The pericardium plays an important role in optimizing cardiac motion and chamber pressures and serves as a barrier to pathology. In addition to pericardial anatomy and function, this review article covers a variety of pericardial conditions, with mention of potential pitfalls encountered during interpretation of diagnostic imaging. Normal and abnormal appearance of pericardium on CT and MR imaging is emphasized, including dynamic imaging correlates of pericardial pathophysiology. 1. Introduction More than just a tissue, the pericardium is an organ with specific functions and an embryologic origin distinct from the heart. Whereas the heart is derived from splanchnic mesoderm, the pericardium is derived from somatic mesoderm [1–3]. Long-recognized functions of the pericardium include anchoring the heart in the mediastinum, minimizing the friction of cardiac motion, and serving as a barrier from infection and neoplasm [4]. More recently, the pericardium has been described as an intracardiac pressure modulator, limiting acute distention of any one cardiac chamber and preserving myofibril function by preventing sarcomere overlengthening [5, 6]. As with other organs, the pericardium is subject to various disease processes, include inflammatory, infectious, fibrotic, metabolic, and neoplastic. Imaging of these processes has advanced significantly in the past decade, with the refinement of multidetector CT and high-field-strength MRI. CT and MR permit visualization of the entire pericardium by virtue of three-dimensional acquisition and multiplanar imaging, respectively, and provide better assessment of surrounding structures than the prior standard of echocardiography [7]. In addition, MR techniques allow the evaluation of pericardial function, particularly as it relates to the problem of differentiating myocardial restriction from pericardial constriction, the latter being surgically treatable [8]. 2. Anatomic Considerations As with the other serosal surfaces of the body, the pericardium has parietal and visceral layers. The parietal layer of pericardium is several times thicker than the visceral pericardium [4]. The normal combined pericardial thickness is 2？mm or less (Figures 1(a) and 1(b)). 2-3？mm is considered equivocal, whereas 4？mm thickness at any point is abnormal [9, 10]. The normal pericardial stabilizers include the great vessel reflections and several ligaments (pericardial-sternal, pericardial-vertebral, and pericardial-diaphragmatic) (Figure 1(c)) [4]. Figure 1: Normal pericardium. (a) Gated contrast-enhanced axial CT and (b) axial double
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