How to identify the posterior boundary of No. 8a and the right side group of No. 9 lymph nodes?

As the development of laparoscopic gastrectomy for gastric cancer in recent years, laparoscopic lymphadenectomy becomes more and more feasible and widely accepted. But there’re still some issues confuse gastric surgeons, such as the precise extent of the lymph nodes (LN), especially the posterior boundary of No. 8a and the right side group of No. 9 LNs. Here we introduce a reasonable and feasible method to identify the posterior boundary of No. 8a and the right side group of No. 9 LNs and demonstrate the detail procedure.