Histological study of the thin membranous dense connective tissue around the middle and lower thoracic esophagus, caudal to the bifurcation of the trachea.

Objective: We previously reported on the thin membranous dense connective tissue around the esophagus in the upper mediastinum. This time, we histologically investigated the existence of similar structures in the middle and lower mediastinum, caudal to the bifurcation of the trachea.

Methods: Semi-sequential transverse sections of the mediastinum were obtained from two cadavers. Hematoxylin and eosin staining and Elastica van Gieson staining were performed.

Results: In the middle mediastinum, the "visceral sheath" could not be observed completely around the esophagus. In the lower mediastinum, the thin membranous dense connective tissue was observed beneath the pericardium on the ventral side of the esophagus. On the dorsal side of the esophagus, two thin membranous dense connective tissues were similarly observed in two cadavers. One existed between the dorsal side of the esophagus and the three vessels (i.e., the descending aorta, the azygos vein and the thoracic duct) and was integrated with the thin membranous dense connective tissue of the ventral side of the esophagus at the bilateral side of the esophagus. This integrated dense connective tissue reached the left subpleural region and the adventitia of the aorta on the left side and the peripleural and pulmonary hilum on the right side. The other thin membranous dense connective tissue, which represents the "vascular sheath", was observed between the descending aorta and the thoracic duct.

Conclusion: These two thin membranous dense connective tissues, which are considered to represent the visceral sheath and vascular sheath, are thought to be available as optimal dissecting layers for radical esophagectomy.