the term anomalous pulmonary venous connection should be explained This is because, in certain circumstances, pulmonary veins connected in normal fashion to the morphologically left atrium can drain anomalously to a systemic site, such as when there is mitral atresia and an atrial septal defect or fenestration to the coronary sinus, or in the presence of the so-called levoatrial cardinal vein (Fig 28.3) FIG 28.3 Example of totally anomalous pulmonary venous drainage in the setting of normally connected pulmonary veins, in this instance because a so-called levoatrial cardinal vein joins the left atrium to the superior caval vein (SCV) with mitral atresia and an intact atrial septum A pulmonary vein is connected anomalously only when it is attached to a site other than the morphologically left atrium In this respect, it is also important to distinguish between the left-sided and the morphologically left atrium In the presence of isomerism of the right atrial appendages, all four pulmonary veins are frequently connected to the roof of an atrium with a morphologically right appendage, which can be left sided Because, in this setting, the atrium possesses a morphologically right appendage, this anatomic pattern is anomalous Indeed, the pulmonary veins must be connected anomalously in the setting of right isomerism irrespective of their site of drainage The topic of pulmonary venous connections in hearts with isomeric appendages, therefore, represents a special situation that is discussed in depth in Chapter 26 In this chapter, we are concerned primarily with totally anomalous connection in the setting of lateralized atrial chambers―in other words, the usual and mirror-imaged arrangements―but reference is made where appropriate to hearts with isomeric appendages When all the pulmonary veins are connected anomalously, they usually drain to the same site In some situations, different pulmonary veins are connected to separate anomalous sites This is called mixed drainage (Video 28.1) The sites of such drainage are the same as when the entirety of the pulmonary venous return reaches an extracardiac site through a confluence These sites of anomalous connection are divided into supracardiac, cardiac, and infracardiac groups The first two, taken together, constitute supradiaphragmatic drainage, whereas infracardiac drainage is at the same time infradiaphragmatic (Fig 28.4) FIG 28.4 Different sites of anomalous pulmonary venous connection Cardiac and intracardiac anomalous connections account for approximately one-quarter each of the total group Supracardiac connection can be to the left brachiocephalic vein, directly to the right superior caval vein, to the azygos system of veins, or to the left superior caval vein, although when the left vein drains to the coronary sinus, this is considered as cardiac drainage In the most common pattern, the four pulmonary veins usually join in turn to a venous channel behind the left atrium This channel is traditionally termed the confluence but the individual veins usually join the channel sequentially From this horizontal channel, a vertical vein typically runs through the left paravertebral gutter to join the left brachiocephalic vein, which terminates in the right superior caval vein (Fig 28.5; Video 28.2) It is the course of the vertical vein that usually determines whether or not the pathway is obstructed If the vein passes anterior to the left pulmonary artery, this course is not associated with obstruction Should the vein pass between the left pulmonary artery and the left bronchus, these two structures clasp the channel in the so-called bronchopulmonary vise (Fig 28.6) Obstruction with this “snowman” pattern of