Aortic hiatus

The aortic hiatus is the lowest and most posterior of the three major diaphragmatic openings. It is situated at the vertebral level T12, slightly to the left of the midline. Anatomically, the hiatus lies posterior to the diaphragm between the right and left crura, beneath the median arcuate ligament.

Strictly speaking, the aortic hiatus is not a true opening within the diaphragm itself. Instead, it is an osseoaponeurotic interval formed between the diaphragm and the vertebral column. Anteriorly, it is bounded by the crura of the diaphragm, while posteriorly it is related to the body of the first lumbar vertebra.

Structures passing through the aortic hiatus

The principal structure passing through the aortic hiatus is the descending aorta, which continues into the abdomen as the abdominal aorta. In addition, the thoracic duct and azygos vein (and hemiazygous vein) also traverse this opening. In some individuals, the azygos vein may instead pass through the right crus of the diaphragm.

Because the aortic hiatus lies posterior to the diaphragm rather than within its muscular fibres, it is relatively unaffected by diaphragmatic contraction during respiration. This arrangement helps maintain uninterrupted blood flow through the aorta during breathing movements.