The embryology of the foregut

Until today, several theories have been developed to explain the occurrence of common foregut malformations as esophageal atresia and tracheoseophageal fistula. Most researchers believe that these malformations are the result of an impaired process of septation of the early foregut. However, a detailed review of the literature makes clear that a unified embryologic concept of the normal foregut development is still missing. This statement is still true after the development of an animal model, the so-called Adriamycin model in rats, which allows the reproduction of embryos, fetuses, and newborns with a huge spectrum of malformations, including foregut malformations. In the first part of this review, data from the literature are presented and analyzed critically, which deal with the differentiation of the foregut into the esophagus and the respiratory tract. In general, it is a shortcoming that reliable illustrations of these crucial embryologic processes still are missing in most of these reports. Therefore, in the second part, scanning electron microscopy pictures of the developing foregut are presented in a series of chicken embryos. In these pictures, signs of a septum are completely missing as an important structure during the differentiation of the foregut. In the third part, the spectrum of theories that should explain abnormal foregut malformations is presented and critically discussed. In the last section, the Adriamycin model and its implications for the current understanding of the foregut malformations is discussed.