1. Introduction
The pericardium is not simply a passive envelope around the heart. Its fibrous and serous components determine the mobility of the heart within the mediastinum, define the transition between intrapericardial and extrapericardial portions of the great vessels, and create predictable surgical spaces around the arterial and venous poles of the heart. These spaces—particularly the transverse and oblique pericardial sinuses—are fundamental landmarks in cardiac surgery.
From a surgical perspective, pericardial anatomy can be understood as three interrelated elements:
- the fibrous pericardial sac, which encloses and stabilizes the heart;
- the serous pericardium, whose parietal and visceral layers define the pericardial cavity; and
- the reflections of serous pericardium around the great vessels, which generate the transverse sinus, oblique sinus, and associated recesses.[1–4]
These relationships become particularly important during cardiopulmonary bypass cannulation, caval mobilization, pulmonary artery banding, pulmonary venous surgery, left atrial exposure, and donor-heart procurement.
2. Layers of the Pericardium
The pericardium consists of an outer fibrous pericardium and an inner serous pericardium.[1,2]
2.1 Fibrous pericardium
The fibrous pericardium is a relatively noncompliant connective-tissue sac surrounding the heart and the proximal portions of the great vessels. Inferiorly, it is intimately related to the central tendon of the diaphragm. Superiorly, its fibers merge with the adventitial connective tissue surrounding the great arteries and veins.[1]
This arrangement stabilizes the heart within the mediastinum while permitting cardiac motion. The fibrous sac also separates the heart from the adjacent pleural spaces and provides an important surgical plane during sternotomy and pericardiotomy.
The transition between the free fibrous sac and its attachment to the great vessels is clinically relevant because it defines which portions of the ascending aorta, pulmonary trunk, venae cavae, and pulmonary veins are intrapericardial.
2.2 Serous pericardium
The serous pericardium has two continuous layers:
- Parietal serous pericardium, which lines the internal surface of the fibrous pericardium.
- Visceral serous pericardium, which invests the external surface of the heart and is conventionally termed the epicardium.[1,2]
Between these layers is the pericardial cavity, a potential space containing a small amount of lubricating serous fluid. The mesothelial surfaces permit nearly frictionless movement of the beating heart against the surrounding pericardial sac.[2]
The parietal and visceral layers are continuous with each other at the roots of the great vessels. It is these reflections—not separate anatomical membranes—that create the pericardial sinuses.
3. Pericardial Reflections
Conceptually, the serous pericardium reflects around two groups of vascular structures:
- an arterial reflection around the ascending aorta and pulmonary trunk;
- a venous reflection around the venae cavae and pulmonary veins.
The complex three-dimensional relationship between these reflections produces channels and recesses within the pericardial cavity. Anatomical and imaging studies demonstrate considerable interindividual variability in their dimensions and morphology.[3–5]
The most surgically important spaces are the transverse sinus, situated principally between the arterial and venous poles of the heart, and the oblique sinus, situated behind the left atrium.
4. Transverse Pericardial Sinus
4.1 Anatomy
The transverse sinus is a passage within the pericardial cavity located behind the ascending aorta and pulmonary trunk and anterior to the structures forming the venous pole of the heart. Its posterior relationships include the superior vena cava, right pulmonary artery, and superior aspect of the left atrium, depending on the precise level examined.[3,4]
The sinus communicates freely with the general pericardial cavity on either side. Rather than being a simple uniform tunnel, it has variable recesses and contours. Cross-sectional studies have described extensions related to the aorta and pulmonary artery, while contemporary CT-based analysis demonstrates substantial variability in its shape and dimensions.[3,5]
This variability is clinically relevant: the apparent space encountered during surgery depends on cardiac filling, great-vessel geometry, congenital anatomy, prior operations, and pericardial adhesions.
4.2 Surgical significance
The transverse sinus provides a natural plane behind the arterial trunks. Historically, passage of a clamp or tape through this space enabled control of the great arteries. It remains an important landmark in several congenital and acquired cardiac procedures.
Pulmonary artery banding provides a practical example. A tape or band may be passed around the main pulmonary artery using the transverse sinus as the posterior passage. The maneuver avoids unnecessary circumferential dissection directly against the posterior pulmonary arterial wall. The band is then positioned on the main pulmonary artery with attention to both the pulmonary valve proximally and the pulmonary artery bifurcation distally.
The anatomy should not, however, be regarded as invariant. In congenital heart disease, the spatial relationship between the aorta, pulmonary trunk, pulmonary arteries, and atria may differ substantially from normal. Before blindly passing a tape through the transverse sinus, the surgeon should establish the positions of the great arteries and confirm an unobstructed plane.
The transverse sinus can also facilitate mobilization of the ascending aorta and pulmonary trunk during complex reconstruction, and its rightward extension is relevant when mobilizing the SVC or gaining access to the superior left atrium and right pulmonary artery.
5. Oblique Pericardial Sinus
5.1 Anatomy
The oblique sinus is a blind recess of the pericardial cavity located posterior to the left atrium. It is formed by the reflection of serous pericardium around the pulmonary veins and inferior vena cava.[1,3,4]
Unlike the transverse sinus, which functions as a passage across the superior aspect of the heart, the oblique sinus is essentially a cul-de-sac extending superiorly behind the left atrium and opening inferiorly into the general pericardial cavity.
Its lateral boundaries are created by the pericardial reflections surrounding the right and left pulmonary veins. Inferiorly, the reflection around the IVC contributes to the inferior boundary of the venous pericardial attachment.
Cadaveric studies have demonstrated substantial variation in the configuration and depth of this space and in the lengths of the intrapericardial pulmonary veins.[4] More recent CT analysis similarly demonstrates variation in both the transverse and oblique sinuses rather than a single stereotyped morphology.[5]
5.2 Surgical relevance
The oblique sinus provides access to the posterior left atrium and pulmonary venous region. A surgeon passing a hand behind the heart from below enters this space and encounters the posterior wall of the left atrium anteriorly.
This relationship is important during:
- pulmonary venous and left atrial surgery;
- mobilization of the pulmonary venous confluence;
- selected approaches to total anomalous pulmonary venous connection;
- posterior left atrial procedures;
- donor-heart procurement; and
- procedures involving the posterior atrial surface.
The pulmonary venous reflections should be understood as three-dimensional structures rather than simple circumferential lines. Excessive dissection directly on a pulmonary vein may narrow or injure the vessel, whereas controlled division or mobilization of adjacent pericardial reflections can improve exposure without compromising the venous lumen.
6. Pericardial Reflections Around the Venae Cavae
The SVC and IVC penetrate the fibrous pericardium before entering the right atrium, leaving portions of both vessels within the pericardial sac. Their pericardial reflections are important during cannulation and caval control.
6.1 Superior vena cava
The pericardial reflection around the SVC is not positioned at an absolutely constant level. Anatomical studies demonstrate that its relationship to the right atrium varies among individuals.[6]
For the cardiac surgeon, the relevant practical distinction is between the intrapericardial SVC, accessible within the opened pericardium, and the more superior extrapericardial segment. Mobilization of the SVC often requires division of surrounding pericardial reflections, particularly when high cannulation, extensive caval control, or reconstruction of the SVC–right atrial junction is required.
6.2 Inferior vena cava
The IVC has a short intrapericardial course before entering the right atrium. The pericardial reflection in this region is closely related to the inferior aspect of the oblique sinus.
For IVC taping or snaring, the surgeon develops the plane around the intrapericardial vessel while maintaining awareness of the adjacent right atrium and posterior pericardial reflection. The available length may be limited, especially in small infants, and excessive traction can distort the IVC–right atrial junction.
7. Pulmonary Veins and the Posterior Pericardial Reflection
The four pulmonary veins normally enter the posterior left atrium within sleeves of pericardial reflection. Their intrapericardial lengths and the configuration of the surrounding reflections vary considerably.[4]
This anatomy is particularly important when wide pulmonary venous mobilization is required. The surgeon should distinguish:
- the pulmonary venous lumen;
- the atrial–pulmonary venous junction;
- the epicardial surface of the posterior left atrium; and
- the surrounding pericardial reflection.
Mobilizing the reflection can substantially increase the apparent length of a pulmonary vein without dividing the vessel itself. Conversely, dissecting directly along the venous wall may sacrifice tissue required for reconstruction or create focal narrowing.
These principles are particularly relevant in anomalous pulmonary venous connections, pulmonary vein stenosis operations, lung transplantation, and donor-heart procurement.
8. Pericardial Anatomy During Heart Procurement
Donor-heart procurement demonstrates the practical importance of the venous pericardial reflections particularly clearly.
For bicaval implantation, adequate lengths of the SVC and IVC must be preserved. Similarly, the pulmonary veins are generally divided in a manner that preserves a generous left atrial cuff for subsequent implantation.[7,8]
After opening the pericardium, the surgeon identifies the caval and pulmonary venous boundaries and dissects the corresponding pericardial reflections. The oblique sinus serves as a posterior landmark for the left atrium and pulmonary veins. Understanding where the pericardium reflects onto each vein allows maximal useful tissue to be obtained while avoiding inadvertent injury to adjacent thoracic organs or to organs being recovered by other procurement teams.
The precise procurement sequence varies according to whether the heart is recovered alone or as part of multiorgan or combined heart–lung procurement. The anatomical principle is constant: recognition of the pericardial reflections determines where maximal vascular and atrial cuffs can safely be preserved.[7,8]
9. Congenital Cardiac Surgical Considerations
Normal pericardial anatomy provides the reference framework, but congenital cardiac surgery frequently violates normal assumptions.
Great-artery malposition, abnormal systemic or pulmonary venous connections, heterotaxy, bilateral SVCs, interrupted IVC, previous shunts, conduits, and prior sternotomy can profoundly alter the usual pericardial planes. Previous surgery may additionally obliterate the transverse or oblique sinus through adhesions.
Accordingly, a structure described anatomically as a “potential space” should never be assumed to remain safely patent after previous intervention. Reoperative dissection requires reconstruction of the original anatomical relationships from imaging and direct surgical exposure.
Key Surgical Principles
- Understand the pericardium as a reflected serous surface. The transverse and oblique sinuses are created by reflections around the arterial and venous poles rather than by separate structures.
- The transverse sinus lies behind the great arteries. It can provide a controlled posterior route around the main pulmonary artery or ascending aorta.
- The oblique sinus lies behind the left atrium. Its boundaries are principally formed by the pulmonary venous and IVC reflections.
- Pericardial reflections determine usable vascular length. This is particularly important during caval mobilization, pulmonary venous surgery, and heart procurement.
- Avoid blind passage in congenital or reoperative anatomy. Great-vessel relationships and pericardial planes may differ substantially from the normal arrangement.
- Pulmonary venous mobilization should exploit the surrounding pericardial planes rather than unnecessarily skeletonizing the veins.
- Think three-dimensionally. The sinuses, recesses, and vascular reflections vary among individuals and change with cardiac filling and prior surgery
References
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