Location and formation
The aortic hiatus is located behind the diaphragm, slightly to the left of the midline, at the level of the twelfth thoracic (Th12) or first lumbar (L1) vertebra.
It is formed by elements of the lumbar part of the diaphragm (pars lumbalis). This part consists of right and left crura (crus dextrum et sinistrum), which originate from the anterior surface of the bodies of the upper lumbar vertebrae and intervertebral discs. The medial tendinous margins of these crura bound the opening laterally.
Above the aorta, the crura are connected by the median arcuate ligament (lig. arcuatum medianum), which forms the aortic hiatus. The margins of the opening are fibrous (tendinous), so they do not contract during inspiration and do not compress the aorta.
What passes through the aortic hiatus?
The following structures pass through this opening:
- Aorta (aorta) — the thoracic part of the aorta (pars thoracica aortae) passes through the aortic hiatus into the abdominal aorta (aorta abdominalis).
- Thoracic duct (ductus thoracicus) — the main lymphatic vessel collecting lymph from 3/4 of the body. It passes through the aortic hiatus to the right and posterior to the aorta.
- Azygos and hemiazygos veins (v. azygos et v. hemiazygos) — sometimes pass through the aortic hiatus; they may also pass through the intermuscular clefts of the diaphragmatic crura.
Topography and adjacent structures
The aortic hiatus is closely related to a number of important anatomical structures of the thoracic and abdominal cavities:
- Superior and to the left of it, at the level of Th10, in the muscular part of the right crus lies the esophageal hiatus (hiatus oesophageus). Unlike the aortic hiatus, it is formed by muscular bundles of the crura, which contribute to sphincter function upon contraction.
- Immediately below the aortic hiatus, at the level of the Th12/L1 border, the short (1–2 cm) celiac trunk (truncus coeliacus) arises from the anterior wall of the abdominal aorta, dividing into the left gastric, common hepatic, and splenic arteries.
- Also inferior to the opening, the inferior phrenic arteries (aa. phrenicae inferiores) arise from the aorta, running toward the inferior surface of the diaphragm and giving off superior suprarenal branches.
- Inferior to the opening, the abdominal aorta lies on the anterior surface of the lumbar spine, to the left of the midline, and extends to the level of the IV–V lumbar vertebrae. Left lumbar lymph nodes are located in the adipose tissue along the aorta.
Class and exam questions
Is the aorta compressed during inspiration?
No. The margins of the aortic hiatus are formed by tendinous tissue—the medial margins of the crura and the median arcuate ligament—so they do not compress the aorta during inspiration.
At what vertebral level is the aortic hiatus located?
It is located at the level of the twelfth thoracic (Th12) or first lumbar (L1) vertebra, slightly to the left of the midline.
How does the thoracic duct pass through the diaphragm?
The thoracic lymphatic duct passes through the aortic hiatus together with the aorta; it is located to the right and posterior to the aorta.
What else to study on this topic
- Lumbar part of the diaphragm and its crura
- Thoracic duct (ductus thoracicus)
- Abdominal aorta and its branches
- Aortic hiatus of the diaphragm
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