Resection of the mesopancreas (RMP): a new surgical classification of a known anatomical space

Abstract

Background: Prognosis after surgical therapy for pancreatic cancer is poor and has been attributed to early lymph node involvement as well as to a strong tendency of cancer cells to infiltrate into the retropancreatic tissue and to spread along the peripancreatic neural plexuses. The objective of our study was to classify the anatomical-surgical layer of the mesopancreas and to describe the surgical principles relevant for resection of the mesopancreas (RMP). Immunohistochemical investigation of the mesopancreatic-perineural lymphogenic structures was carried out with the purpose of identifying possible routes of metastatic spread.

Methods: Resection of the mesopancreas (RMP) was performed in fresh corpses. Pancreas and mesopancreas were separated from each other and the mesopancreas was immunohistochemically investigated.

Results: The mesopancreas strains itself dorsally of the mesenteric vessels as a whitish-firm, fatty tissue-like layer. Macroscopically, in the dissected en-bloc specimens of pancreas and mesopancreas nerve plexuses were found running from the dorsal site of the pancreatic head to the mesopancreas to establish a perineural plane. Immunohistochemical examinations revealed the lymphatic vessels localized in direct vicinity of the neuronal plexuses between pancreas and mesopancreas.

Conclusion: The mesopancreas as a perineural lymphatic layer located dorsally to the pancreas and reaching beyond the mesenteric vessels has not been classified in the anatomical or surgical literature before. The aim to ensure the greatest possible distance from the retropancreatic lymphatic tissue which drains the carcinomatous focus can be achieved in patients with pancreatic cancer only by complete resection of the mesopancreas (RMP).

Figure 1

Pancreas with its arteries and nerve plexuses viewed from dorsally. Schematic depiction of pancreatic innervation. Non-vessel bound vegetative nerves and periarterial nerve plexus. (From Loeweneck 1969, (5)).

Figure 2

Uncovering the Superior Mesenteric Vein (SMV) and consecutively successive separation of the mesopancreas directly lateral of the Superior Mesenteric Vein (SMV).

Figure 3

Schematic depiction of the extraction of specimens (aP1-aP15 = specimens 1–15) of the mesopancreas for histologic and immunohistochemical examinations (ventral view after separation from the pancreas).

Figure 4

A). The pancreatic head was dissected laterally of the Superior Mesenteric Vein (SMV) and is turned to the right side after mobilization. The mesopancreas strains itself dorsally of themesenteric vessels as a whitish-firm, fatty tissue-like layer. PH = Pancreatic Head; SMV = Superior Mesenteric Vein; PV = Portal Vein; MP = Mesopancreas . B). Resection of the pancreas and mesopancreas dorsally of the mesenteric vessels en bloc. PH = Pancreatic Head; MP = Mesopancreas ; PAF = Preaortic Fascia, PC = Plexus Coeliacus, PMS = Plexus Mesentericus superior. C). Macroscopically, in the dissected en-bloc specimen of the pancreas and mesopancreas nerve plexuses are found running from the dorsal surface of the pancreatic head to the mesopancreas to establish a perineural plane. PH = Pancreatic Head;NP = Nerve Plexus; SMV = Superior Mesenteric Vein; PV = Portal Vein; MP = Mesopancreas . D). The nerve plexus of the dorsal site of the pancreatic head is depicted in a detailed view after preparation of the layer between pancreas and mesopancreas. PH = Pancreatic Head; NP = Nerve Plexus of the dorsal margin of the pancreatic head.

Figure 5

A). Pancreatic tissue and surrounding vessel-nerve-bundles. Lymphatic vessels stained brown (D2-40). B). Nerve fibres embedded in the fatty tissue of the mesopancreas. Nervesare marked with blue arrows (H&E). C) Mesopancreas, pancreatic tissue in the left upper area. Vessels and nerves (blue arrows) embedded in fatty tissue, lymphatic vessels stained brown (D2-40).D). x = Lymph node in the mesopancreas, lymphatic vessels stained brown. E). Mesopancreas; x = pancreatic tissue, red arrows: nerves; lymphatic vessels stained brown.

Figure 6

RMP in pancreatic cancer compared to TME in rectal cancer.