At what thoracic level does the aortic arch transition to the descending aorta?

At what thoracic level does the aortic arch transition to the descending aorta?

• A. T2/T3
• B. T6/T7
• C. T9/T10
• D. T4/T5

Answer: (A)

The boundary between the aortic arch and the descending thoracic aorta is at the sternal angle (angle of Louis), which corresponds roughly to the T4–T5 vertebral level. At this level the arch ends and the descending thoracic aorta begins in the posterior mediastinum, continuing down to the diaphragm via the aortic hiatus at T12. This landmark—the sternal angle—is the reliable surface/bony marker used to pinpoint where the arch transitions to the descending aorta. Levels higher or lower than this don’t mark that boundary.

The boundary between the aortic arch and the descending thoracic aorta is at the sternal angle (angle of Louis), which corresponds roughly to the T4–T5 vertebral level. At this level the arch ends and the descending thoracic aorta begins in the posterior mediastinum, continuing down to the diaphragm via the aortic hiatus at T12. This landmark—the sternal angle—is the reliable surface/bony marker used to pinpoint where the arch transitions to the descending aorta. Levels higher or lower than this don’t mark that boundary.