Findings: PA chest shows a well-defined left upper mediastinal mass. The mass is in the middle mediastinum and it is pressing against the trachea (arrows).

It also extends into the posterior mediastinum as it reaches the top of the left apex.
The Lateral view is non-contributory.

A vascular origin for the mass would be a good guess, but there is another possibility: mediastinal fat, which is common, can appear anywhere, and can have a strange appearance.

Diagnosis is confirmed with CT, which shows that the findings in the plain film are due to mediastinal fat extending into the neck.

Final diagnosis: Mediastinal fat

Congratulations to Gus, who gave the correct diagnosis

Teaching point: Vascular lesions and fat may simulate other mediastinal masses. For this reason, all masses should be studied with enhanced CT.