Collateral Venous Pathways in the Transverse Mesocolon and Greater Omentum in Patients with Pancreatic Disease
Executive Summary
Pancreatic diseases, including carcinoma and chronic pancreatitis, often lead to isolated venous occlusions, most notably of the splenic vein or the superior mesenteric vein (SMV). While pathways like the gastroepiploic vein are well-documented, this briefing outlines two significant but less recognized collateral pathways identified through radiologic findings and cadaveric dissection: the pathway in the transverse mesocolon (the venous equivalent of Riolan’s arch) and the pathway in the greater omentum (the venous arch of Barkow).
The identification of these pathways is clinically vital. Dilatation of these veins serves as a diagnostic clue for venous involvement in pancreatic pathology. Furthermore, understanding the precise location and flow dynamics of these vessels is critical to preventing accidental, massive hemorrhaging during pancreatectomies or bypass surgeries.
Overview of Collateral Venous Development
In various pancreatic diseases, gastric varices often develop as collateral pathways due to isolated splenic vein occlusion. While dilated short gastric veins and gastroepiploic veins are common findings, this analysis focuses on two distinct pathways that develop within the mesenteric reflections surrounding the pancreas.
Core Study Data
The findings are based on a retrospective review of 54 patients (35 men, 19 women; mean age 62) with pancreatic diseases, including:
Pancreatic head carcinoma (31 cases)
Pancreatic body carcinoma (12 cases)
Pancreatic tail carcinoma (2 cases)
Mucin-producing tumors (4 cases)
Large pancreatic cysts with chronic pancreatitis (5 cases)
Among these, 21 patients exhibited collateral vessels, with eight specific patients demonstrating the two "unknown" pathways detailed below.
Detailed Analysis of the Transverse Mesocolon Pathway
This pathway is identified as the vena comitans of Riolan’s arch. It is located deep within the abdomen and consists of a network connecting the inferior mesenteric vein (IMV) to the superior mesenteric vein (SMV).
Anatomical Components
Inferior mesenteric vein (IMV)
Left transverse colic vein (LTCV)
Marginal vein of the transverse colon (MV)
Middle colic vein (MCV)
Flow Dynamics
The study classifies this pathway into two types based on the direction of blood flow, dictated by the site of venous obstruction:
Radiologic Recognition
CT Findings: Dilated IMV and marginal veins are visible deep in the abdomen.
Angiography: This pathway typically appears slightly after the gastroepiploic vein on sequential films.
Detailed Analysis of the Greater Omentum Pathway
This pathway is identified as the vena comitans of the arch of Barkow (venous arch of Barkow). It consists of an anastomosis between the left and right epiploic veins, which derive from the gastroepiploic vein.
Anatomical Components and Characteristics
Structure: A venous arch located in the greater omentum, situated approximately 2–4 cm below the transverse colon.
Location: Superficial, positioned just behind the anterior abdominal wall.
Dynamics: Splenic venous flow empties into the epiploic branch of the left gastroepiploic vein, travels through the omental venous arch, and eventually reaches the portal vein via the gastrocolic trunk.
Radiologic Recognition
CT Findings: Due to its superficial location, it is easily differentiated from the deep-seated marginal vein.
Angiography: Appears as a large arch running from the splenic hilum toward the pelvis, then turning right and upward. A large field of view is required for complete visualization because the arch often extends into the lower abdomen.
Clinical and Surgical Implications
The presence and direction of flow in these collateral pathways provide critical intelligence for surgical and diagnostic purposes.
Diagnostic Clue: Dilatation of these veins is a primary indicator of venous involvement (occlusion or compression) by pancreatic tumors or cysts.
Hemorrhage Risk: These dilated veins are thin-walled and easily torn. Knowledge of their location is essential to prevent massive accidental bleeding during surgery.
Surgical Planning:
The Omental Arch: Because it is located superficially, surgeons must exercise extreme caution when opening the abdominal wall to avoid damaging the vessels.
The Marginal Vein: Located deep in the abdomen, this pathway can be easily overlooked during surgery if not identified preoperatively.
Flow Direction: Understanding the direction of flow allows surgeons to make informed decisions regarding vessel ligation.
Methodology and Validation
Imaging Techniques
Thin-section Helical CT: Performed at 3-mm collimation with 1.5-mm reconstruction intervals. Scanning was initiated 60 seconds after IV contrast injection.
Digital Subtraction Angiography (DSA): Performed within one week of CT. Superior mesenteric artery angiography utilized a vasodilator (alprostadil) to enhance venous visualization.
Anatomical Confirmation
To confirm the existence and morphology of these pathways, a cadaveric dissection (67-year-old woman) was performed.
Greater Omentum: Dissection revealed the epiploic venous arch deriving from the gastroepiploic vessels.
Transverse Mesocolon: Dissection identified the left transverse colic vein (running with the accessory middle colic artery) and the left superior colic vein joining the marginal vein of the transverse colon. This confirmed the venous collateral's morphological similarity to the arterial Riolan’s arch.
Comparative Differentiation on CT
The study establishes that clinicians can differentiate three similar-looking arches on CT scans based on depth:
Gastroepiploic Vein: Located along the great curvature of the stomach.
Marginal Vein: Located deep in the abdomen (within the transverse mesocolon).
Epiploic Anastomosis: Located superficially behind the abdominal wall (within the greater omentum).
