Absent inferior vena cava, symmetrical liver, splenic agenesis, and situs inversus, and their embryology.

Several cardiac malformations are known to be associated with situs inversus (Ivemark, 1955; Campbell and Deuchar, 1965, 1966). In addition, there are often some venous and visceral malformations, e.g. bilateral superior venm cavae (SVC), absence of a segment of the inferior vena cava (IVC), agenesis of the spleen, and symmetry of the liver. We shall discuss these five malformations, particularly the correlations between them, and whether their embryological development provides any explanation for the correlations. Until the past 25 years many malformations of the veins were known only from specimens seen at necropsy or in the dissecting room, since as a rule they produce no symptoms. Bilateral SVC provide one example. Campbell and Deuchar (1954) described 40 such cases as well as 6 where a persistent left SVC was the only one. In general, a left SVC alone is a rare malformation, but most of these 6 examples occurred with complete situs inversus, where it is the normal finding. More recently we have discussed the relation of situs inversus and splenic agenesis and the relation of these two with bilateral SVC (Campbell and Deuchar, 1966). The discussion in that paper should, we think, be referred to, since we have tried to avoid repetition from it in this one. Absence of a segment of the IVC, so that most of the blood from the lower part of the body reaches the heart through the azygos vein and the SVC, is another example, and is not very uncommon. For brevity we shall refer to this as "absent IVC" though it is only the greater part of the prerenal segment that is missing. The resulting changes in the circulation were better known as a result that followed thrombosis in this part of the IVC secondary to a growth or some other obstruction.