1. Fetal medicine unit, Kasr Alainy hospital, Cairo University, Egypt;
2. Radiology department, Kasr Alainy hospital, Cairo University, Egypt.

Case report

A 23-year old woman (G2P1) with unremarkable family history was referred to our institution at 24 weeks gestation for fetal cardiac assessment. Ultrasound examination revealed complete transposition of great arteries (D-TGA) with outlet sub pulmonary VSD and mild posterior deviation of the infundibular septum without associated sub pulmonary stenosis. No other associated anomalies were found.

In addition to the basic 2D and color Doppler assessment of the VSD flow across and its direction as well as the anatomy of the sub pulmonary region (LVOT), the STIC volumetric study was much more confirmative in the assessment of flow direction and its timing and the anatomy of LVOT for possible associated obstruction.

There were pan systolic and pan diastolic right to left flow across the outlet VSD revealing the pressure gradient between the systemic right ventricle (higher pressure) and the pulmonary left ventricle (lower pressure) during the systolic and diastolic periods of cardiac cycle. This hemodynamic flow pattern together with the normal anatomic appearance of the LVOT (anterior wall of MPA connected to IVS and the posterior wall of MPA connected to anterior mitral leaflet) and the subtle encroachment of the posteriorly mal aligned infundibular septum on the LVOT not to the degree to cause obstruction, could ensure the absence of anatomic or hemodynamic evidence of sub pulmonary (LVOT) obstruction or pulmonary valve stenosis. This was confirmed on first day after delivery and the baby was scheduled for urgent total repair (arterial switch operation).

Images 1-3; videos 1-3: show the parallel alignment of both great arteries with anterior right aorta connected to right ventricle and posterior left main pulmonary artery connected to left ventricle.

Images 4-6; videos 4 and 5: show the outlet sub pulmonary VSD with right to left flow during systole and diastole. No evidence of high velocity flow across the sub pulmonary region.

Image 7; video 6: show the sub pulmonary region with mild posterior deviation of the conal septum not to the degree to cause obstruction.

Images 8-14; videos 7-11: 4D Color STIC rendered volume confirming the direction and timing of flow across the VSD and the absence of LVOT hemodynamic evidence of obstruction.

Video 12: Translational cine clip to illustrate the ventriculo-arterial discordance and the sub pulmonary region.

Discussion

The frequency of the prenatal diagnosis of complete transposition of great arteries has been increased based upon the characteristic parallelism of both great arteries in the upper mediastinal views with lack of visualization of normal 3 vessel arrangement. It may occur with intact ventricular septum or with ventricular septal defect¹. Our case represents a complete form of TGA with outlet sub pulmonary VSD where the conal (infundibular) septum shows mild posterior deviation with subtle encroachment upon the sub pulmonary region not to the degree to cause obstruction.

In view of different surgical techniques for D-TGA with VSD, the assessment of the LVOT for possible associated stenosis is crucial for management. Various causes of LVOT obstruction related to mitral or tricuspid valve anomalies as well as the LVOT region itself could be present. The most frequent types of these obstructive lesions are the posterior deviation of the infundibular (outlet) septum and the cone shaped appearance (funnel like obstruction) of the LVOT². The absence of sub pulmonary or pulmonary valve stenosis in case of TGA with VSD is an extremely important diagnosis because it will determine the possibility of early neonatal intervention by arterial switch operation or a later repair by Rastelli operation³.

In 2008, Parer referred to normal fetal ventricular and arterial pressures in which the right ventricle is slightly of higher pressure than the left one by 1-2 mmHg with equal both pulmonary and systemic arterial pressures⁴. In the presence of sub valvular or valvular pulmonary stenosis in case of D-TGA with VSD, the left ventricular pressure will be higher than that of the right ventricle and so, flow across the VSD will be from the pulmonary left ventricle to the systemic right one or at least of a bidirectional pattern.

4D STIC volumetric study was of great value in determining the flow direction and its timing across the VSD where we found the continuous systemic to pulmonary ventricle shunting during periods of systole and diastole denoting still higher pressure in the systemic right ventricle than in the pulmonary left ventricle which comes in agreement with normal values of fetal ventricular pressures reported by Parer. Together with the subtle encroachment of the posteriorly mal aligned infundibular septum not to the degree to cause obstruction, we confirmed our basic 2D and color Doppler assessment of the absence of sub pulmonary obstruction or the valvular stenosis even in a mild from. We recommend, whenever techniquelly possible, the use of 4D color STIC volume study on a wide scale to assess the VSD flow timing and the color mapping of the sub pulmonary region for a possible obstruction as it will be an important factor to determine the early neonatal surgical intervention.

References:

1-Shih, Jin-Chung, Shu-Chien Huang, Chia-Hui Lin, Tzu-Hung Lin, Ying-Ning Su, Shin-Yu Lin, En-Ting Wu, Ming-Kwang Shyu, and Chien-Nan Lee. "Diagnosis of Transposition of the Great Arteries in the Fetus." Journal of Medical Ultrasound 20, no. 2 (2012): 65-71.

2-Vázquez-Antona, Clara A., Luis Muñoz-Castellanos, Magdalena Kuri-Nivón, and Jesús Vargas-Barrón. "Left ventricular outflow tract obstruction in transposition of the great arteries. Correlation between anatomic and echocardiographic findings." Revista Española de Cardiología 56, no. 07 (2003): 695-702.

3- Al-Jughiman, Mohammed K., Maryam A. Al-Omair, Glen S. Van Arsdell, Victor O. Morell, and Marshall L. Jacobs. "D-Transposition of the great arteries with ventricular septal defect and left ventricular outflow tract obstruction (D-TGA/VSD/LVOTO): a survey of perceptions, preferences, and experience." Pediatric cardiology 36, no. 5 (2015): 896-905.

4-Parer, J, Glob. Libr. women's med., (ISSN: 1756-2228) 2008; DOI 10.3843/GLOWM.10194.