Aortic arch in MRA and its Variations

The aortic arch is the direct continuation of the ascending aorta. Its origin is defined as sternomanubrial joint. It terminates at the lower border of T4, when it becomes the descending aorta.

Branches :

Three main branches typically originate from the upward convexity of the arch. In order from proximal to distal these are:

1- (right) brachiocephalic artery (or innominate artery) which goes on to divided into the right subclavian and right common carotid arteries.
2- left common carotid artery
3- left subclavian artery

Variations
There are three common variations to the branching pattern:

1. normal (as described above) that seen in ~ 70% of patients.
2. bovine arch : common origin of brachiocephalic and left common carotid artery - seen in approximately 15% of patients (more common in blacks)

3. left common carotid has its origin from the brachiocephalic artery proper, rather than from a common trunk : seen in approximately 10% of patients (also more common in blacks)

 Left ICA coming off the right brachiocephalic.

Additionally there may be additional branches that arise directly from the arch. These include

* thyroidea ima artery, usually between the brachiocephalic and left common carotid
* left vertebral artery, usually between the left common carotid and the left subclavian arteries.
* rarely the right subclavian and right common carotid arise independently.