Surgical Anatomy of the Pancreas and the Periampullary Region
Executive Summary
The pancreas is a complex retroperitoneal organ whose surgical management is dictated by its intricate relationship with major vascular structures, fasciae, and nervous plexuses. Understanding the developmental origins of the pancreas—derived from dorsal and ventral buds—is essential to navigating its ductal and arterial variations. This document outlines the critical anatomical features of the pancreatic head, body, and tail, with a specific focus on surgical implications such as the preservation of replaced hepatic arteries, the management of the inferior pancreaticoduodenal artery (IPDA) to minimize blood loss, and the identification of nerve plexuses during pancreatectomy. Key takeaways include the high frequency of vascular variations, the clinical significance of pancreaticobiliary maljunctions, and the controversial nomenclature surrounding the "mesopancreas."
1. General Anatomy and Fascial Fixation
The pancreas is located transversely in the retroperitoneal sac. Its position is defined by the duodenum to the right, the spleen to the left, and the stomach and omental bursa superiorly.
Fascial Structures
The pancreas is fixed to the retroperitoneum through a series of fused fasciae that must be dissected during surgical procedures:
Treitz Fascia: A retropancreatic fusion fascia formed by the posterior wall of the mesoduodenum and the posterior parietal peritoneum.
Toldt Fusion Fascia: The Treitz fascia continues as the left Toldt fusion fascia at the pancreatic body and tail. The right Toldt fusion fascia is formed by the ascending mesocolon and parietal peritoneum.
Surgical Significance: Pancreaticoduodenal arteries and veins are situated between the pancreatic parenchyma and these fused fasciae; therefore, dissection of these layers is a prerequisite for pancreatectomy.
Posterior Relations
From right to left, the pancreatic bed contains:
Hilum of the right kidney.
Inferior vena cava (IVC) and Aorta.
Left kidney.
Hilum of the spleen.
2. Arterial Supply and Variations
The arterial supply originates from the celiac trunk and the superior mesenteric artery (SMA). While the body and tail are primarily supplied by the splenic artery, the head and uncinate process rely on complex arcades.
Pancreatic Head Arcades
The head receives blood from arcades formed by the gastroduodenal artery (GDA) and the first branch of the SMA:
Superior Arcades: The GDA branches into the Posterior Superior Pancreaticoduodenal Artery (PSPDA) at the superior edge and continues as the Anterior Superior Pancreaticoduodenal Artery (ASPDA).
Inferior Arcades: The Inferior Pancreaticoduodenal Artery (IPDA) typically branches from the SMA (often sharing a common trunk with the first jejunal artery) and divides into anterior (AIPDA) and posterior (PIPDA) branches.
Spiral Formation: The arcade formed by the PSPDA and PIPDA creates an anti-clockwise spiral around the lower common bile duct.
Hepatic Artery Variations
3. Venous Drainage and Clinical Significance
Venous drainage is directed into the portal vein, SMV, and splenic vein. The anatomy of these vessels is a primary determinant of tumor resectability.
Key Venous Structures
Gastrocolic Trunk of Henle: Formed by the superior right colic vein, the right gastroepiploic vein, and the ASPDV; drains into the SMV.
First Jejunal Branch of the SMV: Usually runs behind the SMA to merge with the AIPDV. A minor variation exists where it runs in front of the SMA.
Inferior Mesenteric Vein (IMV): May drain into the splenic vein, the SMV, or the confluence of the two.
Surgical Considerations for Adenocarcinoma
According to NCCN Guidelines, tumor contact with the most proximal draining jejunal branch into the SMV classifies the cancer as unresectable. In cases requiring portal vein resection without splenic vein reconstruction, the IMV and left gastric vein serve as critical drainage vessels for the remnant pancreas and spleen.
4. Pancreatic Ductal System and the Papilla of Vater
The pancreatic ducts are characterized by developmental variations that can impact the flow of pancreatic juice.
Ductal Anatomy
Duct of Wirsung (Main): Originates in the tail, traverses the parenchyma, and terminates at the major papilla (papilla of Vater).
Duct of Santorini (Accessory): Smaller duct that enters the duodenum at the minor papilla (1–2 cm proximal to the major papilla).
Pancreas Divisum: A variation where the main duct is smaller than the accessory duct and the two are not connected. In this case, the accessory duct carries the majority of pancreatic secretions.
The Duodenal Papilla and Maljunctions
The pancreatic and common bile ducts usually merge within the duodenal wall, covered by the sphincter of Oddi.
Pancreaticobiliary Maljunction: Occurs when the ducts merge outside the duodenal wall, creating a long conjunct duct. This can result in pancreatic juice reflux, leading to biliary inflammation and potential malignancy.
5. Neuroanatomy and the "Mesopancreas" Concept
Innervation is provided by the sympathetic (splanchnic) and parasympathetic (vagus) systems, forming the celiac-superior mesenteric plexus.
Pancreatic Head Plexuses
The Japan Pancreas Society differentiates the plexus behind the pancreatic head into two zones:
Pancreatic Head Plexus I (PLphI): Distributed to the dorsal surface of the pancreatic head and the cranial edge of the uncinate process from the right celiac ganglia.
Pancreatic Head Plexus II (PLphII): A wider plexus extending from the superior mesenteric ganglia to the uncinate process; it includes the IPDA and is continuous with the mesojejunum plexus.
The "Mesopancreas" Controversy
The term "mesopancreas" refers to the areolar tissue surrounding the PLphII. Its status as a true mesentery is contested because:
It lacks a formal fascial envelope attaching the pancreas to the posterior abdominal wall.
It does not contain all primary draining lymphatics and blood vessels of the organ.
It is composed of a mixture of nerve fibers, fibrous tissue, fat, lymphatics, and minor vessels.
