Superior Phrenic Arteries

The superior phrenic arteries are small paired arteries that supply the superior (thoracic) surface of the diaphragm. They arise from the lower part of the descending thoracic aorta and contribute to the arterial network that nourishes the diaphragm, particularly its posterior portion. These arteries are relatively small and functionally complemented by other arteries supplying the diaphragm from above and below.

Origin

The superior phrenic arteries typically arise from the posterior aspect of the descending thoracic aorta near the aortic hiatus, usually at the level of the T12 vertebra. They may originate separately on each side or from a common trunk.

• Left superior phrenic artery: Arises directly from the thoracic aorta

• Right superior phrenic artery: May arise from the thoracic aorta or occasionally from the 10th or 11th posterior intercostal artery

Course

After originating from the thoracic aorta, the superior phrenic arteries ascend slightly and pass anteriorly and laterally to reach the superior surface of the diaphragm. They distribute along the posterior aspect of the diaphragm, particularly near the crura and central tendon region.

Distribution

The superior phrenic arteries supply:

• Posterior superior surface of the diaphragm

• Posterior part of the central tendon

• Adjacent areas of the pleura

Anastomoses

These arteries form functional and anatomical anastomoses with other diaphragmatic arteries:

• Pericardiacophrenic arteries: Branches of the internal thoracic arteries that supply the anterolateral diaphragm

• Musculophrenic arteries: Also from internal thoracic arteries, supply the costal margins of the diaphragm

• Inferior phrenic arteries: Branches of the abdominal aorta (or celiac trunk), which supply the inferior surface of the diaphragm

These anastomoses are important in ensuring adequate collateral circulation to the diaphragm, especially when one source is compromised.

Venous Drainage

The superior phrenic veins accompany the arteries and drain into:

• Azygos vein (on the right)

• Hemiazygos or left superior intercostal vein (on the left)

Topographic Relationships

• Posterior: Vertebral bodies (T11–T12), descending thoracic aorta

• Anterior: Diaphragm (posterior surface, near crura)

• Inferior: Aortic hiatus and adjacent abdominal structures

Histological Structure

Like other systemic arteries, the superior phrenic arteries have three distinct layers:

• Tunica intima: Endothelial lining and connective tissue

• Tunica media: Smooth muscle and elastic fibers

• Tunica adventitia: Outer connective tissue layer with small vasa vasorum

Clinical Significance

• Collateral Circulation: These arteries provide an important collateral pathway in cases where inferior phrenic flow is disrupted.

• Surgical relevance: Must be considered during thoracic surgeries involving the posterior diaphragm or lower thoracic aorta.

Topographic Summary

• Number: Two (right and left)

• Origin: Descending thoracic aorta (T12 level)

• Course: Passes anteriorly to posterior diaphragm

• Supply: Superior surface of diaphragm

• Anastomoses: Pericardiacophrenic, musculophrenic, inferior phrenic arteries

• Drainage: Azygos and hemiazygos systems