Should we perform fine needle aspiration cytology of subcentimetre thyroid nodules? A retrospective review of local practice.

In light of the rising rate of incidentally detected subcentimetre thyroid nodules due to improved surveillance and diagnostic imaging, the decision of whether to perform fine needle aspiration cytology is increasingly pertinent. We aim to assess (1) the sampling adequacy of fine needle aspiration cytology, (2) malignancy rate, (3) thyroidectomy rate and (4) diagnostic accuracy of fine needle aspiration cytology. A total of 245 subcentimetre nodules in 220 patients underwent fine needle aspiration cytology between 2011 and 2014. Medical records were reviewed for cytology results, subsequent management and histopathological results in the event the patient underwent thyroidectomy. Sampling adequacy was calculated as the percentage of diagnostic results (Bethesda II-VI). Malignancy rate was defined as the percentage of Bethesda IV-VI diagnoses. Amongst patients with Bethesda IV-VI diagnoses who underwent thyroidectomy, their cytology reports were correlated with post-operative histopathological findings. The sampling adequacy of fine needle aspiration cytology was 77.1%. Malignancy rate (Bethesda IV-VI) was 9.7%. The respective malignancy rates in the < 5 mm nodule group and ≥ 5 mm nodule group were 6.67 and 10.0%. In total, 79.2% (19/24) of the malignant nodules underwent surgical excision. The rest declined surgery and/or were lost to follow-up. Amongst the malignant nodules which were surgically resected, 84.2% (16/19) had definitive malignant histology. Five of these demonstrated multifocal carcinoma and/or extrathyroidal extension of carcinoma on histology. Initial fine needle aspiration cytology and subsequent histopathological diagnoses matched in all cases except for three that had false-positive fine needle aspiration cytology results. Majority of our patients with suspicious cytology results subsequently underwent thyroidectomy, notwithstanding the relatively lower diagnostic accuracy of fine needle aspiration cytology in subcentimetre thyroid nodules.