3.4 Pericardial Cavity

Pericardial Cavity

Definition and General Description

The pericardial cavity is a narrow, fluid-filled potential space located within the thoracic cavity, enveloping the heart. This cavity lies between two layers of the serous pericardium: the outer parietal pericardium and the inner visceral pericardium (also called the epicardium). Although termed a "cavity," under normal physiological conditions it contains only a thin film of serous fluid, which acts as a lubricant to minimize friction during heart movements.

The pericardial cavity does not contain any solid organs; its primary contents are serous fluid and potential spaces formed by the close apposition of the pericardial layers.

Structure and Boundaries

Parietal and Visceral Pericardium

• Parietal Pericardium: This outer serous layer lines the inner surface of the fibrous pericardium, forming the external boundary of the pericardial cavity.
• Visceral Pericardium (Epicardium): This inner layer is closely adherent to the heart's surface and is considered the heart's outermost layer.

The pericardial cavity is the potential space between these two serous layers.

Cavity Regions

• Anterior Region: Lies just behind the sternum and costal cartilages, anterior to the heart.
• Lateral Regions: Extend along the sides of the heart toward the lungs.
• Inferior Region: Sits above the diaphragm and below the heart.
• Posterior Region: Located behind the heart, adjacent to the esophagus and descending aorta.

Pericardial Fluid

The pericardial cavity contains a small amount of clear, straw-colored serous fluid, typically ranging from 15 to 50 milliliters in healthy adults. This fluid is secreted by the serous membranes and functions to:

• Lubricate the surfaces of the pericardium
• Reduce friction as the heart beats and moves within the thorax
• Facilitate smooth and unrestricted cardiac motion

Three-Dimensional Configuration and Cardiac Relations

The pericardial cavity completely surrounds the heart, except at the points where the great vessels enter and exit. It conforms to the contours of the heart and major vessels, creating a three-dimensional enclosure.

• Superiorly: The cavity is continuous with the roots of the aorta, pulmonary trunk, and superior vena cava.
• Posteriorly and Inferiorly: The cavity extends behind and beneath the heart, lying on the diaphragm.
• Laterally: The cavity is adjacent to the mediastinal pleura covering the lungs.

This continuity allows the heart to move freely within the lubricated space but retains it in a central position in the thorax.

Pericardial Recesses

The pericardial cavity forms several recesses or extensions, which are small pouch-like spaces where the serous layers reflect around the great vessels. The main pericardial recesses include:

• Transverse pericardial sinus: Located posterior to the ascending aorta and pulmonary trunk, and anterior to the superior vena cava.
• Oblique pericardial sinus: A blind pouch located posterior to the left atrium, between the pulmonary veins.

These recesses are clinically significant as they can be sites for fluid accumulation or provide surgical access during cardiac procedures.

Clinical Significance

Pericardial Effusion

When excess fluid accumulates in the pericardial cavity, a condition known as pericardial effusion occurs. This can increase pericardial pressure and restrict heart expansion, potentially leading to cardiac tamponade, a life-threatening situation requiring urgent intervention.

Other Clinical Considerations

• Pericarditis: Inflammation of the pericardial layers, often resulting in pain and friction rub.
• Pericardiocentesis: A procedure to aspirate abnormal fluid from the pericardial cavity, typically performed through the subxiphoid or parasternal approach.

Summary of Key Features

• The pericardial cavity is a potential space between the parietal and visceral layers of serous pericardium.
• It contains a small amount of lubricating serous fluid.
• It surrounds the heart and the roots of the great vessels, allowing free movement of the heart with minimal friction.
• It includes anatomical recesses around the great vessels.
• Pathological accumulations of fluid can impair cardiac function and require medical intervention.