Re: What size benign thyroid nodule should be surgically removed?
Absolutely, the surgeon is correct, an I truly believe both must come out. A typical thyroid lobe is 4cm, your nodule/mass is 4 cm! It's like having a thumb growing on your thumb, but it's internal, and there's only so much room for it to smush in there---it can start growing down your windpipe, wrap around it and make it hard to breath---it can also grow down into your chest.
If the 4 cm one grew like crazy, you don't know what will happen to the other one---1.5cm isn't small, it can take off to grown, and then you would need another surgery. It's even possible that the big one is benign, and the other one is cancer. An fna will not get enough cells to determine what those are. They can be benign, but you really won't know until they are removed. Even if benign, the cells in there could mutate in the future, that's always a risk in a tumor.
My suggestion is to get a really great surgeon with tons of thyroid experience---that thing isn't going to be so simple to remove. But for you, it will be easy to get it out now. Then you need to get a great endo. to manage your meds so that you feel well for the future.
I didn't find the surgery tough at all (easier than other procedures), and I live without a thyroid (mine worked great) and my life is no different before than after. Hopefully all will go great for you!