Subcostal arteries

The subcostal arteries are a pair of arteries that arise from the thoracic aorta and represent the most inferior branches of this major artery. They are named "subcostal" because they run below the last (twelfth) rib, distinguishing them from the intercostal arteries, which run between the ribs. These arteries are involved in supplying blood to the muscles, skin, and some structures of the abdominal wall and posterior thoracic region.

Location

The subcostal arteries are located at the level of the twelfth thoracic vertebra (T12). They originate from the thoracic aorta, just below the last rib, and travel laterally along the inferior edge of the twelfth rib. From there, they extend toward the anterior abdominal wall, running between the transversus abdominis and internal oblique muscles. They also pass posteriorly to supply parts of the diaphragm and back muscles.

Anatomy

The subcostal arteries are the lowermost branches of the thoracic aorta and share some characteristics with the posterior intercostal arteries.^[1] They run beneath the twelfth rib and supply various structures of the thoracoabdominal wall. Below is a detailed description of the anatomy of these arteries.

Origin

The subcostal arteries arise from the posterior surface of the thoracic aorta, typically just below the point where the aorta descends behind the diaphragm at the level of the twelfth thoracic vertebra (T12). They are the last pair of arteries branching off from the thoracic aorta before it transitions into the abdominal aorta, making them the most inferior thoracic arteries.

Course

After originating from the thoracic aorta, the subcostal arteries run laterally and follow the inferior margin of the twelfth rib, giving them their name.^[2] Their course resembles that of the posterior intercostal arteries, but they are located below the last rib rather than between the ribs.

• Posterior Course: Initially, the subcostal arteries travel posteriorly in the retroperitoneal space, crossing over the lateral aspects of the vertebral bodies of the thoracic and lumbar spine.
• Lateral and Anterior Course: As they proceed laterally, they move along the inferior border of the twelfth rib. Eventually, they continue toward the anterior abdominal wall, passing between the internal oblique and transversus abdominis muscles, where they contribute to the blood supply of these structures.

Branching Pattern

The subcostal arteries give off several important branches that supply different structures in the thoracoabdominal region:

• Muscular Branches: Along their course, the subcostal arteries give off small muscular branches that supply the muscles of the posterior abdominal wall, including the quadratus lumborum, transversus abdominis, and internal oblique muscles.
• Spinal Branches: Similar to the posterior intercostal arteries, the subcostal arteries send small spinal branches through the intervertebral foramina to supply the vertebrae and spinal cord.^[3] These branches contribute to the blood supply of the spinal tissues in the lower thoracic and upper lumbar regions.
• Cutaneous Branches: The subcostal arteries give rise to cutaneous branches that supply the skin of the lower thoracic and upper abdominal regions. These branches travel anteriorly with the nerve fibers of the subcostal nerve to provide blood flow to the skin.

Relationship to Surrounding Structures

The subcostal arteries have a close relationship with various anatomical structures as they travel along the twelfth rib:

• Diaphragm: The subcostal arteries are located just below the diaphragm, and they contribute to its blood supply by sending small branches to this structure, particularly at its posterior and lateral parts.^[4]
• Twelfth Rib: The arteries course along the inferior border of the twelfth rib, running parallel to the subcostal nerves and veins. These structures form part of the neurovascular bundle in this region.
• Psoas Major Muscle: As the subcostal arteries travel anteriorly, they pass in close proximity to the psoas major muscle, a key muscle of the posterior abdominal wall.
• Subcostal Nerves and Veins: The subcostal arteries travel along with the subcostal nerves and veins. The subcostal nerve, which originates from the twelfth thoracic spinal nerve (T12), accompanies the artery in its course, and the subcostal vein drains blood from the same region.

Termination

The subcostal arteries terminate in the muscles and skin of the anterior abdominal wall. As they move anteriorly, the arteries form anastomoses with branches of the superior epigastric artery and the lower posterior intercostal arteries, ensuring continuous blood flow to the thoracoabdominal wall.

Variations

While the subcostal arteries typically follow the same general pattern, some anatomical variations may occur:

• Number of Branches: The number of branches arising from the subcostal arteries may vary depending on individual anatomy and vascular needs of the region.
• Course: In some cases, the subcostal arteries may have slight variations in their course, particularly in their relationship with the diaphragm and abdominal muscles.^[5] However, their general pathway along the inferior margin of the twelfth rib remains consistent.

Function

The subcostal arteries have important roles in supplying blood to the muscles, skin, bones, and connective tissues of the lower thoracic and upper abdominal regions. Below is a detailed description of their functions.

Blood Supply to the Posterior Abdominal Wall Muscles

One of the primary functions of the subcostal arteries is to provide oxygenated blood to the muscles of the posterior abdominal wall. These include:

• Quadratus Lumborum: The subcostal arteries deliver blood to the quadratus lumborum, a muscle that helps in stabilizing the spine and assisting in lateral bending movements of the torso.
• Transversus Abdominis: These arteries also supply the transversus abdominis muscle, which plays a key role in stabilizing the core and supporting abdominal compression.
• Internal Oblique: The subcostal arteries contribute to the blood supply of the internal oblique muscle, which is involved in flexing and rotating the trunk.

Blood Supply to the Diaphragm

The subcostal arteries provide small branches that help supply the diaphragm, particularly its posterior and lateral regions.^[6] The diaphragm is a critical muscle in respiration, separating the thoracic cavity from the abdominal cavity, and the blood from the subcostal arteries supports its function by maintaining its muscular and connective tissue integrity.

Blood Supply to the Twelfth Rib and Adjacent Structures

The subcostal arteries also supply blood to the twelfth rib and its surrounding structures:

• Twelfth Rib: The arteries help supply the periosteum (the outer layer) of the twelfth rib, supporting the bone's metabolic needs and helping it maintain strength.
• Intercostal Muscles: Though located below the ribs, the subcostal arteries contribute to the vascularization of the intercostal muscles adjacent to the twelfth rib, which play a role in expanding and contracting the chest cavity during respiration.

Blood Supply to the Spinal Cord and Vertebrae

The subcostal arteries give off small spinal branches that provide blood to the vertebrae and the spinal cord:

• Spinal Cord: Through their spinal branches, the subcostal arteries help supply the lower thoracic and upper lumbar segments of the spinal cord. This ensures that the spinal nerves in these regions receive adequate oxygen and nutrients for proper function.
• Vertebrae: The arteries also provide blood to the lower thoracic vertebrae (T12) and the upper lumbar vertebrae (L1), particularly through the periosteum, aiding in the maintenance of vertebral health.

Blood Supply to the Skin and Subcutaneous Tissues

The subcostal arteries play a role in supplying the skin and subcutaneous tissues of the lower thoracic and upper abdominal regions:

• Cutaneous Blood Supply: The arteries give off cutaneous branches that supply the skin overlying the lower thoracic and upper abdominal wall.^[7] This blood supply is critical for skin vitality, temperature regulation, and wound healing.
• Subcutaneous Tissue: In addition to the skin, the subcostal arteries supply the subcutaneous tissues, including fat and connective tissue, in the lower thoracic region.

Blood Supply to the Thoracoabdominal Neurovascular Bundle

The subcostal arteries travel with the subcostal nerves and veins, contributing to the neurovascular bundle beneath the twelfth rib:

• Nerve Supply Support: By accompanying the subcostal nerves, the subcostal arteries help maintain the health of the nerves by providing them with oxygenated blood, ensuring that the lower thoracic nerve (T12) functions optimally.

Contribution to Collateral Circulation

The subcostal arteries are involved in forming collateral circulation by anastomosing (connecting) with other arteries in the region, including:

• Posterior Intercostal Arteries: They form anastomoses with the lower posterior intercostal arteries, ensuring continuity of blood flow to the thoracoabdominal wall.
• Superior Epigastric Artery: The subcostal arteries also contribute to the vascularization of the anterior abdominal wall through connections with the superior epigastric artery, which ensures an alternate route of blood supply.

Nutrient and Oxygen Delivery

Like other arteries, the fundamental role of the subcostal arteries is to deliver oxygenated blood, nutrients, and hormones to the tissues they supply. This enables the muscles, bones, skin, and connective tissues in the lower thoracic and upper abdominal regions to function properly, heal from injuries, and maintain overall health.

Clinical Significance

The subcostal arteries, though small, have notable clinical importance, especially in procedures involving the lower thoracic and upper abdominal regions. They can be encountered in both surgical and traumatic contexts.

• Surgical Considerations: In surgeries such as abdominal wall repairs, retroperitoneal surgeries, or spinal procedures, subcostal arteries can be at risk of injury, leading to bleeding or hematoma formation.^[8] Proper identification and management of these arteries are crucial to avoid complications.
• Trauma: In cases of rib fractures, particularly involving the twelfth rib, the subcostal arteries can be damaged, leading to significant bleeding into the abdominal or retroperitoneal space.
• Collateral Circulation: The subcostal arteries contribute to the collateral circulation of the thoracoabdominal wall. If the main arteries (such as the intercostal or epigastric arteries) are compromised, the subcostal arteries can help maintain blood flow to the region, making them important in maintaining vascular integrity in cases of arterial blockages or injuries.
• Imaging and Diagnostic Use: Knowledge of subcostal artery anatomy is essential for interpreting imaging studies such as CT or MRI scans, particularly when evaluating for vascular injuries or abnormalities in the thoracic or abdominal walls.