I Have Soft Tissue Swelling Under Neck And In Throat

I have soft tissue swelling under neck and in throat for over a year. I have seen an endo and an ENT. I have even had a CT that does not show this swelling nor does it show the knots that are growing on either side of the thyroid. Although they do show on an ultra-sound. Why would that be? Why would a CT not show this swelling? It can be seen with the naked eye as well as felt. There is discomfort that radiates to the ear and down the neck. Again, this has been progressing for over a year.