The morphogenesis and associated anomalous pulmonary venous drainage in sinus venosus defect

Sinus venosus defect (SVD) is an unusual type of interatrial communication (IAC) and is virtually always associated with partial anomalous pulmonary venous drainage (PAPVD) of the right pulmonary veins (RPV) to the superior vena cava (SVC) or right atrium (RA). However, its definite morphogenesis is still elusive, and diagnostic fallibility continues.

We conducted a retrospective review of the echocardiograms, cardiac catheterization data, computed tomographic findings, and surgical notes of 44 children with surgery-confirmed isolated SVD from 1977 to 2016. We investigated the location of the IAC and its boundaries within the atrial septum and its anatomic relationship with the adjacent structures, including the anomalously draining RPV. We also tried to explore any possible associated abnormalities which might be implicated in the morphogenesis of SVD.

Two distinct types of IAC were defined. Forty patients had an IAC that was located posterosuperior to the intact fossa ovalis (superior type), and all were associated with PAPVD of the right upper and often the right middle pulmonary veins to the SVC. The remaining 4 patients had an IAC that was located posterior to the intact fossa ovalis (inferior type), and all were associated with PAPVD of all the RPV to the RA. Another consistently associated abnormality was a defect between the anomalously draining RPV posteriorly and the SVC or RA anteriorly. All these 44 patients underwent successful surgical baffling the associated PAPVD via the IAC into the left atrium.

A defect between the RPV posteriorly and the SVC or RA anteriorly will result in SVD, and an unusual type of IAC, and PAPVD of the RPV to the SVC or RA. The IAC is not a true atrial septal defect in the atrial septum proper, but it actually represents the left atrial orifice of the unroofed RPV.