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Sinus of venae cavae (sinus venarum)

The sinus of venae cavae, also known as the sinus venarum, is the smooth-walled posterior portion of the right atrium. It develops embryologically from the right horn of the sinus venosus, which becomes incorporated into the right atrium during fetal development.

It receives the openings of the superior vena cava (SVC), inferior vena cava (IVC), and the coronary sinus, serving as the main entry point of systemic venous blood into the heart. The sinus venarum is separated from the rough, trabeculated anterior atrial wall (atrium proper with pectinate muscles) by the crista terminalis internally and the sulcus terminalis externally.

Clinically, the sinus venarum is important as the site of venous inflow, and its structures (such as the sinoatrial node at the superior end of the crista terminalis) are critical in cardiac conduction and arrhythmogenesis.

Synonyms

  • Sinus venarum

  • Venous sinus of right atrium

  • Sinus of venae cavae

Function

  • Acts as the entry chamber for systemic venous blood into the right atrium

  • Ensures smooth flow transition from SVC, IVC, and coronary sinus into atrium

  • Houses the sinoatrial (SA) node, the natural pacemaker of the heart

  • Provides anatomical landmarks for atrial catheterization and electrophysiology

MRI Appearance

T1-weighted images:

  • Appears as a smooth-walled, intermediate signal chamber posteriorly in the right atrium

  • Venous blood pool appears low signal (dark) unless contrast is used

T2 TRUFISP (cardiac-gated):

  • Provides bright blood imaging with excellent contrast between sinus venarum and atrial myocardium

  • Clearly shows smooth posterior atrial wall, venous inflow from SVC/IVC, and crista terminalis boundary

  • Cine evaluation demonstrates flow patterns and venous entry dynamics

STIR (Short Tau Inversion Recovery):

  • Fat suppression highlights pericardial and perivenous structures

  • May be useful in detecting edema, infiltration, or masses adjacent to sinus venarum

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Venous blood pool within sinus venarum enhances brightly and homogeneously

  • Helps delineate anatomy, venous entry sites, and exclude filling defects (e.g., thrombus, tumor)

MRA (Magnetic Resonance Angiography):

  • Contrast-enhanced MRA demonstrates systemic venous inflow into the sinus venarum

  • Useful for evaluating SVC/IVC anomalies, obstruction, or collateral circulation

CT Appearance

Contrast-Enhanced CT (Cardiac CT):

  • Sinus venarum visualized as the smooth-walled posterior right atrial chamber

  • SVC, IVC, and coronary sinus openings appear clearly as contrast-opacified venous entries

  • Differentiated from the anterior atrium by the absence of pectinate muscles

  • Excellent for detecting anomalous venous return, atrial tumors, thrombus, or chamber enlargement

MRI image

Sinus of venae cavae (sinus venarum) anatomy MRI CORONAL image -img-00000-00000

CT images

Sinus of venae cavae (sinus venarum) anatomy CT AXIAL image -img-00000-00000

CT images

Sinus of venae cavae (sinus venarum) anatomy CT CORONAL image -img-00000-00000