Arch of Aorta — Extent, Course and Position
Overview
The arch of aorta is the second part of the aorta. It is the curved continuation of the ascending aorta and continues as the descending thoracic aorta. It lies entirely within the superior mediastinum.
Extent
| Boundary | Level | Surface Marking |
|---|---|---|
| Begins | Behind the upper border of the 2nd right costal cartilage at the right half of the sternal angle | Anteriorly, at the sternal angle (angle of Louis) |
| Ends | On the left side of the lower border of T4 vertebra (lower border of T4 / T4–T5 intervertebral disc) | Posteriorly, at the same horizontal level as the sternal angle |
Key fact: The arch begins anteriorly and ends posteriorly — but both points are at the same horizontal level (level of the sternal angle / T4–T5 disc). It begins and ends at the sternal angle.
Course
From its origin, the arch:
- Passes upwards, backwards, and to the left — arching over the left lung root
- Curves over the root of the left lung (arching superior to the left principal bronchus and left pulmonary artery)
- Passes in front of the bifurcation of the trachea
- Descends on the left side of the vertebral column to end as the descending aorta at T4
Position
- Situated in the superior mediastinum, posterior to the lower half of the manubrium sterni
- The summit (highest point) of the arch reaches the level of the middle of the manubrium sterni — approximately 2.5 cm below the suprasternal notch
- The arch lies oblique: its anterior end (origin) is to the right; its posterior end (termination) is to the left
Summary
| Feature | Detail |
|---|---|
| Location | Superior mediastinum |
| Begins | Behind upper border of 2nd right costal cartilage (right half of sternal angle) |
| Ends | Left side of lower border of T4 vertebra (posterior, same horizontal level) |
| Summit | Middle of manubrium sterni (~T3 level) |
| Arches over | Root of left lung |
| Number of branches | 3 (from its convex/superior surface) |