* Radiology department, Kasr Alainy teaching hospitals, Cairo University, Egypt;
** Fetal medicine unit, Cairo University, Egypt.

Case report

A 23-year old woman (G1P0) was referred to our institution at 27 weeks gestation for detailed fetal cardiac assessment. The baby was in cephalic position at time of scan (probe marker was oriented to right side of the mother, as usual). Ultrasound examination revealed the following findings:

- Situs inversus totalis with dextrocardia.

- The morphologic left atrium (right sided and posteriorly located) receives the pulmonary veins and is seen connected to the right sided posteriorly located morphologic right ventricle (thick moderator band, rough septal trabeculations, apical offset of the tricuspid valve with visualized its septal leaflet in short axis view).

- The morphologic right atrium (left sided) receives systemic veins (IVC and SVC) and is seen connected to the anterior retro sternal morphologic left ventricle (absent moderator band with elongated its anechoic lumen reaching cardiac apex, smooth septal endocardial surface, two papillary muscles attached to free wall, two leaflets of mitral valve with no septal attachment in short axis view). This pattern of ventricular looping in the presence of dextrocardia and situs inversus is named D looping with associated discordant atrio ventricular connection.

- Discordant ventriculo arterial connections. The ascending aorta arises from the morphologic right ventricle through sub aortic conus (RVOT) and appears anterior and to the right side of the main pulmonary artery that arises from the morphologic left ventricle.

- Large outlet sub pulmonary VSD (with inlet extension facing the inlet part of LV cavity) is noted with a septal membrane seen flickering between the sub aortic and sub pulmonary regions without aneurysm formation.

- High velocity jet is seen in the sub pulmonary and pulmonary valve region suggesting evidence of pulmonary stenosis. The level of the jet is clearly seen under the pulmonary valve where a discrete sub pulmonary fibro muscular membrane (vs. ridge) is present.

- The tricuspid valve appears patent with no Ebstein malformation, tricuspid dysplasia, straddling over an inlet VSD or significant regurgitation across.

- No evidence of fetal arrhythmia (heart block or re-entrant tachycardia).

- Right sided aortic arch. No evidence of aortic arch coarctation or interruption. Usual branching pattern of the right arch into left inominate, right common carotid and right subclavian arteries is noted with the left inominate artery running in front of the trachea.

Images 1, 2, 3; videos 1 and 2: show discordant atrio ventricular connection, situs inversus with dextrocardia.

Images 4, 5; video 3: show the large outlet (sub pulmonary) VSD with postero inferior extension (inlet extension) facing the inlet cavity of the LV. 

Image 6, video 4: Show patent tricuspid valve (systemic AV valve) with trivial regurgitation across. Pulmonary to systemic ventricle shunt is also noted through the VSD.

Images 7, 8; videos 5, 6, 7 and 8: 2D and color Doppler study showing the parallel arrangement of great vessels in D-transposition (aorta anterior right, pulmonary posterior left) and right sided aortic arch with mirror image branching. 

Images 9, 10, 11, 12; videos 9, 10, 11, 12, and 13: 2D sagittal sweep to show the relation of great vessels to their respective ventricles and to liver and stomach in upper abdomen. Long axis views of the LV to MPA and also in axial view to show the discrete sub pulmonary fibro muscular tissue with high velocity jet across the sub pulmonary region.

Image 13, 14, 15, 16, 17; videos 14, 15, 16, 17, and 18: Surface rendering and inversion mode STIC volume showing the double discordance with parallel arrangement of great vessels, large inlet and outlet sub pulmonary VSD, the sub pulmonary obstructing fibro muscular tissue and the flickering septal membrane without sub pulmonary aneurysm formation. 

Our final diagnosis was congenitally corrected transposition of great arteries associated with discrete sub pulmonary stenosis, large inlet and outlet (sub pulmonary VSD) and situs inversus totalis with dextrocardia. This anatomic type of ccTGA represents the I,D,D type (Inversus situs, Dextrocardia, D-looped ventricles with D-transposition).

Comment: Sub pulmonary stenosis in case of ccTGA is well documented anatomic association in about 30-50% of cases especially in the presence of large outlet sub pulmonary VSD that has a characteristic inlet extension (directed inferiorly and posteriorly facing the inlet cavity of the left ventricle). The combination of both VSD and sub pulmonary stenosis in ccTGA is so frequentbut the anatomic type of ccTGA as the I,D,D one is  rare reaching about 20% of all cases¹.  This pattern of sub pulmonary stenosis may be in the form of fibro muscular tissue, tunnel like hypoplasia, valve stenosis, aneurysm of the membranous septum, accessory mitral valve tissue in the sub pulmonary region or may be systolic anterior motion on the mitral leaflet itself ². An obvious discrete fibro muscular tissue in sub pulmonary region was seen causing sub pulmonary stenosis. To the best of our knowledge, this pattern of discrete sub pulmonary stenosis in case of ccTGA with large VSD has never been prenatally reported before. We noticed a septal membrane in the region of the VSD flickering between both sub aortic and sub pulmonary regions but with no septal aneurysm formation under the pulmonary valve. In absence of other associated anomalies, such as Ebstein malformation of tricuspid valve, Conduction system abnormalities (heart block or re-entrant tachycardia), pulmonary atresia or ventricular hypoplasia, the short term prognosis may be good if closure of VSD and removal of the sub pulmonary obstructing fibro muscular tissue were done as an initial intervention before total repair³.

References:

1-Chung, Hae Yul. "Anatomic Types and Associated Cardiovascular abnormalities of the Congenitally Corrected Transposition of the Great Arteries." Chonnam Medical Journal 39.4 (2003): 244-250.‏
2-Hornung, Tim S., and Louise Calder. "Congenitally corrected transposition of the great arteries." Heart 96, no. 14 (2010): 1154-1161.
3-Dyer, Karrie, and Thomas P. Graham. "Congenitally corrected transposition of the great arteries: current treatment options." Current treatment options in cardiovascular medicine 5, no. 5 (2003): 399-407.