Which malignancy develops in long standing goiter is

Enlargement of the thyroid, or goiter is caused by impaired synthesis of thyroid hormone, which is most often the result of dietary iodine deficiency. Impairment of thyroid hormone synthesis leads to a compensatory rise in the serum TSH level, which, in turn, causes hyperophy and hyperplasia of thyroid follicular cells and, ultimately, gross enlargement of the thyroid gland. The compensatory increase in functional mass of the gland overcomes the hormone deficiency, ensuring a euthyroid metabolic state in most individuals. If the underlying disorder is sufficiently severe (e.g., a congenital biosynthetic defect or endemic iodine deficiency, discussed later), the compensatory responses may be inadequate, resulting in goitrous hypothy- roidism. The degree of thyroid enlargement is propoional to the level and duration of thyroid hormone deficiency. Goiters can broadly be divided into two types: diffuse non- toxic and multinodular.