Congenital absence of the pericardium and its mimics

Abstract

Congenital absence of the pericardium is a rare entity, with less than 400 cases reported in the literature. Pericardial absence is typically left sided, which results in herniation of the great vessels or portions of the heart. Patients may be asymptomatic, typical for complete defects, or can present with various degrees of chest pain in the setting of partial absence and strangulation. The finding may be isolated or associated with complex heart disease. We present a number of cases of pericardial absence that show isolated right- and left-sided defects, as well as entities in the differential diagnosis. Early recognition may decrease morbidity and mortality, resulting from delay in proper treatment.

Introduction

Congenital absence of the pericardium is a rare condition that is most often incidentally discovered at cardiothoracic imaging. Dramatic presentations, such as atypical nonexertional chest pain or cardiac strangulation that requires prompt surgical management, are fortunately uncommon. The entity can be diagnosed by chest radiography, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound scanning, underscoring the importance of recognizing the imaging findings.

The pericardium is formed by an outer fibrous layer and an inner serous layer of mesothelial cells. During embryogenesis, the heart grows into and invaginates the inner serous pericardium, resulting in visceral and parietal layers that are in continuity. The parietal layer lines the outer fibrous layer, whereas the visceral layer lines the epicardial surface of the heart. A fluid-filled potential space between the visceral and parietal layers creates the pericardial cavity. The visceral layer can be up to 1 mm thick, thickening slightly over the right ventricle and thinning over the left ventricle. It encloses the heart, proximal ascending aorta, pulmonary arterial trunk, and portions of left pulmonary veins. It serves to fix the heart in position, reduce friction by pericardial fluid, and isolate the heart from adjacent pathologic processes.¹

Embryologically, the pericardial sac is formed from the embryonic coelom. Within the coelom, the pericardial sac is separated from the peritoneal cavity by the transverse septum and from the pleural by the right and left pleuropericardial folds. Pericardial absence is thought to be the result of malformation of the transverse septum or pleuropericardial folds, possibly because of a compromise of vascular supply (Fig. 1).²

Pericardial absence was first suggested by Italian anatomist and surgeon, M. Realdus Columbus, in 1559³ with a definitive example in 1793 by Baille.⁴ Ellis et al² in 1959 detailed 99 cases, which substantially improved awareness of this rare anomaly with a reported prevalence of 0.002% to 0.004%.⁵ Up to 400 cases have been recorded in the literature to date.⁶

Ellis et al² identified 6 categories of pericardial defects: right-sided (partial or complete), left-sided (partial or complete), total absence, and diaphragmatic defects. Thirty percent to 50% of defects are associated with other cardiopulmonary anomalies such as patent ductus arteriosum, Tetralogy of Fallot, atrial septal defect, sequestration, and bronchogenic cysts.6, 7

Left-sided defects are the most commonly reported, involving up to 70%–80% of cases of pericardial defects.8, 9 Complete left pericardial absence is 3:1 times more common than partial left-sided absence.⁸ The congenital cause is thought to be premature atrophy of the left common cardinal vein (duct of Cuvier) which supplies the left pleuropericardial membrane, resulting in pericardial or diaphragmatic defects (Fig. 1). Patients with complete absence of the left pericardium are typically asymptomatic. Partial absence can cause no symptoms or can result in chest pain, dyspnea, and syncope related to herniation and strangulation of cardiac structures through the defect. Rarely, fatal incarceration of the left ventricle can occur.⁶ Herniation of the left atrial appendage has been frequently reported.¹⁰ Torsion of great vessels, coronary compression on the pericardial rim, and ventricular herniation are other potential complications.⁷ Distortion of ventricular geometry will elongate the chordae of the anterior leaflet of tricuspid, contributing to regurgitation, a common finding in large partial or total left-sided absence.⁷ Electrocardiogram findings usually show right-axis deviation, right bundle branch block, and poor R wave progression.¹¹

CT or MRI is the mainstay for diagnosis, which usually can show the pericardial defect with cardiac herniation. Cardiac MRI may miss absence in up to 10% of patients because of decreased spatial resolution compared with CT, although this is likely less common with current MRI techniques.¹² Multiplanar reformats and interactive 3-dimensional rendering are helpful for detecting subtle defects. Complete absence of the left pericardium (Fig. 2) at CT can be recognized by the typical abnormal position of the heart, which is completely herniated into the left hemithorax. Lung within the preaortic recess, interposed between the aorta and pulmonary artery anteriorly, is a characteristic finding.

Echocardiography can detect pericardial absence with findings to include marked lateral displacement of the apical, parasternal long- and short-axis windows, cardiac hypermobility with swinging motion, and abnormal septal motion on M-mode.¹³

Patients with partial absence of the left pericardium (Fig. 3) will have focal bulging of left-sided cardiac structures through the defect. Careful evaluation of the coronary arteries should be performed to exclude compression by the pericardial rim. Direct visualization of the edges of the normal pericardium is usually possible because of the high spatial resolution of CT.

Right-sided pericardial absence is much rarer than left-sided defects and has been reported in 4%–17% of cases.8, 9 Cause is similar to left-sided defects with premature closure of the right common cardinal vein, resulting in maldevelopment of the right pleuropericardial fold. Partial and complete defects have been reported.8, 9 Patients may have similar complaints of atypical chest pain. Inadvertent right-sided postsurgical defects after pneumonectomy are more common than congenital absence.¹⁴ Such defects, however small, could allow the heart to eventually protrude and undergo organoaxial volvulus.¹⁴ If not immediately detected, mortality approaches 60%.¹⁴ It is not known whether right-sided total absence can undergo volvulus. On cardiac CT, right-sided defects can be identified by focal bulging of portions of the right ventricle or right atrium beyond the confines of the pericardium (Fig. 4).

Total absence of the right and left pericardium is the rarest of all defects, seen in only 9% of cases reported in the literature. It is thought to occur secondary to premature atrophy of both cardial veins. Severe congenital anomalies have been associated such as incomplete closure of the chest wall, ectopia cordis, and omphalocele.⁶ Patients are asymptomatic or have atypical precordial pain of unclear cause.⁶ Cardiac herniation and strangulation do not occur; however, increased tension or strain because of cardiac hypermobility is thought to contribute to pain.⁶ Cases are usually imaged and diagnosed late or found postmortem.8, 9 On CT or MRI, complete absence is obvious, because there would be complete lack of pericardial fat and no border between the heart and lungs.