Location and Formation
The esophageal hiatus (hiatus oesophageus) is one of the three major apertures of the unpaired dome-shaped muscle known as the diaphragm. It projects at the level of the tenth thoracic vertebra (Th10).
Anatomically, the opening lies within 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 upper lumbar vertebral bodies and intervertebral discs. The esophageal hiatus itself is formed primarily by the muscle bundles of the right crus of the diaphragm.
Structures Passing Through the Esophageal Hiatus
The primary function of this opening is to provide communication between the thoracic and abdominal cavities. Passing through the hiatus oesophageus are:
- Esophagus (oesophagus) — at this level, its thoracic part (pars thoracica) ends, and its short abdominal part (pars abdominalis) begins, measuring 1–3 cm before transitioning into the stomach. One of the three physiological constrictions of the esophagus—the diaphragmatic constriction—is located in this region.
- Vagal trunks (trunci vagales) — the anterior and posterior trunks of the vagus nerve (n. vagus). The posterior trunk runs along the posterior wall of the esophagus, while the anterior trunk lies against its anterior wall.
- Blood vessels — branches of the left gastric artery (a. gastrica sinistra) and accompanying veins.
- Lymphatic vessels.
Function and Mechanism
Unlike the caval opening, the margins of which are formed by the fibrous tissue of the central tendon and do not constrict, the esophageal hiatus has muscular borders.
During inspiration, the muscle bundles of the diaphragmatic crura contract. This leads to narrowing of the esophageal hiatus, allowing it to perform a sphincteric function. Contraction of the crura compresses the intra-diaphragmatic segment of the esophagus.
To ensure the reliability of this mechanism, the esophagus is firmly anchored within the hiatus: the adventitia of the esophagus blends with the diaphragmatic musculature, forming a connecting fibrous-elastic layer.
Topography and Neighboring Structures
The esophageal hiatus is positioned between the other two major openings of the diaphragm:
- Superiorly and anteriorly, at the level of Th8, the caval opening (foramen venae cavae) is located in the fibrous central tendon.
- Inferiorly, at the level of Th12, posterior to the diaphragm lies the aortic hiatus (hiatus aorticus), formed by the tendinous median arcuate ligament.
The abdominal surface of the diaphragm where the esophagus makes contact is an exception to the general rule: this area (similar to the bare area of the liver, and areas overlying the kidneys and suprarenal glands) is devoid of peritoneum, whereas the rest of the abdominal surface is lined by it via the subserous fascia.