Benign Thyroid Enlargement
A Goiter is an enlargement of the thyroid gland. The gland can be generally enlarged or have multiple growths (nodules) leading to enlargement of the whole thyroid gland. The latter is termed multinodular goiter (MNG). There are two forms of multinodular goiter: 1) nontoxic MNG and 2) toxic MNG. If the goiter makes normal amounts of thyroid hormone, it is known as a nontoxic MNG. If the goiter makes higher than normal amounts of thyroid hormone leading to a suppressed TSH, it is known as a toxic MNG. (See Hyperthyroidism) The exact causes of thyroid nodules or multinodular goiters are unknown. In general, the development of goiter is due to a complex mix of genetic and environmental factors. Iodine deficiency as a cause of goiter is rare in North America and most of Europe. However, even in areas of iodine deficiency most patients do not develop goiters.
Symptoms of nontoxic MNG may be nonexistent. If the goiter is very slow growing and long-standing, the patient may not notice the slow increase in size. However, some patients may complain of a feeling of fullness in the neck, pressure in their neck when lying flat, a choking sensation, difficulty swallowing large pills or certain foods, or difficulty wearing necklaces. .
A multinodular goiter is often first found on routine physical examination or when the patient seeks medical attention for a neck mass or increased size of the neck. As with all thyroid conditions, initial evaluation includes a detailed history, specifically focusing on hypo – or hyperthyroid symptoms, family history of thyroid disease, history of head and neck irradiation, and factors suggestive of malignancy. These factors include any rapid growth of the neck mass, presence of associated enlarged neck lymph nodes, or new-onset hoarseness. Physical examination of a MNG is used to determine the size of goiter, the possible extension of the large thyroid under the breastbone (i.e. substernal extension), and signs of hyperthyoridism (rapid heart rate, irregular heart beats, tremors, etc). Most patients have normal thyroid function with nontoxic MNG. Therefore laboratory examination is typically limited to TSH and free T4 levels.
Thyroid ultrasound is an important part of evaluating a MNG. It is the best imaging for assessing the size of the goiter more accurately, as well as the size and characteristics of nodules within the goiter. Ultrasound has no radiation exposure and, is therefore, completely safe. Ultrasound can also help guide fine needle aspiration (FNA) biopsy of nodules. Nodules that would be considered for FNA biopsy include those over 1 cm in size or nodules that have certain characteristics that are worrisome for malignancy . These characteristics may include irregular borders, internal tiny calcium deposits (i.e. calcifications), or increased blood flow. Ultrasound and FNA biopsies should be performed by experienced personnel. Once the ultrasound confirms an enlarged thyroid gland, a subset of patients may benefit from a noncontrast CT scan of the neck to evaluate for substernal extension and helps the surgeon appropriately assess the extent of the surgery that may be required.
The natural history of benign goiter is usually slow growth of the nodules. Therefore, observation can be safe if growth has stopped and the thyroid is not causing any compression of nearby structures and is not causign any compressive symptoms (difficulty swallowing, trouble breathing, etc.). MNG is treated if there is a suspicion of the nodules harboring cancer, the goiter is growing quickly, or if the goiter’s large size is causing compressive symptoms, such as hoarseness, difficulty swallowing, or difficulty breathing. While thought to be helpful in the past, use of thyroid hormone to attempt to “suppress” and shrink MNG is no longer recommended (see ATA guidelines) and puts patients at risk for hyperthyroidism.
Surgery for MNG is indicated when FNA of a dominant nodule is indeterminate or suspicious for malignancy, the goiter is growing, or there are compressive symptoms due to the size of the goiter. The extent of surgery is based on the suspicion for malignancy, presence of thyroid dysfunction, and presence of bilateral nodules. In patients who have normal thyroid function, with compressive symptoms due to a single nodule, with a benign biopsy, and no nodules on the opposite side, unilateral thyroid lobectomy is appropriate. Otherwise total thyroidectomy is the operation of choice. For significantly enlarged thyroid glands, the recurrent laryngeal nerve may be displaced from its usual position and extra care must be taken at the time of surgery to ensure preservation of the parathyroid glands (which may need to be re-implanted into the sternocleidomastoid muscle) and recurrent laryngeal nerves.
RAI ablation may be an option in the treatment of MNG. It is usually reserved for patients who are not able to have an operation because of other medical problems which would make surgery too risky.