The pericardium serves as the external protective layer of the heart, providing a barrier to trauma, malignancy, inflammation, and infection. In addition, a thin layer of fluid within the pericardial space lubricates the heart, thereby reducing the energy expenditure and shear stress encountered with cardiac motion. A basic understanding of the anatomy and physiology of the pericardium and pericardial space is necessary to recognize and properly diagnose disease processes affecting this important structure.
The pericardium is a fibrous lining surrounding the heart, consisting of 2 layers: the parietal (outer) layer and visceral (inner) layer. The visceral layer comes into direct contact with the epicardial surface, whereas the parietal layer contains collagenous fibers and serves as an outer protective layer. The pericardium completely envelops the atria and ventricles and terminates just superior to the semilunar valves; it also extends to surround the vena cavae and pulmonary veins near their respective entrances into the heart. Pericardial fluid is a serous, low-viscosity fluid found between the visceral pericardium and the epicardial surface of the heart. In children, approximately 10 mL of fluid is normally found within the pericardial space, with larger volumes (20–30 mL) encountered in adults.
Pericardial effusion is defined as the excess accumulation of fluid within the pericardial space. It is frequently, but not universally, a manifestation of pericardial inflammation. The most common cause of pericardial effusion in children is pericarditis, which in turn has a variety of etiologies. The causes of pericardial effusion and pericarditis can broadly be categorized into infectious, inflammatory/autoimmune, traumatic, toxic, and idiopathic (Table 485-1). Infectious etiologies are the most common, most often in conjunction with viral infections associated with pericardial inflammation or as part of a broader cardiac inflammatory process (ie, myocarditis). Bacterial seeding of the pericardial space occurs less frequently; however, tuberculosis is a common cause of pericarditis and pericardial effusion in developing countries. Many autoimmune processes may have an associated pericarditis, such as systemic lupus erythematosus, in which pericardial effusion may be a presenting sign of the disease. Trauma is a common cause of pericardial effusion, via contusion of the heart or direct perforation of the pericardium by penetrating thoracic injury. Several environmental toxins and drugs can be associated with pericardial effusion; in pediatric practice, this is often associated with chemotherapeutic agents or chest irradiation in the setting of treatment for malignancy. Finally, interruption or obstruction of the lymphatic drainage in the chest, usually encountered in the postoperative setting after cardiac surgery in children, may manifest as pericardial effusion with a high triglyceride content (chylopericardium).
TABLE 485-1ETIOLOGIES OF PERICARDIAL EFFUSION AND PERICARDITIS ||Download (.pdf) TABLE 485-1ETIOLOGIES OF PERICARDIAL EFFUSION AND PERICARDITIS
|Etiology ||Examples/Comments |
|Idiopathic ||Often viral |