From May 2014 to September 2019, 1289 patients (198 men, 1091 women) with BTNs were admitted in the First Affiliated Hospital of Zhengzhou University according to the inclusion criteria and underwent RFA procedures. All patients’ thyroid functions including TSH, FT3 and FT4 were at normal ranges before ablation. Patient demographics and clinical features of appear in Table 1. For solid group patients, the mean maximal diameter, volume and cosmetic scores of nodules before RFA were 2.88 ± 1.39cm, 5.60 ± 4.52ml, 2.35 ± 0.97. For cystic-solid group patients, the mean maximal diameter, volume and cosmetic scores of nodules before RFA were 3.19 ± 1.47cm, 8.12 ± 6.32ml, 2.58 ± 0.94. Comparison of these three variables was different among the two groups (p<0.05). In addition, there were no significant differences in the gender, age and follow-up time (p>0.05). Based on the differences among base-lines, we only chose MDRR, VRR and CSRR to analyze the two groups, while for solid nodules or cystic-solid nodules themselves, we supplemented the analysis with data and reduction rate differences at the 3rd, 6th, 12th month.
Table 1. Clinical features of solid nodule group and cystic-solid nodule group patients. Means ± SD are shown. P < 0.05 was considered to indicate statistically significant difference. (M/F: male/female; cm: centimeter; ml: milliliter).
Characteristics
|
Solid nodule group
|
Cystic solid nodule group
|
P value
|
Gender(M/F)(n)
|
36/226
|
162/865
|
0.472
|
Age(years)
|
45.39±14.52
|
45.26±13.52
|
0.895
|
Maximal diameter(cm)
|
2.88±1.39
|
3.19±1.47
|
0.002
|
Volume(ml)
|
5.60±4.52
|
8.12±6.32
|
0.000
|
Cosmetic score
|
2.35±0.97
|
2.58±0.94
|
0.000
|
Follow-up(months)
|
5.05±5.29
|
5.62±6.88
|
0.286
|
In the solid group, the mean maximal diameters of nodules at the 3rd, 6th, 12th month were 2.12 ± 0.89cm, 2.04 ± 0.76cm, 1.46 ± 0.72cm, respectively, all of which were significantly less than that before RFA (p < 0.001) (Fig. 4A); the volume of nodules at the 3rd, 6th, 12th month were 3.01 ± 2.75ml, 2.40 ± 2.19ml, 0.59 ± 0.58ml, respectively, all of which were significantly less than that before RFA (p < 0.001) (Fig. 4B); the cosmetic scores of nodules at the 3rd, 6th, 12th month were 1.68 ± 0.80, 1.61 ± 0.73, 1.25 ± 0.45, respectively, all of which were significantly less than that before RFA (p < 0.001) (Fig. 4C). Through further pairwise comparison, we found that there were no significant difference between 6mo vs. 3mo and 12mo vs. 6 mo after RFA (p > 0.05). While 12mo vs. 3mo showed significant difference after RFA (p < 0.05), indicating that the solid nodule group shrank markedly at 12mo after operation.
To further verify above results, we selected MDRR, VRR and CSRR associated with nodular maximal diameter (MD), volume (V) and cosmetic score (CS) as study subjects. The same differences could be observed in MDRR (Fig. 4D) and VRR (Fig. 4E). However, CSRR changed significantly at 6mo, which may be explained by the variation of interior and exterior. The maximum diameter and volume of solid nodules have been shrinking after ablation, both of which can be calculated. However, the cosmetic score is an external performance, even though the nodules are still shrinking at 12mo, the appearance has been improved greatly at 6mo in advance. Consequently, we could find that there were no significant differences between 3mo vs. 12mo and 6mo vs. 12mo after RFA (p > 0.05). Nevertheless, 6mo vs. 3mo showed significant difference after RFA (p < 0.05), the cosmetic scores were almost consistent at 6mo and 12mo (Fig. 4F). Taken together, these results demonstrated that the maximum diameter and volume of solid nodules group would become smaller and smaller with the extension of time, both shrank prominently at 12mo during the observation period.
In the cystic-solid group, the mean maximal diameters of nodules at the 3rd, 6th, 12th month were 1.99 ± 0.82cm, 1.58 ± 0.71cm, 1.58 ± 0.89cm, respectively, all of which were significantly less than that before RFA (p < 0.001) (Fig. 5A); the volume of nodules at the 3rd, 6th, 12th month were 1.98 ± 1.81ml, 1.04 ± 0.98ml, 0.49 ± 0.48ml, respectively, all of which were significantly less than that before RFA (p < 0.001) (Fig. 5B); the cosmetic scores of nodules at the 3rd, 6th, 12th month were 1.54 ± 0.74, 1.27 ± 0.54, 1.36 ± 0.68, respectively, all of which were significantly less than that before RFA (p < 0.001) (Fig. 5C).
Some studies have found that larger MDRR and VRR can be achieved in the RFA group at 6 months13. Interestingly, similar results were observed in cystic-solid nodules group. By further analysis, we found that the rangeability of MDRR (Fig. 5D) and VRR (Fig. 5E) was consistent to CSRR (Fig. 5F), all decreased obviously at 6mo. The reason why these three variables showed synchronously is due to the different ablation method of cystic-solid nodules. The cystic fluid was aspirated before ablation, which may artificially accelerate the process of nodular shrinkage. Hence, the decline peak of nodular maximum diameter and volume appears in advance, synchronized with the cosmetic score. These results suggest that cystic-solid nodules shrank obviously at 6mo after RFA.
In order to further compare the efficiency of the two groups after ablation, MDRR, VRR and CSRR were also selected as study subjects. The mean MDRRs of the solid group vs. the cystic-solid group at the 3rd, 6th, 12th month were 25.58 ± 21.21% vs. 32.40 ± 21.43% (p = 0.003), 31.30 ± 23.87% vs. 43.51 ± 22.82% (p < 0.010), 41.33 ± 18.44% vs. 47.92 ± 20.04% (p = 0.229), respectively (Fig. 6A).The mean VRRs of the two groups at the 3rd, 6th, 12th month were 56.61 ± 19.50% vs. 66.58 ± 23.16% (p < 0.001), 65.81 ± 20.24% vs. 77.65 ± 18.70% (p = 0.005), 73.81 ± 18.94% vs. 82.71 ± 16.90% (p = 0.106), respectively (Fig. 6B).The mean CSRRs of the two groups at the 3rd, 6th, 12th month were 26.80 ± 21.77% vs. 32.16 ± 26.30% (p = 0.031), 38.48 ± 20.00% vs. 38.94 ± 27.33% (p = 0.915), 31.25 ± 26.44% vs. 38.64 ± 26.37% (p = 0.335), respectively (Fig. 6C).
The mean nodular MDRRs and VRRs at the 3rd, 6th months showed significant difference between the two groups, but at the 12th month, statistical significance was not found, and the cystic-solid group had a higher MDRR and VRR than that in the solid group. Between the two groups, there was no significant difference in the mean CSRR at the 6th, 12th month. While at the 3rd month of the follow-up, statistical significance was found, and the cystic-solid group had a higher CSRR than that in the solid group.
Those results above may be attributed to different ablation method and transformation of nodular nature. The aspiration of cystic fluid could artificially increase the reduction ratio of cystic-solid nodules, which was higher than that of the solid nodules. Six months after ablation, cystic-solid nodules can completely convert into solid nodules, giving rise to no significant difference at 12mo. Therefore, the 6mo can be regarded as the confluent point of cystic-solid and solid nodules. Previously, the decrease rate of the two groups was different from each other, owing to their diverse composition. While after 6 months, the two groups performed synchronous rate of change due to the shift from cystic-solid to solid, and we can see that the difference was not significant at 12mo.
The whole set of data was applied to testify that BTNs decreased most significantly at the 6th month after RFA13. Six comparative indices (MD, V, C, MDRR, VRR and CSRR) were selected for analysis. In the whole benign thyroid nodules group, the mean maximal diameter, volume and cosmetic scores of nodules before RFA were 3.09 ± 1.04cm, 7.29 ± 5.60ml, 2.53 ± 0.96; the mean maximal diameters of nodules at the 3rd, 6th, 12th month were 2.02 ± 0.84cm, 1.69 ± 0.74cm, 1.56 ± 0.85cm, respectively (Fig. 7A); the volume of nodules at the 3rd, 6th, 12th month were 2.06 ± 1.84ml, 1.28 ± 1.20ml, 1.18 ± 1.29ml, respectively; the cosmetic scores of nodules at the 3rd, 6th, 12th month were 1.57 ± 0.76, 1.35 ± 0.60, 1.34 ± 0.63, respectively (Fig. 7B). The mean MDRRs of BTNs at the 3rd, 6th, 12th month were 30.83 ± 21.38%, 40.68 ± 23.50%, 46.43 ± 19.76%, respectively (Fig. 7C). The mean VRRs of BTNs at the 3rd, 6th, 12th month were 64.35 ± 22.70%, 74.83 ± 19.62%, 77.79 ± 21.98%, respectively (Fig. 7D). The mean CSRRs of BTNs at the 3rd, 6th, 12th month were 30.45 ± 27.46%, 37.42 ± 32.30%, 36.97 ± 26.38%, respectively (Fig. 7E). All the above comparative indices before ablation vs. the observation time in the BTNs group significantly decreased; the P values were less than 0.001.
By pairwise comparison analysis, we found that there was statistical significance between 6mo vs. 3mo after RFA (p < 0.05), while 12mo vs. 6mo had no significant difference after RFA (P > 0.05), indicating that the BTNs shrank obviously at 6mo after operation. Comparing solid nodules, cystic-solid nodules and all benign thyroid nodules, we found that during the one-year follow-up period, solid nodules shrank most significantly at 12mo. Whereas, cystic-solid nodules and benign thyroid nodules shrank most significantly at 6mo, which is in line with most studies’ results13.