Table 1.

Comparison of some specificities of existent risk stratification systems (RSSs). Note: ETE = extra-thyroidal extension; RSS = risk stratification system.

RSS	Number of Classes	Meaning of TIRADS 1	Pattern or Point-Based RSS	Features of High Suspicion	Composition Included in the RSS	ETE Included in the RSS
Chilean TIRADS	6 TIRADS 4 divided into 2 subclasses	Normal examination	Pattern	Irregular margins Irregular shape Multiple peripheral microcalcifications Penetrating vessels	Yes	No
Kwak-TIRADS	5 TIRADS 4 divided into 3 subclasses	No nodule	Point	Marked hypoechogenicity Irregular margins Microcalcifications Taller than wide	No	No
BTA	5	Normal	Pattern	In a solid hypoechoic nodule: Irregular margins Microcalcifications Globular calcifications Intranodular vascularity Taller than wide Lymphadenopathy	Yes	No
AACE	3	Low risk	Pattern	Marked hypoechogenicity Irregular margins Microcalcifications Taller-than-wide Extrathyroidal growth Pathologic lymph node.	No	Yes
ATA	5	Benign	Pattern	In a solid hypoechoic nodule: Irregular margins Microcalcifications Taller than wide Rim calcifications with small extrusive soft tissue component Extra-thyroidal extension	Yes	Yes
K-TIRADS	5	Absence of nodule	Pattern	In a solid hypoechoic nodule: Irregular margins Microcalcification Nonparallel orientation	Yes	No
EU-TIRADS	5	Absence of significant nodule	Pattern	Marked hypoechogenicity Irregular margins Microcalcifications Taller than wide	No	No
ACR-TIRADS	5	Benign	Point	Marked hypoechogenicity All punctate echogenic foci Taller-than-wide Extra-thyroidal extension	Yes	Yes
C-TIRADS	5 TIRADS 4 divided into 3 subclasses	No nodule	Point	Markedly hypoechogenicity Ill-defined and irregular margins Vertical orientation Solid composition Microcalcifications Extra-thyroidal extension	Yes	Yes

For abbreviations of the names of the RSSs, please refer to Section 1.1. Note: ETE = extra-thyroidal extension; RSS = risk stratification system.