Deviated right superior vena cava: fetal echocardiographic sign of intrathymic left brachiocephalic vein.

Abstract

A 25-year-old primigravida was referred at 33 + 5 weeks of gestation for fetal cardiac evaluation with suspicion of bilateral agenesis of the superior vena cava (SVC). Fetal echocardiography revealed no intracardiac anomalies. Two-dimensional color Doppler and high-definition color rendering of the three-vessel view showed a significant deviation of the right SVC (RSVC) to the right side and an unusually increased distance (8 mm) between the ascending aorta and the SVC (Figure 1a–c; Videoclips S1–S4). Visualization of the upper mediastinum using a sweep slightly cephalad to the three-vessels-and-trachea view showed the intrathymic course of the left brachiocephalic vein (LBCV) (Figure 1e,f). The bicaval view showed significant anterior deviation of the RSVC (Figure 1d). There were no extracardiac anomalies. The postnatal course was uneventful. Postnatal echocardiography confirmed the intrathymic course of the LBCV and a structurally normal heart (Figure 2). Normally, the LBCV connects the left jugular vein to the RSVC and crosses the upper mediastinum in an oblique plane anterior and superior to the aortic arch and posterior to the thymus. The presence of thymus gland tissue between the aortic arch branches and the LBCV confirms the intrathymic course of the LBCV1, 2. An increase in distance between the ascending aorta and the RSVC occurs in cases of persistent left SVC with no bridging vein (LBCV) due to lack of traction of the LBCV on the RSVC3. As shown in this case, right and anterior deviation of the RSVC occurred because of the presence of thymus gland tissue between the ascending aorta and the RSVC due to the intrathymic course of the LBCV. Because of the significant deviation of the RSVC, agenesis of the SVC was suspected on examination in the three-vessel view. Bilateral agenesis of the SVC is a rare anomaly, which can be associated with thoracic duct obstruction and congenital hydrothorax4. However, intrathymic LBCV, which has a reported incidence of 1.76%2, is a benign finding with a normal outcome. Hence, determination of the etiology of the wide space between the ascending aorta and the RSVC is necessary to counsel parents regarding the likely prognosis of their pregnancy. Videoclip S1 Two-dimensional color Doppler three-vessel view showing increased distance between ascending aorta and right superior vena cava. Videoclip S2 Visualization of the upper mediastinum using slight cephalad sweep to the three-vessels-and-trachea view showing presence of thymic tissue between left brachiocephalic vein (LBCV) and aortic arch branches due to intrathymic course of LBCV. Videoclip S3 and S4 High-definition color rendering of the three-vessel view showing increased distance between ascending aorta and right superior vena cava (SVC). A, azygos vein; AO, ascending aorta; DA, ductus arteriosus; DAO, descending aorta; LBCV, left brachiocephalic vein; MPA, main pulmonary artery. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.