Compromise of the vascular supply to the pleuropericardial membrane during embryological development is associated with congenital defects in the pericardium. Pericardial defects are rare and usually asymptomatic. The defects vary in size from small communications between the pleural and pericardial cavities to complete (bilateral) absence of the pericardium. The most common form is complete absence of the left pericardium, with preservation of the pericardium on the right. Bilateral and isolated right-sided lesions are very rare. Absence of the pericardium is rarely associated with congenital anomalies of the heart and lungs, including atrial septal defect, tetralogy of Fallot, patent ductus arteriosus, bronchogenic cysts and pulmonary sequestration. Pericardial defects are frequently associated with large defects in the parietal pleura, through which the left lung can herniate and surround the intrapericardial vascular structures.

Complete absence of the pericardium is usually asymptomatic, whereas partial or localised absence of the pericardium may be complicated by herniation and entrapment of a cardiac chamber; in particular, the left atrial appendage in left-sided defects.

Chest radiograph findings are frequently subtle and non-specific. In complete absence of the left pericardium they include displacement of the heart into the left chest and interposition of lung between the aorta and pulmonary artery (as well as between the left hemidiaphragm and cardiac silhouette). Both the medial and lateral borders of the main pulmonary artery may be visualised more clearly, caused by absence of the anterior pericardial reflection between the aorta and the pulmonary artery. Because of leftward displacement and rotation, the right cardiac border may not be seen. In partial pericardial defects, varying degrees of prominence of the pulmonary artery and/or left atrial appendage may be seen, while the heart retains its normal position in the thorax. CT and MRI can depict herniation of cardiac structure through the defect. Discontinuation of the pericardial line can occasionally be detected in the partial form. The most reliable signs of complete absence of the left pericardium are interposition of lung between the aorta and main pulmonary artery, in the aortopulmonary window, and a rotation of the cardiac axis to the left side (rather like a right anterior oblique view).

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