Hi, Hasmimoto s thyroiditis is a auto immune disease in that the body’s immune system is acting after your thyroid gland. This has no direct link to your sinuses although in the body almost every other part is linked in one way or the other. Visiting the hospital and getting inside the cold operation theatre and also the cold air in the room is one association. Also, any surgery puts immune system in the downwards so that can also increase your sinus problems. For now just continue with the surgery and make sure you are well hydrated and kept warm. Also, mention the same to the operating surgeon or the ENT surgeon in the hospital who can also add a decongestant to keep your sinuses from acting up. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Sriram Nathan, ENT Specialist