Substernal goiter (SG) is an intrathoracic extension of cervical thyroid tissue. There is no consensus about the definition of substernal goiter, but most of the authors consider intrathoracic, substernal, or mediastinal goiter as any thyroid mass in which 50% of the mass is located below the thoracic inlet. A primary SG goiter is rare.
The reported incidence of SG ranges from 2% to more than 20%. Most of the SGs are located in the anterior mediastinum. Posterior mediastinal goiters account of 10–15% of all SGs. Nearly all posterior SGs occur on the right side since the great vessels prevent the thyroid mass from descending on the left side.
SGs are of clinical significance because of their tendency to progressively enlarge into the mediastinum, with compression of adjacent organs: the trachea, the oesophagus, and the superior vena cava. SG can also produce symptoms of thyrotoxicosis; although the majority of SGs are benign, malignancy occurs in 2–15% of cases. Although in the majority of patients can be treated successfully with minimal morbidity and mortality, in some patients there is an increased operative risk. Surgeons should perform a careful preoperative evaluation to identify such patients and to plan the best surgical approach.
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