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Epicardium

The epicardium is the outermost layer of the heart wall, also referred to as the visceral layer of the serous pericardium. It consists of a single layer of mesothelial cells supported by connective tissue and fat, which contains coronary arteries, veins, lymphatics, and autonomic nerves. Beneath the epicardium lies the myocardium, the thick muscular layer of the heart.

The epicardium provides a protective covering for the heart, facilitates movement within the pericardial sac, and supports vascular and neural supply to the myocardium. Epicardial fat has additional roles in mechanical cushioning, metabolic activity, and paracrine signaling, but excessive epicardial adiposity has been linked to coronary artery disease and arrhythmias.

Synonyms

  • Visceral pericardium

  • Outer cardiac layer

  • Tunica externa cordis

Function

  • Forms a protective outer covering of the heart

  • Provides a medium for coronary vessels, lymphatics, and nerves

  • Facilitates smooth cardiac motion within the pericardial sac

  • Epicardial fat cushions the myocardium and contributes to metabolic and endocrine signaling

  • Plays a role in cardiac healing, inflammation, and fibrosis

MRI Appearance

T1-weighted images:

  • Epicardial fat appears hyperintense (bright), providing natural contrast

  • Epicardium itself is seen as a thin hypointense line between fat and myocardium

T2 Cine (Cardiac-gated balanced SSFP):

  • Shows the epicardial border as a sharp interface between myocardium and epicardial fat

  • Cine sequences allow assessment of epicardial motion and pericardial effusion

  • Abnormal tethering or restriction may suggest pericarditis or constrictive physiology

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, helping to highlight epicardial inflammation or edema

  • Useful in pericarditis, epicardial fat inflammation, or myocarditis with epicardial involvement

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Epicardium itself does not enhance

  • Pericardial enhancement adjacent to epicardium may indicate pericarditis or fibrosis

  • Late gadolinium enhancement may show epicardial or subepicardial myocardial injury, especially in non-ischemic cardiomyopathies (e.g., myocarditis)

MRA (Magnetic Resonance Angiography):

  • Not used for direct visualization of epicardium

  • Indirectly assesses coronary arteries within epicardial fat

CT Appearance

Contrast-Enhanced CT (Cardiac CTA):

  • Epicardial fat appears as low-attenuation tissue (-80 to -120 HU) around the myocardium

  • Epicardium itself is a thin border separating myocardium from pericardial sac

  • Coronary arteries course within the epicardial fat, making CT excellent for coronary artery imaging

CT Delayed Enhancement (CTDE):

  • May demonstrate epicardial or subepicardial hypo-/hyperattenuation in fibrosis or myocarditis

  • Complements MRI in centers without CMR availability

CT image

epicardium anatomy CT axial image -img-00000-00000

MRI image

Epicardium MRI ANATOMY