Table 1.

US features and US classification system with five categories for the suspicion diagnosis of thyroid nodules

Malignant US features (US-Mal)	Borderline US features (US-Bor)	Benign US features (US-Ben)
Marked hypoechogenicity	Hypoechogenicity	Ovoid shape
Spiculated margins	Irregular shape	Round shape
Microlobulated margins	Ill-defined margins	Isoechogenicity
Microcalcifications	Irregular thick halo	Hyperechogenicity
Taller-than-wide shape	Increased intranodular flow	Well-defined margins
Perithyroidal infiltration	Increased peri-intranodular flow	Regular margins
Perithyroidal invasion	Macrocalcifications	Regular thin halo
Metastatic lymphadenopathy	Interrupted rim calcifications	Perinodular vascularity
		Spongiform appearance
		Pure cystic lesion

1 = Malignant: ≥3 US-Mal (regardless of the existence of US-Bor or US-Ben); 2 = Suspicious for malignancy: ≤2 US-Mal (regardless of the existence of US-Bor or US-Ben); 3 = Borderline: ≥1 US-Bor without US-Mal (regardless of the presence US-Ben); 4 = Probably benign: ≥2 US-Ben (except spongiform appearance and pure cystic lesion), with no US-Mal, and/or US-Bor; 5 = Benign: spongiform nodules, pure cystic lesions, without US-Mal and/or US-Bor.