Aortic hiatus

The aortic hiatus is a hole in the human diaphragm through which the aorta and thoracic duct passes from the thorax into the abdomen. It is the lowest and most posterior of the large apertures.

It is located approximately at the level of the twelfth thoracic vertebra (T12).

Strictly speaking, it is not an aperture in the diaphragm but an osseoaponeurotic opening between it and the vertebral column, and therefore behind the diaphragm; occasionally some tendinous fibers prolonged across the bodies of the vertebræ from the medial parts of the lower ends of the crura pass behind the aorta, and thus convert the hiatus into a fibrous ring.

The hiatus is situated slightly to the left of the middle line, and is bounded in front by the crura, and behind by the body of the first lumbar vertebra.

Through it pass the aorta, the azygos vein, and the thoracic duct; occasionally the azygos vein is transmitted through the right crus.

Additional images
The Aorta does not pass through the aortic hiatus, rather, it passes posterior to it. The Azygos vein and thoracic duct pass through this opening.