Substernal goitre (or retrosternal goitre) is an enlarged thyroid gland with intrathoracic extension.
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Terminology
It remains unclear which goitres are to be termed substernal, but a recently proposed definition is a goitre that requires mediastinal exploration and dissection for complete removal or an intrathoracic component extending >3 cm in the thoracic inlet 1.
Radiographic features
Plain radiograph
Chest x-ray may show a superior mediastinal radiopacity causing the deviation of trachea to the opposite side. The superior margin of the radiopacity/mass is untraceable (cervicothoracic sign).
Ultrasound
On ultrasound, the inability to scan the inferior most of the thyroid due to its extension posterior to the sternum makes substernal thyroid likely.
CT
According to one study, the most important CT features in determining the necessity of sternotomy for goitre excision are the presence of an ectopic goitre, total thyroid gland volume and goitre extension below the tracheal carina 3.
Treatment and prognosis
Most anterior substernal thyroid goitres are accessed via a transcervical approach. For goitres that cannot be removed via neck dissection, such as those with complicated anatomic extensions or posterior mediastinal involvement, the surgeon may need to incorporate a partial upper sternotomy and clavicular head resection or mini-thoracotomy for adequate exposure.
A surgeon with an understanding of the radiologic reporting of a substernal goitre on a dedicated chest CT might perform a sternotomy instead of a simple low-collar incision for resection of substernal goitre.
Some suggested imaging features may indicate requirement for a thoracic approach with a sternotomy include 8
- extension of the goitre below the aortic arch
- extension into the posterior mediastinum
- a dumbbell shape
- thoracic component that is wider than the thoracic inlet
Practical points
A potential pitfall in the assessment of retrosternal extension is the apparent lower position temporarily assumed by the gland when the arms are raised in the case of imaging aimed at the chest. This can be avoided by having the patient's arms by their side when imaging for retrosternal extension 2.