Double retro-aortic left renal vein—a rare anatomical variant

Description

The development of the renal venous system is a complex process occurring between the fourth and eighth weeks of gestation.¹ It involves the transformation and selective regression of three pairs of embryonic veins: the posterior cardinal, subcardinal and supracardinal veins.² Normally, the left renal vein forms from an anastomosis between the subcardinal and supracardinal veins, persisting anterior to the aorta to form the pre-aortic left renal vein.^{3 4} However, in rare cases, such as with double retro-aortic left renal vein (DRALRV), both dorsal and ventral limbs of the embryonic renal collar persist posterior to the aorta, leading to the formation of two left renal veins posterior to the aorta.^{5 6} The incidence of DRALRV is estimated to be less than 1%.⁷

During embryonic development, normal renal veins are formed by the obliteration of certain portions of the primitive venous system (figure 1A). In our case (figure 1B), on the left side, the sub-supracardinal anastomosis and intersupracardinal anastomosis failed to regress which resulted in the superior division of left renal vein (SD-RALRV); the subsupracardinal anastomosis and the supracardinal vein formed the inferior division of left renal vein (ID-RALRV). Conversely, anastomosis of the intersubcardinal vein and dorsal renal vein had undergone obliteration.⁸

Figure 1. Diagram of renal vein development. (A) Normal development of renal veins in adults. (B) Abnormal development of renal vein in the present report. Solid lines represent persistent venous connections, and dotted lines represent obliterated veins. A, aorta; d.RV, dorsal renal vein; IsC-a, intersubcardinal anastomosis; ISC-a, intersupracardinal anastomosis; sCV, subcardinal vein; SCV, supracardinal vein; sSC-a, subsupracardinal anastomosis; v.RV, ventral renal vein.⁸.

In a clinical case involving a male paediatric patient admitted with abdominal trauma post-road traffic incident, a triphasic CT scan of the abdomen revealed a specific anatomical variation incidentally. As seen in figure 2A,B, the venous phase and three-dimensional reconstructed image of the scan showed a single left renal vein (S-LRV) extending 1.25 cm from the hilum before bifurcating into two trunks at an angle of approximately 40° at the L2–L3 intervertebral disc level, 0.4 cm lateral to the left margin of the abdominal aorta. The SD-RALRV, measuring 0.65 cm in calibre, and the ID-RALRV, measuring 0.41 cm in calibre, formed a reclining ‘Y’-shaped course, passing behind the abdominal aorta and separately draining into the inferior vena cava at the level of the inferior border of the L2 and L3 vertebrae, respectively. The left suprarenal vein drained into the S-LRV. The patient underwent surgery given the associated right renal injury. No relevant surgical treatment was done for the anatomical variant, and the patient’s mother was informed about the variant anatomy present. An illustration of the same is shown in figure 3. Literature reports indicate that the right renal vein is incident in 0.6% to 3.7%.⁷

Figure 2. Multi-detector CT contrast-enhanced venography images. (A) Coronal multiplanar reconstruction image (B) Volume rendering three-dimensional image showing the left kidney (LK), from which the single left renal vein (SLRV) arises and distally it is seen bifurcating into two divisions which course behind the aorta (AO) to drain into the inferior vena cava (IVC) separately. The left suprarenal vein (LSV) is seen draining into the SLRV. Thrombi (T) were noted in the IVC and in the superior division of retro-aortic left renal vein (SD-RLRV) just proximal to its entry in the IVC, likely due to traumatic injury aetiology. RRA, right renal artery; LRA, left renal artery.

Figure 3. Schematic representation of single left renal vein (SLRV) originating from the left hilum and bifurcating proximal to the left lateral margin of the aorta into superior and inferior divisions which course behind the aorta; labelled as superior division of retro-aortic left renal vein (SD-RLRV) and inferior division of retro-aortic left renal vein (ID-RLVR). The SD-RLRV and ID-RLRV can be seen draining into inferior vena cava (IVC) separately. LRA, left renal artery; U, ureter.

This case illustrates the utility of multi-detector CT in the detection of rare anatomical variations like DRALRV and the clinical relevance of recognising and emphasising the importance of detailed imaging and anatomical knowledge in managing surgical and radiological challenges in abdominal trauma scenarios and beyond.

In clinical practice, understanding the embryological basis of DRALRV is crucial for accurate interpretation of imaging studies and for surgical planning in the retroperitoneal region.⁹ For instance, DRALRV can complicate surgical procedures involving the left kidney or adjacent structures, such as nephrectomies or surgeries for renal tumours. Surgeons must be aware of this variation to prevent inadvertent injury during procedures.¹⁰ Radiologists also rely on knowledge of DRALRV to interpret imaging studies like CT scans or MRI accurately, facilitating the identification of vascular structures and their relationships with adjacent organs and vessels.^{11 12}

Moreover, recognising the presence of DRALRV is essential for diagnosing conditions such as renal vein thrombosis and for planning interventions such as renal transplantation. This anatomical variation influences the surgical approach and techniques for vascular reconstruction.^{10 12} The existence of DRALRV underscores the wide spectrum of anatomical variations in renal vascular anatomy, contributing to a deeper understanding of human anatomy and its clinical implications.^{11 12}

Learning points.

• Anatomical variants of the renal vessels are commonly encountered. The left renal vein has a long course due to its embryological development, and variants are commonly observed.

• Some of these variants may be complex and not always documented in the available literature. These variants can be easily overlooked in radiological studies, but they should be reported, even if the patient is asymptomatic, as clinical manifestations may arise later or they might affect outcomes in various diagnostic and surgical approaches.

• Multiple radiological investigations are available for the detection of anatomical variation in the renal veins. Multiplanar reconstructed images and Three-Dimension Virtual Reality reconstructions are increasingly used today.