History
    In a 50-year-old man, an abnormality was incidentally found on chest radiograph.

Findings
    Chest radiograph shows cardiomegaly, leftward displacement of the heart shadow, flattened left cardiac silhouette, and unusually prominent main pulmonary artery and a radiolucent cleft between aortic knob and main pulmonary artery. Chest CT scans show inability to identify the fibrous layer of parietal pericardium along the left cardiac border, direct contact of lung and heart structures, and interposition of lung parenchyma between the ascending aorta and pulmonary trunk.

Discussion
    Congenital absence of pericardium is relatively rare; fewer than 400 cases have been reported. The most widely accepted theory as to its pathogenesis suggests that premature atrophy of the left duct of Cuvier (common cardinal vein) leads to loss of blood supply to the left pleuropericardial membrane which, in adult life, forms the left pericardium. The right duct of Cuvier normally persists as the SVC, assuring adequate blood supply to the developing right pericardium. On the left side, complete absence of the pericardium is more common than a partial defect. Right-sided lesions and bilateral complete absence of the pericardium are extremely rare. Pericardial defects were associated with congenital anomaly of the heart, lungs, chest wall, and diaphragm, including such as patent ductus arteriosus, atrial septal defect, tetralogy of Fallot, mitral stenosis, bronchogenic cyst, pulmonary sequestration, pectus excavatum, and diaphragmatic hernia. Most patients were asymptomatic. Occasionally, acute symptoms may occur when the pericardial deficiency is partial; herniation of the heart or its appendages through the defect may lead to dysrhythmia, angina, syncope, and, rarely, sudden death. Complete absence of the parietal pericardium is a benign quite compatible with a normal life span. Absence of the left pericardium may be characterized on chest roentgenograms by 1) leftward displacement of the heart and aortic knob, 2) a flattened left cardiac silhouette, and 3) a long prominent pulmonary artery. The CT findings are 1) inability to identify the fibrous layer of parietal pericardium along the left cardiac border, 2) change in the axis of the main pulmonary artery, which bulges toward the left lung, 3) direct contact of lung and heart structures, and 4) interposition of lung between the great vessels.

References
1. van Son JAM, Danielson GK, Schaff HV, Mullany CJ, Julsrud PR, Breen JF. Congenital partial and complete absence of the pericardium. Mayo Clin Proc 1993; 68: 743-747
2. Fraser RG, Pare JAP, et al. Diagnosis of diseases of the chest. 3rd ed. W.B. Saunders 1991;761-765
3. Balm RS, MacDonald IL, Wise DJ, Lenkel SC. Computed tomography of absence left pericardium. Radiology 1980;135: 127-128
4. Moncada R, Baker M, Salinas M et al. Diagnostic role of computed tomography in pericardial heart disease: congenital defects, thickening, neoplasms, and effusions. Am Heart J 1982; 103:263-282