If the nodule in the isthmus is solid must undergo biopsy due to the following:
ovoid shape,
size,
internal blood flow
the overall echogenic structure of the gland is suggestive of inflammatory process.
Did your report say if the nodules are cold nodules. Cold nodules are nodules that don't take up the iodine which means they are not made up of thyroid tissue. If that is the case then you would have the fine needle aspirations which probably won't tell you much but might save you from surgery. Good Luck