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Three-dimensional anatomical characterization of the first jejunal trunk and its relative venous contribution

This study utilizes 3D-CT to characterize the anatomical variations of the first jejunal trunk (FJT) relative to the superior mesenteric artery, revealing that the Ventral type exhibits more cranial venous confluence and a greater relative venous contribution than the Dorsal type, which has significant implications for preoperative planning in pancreaticoduodenectomy.

Original authors: Ryo Ataka, Yusuke Nakayama, Kazuhiko Kitaguchi, Yoshinobu Ikeno, Eiji Toyoda, Tetsuro Hirose

Published 2026-07-03

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CC BY 4.0

Original authors: Ryo Ataka, Yusuke Nakayama, Kazuhiko Kitaguchi, Yoshinobu Ikeno, Eiji Toyoda, Tetsuro Hirose

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your body's digestive system as a busy city with a major highway (the Superior Mesenteric Artery, or SMA) and a parallel drainage system (the Superior Mesenteric Vein, or SMV) that carries used water away.

This study is like a detailed traffic survey of a specific, often-overlooked exit ramp on that highway: the First Jejunal Trunk (FJT). This is the main "drainpipe" that collects blood from the very first section of the small intestine (the jejunum).

Here is the breakdown of what the researchers found, using simple analogies:

1. The Two Main "Traffic Patterns"

The researchers looked at 114 patients and discovered that this drainpipe (the FJT) usually follows one of two paths relative to the main highway (the SMA):

The "Dorsal" Type (The Back Door): In about 67% of people, this drainpipe runs behind the main highway. This is the standard, expected route.
The "Ventral" Type (The Front Door): In about 33% of people, this drainpipe runs in front of the main highway. This is the less common, "surprise" route.

2. Why the "Front Door" is Tricky

The study found that when the drainpipe takes the "Front Door" (Ventral) route, it behaves differently than the "Back Door" (Dorsal) route:

It joins the main river higher up: Imagine the main drainage river (SMV) flowing south. The "Front Door" pipes tend to dump their water into the river much further north (closer to the head) than the "Back Door" pipes.
It's a bigger pipe relative to the river: The researchers measured the size of the FJT compared to the main portal vein (the "D ratio"). They found that in the "Front Door" group, this drainpipe is significantly larger relative to the main river. It carries a heavier load of traffic.
It mixes with other pipes: The "Front Door" pipes often merge with other major drains (like the middle colic vein) before hitting the main river, creating a complex, tangled junction. The "Back Door" pipes rarely do this.

3. The "Map" Problem

The main goal of this study was to help surgeons who perform a major operation called a Pancreaticoduodenectomy (PD). Think of this surgery as a massive construction project in the middle of this city, right where the highway and the drainage river meet.

The Risk: If a surgeon assumes the drainpipe is always in the "Back Door" position, but a patient actually has the "Front Door" version, the surgeon might accidentally cut the wrong pipe.
The Consequence: Cutting the wrong pipe is like cutting the main water supply to a neighborhood. It can cause the small intestine to get swollen and congested (like a flooded street) because the water has nowhere to go.

4. The Solution: A 3D GPS

The researchers used special 3D CT scans (like a high-tech GPS map) to look at these pipes before surgery.

They found that by looking at the map beforehand, surgeons can spot the "Front Door" (Ventral) type.
They created a simple measurement (the D ratio) to help surgeons understand how "important" or "large" that specific drainpipe is for that specific patient.

The Bottom Line

This paper doesn't claim that cutting this pipe is always bad or that it always causes problems. In fact, they noted that in their group of 114 patients, no one actually suffered from this congestion.

However, the paper argues that knowledge is power. Because the "Front Door" (Ventral) type has a different shape, a different location, and carries more traffic than the "Back Door" type, surgeons need to know exactly which "type" of patient they are operating on before they make the first cut. It's about having the right map so you don't accidentally block the city's main drainage system.

Technical Summary: Three-dimensional anatomical characterization of the first jejunal trunk and its relative venous contribution

Problem Statement
The mesopancreas, defined as the neural and lymphoid tissue between the dorsal pancreatic head and the superior mesenteric artery (SMA), is a critical focus in pancreaticoduodenectomy (PD). While the inferior pancreatoduodenal artery (IPDA) serves as a landmark for mesopancreas resection, it is often obscured by complex fibrous tissues. Consequently, surgeons require alternative landmarks to navigate this region safely. Although the arterial branches of the SMA are well-documented, detailed three-dimensional (3D) anatomical characterization of the proximal jejunal veins, specifically the first jejunal trunk (FJT), remains limited. This lack of detailed anatomical data poses a risk of misidentification and inadvertent sacrifice of the FJT, which can lead to rare but severe complications such as extensive jejunal congestion.

Methodology
This retrospective study analyzed 114 patients who underwent PD at Otsu Red Cross Hospital between 2018 and 2022. Cases involving portal vein circular resection, completion pancreatectomy, tumor compression, or missing imaging data were excluded.

The core of the methodology involved a 3D computed tomography (CT) evaluation using an 80-row CT system. Preoperative images were reconstructed using SYNAPSE VINCENT software to visualize the vascular anatomy around the pancreas. The FJT was defined as the first-order trunk draining into the superior mesenteric vein (SMV).

The anatomical relationship between the SMA and FJT was classified into two groups:

Dorsal Type: The FJT runs dorsal to the SMA.
Ventral Type: The FJT runs ventral to the SMA.

Key parameters measured included:

Confluence Patterns: The relationship of the FJT with the inferior mesenteric vein (IMV), middle colic vein (MCV), and gastrocolic trunk (GCT).
Positional Metrics: The distance from the splenic vein (SpV) to the FJT (L1) and the distance between the FJT and the second jejunal trunk (SJT) (L2).
D Ratio: A novel index defined as the diameter of the FJT divided by the diameter of the portal vein (Df/Dp). Based on the principle that blood flow is proportional to vascular diameter, this ratio serves as an indicator of the relative venous contribution of the FJT within the mesenteric venous system.
Drainage Territory: Defined by the arterial perfusion areas (e.g., J1A, J2A) associated with the FJT.

Statistical analysis utilized the $\chi^2$ test for categorical variables and Student's t-test for continuous variables, with significance set at $P < 0.05$ .

Key Results
Among the 114 patients, 67.5% (77 cases) exhibited the Dorsal type, while 32.5% (37 cases) exhibited the Ventral type. The study identified significant anatomical and hemodynamic differences between these groups:

Confluence Patterns: The Ventral type showed a significantly different venous confluence pattern compared to the Dorsal type ( $P < 0.001$ ). Specifically, 51.4% of Ventral type cases involved the FJT merging with the IMV or MCV, whereas no such merging occurred in the Dorsal type.
Cranial Inflow: The Ventral type demonstrated a more cranial inflow into the SMV compared to the Dorsal type ( $P < 0.0001$ ). In 83.8% of Ventral cases, the FJT entered the SMV at the same level as or cranial to the GCT, whereas in 92.2% of Dorsal cases, it entered caudally.
Relative Venous Contribution: The D ratio was significantly higher in the Ventral type than in the Dorsal type ( $P = 0.003$ ). This indicates a greater relative venous contribution of the FJT in the Ventral configuration.
Diameter vs. Contribution: While the absolute diameter of the FJT did not differ significantly between the two types, the D ratio effectively reflected relative differences in the mesenteric venous system. The D ratio increased stepwise as the arterial perfusion territory expanded and when IMV/MCV drainage was included.

Significance and Claims
The authors claim that 3D-CT analysis reveals distinct imaging features of the Ventral type FJT, characterized by more cranial venous confluence patterns and a greater relative venous contribution within the mesenteric system.

The study posits that preoperative assessment of the SMA-FJT relationship via CT can improve anatomical recognition prior to PD. This is particularly crucial for patients with Ventral-type anatomy, where the FJT may traverse complex mesenteric layers and carry a higher relative venous load. The authors suggest that the D ratio can serve as a supplementary parameter to understand the relative venous contribution of the FJT, aiding in the decision-making process regarding whether to sacrifice the vessel. While the study did not observe jejunal congestion in the analyzed cohort, it emphasizes that inadvertent division of the FJT, especially in the Ventral type, carries a risk of venous congestion. Therefore, careful preoperative anatomical orientation is recommended to avoid venous misidentification and unexpected bleeding.

The paper concludes that classifying the SMA-FJT relationship into Dorsal and Ventral types provides a useful framework for understanding anatomical variability, though it acknowledges limitations regarding its retrospective, single-institution design and the lack of outcome-based thresholds for the D ratio.

1. The Two Main "Traffic Patterns"

2. Why the "Front Door" is Tricky

3. The "Map" Problem

4. The Solution: A 3D GPS

The Bottom Line

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