Congenital absence of the right pericardium: embryology and imaging

Abstract

Though congenital pericardial absence is often asymptomatic, complications can be life threatening. To date, few short case reports, primarily from the pre-CT and MR era, describe congenital absence of the right pericardium. We present a more comprehensive discussion of the embryologic derangements causing such defects and offer an up-to-date review of characteristic radiologic findings. Recognition of characteristic imaging findings of congenital pericardial absence is crucial in guiding diagnosis and management.

Keywords: Absence; congenital; embryology; imaging; pericardium; right pericardium.

Figure 1

Illustration of normal pericardial development from the fourth to sixth week of gestation. (a) At 4 weeks of gestation, the laterally positioned pleuropericardial folds are developed. (b) During the 5^th week of gestation, the pleuropericardial folds grow toward the midline while the root of each fold migrates ventrally. (c) At the end of the 5^th week, the pleuropericardial folds fuse, partitioning the thoracic cavity into a pericardial cavity and two partially formed pleural cavities. Note that union of the pleuropericardial folds and the root of the lungs also occurs during this time. (d) The lungs continue to extend anteriorly to the front of the heart.

Figure 2

77-year-old man with dyspnea. (a) PA chest radiograph reveals a slightly more horizontal ascending aorta due to partial herniation of the ascending thoracic aorta through a pericardial defect (arrow). (b) Lateral radiograph demonstrates abnormal lucency between the ascending aorta and the right pulmonary artery (arrows) resulting in an unusually dense-appearing and prominent right pulmonary artery (RPA). (c) Transaxial CT imaging with lung window confirms this lucency which represents the lung interposed between the aorta and the pulmonary artery through a partially absent right pericardium (arrow), producing the characteristic “retroaortic air” sign. (d) Coronal reformatted images with soft tissue and lung windows demonstrate air insinuating beneath both the aorta and the pulmonary artery (arrows). The right lung resembles the head and body of an open-mouthed dolphin. (e) Right pericardial absence has been associated with other congenital cardiac defects. Echocardiography demonstrates a secundum type atrial septal defect with left to right shunting (arrow).

Figure 3

26-year-old man evaluated following an environmental exposure. (a) Scout view demonstrates a bulging right heart border. (b) Transaxial and (c) Coronal CT images confirm partial right pericardial absence. Part of the right atrial appendage extends laterally through the partial defect (arrow).