What are the locations of the cardiac oblique and transverse sinuses?

Cardiac Oblique and Transverse Sinus Locations

Oblique Sinus

The oblique sinus is located posterior to the left atrium, bounded by the inferior vena cava anteriorly and extending behind the pulmonary veins. 1

Anatomical Boundaries and Access

• The oblique sinus lies posterior to the left atrium and is entered by incising posterior to the inferior vena cava 1
• During surgical approaches, the oblique sinus must be widely opened to release the posterior atrial wall and prevent "tenting" when accessing the left atrium 1
• The incision should extend far enough inferiorly, below the right pulmonary veins, to adequately mobilize the posterior left atrial wall 1

Morphological Variations

• The oblique sinus demonstrates significant individual variability in depth and entrance width 2
• Four morphological types exist: Type 1 (shallow with narrow entrance - most common), Type 2 (shallow with wide entrance), Type 3 (deep with narrow entrance), and Type 4 (deep with wide entrance) 2
• The median volume is 8.4 mL, with a median entrance length of 33.0 mm and depth of 38.2 mm 2

Transverse Sinus

The transverse sinus is located anterior to the ascending aorta and pulmonary artery, running transversely across the base of the heart between the arterial and venous pedicles. 3, 2, 4

Anatomical Boundaries

• The transverse sinus separates the arterial outflow tracts (aorta and pulmonary artery) anteriorly from the venous inflow structures (superior vena cava and pulmonary veins) posteriorly 3, 4
• It can be accessed from either side of the great vessels and serves as a natural anatomical corridor across the cardiac base 4

Morphological Variations and Clinical Relevance

• Four morphological types exist: Concave (most common), Wine-type, Straight, and Convex 2
• The median volume is 14.8 mL with a median length of 52.8 mm 2
• The transverse sinus is frequently visible on electrocardiographically-triggered CT imaging in 95% of patients 5
• This space can be utilized for epicardial device placement, as it provides stable anchoring points for pacing leads with access to both atrial and ventricular epicardial surfaces 4

Clinical Pitfalls

• When entering the pericardium near the pulmonary vein-left atrial junction, careful attention must be paid to avoid phrenic nerve injury, which runs in proximity to this region 1, 6
• The individual anatomical variability of both sinuses necessitates careful preoperative imaging assessment, particularly for minimally invasive procedures 2