Spinal branch of second posterior intercostal artery

The spinal branch of the second posterior intercostal artery is a small arterial branch that arises from the vertebral (proximal) segment of the second posterior intercostal artery near the intervertebral foramen at the T2 level. It enters the vertebral canal through the intervertebral foramen to supply the spinal cord, meninges, and vertebral bodies at that level.

Origin and Parent Vessel

The second posterior intercostal artery (supplying the second intercostal space) typically arises from the supreme intercostal artery, which is a branch of the costocervical trunk of the subclavian artery — unlike the 3rd through 11th posterior intercostal arteries, which arise directly from the descending thoracic aorta. As the second posterior intercostal artery courses posteriorly along the second intercostal space, it gives off a dorsal branch near the vertebral column. This dorsal branch in turn divides into a spinal (medial) branch and a muscular (lateral) branch.

Course and Distribution

The spinal branch passes through the intervertebral foramen at the T2 level and divides into three terminal branches:

• Radicular arteries — supply the anterior and posterior nerve roots of the T2 spinal nerve.

• Medullary (radiculomedullary/radiculopial) arteries — when present, these anastomose with the anterior or posterior spinal arteries to contribute to the longitudinal blood supply of the spinal cord. The upper thoracic region (T1–T3) represents the upper portion of the first vascular territory of the spinal cord, which receives supply from the vertebral and ascending cervical arteries as well as from upper intercostal spinal branches.

• Branches to the vertebral body, periosteum, and meninges (dura mater) — supply the bone, epidural space, and dural coverings at the corresponding level.

Clinical Significance

The spinal branches of the posterior intercostal arteries are collectively critical to spinal cord perfusion. The anterior and posterior spinal arteries are reinforced at multiple levels by radiculomedullary and radiculopial arteries that originate from these spinal branches. The upper thoracic cord (approximately T3–T7) is considered a watershed zone with relatively tenuous blood supply, making the contributions from upper intercostal spinal branches clinically important. Disruption of these vessels — during thoracic surgery, aortic procedures, or spinal instrumentation — can contribute to spinal cord ischemia.