I don't know what an ultrasound scan is about, but I know a CT scan is done specifically to look for tumors/growths inside the body. Who suggested you get an "ultrasound" scan? If it was your doctor trying to diagnose your problem, it is the right thing to do, I believe. I generally do what my doctor tells me is needed when it comes to my health.
But we should all know what the risk/benefit ratio is for any procedure. CT scans are no small deal. But faith in your physician, or anything, is worth its weight in health.
The neck ultrasound should show abnormal growths. Direct visualization, however, seems a good idea when there are concerns.