The pericardium is a tough fibroelastic sac which covers the heart from all sides except at the cardiac root (where thegreat vessels join the heart) and the bottom (where only the serous pericardium exists to cover the upper surface of thecentral tendon ofdiaphragm).[4] 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 theepicardium, resulting in a continuousserous membraneinvaginated onto itself as two opposing surfaces (over the fibrous pericardium and over the heart). This creates a pouch-likepotential space around the heart enclosed between the two opposing serosal surfaces, known as thepericardial space orpericardial cavity, which is filled with a small amount ofserous fluid to lubricate the heart's movements and cushions it from any external jerk or shock.
Thefibrous pericardium is the outside layer of the pericardium, made up ofdense andloose connective tissue.[5] While capable of somechange 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 theouter adventitial layer of the neighboringgreat blood vessels, fused with the central fibrous area of the diaphragm on its posterior aspect[6] and attached to the posterior surface of thesternum by the sternopericardial ligaments.[7]
Theserous pericardium, in turn, is divided into two parts:
Theparietal serous pericardium, which lines the interior side of the superficial portion of the pericardial sac, is fused to and inseparable from the fibrous pericardium
Thevisceral serous pericardium, also known as theepicardium, covers themyocardium of the heart[8] and can be considered itsserosa. It is largely made of a mesothelium overlying someelastin-richloose connective tissue. During ventricular contraction, the wave ofdepolarization moves from theendocardial to the epicardial surface.
Both of these layers function in lubricating the heart to prevent friction during heart activity.
The visceral serous pericardium extends to the root of thegreat vessels and joins the parietal serous pericardium at the anatomical base of the heart. This junction occurs at two areas: theventricular outflow tracts where theaorta andpulmonary trunk leave the heart, and the inflow tracts where thesuperior/inferior vena cava andpulmonary veins enter the heart.[8] The root of the great vessels and the associated reflections of the serous pericardium creates various smaller sacs and tunnels known aspericardial sinuses, as well asradiographically significantpericardial recesses,[9] where pericardial fluid can pool and mimic mediastinallymphadenopathy.[9]
A transverse section of thethorax, showing the contents of the middle and the posteriormediastinum. Thepleural cavity and thepericardial cavity are exaggerated since normally there is no space between the pleurae or between the pericardium andheart. Pericardium is also known as cardiac epidermis.
Surrounds heart and bases of pulmonary artery and aorta.
The pericardium sets the heart in mediastinum and limits its motion, protects it from infection, lubricates it and prevents excessive dilation in cases of acute volume overload.
Illustration of the pericardial sac and the sac when inflamed
Inflammation of the pericardium is calledpericarditis. This condition typically causes chest pain that spreads to the back and is made worse by lying flat. In patients suffering with pericarditis, apericardial friction rub can often be heard when listening to the heart with a stethoscope. Pericarditis is often caused by a viral infection (glandular fever,cytomegalovirus, orcoxsackievirus), or more rarely with a bacterial infection, but may also occur following amyocardial infarction. Pericarditis is usually a short-lived condition that can be successfully treated withpainkillers,anti-inflammatories, andcolchicine. In some cases, pericarditis can become a long-term condition causing scarring of the pericardium which restricts the heart's movement, known asconstrictive pericarditis. Constrictive pericarditis is sometimes treated by surgically removing the pericardium in a procedure called apericardiectomy.[10]
Fluid can build up within the pericardial space, referred to as apericardial effusion. Pericardial effusions often occur secondary topericarditis,kidney failure, ortumours and frequently do not cause any symptoms. Large effusions or effusions that accumulate rapidly can compress the heart and restrictdiastolic ventricular filling in a condition known ascardiac tamponade, causingpulsus paradoxus and potentially fatalcirculatory failure. Fluid can be removed from the pericardial space for diagnosis or to relieve tamponade using a syringe in a procedure calledpericardiocentesis.[11] For cases of recurrent pericardial effusion, an operation to create a hole between the pericardial and pleural spaces can be performed, known as apericardial window orpericardiostomy.
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.[12]
^Byrne, John G; Karavas, Alexandros N; Colson, Yolonda L; Bueno, Raphael; Richards, William G; Sugarbaker, David J; Goldhaber, Samuel Z (2002). "Cardiac Decortication (Epicardiectomy) for Occult Constrictive Cardiac Physiology After Left Extrapleural Pneumonectomy".Chest.122 (6):2256–9.doi:10.1378/chest.122.6.2256.PMID12475875.
^Davidson's 2010, pp. 638–639. sfn error: no target: CITEREFDavidson's2010 (help)
![Cytology of the normal mesothelial cells that line the pericardium, with typical features.[13] Wright's stain.](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aCytology_of_normal_mesothelium.jpg)
