CT and MRI are equally considered the preferred imaging methods for morphological assessment of the pericardial sac and the pericardium. Higher spatial resolution of the CT scan allows improve visualization of the normal pericardium. As a result normal pericardium appears thinner using CT compared with MRI. This is not surprising knowing that most cardiac CT protocols consist of 0.5–1 mm slices, while in cardiac MRI most routine sequences involve 5–8 mm slices. Generally a pericardium thicker than 3 mm is considered abnormal [8]. On the other hand, MRI is the modality of choice for functional evaluation of heart and to differentiate constrictive pericarditis from restrictive cardiomyopathy [9, 10].

Although evaluation of pericardium and pericardial fluid is possible on non-gated CT scans, ECG-gated methods are usually preferred particularly when detailed evaluation of the pathologies is required. For example, pericardial cysts can be characterized in most non-gated CT scans of the heart, while detection of partial absence of pericardium may be optimally performed using gated CT.

Morphological study of the pericardium with MRI can be best obtained with black-blood fast spin-echo (BB-FSA) sequence. Five millimeters axial, coronal, and sagittal images can be obtained to cover the entire pericardium. In this sequence, double inversion recovery (IR) pulses are used to null the blood signal. To remove high signal intensity of fat, a third IR pulse can be included in the pulse sequence, the so-called triple IR. It is important to know that BB-FSE sequence is not designed to be a T1-weighted sequence. As a matter of fact in most applications it is proton density or T2 weighted; as a result the fluid signal may appear bright not dark (Fig. 29.3). To make it T1 weighted, echo time should be lowered. T2-weighted triple IR sequence has the advantage of demonstration of pericardial edema in cases with inflammatory pericarditis. IR pulse can be adjusted to null pericardial fluid signal (Fig. 29.3). The second most important sequence in the evaluation anatomy as well as regional and global myocardial function with MRI is bright-blood balanced steady-state free precession (b-SSFP). This sequence is mainly T2 weighted and the signal of blood, fat, and pericardial fluid appears bright. Both non-ECG-gated and cine versions of b-SSFP are helpful for evaluation of the pericardium. Although advanced sequences such as tagged MRI and free-breathing real-time SSFP may be better choices for complete analysis of constrictive physiology and to study physiologic events such as ventricular coupling [9], by careful reviewing of routine cine images, it is simply possible to diagnose constrictive pericarditis in most cases (Fig. 29.4). Cine viewing allows better differentiation of motion between the rigid constricted pericardium and the underlying moving myocardium.

The pericardial and pleural cavities and diaphragm are so closely related in their development.

The pericardial cavity represents a portion of the original right and left intraembryonic coeloms, and its lining derives from both the parietal (somatic) and the visceral (splanchnic) layers of the mesoderm. Later, the right and left side coeloms fuse, and folds of tissue divide it into separate cavities. The pericardial cavity separates from the peritoneal cavity by the formation of the septum transversum and from the pleura by the growth of the left and right pleuropericardial folds which are linked to the evolution of the incoming cardinal veins of the sinus venosus. Major part of pericardium is derived from the parietal mesoderm which is also primarily the wall of the pericardial cavity. A small dorsal portion is probably derived from the mesoderm at the root of the dorsal mesocardium. The septum transversum (a derivative of the visceral layer) forms the caudal wall of the pericardial cavity. Congenital pericardial defects result from incomplete development of either the septum transversum or the pleuropericardial folds. Premature atrophy of the left common cardinal vein (duct of Cuvier) compromises the blood supply to the left pleuropericardial fold and accounts for absence of the left pericardium [11, 12]. If abnormality occurs in early stages of embryonic development, the pleural serosa and diaphragm may also be affected.

Congenital absence of pericardium has been described in literature for more than four centuries and mainly discovered inadvertently during postmortem and thoracotomy procedures [11–14]. Radiologically, it was undiscovered until 1959 when Ellis et al. reported the first case by x-ray [15]. Subsequently, increasing numbers of cases have been reported. Van Son et al. presented the Mayo Clinic experience on congenital absence of the pericardium (15 cases in 34,000 surgeries) [16]. In all, the diagnosis was made in the operating room.

Congenital absence of pericardium occurs on a spectrum from complete absence of the left, right, or both sides of the pericardium to small regional defects. Partial defect may involve part of the left, right, or diaphragmatic pericardium. Approximately 30 % of patients with pericardial agenesis have additional anomalies such as atrial septal defect, bicuspid aortic valve, mitral stenosis, tricuspid insufficiency, patent ductus arteriosus, tetralogy of Fallot, pulmonary sequestration, bronchogenic cyst, and congenital diaphragmatic hernia [14–19]. Pectus excavatum is a common deformity in these patients [14] (Fig. 29.5). Agenesis of the left pericardium is the most common type accounting for 70 % of cases (Fig. 29.6). It usually involves the entire left side. In Gatzoulis series of ten cases with isolated pericardial defect, 70 % were complete absence of the left side [8]. Partial defects of left pericardium are not uncommon; they are usually located in the upper part of the left pericardium causing herniation of the left atrial appendage or part of the left ventricle (Fig. 29.7). In lower part is involved incarceration of the left ventricle and ischemia by coronary artery compression may ensue [20, 21]. Total aplasia of the pericardium accounts for less than 10 % of the cases identified [8, 16, 17]. It may coexist with an incomplete closure of the anterior chest wall, ectopia of the heart, and omphalocele. In less severe forms, the heart remains intrathoracic but falls over in the left hemithorax and may be associated with diaphragmatic defects. Agenesis of the right pleuropericardial membrane is considered very uncommon (4 %) (Fig. 29.8). Right-sided mediastinal shift of the heart may be observed. In the partial form, the right atrial appendage or ventricle may herniate through the defect or the right lung may herniate in and compress the superior vena cava [22–25]. Defects of the diaphragmatic pericardium are associated with partial diaphragmatic aplasia and intrapericardial herniation of the greater omentum.