The Inferior Mesenteric Artery: A Patient's Guide to Its Anatomy, Variations, and Role in Colorectal Surgery

Table of Contents

• Key Points
• Why This Artery Matters
• The Basic Anatomy: What the Artery Does and Where It Runs
• How the Researchers Conducted the Study
• The 23 Studies Behind the Results
• Key Finding 1: Where the Artery Begins
• Key Finding 2: How the Artery Splits
• Key Finding 3: Artery Diameter and Distances Between Vessels
• Rare and Unusual Variants
• How These Findings Compare With Earlier Research
• What This Means for Colorectal Surgery
• Limitations: What This Study Could Not Prove
• Recommendations and Practical Takeaways
• Frequently Asked Questions
• Source Information

Key Points

• In a pooled analysis of 23 studies and 3,419 patients, the inferior mesenteric artery began at the L3 vertebra in about 70% of cases.
• The most common branching pattern was a bifurcation (about 64%), followed by trifurcation (about 27%) and tetrafurcation (about 12%).
• The single most common subtype was the artery dividing into the left colic artery and a shared trunk for the sigmoid and superior rectal arteries (about 46%).
• Preserving the inferior mesenteric and left colic arteries, when possible, may support better blood flow to the descending colon and a safer anastomosis.
• Anatomical variation is normal, not a disease, but it can affect whether high or low ligation is chosen during colorectal cancer surgery.

Why This Artery Matters

Doctors have studied the blood vessels of the abdomen for decades. They use cadaver dissections, medical imaging, and observations during operations to build a picture of how these vessels normally look — and how often they look different. Evidence-based anatomical meta-analyses (studies that pool many smaller studies into one big picture) offer a thorough summary of the important variants that can change how an operation is done.

The inferior mesenteric artery is one of those vessels. Its surgical importance comes from two things: where it sits in the body, and how it branches. Surgeons frequently tie off (ligate) its branches during colorectal cancer surgery. Getting that anatomy wrong can cause serious problems.

Two earlier reviews of the literature on IMA variants already existed. However, both of them lacked a meta-analytic approach — meaning they described the studies but did not mathematically combine the numbers. This new study fills that gap. It is an evidence-based systematic review with meta-analysis that aims to clarify both the shape (morphology) and the measurements (morphometry) of the IMA. It also discusses what the findings mean for surgery.

The Basic Anatomy: What the Artery Does and Where It Runs

The abdominal aorta (AA) is the large artery that runs down the back of the abdomen. It has three major branches that supply the abdominal organs: the coeliac trunk (CeT), the superior mesenteric artery (SMA), and the inferior mesenteric artery (IMA).

The IMA arises from the front (anterior) surface of the abdominal aorta, at the level of the third lumbar vertebra (L3). The lumbar vertebrae are the five lower back bones, numbered L1 through L5 from top to bottom. The artery sits behind the lower border of the horizontal part of the duodenum (the first section of the small intestine).

From there, the IMA typically gives off the left colic artery (LCA) and the sigmoid artery (SA). It crosses in front of the origin of the left common iliac artery, with the inferior mesenteric vein (IMV) running between the two arteries. Finally, the artery continues downward as the superior rectal artery (SRA). This happens at the root of the sigmoid mesocolon, the fold of tissue that attaches the sigmoid colon to the back wall of the abdomen.

Together, these branches supply a large portion of the gastrointestinal tract known as the hindgut. The hindgut includes the distal third of the transverse colon, the splenic flexure, the descending colon, the sigmoid colon, and the rectum.

Bergman's Comprehensive Encyclopedia of Human Anatomic Variation describes IMA variants as relatively rare. Even so, researchers keep studying the typical branching pattern and origin levels because they matter so much in the operating room.

How the Researchers Conducted the Study

The authors followed the Evidence-based Anatomy Workgroup guidelines for anatomical meta-analysis and the PRISMA 2020 guidelines for systematic reviews. These are internationally accepted rules that keep a review transparent and reproducible.

The team searched four online databases: PubMed, Google Scholar, Scopus, and Web of Science. They combined search terms including "inferior mesenteric artery," "variation," "cadaveric study," "imaging study," and "surgical study."

They also went beyond the databases. The researchers checked the reference lists of every included article. The researchers searched the grey literature, which is material that is not formally published by commercial publishers. The researchers also hand-searched major anatomy journals. These journals included Annals of Anatomy, Clinical Anatomy, Journal of Anatomy, Anatomical Record, Surgical and Radiological Anatomy, and Folia Morphologica. These journals also included European Journal of Anatomy, Anatomical Science International, Anatomy and Cell Biology, and Morphologie.

To be included, a study had to report the prevalence (how common something is) of IMA variants. The team excluded case reports, conference abstracts, animal studies, and studies with irrelevant or insufficient data.

Two independent reviewers extracted the data into Microsoft Excel sheets. They compared their results, and the other authors resolved any disagreements.

The researchers assessed the risk of bias using the Anatomical Quality Assurance (AQUA) tool, which was created by the Evidence-based Anatomy Workgroup specifically for anatomical systematic reviews.

For the statistics, the team used the open-source R programming language and RStudio software (version 4.3.2), applying the "meta" and "metafor" packages. Here is what they did in plain terms:

• Prevalence analysis: They calculated pooled prevalence using inverse variance and random-effects models, with the Freeman-Tukey double arcsine transformation, the DerSimonian-Laird estimator for between-study variance (tau²), and the Jackson method for confidence intervals.
• Mean analysis: They analyzed measurements (such as artery diameter) using untransformed raw means, the restricted maximum-likelihood estimator for tau², and the Q-Profile method for confidence intervals.
• Subgroup analyses: They checked whether geographic distribution or study type affected the pooled prevalence.
• Heterogeneity: Heterogeneity means how much the studies disagreed with each other. They measured it with Cochran's Q statistic (a p-value below 0.10 counted as significant) and the Higgins I² statistic.

The Higgins I² values were interpreted as follows: 0–40% was not significant, 30–60% was moderate heterogeneity, 50–90% was substantial heterogeneity, and 75–100% may represent considerable heterogeneity. A p-value below 0.05 was considered statistically significant.

Finally, the team looked for small-study effects — the phenomenon where smaller studies may show different effects than large ones. For prevalence data, they generated a DOI plot and calculated the LFK index to quantify asymmetry. For measurement data, they used a funnel plot with the Thomson-Sharp test.

Because the included studies did not strictly follow one existing classification system, the authors evaluated each study separately and grouped the results themselves. Their simple system was:

1. Bifurcation: two main branches come off the main trunk.
2. Trifurcation: three main branches come off the main root.
3. Tetrafurcation: four branches come off the main trunk.

Each of these three groups has subtypes based on the exact branching pattern. The authors had used the same approach previously to classify variants of the coeliac trunk.

The 23 Studies Behind the Results

The database search produced 4,018 articles, which were exported to Mendeley version 2.10.9 (Elsevier, London). After removing duplicates and irrelevant papers through title and abstract screening, 74 studies moved on to full-text review. Of these, 20 studies met the inclusion criteria. A secondary investigation — reference searches, grey literature, and hand-searching anatomy journals — found 3 more studies. In total, 23 studies entered the final analysis.

Those 23 studies covered a total sample of 3,419 patients. By study type, 11 were imaging studies, 10 were cadaveric studies, and 2 were surgical studies. By population, 16 were based on Asian populations, 3 on European populations, 2 on American populations, and 1 on an African population. Several studies included children and fetuses alongside adults.

Key Finding 1: Where the Artery Begins

The most common point of origin was the L3 vertebra, which occurred in 70.16% of cases (95% confidence interval: 56.48–82.25%). A confidence interval is the range in which the true value likely falls. In plain terms, about 7 out of every 10 people have an IMA that starts at this level.

The second most common location was the intervertebral disc space between L2 and L3, found in 29.79% of cases (95% CI: 6.41–60.88%). This wide range reflects how much the individual studies varied.

Other origin levels were less common:

• L2 vertebra: 5.27% (95% CI: 2.42–8.99)
• L3–L4 disc space: 10.67% (95% CI: 7.12–14.81)
• L4 vertebra: 13.32% (95% CI: 4.83–24.94)
• L4–L5 disc space: 19.78% (95% CI: 14.47–25.67)
• L5 vertebra: 3.01% (95% CI: 0.00–10.89)

Key Finding 2: How the Artery Splits

The most common overall branching pattern was the bifurcation, with a pooled prevalence of 63.89% (95% CI: 49.35–77.26%). Subgroup analysis by geographic distribution and by study type did not reveal significant differences (p = 0.266 and p = 0.075, respectively). However, the DOI plot showed an LFK index of −2, which indicates asymmetry — meaning smaller studies may have reported different results than larger ones.

The literature describes four distinct bifurcation patterns:

• Most common: The IMA divides into the LCA and a common trunk for both the SRA and SA — 46.09% (95% CI: 39.54–52.71%).
• Second most common: The IMA divides into the SRA and a common trunk for both the LCA and SA — 27.78% (95% CI: 17.61–39.22%).
• Less common: The IMA divides into the LCA and SRA, with the SA arising from both arteries — 5.41% (95% CI: 1.48–11.27%).
• Rare: The IMA divides into the SRA and SA, with no LCA present at all — 3.83% (95% CI: 2.72–5.11%).

Trifurcation — the artery splitting into three branches (LCA, SRA, and SA) — had a pooled prevalence of 27.35% (95% CI: 17.38–38.59%). Subgroup analysis by nationality and study type showed no significant differences (p = 0.1879 and p = 0.5234). The DOI plot had an LFK index of −4.62, suggesting significant asymmetry. The authors emphasize one point: the trifurcated type always shows this same unique pattern, dividing into the LCA, SRA, and SA.

Tetrafurcation — four branches from the main trunk — is minimally documented in the current literature. Its pooled prevalence was 11.62% (95% CI: 7.49–16.46%). Two types of tetrafurcation have been described. One specific form, in which the IMA gives rise to the SRA, SA, LCA, and an accessory left colic artery, had a pooled prevalence of 10.48% (95% CI: 2.78–21.92%). The other form — the typical trifurcation (LCA, SRA, SA) plus an ascending lumbar artery — has been documented only once in the entire literature.

Key Finding 3: Artery Diameter and Distances Between Vessels

The meta-analysis also calculated pooled mean measurements, which give surgeons a sense of the typical dimensions they will encounter.

• Diameter of the IMA at its origin: pooled mean of 41.41 mm (95% CI: 40.37–42.46).
• Distance between the IMA and SMA origins: pooled mean of 64.04 mm (95% CI: 58.16–69.92).
• Distance from the IMA origin to the aortic bifurcation (where the abdominal aorta splits into the common iliac arteries): 37.41 mm (95% CI: 35.74–39.08).
• Distance from the IMA origin to the LCA origin: pooled mean of 40.67 mm (95% CI: 37.61–42.53).

Rare and Unusual Variants

The IMA is widely described as arising from the abdominal aorta — the typical origin. But it does not always do so. The IMA arising from the superior mesenteric artery (SMA) had a pooled prevalence of 0.97% (95% CI: 0.00–3.36%). This variant has also been mentioned in several case reports in the current literature.

Other unusual findings have appeared in isolated reports. The testicular artery was seen arising from the IMA during angiographic procedures (imaging of blood vessels). Kim and Han reported a unique case during dissection in which the IMA was absent entirely. In that case, the typical branches from the middle colic artery, inferior pancreaticoduodenal artery, and SMA were all present.

The authors also note that Balcerzak and colleagues tested whether the level of origin relates to the branching pattern. They found no statistically significant connection.

How These Findings Compare With Earlier Research

Two comprehensive reviews of IMA classification systems exist — one by McSweeney and colleagues and one by Zeng and colleagues. Since those reviews, additional classification systems have been proposed, including one from Balcerzak and colleagues.

The classification most frequently used in the literature comes from Yada and colleagues. Their four types are:

1. Type I: Bifurcation into the LCA and a common trunk for the SRA and SA.
2. Type II: Bifurcation into the SRA and a common trunk for the LCA and SA.
3. Type III: Trifurcation into the LCA, SRA, and SA.
4. Type IV: Absence of the LCA, with bifurcation into the SRA and SA.

Balcerzak and colleagues recently outlined five distinct IMA types. Their system introduced two novel features. The first is the ascending lumbar artery (ALA) arising from the IMA — a phenomenon not previously described. The second is that they did not record any cases of a missing LCA. Instead, they observed that the ascending and descending branches of the LCA can arise independently from the IMA.

Individual branches vary too, not just the main trunk. In a separate systematic review with meta-analysis, Cirocchi and colleagues described several LCA variants:

• Absence of the LCA: 4.1% of patients
• "Spread-out" origin of the LCA: 49%
• "Fan-shaped" origin of the LCA: 51%

The sigmoid artery (SA) is even more variable. Cirocchi and colleagues recorded the following SA origins:

• From the superior rectal artery (SRA): 49.67%
• From the left colic artery (LCA): 25.26%
• Directly from the IMA main trunk: 13.26%
• Multiple sigmoid arteries from both the SRA and LCA: 0.18%

They also noted that the number of sigmoid arteries can range from one to five, with three being the most common. By contrast, the superior rectal artery appears to be the most constant IMA branch, showing little variability.

What This Means for Colorectal Surgery

The IMA is the most important anatomical landmark in colorectal surgery. A thorough understanding of its surgical anatomy is essential. This is especially true during total mesorectal excision, which is removal of the rectum and its surrounding fatty tissue. It is also essential during lymph node dissection near the artery's root and preservation of the pelvic autonomic nerves.

When surgeons treat rectal cancer, lymph node dissection must involve the main trunk of the IMA. Currently, a significant debate continues about the best level for tying off the IMA during left colon or rectal resection: should it be high ligation or low ligation? A related question is whether the left colic artery should be preserved.

Here is what these terms mean in practice:

• High ligation: Tying off the main IMA trunk without preserving the LCA.
• Low ligation: Tying off in the LCA region, with lymph node dissection at the IMA root and preservation of the LCA.

In both cases, the IMA's origin and branching pattern are critically important, because variations may affect which procedure is chosen. Finding the exact origin of the IMA on the front surface of the aorta during surgery helps the surgeon during dissection. This applies in lower anterior resection for rectal cancer using a medial-to-lateral approach, which means working from the middle of the abdomen outward. This also helps harvest the maximum number of regional lymph nodes.

The current meta-analysis gives surgeons measurements to work with. It reports the pooled mean distances from the IMA origin to other key and constant vessels — the SMA and the aortic bifurcation. From a surgical standpoint, the lower border of the duodenum serves as an anatomical landmark. Seeing the root of the inferior mesenteric vein also serves as an anatomical landmark. These landmarks pinpoint exactly where the IMA leaves the aorta.

Proper high ligation means tying off the main trunk of the IMA at a position 1 to 2 cm away from its origin at the abdominal aorta. This ensures a more radical oncological lymphadenectomy (a more complete removal of lymph nodes, known as a D3 dissection) while preventing injury to the pelvic autonomic nerves.

The meta-analysis shows that in most cases the IMA bifurcates, at a pooled prevalence of 63.89%. Low ligation with LCA preservation is technically manageable and yields favorable outcomes. When the tumor and the patient's characteristics allow it, preserving the IMA and the LCA may be crucial. This preservation may support better blood flow to the descending colon, making the reconnection (anastomosis) safer.

But there is a trade-off. Surgeons should remember that a disadvantage of low ligation with LCA preservation is that the descending colon may not reposition well enough to connect with the rectal stump. This happens because the mesocolon, the tissue attaching the colon to the abdominal wall, is too short. That creates inappropriate tension at the connection point. In such situations, tying off both the IMA and LCA may be unavoidable. When high ligation must be performed, blood flow from the marginal artery of Drummond should be adequate to supply the anastomosis.

Surgeons should also know that the sigmoid artery can arise from a common trunk with the LCA (27.78% pooled prevalence) or directly from the LCA (5.41% pooled prevalence). These possibilities can play a role in whether the LCA can be preserved.

The findings show that the pooled mean distance between the IMA and the LCA is approximately 40.67 mm. This measurement may have significant implications for deciding whether high or low ligation is appropriate.

Low ligation with LCA preservation is recommended in patients who have an IMA trifurcation, a pattern that occurred in 27.35% of cases in this analysis.

Limitations: What This Study Could Not Prove

The authors are candid about the limits of the evidence base. The morphological variability of the branching pattern remains ambiguous, and genuine anatomical variations have been insufficiently documented in the existing literature.

The statistical signals also point to caution. The bifurcation analysis showed an LFK index of −2, and the trifurcation analysis showed an LFK index of −4.62. Both indicate asymmetry, suggesting that smaller studies may report different results than larger ones. This is a common problem in anatomical meta-analyses.

The pooled prevalence estimates for several origin levels came with very wide confidence intervals. The L2–L3 disc space, for example, ranged from 6.41% to 60.88%. Such a wide range means the true value is uncertain and varies a lot between populations and studies.

Another limitation is the makeup of the evidence. Sixteen of the studies were based on Asian populations, compared with 3 European, 2 American, and 1 African. That imbalance limits how well these numbers apply to all patient groups worldwide.

Risk of bias was also a concern. Using the AQUA tool, the authors rated most included studies as having a high risk of bias. Only a minority — including the studies by Yada, Bertrand, Koji, Ke, Ekingen, Zhou, and Ding — were rated as low risk.

Finally, the included studies did not consistently use any single existing classification system. To organize the data, the authors created their own grouping based on how many main branches arose from the trunk (two, three, or four). This approach is not a formal validated classification. It is, however, a straightforward way to categorize IMA variants in a unified manner.

Recommendations and Practical Takeaways

This review outlines the levels of origin, the branching patterns, and the measurements of the inferior mesenteric artery. A comprehensive understanding of the surgical anatomy of this vessel is imperative during colorectal cancer procedures. Surgeons operating in this region must possess in-depth knowledge of both typical and variant structures.

For patients, several practical points follow from this research:

1. Anatomical variation is normal, not abnormal. Roughly 6 in 10 people have a bifurcated IMA, about 3 in 10 have a trifurcated IMA, and about 1 in 10 have a tetrafurcated IMA. None of these patterns is a disease.
2. Variation can affect surgical planning. Whether a surgeon can preserve the left colic artery — and whether high or low ligation is safer — may depend on the individual patient's branching pattern.
3. Preoperative imaging matters. Because the IMA typically begins at the L3 level (70.16% of cases), imaging can help the surgical team plan the approach before the operation begins.
4. Ask your surgical team how they will handle your vascular anatomy. If you are having colorectal cancer surgery, it is reasonable to ask whether the left colic artery will be preserved and why.
5. Blood supply to the reconnected bowel is a key concern. Preserving the IMA and LCA, when possible, supports better blood flow to the descending colon and a safer anastomosis.

Frequently Asked Questions

What is the inferior mesenteric artery and why does it matter in colorectal surgery?

The inferior mesenteric artery (IMA) is the main blood vessel feeding the lower gut, including the descending colon, sigmoid colon, and rectum. During colorectal cancer surgery, surgeons often tie off its branches. Knowing the typical and unusual branching patterns helps avoid complications. The IMA usually starts at the third lumbar vertebra and splits into two branches in about 64% of people.

How common is it for the inferior mesenteric artery to start at the L3 vertebra?

In a pooled analysis of 23 studies covering 3,419 patients, the IMA began at the L3 vertebra in about 70% of cases (roughly 7 in 10). Other origin points, such as the L2–L3 disc space or L4 vertebra, were less common. This typical location helps surgeons plan the operation, but individual variation is normal and not a disease.

What are the typical branching patterns of the inferior mesenteric artery?

The most common pattern is a bifurcation (two main branches) in about 64% of people. A trifurcation (three branches) occurs in about 27%, and a tetrafurcation (four branches) in about 12%. The single most common subtype is the IMA dividing into the left colic artery and a shared trunk for the sigmoid and superior rectal arteries, seen in about 46% of cases.

What is the difference between high ligation and low ligation, and how does anatomy affect the choice?

High ligation ties off the main IMA trunk without preserving the left colic artery (LCA). Low ligation ties off in the LCA region while preserving the LCA. The choice may depend on the individual's branching pattern. For example, low ligation with LCA preservation is recommended for patients with an IMA trifurcation, which occurred in about 27% of cases in this analysis.

Can preserving the left colic artery affect recovery after colorectal surgery?

Preserving the IMA and left colic artery, when possible, supports better blood flow to the descending colon and may make the reconnection (anastomosis) safer. However, a disadvantage of low ligation with LCA preservation is that the descending colon may not reposition well enough to connect with the rectal stump, creating tension. In such situations, tying off both the IMA and LCA may be unavoidable.

What should I ask my surgical team about my vascular anatomy before colorectal surgery?

It is reasonable to ask whether your left colic artery will be preserved and why. You can also ask how your surgical team will handle your individual vascular anatomy, especially if preoperative imaging shows a variant. Because the IMA typically begins at the L3 level in about 70% of cases, imaging can help the team plan the approach before the operation begins.

Are variations in the inferior mesenteric artery dangerous or abnormal?

No. Anatomical variation is normal, not abnormal. Roughly 6 in 10 people have a bifurcated IMA, about 3 in 10 have a trifurcated IMA, and about 1 in 10 have a tetrafurcated IMA. None of these patterns is a disease. However, variation can affect surgical planning, so surgeons need detailed knowledge of both typical and unusual arrangements to avoid complications.

If I'm having colorectal cancer surgery, when should I get a second opinion about whether my left colic artery can be preserved?

Whether the left colic artery can be preserved, and whether high or low ligation is safer, may depend on your individual branching pattern. About 6 in 10 people have a bifurcated artery, roughly 3 in 10 a trifurcated pattern, and about 1 in 10 a tetrafurcated pattern. Low ligation with left colic artery preservation is recommended in patients who have a trifurcated artery, which occurred in 27.35% of cases. It is reasonable to ask your surgical team whether the left colic artery will be preserved and why. Diagnostic Detectives Network provides independent expert second opinions.

Source Information

Original article title: The anatomy of the inferior mesenteric artery: a systematic review with meta-analysis.

Authors: George Triantafyllou, Nektarios Belimezakis, Orestis Lyros, Nikolaos Arkadopoulos, Fotis Demetriou, George Tsakotos, and Maria Piagkou

Author affiliations: Department of Anatomy, School of Medicine, Faculty of Health Sciences, National and Kapodistrian University of Athens, Goudi, Athens, Greece; and Fourth Department of Surgery, Attikon University Hospital, National and Kapodistrian University of Athens, Haidari, Greece

Publication: Surgical and Radiologic Anatomy (2025), volume 47, article 144. DOI: 10.1007/s00276-025-03657-1

Publication timeline: Received 12 March 2025; accepted 6 May 2025; published online 24 May 2025

Note: This patient-friendly article is based on peer-reviewed research. It is intended for educational purposes and does not replace personalized medical advice. If you are scheduled for colorectal surgery, discuss your individual anatomy and treatment plan with your surgical team.