Horseshoe lung with bilateral vascular anomalies: a rare variant of hypogenetic lung syndrome (scimitar syndrome).

Horseshoe lung is a rare congenital malformation in which the posterobasal segments of the right and left lungs are fused to each other, behind the pericardial reflection at the cardiac apex.1 Horseshoe lung deformity often has the vascular anomalies seen in hypogenetic lung syndrome (scimitar syndrome),1 which is a rare congenital anomaly characterized by hypoplasia of the lung with hypoplasia of pulmonary artery, anomalous systemic arterial supply, anomalous pulmonary venous drainage, and anomalies of bronchial trees.2 Although the anomalies seen in hypogenetic lung syndrome show considerable variations, the combination of anomalies is usually located unilaterally, almost invariably on the right side.2 We report a female infant with horseshoe lung that bilaterally has the vascular anomalies seen in hypogenetic lung syndrome. The anomalous pulmonary vascular pattern may be an extremely rare variant of hypo­genetic lung syndrome or a new anomaly. A 34-day-old female infant was admitted to our hospital because of retraction and cyanosis. She was born at full-term with no complications and weighed 2870 g at birth. She had no phenotypic abnormalities on inspection. Immediately after birth, cough symptoms and slight retraction without cyanosis were noted. Before admission, retraction deteriorated with cyanosis. On physical examination, reduced breath sounds and wheezing were heard on the left and right lung, respectively. A heart murmur was not heard. The frontal plain chest radiograph showed the small left lung, the cardiac silhouette displaced to the left with ill-defined cardiac border, and markedly increased pulmonary vascular markings in the right lung (Fig. 1). Right atrial and ventricular dilatation without congenital cardiac malformations were demonstrated in the cardioechography. The computed tomography scan of the chest revealed pulmonary vascular dilatation in the right lung and horseshoe deformity. The chest radiogragh revealed cardiac displacement to the left with ill-defined cardiac border and markedly increased pulmonary vascular markings in the right lung. The right pulmonary artery was dilated with anomalous branches, some of which extended across the midline into the left hemithorax (Fig. 2a). The venous drainage of the right lung was also anomalous, passing through only one winding pulmonary vein to the left atrium. There was an abnormal subdiaphragmatic artery from the descending aorta to the lower lobe of the right lung (Fig. 2b). The venous drainage of the flow supplied from this artery passed through the same, only one right pulmonary vein to the left atrium as that of the right pulmonary artery (Fig. 2c), partially producing the left to left shunt. (a) Selective angiography from the right main pulmonary artery revealed a dilated artery with anomalous branches. Some of them extended across the midline into the left hemithorax (arrow). (b) An abnormal subdiaphragmatic artery arose from the descending aorta to the lower portion of the right lung (arrow). (c) The venous drainage of the abnormal subdiaphragmatic artery passed through the same, only one winding pulmonary vein to the left atrium (arrow) as that of the right pulmonary artery, partially producing the left to left shunt. The left pulmonary artery was thin, although the branching pattern of its vascular tree corresponded to a normal pattern. The left pulmonary vein was not observed. The venous drainage of the left lung passed through the abnormal vessel below the diaphragm to the portal vein (Fig. 3). The left venous phase demonstrated the anomalous venous drainage only through the abnormal vessel below the diaphragm to the portal vein (arrow). A right bronchography performed at the age of 1 year and 4 months revealed a hypoplastic right bronchial tree with abnormal branching pattern. A left bronchography was not performed. We performed embolization of the abnormal subdiaphragmatic artery with interventional vascular catheterization techniques using coils at the age of 2 months. After the embolization, she was treated with oxygen therapy and administration of digoxin to prevent congestive heart failure. When she was 2-years-old, the aortography revealed the collateral vessels arising from the abdominal aorta. The collateral vessels into the lower lobe of the right lung drained into only one right pulmonary vein and the other collateral vessels into the lower lobe of the left lung drained upstream into the left pulmonary artery. Furthermore, the left bronchial artery also drained upstream into the left pulmonary artery. She had slight hemoptysis from the left lung twice at 3 years. However, she has not had hemoptysis, since we performed embolization of the collateral vessels into the left lung with interventional vascular catheterization techniques using coils at the age of 3 years. Digoxin was discontinued at the age of 4 years. Although she has had wheezing and dyspnea after upper respiratory infections, the incidence and severity of respiratory symptoms has gradually decreased. Hypogenetic lung syndrome (scimitar syndrome) is the anomaly that usually consists of hypoplasia of the right lung and of the right pulmonary artery, anomalies of the right bronchial trees, anomalous venous drainage from the right lung to the inferior vena cava, displacement of the heart to the right, anomalous systemic supply of the right lung, and occasionally horseshoe lung.2 Hypogenetic lung syndrome shows considerable variations in the pattern of anomalous pulmonary venous drainage.2−4 The venous drainage pattern of the right lung in this case was similar to that of a variant of hypogenetic lung syndrome.4 However, the anomalous venous drainage from the left lung below the diaphragm, which to the portal vein is rare, was also one of the features seen in hypogenetic lung syndrome.2 The anomalies seen in hypogenetic lung syndrome are usually located on the right lung,2 while a few cases had the anomalies on the left lung.5 Although the combination of anomalies is usually located unilaterally, the anomalous pattern that bilaterally has the pulmonary vascular anomalies seen in hypogenetic lung syndrome has not been previously reported to our knowledge. Furthermore, the chest radiograph did not show a small right lung. The dilated right pulmonary artery with anomalous branches may differ from hypoplasia of the right pulmonary artery seen in hypogenetic lung syndrome. Although hypogenetic lung syndrome usually shows cardiac dextroposition with a small right lung, this case displaced the heart to left. Horseshoe lung with left lung hypoplasia is rare.6 However, it is unclear whether the small left lung on the chest radiograph revealed a hypoplastic lung or a lung compressed by cardiac dilatation and whether the thin left pulmonary artery revealed hypoplasia of the artery or not. Therefore, the anomalous pulmonary vascular pattern presented here may be an extremely rare variant of hypogenetic lung syndrome or a new pulmonary vascular anomaly that differs from hypogenetic lung syndrome. The patient with hypogenetic lung syndrome diagnosed in infancy often has cardiac failure or severe respiratory insufficiency due to associated cardiac malformations or pulmonary hypertension caused by a large shunt.7 The successful treatment with ligation7 or embolization8 for the abnormal arterial supply, or lobectomy9 was reported. Although respiratory symptoms decreased after coil embolization for the abnormal systemic artery, she had hemoptysis from the left lung. Left pulmonary hypertension may be more severe than the right, because hypoperfusion of the left pulmonary artery, obstruction of normal venous return from the left lung, and two large shunts between the left pulmonary artery and the collateral vessels from systemic artery or the left bronchial artery coexist. We did not perform embolization of the left bronchial artery that constituted a residual large shunt, because she might have severe pulmonary infarction. The resection of the left lung with more severe pulmonary hypertension might be necessary to improve respiratory symptoms.9,10 However, no severe events have occurred and symptoms have gradually improved without resecting the left lung during the follow-up period until 10 years of age. Further surgical treatment may not be necessary if pulmonary hypertension does not progress.