Pericardial defects are rare diseases that may be partial or complete. The extension of the defect is variable and may occur anywhere but with a preference for the portion of the pericardium covering the left side of the heart [1–3].

Pericardial defects may be associated with other congenital abnormalities (e.g. atrial septal defect, patent ductus arteriosus, bicuspid aortic valve or pulmonary malformations).

Complete absence of the entire pericardium is a rare congenital anomaly that is usually asymptomatic and has no impact on survival. It is commonly an incidental finding because of secondary abnormalities on ECG (usually right axis deviation of the QRS and right bundle branch block pattern) and echocardiography caused by an abnormal motility and displacement of cardiac chambers not fixed by the pericardium as in physiologic conditions.

Displacement of cardiac chambers may simulate abnormalities of the ventricles, especially the right (e.g. arrhythmogenic right ventricular dysplasia). Pericardial defects can be well demonstrated by cardiac magnetic resonance (Fig. 16.1).

Partial defects may be dangerous since herniation of parts of the heart (such as left atrium appendage) may cause ischaemic necrosis and compression of the left coronary artery by herniation may also cause myocardial ischaemia. In these cases, surgical correction of the defect is warranted [3].

Congenital cysts of the pericardium are rare diseases with a reported incidence of 1 in 100,000, but are the most common benign pericardial masses.

Congenital pericardial cysts are generated by the pericardium during its development and may be found anywhere in the mediastinum, but the most common site is the right cardiophrenic angle. Pericardial cysts are typically located at the right cardiophrenic angle (51–70 %) or left cardiophrenic angle (28–38 %) and rarely in other mediastinal locations not adjacent to the diaphragm (8–11 %) [3].

These lesions are typically round or elliptical with a variable size of few centimetres up to >20 cm, well defined and without communication with the pericardial cavity. Histologically these cysts are lined with a single layer of mesothelial cells, with the remainder of the wall composed of connective tissue with collagen and elastic fibres. They contain a clear water-like fluid.

They are usually asymptomatic and incidental finding on imaging studies but may become symptomatic in case of complications (haemorrhage, infection): in this case they usually increase their size and may give symptoms related to their compressive effect on adjacent anatomic structures [4–6].

Congenital pericardial cysts appear as round or elliptical masses with the same density of water on CT imaging. Due to its high water content, they appear with a uniform high signal on T2-weighted images (Fig. 16.2) and usually have intermediate signal intensity on T1-weighted images. The signal may be increased on T1-weighted images if the content is highly proteinaceous. In the absence of complications (e.g. inflammation), pericardial cyst does not show contrast enhancement [1, 2, 5].

As mentioned surgery is routinely not recommended for pericardial cysts, unless symptomatic with compression of adjacent organs. However, 10 % of all cysts may be instead a pericardial diverticulum with a persistent connection to the pericardial space, not apparent from radiologic studies, and that can be identified only at surgery. These lesions may cause atypical symptoms that are relieved only after surgery [7]. Minimally invasive thoracoscopic resection of a pericardial cyst is a less invasive alternative option because it minimizes surgical trauma and postoperative pain and has shorter recovery period. An alternative option is percutaneous aspiration of cyst contents.