Table 1.

Conventional US characteristics of 106 category 4a and 4b thyroid nodules.

Characteristics	4a	4b
Nodules(n=106)	63	43
Maximum diameter
≤1 cm	33	27
1-2 cm	19	12
≥2 cm	11	4
Internal structure
Solid	61	41
Non solid	2	2
Echogenicity
Markedly hypoechoic	28	38
Isoechoic or Mixed echoic	35	5
Margin
ill-defined or irregular	3	35
defined or regular	60	8
Calcification
Microcalcification	2	4
None or Macrocalcification	61	39
Aspect ratio
>1	0	6
<1	63	37
Comet-tail artifact
Present	3	0
None	60	43