Contribution to the development of the heart. Part III: The aortic arch complex. Normal development and morphogenesis of congenital malformation.

The present paper reports our study of the developmental transformation of the aortic arch complex. A system of interarterial septa in the region of the embryonic aortic arch complex is demonstrated by means of microdissection and scanning electron microscopy. Local differences in growth of the dorsal and ventral free edges of these interarterial septa define, together with the commonly known obliteration of arterial segments, the arrangement of the origin of the great arteries. On the basis of this interarterial septal system a concept of disturbed interarterial septal growth, complemental to the long-established mechanism of obliteration, is introduced for interpretation of the formal genesis of malformations of the great arteries and their branches arising from the heart. The following pathogenetic mechanisms are suggested to contribute to the development of malformations in the aortic arch complex: 1. Increase or decrease of the number of interarterial septa 2. Excessive or reduced septal growth or deviating growth directions 3. Origin of septa in abnormal positions 4. Abnormal blending of the free edges of interarterial septa 5. Abnormal connection with the truncus septa 6. Abnormal processes of obliteration.