Atrial Sinus Venosus
Sino-septal defects refer to those that involve the area of the atrial septum derived from
the sinus venosus. Most commonly this includes defects that occur at the junction of the
superior vena cava and the right atrium, although these defects may also occur at the
junction of the inferior vena cava and the right atrium.
The right upper pulmonary veins typically enter the left atrium superiorly and just to the
left of the atrial septum and sinus venosus region. When a defect of the superior sinus
venosus exists, the flow from these veins may be directed toward the right atrium through
the sinus venosus defect. Alternatively, these veins may truly be anomalous in their
drainage and enter the right atrium directly. These defects are known as sinus venosus
defects.
This shows the difficulty of visualizing a sinus venosus defect. The usual
subcostal view (left image) seems to show an uninterrupted atrial septum. By tilting
superiorly (right image) the sinus venosus becomes evident (arrows) near the junction with
the SVC and an anomalous pulmonary vein which often accompanies these type of defects.
sin_ven_papvr_labl This (inverted) subcostal view is labelled to show partial anomalous
pulm. veins (PAPVR) entering a sinus venosus defect in the superior portion of the atrial
septum near the junction with the SVC.
These subcostal images show relevant structures labelled (left
image). The sinus venosus defect lies at the junction of the SVC-RA with a partial
anomalous right pulmonary venous return (Rt PAPVR). Bloodflow patterns are shown in the
color doppler image on the right.
Subcostal color doppler imaging shows the inflow from the SVC at 6
o'clock (in red) across a sinus venosus defect. As is common in this entity, there is also
partial anomalous right pulmonary venous return (entering horizontally near the RA-SVC
junction). At 10 o'clock is the entrance of the IVC.