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Updated: Jun 27, 2026
Multilevel Microdissection and Functional-Structural Profiling of Human Renal Arterial Branches
Published on: September 5, 2025
Proposal for classification of the circumaortic renal collar's morphology
Konstantinos Natsis1, Ioannis Tsitouridis, Trifon Totlis
1Department of Anatomy, Medical School, Aristotle University of Thessaloniki, Greece. natsis@med.auth.gr
Insights
A circumaortic renal collar, a rare vascular variation, was classified into three types based on CT angiography in 319 patients. Understanding this anatomy is crucial for preventing surgical complications.
Area of Science:
- Vascular Anatomy
- Radiology
- Surgical Anatomy
Background:
- The circumaortic renal collar is a rare anatomical variation of the left renal vein.
- Variations in renal venous anatomy can have significant clinical implications, particularly in abdominal surgery.
Purpose of the Study:
- To propose a classification system for the different forms of the circumaortic renal collar.
- To enhance the understanding of this vascular anomaly for improved surgical planning and patient safety.
Main Methods:
- Analysis of CT angiography scans from 319 patients.
- Literature review to support the proposed classification.
- Categorization of observed circumaortic renal collar variations.
Main Results:
- The circumaortic renal collar was identified in 2.5% (8 out of 319) of patients.
- A three-type classification (Type I, II, III) was proposed based on the configuration of the left renal vein and its relationship to the aorta.
- Type I: Single left renal vein with preaortic and retroaortic branches.
- Type II: Separate preaortic and retroaortic left renal veins.
- Type III: Anastomoses or multiple veins without anastomoses.
Conclusions:
- The proposed classification provides a framework for understanding circumaortic renal collar morphology.
- Recognition of this anomaly is vital for preventing intraoperative hemorrhage during procedures like abdominal aortic aneurysm repair and renal transplantation.
- Accurate preoperative identification of the retroaortic component is critical for surgical success.
Abstract:
In the present study, we propose a classification of the different forms of the circumaortic renal collar based on the findings of 319 patients and on a literature review. The patients underwent a CT angiography scan of the abdomen for various diagnostic reasons. The different forms in which the circumaortic renal collar may appear were categorized. The renal collar was observed in eight of the 319 (2.5%) patients. The classification we propose is the following: Type I, one left renal vein splitting into two branches, a preaortic and a retroaortic, draining into the inferior vena cava; Type II, two different left renal veins, the one preaortic and the other retroaortic, draining into the inferior vena cava; and Type III, either anastomoses between the preaortic and retroaortic vein, being multiple or not, or multiple preaortic or retroaortic renal veins without anastomoses. Although the circumaortic renal collar is usually asymptomatic, the knowledge of this variation is useful, mainly before abdominal aortic aneurysm surgery and renal transplantation. Failure to recognize the collar's retroaortic component may lead to hemorrhage and death during retroperitoneal surgery. We believe that our classification contributes to recognize the circumaortic renal collar's morphology both preoperatively and intraoperatively.
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