During cardiopulmonary bypass, the surgeon passes a finger and then a clamp through a space within the pericardial cavity that lies posterior to the ascending aorta and pulmonary trunk but anterior to the superior vena cava and left atrium. Which structure has the surgeon entered?

• A Transverse pericardial sinus ✓
• B Oblique pericardial sinus
• C Pericardial cavity proper around the inferior vena cava
• D Costomediastinal recess

Explanation

The transverse sinus is the passage between the arterial mesocardium (aorta, pulmonary trunk) anteriorly and the venous mesocardium (SVC, left atrium) posteriorly. It develops from degeneration of the dorsal mesocardium and allows a clamp to be passed around the great arteries to isolate them on bypass. The oblique sinus is a blind cul-de-sac behind the left atrium bounded by the pulmonary veins and cannot be traversed.

Reference: Gray's Anatomy for Students, 4th ed.

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Written and medically reviewed by the StethoPrep medical team.