Central tendon of the diaphragm

Structure and location

The central tendon occupies the middle of the unpaired dome-shaped muscle—the diaphragm—which closes the inferior thoracic aperture and separates the thoracic and abdominal cavities.

• Shape: the structure appears as a pale triangular plate resembling a trefoil.
• Feature: the center contains no muscle fibers.

The height of the diaphragmatic domes depends on several factors:

• Dome projection: the right dome lies higher than the left—at the level of the 4th intercostal space, while the left is at the level of the upper border of the 5th rib anteriorly. Posteriorly, the projection is at the level of the 9th intercostal space.
• Chest shape: with a short and wide chest, the diaphragm is positioned high; with a long and narrow chest, it is low.
• Age and pathology: with age, as well as in the presence of exudate in the pleural or abdominal cavities, the diaphragmatic dome flattens.

Connection with the muscular parts of the diaphragm

The muscle bundles of all three parts of the diaphragm converge toward the central tendon:

• Sternal part (pars sternalis) is a narrow part originating from the posterior surface of the xiphoid process.
• Costal part (pars costalis) is the largest part, forming the lateral walls of the domes. It originates from the inner surface of the lower six ribs and their cartilages.
• Lumbar part (pars lumbalis) consists of the right and left crura (crus dextrum et sinistrum), originating from the bodies of the upper lumbar vertebrae (L1–L3/L4), as well as arcuate ligaments.

What passes through the central tendon?

The central tendon contains one of the most important openings of the diaphragm:

• Opening of the inferior vena cava (foramen venae cavae).
• Level of location: Th8.
• Contents: the inferior vena cava (v. cava inferior) passes through the opening, along with frequently branches of the right phrenic nerve (n. phrenicus).
• Mechanism of action: the margins of the opening are formed by the fibrous tissue of the central tendon. Consequently, when the diaphragm contracts during inspiration, the opening does not compress, which facilitates venous blood return.

Unlike the caval opening located in the central tendon, the other major openings of the diaphragm—the esophageal hiatus at the Th10 level and the aortic hiatus at the Th12 level—are formed by the muscular bundles of the crura or lie posterior to the diaphragm. The esophageal hiatus, formed by muscle, acts as a sphincter upon contraction.

Topography and serous coverings

The central tendon is in contact with the organs of the thoracic and abdominal cavities:

• Anteriorly: the central tendon lies adjacent to the pericardium.
• Thoracic surface: covered by the parietal pleura via the endothoracic fascia — fascia endothoracica.
• Abdominal surface: covered by the peritoneum via the subperitoneal fascia. The exceptions are areas lacking peritoneal coverage: the bare area of the liver (area nuda), as well as the areas adjacent to the kidneys, suprarenal glands, and esophagus.

Do not confuse with: the perineal body

The term "central tendon" is also applied to a structure of the pelvic floor — the perineal body (centrum tendineum perinei). This is a central fascial node where the fibers of the perineal muscles converge, interlace, and decussate:

• bulbospongiosus muscle (m. bulbospongiosus — posterior part);
• external anal sphincter (m. sphincter ani externus);
• superficial transverse perineal muscle (m. transversus perinei superficialis).

This area is reinforced by tendinous fibers, ensures the functional interdependence of the muscles, and serves as a landmark in surgery.

Class and exam questions

What else to study on this topic

• Diaphragm (diaphragma)
• Vena cava hiatus
• Perineal body
• Crura of the diaphragm

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.