Scimitar Syndrome

Scimitar Syndrome (SS) is a congenital pulmonary anomaly consisting of an anomalous vein that drains part or all of the right lung blood flow into the systemic venous circulation, usually the inferior vena cava (IVC.) It is associated with  ipsilateral pulmonary hypoplasia, underdevelopment of the pulmonary artery, and sometimes an anomalous systemic arterial supply from the descending aorta to the hypoplastic lung.¹ Although SS has been classically described as involving the right lung, this might be due to the extreme rarity of a left-sided vena cava, because some case reports of left-sided SS have also been described.^2-4
The term scimitar was first used by Halasz et al.⁵ to describe the radiographic appearance of the anomalous pulmonary vein trajectory that drains into the IVC just below or above the right hemidiaphragm as a broad, gently curved shadow resembling the silhouette of the short, curved Persian sword shimshir.  
 

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The majority of cases have been reported  in adults or older children, accounting for 1:2000 cases of congenital heart disease (CHD).⁶ Only a few prenatal cases have been reported^7-9 with an estimated incidence of 1:100,000 - 3:100,000 live births and a clear female predominance.^{6, 10}  

The pathogenetic mechanism of SS is unclear. It seems to originate from abnormal lung development during embryogenesis.¹¹ It has been hypothesized that connections between the pulmonary and systemic plexus of capillaries, normally present during embryonic development, remain patent, leading to pulmonary hypoplasia and underdevelopment of the ipsilateral pulmonary artery. There is no evidence of the influence of common teratogens in the genesis of SS.

Scimitar syndrome (SS) is a rare congenital anomaly characterized by a partial (usually the right lower lobe) or complete unilateral anomalous pulmonary venous drainage in association with ipsilateral lung hypoplasia.¹² The anomaly is also known as pulmonary venolobar syndrome or hypogenetic lung syndrome.

SS is usually sporadic and not associated with chromosomal or genetic abnormalities, but in the presence of associated malformations, the risk of chromosomal defects increases to 50%. Association with other malformations is common, including CHD in 75%, lung congenital cystic malformations, congenital diaphragmatic hernia (CDH), and vertebral anomalies.^{8, 13-15} The most commonly reported congenital heart malformation is persistent left superior vena cava, draining to the coronary sinus¹⁶; other abnormalities that have been described include tetralogy of Fallot, coarctation of the aorta, abnormalities of the aortic arch, atrial septal defects, absent IVC, and pulmonary vein stenosis contralateral to the hypoplastic lung.^{8, 9, 13, 17, 18}

This sporadic anomaly has no recurrence risk reported for future pregnancies.  

A prenatal diagnosis can be established on routine ultrasound (US) by the identification of anomalous drainage of any pulmonary vein (Figures 5-1 and 5-2) together with ipsilateral lung hypoplasia and mediastinal shift. SS can usually be detected on US during the second trimester of pregnancy. The anomalous venous drainage is usually into the IVC below the diaphragm,  but may join with the hepatic vein, portal vein, coronary sinus, right atrium,^{12, 13} or, more unusually, with the superior vena cava¹⁹ or the left atrium.²⁰ 
When SS is suspected prenatally, the diagnosis must be confirmed postnatally by radiography, angiography, transthoracic or transesophageal echocardiography, noninvasive computed tomography or magnetic resonance angiography. The most evident postnatal sign is the radiologic presence of mediastinal shift. The typical pathognomonic finding is postnatal radiographic identification of the classic scimitar sign – an anomalous pulmonary vein appearing as a curvilinear density in the right lower lobe directed toward the right hemidiaphragm. 
 

The most common conditions considered in differential prenatal diagnosis of SS are pulmonary defects, including CDH and bronchopulmonary sequestration (BPS). BPS shows overlapping features or may coexist in 50 to 60% of cases.²¹ The differential diagnosis of CDH should be straight forward when the homogeneous US appearance of the lung parenchyma is confirmed. Regarding BPS, the differential diagnosis should be easy in most cases, when the following features are considered: 

• SS mainly affects the right lung, whereas BPS often affects the left lung. 
• Lung echogenicity in SS is not increased, and tends to be increased in BPS.
• Abnormal systemic arterial supply is normally not found in SS.⁷
• Mediastinal shift is rare in BPS, and if present, it is contralateral to (i.e; away from) the affected lung.  

Several prenatal ultrasound findings of this condition have been described consisting of signs related to abnormal lung development.⁸ 

• In axial views, there is a clear mediastinal shift to the right secondary to right lung hypoplasia with normal abdominal situs. There is an apparent reduction in the size of the right lung but with no signs suggesting CDH or a pulmonary mass.⁷ 
• Anomalous drainage of a pulmonary vein to the IVC and mild narrowing of the right pulmonary artery can be detected using spectral or power Doppler US, but detection is extremely difficult or impossible in most cases because of the small size of the vessels and lower systemic blood pressure and pulmonary impedance during foetal life.^{7, 9} Aberrant drainage can be shown in only 70% of cases by postnatal cardiac catheterization.⁷  

SS is usually a non-lethal anomaly. Although extremely rare, coexistence with stenosis of the pulmonary vein contralateral to the hypoplastic lung may be associated with a high neonatal mortality rate.¹⁷ In the absence of additional congenital malformations, the prognosis depends on the degree of lung hypoplasia and the presence of abnormal arterial blood supply to the affected lung, which can lead to pulmonary hypertension with a left-to-right cardiac shunt in 50% of the cases.⁶ In cases with mild pulmonary hypoplasia and absence of any abnormal systemic artery supplying the right lung, the prognosis is normally good. In many instances, the condition is asymptomatic after birth and remains clinically silent for a long time-sometimes to adulthood. In more severe cases manifesting in infancy and childhood, common clinical manifestations are dyspnea, cyanosis, respiratory distress or cardiac failure owing to increased pulmonary blood flow secondary to the aberrant pulmonary arterial supply, and recurrent respiratory tract infections during infancy.^{6, 22}

SS seldom requires surgical correction. Surgery is indicated for cases with severe symptoms or cases with significant pulmonary hypertension with left-to-right shunt. If the anomalous systemic arterial blood supply to the hypoplastic lung is confirmed postnatally, embolization of the abnormal arteries is a postnatal management option. Similarly, cases with left-to-right shunt could be surgically treated by redirecting the scimitar vein into the left atrium.²³ In addition, pulmonary lobectomy may be indicated for cases with repeated lung infections. In contrast, cases with isolated anomalous pulmonary venous drainage usually require no postnatal intervention.

1. Midyat L, Demir E, Askin M, Gulen F, Ulger Z, Tanac R, Bayraktaroglu S: Eponym. Scimitar syndrome. Eur J Pediatr 2010;169:1171-1177.
2. Agayev A, Yekeler E: Left-sided scimitar syndrome. Pediatr Radiol 2009;39:191.
3. Juraszek AL, Cohn H, Van Praagh R, Van Praagh S: Isolated left-sided scimitar vein connecting all left pulmonary veins to the right inferior vena cava. Pediatr Cardiol 2005;26:846-847.
4. Rutledge JM, Hiatt PW, Wesley Vick G, 3rd, Grifka RG: A sword for the left hand: an unusual case of left-sided scimitar syndrome. Pediatr Cardiol 2001;22:350-352.
5. Halasz NA, Halloran KH, Liebow AA: Bronchial and arterial anomalies with drainage of the right lung into the inferior vena cava. Circulation 1956;14:826-846.
6. Wang CC, Wu ET, Chen SJ, Lu F, Huang SC, Wang JK, Chang CI, Wu MH: Scimitar syndrome: incidence, treatment, and prognosis. Eur J Pediatr 2008;167:155-160.
7. Bhide A, Murphy D, Thilaganathan B, Carvalho JS: Prenatal findings and differential diagnosis of scimitar syndrome and pulmonary sequestration. Ultrasound Obstet Gynecol 2010;35:398-404.
8. Grisaru D, Achiron R, Lipitz S, Yahav J, Hegesh J, Rotstein Z: Antenatal sonographic findings associated with scimitar syndrome. Ultrasound Obstet Gynecol 1996;8:131-133.
9. Michailidis GD, Simpson JM, Tulloh RM, Economides DL: Retrospective prenatal diagnosis of scimitar syndrome aided by three-dimensional power Doppler imaging. Ultrasound Obstet Gynecol 2001;17:449-452.
10. Gudjonsson U, Brown JW: Scimitar syndrome. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu 2006:56-62.
11. Healey JE, Jr.: An anatomic survey of anomalous pulmonary veins: their clinical significance. J Thorac Surg 1952;23:433-444.
12. Biyyam DR, Chapman T, Ferguson MR, Deutsch G, Dighe MK: Congenital lung abnormalities: embryologic features, prenatal diagnosis, and postnatal radiologic-pathologic correlation. Radiographics 2010;30:1721-1738.
13. Cirillo RL, Jr.: The scimitar sign. Radiology 1998;206:623-624.
14. Gao YA, Burrows PE, Benson LN, Rabinovitch M, Freedom RM: Scimitar syndrome in infancy. J Am Coll Cardiol 1993;22:873-882.
15. Gikonyo DK, Tandon R, Lucas RV, Jr., Edwards JE: Scimitar syndrome in neonates: report of four cases and review of the literature. Pediatr Cardiol 1986;6:193-197.
16. Sun J, Zhang S, Jiang D, Yang G: Scimitar syndrome with the left persistent superior vena cava. Surg Radiol Anat 2009;31:307-309.
17. Argueta-Morales IR, Meador LC, Nykanen DG, DeCampli WM: Infantile form of scimitar syndrome with contralateral pulmonary vein stenosis. Pediatr Cardiol 2010;31:550-552.
18. Khalilzadeh S, Hassanzad M, Khodayari AA: Scimitar syndrome. Arch Iran Med 2009;12:79-81.
19. Demir E, Askin M, Midyat L, Gulen F, Ulger Z, Tanac R, Bayraktaroglu S: Scimitar syndrome associated with partial anomalous pulmonary venous draining into superior vena cava. Eur J Pediatr 2010;169:1263-1265.
20. Holt PD, Berdon WE, Marans Z, Griffiths S, Hsu D: Scimitar vein draining to the left atrium and a historical review of the scimitar syndrome. Pediatr Radiol 2004;34:409-413.
21. Najm HK, Williams WG, Coles JG, Rebeyka IM, Freedom RM: Scimitar syndrome: twenty years' experience and results of repair. J Thorac Cardiovasc Surg 1996;112:1161-1168; discussion 1168-1169.
22. Ziora D, Kozielski J, Glowacki J, Rycaj M, Niepsuj G: Repeated lung infections. Scimitar syndrome. Eur Respir J 1994;7:617-619.
23. Murphy JW, Kerr AR, Kirklin JW: Intracardiac repair for anomalous pulmonary venous connection of right lung to inferior vena cava. Ann Thorac Surg 1971;11:38-42.
24. Domadia S, Kumar SR, Votava-Smith JK, Pruetz JD. Neonatal Outcomes in Total Anomalous Pulmonary Venous Return: The Role of Prenatal Diagnosis and Pulmonary Venous Obstruction. Pediatr Cardiol. 2018 Oct;39(7):1346-1354. 
25. Paladini D, Pistorio A, Wu LH, Meccariello G, Lei T, Tuo G, Donarini G, Marasini M, Xie HN. Prenatal diagnosis of total and partial anomalous pulmonary venous connection: multicenter cohort study and meta-analysis. Ultrasound Obstet Gynecol. 2018 Jul;52(1):24-34. 
26. Wang H, Kalfa D, Rosenbaum MS, Ginns JN, Lewis MJ, Glickstein JS, Bacha EA, Chai PJ. Scimitar Syndrome in Children and Adults: Natural History, Outcomes, and Risk Analysis. Ann Thorac Surg. 2018 Feb;105(2):592-598. 
 

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