inclusion of outflow tracts and three vessel trachea in fetal echocardiography has improved the prenatal diagnosis of anomalies of aortic arch . we report the features of one such pattern with left aortic arch and right ductus arteriosus . a 23-year - old low risk pregnant woman , gravida 1 , para 0 presented for the routine anomaly scan at 28 weeks . the axial sweep of the fetal heart revealed the normal four chamber view and left ventricular outflow tract [ figure 1a ] . the aortic arch was to the left of the trachea [ figure 1c ] . after the origin of branch pulmonary arteries , the ductus arteriosus extended to the right of the trachea and joined the descending aorta behind the trachea to form a complete vascular ring . the patient reported loss of fetal movements at 32 weeks and sonography revealed intrauterine fetal death . ( a ) left ventricular outflow tract view showing the normal origin of aorta from the left ventricle and directed towards the right shoulder . ( b ) section just cephalic to a showing the origin of the main pulmonary artery from right ventricle and extending to the right and giving off the branches of right ( rpa ) and left ( lpa ) pulmonary arteries and continues to the right of the trachea ( arrow head ) as ductus arteriosus . ( c ) section just cephalic to b shows the aortic arch ( ao ) extending to the left of the trachea ( arrow head ) . ( d ) slightly oblique scan showing the aortic arch to the right and the ductus arteriosus to the left of the trachea and joining together behind the trachea giving a cross - ribbon appearance ( e ) line diagram showing the cross ribbon sign aortic arch anomalies refer to a variety of congenital abnormalities of the position or branching pattern or both of the aortic arch . they may be associated with congenital cardiac defects , chromosomal anomalies , or present as incidental findings in asymptomatic infants . some anomalies of the aortic arch , particularly those with aberrant branching , may form vascular rings , causing clinical symptoms from tracheal or esophageal compression . various types of congenital aortic arch abnormalities have been described ; however , most have been reported in the pediatric or radiological literature using magnetic resonance imaging ( mri ) and spiral computed tomography ( ct ) . although aortic arch anomalies are not uncommon , there are few reports on their prenatal diagnosis . normal and abnormal development of the aortic arch can be easily understood by reference to the hypothetical double aortic arch model described by dr . an aortic arch connects the ascending aorta to the descending aorta , and a ductus arteriosus ( ductus ) connects the ipsilateral pulmonary artery to the descending aorta , on each side of the trachea and esophagus , forming a complete vascular ring . normally , the left aortic arch and left ductus persist , and the right aortic arch distal to the origin of the right subclavian artery and the right ductus regress . most of the aortic arch anomalies are assumed to result from abnormal persistence of a part or parts that should have regressed and/or abnormal regression of a part or parts that should have persisted . the left or right - sidedness of the aortic arch refers to the position of the aortic arch relative to the trachea . the left and right - sidedness of the ductus can also be defined by its position relative to the trachea . this relationship is best seen in the three vessel trachea ( 3vt ) view of the fetal heart , as described by yagel et al . v  to the left of the trachea with the apex pointing posteriorly . in the right aortic arch , with mirror image branching and right ductus arteriosus , left aortic arch distal to the origin of the left subclavian artery and the left ductus arteriosus regress . in this condition , the aortic arch and ductus arteriosus are seen to the right of the trachea on fetal echo , and seen as a in right aortic arch with left ductus arteriosus , the left aortic arch between common carotid and subclavian arteries and right ductus arteriosus regress . on fetal echo , there is u sign with aortic arch to the right of the trachea and ductus arteriosus to the left of the trachea . in double aortic arch , aortic arch of both the sides persists and right ductus arteriosus regresses . ( a ) hypothetical double aortic arch model described by edwards je ( modified from reference ) and the developmental model of the anomaly described in this case report showing the segments of the right aortic arch and left ductal arch that regress . ( c ) postnatal circulation when the right ductus remains as the ligamentum ductus in the fetus described here , there was left aortic arch with right ductus arteriosus . this results from regression of the right aortic arch distal to subclavian artery and the left ductus arteriosus [ figure 2 ] . in left ventricular outflow tract view , the ascending aorta is directed to the right and then turns to the left and extends to the left of trachea . the main pulmonary artery and the ductus arteriosus are seen to extend to the right of the trachea . the aortic arch and ductus arteriosus unite behind the trachea to form a complete vascular ring around the trachea and esophagus . consequently , the aorta and ductus arteriosus are in the form of a cross ribbon . because of a complete vascular ring , the trachea and esophagus may be compressed and result in polyhydramnios . to our knowledge , this pattern of anomaly of aortic and ductal arches has not been reported so far .
here , we report a fetus with a rare aortic arch anomaly with left aortic arch and right ductus arteriosus , which has not been reported so far . in this condition , the aorta extends to the left of the trachea as in normal , while the ductus arteriosus extends to the right of the trachea and joins the descending aorta posterior to the trachea , with a cross - ribbon sign .