A thrombus in the first branch of the arch of the aorta would affect blood flow to which region?

• A. Left side of head and neck
• B. Right side of head and neck and right upper arm
• C. Left upper limb
• D. Entire brain

Answer: (B)

A thrombus in the first branch of the arch of the aorta affects the vessels that originate from that branch. The first branch is the brachiocephalic trunk, which splits into the right common carotid artery and the right subclavian artery. The right common carotid supplies the right side of the head and neck, while the right subclavian supplies the right upper limb. So a blockage here would reduce blood flow to the right side of the head and neck and to the right arm. The left side of the head/neck and left upper limb would still receive blood from the left-sided branches, and the entire brain is unlikely to be affected as a whole by occlusion of this single trunk, given collateral circulation.