Fibrous Pericardium

The fibrous pericardium is the strong outer connective tissue component of the pericardial sac surrounding the heart and the roots of the great vessels. It forms a relatively inelastic protective enclosure around the heart within the middle mediastinum.

Unlike the serous pericardium, which consists of parietal and visceral layers associated with a lubricated pericardial cavity, the fibrous pericardium is composed predominantly of dense connective tissue. Its mechanical strength helps maintain the position of the heart and limits sudden excessive expansion.

The fibrous pericardium is firmly related to the diaphragm inferiorly and blends with the outer connective tissue of the great vessels superiorly. These attachments help stabilize the heart while still permitting the repetitive movement required during each cardiac cycle.

Location

The fibrous pericardium is located within the middle mediastinum and surrounds the heart together with the proximal portions of the great vessels.

It forms the external layer of the pericardial sac and lies external to the parietal layer of serous pericardium.

Pericardial Layers

The pericardium can be divided into a fibrous component and a serous component.

Layer	Position	Major Characteristic
Fibrous pericardium	Outermost	Tough connective tissue sac
Parietal serous pericardium	Internal to fibrous pericardium	Lines inner surface of fibrous sac
Visceral serous pericardium	Directly covers heart	Forms epicardium

Relationship to the Serous Pericardium

The parietal layer of the serous pericardium lines the internal surface of the fibrous pericardium and is closely adherent to it.

The visceral layer of serous pericardium covers the external surface of the heart and is separated from the parietal layer by the potential pericardial cavity.

Structure

The fibrous pericardium consists primarily of dense collagenous connective tissue.

Its strong fibrous composition provides substantial tensile strength and makes it much less distensible than the surrounding serous membranes.

Shape

The fibrous pericardium forms a roughly conical sac around the heart.

Its broad inferior surface is related to the diaphragm, while its narrower superior portion surrounds and blends with the connective tissue associated with the great vessels.

Base of the Fibrous Pericardium

The base of the fibrous pericardium is firmly attached to the central tendon of the diaphragm.

This attachment is particularly important in linking the position and movement of the heart with respiratory movement of the diaphragm.

Attachment to the Diaphragm

The inferior fibrous pericardium is fused with the central tendon of the diaphragm.

As the diaphragm moves during respiration, the pericardial sac and heart undergo corresponding positional movement within the thorax.

Superior Attachment

Superiorly, the fibrous pericardium blends with the external connective tissue of the great vessels entering and leaving the heart.

These vessels include the ascending aorta, pulmonary trunk, pulmonary veins, and venae cavae.

Great Vessel Roots

The fibrous pericardium surrounds the roots of the great vessels rather than ending abruptly at the superior surface of the heart.

Its connective tissue becomes continuous with the adventitial connective tissue of these vessels.

Anterior Attachments

The fibrous pericardium is connected anteriorly to the posterior surface of the sternum by fibrous bands commonly described as sternopericardial ligaments.

These connections contribute to stabilization of the pericardial sac within the mediastinum.

Sternopericardial Ligaments

The sternopericardial ligaments are connective tissue attachments extending between the fibrous pericardium and sternum.

They are often described as superior and inferior sternopericardial attachments, although their distinctness and strength can vary.

Posterior Relationships

Posteriorly, the pericardial sac is related to structures of the posterior mediastinal region, including the esophagus and descending thoracic aorta.

The left atrium and posterior pericardial surface lie particularly close to the esophagus.

Lateral Relationships

On each side, the fibrous pericardium is related to the mediastinal pleura.

The phrenic nerves and pericardiacophrenic vessels descend between the fibrous pericardium and mediastinal pleura.

Relationship to the Pleura

The mediastinal pleura forms the medial boundary of each pleural cavity and lies lateral to the fibrous pericardium.

This close relationship is important during procedures involving the pericardium because the pleural cavities are nearby.

Phrenic Nerves

The right and left phrenic nerves descend through the thorax along the lateral surfaces of the fibrous pericardium.

They pass anterior to the roots of the lungs and travel between the fibrous pericardium and mediastinal pleura toward the diaphragm.

Pericardiacophrenic Vessels

The pericardiacophrenic arteries and veins accompany the phrenic nerves along the fibrous pericardium.

These vessels contribute to the vascular supply and drainage of the pericardial region and diaphragm.

Relationship to the Heart

The fibrous pericardium does not directly contact the myocardium.

The heart is covered by visceral serous pericardium, while the parietal serous layer lines the internal surface of the fibrous sac.

Pericardial Cavity

The pericardial cavity is a potential space between the parietal and visceral layers of serous pericardium.

It normally contains a small amount of serous fluid that reduces friction as the heart moves.

Fibrous Pericardium and Cardiac Movement

Although the fibrous pericardium is relatively inelastic, the heart can move freely within the lubricated serous pericardial arrangement.

This combination provides external mechanical support while minimizing friction during continuous cardiac contraction and relaxation.

Functions

The fibrous pericardium performs several mechanical and protective functions.

• Helps maintain the position of the heart within the mediastinum
• Provides a strong external protective sac
• Limits sudden excessive distension of the heart
• Provides attachment to the diaphragm and great vessels
• Contributes to separation of the heart from surrounding thoracic structures

Anchoring the Heart

Attachments to the diaphragm, sternum, and great vessels help prevent excessive displacement of the heart within the thoracic cavity.

The heart is not rigidly fixed, but these attachments provide controlled stability while permitting normal motion.

Limitation of Acute Overdistension

Because the fibrous pericardium is relatively noncompliant, it resists rapid expansion.

This property can help limit sudden overfilling of the cardiac chambers, although it also becomes clinically important when fluid or blood accumulates rapidly within the pericardial sac.

Mechanical Protection

The dense connective tissue of the fibrous pericardium provides a durable external enclosure around the heart.

It contributes to mechanical separation between the heart and adjacent mediastinal and pleural structures.

Respiratory Movement

Because the fibrous pericardium is attached to the central tendon of the diaphragm, movement of the diaphragm during respiration influences the position of the pericardial sac.

This anatomical continuity integrates cardiac position with respiratory mechanics.

Blood Supply

The fibrous and parietal portions of the pericardium receive arterial blood from several nearby vessels.

The pericardiacophrenic artery, a branch of the internal thoracic artery, is an important contributor.

Additional Arterial Sources

Additional blood supply may arise from branches of the musculophrenic, bronchial, esophageal, and superior phrenic arteries.

The precise contribution of individual vessels varies among regions of the pericardium.

Venous Drainage

Venous drainage generally accompanies the arterial supply.

Pericardiacophrenic veins drain toward the internal thoracic or brachiocephalic venous systems, while other small veins communicate with neighboring thoracic venous channels.

Innervation

The fibrous pericardium and parietal serous pericardium receive important sensory innervation from the phrenic nerves.

This somatic sensory innervation makes these layers sensitive to pain, particularly when inflamed or mechanically irritated.

Phrenic Nerve Roots

The phrenic nerve arises primarily from spinal cord segments C3, C4, and C5, with C4 typically providing the major contribution.

These cervical spinal levels explain the pattern of referred pain associated with irritation of the fibrous and parietal pericardium.

Referred Pain

Pain arising from the fibrous or parietal pericardium may be referred to the shoulder region because sensory fibers carried by the phrenic nerve enter spinal cord levels that also receive somatic input from the supraclavicular region.

Pericarditis

Pericarditis is inflammation involving the pericardium.

Inflammation affecting the pain-sensitive fibrous and parietal layers can produce chest pain that may be influenced by body position or respiratory movement.

Pericardial Effusion

A pericardial effusion is accumulation of excess fluid within the pericardial cavity.

Because the fibrous pericardium has limited ability to expand rapidly, the physiological effect of an effusion depends strongly on both its volume and the rate at which it accumulates.

Slow Versus Rapid Fluid Accumulation

A slowly developing effusion may allow gradual stretching and adaptation of the pericardial sac, permitting a relatively large volume to accumulate before severe hemodynamic effects occur.

Rapid accumulation can produce dangerous increases in intrapericardial pressure with a much smaller volume.

Cardiac Tamponade

Cardiac tamponade occurs when pressure within the pericardial sac becomes sufficient to impair cardiac filling.

The limited acute distensibility of the fibrous pericardium is a major anatomical factor in the development of tamponade.

Effect on Cardiac Chambers

Increasing pericardial pressure can compress cardiac chambers and interfere with venous return and ventricular filling.

Right-sided chambers are particularly susceptible because their intracavitary pressures are normally lower than those of the left side.

Hemopericardium

Hemopericardium refers to accumulation of blood within the pericardial cavity.

Potential causes include trauma, rupture involving the heart or proximal great vessels, and complications of cardiovascular procedures.

Pericardiocentesis

Pericardiocentesis is the removal of fluid from the pericardial cavity using a needle or catheter.

Knowledge of the relationships among the fibrous pericardium, pleura, diaphragm, internal thoracic vessels, coronary structures, and heart is essential for safe access.

Subxiphoid Approach

A subxiphoid or subcostal route can provide access to the pericardial cavity while attempting to avoid the pleural cavities.

Modern pericardiocentesis is generally performed with imaging guidance to improve safety and accuracy.

Parasternal Access

Selected approaches may access the pericardium near the left sternal margin where the cardiac notch of the left lung creates an area in which the pericardium is relatively less covered by pleura.

The internal thoracic vessels and other nearby structures remain important considerations.

Pericardial Window

A pericardial window is a surgically created opening that permits drainage of pericardial fluid.

It may be used in selected recurrent or clinically significant pericardial effusions.

Constrictive Pericarditis

Constrictive pericarditis occurs when chronic inflammation leads to fibrosis, thickening, and sometimes calcification of the pericardium.

The resulting rigid enclosure can restrict normal diastolic expansion of the heart.

Pericardial Calcification

Calcification can occur in chronically diseased pericardium and may be visible on radiographic imaging or computed tomography.

Its presence does not by itself establish the physiological severity of constriction, which requires clinical and hemodynamic assessment.

Pericardiectomy

Pericardiectomy is surgical removal of part or most of the pericardium.

It may be performed in selected patients with severe constrictive pericardial disease.

Relationship to the Coronary Arteries

The coronary arteries lie on the surface of the heart within the subepicardial connective tissue, deep to the visceral serous pericardium.

They therefore lie internal to the fibrous pericardial sac rather than within the fibrous layer itself.

Relationship to the Great Arteries

The ascending aorta and pulmonary trunk begin within the pericardial sac.

The fibrous pericardium surrounds their proximal portions and blends with their outer connective tissue superiorly.

Relationship to the Venae Cavae

Segments of the superior and inferior venae cavae near their entry into the right atrium are related to the pericardial reflections.

The fibrous sac contributes to the supporting connective tissue around these venous roots.

Relationship to the Pulmonary Veins

The pulmonary veins enter the posterior aspect of the left atrium and are enclosed for short distances by pericardial reflections.

The fibrous pericardium surrounds the general region of these vessel roots.

Pericardial Sinuses

The transverse and oblique pericardial sinuses are spaces formed by reflections of the serous pericardium around the great vessels.

They are located within the fibrous pericardial sac but are features of the serous pericardial arrangement rather than spaces within the fibrous tissue itself.

Transverse Pericardial Sinus

The transverse pericardial sinus lies posterior to the ascending aorta and pulmonary trunk and anterior to structures associated with the atria and superior vena cava.

Its anatomy is important during cardiac surgery because it provides a passage behind the major arterial outflow vessels.

Oblique Pericardial Sinus

The oblique pericardial sinus is a blind recess posterior to the left atrium formed by serous pericardial reflections around the pulmonary veins and inferior vena cava.

Imaging

The normal fibrous pericardium is thin and may not be conspicuous on all imaging studies.

Computed tomography and magnetic resonance imaging can demonstrate abnormal pericardial thickening, calcification, masses, and associated effusions.

Echocardiography

Echocardiography is commonly used to evaluate pericardial effusion and its effects on cardiac filling.

Although ultrasound does not separately display every microscopic pericardial layer, it provides important functional information about the heart within the pericardial sac.

CT of the Pericardium

CT is particularly useful for demonstrating pericardial calcification and can also assess thickening, fluid, and relationships with adjacent thoracic structures.

MRI of the Pericardium

Cardiac MRI can evaluate pericardial morphology, inflammation, thickening, ventricular interaction, and associated abnormalities without ionizing radiation.

Fibrous Versus Serous Pericardium

Feature	Fibrous Pericardium	Serous Pericardium
Tissue	Dense connective tissue	Serous membrane
Position	Outermost layer	Internal to fibrous layer and covering heart
Major function	Mechanical support and limitation of acute distension	Low-friction movement
Layers	Single fibrous sac	Parietal and visceral layers
Cavity	No cavity within fibrous tissue	Pericardial cavity lies between serous layers

Key Anatomical Relationships

Direction	Major Relationship
Inferior	Central tendon of diaphragm
Superior	Roots of great vessels
Anterior	Sternum and sternopericardial attachments
Lateral	Mediastinal pleura, phrenic nerves and pericardiacophrenic vessels
Posterior	Structures including esophagus and descending thoracic aorta

Key Features of the Fibrous Pericardium

Feature	Key Point
Location	Middle mediastinum
Composition	Dense fibrous connective tissue
Inferior attachment	Central tendon of diaphragm
Superior continuity	Connective tissue of great vessels
Sensory innervation	Primarily phrenic nerves
Important arterial supply	Pericardiacophrenic arteries
Main functions	Support, protection and limitation of acute cardiac overdistension

Anatomical and Clinical Importance

The fibrous pericardium forms the strong external framework of the pericardial sac. Its attachments to the diaphragm, great vessels, and anterior mediastinal connective tissues stabilize the heart while allowing the continuous movement required for cardiac function and respiration.

Its limited acute distensibility is both protective and clinically significant. It helps resist sudden cardiac overexpansion, but rapid accumulation of fluid or blood inside the pericardial cavity can sharply increase pressure around the heart and impair filling, producing cardiac tamponade.

The fibrous pericardium is also closely related to several important thoracic structures, particularly the phrenic nerves, mediastinal pleura, diaphragm, and great vessels. These relationships explain patterns of referred pain and are essential during pericardiocentesis, pericardial surgery, and other procedures involving the middle mediastinum.