Development of the infracarinal posterior mediastinum in human embryos and fetus. Comparison with the adult anatomy

In the Western world, esophageal adenocarcinomas account for 85% of all esophageal cancers, with most located in the infracarinal area, making adequate infracarinal dissection with mediastinal lymphadenectomy followed by intrathoracic anastomosis (the Ivor Lewis procedure) the standard operative technique. Esophagectomy is a complex procedure due to the intricate anatomy of the mediastinum, and understanding this complexity requires knowledge of the embryological development of the posterior mediastinum to interpret the interrelation of mediastinal organs and the planes between them. To this end, we conducted a study on the embryogenic development and beyond of the posterior mediastinum, focusing on the infracarinal mesoesophagus, a pivotal structure for performing an adequate infracarinal dissection. We examined the posterior mediastinum of five embryos (stages 15 to 23) and one twelfth-week fetus, analyzing the region from the carina to the esophageal hiatus. Along with a general description of the esophagus, the vascular system, and the vagus nerves, we provided a detailed account of the development of these structures, specifically the infracarinal mesoesophagus, which is a mesenteric-like bilayer extending from the descending aorta to the infracarinal esophagus and incorporating vessels, lymphatics, and nerves. Our findings show that the infracarinal mesoesophagus is well developed at all stages of embryogenesis, initially appearing short and broad proximally, and gradually elongating and thinning distally toward the hiatus, resembling its adult anatomical counterpart in later stages. This study describes the formation of the infracarinal posterior mediastinum and highlights significant changes in the development of mediastinal structures, including the esophagus, the vascular system, the vagus nerve, and the primordium of the lungs, while also offering insight into the evolution of the infracarinal mesoesophagus. A thorough understanding of the development of the infracarinal posterior mediastinum is essential for upper gastrointestinal surgeons to enhance their comprehension of surgical anatomy, ultimately improving the adequacy and reproducibility of esophageal surgery.