Substernal Goiter: From Definitions to Treatment.

The enlargement of multinodular goiter into the mediastinum through the thoracic inlet or ectopic thyroid tissues directly in the mediastinum is defined as Substernal Goiter (SG). However, there is no clear consensus in the literature on this definition. There are many definitions for SG in the literature. Most definitions are similar or overlapping. Since the thyroid is located in the neck above the thoracic inlet in its normal anatomical position, the simplest clinical definition should be preferred among the definitions regarding its descent below the thoracic inlet and adjacent to the mediastinal organs. In the American Thyroid Association guideline, SG is defined as clinical or radiological protrusion of the thyroid gland over the sternal notch or clavicle in a patient with a slightly extended neck in the supine position. SGs can be classified as primary or secondary according to their origins. In addition, there are combined SGs resulting from the enlargement of the primary SG, which is the growth of the cervical thyroid gland toward the mediastinum, and the secondary SG, which is defined as an ectopic mediastinal mass, together. We find it appropriate to define such SGs as mixed SGs. In this disease, which has the same etiology and etiopathogenesis as cervical goiter, the descent of the thyroid gland into the mediastinum due to some anatomical factors explains the physiopathology. Compression symptoms of mediastinal major vascular structures, trachea, and esophagus cause the symptoms and findings of SGs due to its localization. In addition, the relationship of SGs with possible malignancy risk and hyperthyroidism affecting the indications and methods of treatment has been discussed for a long time. In this study, we aimed to evaluate the definitions, classification, physiopathology, laboratory and imaging methods used for diagnosis, the relationship of SG with hyperthyroidism and malignancy, and briefly the treatment methods, according to the current studies from literature.