Normal pericardial anatomy
Pericardium consists of two layers surrounding the heart:
- visceral pericardium - serous surface which is contiguous with the epicardium, and
- parietal pericardium - thin fibrous sac that is closely to the pleural surfaces laterally and with diaphragm inferiorly.
The pericardium surrounds all four chambers of the heart and extends 1 to 2 cm up the great vessels, and also around the pulmonary veins. Between pericardial layers there is a very small amount of fluid, 5-10ml.
Diagnosis of pericardial effusion
Pericardial effusion is an increase amount of fluid between two pericardial layers, as a result of a different pathological conditions affecting the pericardium:
- Inflammatory diseases: infective etiology (viral, bacterial, fungal), associated with autoimmune disorders, post-myocardial infarction, post cardiac surgery, associated with myocarditis, post-chemotherapy and post- radiation therapy
- Malignancy: direct tumor involvement, metastatic, due to lymphatic obstruction,
- Associated with metabolic disorders: uremic status, hypothyroidism, cirrhosis
- Traumatic diseases: chest trauma, aortic dissection, rupture of the ventricular free wall.
Echocardiography characteristics of pericardial effusion
Echocardiography is a technique of choice for the diagnosis of pericardial effusion. Pericardial effusion can be evaluated by M-mode, two-dimensional (2D) and three-dimensional (3D) echocardiography. With echocardiography it is possible to discover a very small amount of pericardial effusion, big pericardial effusion, cardiac tamponade, to guide appropriate treatment and also to guide pericardiocentesis in case of cardiac tamponade. On M-mode echocardiography and also in 2D echocardiography pericardial effusion appears as an echo-free space (echo lucenet space) between two pericardial layers, in localized areas, or around the heart. The first choice echocardiographic modality for detection and evaluation of pericardial effusion is 2D echocardiography. The size of echo-free space depends on the amount of fluid in the pericardial sac. Normally, there may be very small amount of fluid (5-10ml) between the two layers in the posterior atrioventricular junction on parasternal long axis view (PLAX), increasing the echo free space in systole when echo-free space becomes bigger and can be clearly visualized. When the effusion is bigger, the echo free space extends circumferentially around the heart.
Differentiation between pericardial effusion and pericardial fat
Isolated anterior echo (under the right ventricle) free space may be due to mediastinal fat or fibrosis.This condition doesn’t have any pathological consequences, and it can be differentiated from effusion because of its higher density.
Differentiation between pericardial and pleural effusion
Echocardiography allows distinguishing pleural from pericardial effusion. Echo free space anteriorly from descending thoracic aorta in PLAX view is pericardial effusion, and if there is free echo space posteriorly from descending aorta it is usually pleural effusion.
Making all views (parasternal long and short axis, apical, sub-costal), 2D-echocardiograpy will allow the localization of the effusion, especially when localized, with the presence of fibrin which creates adhesion between pericardial layers
|Image No.5. 2D echocardiography in patient with acute (tuberculosis) pericarditis, with fibrin strands in a large pericardial effusion|
Three dimensional echocardiography potentially provides an accurate technique for determining pericardial effusion and fluid distribution, but still, there are no enough clinical data for determining precise pericardial volumes and its hemodynamic effects.
Quantification of pericardial effusion and hemodynamic consequences
There are no accurate quantification of absolute volume of pericardial fluid, but many laboratory defined pericardial effusion as small if a circumferential echo-free space is smaller than 0,5 cm(<100ml), moderate effusion if echo-free space is about 1 cm (100-500ml), and large if echo free space is more than 1 cm (>500ml).M-mode measurements of echo-free space allows semi quantitative assessment of fluid amount.
The physiological consequences of pericardial effusion depends on the following factors:
- Amount of effusion.
- Rate of fluid accumulation. A slowly expanding pericardial effusion can become large (>1000ml) with little increase in pericardial pressure, and without important hemodynamic consequences. But, rapid accumulation of even a small volume of fluid (50-100ml) can lead to a marked increase in intrapericardial pressure, with subsequent compression of cardiac chambers.
- Otto M.C.:Textbook of Clinical Echocardiography, Sunders Elsevier, Fourth Edition, 2009(242-258)
- Galiuto L., Badano L., Fox K. and Siciari R.: EAE Textbook of Echocardiography, Oxford University press, 2011(345-355)
- Amstrong W.F. and Ryan T.: Feigenbaum’s Echocardiography; Lippincott Williams&Wilkins, Seventh Edition, 2010( 241-261)