Scimitar syndrome describes a specific subset of partial anomalous pulmonary venous return (PAPVR) in which an anomalous right sided pulmonary vein(s) drains either above or below the diaphragm into the inferior vena cava. “Scimitar” is in reference to the classic chest x-ray appearance of the right chest in which the anomalous vein curves downward toward the diaphragm and resembles the shape of a curved middle eastern sword.
Scimitar syndrome is often associated with hypoplasia of the right lung resulting in secondary dextroposition of the heart, hypoplasia of the right pulmonary artery, and abnormalities of the bronchial tree. There are often aortopulmonary (AP) collaterals from the descending aorta to the right lung. Sequestered lung segments (portions of the lung which do not directly communicate with the bronchial tree) are also common.
Clinically, patients with scimitar syndrome often present in infancy with pulmonary overcirculation due to large AP collaterals. Children who present in the school-age years often complain of complications related to pulmonary and bronchial hypoplasia. The disease can also remain subclinical until well into adulthood when patient present with right heart dilation and/or early pulmonary hypertension from the left-to-right shunt.
Scimitar syndrome is rare and is estimated to affect ~2/100,000. It makes up only 3-6% of all PAPVR. Approximately 40% of patients will have an associated ASD. 25% will have other associated variants of congenital heart disease.
Scimitar syndrome arises due to an embryological problem with the right lung bud. Due to hypoplasia and abnormal development, the endodermal tissue from the lung bud which forms the pulmonary venous plexus fails to grow to meet the mesodermal pulmonary vein outpouchings from the mesodermal tissue of the common atrium. As a result, the venous blood from the right lung forms the scimitar vein.
Early symptoms and presentation are due to overcirculation from AP collaterals from the descending aorta to the right lung. This high pressure left-to-right shunting causes congestive heart failure and can lead to pulmonary hypertension if not addressed early in life. Patients who do not have significant AP collateral flow have physiology similar to an ASD or other types of PAPVR with low-pressure left-to-right shunting. Over time, this can lead to right heart dilation and pulmonary hypertension. Due to the hypoplasia of the right lung, however, the amount of shunting is often small and many patients never require intervention.
Goals of echocardiography exam
Determine cardiac position (patients often with dextroposition)
Determine the location of pulmonary venous connections and if they are obstructed in any way
Assess for presence and location of AP collaterals
Assess for associated ASD or other CHD lesions
Assess for right heart dilation
Assess for right pulmonary artery hypoplasia
Assess for evidence of pulmonary hypertension (septal flattening, use tricuspid regurgitation to assess RV pressures)
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Vida VL et al. (2010). Scimitar Syndrome: A European Congenital Heart Surgeons Association (ECHSA) Multicentric Study. Circulation. 122: 1159-1166.