Table 1. US features of thyroid nodules based on the Korea Society of Thyroid Radiology (KSThR) guidelines.

	US features
Probable benign	Simple cyst, predominantly cystic, cystic nodule with reverberation artifact, spongiform nodule
Indeterminate	Isoechogenecity, hypoechogenecity (compared to thyroid parenchyma), hyperechogenecity, ovoid-to-round shape, irregular shape, smooth or ill-defined margin, rim calcification
Suspicious malignant*	Taller than wide shape, speculated margin, marked hypoechogenicity (compared to strap muscle), microcalcification (<1mm), macrocalcification (>1mm)

*: The presence of at least one of the findings for malignancy defines a nodule as a suspicious malignant nodule