Scimitar syndrome, also known as hypogenetic lung syndrome,is characterized by a hypoplastic lung that is drained by an anomalous pulmonary vein into the systemic venous system. It is a type of partial anomalous pulmonary venous return and is one of the several findings in congenital pulmonary venolobar syndrome.
Infants present with signs of heart failure, which may be due to associated congenital heart disease . Adults are most frequently asymptomatic but may have recurrent pulmonary infection or dyspnea on exertion.
It is essentially a combination of pulmonary hypoplasia and partial anomalous pulmonary venous return (PAPVR). It almost exclusively occurs on the right side.
Haemodynamically, there is an acyanotic left to right shunt. The anomalous vein usually drains into:
- inferior vena cava: most common
- right atrium
- portal vein
In some variants, the abnormal lung segment may receive arterial blood supply from the aorta or its branches . Some cases may show the anomalous systemic arteries supplying an area of associated pulmonary sequestration .
- congenital heart disease, e.g. ASD, VSD, tetralogy of Fallot, patent ductus arteriosus
- ipsilateral diaphragmatic anomalies, e.g. accessory diaphragm, diaphragmatic hernia
- localized bronchiectasis
- horseshoe lung
- vertebral anomalies, e.g. hemivertebrae
- genitourinary tract abnormalities
- pulmonary sequestration
The diagnosis is made by transthoracic or transesophageal echocardiography, angiography, or by CT or MR angiography.
Chest radiographic findings are that of a small, hypoplastic lung with ipsilateral mediastinal shift, and in one-third of cases, the anomalous draining vein may be seen as a tubular structure paralleling the right heart border in the shape of a Turkish sword (“scimitar”). The right heart border may be blurred.
Treatment and prognosis
Surgical correction should be considered in the presence of significant left to right shunting and pulmonary hypertension. This involves the creation of an interatrial baffle to redirect the pulmonary venous return into the left atrium. Alternatively, the anomalous vein can be re-implanted directly into the left atrium.
The presence of a left-to-right shunt may lead to the development of pulmonary hypertension and Eisenmenger phenomenon.
History and etymology
The term was first given by C A Neill et al. in 1960 .
General imaging differential considerations include:
- pulmonary sequestration
- right middle lobe atelectasis (on AP plain radiograph)
- unilateral absence of pulmonary artery (UAPA)
- totale Lungenvenenfehlmündung
- meandernde Pulmonalvenen