Anomalous Pulmonary Venous Connection
Total anomalous pulmonary venous connection (TAPVC) is a condition in which all the pulmonary venous return drains either directly into the right atrium or into channels that ultimately terminate in the right atrium. In all cases, a right-to-left shunt (atrial septal defect [ASD]) is present, allowing return of blood to the left heart and systemic circulation. TAPVC is also referred to as total anomalous pulmonary venous return.
Although several different classification systems have been proposed for TAPVC, the most widely used is that of Craig et al,1 which is based on the anatomical location of the anomalous connection.1 With this system, TAPVC is divided into four categories (Fig. 16–1), listed here in order of frequency:
There is some variation in the reported frequencies for these four types of TAPVC; however, in most large series, the order of frequency is as listed, with supracardiac anomalous connection comprising the majority of cases.2 A large retrospective study reviewed the medical records of 377 children with TAPVC between 1946 and 2005. In this study the anomalous venous connection was supracardiac in 44%, infracardiac in 26%, cardiac in 21%, and mixed in 9%.3
Obstruction to pulmonary venous return can occur at any level between the pulmonary veins (or the common pulmonary venous confluence characteristic of TAPVC) and the right atrium. Obstruction may occur at a discrete level because of intrinsic narrowing of a vessel or compression from external structures, or it may be more generalized as when a large volume of pulmonary venous blood is forced through the liver in the setting of TAPVC of the infracardiac type. Karamlou et al3 found that at the time of presentation 48% of children with TAPVC had some degree of obstruction.
Most cases of TAPVC fall into the supracardiac category. Most commonly, the four pulmonary veins (two from each lung) form a confluence posterior to the left atrium. An anomalous vertical vein originates from the left aspect of the confluence and courses cephalad and anterior to the left main bronchus and left pulmonary artery, to join the left innominate vein, which, in turn, enters the right superior vena cava (SVC). A second, less common type of anomalous supracardiac connection consists of a connection between an anomalous trunk arising from the right side of the pulmonary venous confluence and the right SVC.
Obstruction is rare with both types of supracardiac connection; however, it may occur when the left vertical vein is compressed between the left main stem bronchus and pulmonary artery or when there is a restrictive connection to the SVC. Complex cardiac malformations are common with anomalous connection to the right SVC.4
In the cardiac type of TAPVC, the anomalous veins empty into the coronary sinus (more common) or into the posterior right atrium directly (less common) or through a short common trunk. Although several studies have suggested that obstruction is rare with direct cardiac connection,5,6 a subsequent series found obstruction in 22% of patients with TAPVC to the coronary sinus.7
In infracardiac TAPVC, the four pulmonary veins generally join to form a confluence posterior to the left atrium. An anomalous descending vein extends from the confluence downward just anterior to the esophagus and accompanies the esophagus through the diaphragm by way of esophageal hiatus. In approximately 80% of cases, the anomalous vein drains into the portal venous system (usually at the portal confluence or splenic vein).1,8 Rarely, this anomalous descending vein empties into one of the hepatic veins, the ductus venosus, or the inferior vena cava (IVC).8
Infracardiac TAPVC, unlike supracardiac TAPVC, is almost always associated with some degree of obstruction. This obstruction to venous return is frequently severe and may occur at any level, including the esophageal hiatus, the portal vein–to–anomalous vessel connection, or the ductus venosus (particularly after the normal obliteration of this vessel). In all cases, some degree of generalized obstruction occurs at the hepatic sinusoidal level when the large volume of pulmonary venous blood entering the portal venous system is forced through the liver.
Mixed anomalous connection is the least common type of TAPVC. A large variety of pulmonary venous drainage patterns may occur in this subgroup. Most commonly, the left pulmonary veins drain into the left innominate vein through an anomalous vertical vein and the right pulmonary veins drain into the coronary sinus or directly into the right atrium. Obstruction can occur at one or more levels.
With partial anomalous pulmonary venous connection (PAPVC), one or more, but not all four, pulmonary veins connect directly to the right atrium or to a tributary that terminates in the right atrium. PAPVC is also commonly referred to as partial anomalous pulmonary venous return (PAPVR).
• The right pulmonary veins enter the right atrium via the IVC. The left pulmonary veins enter the left atrium. In this form, the atrial septum is usually intact (excluding the normal foramen ovale). This type of PAPVC has been associated with hypoplasia of the right lung, hypoplasia of the right pulmonary artery, dextroposition, and other cardiac anomalies.10
• The left pulmonary veins enter the left innominate vein, which then connects with the SVC and drains into the right atrium. The right pulmonary veins may enter the left atrium, the coronary sinus, the IVC, the SVC, or the left subclavian vein. An ostium secundum ASD is often present. This form of PAPVC has been associated with a variety of cardiac anomalies and syndromes, including polysplenia, asplenia, Turner syndrome, and Noonan syndrome.
• The least common form of PAPVC involves the left pulmonary veins draining into the coronary sinus, the IVC, the SVC, the right atrium, or the left subclavian vein. The right pulmonary veins usually maintain their normal connection to the left atrium.
The embryonic lungs, larynx, and tracheobronchial tree are derived from the foregut. The primitive lungs are in close contact with the vascular plexus of the foregut (the splanchnic plexus), a portion of which later forms the pulmonary vascular bed. Initially, there is no direct venous connection between the heart and the lungs, and the pulmonary vascular bed drains with the splanchnic system into the cardinal and umbilicovitelline venous systems. Between 27 and 29 days’ gestation, the common pulmonary vein begins to form from an outpouching located to the left of the septum primum on the roof of the common atrium (Fig. 16–3, A). By gestational day 30, the atrial outpouching (common pulmonary vein) and the pulmonary venous portion of the splanchnic system have joined, forming a direct connection between the heart and the pulmonary veins (Fig. 16–3, B