The initial chest x-ray demonstrates a right paramediastinal opacity confluent with and widening the right paratracheal stripe. Compare this case to case 75. In that case the right paramediastinal mass opacity did not efface and widen the right paratracheal stripe and so was not anatomically right paratracheal. The current case chest radiographic appearances suggest that the findings are due to a mass lesion adjacent to the right margin of the trachea.
Is the rest of the chest x-ray normal? Well actually no it is not. Look at the more superior trachea. It is displaced to the right, suggesting a more superior cervical. The most common cause for this would be a thyroid goitre. Could this be causing both the left and right paratracheal abnormalities?
Now let us review the CT imaging. We can see that there is enlargement of the left lobe of the thyroid and that accounts for the displacement of the trachea to the right. As suggested on the chest x-ray there is indeed a right paratracheal abnormality and this is confirmed on the coronal reconstructions explaining why the chest radiograph right paratracheal stripe is widened.
In viewing the characteristics of the right paratracheal tissue it is clear that this has a very similar consistency to the left paratracheal thyroidal tissue, containing heterogenous low attenuation areas as well as a focal calcification. However, axial and coronal images demonstrate that there is no connection between the inferior margin of the right thyroid and the right paratracheal mass.
What is the differential for these appearances? Well we can consider causes of anterior mediastinal masses. However, the appearances are too heterogenous for a diagnosis of lymphoma. Too lateral for a diagnosis of thymoma or a teratoma. In this location we should also consider a focal enlarged node, due to metastatic disease or perhaps due to granulomatous aetiology. However, no other nodes were present elsewhere. Other rarer lesions to consider would include ectopic parathyroid lesions or paraganglioma lesions, although both these are more typically hyperenhancing.
So what does this leave is with? Well the lesion looks exactly like a thyroid goitre even though it is not connected to the right lobe. Well if it looks like a duck and quacks like a duck the saying is it usually is a duck! My thought was that this was ectopic thyroid with a goitre. The lesion processed to biopsy by endobronchial ultrasound for confirmation revealing typical colloid material suggestive of a thyroid goitre. The biopsy confirms a benign goitre in ectopic mediastinal thyroid tissue.
Ectopic thyroid tissue is not uncommon, occurring during in the embryonal migration of thyroid tissue from the base of the foramen caecum to the typical pretracheal region. However inferior mediastinal ectopy is far more uncommon, likely less than 1% of ectopic cases, although the right paratracheal location has been reported. This should be differentiated from a multinodular thyroid gland with a small atretic band from the right lobe to the right paratracheal mass. Typical thyroid goitres extending from the neck descend in the right paratracheal or left paratracheal location. It is usually only the rarer isthmic lesions that extend anteriorly into the anterior mediastinum as the list books suggest.
This case was primarily included as a companion training exercise for case 75 to evaluate the right paratracheal region on chest radiographs. Compare these chest radiographs, the corresponding coronal CTs, to improve your interpretation of the right paratracheal region.