The pericardium (), also called pericardial sac, is a double-walled fluid filled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong inelastic connective tissue (fibrous pericardium), and an double -layered inner layer made of serous membrane (serous pericardium). It encloses the pericardial cavity, which contains pericardial fluid,

Anatomy

The pericardium is a tough fibroelastic sac which covers the heart from all sides except at the cardiac root (where the great vessels join the heart) and the bottom (where only the serous pericardium exists to cover the upper surface of the central tendon of diaphragm). The fibrous pericardium is semi-rigid, while the serous pericardium is quite pliable.

The same mesothelium that constitutes the serous pericardium also covers the heart as the epicardium, resulting in a continuous serous membrane invaginated onto itself as two opposing surfaces (over the fibrous pericardium and over the heart). This creates a pouch-like potential space around the heart enclosed between the two opposing serosal surfaces, known as the pericardial space or pericardial cavity, which is filled with a small amount of serous fluid to lubricate the heart's movements and cushions it from any external jerk or shock.

Fibrous

The fibrous pericardium is the outside layer of the pericardium, made up of dense and loose connective tissue. While capable of some change in shape, it is largely non-pliable, which acts to protect the heart against blunt forces and sudden pressure change from the outside. It is continuous with the outer adventitial layer of the neighboring great blood vessels, fused with the central fibrous area of the diaphragm on its posterior aspect and attached to the posterior surface of the sternum by the sternopericardial ligaments.

Serous

The serous pericardium, in turn, is divided into two parts:

  • The parietal serous pericardium, which lines the interior side of the superficial portion of the pericardial sac, is fused to and inseparable from the fibrous pericardium
  • The visceral serous pericardium, also known as the epicardium, covers the myocardium of the heart The root of the great vessels and the associated reflections of the serous pericardium creates various smaller sacs and tunnels known as pericardial sinuses, as well as radiographically significant pericardial recesses, where pericardial fluid can pool and mimic mediastinal lymphadenopathy.

Fluid can build up within the pericardial space, referred to as a pericardial effusion. Pericardial effusions often occur secondary to pericarditis, kidney failure, or tumours and frequently do not cause any symptoms. Large effusions or effusions that accumulate rapidly can compress the heart and restrict diastolic ventricular filling in a condition known as cardiac tamponade, causing pulsus paradoxus and potentially fatal circulatory failure. Fluid can be removed from the pericardial space for diagnosis or to relieve tamponade using a syringe in a procedure called pericardiocentesis. For cases of recurrent pericardial effusion, an operation to create a hole between the pericardial and pleural spaces can be performed, known as a pericardial window or pericardiostomy.

The congenital absence of pericardium is rare. When it happens, it usually occurs on the left side. Those affected usually do not have any symptoms and they are usually discovered incidentally. About 30 to 50 percent of the affected people have other heart abnormalities such as atrial septal defect, patent ductus arteriosus, bicuspid aortic valve, and lung abnormalities. On chest X–ray, the heart looks posteriorly rotated. Another feature is the sharp delineation of pulmonary artery and transverse aorta due to lung deposition between these two structures. If there is partial absence of pericardium, there will be bulge of the left atrial appendage. On CT and MRI scans, similar findings as chest X–ray can be shown. The left sided partial pericardium defect is difficult to see because even a normal pericardium is difficult to be seen on CT and MRI. A complete pericardial defect will show the heart displaced to the left with part of the lungs squeezed between inferior border of heart and diaphragm.

Additional images

<gallery>

File:Slide15gggg.JPG|Fibrous pericardium

File:Cytology of normal mesothelium.jpg|Cytology of the normal mesothelial cells that line the pericardium, with typical features. Wright's stain.

File:3D still showing the pericardium layer.jpg|3D still showing the pericardium layer

</gallery>

References

  • – "Mediastinum: Pericardium (pericardial sac)"
  • ()
  • – "MRI of chest, lateral view"