대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Intrathoracic Goiter

Radiologic Findings

Chest radiographs show a large left anterior mediastinal mass with displacement of the trachea to the right side.
Precontrast CT scan shows a well-defined, homogeneous, and iso-attenuation mass just left lateral to the trachea.
Contrast-enhanced CT scans demonstrate moderately enhancing mass, which is continuous with the lower pole of left thyroid gland.
Left innominate vein is swept downward by the mediastinal mass.

Brief Review

Goiters in the superior mediastinum arise from one or both lower poles of the thyroid gland or from the isthmus. With growth of the goiter, aided by deglutition, gravity, and negative intrathoracic pressure, the goiter enters the thorax, generally taking its cervical blood supply with it.

Intrathoracic goiters can be classified primary and secondary. The presence of vascular stalks with cervical thyroid gland makes intrathoracic goiter secondary, while absence of them makes it primary (or ectopic). Primary intrathoracic goiters are very rare, with a reported incidence of 0.2 to 1 per cent of all goiters.


Although clear continuity between the cervical and intrathoracic components should be present in cases of mediastinal goiter extension, the connection may only be a narrow fibrous or vascular pedicle. In such cases, as well as in the presence of a primary intrathoracic goiter, lack of continuity between the cervical gland and the thoracic mass does not exclude goiter as the diagnosis.


Pathologically the nontoxic nodular goiter has distended follicles with colloid and hyperplasia of the thyroid tissue. The follicles can rupture with resultant inflammatory changes, and ultimate degeneration can occur with hemorrhage, infarction, fibrosis, cyst formation, and calcification.

Normal thyroid tissue has higher attenuation values than soft tissue because of its high iodine content and shows intense postcontrast enhancement. The high attenuation of an intrathoracic goiter may depend on the density of iodine per unit volume and the extent of degeneration.

The typical CT features of intrathoracic goiter can be summarized as follows:
1. continuity with the cervical thyroid gland,
2. well-defined borders,
3. punctate, coarse, or ringlike calcifications,
4. nonhomogeneity often with minimal or nonenhancing, well defined, low-density areas,
5. precontrast attenuation values often at least 15 H greater than adjacent musculature with at least 25 H enhancement after intravenous contrast,
6. patterns of extension of the goiter into the mediastinum with cradling of the goiter by the right and left bracheocephalic vessels high in the mediastinum and extension behind the great vessels to the paratracheal or retrotracheal region.

References

1. Bashist B, Ellis K, Gold RP. Computed tomography of intrathoracic goiters. AJR 1983;140:455-460
2. Lee KS, Im J-G, Han MC. Computed tomographic findings of a primary intrathoracic goiter. J Korean Radiol Society 1984;20:525-527

Keywords

Mediastinum, Benign tumor,