Location and Formation
The aortic hiatus lies posterior to the diaphragm, slightly to the left of the midline, at the level of the 12th thoracic (Th12) or 1st lumbar (L1) vertebra.
It is formed by elements of the lumbar part (pars lumbalis) of the diaphragm. This part consists of the right and left crura (crus dextrum et sinistrum), which originate from the anterior surfaces of the upper lumbar vertebral bodies and intervertebral discs. The medial tendinous margins of these crura bound the opening laterally.
Superiorly, the crura are connected by the median arcuate ligament (lig. arcuatum medianum), which forms the upper border of the aortic hiatus. Because the margins of the opening are fibrous and tendinous, they do not contract during inspiration and thus do not compress the aorta.
Contents of the Aortic Hiatus
The following structures pass through this passage:
- Aorta (aorta): The thoracic aorta (pars thoracica aortae) transitions into the abdominal aorta (aorta abdominalis) as it passes through the aortic hiatus.
- Thoracic duct (ductus thoracicus): The main lymphatic trunk collecting lymph from three-quarters of the body. It passes through the aortic hiatus posterior and to the right of the aorta.
- Azygos and hemiazygos veins (v. azygos et v. hemiazygos): Occasionally pass through the aortic hiatus, though they may also traverse the intermuscular clefts of the diaphragmatic crura.
Topography and Related Structures
The aortic hiatus is closely related to several important anatomical structures of the thoracic and abdominal cavities:
- Superiorly and to the left, at the level of Th10 within the muscular part of the right crus, lies the esophageal hiatus (hiatus oesophageus). Unlike the aortic hiatus, it is formed by muscle fibers of the crura that contribute to a sphincter-like function during contraction.
- Immediately inferior to the aortic hiatus, at the Th12/L1 vertebral level, the short (1–2 cm) celiac trunk (truncus coeliacus) arises from the anterior wall of the abdominal aorta, branching into the left gastric, common hepatic, and splenic arteries.
- Also inferior to the hiatus, the inferior phrenic arteries (aa. phrenicae inferiores) branch off the aorta to supply the inferior surface of the diaphragm and give rise to the superior suprarenal branches.
- Inferior to the hiatus, the abdominal aorta descends along the anterior surface of the lumbar spine, slightly to the left of the midline, extending down to the level of the 4th or 5th lumbar vertebrae. The surrounding retroperitoneal tissue houses the left lumbar lymph nodes.