Which chest X-ray feature is indicative of aortic dissection?

A widened mediastinal knob on a chest X-ray is indeed indicative of aortic dissection. In the event of an aortic dissection, the aorta behaves differently than under normal circumstances; it may split or tear, leading to significant hemorrhage that can accumulate in the mediastinum. This condition typically presents as a widening of the mediastinum on an X-ray due to the presence of blood or fluid in the area surrounding the aorta.

The mediastinal knob, which represents the contour of the aorta as it curves over the left main bronchus, becomes exaggerated in size as the dissection progresses and the aorta expands. Therefore, observing a widened mediastinal knob can be a critical clue in diagnosing aortic dissection, guiding urgent intervention.

Other features of aortic dissection may not be as prominent on a chest X-ray or can be associated with alternative conditions, making the identification of a widened mediastinal knob a strong indicator for this life-threatening pathology.