Repeat fine-needle aspiration can be performed at 6 months or more after initial atypia of undetermined significance or follicular lesion of undetermined significance results for thyroid nodules 10 mm or larger.

OBJECTIVES: To investigate whether repeat ultrasound-guided fine-needle aspiration (US-FNA) in initial atypia of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS) results could be performed 6 months after or more.
METHODS: A total of 221 AUS/FLUS ≥10 mm with any follow-up were grouped according to the first follow-up interval at less than 6 months (group 1, n = 87) and 6 months or more (group 2, n = 134). Clinical features, final assessment of ultrasound (US) or the Thyroid Imaging Reporting and Data System (TIRADS), tumour size, extrathyroidal extension and lymph node metastasis in malignancies were compared.
RESULTS: Thirty-four (15.4 %) were malignant. Age, gender, size, final assessment, TIRADS and malignancy rate were not significantly different between the two groups (p = 0.660, 0.691, 0.502, 0.237, 0.819 and 0.420). Tumour size, extrathyroidal extension and lymph node metastasis were not significantly different between the two malignancy groups (p = 0.770, 0.611 and 0.068). Two of 10 nodules with increased size were malignancies found at 7.1 and 25.0 months. None of 33 nodules (14.9 %) with decreased size at a median 10 months were malignant.
CONCLUSIONS: Repeat US-FNA performed on nodules ≥10 mm at 6 months or more after initial AUS/FLUS results can reduce unnecessary repeat US-FNAs without progression of malignancy. KEY POINTS: • Follow-up intervals of AUS/FLUS did not affect the malignancy rate • Tumour stage was not different according to the follow-up intervals • None of the nodules with decreased size were malignant • Repeat US-FNA can be performed at ≥6 months after initial AUS/FLUS.