Endocrine Abstracts

Objective: To understand the factors associated with changes in thyroid nodule volume with previous benign citology.

Material and Methods: This is a prospective single-center observational study. We included patients with a benign citology from March/2016 to May/2018 and ultrasound follow-up after 12–24 months. Initially we determined the nodule size (volume in ml), and its risk of malignancy was classified according to ATA 2015 criteria. Volume changes were defined as following: decrease (decrease >20%), stability (between –20% and +20%), non-significant growth (increase between 20% and 50%) or significant growth (increase >50%). We defined the nodule growth rate as the time it takes for a nodule to double its inicial volume (volume doubling time, VDT), measured in months. Statistic analysis was performed with SPSS 20.0.

Results: There were included 200 thyroid nodules (186 patients) with a mean follow-up of 18.2 ± 6.4 months. The mean age was 50.4 ± 13.6 years; 27 (13.5%) were males; initial TSH was 1.6 ± 1.3 mU/l; 54 (27%) had positive autoimmunity and 142 (71%) were multinodular. Mean characteristics of node size: larger diameter 28.8 ± 11.5 mm; volume 8.6 ml (range 0.26–69.8). Risk of malignancy according to ATA criteria: 44 (22%) very low; 119 (59.5%) low; 16 (8%) intermediate; 3 (1.5%) high and 18 (9%) not classifiable. The distribution of the nodules by volume change was: 25 (12.5%) decreased; 94 (47%) remained stable; 53 (26.5%) presented non-significant growth and 28 (14%) showed significant growth.

None of the basal characteristics of the nodules (sex, age, TSH, autoimmunity, nodularity, volume or ATA criteria) was significant in association with significant growth. However, we observed that the very low risk nodules decreased in a greater proportion than the others (P < 0.001). From among the nodules with any growth, only 14 (10.1%) had a VDT less than 24 months.

Six malignant nodules (3.3%) were detected after follow-up. Four (66.6%) did not show significant growth. Their risk of malignancy according to ATA criteria were: 3 (2.5%) low risk; 2 (12.5%) intermediate risk; 1 (33.3%) high risk.

Conclusions: 1) a low proportion of thyroid nodules show significant growth after follow-up; 2) none of the variables studied are able to predict the significant growth of the nodules; 3) The ATA criteria have been useful for detecting misdiagnosed malignancy in the initial assessment.