To review the retrospective imaging findings of thyroid cancer initially assessed as no suspicious malignancy.

Of 338 nodules confirmed to be thyroid cancer, this study included 38 patients with 39 nodules assessed as no suspicious malignancy on initial sonography. (mean age: 39 years, 36 females and 2 males). We evaluated sonographic findings by shape, margin, echogenecity, calcification, cystic degeneration and peripheral hypoechoic rim retrospecively. We analyzed whether sonographic findings were different according to the size (standard: 1 cm).

The most frequent sonographic findings were ovoid to round shape 90%, well-defined smooth margin 64%, hypoechogenecity 54%, no calcification 92%, no cystic degeneration 77% and peripheral hypoechoic rim 56%. Suspicious malignancy findings were taller than wide shape 10%, well-defined spiculated margin 36%, markedly hypoechogenecity 10% and microcalcifications 8%. Isoechogenecity, cystic degenetaion and peripheral hypoechoic rim were common in 1 cm more than nodules. Well-defined spiculated margin was common in 1 cm less than nodules. In retrospective, 56% showed no suspicious malignancy finding.

Although nodules assessed as no suspicious malignancy on initial US had many retrospectively suspicious malignancy findings, still many nodules showed no suspicious malignancy finding. Suspicious findings were ignored due to equivocal finding in small size, isoechogenecity, cystic degeneration or peripheral hypoechioic rim. We need careful observation.