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Sternal part of diaphragm

The sternal part of the diaphragm is the smallest portion of the diaphragm, consisting of two muscular slips that arise from the posterior surface of the xiphoid process of the sternum. These fibers curve posteriorly and laterally to insert into the central tendon of the diaphragm. Between the sternal and costal parts lies the sternocostal triangle (foramen of Morgagni), a potential weak spot that can be a site of congenital diaphragmatic hernia. Despite its small size, the sternal part contributes to the overall respiratory movement of the diaphragm.

Synonyms

  • Sternal slips of the diaphragm

  • Sternal origin of diaphragm

  • Xiphoid part of diaphragm

Function

  • Contributes to inspiration by contracting and pulling the central tendon downward

  • Helps maintain intra-abdominal and intrathoracic pressure differentials

  • Provides a passageway near the sternocostal triangle for superior epigastric vessels

  • Plays a role in diaphragmatic stability and movement

Arterial Supply

  • Supplied by the pericardiacophrenic artery (branch of internal thoracic artery)

  • Additional contributions from musculophrenic artery (branch of internal thoracic artery)

  • Small branches from the superior epigastric artery

Venous Drainage

  • Drains into the pericardiacophrenic and musculophrenic veins → internal thoracic vein system

  • Additional drainage into brachiocephalic veins and azygos system

Nerve Supply

  • Innervated by the phrenic nerve (C3–C5)

  • Provides motor supply to the muscle slips

  • Carries sensory fibers from the central diaphragm

MRI Appearance

T1-weighted images:

  • Appears as a thin, low signal intensity muscular slip at the posterior surface of the xiphoid process

  • Central tendon is hypointense; adjacent fat planes are hyperintense, enhancing contrast

T2-weighted images:

  • Sternal part appears low to intermediate signal compared with surrounding fat and liver

  • Hyperintense signal may indicate edema or inflammation

STIR (Short Tau Inversion Recovery):

  • Fat suppression allows clear visualization of edema, trauma, or herniation

  • Abnormalities (injury, inflammation, tumor infiltration) appear bright hyperintense

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal sternal slips show mild homogeneous enhancement

  • Pathological changes (tumor invasion, inflammation) show asymmetric or nodular enhancement

CT Appearance

Non-contrast CT:

  • Seen as a thin muscular structure arising from posterior xiphoid process

  • May appear subtle, outlined better by adjacent fat planes

  • Morgagni’s foramen appears as a triangular soft tissue gap near the sternocostal junction

Contrast-enhanced CT (CECT):

  • Sternal slips enhance uniformly

  • Excellent for detecting diaphragmatic hernias, traumatic defects, or masses

  • Multiplanar reconstructions (coronal, sagittal) provide optimal evaluation of the sternal origin and sternocostal triangle

MRI images

Right sternal part of diaphragm MRI coronal image -img-00000-00000

CT image

sternal part of diaphragm CT coronal image -img-00000-00000