Generally, the renal vein (RV) is a paired vein, which arises from the renal hilus anteriorly to the ipsilateral renal artery (RA), and is drained into the inferior vena cava (IVC). The left testicular vein (TV) is drained into the left RV, while the right one joins directly into the IVC. The RA and testicular artery (TA) are also a paired arteries arising from the abdominal aorta (AA). The origin of the TA is lower than that of the RA. However, the origin, number, and course of the renal and testicular vessels frequently varies, and multiple variations may occur in combination [1-4]. Abnormal renal vessels are sometimes accompanied by abnormal connections with the lumbar vein (LV) and the azygos venous system [1, 5]. Combined variation increases the risk of injuring the associated vessels during surgery, highlighting the importance of understanding potential individual variations to minimize the risk.

Therefore, we report on the complex variations in the branching pattern of the testicular and renal vessels found in an 88-year-old Japanese male cadaver during a routine gross anatomy class for undergraduate students at the National Defense Medical College.

The cadaver used in the present study was donated to our institution with written comprehensive consent from the donors and his family, agreeing to its use for anatomical education and research. The research protocol and manuscript preparation were conducted in accordance with the “Guidelines for the research involving cadavers” published in 2021 by the Japanese Association of Anatomists.

On the right side, the anterior renal vein (ARV) and posterior renal vein (PRV) [5] emerged from the renal hilus, passed anteriorly and posteriorly to the right RA, and drained into the IVC at the level of the L1/2 intervertebral disc and L2 vertebra, respectively (ARV and PRV in Fig. 1A–C). The anterior vein collected the right TV in (Fig. 1A, B). In addition, two retrocaval TAs arose from the AA at the levels of the L1 and L2 vertebrae (superior testicular artery [STA] and inferior testicular artery [ITA] in Fig. 1B, C). Both passed through the space between the ARV and PRV and descended to the deep inguinal ring (STA and ITA in Fig. 1B, C). We did not find any communicating branches between these two TAs. Moreover, the STA sent two suprarenal branches (Fig. 1B, C). The right RA emerged from the AA at the level of the L1/2 intervertebral disc (RA in Fig. 1B).

On the left side, two TVs (lateral testicular vein [LTV] and medial testicular vein [MTV] in Fig. 1A, B, D) and ARV and PRV (Fig. 1B, D) were detected. The ARV collected the blood from the lateral TV and perinephric vein (PNV) [6]. The PNV collected the blood from the abdominal wall and suprarenal gland (LTV and PNV in Fig. 1A, B, D). The PRV drained the medial testicular and first to third LVs (PRV, fLV, sLV, tLV, and MTV in Fig. 1B, D). The ARV, PRV, and confluence of the suprarenal and inferior phrenic veins united to form a common trunk (RV in Fig. 1) and drained into the IVC at the level of the L1 vertebra (ARV, PRV, and suprarenal vein in Fig. 1B, D). Besides, the left RA emerged from the AA at the level of the L1/2 intervertebral disc (RA in Fig. 1A, B, D).

In the present case, we observed the PRV, medial TV, PNV, first to third LVs as abnormal tributaries to the left RV. The left RV and tributaries are derived from the left subcardinal, supracardinal veins, and anastomoses between them: left sub-supracardinal, inter subcardinal, and inter supracardinal anastomoses [7, 8]. The primitive left RV may collect the PRV, medial TV, and first to third LVs via the left sub-supracardinal anastomosis [7, 8]. Thus, the abnormal ramification pattern of the left RV in the present case may be attributed to the residual of the left sub-supracardinal anastomosis. Moreover, the PNV emerged from the abdominal wall and suprarenal gland and joined the ARV. Few reports exist regarding the branching pattern of this vein [6, 9], and its developmental process remains unclear. In the early stage of the venous developmental process, the drainage area and course to the postcardinal vein and post-subcardinal anastomosis seem to be similar to that of the PNV in the present case [7, 10]. Thus, the residuals of the postcardinal vein and post-subcardinal anastomosis could potentially contribute to the formation of the PNV.

For arteries, two retrocaval right TAs emerged from the aorta at the level of the L1 and L2 vertebrae and passed through the space between the ARV and PRV. The positional relationship between the TA and the IVC is different depending on the height of the origin of the mesonephric artery, which becomes the TA [11, 12]. The right mesonephric arteries originating from the aorta at the level of L1 and L2 vertebrae may run posteriorly to the IVC [12]. However, the positional relationship between the mesonephric and primitive RV is uncertain. It is inferred from the present case that the mesonephric artery with a higher origin than in typical cases can pass through the space between the ARV and PRV.

In conclusion, the present study shows a complex combined variation in the renal and testicular vessels, including the presence of the right ARV and PRV, abnormal tributaries of the left RV such as the PNV and LVs, and two retrocaval right TAs. Although this is a single case report and we need further research to better clarify the incidence and developmental process of similar variations, the understanding of detailed possible variations in these vessels would help minimize the risk of their damages in surgical approach to the kidneys.