The Prevalence of Thyroid Papillary Microcarcinoma in Patients With Benign Thyroid Fine Needle Aspiration

Introduction Thyroid nodules are a very common clinical finding in the general population. We use fine needle aspiration (FNA) as the gold standard workup test for a thyroid nodule, as it is capable of differentiating malignant nodules from benign in the majority of cases. Usually, FNA is done for nodules that are more than 1 cm; small malignant lesions that are less than 1 cm in size can be missed. That's why the risk of having undiagnosed microcarcinomas in an otherwise benign FNA needs to be explored. Aim To estimate the prevalence of thyroid papillary microcarcinoma in patients with benign FNA and evaluate and correlate the FNA cytological results with the final histopathological diagnoses. Methods This was a retrospective study of 1543 post-thyroidectomy patients who underwent FNA cytology, were classified according to the Bethesda scoring system, and were admitted to two tertiary care hospitals in Riyadh, Saudi Arabia, from 2010 to 2019. Results Six-hundred-seven (607) out of 1543 FNA cytology results were reported as benign, 215 as malignant, and 73 as suspicious of malignancy. On final histopathology diagnosis, 81/607 (13.34%) of benign cases and 35/215 (16.28%) of malignant cases did not meet the initial cytology and were confirmed as papillary microcarcinoma. In patients with microcarcinoma after initial benign FNA (89.2%) found to have benign multinodular changes, compared to only (31%) of initial malignant FNA patients. Conclusion  When non-surgical intervention is chosen in patients with benign FNA, the possibility of coexisting microcarcinoma with its variable prognosis should be taken into account and explained to the patient.