Scimitar syndrome usually presents in a child with recurrent respiratory infections, heart murmur, and dyspnea on exertion, due to partial anomalous pulmonary venous return (PAPVR) from the right lung to the inferior vena cava, and a hallmark curvilinear scimitar shadow on chest radiography, resembling the Turkish sword from which it derives its name.
Description
Scimitar syndrome, also known as pulmonary venolobar or hypogenetic lung syndrome, is a rare congenital cardiovascular anomaly. It is characterised by a constellation of abnormalities including partial anomalous pulmonary venous return (PAPVR) of the right lung to the inferior vena cava, hypoplasia of the right lung and pulmonary artery, systemic arterial supply to the right lung from the aorta and cardiac dextroposition. The syndrome may present in infancy with severe cardiac and respiratory symptoms or may be incidentally discovered in asymptomatic adults.
Partial Anomalous Pulmonary Venous Return (PAPVR) is a congenital cardiac anomaly where one or more, but not all, pulmonary veins aberrantly drain into the right atrium or its venous tributaries instead of the left atrium.
Pathogenesis
The syndrome results from a developmental anomaly occurring early in foetal life, leading to abnormal formation of the pulmonary veins and potentially the lung parenchyma and pulmonary arteries. The aberrant venous return causes a left-to-right shunt, leading to increased blood flow to the right heart and pulmonary hypertension.
Epidemiology, Risk Factors & Associations
- Rare, with no clear gender predilection.
- The infantile form presents with more severe symptoms and has a worse prognosis.
- Associations: Other congenital heart defects may coexist, such as atrial septal defect (ASD) and ventricular septal defect (VSD).
Clinical Features
- In infants, symptoms include tachypnea, recurrent respiratory infections, failure to thrive, and heart failure.
- Adults are often asymptomatic but may present with dyspnoea on exertion, recurrent respiratory infections, or pulmonary hypertension.
- A heart murmur may be detected on physical examination.
Complications
- Pulmonary hypertension.
- Right heart failure.
- Recurrent pneumonia.
- Hemoptysis in cases with significant systemic arterial supply to the lung.
Pathological Features
Histopathology
- Macroscopic: Hypoplasia of the right lung, with an aberrant vein draining into the inferior vena cava.
- Microscopic: Can show signs of pulmonary arterial hypertension such as medial hypertrophy of the pulmonary arteries.
Radiological Features
General Features
- Drainage into the IVC is most common. Drainage into the right atrium and portal vein is also possible.
XR
- Chest X-ray: Demonstrates the scimitar sign, a curvilinear shadow along the right heart border, representing the anomalous pulmonary vein.
CT
- Angiography: Anomalous vein drains a portion or the entire right lung into the systemic venous circulation.
Grading and Staging
- Scimitar syndrome does not have a specific grading or staging system but is evaluated based on the extent of the anatomical abnormalities and physiological impact, particularly the degree of pulmonary hypertension and right heart strain.
Diagnosis
- Based on clinical presentation and imaging findings. Chest X-ray, CT, and MRI are key diagnostic tools, with echocardiography useful for assessing associated cardiac anomalies and hemodynamics.
Differential Diagnosis
- Other causes of partial anomalous pulmonary venous return (PAPVR): Other forms of PAPVR may involve the left lung or different anomalous connections, such as to the superior vena cava or right atrium. The differentiation is based on the specific venous drainage pattern seen on imaging.
- Congenital pulmonary airway malformation (CPAM): Characterised by cystic masses within the lung parenchyma, distinguishable from Scimitar syndrome by the absence of anomalous venous return and systemic arterial supply to the lung.
- Pulmonary sequestration: Involves non-functioning lung tissue with systemic arterial supply, typically lacking the anomalous venous return to the inferior vena cava characteristic of Scimitar syndrome. It may be intralobar or extralobar, distinguished by the presence or absence of its own visceral pleura.
- Atrial septal defect (ASD): While ASD can coexist with Scimitar syndrome, isolated ASDs do not involve anomalous pulmonary venous return or pulmonary hypoplasia. Diagnosis is primarily through echocardiography.
- Primary pulmonary hypertension: Presents with signs of pulmonary hypertension but lacks the anatomical abnormalities of Scimitar syndrome. Diagnosis involves echocardiography and right heart catheterisation to measure pulmonary artery pressures.
- Bronchopulmonary dysplasia (BPD): Seen in premature infants exposed to high levels of oxygen and mechanical ventilation, characterised by chronic lung disease and not associated with the vascular anomalies of Scimitar syndrome.
Management
- Surgical correction is indicated for symptomatic individuals or those with significant shunt, pulmonary hypertension, or heart failure. Procedures may include repair of the anomalous venous return, closure of associated ASDs, and resection of systemic arterial supply.
- Management of pulmonary hypertension and right heart failure with medical therapy as needed.