Second posterior intercostal artery

The second posterior intercostal artery is a paired vessel that supplies the second intercostal space and its associated structures. Unlike the 3rd through 11th posterior intercostal arteries, which arise directly from the descending thoracic aorta, the second posterior intercostal artery has a distinct origin from the costocervical trunk via the supreme (superior) intercostal artery, a branch of the subclavian artery.

Origin and embryology

The costocervical trunk arises from the posterior aspect of the subclavian artery and divides into the deep cervical artery and the supreme intercostal artery. The supreme intercostal artery descends anterior to the necks of the first and second ribs and gives off the first and second posterior intercostal arteries, which supply the first and second intercostal spaces, respectively. From an embryological standpoint, the costocervical trunk provides the first and second posterior intercostal arteries (corresponding to the 8th and 9th intersegmental arteries), and the supreme intercostal artery also incorporates the last cervical intersegmental artery (C7).

Course and branches

Once the second posterior intercostal artery enters the second intercostal space, it courses along the inferior border (costal groove) of the second rib, running between the internal intercostal and innermost intercostal muscles. Like other posterior intercostal arteries, it gives off:

• A dorsal branch, which passes posteriorly to supply the paraspinal muscles, vertebral column, and overlying skin via cutaneous perforators.

• A spinal branch (from the dorsal branch), which enters the intervertebral foramen to supply the spinal cord, meninges, and vertebral body.

• A lateral cutaneous branch, which pierces the intercostal muscles to supply the lateral thoracic wall.

• Collateral branches that run along the superior border of the rib below.

The posterior intercostal artery is divided into four segments based on its neurovascular branching pattern: vertebral, costal, intermuscular, and rectus segments. Dorsal branches arise from the vertebral segment, while musculocutaneous perforators and a lateral branch originate from the costal segment.

Territories of supply

The second posterior intercostal artery supplies the intercostal muscles, parietal pleura, overlying skin, and vertebral structures at the T2 level. The dorsal branches contribute to the blood supply of the paraspinal muscles and the posterior thoracic skin. The superior and posterior intercostal arteries consistently supply the spinal muscles in the thoracic region, and small anastomotic vessels posterior to the laminae connect the intercostal artery perforators.

Anatomical variations

The costocervical trunk is absent in approximately 24% of cases, in which case the supreme intercostal artery and its branches (including the second posterior intercostal artery) may arise directly from the subclavian artery or from other variant configurations. A classification of costocervical trunk branching patterns has identified four types, with the most prevalent (Type 1, ~76%) matching the classical textbook description. In rare cases, the supreme intercostal artery may arise from the vertebral artery and course in a thoracic vertebral artery configuration, descending posterior to the necks of the upper ribs.

Clinical significance

Recognition of the anatomy and variations of the second posterior intercostal artery is important in vascular and thoracic surgery, spinal angiography, and interventional radiology. The intercostal artery is exposed within the intercostal space in the first 6 cm lateral to the spine, with greater positional variability in older patients and more cephalad rib spaces, which is relevant for procedures such as thoracentesis and chest tube placement. Additionally, the right bronchial artery may originate from the second to fifth posterior intercostal arteries, forming the right intercostobronchial trunk, a variant present in approximately 58% of individuals.