pericardiums

The pericardium is the double-walled sac that surrounds the heart and the roots of the great vessels. It consists of two main parts: the fibrous pericardium, a tough outer layer, and the serous pericardium, a thinner membrane that forms a parietal layer lining the fibrous sac and a visceral layer that covers the heart (the epicardium). The serous layers enclose the pericardial cavity, which normally contains a small amount of lubricating fluid.

The fibrous pericardium is a dense connective tissue structure that protects the heart, anchors it within the mediastinum, and prevents overfilling. It attaches to the diaphragm inferiorly, the sternum and posterior sternum via sternopericardial ligaments, and continues around the roots of the great vessels.

The serous pericardium comprises the parietal layer, which lines the inner surface of the fibrous pericardium, and the visceral layer, or epicardium, which adheres directly to the heart. The pericardial cavity between these layers contains fluid that reduces friction during cardiac movements.

Blood supply to the pericardium is mainly via the pericardiacophrenic arteries (branches of the internal thoracic artery), with contributions from other arteries. Venous drainage occurs mainly through pericardiacophrenic and other tributaries to the internal thoracic and azygos systems. Innervation is primarily via the phrenic nerve, with autonomic fibers influencing the pericardial sensation and blood flow.

Clinical relevance includes pericarditis (inflammation), pericardial effusion (accumulation of fluid), and cardiac tamponade, as well as constrictive pericarditis. Diagnosis often relies on imaging such as echocardiography, and treatment can involve pericardiocentesis or surgical creation of a pericardial window.