The superior pericardial sinus: normal appearance on gradient-echo MR images

Area of Science:

• Radiology
• Medical Imaging
• Cardiovascular Imaging

Background:

• The superior pericardial sinus, an extension of the superior pericardial recess, can present diagnostic challenges on MRI.
• Gradient-recalled-echo (GRE) sequences may produce signals from this sinus that resemble flowing blood.

Purpose of the Study:

• To characterize and explain the typical appearance of the superior pericardial sinus on gradient-recalled-echo (GRE) magnetic resonance imaging (MRI) sequences.
• To differentiate the sinus's signal from actual vascular structures or aortic dissection.

Main Methods:

• MRI of the mediastinum was performed in six patients, with CT in two.
• T1- and T2-weighted spin-echo, ECG-gated images were acquired.
• Gradient-recalled acquisition in the steady state (GRASS) sequences with varying flip angles were used to image the superior pericardial sinus.

Main Results:

• The superior pericardial sinus was well-visualized, showing low signal on T1-weighted and high signal on T2-weighted images.
• On GRE and cine images with low flip angles (<20 degrees), the sinus signal mimicked flowing blood.
• This high signal was attributed to high proton density and long T2* of pericardial fluid, not flow.

Conclusions:

• The superior pericardial sinus exhibits a high signal on flow-sensitive GRE MRI with low flip angles, resembling flowing blood.
• This appearance is due to intrinsic fluid properties, not actual flow.
• Awareness of this GRE MRI artifact is essential for accurate diagnosis and avoiding misinterpretation as aortic dissection or vascular anomalies.