Enlargement of the thyroid gland, visible as a swelling on the neck. The thyroid gland may enlarge (without any disturbance of its function) at puberty, during pregnancy, or as a result of taking oral contraceptives. In many parts of the world the main cause of a goitre is lack of iodine in the diet. A condition called toxic goitre develops in Graves’ disease and in other forms of hyperthyroidism that lead to thyrotoxicosis. A goitre is also a feature of different types of thyroiditis. Other causes include a tumour or nodule in the gland and, in rare cases, thyroid cancer. A goitre can range in size from a barely noticeable lump to a large swelling, depending on the cause. Large swellings may press on the oesophagus or trachea, making swallowing or breathing difficult. A goitre not caused by disease may eventually disappear. Goitre due to iodine deficiency can be treated by dietary measures. When a goitre is the result of disease, treatment is for the underlying disorder. Large goitres can be treated surgically (see thyroidectomy).