Table 4. Malignancy Risk According to Category in Korean Thyroid Imaging Reporting and Data System.

Category		US Features	Malignant Risk (%)	Calculated Malignant Risk (%)	Frequency (%)
5	High suspicion	Solid hypoechoic nodule with any of three suspicious US features*	> 60	73.4 (210/286)	31.7 (286/902)
4	Intermediate suspicion	1) Solid hypoechoic nodule without any of three suspicious US features*	15–50	19.0 (44/231)	25.6 (231/902)
		2) Partially cystic or isohyperechoic nodule with any of three suspicious US features*
3	Low suspicion	Partially cystic or isohyperechoic nodule without any of three suspicious US features*	3–15	3.5 (12/340)	37.7 (340/902)
2	Benign	1) Spongiform	< 3	0.0 (0/45)	5.0 (45/902)
		2) Pure cystic or partially cystic nodule with comet-tail artifact	< 1
1	Normal	-	-	-

^*Malignant ultrasonography (US) features were spiculated/microlobulated margins, non-parallel orientation, and microcalcifications.