Published online Jul 27, 2023. doi: 10.4240/wjgs.v15.i7.1331
Peer-review started: March 20, 2023
First decision: April 13, 2023
Revised: April 20, 2023
Accepted: May 22, 2023
Article in press: May 22, 2023
Published online: July 27, 2023
Processing time: 123 Days and 11.8 Hours
In Japan, the transhiatal approach, including lower mediastinal lymph node dissection, is widely performed for Siewert type II esophagogastric junction adenocarcinoma. This procedure is generally performed in a magnified view using laparoscopy or a robotic system, therefore, the microanatomy of the lower mediastinum is important. However, mediastinal microanatomy is still unclear and classification of lower mediastinal lymph nodes is not currently based on fascia or other microanatomical structures.
To clarify the fascia and layer structures of the lower mediastinum and classify the lower mediastinal tissue.
We dissected the esophagus and surrounding organs en-bloc from seven cadavers fixed in 10% formalin. Organs and tissues were then cut at the level of the lower thoracic esophagus, embedded in paraffin, and serially sectioned. Tissue sections were stained with Hematoxylin-Eosin (all cadavers) and immunostained for the lymphatic endothelial marker D2-40 (three cadavers). We observed the periesophageal fasciae and layers, and defined lymph node boundaries based on the fasciae. Lymphatic vessels around the esophagus were observed on immunostained tissue sections.
We identified two fasciae, A and B. We then classified lower mediastinal tissue into three areas, paraesophageal, paraaortic, and intermediate, using these fasciae as boundaries. Lymph nodes were found to be present and were counted in each area. The dorsal part of the intermediate area was thicker on the caudal side than on the cranial side in all cadavers. On the dorsal side, no blood vessels penetrated the fasciae in six of the seven cadavers, whereas the proper esophageal artery penetrated fascia B in one cadaver. D2-40 immunostaining showed lymphatic vessel connections between the paraesophageal and intermediate areas on the lateral and ventral sides of the esophagus, but no lymphatic connection between areas on the dorsal side of the esophagus.
Histological studies identified two fasciae surrounding the esophagus in the lower mediastinum and the layers separated by these fasciae were used to classify the lower mediastinal tissues.
Core Tip: The transhiatal procedure including lower mediastinal lymph node (LN) dissection is widely performed to treat esophagogastric junction (EGJ) adenocarcinoma. However, microanatomy of the lower mediastinum is unclear and the classification of lower mediastinal LNs is obscure. Therefore, we performed a histological study to investigate the microanatomy of the lower mediastinum in seven cadavers. We identified two fasciae surrounding the esophagus in the lower mediastinum and classified the periesophageal lower mediastinal tissue into three areas based on these fasciae. LNs were found within all classified areas. These data provide useful landmarks for EGJ adenocarcinoma surgery.