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 varies considerably between individuals. Contemporary CT studies demonstrate meaningful differences in the depth, entrance width, and overall configuration of both sinuses. Textbook diagrams therefore provide an anatomical framework rather than an invariant operative 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. These reflections do not form a single circular line; instead, they are molded around 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 adjacent venous structures 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 precise morphology depends on pulmonary venous anatomy, caval geometry, atrial size, and the intrapericardial lengths of the vessels. [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 length of each vein, and the relationship between the pulmonary veins and adjacent pericardial folds. [4] These differences directly affect posterior left atrial dissection, pulmonary venous mobilization, atrial fibrillation procedures, transplantation, and creation of an adequate left atrial cuff during procurement.
The posterior fibrous pericardium is also closely related to the esophagus behind the left atrium. This relationship becomes particularly relevant during posterior left atrial dissection, epicardial procedures, and reoperations in which adhesions obscure the normal pericardial 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 contributes to its posterior-superior boundary, while the SVC defines the right-sided limit of the operative field. [1,3,6]
From a surgical perspective, the central concept is that the sinus provides a natural route behind the great arterial trunks. Once the pericardium is opened and the great vessels are mobilized, a finger or instrument can often be passed through this space without entering a cardiac chamber. This permits circumferential vessel control while limiting unnecessary dissection of the posterior arterial wall.
The transverse sinus is not a uniform cylindrical tunnel. Anatomical and CT studies demonstrate variation in curvature, depth, length, and lateral extension. Burysz and colleagues classified several morphologic configurations and documented substantial interindividual variability. [3] This explains why the plane may be generous in one patient and restrictive in another despite 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 fundamental to proximal great-vessel control. During cardiac surgery, the surgeon may pass a tape or clamp around the ascending aorta through this plane when the anatomy and exposure permit.
The same principle applies to the pulmonary artery. During main pulmonary artery banding, the band can be passed through the transverse sinus behind the great arterial roots and around the main pulmonary artery. The objective is to achieve a true circumferential path without including adjacent structures or distorting the pulmonary valve or branch pulmonary arteries. The final band should lie on the intended main pulmonary artery segment, and the surgeon should directly verify that the right and left pulmonary arteries remain unobstructed.
This application illustrates why the transverse sinus is best understood as an operative corridor rather than merely an anatomical recess. The sinus facilitates passage around the great artery, but the surrounding structures must still be identified. Prior surgery, pericardial inflammation, congenital malposition of the great arteries, atrial enlargement, or anomalous vascular anatomy may substantially alter the expected pathway.
3.2 Lateral Extensions and Recesses
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 form recesses that can be visualized on cross-sectional imaging. [6,7]
These recesses may contain pericardial fluid. On CT, fluid in the superior aortic, pulmonic, or other transverse sinus recesses can mimic mediastinal lymphadenopathy or cystic lesions if the expected pericardial anatomy is not recognized. [6,7]
4. Oblique Pericardial Sinus
The oblique pericardial sinus is a blind recess posterior to the left atrium. It is formed mainly 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 viewed simply as “the space behind the left atrium.” Its margins are defined by the pulmonary venous and caval reflections, and its depth and entrance width vary markedly. In a contemporary CT series, oblique sinuses could be categorized as relatively shallow or deep and as having narrow or wide entrances. [3]
For the surgeon, the oblique sinus is relevant during mobilization of the posterior left atrium and inferior pulmonary venous region. A hand or finger placed posterior to the heart may enter this recess, 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, posterior mediastinum, and descending aortic region.
These relationships matter during pulmonary venous mobilization, left atrial exposure, and transplantation. A pericardial reflection that is opened too close to the venous wall may shorten the available vessel or atrial cuff, whereas excessive posterior dissection may approach the esophagus or adjacent mediastinal structures.
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 may lie close to the right atrial-IVC junction, especially in infants or patients with altered systemic venous anatomy.
IVC taping should therefore be performed with deliberate identification of the true 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 aim is to obtain adequate circumferential control for a tourniquet or snare while minimizing injury to the caval wall or right atrium.
The SVC is often more accessible, but its right lateral and posterior relationships are similarly influenced by the pericardial reflection and right pulmonary venous anatomy. This is particularly relevant when mobilizing the SVC for congenital procedures, placing a caval snare, or extending a right atrial incision toward the cavoatrial junction.
6. Surgical Applications
6.1 Great-Vessel Taping and Control
The transverse sinus is routinely used when circumferential control of the great arteries is required. The surgeon should first establish that the plane is free and that the instrument tip remains within the expected pericardial space. In primary operations the plane is usually smooth; in reoperations it may be obliterated by adhesions, making blind passage hazardous.
6.2 Pulmonary Artery Banding
When a pulmonary artery band is passed through the transverse sinus, its final course must be inspected directly. The band should encircle only the intended main pulmonary artery segment, without including the ascending aorta or impinging on the branch pulmonary arteries.
Because congenital great-artery relationships vary, the path of the sinus cannot always be assumed from normal anatomy. In DORV, transposition, conotruncal malalignment, or markedly dilated great arteries, the relationship between the aorta, pulmonary artery, and transverse sinus may differ substantially from the usual pattern.
After tightening, completion assessment should include ventricular function, pulmonary valve competence, branch pulmonary artery geometry, systemic oxygen saturation, and the pressure or Doppler gradient appropriate to the physiological objective. The sinus provides a route for the band; it does not determine the optimal degree of restriction.
6.3 Caval Taping and Cannulation
During bicaval cannulation, the SVC and IVC are dissected sufficiently to pass vessel loops or caval tapes. Excessive circumferential dissection is usually unnecessary and may injure small tributaries or the thin caval wall. The posterior pericardial reflection helps define the limits of the intrapericardial segment and should be recognized before an instrument is passed behind the vessel.
6.4 Heart Procurement
Posterior pericardial anatomy is particularly important during heart procurement. After decompression and cardioplegic arrest, the surgeon must preserve adequate great-vessel length and an appropriate left atrial cuff while avoiding injury to structures required for lung or other thoracic organ procurement.
The pulmonary venous pericardial reflections help define the transition between the posterior left atrial cuff and the surrounding mediastinum. The left atrium is divided to leave an adequate cuff containing the pulmonary venous orifices, with coordination required when the lungs are also being recovered. The SVC and IVC are divided with sufficient length for recipient implantation.
Recognizing the natural pericardial planes allows the procurement surgeon to progress systematically from the arterial pole to the caval and pulmonary venous structures. The transverse sinus serves as a familiar landmark between the arterial and venous poles, while the oblique sinus helps orient posterior left atrial dissection.
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 is seen behind the ascending aorta and pulmonary trunk, whereas the oblique sinus is identified posterior to the left atrium. Smaller pulmonary venous, postcaval, and aortic recesses may also be visible. [6,7]
Recognition of these normal spaces prevents diagnostic errors. Physiologic or pathologic pericardial fluid within a recess can resemble a mediastinal cyst or enlarged lymph node. [6,7] Cross-sectional imaging is also useful preoperatively when prior surgery, abnormal great-vessel relationships, or complex pulmonary venous anatomy is expected to alter the usual surgical planes.
Most evidence describing pericardial sinus morphology is anatomical, imaging-based, or observational. These studies establish substantial variability but do not define a single optimal surgical configuration. Operative use of the transverse and oblique sinuses therefore remains anatomy-driven and procedure-specific.
Key Surgical Principles
- Think in reflections, not isolated vessels. Posterior pericardial spaces are created by the relationship between arterial and venous serosal reflections.
- The transverse sinus is an operative corridor behind the great arteries. It facilitates vessel control and passage of a pulmonary artery band.
- The oblique sinus is a blind posterior left atrial recess. Its boundaries are formed primarily by pulmonary venous and IVC reflections.
- Caval taping requires controlled circumferential dissection. Identify the true vessel wall before passing an instrument posteriorly.
- Pulmonary venous reflections matter during procurement and left atrial surgery. They help define the available left atrial cuff and posterior dissection plane.
- Anatomical variability is expected. Congenital malposition, chamber enlargement, and individual sinus morphology can alter textbook relationships.
- Do not use a pericardial sinus blindly in a reoperation. Adhesions may eliminate the normal potential space and convert a safe plane into a hazardous dissection.
References
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