Pericardial Sinuses

Expansion

• Transverse sinus - a passage behind the ascending aorta and pulmonary trunk, in front of the superior vena cava and atria
• Oblique sinus - a blind cul-de-sac behind the left atrium, bounded by the reflections around the pulmonary veins and inferior vena cava

Both are consequences of how the serous pericardium reflects around the great vessels in two tubes, arterial and venous. The transverse sinus is the gap between those tubes; the oblique sinus is the recess within the venous reflection.