Scimitar syndrome is a rare disorder of the pulmonary circulation in which the pulmonary vein of the right lung drains into the inferior vena cava or the right atrium, instead of the left atrium, and is accompanied by other cardiopulmonary anomalies. Adult patients are often asymptomatic, while infants present with significant symptoms. The diagnosis is made through radiographic findings, and the choice of treatment is surgery, although with significant risks.
Clinical presentation of Scimitar syndrome varies greatly from one individual to another. However, an asymptomatic course is usually observed in adult patients, in whom this syndrome may be incidentally diagnosed. On the other hand, a symptomatic and often more severe course is observed in infants, with symptoms of heart failure, tachypnea, tachycardia, and sometimes hemoptysis [10].
Physical examination may reveal the presence of heart murmurs, and auscultation of the heart may reveal dextrocardia, which can be confirmed by radiographic studies. Family history may reveal prior heart disease in the family, but not necessarily.
Scimitar syndrome is diagnosed through radiographic findings, most commonly through the presence of characteristic "Scimitar sign" (A curved Turkish sword) on plain chest X-rays, which describes the shadow created by the right pulmonary vein as it descends toward the cardiophrenic angle, and drains into the inferior vena cava [11]. To confirm the diagnosis, echocardiography may be performed, or a CT scan may be done. Magnetic resonance imaging (MRI) may also provide a good view into the vascular anatomy of the mediastinum, as well as angiography, but angiography is an invasive procedure and is reserved only if the mentioned methods do not provide sufficient data.
Fetal echocardiography will usually reveal the presence of anomalous venous drainage during pregnancy, and treatment strategies may be discussed early on to decide on optimal treatment.
Surgery is the treatment of choice for patients with Scimitar syndrome, especially for those who have symptomatic and severe forms of the disease, such as those with severe left-to-right shunting, pulmonary hypertension, and signs of heart failure [12].
For patients in whom the anomalous venous drainage is small and partial, no therapy is required, as the heart is able to compensate these changes. On the other hand, for patients in whom development of complete anomalous drainage occurs, surgical therapy is necessary. The principal mechanism of surgical treatment is to somehow reestablish delivery of blood from the right lung into the left atrium, either through re-implanting the pulmonary vein into the left atrium, or creating an inter-atrial baffle, so that pulmonary venous circulation into the left atrium can be restored. Ligation of the vessel is also sometimes performed, but it is important to mention that all surgical procedures carry a significant risk, since patients in whom these procedures are performed have accompanying factors which further complicate treatment, such as pulmonary hypertension, hemodynamic instability, while other accompanying congenital heart defects also cause further issues.
The prognosis depends on the severity of disease and its presentation. Patients who are asymptomatic usually have a better prognosis with proper treatment, while infants who present with symptoms of the disease require extensive surgical treatment, and this syndrome is potentially fatal when presenting in severe forms [7]. Surgical procedures in infants carry a high mortality rate [8] [9], and treatment is further complicated by the presence of other accompanying defects.
When this disorder is diagnosed early, prompt surgical intervention may significantly benefit, and provide better outcomes, which is why an early diagnosis is vital in having a good prognosis.
The exact cause of Scimitar syndrome is not known, but a genetic component has been implied since some cases have occurred in patients with a positive family history of cardiopulmonary disorders.
Scimitar syndrome is a rare occurrence, and its incidence rate is approximately 1 to 3 per 100 000 live births [4]. However, the actual number of cases is speculated to be higher, since a significant number of patients are asymptomatic, and are yet to be diagnosed.
Under physiological circumstances, the left atrium receives oxygen-rich blood from the left and right pulmonary veins, and this blood is then pumped by the left ventricle into systemic circulation. In patients with Scimitar syndrome, the left atrium receives either partially or no blood at all from the right lung, because of the right pulmonary vein, which is responsible for bringing oxygen-rich blood into the left atrium, drains into the inferior vena cava, or sometimes into the right atrium and even the portal vein. Other associated conditions include hypoplasia of the right lung, dextrocardia, as well as several forms of congenital heart disease, such as atrial septal defect (ASD), ventricular septal defect (VSD), tetralogy of Fallot, and others [5].
From a functional point of view, this syndrome behaves as a left-to-right shunt, which implies a possible asymptomatic course, but infants often have severe forms of the disease with heart failure and development of pulmonary hypertension [6].
Having in mind the fact that the cause of Scimitar syndrome is not known, and that little is understood about the pathogenesis of this disorder, prevention strategies do not currently exist. Genetic counseling has been suggested to patients with congenital heart disease, and to those who already have Scimitar syndrome.
Scimitar syndrome is characterized by anomalous venous drainage of the right lung, usually into the right atrium or the inferior vena cava, rather than the left atrium [1], and this abnormal venous drainage may be either partial or total. The name is derived from a "Scimitar-like" appearance of the pulmonary vein that drains into the inferior vena cava on chest X-rays. Other accompanying disorders include hypoplasia of the right lung, dextrocardia, and deranged systemic circulation [2]. The cause is unknown, and it is uncertain why does this syndrome occur exclusively on the right side. This disorder is rarely observed, with incidence rates of 1 to 3 per 100,000 live births. The clinical presentation may vary from asymptomatic and present as an incidental finding, which is more commonly observed in adults, to possibly life-threatening heart failure and pulmonary hypertension [3], which is usually the case in infants, and necessitates rapid treatment. A significant number of patients who present with symptoms during childhood have accompanying congenital heart disease, most common being an atrial septal defect (ASD). The diagnosis is made using radiographic techniques, including echocardiography and computed tomography (CT) as the primary choices, and treatment is aimed at correcting the anatomical anomaly through various surgical procedures.
Scimitar syndrome is a condition in which the part of the circulation which is responsible for delivering oxygen-rich blood into the heart is not properly connected. Namely, the blood vessel of the right lung, which should carry blood filled with oxygen from the lungs into the heart, specifically into the left atrium, from where the blood travels into the left ventricle, and into the systemic circulation through the aorta, instead carry blood into other sites, such as the right atrium. This abnormal drainage may be either partial (meaning only a fraction of blood follows the unusual course) or total, and as a result, there is less oxygenated blood available for the heart to pump it into the body, which can sometimes lead to heart failure and pulmonary hypertension, and is life-threatening if left untreated.
It is not known how or why this syndrome occurs, and it is rarely encountered, about 1 to 3 cases per 100 000 live births, and these patients usually have some additional conditions, such as dextrocardia (the heart is situated on the right side, instead of the left), an underdeveloped right lung, or they may have some form of congenital heart disease, most commonly atrial septal defect.
It is important to distinguish two forms of disease - asymptomatic, which is usually observed in adults, who present without complaints, and in whom the diagnosis is made incidentally, and symptomatic (and usually severe) form, which is encountered in infants in most cases, as their condition severely impairs the circulatory system from birth. The diagnosis can be made on chest X-rays, where a Scimitar-like (derived from a curved Turkish sword Scimitar) finding of the pulmonary vein can be observed, while echocardiography, computed tomography (CT scan), or magnetic resonance imaging, may provide a definite diagnosis.
Treatment includes surgical repair of the anomaly, and the principle is to reestablish normal circulation of the right lung and the heart, although these techniques carry a significant risk, especially in infants who have severe forms of the disease.