Anatomy of the Pericardial Sinuses
Oblique Sinus
The oblique sinus is a J-shaped pericardial recess located posterior to the left atrium, bounded by the reflections of the serous pericardium around the pulmonary veins and inferior vena cava. 1, 2
Anatomical Location and Boundaries
- Position: Lies posterior to the left atrium and inferior vena cava
- Boundaries:
- Anteriorly: Posterior wall of the left atrium
- Posteriorly: Parietal pericardium overlying the esophagus and descending aorta
- Laterally: Reflections around the right and left pulmonary veins
- Inferiorly: Reflection of pericardium onto the inferior vena cava
Morphological Classification
The oblique sinus demonstrates significant anatomical variability and can be classified into four distinct types 1:
- Type 1: Shallow depth with narrow entrance (most common)
- Type 2: Shallow depth with wide entrance
- Type 3: Deep with narrow entrance
- Type 4: Deep with wide entrance
Typical dimensions: Median volume of 8.4 mL, entrance length of 33.0 mm, and depth of 38.2 mm 1
Surgical Relevance
During minimally invasive mitral valve surgery, the oblique sinus must be widely entered posterior to the inferior vena cava 3. The incision must be carried far enough inferiorly to "release" the posterior atrial wall and prevent posterior atrial wall "tenting" - a critical technical point that ensures adequate exposure of the mitral valve 3.
Transverse Sinus
The transverse sinus is a horizontally oriented pericardial passage that lies between the arterial and venous pedicles of the heart, passing posterior to the ascending aorta and pulmonary trunk, and anterior to the superior vena cava and left atrium. 2, 4
Anatomical Location and Boundaries
- Position: Runs transversely across the base of the heart
- Boundaries:
- Anteriorly: Posterior surface of ascending aorta and pulmonary trunk
- Posteriorly: Anterior surface of superior vena cava and left atrium
- Superiorly: Pericardial reflection at the arterial pedicle
- Inferiorly: Opens into the main pericardial cavity
Morphological Classification
The transverse sinus exhibits four distinct morphological patterns 1:
- Concave type (most common): Curves posteriorly
- Wine-type: Resembles a wine glass shape
- Straight type: Linear configuration
- Convex type: Curves anteriorly
Typical dimensions: Median volume of 14.8 mL and median length of 52.8 mm 1
Clinical Significance
The transverse sinus serves as an important anatomical landmark during cardiac surgery, allowing surgeons to pass instruments or tapes around the great vessels for vascular control 5, 2. Understanding its variable anatomy is crucial for minimally invasive procedures and avoiding misinterpretation on cardiac imaging 6, 5.
Important Clinical Considerations
Imaging Pitfalls
Both sinuses can be mistaken for pathological masses or fluid collections on CT and echocardiography 6, 7. The transverse sinus, in particular, may appear as an abnormal fluid collection when distended, leading to diagnostic confusion 5.
Procedural Relevance
Knowledge of sinus anatomy is essential for:
- Epicardial ablation procedures: The sinuses create natural barriers to catheter movement 8, 4
- Cardiac surgery: Proper identification prevents injury to adjacent structures 3
- Pericardial access: Understanding the three-dimensional relationships guides safe intervention 4
The individual variability in sinus morphology emphasizes the importance of reviewing pre-procedural imaging to understand each patient's specific anatomy 1.