Anatomy is never truly standard

In anatomy textbooks, the kidney has one artery and one vein. In clinical reality, vascular variants are the rule, not the exception. Large-scale studies based on multidetector CT angiography have documented that more than 30% of patients present at least one variant of renal vascular anatomy.

For a surgeon planning a partial nephrectomy, identifying these variants before surgery is not an academic detail — it can make the difference between a smooth operation and an intraoperative complication with potentially serious consequences.

Arterial variants

Accessory renal arteries

The presence of multiple renal arteries is by far the most frequent variant. A meta-analysis of CT angiography data reported an overall prevalence of 31.3% for multiple renal arteries:

| Configuration | Prevalence | | -------------------- | ---------- | | Two renal arteries | 22.2% | | Three renal arteries | 7.5% | | Four renal arteries | 1.4% | | Five renal arteries | 0.2% |

Accessory arteries may arise from the aorta at different levels and supply specific portions of the kidney — particularly the upper and lower poles. An unidentified accessory polar artery represents a concrete risk: inadvertent clamping causes segmental ischemia, while injury during dissection can produce significant bleeding.

Prevalence varies between the right side (10%) and the left (13%), a difference reflecting different embryological origins and asymmetric anatomical relationships with the aorta.

Early-branching segmental arteries

In some patients, segmental arteries branch very early from the main renal artery, sometimes before entering the hilum. This variant, known as early branching, radically alters the selective clamping strategy.

In a standard configuration, the surgeon can clamp the main renal artery at the hilum to obtain controlled global ischemia. With early branching, clamping must be planned more distally — on the specific branch supplying the segment to be resected — requiring precise knowledge of the vascular map.

Prehilar branching

Prehilar branching has been reported with a prevalence of 6.5%. In these cases, the renal artery divides into its segmental branches before reaching the renal hilum, making the hilum itself harder to dissect and selective clamping more delicate.

Venous variants

Renal vein duplication

The renal vein may appear duplicated, with two distinct branches draining into the caval system. The prevalence of multiple renal veins differs markedly between sides:

| Side | Multiple-vein prevalence | | ----- | ------------------------ | | Right | 16.6% | | Left | 2.1% |

This pronounced asymmetry is explained by embryological development: the right renal vein has a shorter course and a more variable configuration.

Venous duplication is especially relevant in left-kidney surgery, where the renal vein crosses the midline anterior to the aorta. An unidentified duplication may be injured during dissection, with significant hemorrhagic consequences.

Circumaortic renal vein

The circumaortic renal vein is a variant in which the renal vein forms a ring around the aorta, with an anterior branch (in the usual position) and a posterior branch (retroaortic). The reported prevalence is 3.5–5.2% depending on the study and imaging modality used.

This configuration carries significant risk of venous injury during renal hilum dissection. The retroaortic branch in particular runs in an unexpected position and can easily be injured if the surgeon is not aware of it. Injury to a retroaortic vein is technically difficult to repair given its posterior location.

The circumaortic vein has also been associated with other concomitant vascular anomalies, making preoperative identification all the more important.

Retroaortic renal vein

In the retroaortic vein (prevalence ~3%), the renal vein runs behind the aorta rather than in front. This variant is particularly insidious because the vein lies in a position where the surgeon does not expect to find it during the standard approach.

The limit of two-dimensional CT

Contrast-enhanced CT images can visualize these variants, but their interpretation requires careful analysis of axial, coronal, and sagittal sections. The surgeon must mentally reconstruct vessel tridimensionality — a process that depends on individual experience and introduces variability.

The problem is particularly evident in three situations:

Structural overlap

On a single section plane, vascular structures may overlap, making it impossible to distinguish one vessel from another. A duplicated vein running parallel and close to the artery can be mistaken for a single structure on axial slices.

Vascular tortuosity

Renal arteries — especially in elderly or hypertensive patients — frequently present tortuosities that make it difficult to track the vessel's course across consecutive sections. A tortuous segmental artery may appear and disappear on adjacent slices, complicating mental reconstruction.

Tumor-vessel relationships

The spatial relationship between a tumor mass and the adjacent segmental vessels is one of the most critical pieces of information for surgical planning, but also one of the most difficult to assess on 2D images. The question "does this vessel pass above, below, or through the tumor?" does not always have a clear answer on two-dimensional sections.

The 3D model advantage

With an interactive 3D model, the surgeon completely overcomes the limits of mental reconstruction. The model transforms a complex and subjective analysis into a direct and objective exploration:

Freely rotate the model to appreciate the full course of each vessel in continuity, without having to correlate consecutive sections
Isolate structures by toggling individual anatomical layers — arteries, veins, urinary tract, neoplasm, parenchyma — to study each component individually or in combination
Adjust opacity to visualize relationships between deep and superficial structures: by making the parenchyma transparent, intrahilar vessels become immediately visible
Measure distances between the tumor mass and the main vessels with millimetric precision
Identify variants with visual certainty: a venous duplication, an accessory artery, or a circumaortic vein are immediately recognizable without ambiguity

These capabilities turn a subjective mental reconstruction into an objective, reproducible exploration that is — crucially — shareable with the surgical team and with trainees.

Clinical cases from our series

In the jst/medics case series, vascular variants had a direct impact on surgical planning in numerous cases. Three examples illustrate the variety of situations encountered:

Case 1: Vena cava duplication with peri-hilar cyst

A case of right renal neoplasm with vena cava duplication and a simple renal cyst near the hilum. The venous duplication, immediately visible on the 3D model, required particularly careful planning of the hilar dissection to avoid injuring the accessory venous branch. On 2D CT, distinguishing between the two caval veins required detailed coronal analysis.

Case 2: Renal vein duplication with interposed artery

A tumor at the upper pole of the left kidney with left renal vein duplication. The renal artery ran between the two venous branches — an anatomical configuration that made arterial clamping particularly delicate. The tumor was adjacent to a segmental branch of the renal artery and to the excretory tract. The 3D model made it possible to plan an approach that avoided injury to either venous branch during access to the artery.

Case 3: Circumaortic vein with arterial tortuosity

A case of an exophytic posterior mesorenal tumor of the left kidney with a circumaortic renal vein and significant tortuosities of the renal artery before the segmental branches. The segmental arteries showed early branching at the lower pole. The 3D model made the circumaortic venous ring immediately visible — a variant that on axial CT can easily be missed if the retroaortic branch is small in caliber.

In each of these cases, the 3D model made it possible to identify the variant with certainty and to plan the safest surgical approach before entering the operating room.

Implications for surgical training

Renal vascular variants also represent a significant educational challenge. Urology residents must learn to recognize these variants on preoperative imaging — a skill traditionally developed over years of experience.

3D models accelerate this learning process because they make variants visually obvious rather than requiring a mental reconstruction ability that only experience can develop. A model in which the circumaortic vein is visible as a colored ring around the aorta is immediately understandable even for a surgeon in training.

This educational aspect is particularly relevant in modern surgery, where the learning curve of robotic partial nephrectomy must be made as fast and safe as possible.

Conclusions

Vascular anatomical variants are not rare exceptions: with an overall prevalence above 30%, they are a daily reality of renal surgery. Their preoperative identification is essential for surgical safety and for planning the clamping and resection strategy.

3D models do not create these variants — they make them visible, measurable, and communicable. For the surgeon, this translates into greater safety and more conscious planning. For the patient, into a more precise and less risky procedure. For the trainee, into a learning opportunity that accelerates the experience curve.

References

Anatomical study about the variations in renal vasculature. Anat Sci Int. 2023. PubMed
Anatomical variants of renal veins: A meta-analysis of prevalence. Clin Anat. 2019. PubMed
Prevalence of renal vascular variations: Evaluation with MDCT angiography. Diagn Interv Imaging. 2016. PubMed
The significance of the circumaortic left renal vein and other venous variations in laparoscopic living donor nephrectomies. Transplant Proc. 2011. PubMed
Anatomical Variants of the Renal Veins and Their Relationship with Morphofunctional Alterations of the Kidney: A Systematic Review and Meta-Analysis of Prevalence. J Clin Med. 2024. PubMed