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Oblique pericardial sinus

The oblique pericardial sinus is a blind recess of the pericardial cavity located posterior to the left atrium. It is formed by the reflection of the serous pericardium around the pulmonary veins and inferior vena cava (IVC). Unlike the transverse sinus, which is a passage, the oblique sinus is a cul-de-sac that extends upward behind the left atrium.

It is bounded laterally by the reflections surrounding the pulmonary veins, inferiorly by the pericardium near the IVC, and superiorly it extends behind the left atrium where it ends blindly.

Clinically, the oblique sinus is important in pericardial effusion, as fluid often accumulates here first in the supine position. It also serves as a landmark during cardiac surgery and may be enlarged in pericardial pathology or atrial dilatation.

Synonyms

  • Pericardial oblique sinus

  • Sinus obliquus pericardii

Function

  • Forms a pericardial recess allowing posterior left atrial movement during the cardiac cycle

  • Acts as a dependent space for pericardial effusion in supine patients

  • Serves as an imaging and surgical landmark for posterior pericardial anatomy

MRI Appearance

T1-weighted images:

  • Appears as a low-signal recess filled with pericardial fluid, posterior to the left atrium

T2-weighted images:

  • Sinus fluid appears bright (hyperintense) relative to adjacent atrial myocardium

  • Clearly defines pericardial reflections around pulmonary veins and IVC

T2 TRUFISP (cardiac-gated):

  • Demonstrates the oblique sinus as a bright fluid-filled pocket behind the left atrium

  • Cine imaging shows dynamic relation to the atrium and pulmonary veins

  • Helpful for detecting extension of effusion or pericardial constriction

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, making the sinus fluid bright against surrounding pericardial tissue

  • Useful in detecting inflammatory changes or loculated effusion

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Fluid remains non-enhancing

  • Enhancing pericardium indicates inflammation, tumor infiltration, or thickening

MRI Non-Contrast 3D Cardiac-Gated Imaging (Whole-heart):

  • Provides 3D visualization of the posterior pericardial recess behind the left atrium

  • Shows boundaries with the pulmonary veins and IVC

  • Valuable in assessing effusion, atrial dilation, or congenital pericardial defects

CT Appearance

CT Coronary Angiography (CCTA):

  • Oblique sinus appears as a fluid-filled recess posterior to the left atrium, between pulmonary veins and IVC

  • Clearly demonstrated on axial and coronal reconstructions

  • Useful for distinguishing pericardial recesses from mediastinal cysts or lymphadenopathy

  • Sensitive in detecting pericardial effusion accumulation in the posterior sinus

CT image

Oblique pericardial sinus anatomy CT axial image -img-00000-00000

MRI image

Oblique pericardial sinus mri axial image