Congenital abnormalities of the pulmonary venous system are rare, although they probably occur more frequently than is indicated by clinical and autopsy studies. Their variety is diverse, although certain patterns of abnormality predominate.

Instead of draining to the left atrium, the pulmonary veins are connected to the right atrium or one of its tributaries. The condition is termed total anomalous pulmonary venous connection when all the veins connect anomalously, and partial anomalous pulmonary venous connection when one or more (but not all) of the veins connect anomalously.

Although the pulmonary veins drain as normal to the left atrium, there is some obstruction to blood flow. When obstruction occurs at a single point in the left atrium, the condition is referred to as cor triatriatum. The obstruction may also selectively involve one or more pulmonary veins, causing pulmonary vein stenosis.

The veins connect without obstruction to the left atrium. Physiology is normal, and the condition is chiefly of interest to the thoracic surgeon, as it may modify the technique necessary for a pulmonary resection.

The venous drainage of the primitive lung buds is into a common pulmonary vein which drains to the cardinal veins. The latter form the future superior vena cava, left innominate vein, and coronary sinus. The connections with the cardinal veins become atretic when the common pulmonary vein fuses with an outgrowth of the left atrium: any abnormality of this developmental pathway leads to an anomalous connection. For example, if the common pulmonary vein fails to fuse with the left atrium, and one or more of the connections to the cardinal veins persists, total anomalous pulmonary venous connection results.

The common pulmonary vein is retained, and connects anomalously to one or more of three sites: supracardiac, to the left innominate vein or superior vena cava; cardiac, to the right atrium or coronary sinus; infracardiac, to the inferior vena cava or portal vein. Blood flow in the anomalous connection may be obstructed, especially in those with infracardiac total anomalous pulmonary venous connection; in 30 per cent of patients there may be other associated congenital heart defects.

Since all pulmonary venous blood flows eventually to the right atrium, systemic and pulmonary venous blood are mixed. Distribution of pulmonary venous blood depends on the presence and size of the atrial septal defect which is invariably present, any associated pulmonary artery hypertension, and its effects on flow across the atrial septal defect. As the pulmonary venous blood is highly saturated with oxygen, the right-to-left shunt through this defect does not usually lead to deep cyanosis.

Any additional obstruction in the pulmonary venous drainage leads to pulmonary venous congestion, elevated pulmonary vascular resistance, and decreased pulmonary blood flow. This produces a clinical picture of pulmonary congestion with deepening cyanosis.

Tachypnoea occurs in the first few weeks of life; non-cardiac causes must be excluded. Deep cyanosis is unusual; a pulmonary systolic flow murmur is usually present, but the clinical signs are usually unimpressive.

The chest radiograph is usually normal, although an abnormal shadow may indicate an anomalous vessel: the figure-of-eight or ‘snowman’ sign reveals total anomalous pulmonary venous connection to the left innominate vein. Pulmonary venous obstruction may manifest as a diffuse haziness and congestion. The electrocardiogram shows right ventricular hypertrophy, resulting from pulmonary hypertension.

Although echocardiography is usually diagnostic, showing the common pulmonary vein lying posterior to the left atrium, cardiac catheterization and angiography are still indicated at many institutions for accurate assessment.

This is surgical in all cases, and should be undertaken urgently following diagnosis: the only exception is in the rare case of the adult patient with established pulmonary vascular disease, in whom surgical repair is contraindicated. Balloon atrial septostomy at the time of catheterization is sometimes performed in seriously ill infants to try to stabilize their condition prior to surgery. However, there is little evidence that it is helpful, and it may damage septal structures necessary for optimum surgical repair of the defect.

Surgery is performed on cardiopulmonary bypass, usually with deep hypothermia and circulatory arrest. It is always necessary to redirect pulmonary venous blood to the left atrium: this is usually achieved by direct anastomosis between the common pulmonary vein and the back of the left atrium (Fig. 2) 1749: abnormal connections are ligated, and the atrial septal defect is closed. When total anomalous pulmonary venous connection is to the right atrium, a pericardial baffle can be used to direct blood through the atrial septal defect into the left atrium.

Postoperative severe pulmonary hypertension and right ventricular failure may be a significant problem, particularly in patients with preoperative pulmonary venous obstruction. This is managed by deep sedation and respiratory support, control of acidosis, and sometimes by administration of vasodilators. Such treatment may be required for several days before successful ventilatory weaning can be achieved. Postoperative management can be optimized by pulmonary artery pressure monitoring.

Untreated, 80 per cent of patients die within 1 year, and most die in the first 3 months of life. Those who survive develop fixed pulmonary vascular disease, right ventricular failure, and deepening cyanosis (Eisenmenger's syndrome) by their second decade.

The results of surgery have improved since the first repair, performed in 1956 by Lewis and Varco. Current hospital mortality is below 10 per cent, and most of these die from pulmonary hypertension. Late complications are uncommon, but the principal problem is pulmonary venous obstruction, which usually manifests itself within 6 months of the original surgery. If this is due to an anastomotic stricture, the anastomosis should be revised. However, obstruction is usually due to diffuse fibrosis in individual pulmonary veins, and is difficult to treat surgically: some patients may be suitable candidates for percutaneous balloon dilation. Long-term prognosis is excellent, and many treated patients with no pre-existing pulmonary vascular disease have a normal lifespan.

This is present in 0.7 per cent of all individuals autopsied. Nine per cent of patients with an atrial septal defect have associated partial anomalous pulmonary venous connection.

The most common varieties are connection of the left superior pulmonary vein to the left innominate vein, and connection of the right superior and/or inferior pulmonary veins to the superior vena cava. When a defect is present high in the atrial septum, this is termed the sinus venosus syndrome. Other common connections are from the right superior and/or inferior pulmonary veins to the right atrium, or to the inferior vena cava. In the latter, hypoplasia of the right lung is common, as are other congenital defects involving the heart and diaphragm.

The majority of patients with partial anomalous pulmonary venous connection have an associated atrial septal defect.

High pulmonary blood flow results from a left-to-right shunt, as in uncomplicated atrial septal defect. A single anomalous vein alone causes an increase in pulmonary flow of about 20 per cent and is therefore of minimal haemodynamic significance unless a large atrial septal defect is present. Several anomalously connected veins produce a more variable pattern, which depends on the presence, size, and location of any atrial septal defect and the relative resistances of pulmonary and systemic vascular beds.

This depends on the number of anomalously connected veins. One anomalous vein is usually undetectable clinically, and most patients have a normal lifespan. When most of the veins are involved, the clinical picture is similar to that of total anomalous pulmonary venous connection.

The presentation of the majority of patients is similar to that of uncomplicated atrial septal defect. There are no symptoms in childhood, but if pulmonary blood flow is very high, patients may develop pulmonary hypertension and right ventricular failure in later years. Most are diagnosed by the presence of a pulmonary flow murmur and wide, fixed splitting of the second heart sound, as in atrial septal defect. When there is hypoplasia of the right lung, as in patients with partial anomalous pulmonary venous connection to the inferior vena cava, respiratory infections are common.

The chest radiograph may show the abnormally draining vessel. When the connection is to the inferior vena cava, also known as the ‘scimitar syndrome’, a crescentic shadow in the right lower lung field is usually visible. The electrocardiogram shows peaked P waves and right ventricular hypertrophy.

Echocardiography may show abnormal entry sites of anomalous veins and may suggest the magnitude of the left-to-right shunt. As the main differential diagnosis is uncomplicated atrial septal defect, cardiac catheterization is often omitted. A search for a possible associated partial anomalous pulmonary venous communication should be made during repair of any atrial septal defect; thus it may be diagnosed perioperatively, providing the surgeon has a high index of suspicion.

Surgical correction of partial anomalous venous communication should be undertaken in any patient with a ratio of pulmonary to systemic blood flow greater than 2:1, and without severe pulmonary hypertension that would preclude surgery. Isolated partial anomalous venous correction of the whole of one lung is also an indication for repair, since the opposite lung is the only one able to return oxygenated blood to the systemic circulation; should this lung become diseased later in life, fatal anoxia is a potential hazard.

Cardiopulmonary bypass with or without circulatory arrest is always required. The anomalous flow of blood into the left atrium is usually corrected by the use of an intracardiac baffle, which is positioned to ‘tunnel’ blood from the anomalous entry site, via the atrial septum to the left atrium (Fig. 3) 1750. When the anomalous connection is to the left innominate vein, the anomalous vein can be transferred to the left atrial appendage.

This is similar to that of uncomplicated atrial septal defect, hospital mortality being less than 1 per cent. Long-term survival is excellent when surgery is undertaken before the development of pulmonary hypertension, when the prognosis is poorer.

This constitutes 0.4 per cent of congenital heart disease.

The pulmonary veins drain into a single chamber, the so-called ‘third atrium’, which lies posterior to the left atrium. The two chambers share a common wall, composed of a diaphragm of tissue with a central aperture. This aperture is only 3 mm to 1 cm in diameter, resulting in pulmonary venous obstruction.

The condition presents in the first few years of life with the symptoms and signs of pulmonary congestion: the narrower the aperture the earlier the onset and the more severe are the symptoms. Echocardiography shows the abnormal chamber, the diaphragm, and the size of the aperture. Cardiac catheterization is performed if other abnormalities are suspected.

The prognosis of untreated patients depends on the size of the aperture; however, since 75 per cent die in infancy, surgery is usually performed urgently. Cardiopulmonary bypass is established and the diaphragm is removed via an incision through the right atrium and atrial septum. Operative mortality depends on the degree of preoperative pulmonary venous congestion and pulmonary hypertension. Long-term results are excellent; there is a risk of pulmonary vein stenosis.

In this rare condition one or more pulmonary veins are locally or diffusely narrowed, often near their junction with the left atrium. Associated cardiac abnormalities are the rule. Pulmonary venous congestion results, leading to right heart failure. Despite medical treatment, most patients die by the age of 4 years. Surgical therapy is unrewarding, particularly when stenosis is diffuse, and the condition often progresses postoperatively, despite an initially good result. Percutaneous dilatation of localized pulmonary vein stenoses is now being undertaken: although short-term results are encouraging, the long-term benefits are unknown.

Abnormalities of the systemic veins are common, and most have no physiological consequences. They may, however, complicate the placement of central venous cannulas and pulmonary artery catheters; they may also modify the technique of venous cannulation for cardiopulmonary bypass, as well as some thoracic operations. Right-to-left shunting results when a systemic vein connects to the left atrium.

This vessel connects the left innominate vein to either the coronary sinus or the left atrium. The latter causes right-to-left shunting which may be sufficient to lead to cyanosis. Operative treatment is advised to prevent systemic embolism. If a rightsided superior vena cava is also present, the abnormal left superior vena cava may simply be ligated; otherwise it must be transposed to the right atrium.

In this condition the coronary sinus communicates normally with the right atrium, but there is a defect in its common wall with the left atrium. The result is a left-to-right shunt comparable to an atrial septal defect. Closure of the opening of the coronary sinus into the right atrium allows coronary sinus blood to drain into the left atrium. The small right-to-left shunt that results is haemodynamically insignificant.

The inferior vena cava has complex embryological origins, and it may drain anomalously into either the azygous vein or left atrium. Only in the latter case is surgical correction indicated, for the same reasons as in a left superior vena cava connection to the left atrium.

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