Reframing gastric lymph nodes as a parapancreatic lymph chain: an embryology-driven rationale for omento-bursectomy and omentum-preserving gastrectomy to facilitate safe infrapyloric lymph node dissection

The infrapyloric lymph nodes (LNs) are defined as No. 6 LNs and as one of the regional gastric LNs in the Japanese classification of gastric carcinoma. No. 6 LNs are recommended to be dissected completely even in D1 lymphadenectomy for distal and total gastrectomy in the Japanese Gastric Cancer Treatment Guideline. Omento-bursectomy, whose survival advantage for advanced gastric cancer patients was not shown by the Japanese Clinical Oncology Group 1001 trial, has been proposed to be a useful technique for safe and secure dissection of No. 6 LNs in gastric cancer surgery. In the present review, we first discuss the reason why omento-bursectomy is considered to be a useful technique for dissection of No. 6 LNs, reframing the gastric LNs as a parapancreatic lymph chain based on the dorsal pancreas, mesogastrium, and mesoduodenum embryology. Second, we introduce the outermost layer-oriented dissection (OLD) of No. 6 LNs in performing an omentum-preserving gastrectomy (OPG) devised at Fujita Health University and their favorable outcomes. Last, we discuss the reason why the incidence of postoperative pancreatic fistula in laparoscopic distal gastrectomy is significantly higher than open gastrectomy for stage Ⅰ gastric cancer patients, for whom the OPG is likely performed, in a retrospective cohort study based on the Japanese National Clinical Database. Although single-institution retrospective clinical studies are referenced in this review, it is considered that reframing the gastric LNs as a parapancreatic lymph chain based on the embryology can enhance safe No.6 LNs dissection in the various types of gastric cancer surgery.