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Circumaortic renal collar

Circumaortic renal collar is an anomaly of left renal vein when a supernumerary/accessory left renal vein passes posterior to aorta, apart from the normal renal vein passing anterior to aorta. This anomaly is potentially hazardous, if unrecognised during retroperitoneal surgery 1.


By the 8th week of life, posterior cardinal system (which represents iliac bifurcation in adults) is replaced by four longitudinal channels - a paired supracardinal veins posterior to aorta and paired supracardinal veins anterior to aorta. Connections between these veins form a circumaortic plexus. Usually, the ventral portion of this plexus forms the normal left renal vein. If both the dorsal and ventral venous plexus persists, they form a circumaortic renal venous collar.


Incidence of circumaortic renal vein 2 is reported to be ~10% (range 2-17%).  A more common variant is a retro-aortic single left renal vein.

Radiographic features

CT or conventional angiography may accurately delineate this abnormality, where an accessory renal vein is seen to pass posterior to aorta.


During retroperitoneal surgery or nephrectomy, the surgeon may be falsely assured by the normal anterior renal vein, confidently clamp the aorta and mobilise the kidney. In this process, retro-aortic renal vein may shear off, leading to fatal haemorrhage.

See also

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