<prompt> Posterior marking on Ba column in Ba swallow study is caused by?Aoic knuckleLeft atriumAberrant right subclan aeryPulmonary aery sling  <response>: C i.e. Aberrant right subclan aery An aberrant right subclan aery arises from the aoic arch distal to the origin of left subclan aery, and passes upwards to the right behind the oesophagus. This gives rise to a classical smooth, oblique indentation on posterior wall of barium filled oesophagusQ. 