Relations of the Arch of Aorta

The arch of aorta has five important relations on each of its four aspects. This is a high-yield pattern for examination.

Anterior and to the Left (Left Surface)

Five structures cross or lie on the left surface of the arch from anterior to posterior:

Order	Structure	Notes
1	Left phrenic nerve	Crosses the arch anteriorly, descending to the diaphragm
2	Inferior cervical cardiac branch of the left vagus (left cardiac nerve)	Descends to join the superficial cardiac plexus
3	Superior cervical cardiac branch of the left sympathetic trunk	Descends to join the superficial cardiac plexus
4	Left vagus nerve	Crosses the left surface; gives off the left recurrent laryngeal nerve at the inferior border of the arch
5	Left superior intercostal vein	Drains the 2nd and 3rd intercostal spaces; crosses the arch deep to the phrenic nerve and superficial to the vagus nerve

Also on the left: Left lung and pleura (most superficial), and remains of the thymus (anteriorly).

Memory aid: The left superior intercostal vein lies deep to the phrenic nerve and superficial to the vagus nerve — between them.

Superior (Convex Surface — Three Branches)

Five structures related superiorly from right to left:

Order (Right → Left)	Structure
1	Brachiocephalic trunk (largest branch)
2	Left common carotid artery
3	Left subclavian artery
4	Left brachiocephalic vein (crosses in front of all three branches)
5	Thymus (or its remnant)

The left brachiocephalic vein passes anteriorly across all three branches of the arch.

Posterior and to the Right (Right Surface / Concavity)

Five structures in the concavity of the arch (inferior and to the right):

Structure	Notes
Trachea	Lies to the right of the arch; the arch indents the left surface of the trachea
Oesophagus	Posterior to trachea; the arch crosses in front
Left recurrent laryngeal nerve	Hooks under the arch at the inferior border (posterior to the ligamentum arteriosum) and ascends in the left tracheo-oesophageal groove
Thoracic duct	Runs posterior and to the right of the oesophagus in this region
Vertebral column	T3–T4

Note: The deep cardiac plexus lies on the tracheal bifurcation — posterior to the arch.

Inferior (Concavity)

Five structures related to the concave (inferior) surface of the arch — the root of the left lung:

Structure	Notes
Left principal bronchus	Immediately below the arch
Bifurcation of the pulmonary trunk	Below and slightly anterior; the arch arches over it
Left pulmonary artery	Passes below the posterior part of the arch to the left lung root
Ligamentum arteriosum	Connects the arch to the root of the left pulmonary artery
Left recurrent laryngeal nerve	Curves under the arch at the level of the ligamentum arteriosum
Superficial cardiac plexus	Lies on the ligamentum arteriosum, in the concavity of the arch

Cross-Section Summary (at T4 Level)

           SUPERIOR
    Brachiocephalic trunk
    Left CCA, Left subclavian
    Left brachiocephalic vein
           |
LEFT       |      RIGHT
Phrenic  ARCH   Trachea
Vagus     |     Oesophagus
LSupICV   |     Left RLN
           |     Thoracic duct
           |     Vertebral column
         INFERIOR
    L. bronchus, Pulm. trunk bifurcation
    Lig. arteriosum, Superficial cardiac plexus