Topographic anatomy of the fetal inferior vena cava, coronary sinus, and pulmonary veins: Variations in Chiari's network

To understand anomalies in Chiari's network better, we assessed the topographical anatomy of the fetal inferior vena cava (IVC), coronary sinus, and atria. We examined sagittal serial paraffin sections of 15 human fetuses of crown-rump length 24-36 mm, corresponding to a gestational age of 8 weeks. Although their outflow tract morphologies were similar, these 15 specimens could be classified into two groups. In eight specimens, the left common cardinal vein reached the body wall, whereas in the other seven the vein was obliterated near the left pulmonary vein. Irrespective of the group in which the specimen was included, the anteroposterior arrangement of the coronary sinus, the sinus septum (septum), and the right sinus valve (right valve) could be classified into three types: the right valve-septum-coronary sinus arrangement in seven specimens; the right valve-coronary sinus-septum arrangement in five; and the coronary sinus-right valve-septum arrangement in three. Depending on differences in topographical anatomy, the sinus septum separated the coronary sinus opening from either the right or the left atrium. Likewise, the coronary sinus opening was either adjacent to or distant from the IVC terminal. Rather than the counter-side position of the right valve being at the IVC terminal, the left sinus valve protruded leftward, forming an incomplete interatrial septum. Fetal variations seemed to be closely connected with individual variations and a high frequency of Chiari's network anomalies in adults.