Pericardium – Medical Sciences Hub

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Competency

AN22.1: Describe and demonstrate subdivisions, sinuses in pericardium, blood supply and nerve supply of pericardium.

Introduction

The pericardium is a conical fibroserous sac that encloses the heart and the roots of the great vessels. It is located in the middle mediastinum.
Anteriorly, the pericardium lies behind the body of the sternum and the second to sixth costal cartilages.
Posteriorly, it is related to the esophagus, descending thoracic aorta, and bodies of the fifth to eighth thoracic vertebrae.

Functions of Pericardium

The pericardium protects the heart and helps absorb mechanical shock.
It limits excessive movement of the heart within the thorax.
It prevents excessive expansion of the heart when the blood volume increases.
It helps prevent kinking of the great blood vessels.
It reduces friction between the heart and surrounding structures.
It acts as a mechanical barrier that limits the spread of infection and other pathological processes to the heart.
Complete absence or surgical removal of the pericardium may not produce obvious clinical disease.

Subdivisions

The pericardium has two main components: the fibrous pericardium and the serous pericardium.

Fibrous Pericardium

The fibrous pericardium forms the outer layer of the pericardium. It is a thick, single-layered, cone-shaped sac. It encloses the heart and blends with the roots of the great vessels.

Serous Pericardium

The serous pericardium is an inner, double-layered blind sac. It consists of parietal and visceral layers. The parietal layer lines the inner surface of the fibrous pericardium. The visceral layer, also called the epicardium, covers the outer surface of the heart and extends onto the great blood vessels.

Development

The subdivisions of the pericardium can be understood more clearly by studying its development. During formation of the head fold, the pericardial sac comes to lie anterior to the developing heart tube.
As the heart tube grows and folds, it projects into the posterior wall of the pericardial sac.
The arterial and venous ends of the heart tube are initially connected to the posterior wall of the pericardial sac by a fold called the dorsal mesocardium. The dorsal mesocardium later degenerates, creating a space known as the transverse pericardial sinus.
The fibrous pericardium and parietal layer of the serous pericardium develop from the somatopleuric layer of the pericardial sac. The visceral layer of the serous pericardium develops from the splanchnopleuric layer of the pericardial sac.

Fibrous Pericardium

The fibrous pericardium is a thick, cone-shaped sac composed of fibrous connective tissue.

Features of Fibrous Pericardium

The fibrous pericardium is conical and has an apex and a base (Flowchart 11.2).
Its apex is directed superiorly and blends with the outer coats of the ascending aorta and pulmonary trunk.
Its broad base is firmly fused with the central tendon of the diaphragm.
The central tendon of the diaphragm develops from the septum transversum.
Anteriorly, the fibrous pericardium is attached to the body of the sternum by the superior and inferior sternopericardial ligaments.
Posteriorly, it is related to the principal bronchi, esophagus, and descending thoracic aorta.
On each side, it is related to the mediastinal pleura, phrenic nerve, and pericardiophrenic vessels.
The fibrous pericardium protects the heart and helps maintain its position within the thorax.
It limits excessive distension of the heart and helps prevent kinking of the great vessels.

Serous Pericardium

The serous pericardium is a thin, double-layered serous sac located within the fibrous pericardium. Its surface is lined by simple squamous epithelium called mesothelium.

Layers of Serous Pericardium

The serous pericardium consists of parietal and visceral layers.
The parietal layer is the outer layer and lines the inner surface of the fibrous pericardium. The parietal layer is closely adherent to the fibrous pericardium.
The visceral layer, also called the epicardium, is the inner layer and covers the external surface of the heart and the roots of the great vessels. The visceral layer is separated from the myocardium, particularly along the cardiac grooves, by subserous areolar tissue, adipose tissue, and blood vessels. The visceral layer becomes continuous with the parietal layer around the roots of the great vessels.

Table 11.1: Differences between parietal and visceral pericardia.

Feature	Parietal pericardium	Visceral pericardium (epicardium)
Position	It forms the outer layer of the serous pericardium.	It forms the inner layer of the serous pericardium.
Relation	It lines the inner surface of the fibrous pericardium.	It covers the external surface of the heart.
Attachment	It is firmly adherent to the fibrous pericardium.	It is separated from the myocardium by subserous areolar tissue, adipose tissue, and blood vessels.
Development	It develops from somatopleuric mesoderm.	It develops from splanchnopleuric mesoderm.
Innervation	It receives somatic sensory innervation, mainly through the phrenic nerves.	It receives autonomic innervation.
Pain sensitivity	It is sensitive to pain.	It is relatively insensitive to pain.

Pericardial Cavity

The pericardial cavity is a potential space between the parietal and visceral layers of the serous pericardium.
Normally, it contains about 15–20 mL of serous fluid called pericardial fluid.
Pericardial fluid lubricates the opposing serous surfaces and reduces friction during movements of the heart.

Contents of Pericardium

The pericardium encloses the heart.
It also encloses the proximal parts of the great vessels, including the ascending aorta and pulmonary trunk.
It surrounds the lower half of the superior vena cava.
It encloses the terminal part of the inferior vena cava.
It also surrounds the terminal portions of the pulmonary veins.

Blood Supply and Nerve Supply

Blood Supply

Fibrous Pericardium and Parietal Layer of Serous Pericardium

Their arterial supply is derived from branches of the internal thoracic arteries, musculophrenic arteries, and descending thoracic aorta.
Venous blood drains mainly into the internal thoracic and azygos veins.

Visceral Pericardium

The visceral pericardium receives its arterial supply from the coronary arteries.
Its venous blood drains into the coronary venous system and ultimately into the coronary sinus.

Nerve Supply

The fibrous pericardium and parietal layer of the serous pericardium develop from somatopleuric mesoderm. They receive somatic sensory innervation mainly through the phrenic nerves. These layers are sensitive to pain.
The visceral pericardium develops from splanchnopleuric mesoderm. It receives autonomic innervation through sympathetic fibers and the vagus nerves. The visceral pericardium is relatively insensitive to pain.

Sinuses of Pericardium

The pericardial sinuses are communicating spaces formed by reflections of the serous pericardium.
There are two pericardial sinuses: the transverse sinus and the oblique sinus.

Reason behind sinuses of pericardium

The visceral pericardium forms two tubular sleeves around the great vessels of the heart. One arterial tube surrounds the embryonic arterial end of the heart and later encloses the ascending aorta and pulmonary trunk. One venous tube surrounds the embryonic venous end of the heart and later encloses the superior vena cava, inferior vena cava, and pulmonary veins. Initially, the arterial and venous ends of the heart are connected by the dorsal mesocardium.

Transverse Sinus

The transverse pericardial sinus is a horizontal passage located between the arterial and venous ends of the heart. It develops after degeneration of the dorsal mesocardium.

Boundaries

Anteriorly, it is bounded by the ascending aorta and pulmonary trunk.
Posteriorly, it is bounded by the superior vena cava.
Inferiorly, it is related to the left atrium.
Superiorly, it is related to the bifurcation of the pulmonary trunk.
On both sides, it communicates with the main pericardial cavity.

Oblique Sinus

The oblique pericardial sinus is a blind recess, or cul-de-sac, located behind the left atrium. It is formed by a J-shaped reflection of the serous pericardium around the venous end of the heart. This pericardial reflection surrounds the superior vena cava, inferior vena cava, and four pulmonary veins.

Development

The oblique sinus develops partly because the pulmonary vein is incorporated into the developing left atrium, resulting in the formation of four pulmonary veins.
It also develops as the sinus venosus is incorporated into the developing right atrium, separating the superior vena cava from the inferior vena cava.

Boundaries

Anteriorly, it is bounded by the left atrium.
Posteriorly, it is bounded by the parietal pericardium.
On the right, it is bounded by the two right pulmonary veins and the inferior vena cava.
On the left, it is bounded by the two left pulmonary veins.
Superiorly, it is closed by the reflection of the visceral pericardium along the right and left superior pulmonary veins at the upper margin of the left atrium.
Inferiorly, it communicates with the main pericardial cavity.

Clinical Anatomy

Significance of the transverse pericardial sinus: During cardiac surgery, a temporary ligature or vascular clamp may be passed through the transverse pericardial sinus to control blood flow through the ascending aorta and pulmonary trunk.
Pericarditis: Pericarditis is inflammation of the pericardium. The fibrous pericardium and parietal layer of the serous pericardium are sensitive to pain, so inflammation of these layers may produce chest pain.
Pericardial friction rub: In pericarditis, the normally smooth opposing surfaces of the serous pericardium become rough. Their movement against each other produces a characteristic pericardial friction rub that can be heard with a stethoscope.
Pericardial effusion: Pericardial effusion is the abnormal accumulation of excess fluid within the pericardial cavity. Common causes include pericarditis, tuberculosis, congestive heart failure, renal failure, and cardiac surgery. A large effusion may compress the heart and interfere with normal filling of the cardiac chambers. Patients may present with symptoms such as chest discomfort or pain.
A large chronic pericardial effusion may produce an enlarged, flask-shaped cardiac silhouette on a chest radiograph, classically described as a water-bottle heart.
Cardiac tamponade: Cardiac tamponade occurs when fluid accumulating within the pericardial cavity produces significant compression of the heart.
The relatively inelastic fibrous pericardium limits outward expansion of the pericardial sac. Increased intrapericardial pressure restricts filling of the cardiac chambers during diastole. Reduced ventricular filling leads to decreased cardiac output.
Pericardial cyst: A pericardial cyst is a congenital, encapsulated cyst that develops from an isolated portion of the developing pericardial cavity.
Pentalogy of Cantrell: Pentalogy of Cantrell, also called thoracoabdominal syndrome, is a rare congenital disorder characterized by a combination of midline developmental defects. These defects may include an omphalocele. An anterior diaphragmatic defect may also be present. A defect of the lower sternum is another characteristic feature. Defects involving the pericardium may be associated with ectopia cordis. Congenital cardiac malformations are also commonly present.

Pericardiocentesis

Pericardiocentesis is the aspiration of fluid from the pericardial cavity using a needle or catheter (Fig. 11.12).
The patient is usually placed in a supine or semi-recumbent position, with the head end of the bed elevated by approximately 30°–60°.
The procedure is preferably performed under imaging guidance.
Subxiphoid approach: The needle is introduced near the left xiphocostal angle and directed upward toward the pericardial cavity.
Parasternal approach: The needle may be introduced through the left fifth or sixth intercostal space close to the sternal border under ultrasound guidance.

Important Questions

Q. Write a short note on fibrous pericardium.
Q. Write a short note on sinuses of pericardium.
Q. Write a short note on transverse sinus of pericardium.
Q. Write a short note on oblique sinus of pericardium.

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