1. Overview
Posterior pericardial anatomy is defined by the way the serous pericardium reflects around the great arteries, venae cavae, pulmonary veins, and atrial surfaces. These reflections create a three-dimensional set of spaces rather than simple lines: the transverse pericardial sinus, the oblique pericardial sinus, and several smaller recesses. For the surgeon, these spaces are practical dissection planes. They determine where the ascending aorta and pulmonary artery can be encircled, how the superior and inferior venae cavae can be mobilized and taped, how the posterior left atrial and pulmonary venous structures are approached, and how donor cardiac structures are divided during procurement. [1–4]
The posterior pericardial reflections are best understood by separating the arterial and venous poles of the heart. The arterial reflection surrounds the ascending aorta and pulmonary trunk, whereas the venous reflection surrounds the superior vena cava (SVC), inferior vena cava (IVC), and pulmonary veins. The space between the arterial and venous reflections forms the transverse sinus. The venous reflections around the pulmonary veins and IVC fold behind the left atrium and create the oblique sinus. [1,2]
This geometry is variable between individuals. Modern CT studies demonstrate substantial differences in the depth, entrance width, and overall configuration of both sinuses. Therefore, textbook diagrams should be used as a three-dimensional framework rather than as an invariant map. [3]
2. Posterior Pericardial Reflections
At the posterior surface of the heart, the serous pericardium transitions from the visceral layer covering the heart to the parietal layer lining the fibrous pericardial sac. The reflections do not form one continuous circular line. Instead, they are shaped by the entry and exit of the major vessels.
Around the arterial pole, the serosa reflects over the proximal ascending aorta and pulmonary trunk. Posteriorly, these great arteries are separated from the atrial roof and right pulmonary artery by the transverse sinus. Around the venous pole, the serosa reflects around the SVC, IVC, and pulmonary veins. These venous reflections create irregular recesses whose exact morphology depends on pulmonary venous anatomy, caval geometry, atrial size, and the extent of intrapericardial vessel length. [1,4]
The venous reflection is particularly important around the pulmonary veins. Cadaveric studies demonstrate variation in the number of pulmonary venous ostia, the intrapericardial lengths of the veins, and the relationship between the pulmonary veins and adjacent pericardial folds. [4] These variations directly influence posterior left atrial dissection, atrial fibrillation procedures, pulmonary transplantation, and procurement of an adequate left atrial cuff.
The posterior fibrous pericardium is also related to the esophagus behind the left atrium. This relationship is most relevant during posterior left atrial dissection, epicardial procedures, and reoperations in which adhesions may obscure the normal tissue planes. [5]
3. Transverse Pericardial Sinus
The transverse pericardial sinus is the passage between the arterial and venous reflections. It lies posterior to the ascending aorta and pulmonary trunk and anterior to the atrial roof and adjacent venous structures. The right pulmonary artery forms an important posterior-superior relationship, while the SVC defines the right-sided boundary of the operative field. [1,3,6]
From a surgeon’s perspective, the key concept is that the sinus provides a natural route behind the great arterial trunks. When the pericardium is opened and the great vessels are mobilized, a finger or instrument can be passed through this space without entering a cardiac chamber. This permits circumferential control of an artery while minimizing unnecessary dissection of the posterior vessel wall.
The transverse sinus is not a uniform cylindrical tunnel. Anatomical and CT studies demonstrate substantial variation in curvature, depth, length, and extension. Burysz and colleagues classified the sinus into several morphological configurations and showed measurable interindividual differences. [3] Such variability explains why the space may feel generous in one patient and restrictive in another despite otherwise similar external cardiac anatomy.
3.1 Relationship to the Ascending Aorta and Pulmonary Artery
The posterior surfaces of the ascending aorta and pulmonary trunk form the anterior boundary of the transverse sinus. This relationship is central to proximal great-vessel control. During cardiac surgery, the surgeon may pass a tape or clamp around the ascending aorta through this plane when exposure permits.
The same anatomical principle applies to the pulmonary artery. For main pulmonary artery banding, one method is to pass the band through the transverse sinus behind the great arterial roots and around the main pulmonary artery. The goal is to obtain a true circumferential path without entrapping adjacent structures or distorting the pulmonary valve or branch pulmonary arteries. The band should lie on the intended main pulmonary artery segment, and the surgeon should confirm that the right and left pulmonary arteries remain unobstructed.
This technique is an example of why the sinus is better understood as an operative corridor than as an abstract anatomical recess. The plane can facilitate safe encirclement, but the surrounding structures must still be identified. Prior surgery, inflammation, congenital malposition of the great arteries, markedly enlarged atria, or anomalous vascular anatomy can alter the expected geometry.
3.2 Right and Left Extensions
The transverse sinus communicates laterally with the general pericardial cavity. On the right, its anatomy is closely related to the SVC and right upper pulmonary venous region. On the left, extensions around the pulmonary artery and left atrial appendage may create recesses that are visible on CT. [6,7]
These recesses can accumulate pericardial fluid. On cross-sectional imaging, fluid within a pericardial recess may mimic lymphadenopathy or a mediastinal cyst if its expected anatomical location is not recognized. [6,7]
4. Oblique Pericardial Sinus
The oblique pericardial sinus is a blind recess located posterior to the left atrium. It is formed primarily by the venous pericardial reflections around the pulmonary veins and IVC. Inferiorly, it communicates with the general pericardial cavity; superiorly, it terminates as a cul-de-sac. [2–4]
The oblique sinus should not be conceptualized simply as “the space behind the left atrium.” Its margins are defined by the venous reflections, and its depth and entrance width vary substantially. In the CT series by Burysz and colleagues, oblique sinuses could be categorized as relatively shallow or deep and as having narrow or wide entrances. [3]
For surgery, the oblique sinus is relevant when mobilizing the posterior left atrium or approaching the inferior pulmonary venous region. A hand or finger placed posterior to the heart may enter the oblique sinus, but blind forceful dissection should be avoided because the pulmonary veins, IVC, esophagus, and posterior pericardium lie in close proximity.
5. Pulmonary Venous and Caval Reflections
The pulmonary veins enter the posterior left atrium while traversing the fibrous and serous pericardial reflections. Their intrapericardial segments therefore vary in length. The right-sided pulmonary veins are related to the SVC and right atrial structures, whereas the left-sided veins are related to the left atrial appendage, descending aortic region, and left-sided posterior pericardium.
The IVC enters the right atrium inferiorly after traversing the diaphragm and pericardium. In most operative exposures, there is a short intrapericardial segment that can be dissected circumferentially for bicaval cannulation or taping. The pericardial reflection at this site may be close to the right atrial-IVC junction, particularly in small infants or patients with altered venous anatomy.
IVC taping should therefore be performed with deliberate identification of the vessel wall. A right-angle clamp is passed around the intrapericardial IVC in a controlled plane, avoiding deep posterior dissection toward the diaphragm or adjacent structures. The objective is to create sufficient circumferential control for a tourniquet or snare while preserving the IVC wall and avoiding atrial injury.
The SVC is generally more accessible, but its right lateral and posterior relationships are similarly influenced by the pericardial reflection and right pulmonary venous anatomy. Knowledge of this fold is particularly important when mobilizing the SVC for congenital procedures or when extending a right atrial incision toward the cavoatrial junction.
6. Surgical Applications
6.1 Great-Vessel Taping and Control
The transverse sinus is routinely exploited when circumferential control of the great arteries is needed. The surgeon should first establish that the plane is free and that the instrument tip remains in the expected pericardial space. In primary operations this plane is often smooth; in reoperations it may be obliterated by adhesions, making blind passage hazardous.
6.2 Pulmonary Artery Banding
When a band is passed through the transverse sinus, its final course must be confirmed directly. The band should encircle the intended main pulmonary artery segment without including the ascending aorta or impinging on a branch pulmonary artery. Because congenital great-artery relationships vary, the expected path of the transverse sinus should not be assumed from normal anatomy alone.
After tightening, completion assessment should include ventricular function, pulmonary valve competence, branch pulmonary artery geometry, oxygen saturation, and the pressure or Doppler gradient appropriate to the physiological objective. The sinus provides the route for the band; it does not determine the correct degree of restriction.
6.3 Caval Taping and Cannulation
During bicaval cannulation, the SVC and IVC are dissected sufficiently for vessel loops or caval tapes. Excessive circumferential dissection is unnecessary and can injure small tributaries or the thin caval wall. The posterior pericardial reflection provides the boundary of the intrapericardial segment and should be recognized before passing an instrument behind the vessel.
6.4 Heart Procurement
Posterior pericardial anatomy is particularly important during heart procurement. After the heart is decompressed and the great vessels are divided, the surgeon must preserve adequate vessel length and an appropriate left atrial cuff while avoiding injury to adjacent donor structures when other thoracic organs are also being procured.
The pulmonary venous pericardial reflections help define the plane between the left atrial cuff and the surrounding posterior mediastinum. The left atrium is typically divided to leave a generous cuff containing the pulmonary venous orifices, with coordination required when lungs are being recovered. The IVC and SVC are divided with sufficient length for recipient implantation. Understanding where the serosal reflections transition to extrapericardial tissue facilitates rapid dissection while maintaining orientation in a time-sensitive operation.
In procurement, the transverse sinus can also be used as a familiar landmark between the arterial and venous poles. Rather than dissecting each posterior structure independently, recognizing the established pericardial planes allows the surgeon to work systematically from the great arteries to the caval and pulmonary venous structures.
7. Imaging Correlation and Anatomical Variation
CT and CMR depict the pericardial reflections and recesses particularly well when fluid outlines the spaces. The transverse sinus appears behind the ascending aorta and pulmonary trunk, whereas the oblique sinus is identified posterior to the left atrium. Smaller pulmonary venous and caval recesses may also be visible. [6,7]
Recognition of these normal spaces prevents diagnostic errors. Pericardial fluid within the superior aortic, pulmonic, postcaval, or pulmonary venous recesses can resemble mediastinal soft-tissue lesions. [6,7] Cross-sectional imaging is also useful preoperatively when prior surgery, abnormal great-vessel position, or complex pulmonary venous anatomy is expected to alter the usual relationships.
The available evidence describing sinus morphology is primarily anatomical, imaging-based, or observational. It supports the existence of substantial anatomical variability but does not define a single “optimal” surgical configuration. Operative use of these spaces therefore remains anatomy-driven and procedure-specific.
Key Surgical Principles
- Think in reflections, not isolated vessels. The posterior pericardial spaces are created by the relationship between arterial and venous serosal reflections.
- The transverse sinus is a surgical corridor behind the great arteries. It can facilitate aortic or pulmonary arterial encirclement and passage of a pulmonary artery band.
- The oblique sinus is a blind posterior left atrial recess. Its boundaries are formed by the pulmonary venous and IVC reflections.
- Caval taping requires controlled circumferential dissection. Identify the true intrapericardial vessel wall before passing a right-angle instrument posteriorly.
- Pulmonary venous reflections matter during procurement and left atrial surgery. They help define the available atrial cuff and posterior dissection planes.
- Anatomical variability is expected. Congenital malposition, reoperation, chamber enlargement, and individual sinus morphology may substantially alter the textbook relationships.
- Do not use a sinus blindly in a reoperation. Adhesions may obliterate the normal potential space and convert a safe plane into a high-risk dissection.
References
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