The regular gross and microscopic structure of the human pericardium is the evaluation in detail. Based upon the structural contents of the pericardium, the pathologic responses frequently seen in clinical specimens room shown. This gives a correlative explanation come clinical evolution and diagnostic imaging result such together delayed improvement in the workup that pericardial disease.

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We present the gross and microscopic structure of the pericardium together a framework of referral that can be correlated with existing cardiac imaging techniques and interventions. The restricted repertoire the responses of the pericardium to diverse pathologic stimuli is depicted in the context of its typical structure.

A. Gross structure of the Parietal and also Visceral Pericardium

The pericardium is a approximately flask-shaped sac that consists of the heart and proximal portions of the good vessels

. The lateral surfaces of the pericardium space invested by the mediastinal part of the parietal pleura other than in those areas where ligaments anchor the pericardium to the sternum, the diaphragm, and the vertebral column. The phrenic nerves and also pericardiophrenic vessels are consisted of in 2 bundles flanking the lateral border of the love
.

The pericardium is conventionally divided into parietal and visceral pericardium . The parietal pericardium consists of an external fibrous connective tissue sac lined by serosa. The serosal component is composed of a single continuous layer that mesothelium the invests the fibrosa layer of the pericardium and also extends over the root of the an excellent arteries to fully cover the outside surface of the heart. The layer of mesothelium investing the external surface the the heart is referred to as the visceral pericardium or epicardium. The fibrosa great of the parietal pericardium is between 0.8 and 1 mm thick yet may appear slightly more thickness on imaging.1 The pericardial sac is extended by variable quantities of adipose organization in the mediastinal surface, particularly in the cardiophrenic angles

.

Figure 1A


*

Anterior view of the intact pericardial sac. An undamaged pericardium attached to the diaphragm is displayed with the mediastinal pleura spanning the lateral surface of the pericardial sac. Note the abundant epipericardial adipose organization in the anterior mediastinum and anterior cardiophrenic angles. The arrowheads flank the boundaries of the sternopericardial ligament. LCC = left usual carotid artery. SVC = premium vena cava.

Figure 1B


*

Right lateral view of the heart and also pericardium. The best phrenic nerve and pericardiophrenic ship lie between the parietal pericardium and also mediastinal pleura anterior to the pulmonary hilum. The arrowheads to mark these structures. Keep in mind the abundant adipose tissue spanning the mediastinal surface ar of the pericardium in the anterior and also lateral surfaces. RIPV = best inferior pulmonary vein. RPA = ideal pulmonary artery. RSPV = ideal superior pulmonary vein. SVC = remarkable vena cava.

Figure 1C


*

Left lateral view of the heart and pericardium. The food of the left phrenic nerve and also historicsweetsballroom.comompanying vessels are highlighted through the arrowheads. Ao = aorta. LIPV = left worse pulmonary vein. LPA = left pulmonary artery. LSPV = left premium pulmonary vein.

Figure 2


*

Parietal vs. Visceral pericardium. The pericardium has, as plenty of other serosal surfaces, a parietal and also a visceral component. The parietal pericardium is composed of 2 layers: a serosal lining (thin red line) and a fibrous sac (thicker yellow line). The visceral pericardium or epicardium is created of a single layer of serosal investment extending the whole heart (thin red line overlying the myocardium in blue). Note that the serosal lining of the parietal and also visceral pericardium is a consistent layer that mesothelial cells. The serosal class of the parietal and also visceral pericardium face each other. The potential an are lined through the serosal class is the pericardial cavity.

Figure 3


*

Parietal and visceral pericardium. A: Coronal ar of the heart shows the ventricles, ascending aorta (Ao), and also partial views of the right and left atrial appendages, the superior vena cava (SVC), the aortic valve, and the pulmonary artery stems (PA). B: The inset of the left lateral ventricular wall is magnified. The visceral and parietal pericardium space in close apposition and the an are between these two layers is virtual. The arrowheads display an area of urgently of the parietal pericardium whereby it separates indigenous the visceral pericardium. Keep in mind the absence of subepicardial fat in the lateral left ventricle. C: irradiate microscopic exam shows a thin layer that fibrous tissue (yellow) overlying the cardiac muscle (red). The "hobnail" cell lying end the slim fibrous sheet are the mesothelial cell which kind the visceral pericardium. Keep in mind the close proximity that the myocardial capillaries to the mesothelium of the visceral layer. This affluent network of ship can provide fast move of liquid material in and also out the the pericardial space. D: A close up of the inset top top the right ventricle in 3A is shown. There is a distinct room between the parietal pericardium (arrowheads) and the epicardium extending the adipose tissue that overlies the right ventricular myocardium (RV). E: light microscopy that the mesothelial lining end the adipose tissue of the right ventricle (visceral pericardium). Quick elastic fibers (black) are existing in the subepicardium. F: This micrograph of complete thickness pericardial sac mirrors the fibrosa class of the parietal pericardium. Keep in mind the thin vascularization of the fibrosa. The mesothelial cell of the parietal pericardium are directly attached to the fibrosa in the upper part of the photo. The mediastinal facet (lower part) that the pericardium reflects adipose organization which, in turn, is additionally covered by mesothelial cells forming the serosa the the mediastinal pleura. Ao = aorta. LV = left ventricle. PA = pulmonary artery. RV = best ventricle. SVC = premium vena cava. * = inferior aortic recess. ** = left pulmonic recess.

B. Pericardial Sinuses and also Recesses

The reflect of the serosa about the good vessels entering and also leaving the heart kind the pericardial sinuses and recesses.2 The ascending aorta and also main pulmonary artery together are totally ensheathed by an invest of the visceral pericardium. This investment creates a potential space, the transverse sinus, i beg your pardon separates the anteriorly located great arteries indigenous the veins posteriorly

. The floor the the transverse sinus is developed by the roof the the left atrium. The transverse sinus is consistent with the remarkable aortic recess in between the aorta and also the superior vena cava and the inferior aortic recess in between the aorta and the appropriate atrium
. The lateral expansions of the transverse sinus are referred to as the right and also left pulmonic recesses.

A 2nd investment of visceral pericardium separately covers the venae cavae and pulmonary veins. The postcaval recess lies behind the remarkable vena cava and also is bounded by the appropriate pulmonary artery superiorly and also right superior pulmonary vein inferiorly. The right and left pulmonary venous recesses are created by the pericardial reflection between the corresponding superior and inferior pulmonary veins. The cul-de-sac located behind the posterior wall surface of the left atrium is the slope sinus

. It is bounded by the pericardial reflection follow me inferior pulmonary veins and the worse vena cava. It directly abuts the carina and also the esophagus posteriorly.

Figure 4


Sinuses and also recesses of the pericardium. In this image the anterior (ventral) portion of the pericardium and also the heart have been gotten rid of to show the good vessels at the basic of the heart. The aorta and also pulmonary artery has been transected to present the path of the transverse sinus (dotted line) that separates the arteries from the venae cavae and pulmonary veins. The pericardial have fun extends come the proximal aortic arch and the recess in between the aorta and also the exceptional vena cava is referred to as the exceptional aortic recess (dotted line). The left lateral expansion of the transverse sinus is the left pulmonic recess bordered through the left pulmonary artery and left superior pulmonary vein. The slope sinus is the cul-de-sac behind the left atrium and also bound through the pericardial reflection end the worse pulmonary veins and the inferior vena cava. IVC = inferior vena cava. LPA = left pulmonary artery. LPV = left pulmonary veins. RPA = appropriate pulmonary artery. RPV = right pulmonary veins. SVC = superior vena cava.

C. Microscopic company of the Pericardium

Three unique layers have the right to be identified in the parietal pericardium by microscopic exam: the serosa, the fibrosa, and also an external layer the epipericardial connective tissue. The serosa is the innermost surface of the pericardial sac and also is created by mesothelial cells

. The mesothelial cells are level to cuboidal epithelial cells rich in microvilli which are crucial for the formation and also reabsorption the pericardial liquid
. The fibrosa is written of dense collagen bundles v interspersed scant elastic fibers
. The fibrous organization bundles subjacent to the mesothelium often tend to have actually a cephalocaudal orientation; whereas the much more external bundles have a much more weaved organization which permits for part distensibility that the pericardial fibrosa. The fibrosa contains scant connective organization cells and small vessels. The outer pericardial layer mirrors somewhat much more abundant elastic fibers, adipose tissue, neural elements, and blood vessels. Rarely mast cells and mononuclear cells have actually been described in this layer.3

The visceral pericardium

is formed by a thin layer that fibrous tissue overlying the myocardium invest by mesothelial cell (the serosal ingredient of the visceral pericardium) over the whole surface the the heart.

Figure 5


A sheet of mesothelial cell is shown at high magnification. This cells deserve to vary from level to cuboidal in shape. Microvilli (arrowheads) are present on the surface facing the pericardial cavity to rise the surface ar area of these cells. The microvilli send a "fuzzy" look come the luminal border that the mesothelial cells.

D. Pericardial Responses come Injury

1. Distensibility

While the fibrous tissue bundles in the within fibrosa through its cephalocaudal orientation carry out not distend very much; in comparison, the weaved organization of the fibrous organization bundles of the outside fibrosa enables for some distention of the pericardial sac before physiologic constriction is clinically evident. The devoted nature of the mesothelial cell with numerous microvilli and also the liquid transport systems through this cells permit for high move capacity through the serosal pericardium. The extremely vascularized epicardium deserve to provide large transfer of fluid to the mesothelial cells because that these to develop transudates and also exudates. This defines how simple transudates and/or very fibrinous exudates deserve to readily type in the pericardial cavity as soon as there is injury.

2. Exudative and inflammatory response

The pericardium (parietal and visceral) has actually a limited response to injury, i beg your pardon is at first manifested as boosted production the pericardial fluid.4 The effusion could be a transudate i m sorry is composed mainly of thin fluid or one exudate i beg your pardon contains large amounts that fibrin and, as a function of severity, variable numbers and varieties of inflammatory cell

. The fibrinous exudate creates adhesions and also strands between the parietal and visceral pericardium. These fibrinous adhesions space the communication of the friction obstacle detected on physical examination
. V fibrinolysis, the fibrin deposits typically organize or cure into loosened fibrous strands quite than thick fibrous organization
. This form of fix does not result in constriction, due to the fact that pockets lined v normal mesothelial cells space formed, which lubricate the remaining pericardial space. ~ above the other hand, recurring bouts the fibrinous depositions or a an ext severe inflammatory injury can elicit a fibrogenic fix process.

Figure 6


Fibrinous exudate. Irradiate micrograph the the epicardial surface ar of the myocardium mirroring mild inflammatory infiltrate in the myocardium and also an exuberant eosinophilic fibrinous exudate on the surface of the visceral pericardium. The pistol pathology of this fibrinous exudate is shown in figure 7.

Figure 7


Gross specimen the a love of a patient through uremic pericarditis completely covered v fibrinous strands i beg your pardon in addition show yellow/green discoloration as the patient had actually jaundice. Note that the fibrin strands surround the source of the an excellent vessels together these segments room intrapericardial. Ao = aortic valve and aortic root. LV = left ventricle. PA = pulmonary artery and also valve. RV = best ventricle. RVOT = ideal ventricular outflow tract. SVC = remarkable vena cava.

Figure 8


Coronal section of the heart showing arranged fibrous (not fibrinous) strands (asterisk) formed between the visceral pericardium and also the parietal pericardium. Note that the parietal pericardium is slightly thicker than the normal examples in figure 3. LA = left atrium. LAA = left atrial appendage. LLL = left lower lobe of the lung. PA = pulmonary artery in ~ bifurcation.

3. Reabsorption, organization and repair the the exudative inflammation response

The healing process may show several different predominant trends as shown in number 9. These responses deserve to be of a single form or linked processes

. In some patients, the inflammation infiltrates show off both the serosa of the pericardium and the serosa the the pleura
.

Figure 9


Common responses of the pericardium to noxious stimuli an outcome in varied non-exclusive types of effusions. A serous effusion may occur and be reabsorbed totally without leaving any type of histologic alteration. On the other hand, exudative effusions constantly leave a trace of the pericardial an answer to the injury. The exudate the fibrin is the most usual finding nevertheless of the resource of injury: chemical (uremic, pharmaceuticals), physics (open love surgery, therapeutic ablation, radiation), or infectious (viral, bacterial, fungal, parasitic). When the fibrinous or fibrino-hemorrhagic exudate occurs, over there is normally an inflammatory solution elicited that will certainly "clean" the fibrinous debris. Throughout this phase, the inflammatory cells promote the development of neovascularization and also early extracellular procession deposition (granulation tissue). If the noxious economic stimulation ends, the result is normally mild fibrosis. If the noxious stimulus persists, the an answer of the pericardium is lengthy in regards to the procedure of exudation, inflammation, and also repair. In recurrent pericarditis, the inflammatory solution may wax and also wane. The red arrows illustrate points wherein a recurrent insult can take place again, hence modifying and also lengthening the heal process. The repetitive injury-repair cycles an outcome in thickening of the parietal pericardium and adhesion come the visceral pericardium v obliteration of the pericardial cavity. While generally seen, calcification is not always a feature existing during the healing of the pericardium.

Figure 10


Acute fibrinous pericarditis. A and B: Fibrinous exudates with abundant inflammatory cells are shown. The fibrosa layer shows dilated vessels. The inset shows a close up of the inflammatory infiltrates intermingled with the fibrinous strands and also reactive mesothelial cell in the serosa great of the parietal pericardium. C and D: Parietal pericardium with plentiful inflammatory infiltrates and also early deposition that extracellular procession (yellow green shade in D ~ above top and below the fibrosa). This is very early stage of company of the exudate. The newly created connective tissue at some point is invaded by capillaries that kind extensive vascular network. The fibrosa class of the parietal pericardium is delineated by the dotted lines. Keep in mind that in this instance the inflammatory process is entailing both the pericardial serosa (mesothelial) layer and also the mediastinal pleural serosa layer. If a pericardiectomy is performed, the inflammation existing in the mediastinal pleura might still current clinically as residual "pericardial" advert pain. (A and C: H&E stain. B and D: Movat pentachrome stain).

If no additional injurious stimuli room present, the inflammatory cell within the fibrinous exudate promote neovascularization and fibroblast proliferation. Extracellular matrix is laid down and as it matures, the loose granulation organization becomes organized with much more mature fibrous organization while the neovascularization and chronic inflammation end up being less conspicuous

. If the injurious stimulus that originated the effusion does no relapse, the healing procedure eventually leader to the maturation of the granulation tissue into a dense fibrous scar.

Figure 11


Organizing pericarditis with conspicuous neovascularization. Note that the fibrosa layer does not have very conspicuous vessels compared to the area of organizing fibrosis. (H&E stain and also Movat pentachrome stain).

The fibrous proliferation of the pericardium might predominantly show off only one of the serosal components or may involve both the parietal and also visceral pericardium. If recurring episodes the pericarditis occur (regardless that the etiology), the an answer of the pericardium is similar in producing new acute fibrinous and/or fibrino-hemorrhagic exudates which command to brand-new granulation tissue and much more neovascularization . Thus, chronic effusions may be associated with pericardial thickening. The neovascularization existing in various stages that the company of the pericardial effusion is the anatomic substrate that the late gadolinium enhancement on CMR imaging research studies of pericarditis. Calcific deposition may be focal distance or extensive and also likely represents an end-stage reaction to injury

. Since of the limited repertoire of tissue solution of the pericardium to noxious stimuli, the histologic functions of excised pericardium for constrictive pericarditis are typically nonspecific in regards to etiologic diagnosis and most often reflect a spectrum from arranging fibrinous pericarditis to organized fibrocalcific pericarditis.

Figure 12


Maturing organizing pericarditis. Loosened edematous granulation tissue becomes organized right into denser, more thickness fibrous tissue as the amount of extracellular matrix and also inflammation diminishes. Family member abundance that fibroblasts (fibroplasia) and newly-formed blood ship are indications of the task of the process. Compare to number 13. (H&E stain and also Movat pentachrome stain).

Figure 13


Organized pericarditis through recurrent insult. This micrographs display dense, mature majority of fibrous organization overlying the fibrosa layer of the pericardium. The neovascularization is less conspicuous 보다 in the earlier stages of company (Figures 11 and 12). In this example, there is boosted cellularity in the top strata that the pericardium towards the pericardial cavity. This innermost area in the direction of the pericardial cavity shows numerous fibroblast proliferation or fibroplasia, presented as dark blue infiltrates in upper left area of the images. In addition, there is likewise fibrin and also hemorrhage. This is a typical example the a recurrent process. (H&E stain and also Movat pentachrome stain).

Figure 14


Dense fibrous pericarditis there is no calcification. The parietal pericardium is thickened as result of the extr dense (yellow) fibrous organization that mirrors no fibroblasts, inflammation infiltrates or neovascularization. This to represent a quiescent phase but may currently be linked with pericardial constriction. (H&E stain and also Movat pentachrome stain).

If the cause of the pericardial effusion is major or metastatic malignant neoplasm, the malignant cells deserve to be conveniently seen during microscopic check

.

Figure 15


Metastatic lung adenocarcinoma. An arranging fibrinous exudate comprise metastatic tumor cells is present. Mild inflammatory infiltrate is detailed in the fibrosa class of the parietal pericardium. The inset reflects a swarm of metastatic tumor cells with large pleomorphic nuclei in a channel inside wall by level endothelial cells. (H&E stain and also Movat pentachrome stain).

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References

Ferrans VJ IT, Roberts WC. Anatomy of the pericardium. In: Reddy PS LD, Shaver JA, eds. Pericardial Disease. Brand-new York: crow Press; 1982:15-29.Levy-Ravetch M, Auh YH, Rubenstein WA, Whalen JP, Kazam E. CT of the pericardial recesses. AJR am J Roentgenol 1985;144:707-14.Ishihara T, Ferrans VJ, Jones M, Boyce SW, Kawanami O, Roberts WC. Histologic and also ultrastructural functions of normal human being parietal pericardium. Am J Cardiol 1980;46:744-53.Klein AL, Abbara S, Agler DA, et al. American society of Echocardiography clinical recommendations for multimodality cardiovascular imaging the patients through pericardial disease: endorsed by the culture for Cardiovascular Magnetic Resonance and culture of Cardiovascular Computed Tomography. J am Soc Echocardiogr 2013;26:965-1012.

Clinical Topics: Cardiac Surgery, Invasive Cardiovascular Angiography and also Intervention, Noninvasive Imaging, Pericardial Disease, Vascular Medicine, Aortic Surgery, Interventions and Imaging, Interventions and also Vascular medication

Keywords: Pericardium, Adenocarcinoma, Adipose Tissue, Aorta, Thoracic, Aortic Valve, Cardiac Imaging Techniques, Carotid Artery Thrombosis, Cicatrix, coloring Agents, Constriction, Endothelial Cells, Epithelial Cells, Extracellular Matrix, Fibrinolysis, heart Ventricles, Inflammation, Mast Cells, Microvilli, Myocardium, Pericardial Effusion, Pericardiectomy, Pericarditis, Constrictive, Phrenic Nerve, Pulmonary Artery, Pulmonary Veins, Sagittaria, Vena Cava, Inferior, Vena Cava, premium


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