Scimitar Syndrome

Scimitar syndrome (pulmonary venolobar or hypogenetic lung syndrome) is a rare congenital anomaly in which all or part of the right lung drains through an anomalous vein into the inferior vena cava, usually near its junction with the right atrium. The vein gives a curved sword shaped shadow on chest X-ray.

Associated features are right lung hypoplasia, dextroposition of the heart, hypoplastic right pulmonary artery, abnormal bronchial branching, systemic arterial supply to the right lower lobe from the abdominal aorta (with or without sequestration), and atrial septal defect.

It accounts for 3 to 6% of partial anomalous pulmonary venous connection, with an incidence of about 1 to 3 in every 100,000 live births and a female predominance. Left sided forms are exceptional.

Pathophysiology. The anomalous vein produces a left-to-right shunt, and pulmonary venous obstruction in the vein itself adds to this. Pulmonary hypertension is the main determinant of outcome. It is severe in the infantile form, which presents in the first year, and mild or absent in the adult form.

Systemic arterial supply to the lung adds a further left-to-right shunt and a source of haemoptysis.

• Infantile form: tachypnoea, heart failure, failure to thrive, recurrent pneumonia and pulmonary hypertension.
• Adult form: often asymptomatic and found on a chest X-ray. Symptoms include exertional dyspnoea, fatigue, recurrent right sided chest infections and haemoptysis.
• Examination: apex displaced to the right with reduced right chest expansion, flow murmur from the left-to-right shunt, fixed splitting of the second sound if an atrial septal defect is present, and signs of pulmonary hypertension.

Red flags.

• Infant with pulmonary hypertension or heart failure
• Haemoptysis
• Recurrent right sided pneumonia
• Cyanosis
• Right ventricular dilatation with a shunt ratio of 1.5 or more

• Chest X-ray: small right lung, mediastinal shift to the right, and the scimitar vein as a curvilinear opacity along the right heart border.
• ECG: right axis deviation and right ventricular hypertrophy.
• Echocardiography: dilated right ventricle, estimated pulmonary pressure, atrial septal defect, and sometimes the vein entering the inferior vena cava.
• CT angiography: the best test. It defines the anomalous vein and its drainage site, systemic arterial supply, bronchial anatomy, lung hypoplasia and sequestration.
• Cardiac MRI: phase contrast flow gives the pulmonary to systemic flow ratio (Qp:Qs).
• Cardiac catheterisation: pulmonary artery pressure, pulmonary vascular resistance, Qp:Qs and aortography for systemic arterial supply.

Differential diagnosis.

• Partial anomalous pulmonary venous connection without a scimitar vein (for example, right upper lobe to the superior vena cava)
• Pulmonary arteriovenous malformation
• Isolated pulmonary sequestration
• Right lung agenesis or hypoplasia
• Dextrocardia with situs inversus
• Swyer-James syndrome
• Congenital diaphragmatic hernia with pulmonary hypoplasia

• Asymptomatic, Qp:Qs under 1.5, no pulmonary hypertension: observation.
• Indications for surgery: symptoms, Qp:Qs of 1.5 or more with right ventricular volume overload, pulmonary hypertension, or recurrent infections.
• Repair: baffle the scimitar vein to the left atrium through an intra-atrial tunnel (or reimplant it directly), with closure of the atrial septal defect. Obstruction of the baffle or vein is the main late complication.
• Coil or plug occlusion of anomalous systemic arterial supply to the lung to remove the shunt and control haemoptysis.
• Lobectomy for a sequestered segment with recurrent infection. Pneumonectomy for a non-functioning hypoplastic lung in selected cases.
• Infantile form with pulmonary hypertension: furosemide 0.5 to 1 mg/kg intravenously every 6 to 12 hours, or 1 to 2 mg/kg orally every 6 to 12 hours, maximum 6 mg/kg daily, with monitoring of sodium, potassium, creatinine and weight. Pulmonary vasodilator therapy in a specialist unit. Mortality is higher in this group.
• Treat intercurrent chest infections promptly.

Special groups. Pregnancy is tolerated when there is no pulmonary hypertension and no significant residual shunt. It is high risk with pulmonary hypertension.

Monitoring. CT or MRI at 6 to 12 months after repair to check the baffle and vein, with echocardiography yearly. Lung perfusion scanning when right lung function needs quantifying.

Referral and escalation. Refer all patients to a congenital heart disease centre. Urgent for infants with pulmonary hypertension or heart failure, and for haemoptysis.