Posterior intercostal arteries !

The posterior intercostal arteries leave the thoracic aorta and run along the ribs; they feed the ribs, thoracic vertebrae and back muscles.

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What it is

Small arteries from the thoracic aorta running along the ribs and into the thoracic spine.

What it does

Feed the ribs, thoracic vertebrae, back muscles and, through some branches, the spinal cord.

Key facts

Origin: 1st–2nd: supreme intercostal artery (costocervical trunk); 3rd–11th: thoracic aorta
Branches: Dorsal branch (spinal branch into the canal, back muscles, skin); collateral and lateral cutaneous branches; mammary branches from the 2nd–4th spaces to the lateral breast; anastomose with anterior intercostals
Supplies: Intercostal spaces, ribs, thoracic vertebrae, back muscles; thoracic cord via segmental medullary arteries

Relations

Course: From the back of the thoracic aorta each runs out across the vertebral body (the right ones behind the oesophagus, thoracic duct and azygos vein), behind the sympathetic trunk, into the intercostal space; near the rib angle it enters the costal groove and runs forward to meet the anterior intercostal arteries
Above: Posterior intercostal vein, in the costal groove of the rib above
Below: Intercostal nerve, lowest in the groove and least protected
Deep: Parietal pleura and lung, with only the innermost intercostal muscle and fascia between them
Superficial: External and internal intercostal muscles; near the spine, the deep back muscles

How to find it

They cannot be felt. Near the spine the artery runs across the middle of the space and is tortuous; only beyond the rib angle does it settle into the costal groove. A collateral branch runs along the upper border of the rib below.

On imaging

Not seen on plain films, but the chest radiograph shows the classic sign of aortic coarctation: notching of the lower rib borders by enlarged collaterals, sparing the first two ribs. CT angiography shows them leaving the back of the aorta and, in a haemothorax after a chest drain or rib fracture, an active contrast leak. Doppler ultrasound can find the artery before a puncture.

Clinical notes

Injury during chest drain insertion, thoracentesis or rib fracture causes haemothorax; procedures close to the spine, where the artery lies mid-space, carry more risk
Rib spreading in thoracotomy can injure the main and collateral neurovascular bundles, one cause of bleeding and of pain after the operation

Anatomical variants

The supreme intercostal artery for the first two spaces usually comes from the costocervical trunk, sometimes from the thyrocervical trunk

Development

Like the lumbar arteries, they come from the segmental branches of the dorsal aorta, one pair per segment; the first two spaces are supplied from the subclavian side through the costocervical trunk instead.

Memory aid

Top to bottom in the costal groove: "VAN" (Vein, Artery, Nerve).

Test yourself

Think of the answer, then tap the question to see it.

What is the order of structures in the costal groove from above down, and how does it guide a chest drain?

Vein, artery, nerve (VAN); needles and chest drains pass just above the upper border of a rib to avoid the bundle.

What rib sign do enlarged posterior intercostal arteries produce in coarctation of the aorta?

Notching of the lower rib borders, sparing the first two ribs, because the arteries carry collateral flow around the narrowing.

Where do the first two posterior intercostal arteries come from, unlike the 3rd to 11th?

From the supreme intercostal artery (usually of the costocervical trunk); the 3rd to 11th come straight from the thoracic aorta.

Why do procedures close to the spine carry more risk to the posterior intercostal arteries?

Near the spine the artery runs across the middle of the intercostal space and is tortuous; it only settles into the costal groove beyond the rib angle.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): arteriae intercostales posteriores; arteria subcostalis TA2 4191
Official Spanish (DeCS): Arterias intercostales posteriores
English (TA2): Posterior intercostal arteries
Also called: arteriae intercostales

Sources: Terminologia Anatomica (TA2); Anatomy, Thorax, Superior Intercostal Arteries; Anatomy, Thoracotomy and the Collateral Intercostal Neurovascular Bundle; Anatomy of the Human Body (20th ed.): Development of the Vascular System (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.

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Representative model, for educational purposes only.

Posterior intercostal arteries highlighted on the Durgical 3D model