http://www.aace.com/pub/pdf/guidelines/thyroid_nodules.pdf
A good technical document that has helped me understand the decision flow. : )
It means that if these nodules are going to grow fast, the have higher chance to be a cancerous.
Hypoechoic means:
a) the nodule reflects less of the ultrasound waves then surrounding tissue;
b) the nodule may have internal blood flow
However if nodule is less then 1 cm in diameter, it is monitored; once nodule is larger then 1 cm the biopsy is recommended for solid nodules