Pericardial lesions typically are associated with a pathologic process elsewhere in the heart or surrounding structures, or are secondary to a systemic disorder. Pericardial disorders include effusions and inflammatory conditions, sometimes resulting in fibrous constriction.
Normally, the pericardial sac contains less than 50 cc of thin, clear, straw-colored fluid. Under various circumstances, the pericardial sac may be distended by accumulations of serous fluid (pericardial effusion), blood (hemopericardium), or pus (purulent pericarditis).
Pericardial effusions and their causes include the following:
Serous: Congestive heart failure, hypoalbuminemia of any cause
Serosanguineous: Blunt chest trauma, malignancy, ruptured MI, or aortic dissection
Chylous: Mediastinal lymphatic obstruction
With long-standing cardiac enlargement or with slowly accumulating fluid, the pericardium has time to dilate. This permits chronic pericardial effusions to become quite large without interfering with cardiac function. Thus, with chronic effusions of less than 500 cc in volume, the only clinical significance is a characteristic globular enlargement of the heart shadow on chest radiograph. In contrast, rapidly developing fluid collections of as little as 200 to 300 cc (e.g., due to hemopericardium caused by a ruptured MI or aortic dissection) can produce clinically devastating compression of the thin-walled atria and venae cavae, or the ventricles themselves; cardiac filling is thereby restricted, producing potentially fatal cardiac tamponade.
Primary pericarditis is uncommon. It is typically due to viral infection (often with concurrent myocarditis), http://ebooksmedicine.net although bacteria, fungi, or parasites may also be involved. In most cases, pericarditis is secondary to acute MI or cardiac surgery (so-called “Dressler’s syndrome”), radiation to the mediastinum, or processes involving other thoracic structures (e.g., pneumonia or pleuritis). Uremia is the most common systemic disorder associated with pericarditis. Less common secondary causes include rheumatic fever, systemic lupus erythematosus, and metastatic malignancies. Pericarditis can (1) cause immediate hemodynamic complications if it elicits a large effusion (resulting in cardiac tamponade), (2) resolve without significant sequelae, or 3) progress to a chronic fibrosing process.
MORPHOLOGYInpatientswithacuteviralpericarditisoruremia, theexudatetypicallyisfibrinous,impartinganirregular,shaggyappearancetothepericardialsurface(so-called“breadandbutter”pericarditis).Inacutebacterialpericarditis, theexudateisfibrinopurulent(suppurative),oftenwithareasoffrankpus(
Fig.11.29 );tuberculouspericarditiscanexhibitareasofcaseation.Pericarditisduetomalignancyoftenisassociatedwithanexuberant,shaggyfibrinousexudateandabloodyeffusion;metastasescanbegrosslyevidentasirregularexcrescencesormaybegrosslyinapparent,especiallyinthecaseofleukemia.Inmostcases,acutefibrinousorfibrinopurulentpericarditisresolveswithoutanysequelae.Withextensivesuppurationorcaseation,however,healingcanresultinfibrosis(chronicpericarditis).
Chronic pericarditis maybeassociatedwithdelicateadhesionsordense,fibroticscarsthatobliteratethepericardialspace.Inextremecases,theheartissocompletelyencasedbydensefibrosisthatitcannotexpandnormallyduringdiastole—resultingintheconditionknownasconstrictive pericarditis.