The renal veins (RVs) are paired vessels that emerge from the renal hilus and drain into the inferior vena cava. Before draining into the inferior vena cava, the left RV collects blood from the ipsilateral suprarenal and gonadal veins and passes anterior to the aorta. By contrast, the right RV exits the renal hilus and drains directly into the inferior vena cava without tributaries.

The left RV shows frequent variations in its ramification patterns, including differences in its course, number, and tributaries [1]. These variations are often associated with variations in the gonadal and suprarenal vessels, resulting in variable positioning of these vessels [2-4]. Preoperative recognition of possible variations in the vascularity of the kidney, genital glands, and suprarenal glands is essential to avoid unexpected complications during retroperitoneal procedures.

Fenestration of the left RV is a rare anatomical variant with a reported incidence of 3.34% [5]. In most previously reported cases, the testicular artery (TA), which arises from the abdominal aorta (AA), passes through the fenestration [5-8]. The left renal artery can also pass through the fenestration [5, 9]. Fenestrations of the left RV represent complex variations involving arteries to the gonads and kidneys and have significant implications in diagnostic imaging and surgical procedures. Knowledge of these rare variants is clinically beneficial and valuable for understanding the morphogenesis of retroperitoneal veins, including the left RV.

Here, we report two cases (male and female cadavers) showing fenestration in the left RV, through which the renal and testicular arteries or the suprarenal and ovarian arteries (OAs) passed, respectively, observed in a routine gross anatomy class for undergraduate students at the National Defense Medical College.

Here, the TA and RA or the OA and MSA passed through the fenestration of the left RV. Previous studies have reported that fenestrations in the left RV are usually singular and found near the confluence of the gonadal and suprarenal veins [5-9]. Moreover, only the RA and TA passed through the fenestration of the left RV [5-9]. Thus, the case of the MSA passing through a fenestration in the left RV as well as the incidence of two different arteries passing through the same fenestration, as detected in Case 2, is extremely rare.

Fig. 3 illustrates the developmental process of the left RV and inferior vena cava. These veins are primarily formed through the persistence and regression of paired supracardinal and subcardinal veins and their anastomoses, namely the sub-supracardinal, inter-subcardinal, and inter-supracardinal anastomoses (Fig. 3) [10]. The segment of the RV near the renal hilus is thought to be formed by sub-supracardinal anastomosis, from which RVs emerge (Fig. 3) [7, 10]. The presence of an artery running between the ventral renal vein (VRV) and dorsal renal vein (DRV) is thought to be a factor in the formation of fenestrations, as it impedes complete venous fusion [7]. In the fetus, the RV drains into the inferior vena cava between T12 and L3 [10]. Consequently, arteries such as the gonadal artery or MSA which arise from the aorta at this branching level range, potentially become entrapped in the fusion of the VRV and DRV and sub-supracardinal anastomosis. In the present case, the gonadal artery and MSA arising either from the aorta at a level close to or arising directly from the RA may have been entrapped in the fusion of the VRV and DRV (Fig. 3).

Our cases are unique in the following ways. First, the testicular, renal, suprarenal, and OAs passed through a fenestration in the left RV. Second, in Case 1, the TA arose from the RA and passed through a fenestration in the left RV. Third, in Case 2, two different arteries passed through the same fenestration. The findings in our cases may contribute to a better understanding of the developmental processes of the left RV and its related vessels.