Aortic Hiatus Contents

Expansion

At the level of T12, behind the median arcuate ligament:

• A - Aorta
• A - Azygos vein (and often the hemiazygos)
• T - Thoracic duct

Strictly this is an osseoaponeurotic opening posterior to the diaphragm rather than a hole through it. The boundaries are the two crura on either side, the median arcuate ligament in front and the body of T12 behind.

Because the aorta is not surrounded by muscle here, it is not compressed when the diaphragm contracts, unlike the oesophagus at T10, which is deliberately pinched by the right crus. That difference is worth carrying: the two openings that need to stay open under pressure, the caval and aortic, avoid the muscle, while the one that benefits from being squeezed shut passes straight through it.