There are three conditions like, hypothyroidism or under active thyroids, hyperthyroidism or overactive thyroids and prominent thyroids. Now let me explain your brother's case. Your brother has hypothyroidism or under active thyroids. Thyroid gland produce a hormone under the influence of TSH which is secreted by pituitary gland. This pituitary gland secretes TSH under the influence of TSH-RH from the hypothalamus which is a part of brain. In hypothyroidism, this gland is unable to produce his hormone. Defect can be in thyroid gland, pituitary gland or in hypothalamus. If the defect is in the thyroid gland and when unable to produce thyroid hormone, the levels of TSH increase in blood. These increased levels stimulate the cells of thyroid gland causing increase in size of the thyroid gland making it a "prominent thyroid" leading to goiter. These are usually non cancerous. For more details, visit hypothyroidism.