Correct!
3. The mediastinum
The left mediastinum is the most likely source of the contour abnormality detected at chest radiography. In general, when a smoothly contoured soft tissue lesion shows extensive contact with the mediastinum, with no lung visible between the medial margin of the lesion and the mediastinum itself, and the center of a circle extrapolated from the lesion’s margins triangulates within the mediastinum, a mediastinal origin should be suspected. It is technically possible that the lesion at chest radiography arises from the medial left superior pleura, but a mediastinal location is more likely. The thoracic aorta shows a normal contour and appears normal in caliber. While the contour abnormality along the left superior mediastinum appears to be in close proximity to the aortic arch, the aortic arch itself can be seen “through” the abnormality and therefore is probably unrelated to that abnormality. The contour abnormality does not contact the heart and therefore does not arise from this structure. The esophagus is an unlikely origin for the lesion. Often gas or an air-fluid level will be evident if the cause of a contour abnormality at chest radiography is due to a dilated esophagus, but no gas or air-fluid level is present in this circumstance. An esophageal mass of this size, in this location, while technically possible, would be very unlikely.
The frontal chest radiograph (Figure 1) shows which chest radiographic sign? (Click on the correct answer to proceed to the fourth of nine pages)