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Congenital anomalous venous drainage of the right pulmonary veins into the inferior vena cava, associated with hypoplasia or aplasia of one or more lobes of the right lung.

Scimitar syndrome

Mild to moderate hypoplasia of the right lung results in displacement of the heart to the right side in a 6-year-old girl with scimitar syndrome. Right ventricular enlargement is seen. There is an anomalous pulmonary vein on the right side (because of its shape called scimitar vein (see text, white arrows) draining into the inferior vena cava. This vein has been surgically clipped (black arrow). Furthermore, the persistent ductus arteriosus had to be coiled (triangle).

Scimitar syndrome

In this posterior view of the three dimensional reconstruction of the chest CT scan of the same patient, the scimitar vein can easily be identified (white arrows) draining into the inferior vena cava. The triangles indicate the aorta.

The name scimitar syndrome originates from the anomalous pulmonary vein on the right side, which drains into the inferior vena cava. This vein is sometimes visible on the radiograph of the chest resulting in a curvilinear shadow just above the right diaphragm. The shape of this shadow resembles a scimitar, a saber typically used by Arabs and Turks.

1:300,000 live births.

Anomalous venous drainage of the right lung into the inferior vena cava represents a large left-to-right shunt. If an atrial septal defect is present and is not restrictive, right-to-left shunting occurs at the atrial level and compensates for the shunt caused by the anomalous pulmonary venous drainage. The left side of the heart is volume underloaded while the right side has an increased load. The scimitar syndrome is associated with pulmonary artery hypoplasia or atresia, predisposing to right ventricular failure. Obstruction of the anomalous venous drainage may occur at the level of the diaphragm or at insertion into the inferior vena cava, resulting in pulmonary venous congestion and pulmonary hypertension.

Cyanotic heart disease in presence of 'scimitar sign' on chest radiograph. Echocardiography is nonspecific. Anomalous venous drainage confirmed by cardiac catheterization.

Failure to thrive, cyanosis, tachycardia, signs and symptoms of right ventricular failure. Auscultation may reveal fixed, wide splitting of the second heart sound, a diastolic murmur of tricuspid origin, and a pulmonary ejection murmur in the presence of pulmonary hypoplasia. Presentation may be delayed in the presence of a nonrestrictive atrial septal defect until growth results in the atrial septal defect becoming restrictive causing a fall in arterial oxygen pressure (PaO2). The ECG shows right axis deviation and signs of right ventricular strain. The anomalous vein(s) cause a vertical scimitar shape on chest radiograph.

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