Surgery (thyroidectomy to remove the whole thyroid or a part of it) is not extensively used because most common forms of hyperthyroidism are quite effectively treated by the radioactive iodine method, and because there is a risk of also removing the parathyroid glands, and of cutting the recurrent laryngeal nerve, making swallowing difficult, and even simply generalized staphylococcal infection as with any major surgery.
It may occur in situations with an increased blood volume, from excess of water and salt (renal pathology, excess of fluid or blood administration, treatment with retaining water steroids), chronic and severe anemia, large arteriovenous fistula or multiple small arteriovenous shunts as in Paget's disease of bone, some forms of severe hepatic or renal disorders, hyperthyroidism, beriberi.