3.5 Pericardial Sinuses and Recesses

Pericardial Sinuses and Recesses are specialized spaces within the pericardial cavity formed by the complex folding of the serous pericardium around the great vessels of the heart. These anatomical features are important because they provide potential spaces that can accommodate changes in cardiac size and function, and they serve as landmarks during cardiac surgery and imaging. The main pericardial sinuses are the transverse pericardial sinus and the oblique pericardial sinus, each with distinct boundaries and clinical significance. Additionally, smaller pericardial recesses are found in association with the venous structures entering and leaving the heart.

Transverse Pericardial Sinus

The transverse pericardial sinus is a horizontal passage within the pericardial cavity, situated posterior to the ascending aorta and pulmonary trunk and anterior to the superior vena cava. It is created by the reflection of the serous pericardium around these great vessels. The sinus forms an important surgical landmark, particularly during procedures such as cardiopulmonary bypass, where passing a finger or instrument through the sinus helps isolate the arterial vessels.

Anterior Boundary

The anterior boundary of the transverse pericardial sinus is formed by the posterior surfaces of the ascending aorta and the pulmonary trunk. These vessels lie immediately in front of the sinus, separating it from the anterior pericardial sac.

Posterior Boundary

The posterior boundary is constituted by the anterior surface of the superior vena cava and the upper left atrium. This side of the sinus is adjacent to these venous structures and forms the back wall of the passage.

Superior Boundary

Superiorly, the transverse pericardial sinus is bounded by the reflection of the serous pericardium onto the ascending aorta and pulmonary trunk, which continues onto the superior vena cava.

Inferior Boundary

The inferior boundary is defined by the atrial roof, specifically the upper surface of the left atrium where the serous pericardium reflects around the vessels.

Oblique Pericardial Sinus

The oblique pericardial sinus is a cul-de-sac or blind recess located posterior to the left atrium. It is formed by the serous pericardial reflection around the pulmonary veins and the inferior vena cava. The oblique sinus allows expansion of the left atrium and provides a potential space for fluid accumulation in certain pathological conditions.

Anterior Boundary

The anterior boundary of the oblique sinus is formed by the posterior surface of the left atrium.

Posterior Boundary

Posteriorly, the sinus is bounded by the parietal pericardium covering the esophagus and descending thoracic aorta.

Lateral Boundaries

Laterally, the oblique sinus is limited by the serous pericardial reflections around the right and left pulmonary veins.

Superior Opening

The oblique sinus opens superiorly into the general pericardial cavity, bordered by the right and left pulmonary veins and the inferior vena cava.

Pericardial Recesses

Pericardial recesses are small extensions of the pericardial cavity that protrude along the major veins and arteries as the serous pericardium reflects onto these structures. While not as clinically significant as the major sinuses, they are important in imaging because they can mimic or mask pathology, such as fluid collections.

Pulmonary Venous Pericardial Recesses

These recesses occur where the pericardium reflects around the right and left pulmonary veins. They are located between the veins and the posterior pericardial wall, and may be seen as small fluid-filled spaces in imaging studies.

Caval Pericardial Recesses

Caval recesses are found adjacent to the superior and inferior vena cava where the pericardium reflects onto these vessels. The superior aortic recess, a specific pericardial recess, is located between the ascending aorta and the superior vena cava.

Clinical Significance

Pericardial sinuses and recesses are important in both surgical and diagnostic contexts. During cardiac surgery, especially procedures that involve clamping or cannulating the great vessels, the transverse pericardial sinus serves as a crucial anatomical landmark. Knowledge of the location of the oblique sinus is essential for understanding the spread of pericardial fluid or infection.

On imaging studies such as CT or MRI, pericardial recesses can be mistaken for pathological fluid collections or masses. Awareness of their typical locations and appearances helps avoid unnecessary interventions. Fluid can accumulate in these spaces in pericardial effusion, and understanding their anatomy enables accurate interpretation of cardiac imaging.

Summary

Pericardial sinuses and recesses are specialized spaces created by the reflections of the serous pericardium around the heart’s great vessels. The transverse and oblique pericardial sinuses are the most prominent, each with distinct boundaries. Smaller recesses are found near the pulmonary veins and vena cavae. These structures are significant for surgical access, imaging interpretation, and the pathophysiology of pericardial diseases.