Early in the development of the embryo, the primitive heart tube is divided into the bulbus cordis, the ventricle, the atrium, and the sinus venosus. Three pairs of large veins are connected to the rear of the sinus venosus. The outermost pair is composed of the cardinal veins. The two pairs in the middle are the umbilical veins and the vitelline veins.

The cardinal veins include the common cardinal vein (duct of Cuvier), anterior cardinal vein, and posterior cardinal vein. The left common cardinal vein develops into the right SVC, and the right common cardinal vein develops into the coronary sinus. Both sides of the posterior cardinal veins join to form the azygos vein-half azygos vein (formed by the supracardinal vein) and the middle and distal segments (formed by the subcardinal vein) of the IVC.

The right vitelline vein develops into the proximal segment of the IVC, and the left vitelline vein develops into the portal vein. The umbilical vein is also involved in the formation of the hepatic vein. Between the portal vein and the IVC, in the embryonic period there is a direct channel called the ductus venosus that degrades after birth.

The above segments of the vein may be associated with anomalous pulmonary venous connection. Common situations are summarized as follows:

Originating from the venous plexus of the lung bud, the pulmonary veins merge into the main branch of the four pulmonary veins. The pulmonary venous plexus is located at the rear of the atrium and has collateral connection with each pair of the systemic venous veins. At the same time, a cystic protrusion from the left posterior wall of the primitive atrium forms the common trunk of the pulmonary veins and connects with the four pulmonary veins. After the common trunk enlarges into a part of the LA, the four pulmonary veins are drained into the LA.

Not all branches (1–3) of the pulmonary veins fail to connect with the LA normally. Some are defined as partial anomalous pulmonary venous drainage (PAPVD). According to the number of abnormally connected pulmonary veins, we can divide the PAPVD into the unilateral single-branch type, unilateral two-branch type, and bilateral single-branch type. According to the site of the abnormal connection, a PAPVD can be categorized into supracardiac type, cardiac type, or infracardiac type. The cardiac type is the most common.

The cardiac type of PAPVD usually occurs concurrently with an ASD. With repair of the ASD, the abnormal pulmonary vein can be drained to the LA by using a large patch. In the case of an abnormal pulmonary vein returning to the vena cava, surgery is more complex. Depending on any specific circumstance, different techniques, such as widening of the SVC or other diversion surgery, may be necessary (Figs. 14.1, 14.2, 14.3, and 14.4).

Total anomalous pulmonary venous drainage (TAPVD) is defined as a condition in which all four pulmonary veins fail to connect normally with the LA. The four pulmonary veins can converge together prior to connecting with the LA, or they can connect directly with the RA. In most cases, the four pulmonary veins converge into a horizontal pulmonary trunk behind the atrium and then drain into the left SVA or the IVC through the vertical vein. TAPVD is generally associated with a large ASD, which can compensate for hemodynamic disorders.

According to the site of the abnormal connection, TAPVD can be categorized into supracardiac type, cardiac type, and infracardiac type. The cardiac type is the most common, and the infracardiac type is rare.