Localized neck swelling may occur in response to various pathologies. Most often, however, a swollen neck is a symptom of goiter which corresponds to an increase in volume of the thyroid gland in the lower neck. Some diseases affecting the thyroid, such as Graves' disease or certain thyroidites are responsible for goiter and give the neck a swollen appearance. An iodine deficiency is also a cause leading to a gradual increase in the size of the thyroid. An ultrasound may be performed to identify the cause of the swelling. When the neck is swollen locally and only on one side, it can also be a symptom of lymphadenopathy, a swelling of lymph nodes, most commonly in response to an infection.