.217±0.843	0.087	4.358±0.924
Width (R)	2.376±0.457	2.434±0.386	0.633	2.486±0.308	2.393±0.433	0.360	2.393±0.340	2.440±0.428	0.636	2.424±0.397
Width (L)	2.274±0.405	2.323±0.296	0.622	2.417±0.299	2.263±0.314	0.055	2.380±0.303	2.276±0.320	0.190	2.314±0.316
Thickness (R)	2.135±0.367	2.196±0.334	0.561	2.274±0.269	2.141±0.362	0.124	2.274±0.366	2.135±0.315	0.099	2.185±0.338
Thickness (L)	2.204±0.451	2.243±0.281	0.689	2.313±0.269	2.198±0.332	0.153	2.286±0.315	2.208±0.316	0.325	2.236±0.316

Notes: CSA values are expressed in mm². The other values are expressed in mm.

Abbreviations: BMI, body mass index; CSA, cross-sectional area; R, right RLN; L, left RLN.

Table 4 Summary of Ultrasound Features of Thyroid Tumors and Recurrent Laryngeal Nerve (RLN) in Patients with Tumor Infiltration of the RLN

Patient No. Features	1	2	3	4	5	6	7	8
Ultrasound features of the tumor
Largest diameter (mm)	26	9	19	15	55	14	11	8
Margin	Indistinct	Indistinct	Indistinct	Indistinct	Indistinct	Indistinct	Indistinct	Indistinct
Taller than wider	Yes	Yes	No	Yes	No	Yes	Yes	Yes
Longitudinal location	Median	Median	Median	Inferior	Whole gland	Inferior	Median	Median
Sagittal location	Posterior	Posterior	Posterior	Posterior	Whole gland	Posterior	Posterior	Posterior
Near cricoid cartilage	Yes	Yes	No	Yes	Yes	No	No	No
Near trachea	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Near esophagus	Yes	No	No	No	Yes	No	No	Yes
Extrathyroidal extension	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Multifocal or unifocal	Multifocal	Unifocal	Unifocal	Multifocal	Unifocal	Unifocal	Unifocal	Unifocal
Ultrasound features of the RLN
Location	Left	Right	Right	Right	Left	Left	Left	Left
Margin with tumor	Indistinct	Indistinct	Indistinct	Indistinct	Indistinct	Indistinct	Indistinct	Indistinct
Continuous Shape	No	No	No	No	No	No	No	No
Display the RLN around Berry’s ligament	Not clear	Not clear	Not clear	Not clear	Not clear	Not clear	Not clear	Clear

Figure 4 Gray-scale ultrasound image of a 65-year-old woman with a papillary thyroid tumor. The largest diameter of the tumor was 8 mm, and its infiltration of the RLN around Berry’s ligament was confirmed intraoperatively (white arrow, RLN; yellow arrow, thyroid tumor).