Incidence of microcarcinoma and non‐microcarcinoma in ultrasound‐found thyroid nodules

BACKGROUNDS: The incidence of thyroid nodules is increasing year by year around the world. However, ultrasound is not recommended as a screening test for the general population or patients with a normal thyroid on palpation by the American Association of Clinical Endocrinologists (AACE). In practice, some individuals with normal thyroid palpation have nodules that can just be found out by ultrasound. No studies have directly described the risk of nodules found by ultrasound or by palpation up to now. More evidence is needed to carry out for helping us balance the over diagnosis and missed diagnosis of malignant lesions. Therefore, we carried out a retrospective study to investigate the incidence of malignant lesions in ultrasound-found nodules in a large cohort. METHODS: We conducted a retrospective analysis involving 2957 patients who underwent thyroid ultrasound evaluation and fine-needle aspiration (FNA) between Jan 2013 and Dec 2019. The cytologic examinations were analyzed based on the Bethesda system. For nodules suspected to be follicular neoplasm or other malignant tumors by cytological tests, patients were recommended for surgery and histopathology examinations. RESULTS: Compared with palpation-found nodules, ultrasound-found nodules were presenting less as purely cystic nodules (10.1 % vs. 39.9 %, x(2) = 355.69, p = 0.000), smaller size (17.5 ± 9.9 mm vs. 28.0 ± 12.5 mm, t = 23.876 p = 0.000), and higher TI-RADS score (5.5 ± 2.9 vs. 3.4 ± 3.3, t = 18.084, p = 0.000), respectively. More ultrasound-found nodules were diagnosed as carcinoma by histology examinations [136 (11.2 %) nodules found by ultrasound vs. 68 (3.9 %) by palpation, x(2) = 59.737, p = 0.000], and 88 (64.7 %) nodules found by ultrasound were non-microcarcinoma. Among the malignant nodules confirmed by histopathology, a higher proportion of microcarcinoma was detected in ultrasound-found nodules [35.3 % (48/136) vs. 16.2 % (11/68), x(2) = 8.183, p = 0.004]. CONCLUSIONS: In view of the results observed in our research, malignant nodules were more common in nodules screened out by ultrasound, and nearly two thirds of them were non-microcarcinoma. We suggest the recommendation against screening thyroid nodules by ultrasound needs to be re-evaluated.