In anatomy, a<unk>  is the most common variation of the thoracic venous system. It is present in between 0.3% and 0.5% of the population, and is an embryologic remnant that results from a failure to involute.
Persistent left superior vena cava
Tracheal agenesis
Right-sided aortic arch
Congenital stenosis of vena cava
Aberrant subclavian artery
Persistent thyroglossal duct
Interrupted aortic arch
Overriding aorta