Congenital absence of the pericardium is a rare anomaly which usually (67%) occurs on the left side. A complete form exists and is usually diagnosed incidentally. Normally, the aortopulmonary window is covered by pericardium and contains some fat. Left sided pericardial absence absence allows interposition of lung between the aorta and and the main segment of the pulmonary artery. The defect usually causes the heart to rotate to the left. Sometimes, the left atrial appendage can bulge through the defect. Associated congenital heart defects include atrial septal defect, patent ductus arteriosus, mitral valve stenosis, or tetralogy of Fallot.

Clinical:
Patients are often asymptomatic and the defect is found incidentally. The defect may cause herniation and strangulation of parts of the left heart. Symptoms can include syncope, chest pain or arrhythmias. Death may be caused by torsion of the great arteries, constriction of a coronary artery or herniation and/or incarceration of the left atrial appendage.

Imaging:
Chest x-ray shows left-sided displacement and posterior bulging of the heart. Herniation of the left atrial appendage resembles enlargement of the pulmonary artery. On echocardiography excessive cardiac motion and enlargement of the left atrial appendage may be seen. Definitive diagnosis can by obtained with MRI and CT. Interposition of lung between the aorta and left pulmonary artery is diagnostic.

Treatment:
The defect can be enlarged or patched surgically to alleviate herniation.