Radiologic and pathologic findings of nonpalpable thyroid carcinomas detected by ultrasonography in a medical screening center

Objective. The purpose of this study was to investigate the ultrasonographic and pathologic findings of nonpalpable thyroid carcinomas and reliable guidelines for fine-needle aspiration (FNA). Methods. Our study was approved by our Institutional Review Board, and written informed consent was waived. Between April 2004 and June 2006, screening ultrasonography was performed for 16,352 self-referred patients in the health care center. Among 1325 nonpalpable thyroid nodules in 1009 patients, pathologic results of FNA revealed 823 benign, 154 indeterminate, 198 nondiagnostic, and 150 malignant nodules. Fifty-eight malignant thyroid nodules (39 microcarcionomas and 19 carcinomas >1 cm, confirmed by both FNA and thyroidectomy) in 55 patients and 82 benign nodules (confirmed by both FNA and follow-up over 2 years) in 75 patients were included for the analysis. Three radiologists retrospectively analyzed the ultrasonographic features of these nonpalpable thyroid nodules for echogenicity, shape, margin, calcification, degree of cystic changes, and size. We compared the radiologic and pathologic findings between microcarcinomas and carcinomas larger than 1 cm for extracapsular invasion, lymph node metastasis, bilaterality, and multicentricity using univariate analysis. Results. Marked hypoechogenicity, an irregular shape, a taller-than-wide shape, a well-defined spiculated margin, microcalcification, and an entirely solid nature were significant predictors for malignancy (P <.05), whereas a cutoff value of 1 cm in the longest diameter was not significant (P =.184). However, extracapsular invasion (P =.024) and lymph node metastasis (P =.019) were observed more frequently in carcinomas larger than 1 cm (73.7% and 42.1 %, respectively) than in microcarcinomas (38.5% and 12.8%). Conclusions. Ultrasonographic findings suggesting malignancy should be preferentially considered as indicators for FNA, regardless of size, in nonpalpable thyroid nodules. However, extracapsular invasion and lymph node metastasis are closely related to the size of the thyroid nodule.