What is the main finding on this chest radiograph (AP and lateral)
Large circular density projected lateral and inferior to the aortic arch and superior to the left hilum.
Is the mass pulmonary or mediastinal?
The mass has broad margins with the left side of the mediastinum and aortic arch suggesting that the mass arises from the mediastinum. A parenchymal lesion isn't completely excluded, but for a mass of this size, the lung markings are very prominent. Plus, its not seen on the lateral view.
What is the main differential you would like to exclude - what's the next best test?
The answer to the second question is almost always going to be CT, but protocolling the CT will depend on the answer to the first. The most likely diagnosis here is aortic aneurysm and despite the patient being well, it needs to be further characterised.
Non-contrast and arterial phase imaging were suggested. Why is the non-contrast imaging helpful?
Assessment of calcification and acute haemorrhage (unlikely in this case). Following contrast administration, subtle calcification or haemorrhage can be missed or incorrectly characterised.
When would you not give contrast?
In cases of moderate to severe renal failure, discussion with the clinical team about the risks and benefits of contrast use will be required; if contrast is needed, adequate hydration will be required and if necessary dialysis could be arranged. In this case, the patient had had a previous allergic reaction to contrast and only a non-contrast examination was performed.
Chest x-ray demonstrates a large rounded opacity projecting from the mediastinum laterally on the left. Note is also made of cardiomegaly and calcific atherosclerotic disease of the arch of the aorta.