This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
On barium swallow which of the following will cause posterior impression - 
Select and explain. 
A. Left atrium, B. Aortic knuckle, C. Pulmonary sling, D. Aberrant right subclavian artery
D: Aberrant right subclavian artery
Answer: D: Aberrant right subclavian artery 
Explanation: Aberrant right subclavian artery arises from aortic arch just distal to the left subclavian artery. It travels behind the esophagus and after crossing the esophagus (from left to right) it courses as the right subclavian artery. Aberrant right subclavian artery produces the classical appearance of a posterior impression on the proximal esophagus and left sided aortic arch impression (as it arises from left side of aortic arch) on barium swallow.
Plain Radiograph with barium swallow

Aberrant right subclavian artery :-   
	i) Left sided aortic arch impression 
	ii) Posterior impression on esophagus
Aberrant left subclavian artery :-     
	i) Right sided aortic arch impression
	ii) Posterior impression on esophagus
	iii) Anterior displacement of esophagus
	iv) Compression of trachea