Vocal cord paresis following single-session high intensity focused ablation (HIFU) treatment of benign thyroid nodules: incidence and risk factors

Figures & data

Figure 1. A treatment image captured before the ablation pulse. FP: focal point of the beams; TEG: tracheoesophageal groove; ESO: oesophagus; TN: thyroid nodule; CA: common carotid artery.

Figure 2. A treatment image captured during the 8-s ablation pulse. FP: focal point of the beams; TEG: tracheoesophageal groove; ESO: oesophagus; TN: thyroid nodule; CA: common carotid artery.

Table 1. A Comparison of baseline characteristics between patients who did not suffer from vocal cord paresis (group I) and those who did (group II) following single-session high intensity focused ultrasound (HIFU) treatment.

Variable	Group I (n = 99)	Group II (n = 4)	p-Value
Age at treatment (years)	49.6 ± 12.6	43.0 ± 5.0	0.306
Sex (male:female)	15:84	1:3	0.497
Body mass index (kg/m^2)	23.6 ± 4.2	21.8 ± 2.3	0.453
WHO nodule grade on presentation			0.802
- Grade 1a (palpable but not visible)	2 (2.0)	0 (0.0)
- Grade 1b (palpable and visible)	7 (7.1)	0 (0.0)
- Grade 2 (visible in the normal position)	61 (61.6)	2 (50.0)
- Grade 3 (visible from distance)	29 (29.3)	2 (50.0)
Location of nodule			0.819
- Upper third	12 (12.1)	0 (0.0)
- Middle third	45 (45.5)	4 (100.0)
- Lower third	32 (32.3)	0 (0.0)
Side of nodule			0.791
- Right	57 (57.6)	3 (75.0)
- Left	40 (40.4)	1 (25.0)
- Isthmus	2 (2.0)	0 (0.0)
Nodule dimensions
- Width (mm)	30.3 ± 14.6	29.1 ± 7.1	0.824
- Length (mm)	39.6 ± 15.3	41.7 ± 9.4	0.349
- Depth (mm)	24.4 ± 12.4	23.8 ± 6.7	0.736
Nodule volume (mL)+	18.6 ± 22.0	17.9 ± 10.7	0.663
Serum TSH (mIU/L)	1.4 ± 1.4	1.9 ± 0.9	0.101
Serum free T4 (pmol/L)	16.1 ± 2.1	18.7 ± 3.1	0.136

Continuous variables are expressed in mean ± standard deviation.

WHO: World Health Organisation; TSH: thyroid stimulating hormone.

+Volume of a nodule = (width × depth × length) × (π/6) where π was taken as 3.1416.

Table 2. A Comparison of 3- and 6-month treatment efficacy between patients who did not suffer from vocal cord paresis (group I) and those who did (group II) following single-session high intensity focused ultrasound (HIFU) treatment.

	Group I (n = 99)	Group II (n = 4)	p-Value
Size/volume of index nodule (mL)
- at baseline	18.6 ± 22.0	17.9 ± 10.7	0.663
- at 3rd month	9.4 ± 12.4	7.5 ± 4.3	0.547
- at 6th month	6.1 ± 10.6	5.2 ± 3.4	0.307
Volume reduction ratio
- at 3rd month (%)	51.0 ± 19.0	53.1 ± 8.4	0.748
- at 6th month (%)	72.6 ± 16.2	67.6 ± 9.8	0.403
WHO nodule grade at 6th month			0.750
- Grade 0 (not palpable or visible)	7 (7.1)	0 (0.0)
- Grade 1a (palpable but not visible)	21 (21.2)	1 (25.0)
- Grade 1b (palpable and visible)	55 (55.6)	3 (75.0)
- Grade 2 (visible in normal position)	16 (16.2)	0 (0.0)
- Grade 3 (visible from distance)	0 (0.0)	0 (0.0)

WHO: World Health Organisation.

Table 3. A Comparison of treatment parameters between patients who did not suffer from vocal cord paresis (group I) and those who did (group II) following single-session high intensity focused ultrasound (HIFU) treatment.

Variable	Group I (n = 99)	Group II (n = 4)	p-Value
Treatment parameters
- Total number of treated voxels/nodule	58.3 ± 25.7	55.7 ± 4.7	0.306
- Mean adapted energy (J)/voxel	284.2 ± 36.6	320.7 ± 18.2	0.045
- Total energy delivered (KJ)/nodule	16.1 ± 8.4	17.9 ± 2.0	0.295
- Treatment time (minutes)	65.2 ± 30.1	70.7 ± 13.0	0.379
First closest FP from TEG
- Distance from TEG (mm)	12.5 ± 2.9	9.4 ± 1.8	0.025
- Depth from skin (mm)	18.5 ± 3.9	19.5 ± 1.7	0.762
- Adapted power (W)	38.3 ± 5.4	39.0 ± 2.9	0.910
- Acoustic power (W)	71.6 ± 17.4	74.4 ± 6.1	0.736
Second closest FP from TEG
- Distance from TEG	13.6 ± 3.1	10.2 ± 2.2	0.024
- Depth from skin (mm)	18.0 ± 3.4	18.1 ± 1.9	0.907
- Adapted power (W)	38.3 ± 4.8	38.8 ± 3.3	0.821
- Acoustic power (W)	69.9 ± 15.6	69.9 ± 10.0	0.978
Third closest FP from TEG
- Distance from TEG (mm)	14.7 ± 3.7	11.3 ± 2.9	0.087
- Depth from skin (mm)	18.1 ± 3.9	20.1 ± 2.0	0.295
- Adapted power (W)	37.8 ± 5.2	40.3 ± 5.3	0.425
- Acoustic power (W)	69.8 ± 17.1	76.4 ± 9.2	0.448

Bold signifies statistical significance with p < 0.05.

FP: focus point of the HIFU beams during treatment; TEG: tracheoesophageal groove.

Figure 3. A scatterplot comparing distances from tracheoesophageal groove between those without and with vocal cord paresis.

Table 4. A univariate analysis of factors leading to vocal cord palsy after single-session high intensity focused ultrasound (HIFU).

Variable	ß-Coefficient	Odds ratio (95%CI)	p-Value
Age at treatment (years)	−0.039	0.962 (0.893–1.036)	0.302
Male sex	−0.624	0.536 (0.052–5.500)	0.599
Nodule volume at baseline (mL)	−0.004	0.996 (0.945–1.049)	0.878
VRR at 6th months (%)	−0.019	0.981 (0.925–1.042)	0.535
Distance of the closest FP from TEG (mm)	0.535	1.706 (1.001–2.915)	0.050
Depth of the closest FP from skin (mm)	0.073	1.076 (0.817–1.416)	0.603
Adapted power (W) used at the closest FP from TEG	0.026	1.027 (0.842–1.252)	0.795
Acoustic power (W) used at the closest FP from TEG	0.010	1.010 (0.950–1.074)	0.744

Bold signifies statistical significance with p < 0.05.

FP: focus point of the HIFU beams during treatment; TEG: ipsilateral tracheoesophageal groove; VRR: volume reduction ratio.