Substernal Thyroid Goiter

• Extension of a thyroid goiter arising in the neck inferiorly into the thorax is relatively uncommon

• Most (75-80%) arise from lower pole or isthmus of the thyroid and extend into anterior mediastinum

• Some arise from posterior aspect of the thyroid and extend into posterior mediastinum, almost always on the right

• Usually nodular, colloid goiters

            •Thyrotoxicosis and carcinoma are rare

• Thyroid mass is typically well-encapsulated and may show degeneration (calcification)

• Most patients are asymptomatic

Imaging

• Sharply defined, smooth or lobulated soft tissue mass which characteristically displaces the trachea

• They do not usually project below the arch of the aorta differentiating them from thymomas and teratomas

• Those in the posterior mediastinum characteristically interpose between the trachea in front and the esophagus in back

• On CT, they usually contrast enhance and many times are found to contain calcification.

• Contrast enhancement is usually prolonged.

• Curvilinear calcifications are highly suggestive of a degenerated thyroid adenoma

• Radioisotope scan is diagnostic

Substernal Thyroid Goiter. Contrast-enhanced CT of the chest shows a large, contrast-enhancing
mass in the anterior mediastinum containing calcifications and areas of necrosis.
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Substernal Thyroid Goiter. Contrast-enhanced CT of the chest shows a large, contrast-enhancing
mass in the anterior mediastinum (red arrows) displacing the trachea (White arrow) to the right.

Substernal Thyroid Goiter. Frontal chest radiograph shows a large superior/anterior mediastinal mass (white arrows) displacing the trachea (black arrow) to the right of midline.