Pericardium and extra-pericardic structures
From Echocardiography in ICU
The serous pericardium is a closed sac which consists of two layers: the visceral pericardium contiguous with the epicardium, and the parietal layer contiguous with the fibrous pericardium.
The visceral pericardium reflects near the origins of the great vessels:
-a few centimeters proximal to the junctions of the caval vessels with the right atrium
-posterior to the left atrium: oblique sinus of the pericardium. The left atrium is largely extrapericardial.
The pericardial cavity normally contains up to 20 ml of serous fluid.
On 2D images, the pericardium will appear as a bright white linear echo surrounding the heart.
In echo (2 dimensional or Mmode), pericardial effusion will appear as an anechoic (black) space delineated by the two hyperechoic (white) layers of the pericardium:
Remember that the left atrium is mainly extra-pericardial, as you can see on the parasternal long axis view. The visceral pericardium reflects at the oblique sinus: anterior to the descending aorta in parasternal long axis.Parasternal long axis view Subcostal 4 chamber view
The quantity of pericardial fluid is not clinically as important as the rate of constitution of the effusion. Thus, the hemodynamic tolerance is more important to assess than the amount of fluid.
Please go to tamponade chapter for the explanation of tamponade physiology and the 2D and Doppler criteria of tamponade.
It is possible to follow the evolution of a pericardial effusion by serially measuring its extension: measurement of the echo-free space between the two pericardial layers in diastole, in determined locations (anterior to the RV and posterior to the LV in PSL, against the LV lateral wall in apical 4 chamber for example).
Example: mild circumferential pericardial effusionParasternal long axis view. The pericardial effusion is located between the two layers of the pericardium, before the free wall of the right ventricular outflow tract and behind the posterior left ventricular wall (before the descending aorta). The high reflectivity of the parietal pericardium creates a mirror artifact appearing as a pseudo-effusion behind the parietal pericardium.
Parasternal short axis view. The pericardial effusion is located around the heart, mainly visible behind the inferior wall of the left ventricle.
Apical 4 chamber view. There is a pericardial effusion all around the heart: black echo delineated by the two white layers of the pericardium. Notice that there is no effusion around the left atrium. There is a small diastolic collapse of the right atrium, which is not specific of tamponade.
Subcostal 4 chamber view. There is a circumferential pericardial effusion, more abundant next to the right ventricle free wall: declive accumulation of fluid.
Please go to image library for more examples of pericardial effusion.
Fat has the same echo intensity than blood, it can be difficult to distinguish between a fat pad and a localized pericardial effusion.
-presence and size of fat pad is related to the presence of abdominal fat. Presence of a pericardial fat pad is unlikely in a cachectic patient.
-fat pads are usually localized, located only anteriorely to the right ventricle outflow tract and right ventricle free wall.
It can be difficult to diagnose pericardial versus pleural effusion. The most specific criterion is from parasternal long axis view, localization of the effusion compared to the descending aorta:
-pericardial effusion is located before the descending aorta, between the aorta and the left atrium. The pericardium reflects at the oblique sinus, so the pericardial effusion ends as a tail anterior to the descending aorta. The left atrium is mainly extra-pericardial.
-pleural effusion is located behind the descending aorta. The effusion will be more important in declive areas: behind the left atrium is the patient is lying on his left side.
Compared to pericardial effusion, pericardial thickening will not show the black area limited by the double layer of the pericardium
Pericardial tumors are rare. They are visualized as localized thickened pericardium, and are often accompanied by pericardial effusion.