Topography and location
The opening is localized in the tendinous center (centrum tendineum) of the diaphragm. This center is a triangular pale plate where all the muscle bundles—sternal, costal, and lumbar parts—converge. Anteriorly, the tendinous center adjoins the pericardium.
- Skeletotopy: projected at the level of the eighth thoracic vertebra (Th8).
- Relation to other openings: the esophageal hiatus (hiatus oesophageus) is located at the level of Th10, and the aortic hiatus (hiatus aorticus) is at the level of Th12.
- Syntopy of the vessel prior to the opening: before entering the foramen venae cavae, the inferior vena cava heads toward the posterior part of the diaphragmatic surface of the liver, where it lies in the groove for the inferior vena cava (sulcus venae cavae). The uppermost end of the vein before the diaphragm is slightly dilated and surrounded on three sides by the liver parenchyma.
Structure of the opening margins
Unlike the esophageal hiatus, which is formed by the muscular bundles of the diaphragmatic crura and performs a sphincter function, the margins of the foramen venae cavae have a fibrous structure.
- Fibrous tissue: the margins of the opening are fibrous.
- Fusion with the vessel: the adventitia of the inferior vena cava is fused with the margins of the opening by connective tissue strands.
What passes through the opening?
The following anatomical structures pass through this passage into the pericardial cavity:
- Inferior vena cava (v. cava inferior) — passes through the diaphragm into the pericardial cavity and immediately empties into the right atrium.
- Branches of the right phrenic nerve (n. phrenicus) — frequently pass through the same opening.
Biomechanics and function
The margins of the opening are fibrous, therefore they do not compress during inspiration. The fusion of the inferior vena cava adventitia with the margins of the opening by connective tissue strands keeps the vessel lumen open and promotes better venous return.
Do not confuse: opening in the right atrium
In anatomical terminology, there is a similarly sounding structure — the orifice of the inferior vena cava of the right atrium (ostium venae cavae inferioris atrii dextri). It is important to distinguish these structures: foramen venae cavae is an opening in the tendinous center of the diaphragm, while ostium is the opening of the inferior vena cava into the right atrium.
Vena cava — Th8, esophagus — Th10, aorta — Th12.
Class and exam questions
At which spinal level is the vena cava hiatus located?
It is projected at the level of the eighth thoracic vertebra (Th8), located in the tendinous center of the diaphragm.
Why is the inferior vena cava not compressed during diaphragmatic contraction?
The margins of the opening are fibrous and do not compress during inspiration. In addition, the adventitia of the vein is fused with the margins of the opening by connective tissue strands, which keeps the vessel lumen open and helps improve venous return.
Which nerves pass through the foramen venae cavae?
Branches of the right phrenic nerve (n. phrenicus) frequently pass through this opening along with the vein.
What else to study on this topic
- Diaphragm (diaphragma)
- Inferior vena cava (v. cava inferior)
- Esophageal hiatus (hiatus oesophageus)
- Aortic hiatus (hiatus aorticus)
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