This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Arterial Disorders, Subject name: Surgery
Most reliable sign of injury to intrathoracic aorta is - 
Select and explain. 
A. Presence of apical cap of pleural fluid, B. Depression of left main stem bronchous, C. Obliteration of aortic knob contour, D. Funny looking mediastenum
C: Obliteration of aortic knob contour
Answer: C: Obliteration of aortic knob contour 
Explanation: Ans. is 'c' i.e., Obliteration of aortic knob contour * Several findings on the chest X ray are associated with the blunt injury to the intrathoracic great vessels.* The most reliable of these signs for the blunt aortic injury is loss of the aortic knob contour.Finding on Chest X-Ray Associated with Blunt Aortic InjuryPresence of widened mediastinum (> 8 cm at the aortic knob in adults)Deviation of the trachea, nasogastric tube, or endotracheal tube to the rightPresence of an apical cap of pleural fluidDepression of the left mainstem brochus > 140deg from trachea Obliteration of aortic knob contour"Funny" looking mediastinum