On barium swallow which of the following will cause posterior impression -
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
Left atrium
Aortic knuckle
Pulmonary sling
Aberrant right subclavian artery