"Can they tell if it's benign or do you need a biopsy for that?" No. need a biopsy.
Ultra sound makes a picture, thats it. Shows irregularities that autoimmune thyroid antibodies can be responsible for. What it's used for mostly is to keep track / record nodules - many of us have them and usually are non-cancerous. Ones that grow fast are looked at more - sometimes biopsied later.
ENT? Usually an Endocrinologist is asked to review ultra sounds.
Agree with LM about the need for biopsy, but that will depend on the size of the nodules. Most nodules aren't biopsied until they are at least 2 cm in size.
Also agree that most nodules aren't cancer and that most/many of us with Hashimoto's have "some"/many........ my u/s report simply says "multiple".
ENT? Yes, if I were to need a thyroid biopsy or removal, I'd insist on my ENT vs my endo........ endo "treats" thyroid disorders (some, not very well), many/most are not surgeons, so don't go there. My ENT did 2 surgeries on my vocal cords, prior to my hypo dx and was the one who ordered the tests (blood and u/s) to determine Hashi's when my pcp refused further testing and was trying to take away my med, because of low TSH. Once Hashi was confirmed via blood tests and ultra sound, my ENT referred me to endo, with the promise that he'd be there for me, if I need him.
My situation could be different from others because this ENT had done 2 previous surgeries on me, and is the reason I can still make sound; I'd trust him to the hilt, but wouldn't dream of letting endo put a scalpel to my neck......