Pericardium Anatomy
The fibrous pericardium is a sac of
dense connective tissue surrounding the heart. In addition to the heart, it
encloses the roots of the great arteries and veins and is covered on its inner
surface by serous pericardium (see below). The broad base of the fibrous
pericardium is attached to the central tendon of the diaphragm (Fig.
2.29) and is pierced by
the inferior vena cava.
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Fig.
2.29 The fibrous pericardium and phrenic nerves revealed after removal of the
lungs.
Superiorly, the sac
fuses with the adventitial layers of the aorta, pulmonary trunk and superior
vena cava. On each side, the posterior part of the sac blends with the walls of
the pulmonary veins.
The anterior aspect of the fibrous
pericardium is related to the anterior parts of the two lungs and the anterior
reflections of the pleura. Between the pleural reflections, the pericardium
lies close to the body of the sternum and to the medial ends of the adjacent
fourth and fifth left costal cartilages and associated intercostal structures.
During infancy and childhood, the
thymus (most of which lies in the superior mediastinum) is related to the
anterior surface of the pericardium, but after puberty, the thymus regresses
and is gradually replaced by fat.
Laterally, the pericardium is covered
by mediastinal pleura and is crossed by the right and left phrenic nerves as
they descend to the diaphragm. These nerves supply sensory fibres to the
fibrous peri- cardium, the parietal serous pericardium and the
mediastinal pleura. Most
of the blood supply to the fibrous
pericardium is provided by the internal thoracic arteries and veins via
pericardiacophrenic vessels that accompany the phrenic nerves.
Behind the fibrous pericardium lie the
oesophagus, the descending thoracic aorta and the thoracic duct (pp 62, 63).
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Fig. 2.30 The fibrous pericardium has been opened to expose the
visceral pericardium covering the anterior surface of the heart.
Serous pericardium
Deep to the fibrous pericardium lies
the serous pericardium, consisting of parietal and visceral layers. Between the
two layers is the pericardial cavity, a narrow space containing a thin film of
serous fluid. The parietal layer lines the inner surface of the fibrous
pericardium, to which it is firmly attached. The visceral layer covers the
outer surface of the heart and the roots of the great vessels (Fig.
2.30).
These two layers slide freely against
each other and are in continuity where the great vessels pierce the fibrous
pericardium. The reflections between the parietal and visceral layers form two
sleeves. One sleeve surrounds the ascending aorta and pulmonary trunk; the
second is more extensive and surrounds the superior and inferior venae cavae
and pulmonary veins. The two pericardial sleeves lie adjacent to each other and
the narrow intervening channel is called the transverse pericardial sinus (Fig.
2.40). A second sinus lies behind the left atrium of the heart. This is the
oblique pericardial sinus, which is limited superiorly by the pericardial
reflection around the pulmonary veins and superior vena cava (Fig. 2.35). An
accumulation of fluid (e.g. blood) within the pericardial cavity may compromise
venous return to the heart and therefore reduce cardiac output (cardiac
tamponade).
