Introduction
Partial anomalous pulmonary venous return (PAPVR) or partial anomalous pulmonary venous connection (PAPVC) is a birth defect in which some of the pulmonary veins have an anomalous (abnormal) connection. Total anomalous pulmonary venous return (TAPVR) or total anomalous pulmonary venous connection (TAPVC) is a congenital heart defect in which pulmonary veins do not have a normal connection to the left atrium; instead, they have an abnormal connection. Pulmonary veins are the blood vessel that usually carries oxygenated blood from the lungs to the left atrium of the heart. Pulmonary veins are the only vein that carries oxygenated blood, whereas other veins carry deoxygenated blood.
What Are the Different Types of Total Anomalous Pulmonary Venous Return?
Total anomalous pulmonary venous return (TAPVR) is classified into four types based on the areas of draining of pulmonary veins.
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Supracardiac TAPVR - In supra-cardiac TAPVR, the pulmonary veins form an abnormal connection above the heart, commonly to the left innominate vein, superior vena cava (SVC), and azygous vein. This is the most common type of TAPVR.
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Infracardiac TAPVR - In infra cardiac TAPVR, the pulmonary veins form an abnormal connection below the heart into the right atrium through the veins of the liver and inferior vena cava.
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Cardiac TAPVR - In cardiac TAPVR, the pulmonary veins join behind the heart and form an abnormal connection with the right atrium or coronary sinus.
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Mixed TAPVR - In mixed TAPVR, the pulmonary veins connect at different levels. This type is less common.
What Are the Signs and Symptoms of Total Anomalous Pulmonary Venous Return?
The signs and symptoms of TAPVR include:
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Cyanotic (bluish-colored) skin, lips, and nails.
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Breathing problems include grunting, rapid breathing, and retraction of the rib cage muscles.
What Is the Pathophysiology of TAPVR and PAPVR?
PAPVR:
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In PAPVR, there is a left-to-right shunt at the arterial level resulting in the recirculation of oxygenated blood through the pulmonary vasculature.
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The increased blood level on the left side results in pulmonary hypertension and dilation of the right ventricle and atrium.
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Certain factors determine left to right shunt, including the number and size of the pulmonary veins, the size of the atrial septal defect (ASD), the site of origin of abnormal veins, and pulmonary vascular resistance.
TAPVR:
In TAPVR, the oxygenated blood from the lungs reaches the right atrium. Hence in the right atrium, the oxygenated and deoxygenated blood mixed and then shunted right to the left at the atrial level. This results in cyanosis in TAPVR patients.
TAPVR Without Obstruction:
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Cardiac and supra-cardiac TAPVR types are often non-obstructed.
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Due to the decreased pulmonary vascular resistance in the early week of life, there is an increased recirculation in the lungs resulting in pulmonary over circulation.
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Over time the pulmonary vascular changes result in pulmonary hypertension and right heart failure.
TAPVR With Obstruction:
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Infra cardiac TAPVR is the common cause of obstructive TAPVR.
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Pulmonary venous obstruction can occur at the level of hepatic sinusoids, diaphragm, and veins entering the inferior vena cava.
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Increased pressure in the pulmonary venous system results in pulmonary edema, pulmonary hypertension, pulmonary vascular resistance, right heart failure, and right ventricular hypertrophy.
What Are the Imaging Techniques Used in the Diagnosis of TAPVR and PAPVR?
The imaging techniques used in the diagnosis of TAPVR and PAPVR include:
Radiography:
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The radiography of patients with TAPVR appears as supra cardiac shadow along with normal cardiac shadow having a “snowman” appearance.
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In patients without obstruction, the heart appears enlarged with the prominent right ventricle and pulmonary artery. The vascularity of the lungs is increased.
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The chest radiography of neonates having pulmonary venous obstruction shows a small heart and pulmonary edema in a perihilar pattern.
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In PAPVR patients, chest radiography shows abnormal drainage of more than two pulmonary veins, pulmonary hypertension, increased pulmonary vasculature, and right ventricular dilatation.
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Sometimes, dilatation of the superior vena cava, presence of an azygous vein, and left vertical vein are seen in PAPVR.
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In cases with abnormal drainage of right pulmonary veins into the inferior vena cava, the pulmonary veins exhibit a scimitar-shaped or crescent-shaped curve along the right side border of the heart in the right lower lung area. It is called scimitar syndrome.
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Due to the presence of the thymus, the “snowman” appearance is not seen in the chest radiography of early infants. Sometimes in patients with obstruction, the findings of small heart and pulmonary congestion may be misinterpreted as primary pulmonary disease.
Computed Tomography Scan:
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In patients with TAPVR or PAPVR, the abnormal draining pulmonary veins and associated cardiac and extracardiac abnormalities are reliably detected with a low dose, high-pitch CT without sedation in pediatric patients.
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In most patients, a CT scan shows atrial septal defect, patent ductus arteriosus, persistent superior vena cava, and aortic coarctation.
Magnetic Resonance Imaging Scan:
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Magnetic resonance imaging (MRI) of TAPVR patients shows a lack of pulmonary vein draining into the left atrium, the presence of abnormally draining pulmonary veins, large right ventricular, asymmetric pulmonary vasculature, large right atrium, and right to left interatrial shunt.
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Two-dimensional cine phase-contrast MRI is helpful in identifying and also quantifying the shunt flow.
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Fast imaging employing- state acquisition (FIESTA) sequence of MRI helps in visualizing the entire atria, which is useful for identifying pulmonary venous return.
Echocardiography:
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Transthoracic echocardiography is useful in detecting the abnormal connections of pulmonary veins and in assessing the hemodynamic consequences in TAPVR and PAPVR.
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Echocardiography shows right ventricular dilation and hypertrophy, right atrial dilation, and leftward flattening or bowing of the interventricular septum.
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Compressed left chambers result in the underfilled left atrium and ventricle.
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In supra cardiac TAPVR, the superior vena cava appears dilated.
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In infra-cardiac TAPVR, the inferior vena cava seems to be dilated, and the presence of a vertical vein might connect with a hepatic or portal vein.
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In Doppler ultrasound, venous flow away from the heart below the diaphragm indicates TAPVR.
Angiography:
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In mixed TAPVR, cardiac catheterization shows more or less similar levels of oxygen saturation in both ventricles, both atria, and the aorta.
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Increased systemic venous saturation occurs at the entry site of the anomalous pulmonary venous channel.
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Pulmonary hypertension is seen in infants with pulmonary venous obstruction, whereas in older patients, the pulmonary arterial and ventricular pressure is moderately elevated.
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Selective pulmonary arteriography or venography shows the anatomy of pulmonary veins and their connection to systemic venous circulation.
What Are the Differential Diagnoses of PAPVR and TAPVR?
The differential diagnoses of PAPVR and TAPVR are:
PAPVR:
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Atrial septal defect (ASD).
TAPVR:
Obstructed TAPVR -
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Respiratory distress syndrome.
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Persistent pulmonary hypertension of the newborn.
Unobstructed TAPVR -
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Truncus arteriosus.
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AV (atrioventricular) canal disease.
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Large ASD and VSD (ventricular septal defect).
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Single ventricle lesion.
Conclusion
Total anomalous pulmonary venous return (TAPVR) and partial anomalous pulmonary venous return (PAPVR) can be diagnosed prenatally with the help of an ultrasound, whereas a fetal echocardiogram helps confirm the diagnosis. However, it is hard to detect pulmonary veins prenatally as the lungs receive less blood when the baby is inside the womb. TAPVR and PAPVR can be corrected surgically by closing the abnormal pulmonary venous connection. Once after the surgical repair, the infants or adults need regular follow-ups to monitor the improvement and to avoid complications.
