The pericardium is a fibroserous double-walled sac that encloses the heart, the pericardial fluid and the roots of the great vessels, and is situated within the middle mediastinum. Its function is to lubricate the moving surfaces of the heart. In this article, the anatomy of the pericardium will be discussed in detail along with the pathological disorder known as pericarditis.
The outer layer of the pericardium is known as the fibrous layer and consists of dense connective tissue. It is attached to the central tendon of the diaphragm via the pericardiacophrenic ligament whose fibers merge with the tunica adventitia of the vessels which enter and exit the heart. The pericardial sac also attaches via ligamentous fibers to the sternum and due to these attachments it is affected by the movements of the heart, the great vessels, the sternum and the diaphragm.
This fibrous exterior lining mechanically functions to prevent the heart from overfilling, because the fibrous tissue as a whole is resilient and although flexible, it does not stretch.
The inner layer of the pericardium is known as the serous layer or the parietal layer and is in direct contact with the pericardial fluid. It consists of a mesothelial layer which reflects onto the roots of the great vessels and runs directly over the external surfaces of the heart as the epicardium or visceral pericardium.
The pericardial cavity is the potential space created by the pericardial reflection and this is where the thin film of pericardial fluid is kept, allowing for the two surfaces to be lubricated and rub against one another without any friction.
Two sinuses exist within the cavity that include the transverse sinus and the oblique sinus. The transverse pericardial sinus extends transversely across the pericardium in between the roots of the great vessels, posterior to the ascending aorta and the pulmonary trunk and anterior to the superior vena cava. The oblique pericardial sinus exists in the posterior part of the pericardium and is bordered laterally by the pulmonary veins which enter the heart and inferiorly by the inferior vena cava which is also returning to the heart.
The blood supply of the pericardium comes from the pericardiacophrenic arteries and the internal thoracic arteries.
The internal thoracic veins are responsible for the venous drainage of the area.
The innervation of the pericardium is governed by several different branches, including the phrenic nerves which give sensory fibers that control pain sensation, and the sympathetic trunks which carry vasomotor fibers.
Pericarditis is the inflammation of the pericardium which causes it to swell. It has acute, recurring and chronic forms. In most cases the etiology is unknown, although a bacterial or viral infection is usually suspected. Other known causes include a chest injury, cancer and its varying forms of treatment. Those who are immunosuppressed can be prone to recurrent pericarditis, due to their increased risk of infection. Treatment includes nonsteroidal antiinflammatory drugs and antibiotics.