There are numerous vessels and nerves that course throughout the bony and muscular architecture of the thoracic wall, and they provide innervation and blood supply to the structures within and around the thoracic cage.
First, let’s have a look at the contents of the intercostal space, specifically the neurovascular bundle containing the intercostal nerve, artery and vein.
It is important to remember the order of these structures, with the most superior structure being the intercostal vein and below it comes the artery and below the artery, the nerve.
To easily remember this, think V-A-N or think about a VAN that’s blue at the top, red in the middle and yellow in the inferior part.
The inferior portion of the ribs also have a costal groove which only provides partial protection for these structures, so they can be damaged during penetrating intercostal injuries or any intervention that requires intercostal access
Now, let’s talk about the nerves.
There are 12 pairs of thoracic spinal nerves which supply the thoracic wall.
They leave the intervertebral foramina as soon as they are formed, dividing into anterior and posterior rami.
Now, the anterior rami of nerves T1 through T11 form the intercostal nerves that run along the intercostal spaces along the inferior borders of the ribs, with the third intercostal nerve travelling between the third and fourth ribs.
The anterior ramus of nerve T12 that courses inferior to the 12th rib is the subcostal nerve.
The intercostal nerves give anterior and lateral cutaneous branches to innervate the thorax and abdominal wall, muscular branches to supply the muscles of the thoracic wall, and they give rami communicantes or communicating branches that connect the intercostal nerves to a sympathetic trunk on the same side.
The posterior rami of thoracic spinal nerves pass posteriorly, lateral to the articular processes of the vertebrae in order to supply the joints, deep back muscles and skin of the posterior thoracic region.
Now, the intercostal nerves are either typical or atypical, and the typical ones are the 3rd through the 6th pair.
These nerves enter the medial-most parts of the posterior intercostal spaces.
Initially, they run within the endothoracic fascia just between the parietal pleura and the internal intercostal membrane.
Near the angles of the ribs, these nerves pass between the internal intercostal and the innermost intercostal muscles.
From here, they continue to course in or inferior to the costal grooves, running inferior to the intercostal arteries.
Keep in mind that the arteries run inferior to the intercostal veins.
Near the angles of the ribs, collateral branches arise and run along the superior border of the rib below.
The nerves continue anteriorly between the internal and innermost intercostals and supply these muscles and other muscles and also give rise to lateral cutaneous branches in the midaxillary line.
Anteriorly, the nerves appear on the internal surface of the internal intercostal muscle.
Near the sternum, these nerves turn anteriorly and pass between the costal cartilages to become anterior cutaneous branches.
Atypical intercostals are the first 2 intercostal nerves which run on the internal surface of the 1st and 2nd ribs, not along the inferior margin in the costal groove, and the 7th through 11th nerves which eventually become thoracoabdomial nerves of the anterior abdominal wall.
Most thoracic spinal nerves, specifically T2 through T12, give rise to the dermatomal map of the trunk through their posterior ramus and the lateral and anterior cutaneous branches of its anterior ramus.
This dermatomal map extends from the posterior median line to the anterior median line and it represents the area of skin supplied by the spinal nerves.
Exact dermatomal distributions may vary depending on the source, however they are generally agreed upon with certain dermatomes acting as key landmarks.
For example, dermatome T4 includes the nipple, and T10 includes the umbilicus.
Let’s see if you can identify the typical intercostal nerves in this picture.
Alright, finally, let’s look at the arterial supply to the thoracic wall, which comes from the posterior intercostal and subcostal arteries arising from the thoracic aorta, the internal thoracic, or mammary, artery coming from the subclavian artery, and the supreme, or superior, intercostal artery arising from the costocervical trunk of the subclavian artery, and the superior and lateral thoracic arteries from the axillary artery.
With the exception of intercostal space 10 and 11, each intercostal space is supplied by a large posterior intercostal artery, and a small pair of anterior intercostal arteries.
The posterior intercostal arteries of the 1st and 2nd intercostal spaces arise from the supreme or superior intercostal artery which is a branch of the costocervical trunk of the subclavian artery.
The posterior intercostal arteries of the 3rd through the 11th intercostal spaces arise posteriorly from the thoracic aorta.
All posterior intercostal arteries give rise to a dorsal branch that accompanies the posterior ramus of the spinal nerve to supply the spinal cord, vertebral column, back muscles and skin.
They also give rise to a small collateral branch that crosses the intercostal space and runs along the superior border of the rib below.
The posterior intercostal arteries accompany the intercostal nerves through the intercostal spaces.
Close to the angle of the rib, the arteries enter the costal grooves, where they lie between the intercostal vein and nerve.