A separate chapter is devoted to the pericardium, beginning with congenital absence of pericardium and other congenital defects and cysts. Pericardial effusion is treated in some detail together with the related topics of tamponade and haemorrhage. There are sections on inflammation of the pericardium that also include discussion of post-pericardiotomy syndrome and of constrictive pericarditis. The chapter closes with a short discussion of pericardial tumours.
The anatomy of the normal pericardium has already been discussed in detail in Chapter 1 and its development in Chapter 3. The principal congenital abnormality of the pericardium is its partial absence. The pericardium has a very restricted repertoire of reactions to injury and these consist of haemorrhage, exudation of fluid, fibrin or inflammatory cells, or fibrous proliferation . The reactions are not mutually exclusive and may all develop sequentially or in parallel. Accumulation of fluid within the confined pericardial space may precipitate cardiac tamponade. Repair of injury by fibrosis may result in fibrous obliteration of the pericardial space and, if exuberant, may cause constrictive pericarditis, mimicking restrictive cardiomyopathy. Tumours of the pericardium are very rare.
11.2 Congenital Defects of the Pericardium
The parietal pericardium may be defective, the size of the defect varying from a small hole adjacent to the pulmonary trunk to near complete absence . The defect is more usually on the left side. The parietal pleura on the left side may also be absent with a common serous cavity on the left side (Figure 11.1). The defect, otherwise, is usually isolated, but 30–50% of cases of congenital absence of the pericardium are reported to have associated abnormalities . These defects include cardiac abnormalities, sequestered lung, diaphragmatic hernia and VATER association. On its own, absence of the pericardium is usually symptomless. Most defects are identified incidentally at the time of imaging, surgery or post-mortem. Cardiac MR is the preferred imaging method for demonstration of absent pericardium. Herniation of atrial appendages  or ventricular myocardium through the defect with constriction and infarction have been reported, including in the fetus, and intrauterine fetal death has been ascribed to this condition . A case is also recorded of defect in the central part of the diaphragmatic pericardium with herniation of liver into the pericardium in association with a diaphragmatic hernia .
Defects in the pericardium are frequently associated with defects in the sternum (Figure 11.2) . A defect in the pericardium is a defining feature of ectopia cordis, as in pentalogy of Cantrell. The pericardium may, of course, be removed surgically for the treatment of constrictive pericarditis.
11.3 Cysts and Diverticula
Pericardial cysts are thin-walled mesothelial cysts that may be unilocular or multilocular and are usually situated in the cardio-phrenic angles and may be up to several centimetres in diameter . They are lined by mesothelium and have a thin, fibrous wall that may show mild chronic inflammation (Figure 11.3). They contain clear fluid. They are usually incidental findings and require no treatment . Pericardial diverticula are closely related to pericardial cysts with the crucial difference that they show communication with the pericardial cavity while pericardial cysts do not .
11.5 Effusions and Tamponade
A small amount of fluid is a feature of the normal pericardial sac. The fluid is formed as an ultrafiltrate of plasma . The pericardial reserve volume is small and quickly becomes overwhelmed with rapid accumulation of fluid. Even small, or relatively small, effusions may cause tamponade – compromise of ventricular filling and cardiac output as a result of accumulation of fluid in the pericardial space. Fluid that accumulates more slowly may well lead to accommodation and expansion of the pericardium without development of tamponade .
Causes of increased pericardial fluid accumulation are listed in Table 11.1.
|Hydrostatic – heart failure and hydrops|
|Inflammatory – infective, autoimmune|
|Metabolic – uraemia|
In the uncomplicated case the fluid is serous and may contain fibrin and other proteins. Infective cases may show a cellular infiltrate, either lymphocytic or neutrophilic. Neoplasms and tuberculosis typically also have blood in the effusion.
Iatrogenic effusions may develop following the use of central venous catheters with perforation of the intrapericardial parts of the caval veins or right atrial wall. Perforation of the wall is not necessary for fluid to accumulate in the pericardial space . In premature infants it is sufficient for the tip of the catheter merely to press against the atrial wall; the atrial wall is extremely thin and fluid exudes through it into the pericardial cavity, on occasion causing fatal tamponade (Figure 11.4) [15–18].
(A) The opened right atrium shows yellow lipid plaques in the atrial wall.
(B) A section of the right atrial wall shows numerous extracellular large lipid droplets (black) between the muscle fibres (Tissue post-fixed in osmium tetroxide, H&E).
11.6 Epicardial Haemorrhage
Petechial haemorrhages in the epicardium are frequent findings of sudden infant death  and, indeed, in sudden death at any age (Figure 11.5). They may be associated with imposed upper airway obstruction and occur in some cases of drowning . Petechial haemorrhage or ecchymosis are frequent findings with systemic sepsis, and are universal after cardiac surgery. Epicardial haemorrhage is also a feature of coagulation disorders. The epicardial haemorrhages tend to be concentrated along the epicardial surface of the epicardial coronary arteries. They also occur over the adventitia of the great arteries. A small haematoma over the adventitia of the arterial duct is a common finding in perinatal asphyxia . Epicardial haemorrhages also occur with underlying pericarditis and myocarditis and are also associated with underlying myocardial infarction.
Accumulation of blood in the pericardial sac may be caused by penetrating injury to the heart , rupture of an epicardial vessel (because of disease or by medical intravascular intervention) [23,24], blunt trauma with myocardial contusion, systemic coagulopathy  or neoplasia. Rupture of congenital diverticulum of the left ventricle has also been described (Figure 11.6) [26–29]. Needling of the heart during attempted resuscitation or for obtaining blood immediately post-mortem may result in a moderate quantity of liquid blood in the pericardial sac (Figure 11.7). It is usually not difficult to distinguish from haemopericardium with tamponade. Small blood clots may also be present in the pericardial cavity where feticide has been undertaken by intracardiac injection of potassium chloride.
Figure 11.7 Blood in pericardium following post-mortem needling. Seven-day-old male infant who died suddenly and unexpectedly. As part of the resuscitation procedure, there was cardiac puncture. At least three puncture marks are evident over the epicardium. There is unclotted blood in the pericardial sac attributable to the procedure. The amount of blood is insufficient to be mistaken for haemopericardium with cardiac tamponade.
Pneumopericardium refers to air in the pericardial cavity and may be associated with pneumothorax or pneumomediastinum . The air is introduced either directly iatrogenically or via the oesophagus or airways. It has been reported with foreign bodies that perforate the oesophagus leading to communication between the oesophageal lumen and the pericardial cavity (Figure 11.8) .
(A) shows the air distending the pericardial cavity. On removal of the sternum and thymus, the bulging pericardium can be seen
Inflammation of the pericardium – pericarditis – may be classified according to its duration (acute, subacute, chronic) or according to the initiating agent: infective (bacterial, viral, fungal); autoimmune; iatrogenic; traumatic; neoplastic; metabolic.
Acute pericarditis usually begins suddenly with retrosternal chest pain, usually with pyrexia, and may last up to six weeks. Typically, there is a pericardial friction rub. There may be a small effusion and a small number of cases are complicated by the development of tamponade. Acute infective pericarditis is usually viral in origin. Recurrent pericarditis may be a problem in a small number of cases . Most cases of recurrent effusion follow viral or idiopathic pericarditis, and only about 10% of cases have preceding post-pericardiotomy syndrome .
11.9.1 Acute Purulent Pericarditis
This condition nowadays is uncommon. The mean age of occurrence is around three years. Staphylococcus aureus is the most common bacterial cause , but Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis and group A streptococcus also cause it. Infection may be primary but is usually secondary to pneumonia, osteomyelitis or cellulitis. The presentation is that of an acute illness with fever. The pericardial exudate is initially serous and or fibrinous (Figure 11.9) and later becomes purulent (Figure 11.10). The amount of fluid may be sufficient to cause cardiac tamponade. The disease heals with fibrous obliteration of the pericardial cavity. Constrictive pericarditis is an uncommon sequela . If submitted for pathology, the excised pericardium is thickened and fibrous. It may show evidence of acute inflammation with fibrinous exudates that show evidence of organisation with depth.
(A) A case from the Great Ormond Street Hospital archives from 1872. A patient of Dr Charles West (founder of the hospital). A girl aged 10 years who had acute rheumatic fever one year before death. A friction rub was heard a fortnight before death. At post-mortem the heart is described as enlarged with ventricular dilatation and normal valves, but with pericarditis. The heart is drawn with the pericardium partly open to demonstrate a haemorrhagic, acute pericarditis with a typical “bread and butter” appearance.
(B) Pericardium from a case of a patient who died a week following cardiac surgery. The parietal pericardium shows haemorrhage and a thick layer of golden-brown fibrin with a “bread and butter” appearance.
Figure 11.10 Acute bacterial pericarditis. The causative organism in this case was meningococcus and macroscopically the pericardial cavity contained pus. Histologically there is a neutrophilic infiltrate in the epicardium.