Most of the time, a person only knows if there is a thyroid nodule or cyst when a doctor discovers it while performing a routine exam, according to Mayo Clinic. However, some thyroid nodules and cysts may become large enough to see through the skin, or a person can have difficulty swallowing or breathing.
A thyroid cyst and a nodule are two different things, but a cyst may cause the formation of a nodule, explains Mayo Clinic. A cyst on a thyroid usually appears due to thyroid adenomas that degenerate. The cysts are typically benign but occasionally may contain solid components that become malignant. When a nodule forms, it usually remains benign, but a small number turn malignant.
To diagnose a thyroid nodule or cyst, a doctor starts with a physical exam, as the goal is to determine if the lump is cancerous or benign, states Mayo Clinic. A doctor may also perform thyroid function tests, which measure the amount of hormones from the thyroid and pituitary glands. A doctor also might perform ultrasonography to treat and diagnose a thyroid cyst or nodule. This method uses sound waves to produce images of the nodules and can distinguish the cysts from a fully formed nodule. It is also useful when a doctor is performing a biopsy, which is a test to determine if the nodule is benign or malignant.