Some thyroid cysts can grow larger. A thyroid cyst refers to a fluid-filled sac found in the thyroid gland, typically round in shape with a diameter ranging from two to five centimeters. Generally, these cysts are painless or only mildly painful. Most are solitary nodules, though a few are found in multiple nodules. Thyroid cysts are not an independent disease; they can result from simple goiter, nodular goiter, or degenerative changes in thyroid adenomas. Some cysts may also form due to thyroid cancer, through processes like hemorrhaging and necrosis. At least 4% of the population can feel thyroid nodules larger than one centimeter, and about 5% to 20% of these nodules are cystic. Particularly when individual nodules exceed four centimeters in diameter, thyroid cysts have a 4% to 5% rate of malignancy. Therefore, it is possible for thyroid cysts to grow larger.