Development of the supracarinal posterior mediastinum in human embryos and fetuses: a comparative study with adult anatomy

Radical esophagectomy is widely regarded as one of the most complex surgical procedures in Upper Gastrointestinal surgery due to the intricate anatomy of the mediastinum, and a deep understanding of its embryological development is essential for navigating the interrelated structures and fascial planes involved. In this study, we investigated the embryogenesis of the supracarinal area of the posterior superior mediastinum, focusing on key anatomical structures such as the alar fascia and the supracarinal mesoesophagus—the latter being the fascial structure between the esophagus and the subclavian arteries that incorporates the recurrent laryngeal nerves, and is critical for performing precise esophagectomy and supracarinal lymphadenectomy. Our primary objective was to trace the embryological origins of these supracarinal fasciae; however, due to the absence of clearly distinguishable fasciae in early embryonic development, we adopted a second approach—utilizing anatomical knowledge from adult surgical dissections to identify analogous structures in late-stage embryos. To achieve this, we studied the posterior mediastinum of five embryos, ranging from stage 15 (33 days) to stage 23 (57 days), and one fetus at twelve weeks. Our results reveal a progressive transformation of the vascular system from primitive pharyngeal arch arteries to a definitive aortic system by stage 19, with the vagus nerves appearing at stage 17 and the recurrent laryngeal nerves becoming recurrent by stage 19. While the mediastinum consists of homogeneous mesenchymal tissue in early development, the boundaries of the supracarinal mesoesophagus are more defined in initial stages but become indistinct in later ones. Through comparative analysis with adult anatomy, we were able to delineate the development and positioning of both the alar fascia and the supracarinal mesoesophagus in late-stage embryos. This embryological insight is particularly valuable for anatomists and upper GI surgeons, as it enhances the understanding of the development and spatial organization of critical mediastinal structures—such as the esophagus, trachea, vascular elements, vagus and recurrent laryngeal nerves—which can contribute to safer, more consistent surgical outcomes in esophagectomy.