Follow-up ultrasound may be enough for thyroid nodules from 5 mm to 1 cm in size.

We investigated whether follow-up ultrasound (US) is enough for thyroid nodules 5-10 mm, and whether 3 years of interval between the initial US and next US is appropriate. This retrospective study was approved by the Institutional Review Board, and the need to obtain informed consent was waived. The study included 447 thyroid nodules 5-10 mm from 378 patients who underwent initial thyroid US, and underwent 3 years or more of follow-up US. The presence and characteristics of malignancy detected on follow-up were reviewed. Maximal diameters of each nodule at the initial and last US were measured. Univariate and multivariate analysis were used to assess association with nodule growth 3 mm or larger. Seven malignancies (1.6 %, 7 of 447) were detected on a mean 70.6 ± 20.3 months (range 36-104 months). Only one had growth 3 mm or larger, and all malignancies did not have extensive extrathyroidal extension, lateral lymph nodes, or distant metastasis. 6.0 % (27 of 447) of nodules had growth 3 mm or larger. Nodules in older patients were less likely to grow, and benign-looking nodules were more likely to grow. Longer follow-up time 6 years or more was not associated with growth, and no cancers were detected during the long follow-up time. Immediate US-FNA for thyroid nodules 5-10 mm are discouraged, unless suspicious metastatic lymph nodes are present. Also, a follow-up US 3 years after the initial US may be enough for these nodules.