Pericardium

General structure and layers

The pericardial sac is an anatomically complex pouch. Inside it lies the heart muscle, as well as the initial segments of the major blood vessels: the ascending aorta (up to its arch), the pulmonary trunk (up to the bifurcation), and the ostia of the pulmonary and venae cavae.

The structure of the sac comprises two main layers:

1. Outer layer — fibrous pericardium (pericardium fibrosum). This is a tough connective tissue membrane that gradually transitions into the walls of the exiting major vessels, taking a direct part in forming their vascular sheaths.
2. Inner layer — serous pericardium (pericardium serosum). It has a more complex structure and is divided into two separate plates. The parietal plate (lamina parietalis) lines the inner surface of the fibrous sac. The visceral plate (lamina visceralis), also called the epicardium, directly covers the heart tissues.

The smooth transition from the parietal layer to the visceral layer occurs in the region of the large blood vessel ostia. Between these two serous layers forms the pericardial cavity (cavitas pericardialis) — a narrow slit-like space containing normally a small amount of serous fluid that reduces friction.

It is important to consider that not all areas of the heart wall are covered by the serous membrane. Remaining free from it are the posterior surface of the left atrium (in the area where the pulmonary veins enter) and a narrow strip on the posterior wall of the right atrium between the ostia of the venae cavae. At the same time, inside the cavity itself, the superior and inferior venae cavae are surrounded by the epicardium from the anterior and lateral sides.

Sections of the pericardial sac

Topographically, the pericardial sac is conventionally divided into four main sections, each having specific features of adjacency to surrounding structures:

• Anterior (sternocostal) section. Extends from the transitional fold on the aorta and pulmonary trunk down to the diaphragm. Anteriorly, it is firmly attached to the sternum via sternopericardial ligaments. It is here that the surgical safety zone is located — the area of the sac adjacent to the left half of the xiphoid process and the cartilages of the left V–VII ribs. In this zone, the membrane is not covered by the pleura, which allows for puncture or incision of the cavity without the risk of damaging the pleural layers.
• Inferior (diaphragmatic) section. Firmly fuses with the tendinous center of the diaphragm muscle. Along the edges of the tendinous center, phrenicopericardial ligaments are additionally stretched.
• Lateral (pleural) sections. Are in direct contact with the mediastinal part of the pleura.
• Posterior (mediastinal) section. Represents an irregularly shaped plate (often triangular or pentagonal) located in the space between the large vessels of the heart root.

Pericardial sinuses

During the transition of the parietal layer into the visceral layer (epicardium) on the vessel walls, special folds are formed. They create a complex relief on the posterior wall of the cavity and bound slit-like spaces — sinuses.

• Anteroinferior sinus. Located at the level of the transition of the anterior wall of the sac into the inferior one, in the frontal plane between the sternum and the diaphragm. This is the largest and deepest sinus (its depth reaches several centimeters). It is of paramount clinical importance: it is here that blood or pathological exudate accumulates, and it serves as the target point for puncture.
• Transverse sinus (sinus transversus pericardii). Isolated from other recesses and has exactly two entrances (right and left). Anteriorly and superiorly it is bounded by the ascending aorta and pulmonary trunk, posteriorly by the superior vena cava, the right pulmonary artery, and the posterior wall of the sac, and inferiorly by the groove between the left ventricle and atria. To visualize it, it is necessary to pull the pulmonary artery and aorta anteriorly, and the superior vena cava posteriorly.
• Oblique sinus (sinus obliquus pericardii). Located within the pericardial folds between the veins of the right and left parts of the posterior wall. Anteriorly it is bounded by the posterior surface of the left atrium, posteriorly by the posterior wall of the sac. To the left of the sinus run the terminal parts of the pulmonary veins, to the right — the inferior vena cava. The transverse size of the entrance is 4.5–6.0 cm. To examine this recess, it is necessary to pull the apex of the heart upward and forward.

Topography, nerves, and lymphatic drainage

Cellular spaces and ligaments around the pericardial sac play a significant role in topographical anatomy. In the cleft between the mediastinal pleura and the lateral sections of the pericardium (anterior to the lung roots), the phrenic nerves (n. phrenicus) and accompanying blood vessels descend from top to bottom.

The ligamentous apparatus includes superior and inferior sternopericardial ligaments (ligamenta sternopericardiaca). They extend from the outer fibrous layer to the endothoracic fascia through the prepericardial tissue. During surgical interventions, these ligaments can impede the mobilization of the anterior transitional pleural folds when accessing mediastinal organs.

The lymphatic system of this area is represented by nodes lying in the prepericardial tissue. These include the anterior mediastinal lymph nodes and several (2–3) prepericardial nodes. The latter are localized anterior to the sac near the xiphoid process and in the area where the diaphragm attaches to the level of the VIII rib.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Technique of anteroinferior sinus puncture
• Topographical anatomy of the phrenic nerves in the mediastinum
• Surgical approaches to the mediastinum and mobilization of pleural folds
• Formation of vascular sheaths for major vessels
• Lymphatic drainage from the organs of the anterior mediastinum

Other topics in the section "Topographic Anatomy of the Chest"

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