The value of second fine needle aspiration cytology tests when investigating benign thyroid nodules (Thy2/Thy2c)

Although the vast majority of thyroid nodules are benign, evaluation by ultrasound-guided fine needle aspiration (FNA) biopsy is usually necessary to exclude underlying malignancy. Partially in recognition of reported variability in FNA sensitivity and specificity, the 2007 British Thyroid Association (BTA) guidelines recommended two benign results 3–6 months apart to exclude neoplasia. The 2014 BTA guidance states that a second FNA is not required for nodules with benign Thy2 cytology and ultrasound characteristics unless there is strong clinical evidence to suggest malignancy. We report a retrospective analysis of patients from two large teaching hospitals who had repeat ultrasound-guided FNA biopsy between 2009 and 2014 following an initial report of Thy2/Thy2c. Radiology and cytology findings for first, second and any subsequent investigations were reviewed. Of the 162 patients with a first FNA of Thy2/2c, 25 repeat biopsies were non-diagnostic (Thy1/1c), and 130 patients again had benign Thy2/2c cytology, although 14 of these repeat biopsies were taken from the opposite side; one of these patients was later diagnosed with an incidental follicular variant of papillary thyroid cancer, another with Hurthle cell adenoma. Seven of the 162 patients with a first FNA of Thy2/2c were found to have Thy3 cytology or higher (3 Thy3a, 2 Thy3, 1 Thy4 and 1 Thy5) on repeat biopsy and progressed to thyroid surgery, where four were diagnosed with thyroid carcinoma. There was no strong clinical evidence to suggest malignancy in any of these patients, and initial ultrasound characteristics were also unremarkable. These results suggest that a second ultrasound-guided FNA biopsy may be necessary to avoid incorrect exclusion of neoplasia in patients initially found to have benign cytology, unless it is proven beyond doubt that by doing so we do not alter clinical outcomes in these generally indolent tumours.