3.12 Pericardial Relationships to the Great Vessels

Pericardial Relationships to the Great Vessels refers to the anatomical associations and spatial connections between the pericardium—the fibroserous sac enclosing the heart—and the major blood vessels entering or leaving the heart. These relationships are crucial for understanding cardiac anatomy, surgical approaches, and the spread of disease processes in the mediastinum.

Structure of the Pericardium

Fibrous and Serous Layers

The pericardium consists of two main layers:

• The fibrous pericardium is the tough outer layer that anchors the heart within the mediastinum.
• The serous pericardium is a double-layered membrane: the parietal layer lines the inside of the fibrous pericardium, and the visceral layer (epicardium) covers the surface of the heart.

The space between the serous layers is the pericardial cavity, containing a small amount of lubricating fluid.

Pericardial Reflections

Where great vessels enter or leave the heart, the serous pericardium reflects onto these vessels, forming tubular sheaths known as pericardial reflections. These are important for the formation of pericardial sinuses and define the transition between intrapericardial and extrapericardial segments of the great vessels.

Intrapericardial Portions of the Great Vessels

Ascending Aorta

The ascending aorta emerges from the left ventricle and is ensheathed by the pericardium as it rises. It remains intrapericardial until it exits through the arterial pericardial reflection at the level of the aortic root.

Pulmonary Trunk

The pulmonary trunk arises from the right ventricle within the pericardial sac, bifurcating into right and left pulmonary arteries. Its proximal segment is intrapericardial, passing through the arterial reflection as it exits.

Superior and Inferior Vena Cava

• The superior vena cava (SVC) enters the pericardium shortly before it joins the right atrium. Its terminal portion is intrapericardial.
• The inferior vena cava (IVC) pierces the diaphragm and traverses a short intrapericardial segment before entering the right atrium.

Pulmonary Veins

Typically, four pulmonary veins (two from each lung) enter the left atrium. The terminal parts of these veins are enveloped by the pericardium.

Pericardial Reflections and Sinuses

Arterial Pedicle (Transverse Sinus)

The pericardial reflection around the ascending aorta and pulmonary trunk forms the arterial pedicle. The transverse pericardial sinus lies posterior to this pedicle and anterior to the atria, serving as a passage between arterial and venous sides.

Venous Pedicle (Oblique Sinus)

The pericardial reflection surrounding the pulmonary veins and venae cavae forms the venous pedicle. The oblique pericardial sinus is a blind pouch located posterior to the left atrium, bordered by these veins.

Entry and Exit of Great Vessels from the Pericardial Sac

Entry Points

• The SVC enters the pericardial sac from superiorly.
• The IVC enters from inferiorly, after traversing the diaphragm.
• Pulmonary veins enter from the posterior aspect.

Exit Points

• The ascending aorta and pulmonary trunk exit the pericardial sac superiorly, after their initial intrapericardial course.

Map of Great Vessel–Pericardial Relationships

The following schematic illustrates the spatial relationships between the pericardium and the great vessels:

Clinical Significance

Surgical Access

Knowledge of pericardial relationships is essential in cardiac surgery, especially during procedures like pericardiotomy, valve replacement, and coronary artery bypass. The transverse sinus is used as a surgical plane to clamp the aorta and pulmonary trunk during cardiopulmonary bypass.

Spread of Disease

Pericardial reflections can act as barriers or conduits for the spread of infection, malignancy, or hemorrhage between the heart and mediastinum.

Imaging and Diagnosis

Understanding these relationships assists radiologists and clinicians in interpreting imaging studies such as echocardiography, CT, and MRI, particularly in the evaluation of masses, effusions, or congenital anomalies.

Summary Table: Intrapericardial Great Vessel Segments

Key Points

• The pericardium envelops the heart and proximal segments of the ascending aorta, pulmonary trunk, SVC, IVC, and pulmonary veins.
• Pericardial reflections form sinuses (transverse and oblique) and define intrapericardial vessel segments.
• These relationships are critical for surgical approaches, understanding disease spread, and interpreting diagnostic imaging.