Instead of being the first branch (with the right common carotid as the brachiocephalic artery), aberrant right subclavian artery (ARSA) arises on its own as the fourth branch, after the left subclavian artery. It then hooks back to reach the right side. Aberrant right subclavian arteries relationship to the esophagus is variable:

• 80 % posterior to esophagus
• 15 % between esophagus and trachea
• 5 % anterior to the trachea