Multiple variation of right renal and gonadal vascularization: report of two cases

Abstract We present two cases of multiple anatomical variations of the renal and gonadal vessels. The first case presented duplication of the renal vein and the presence of an accessory renal artery. However, the most interesting fact, in this case, was that the right gonadal vein emptied into the inferior right renal vein instead of ending in the inferior vena cava as would typically be the case. In the second case, we also found an accessory renal artery and the right gonadal vein emptied at the exact junction between the right renal vein and the inferior vena cava. Clinicians and surgeons should be familiar with anatomical variations to provide an accurate diagnosis during preoperative studies and to avoid surprises in abdominal surgical procedures.


INTRODUCTION
][3][4][5] Usually, the large renal veins are located anterior to the renal arteries and open into the inferior vena cava at almost a right angle.The right renal vein lies posterior to the descending part of the duodenum, is often less than 1 cm long, and because it is very short, makes safe nephrectomy difficult and may make resection of a cuff of the inferior vena cava necessary.The left renal vein is three times as long and the left is therefore the preferred side for living donor nephrectomy. 5,6n adults, the right gonadal vein enters the inferior vena cava directly on its anterolateral aspect at an acute angle about 2 cm below the left renal vein and occasionally it drains into the right renal vein, 7 ending at a right angle as the left gonadal vein does, in which case, the likelihood of development of venous incompetence is increased. 2,6s for the arterial supply to the kidneys, we can consider a single renal artery to each kidney to be the standard pattern, usually present in almost 70% of individuals.Near the hilum of the kidney, each artery divides into an anterior and a posterior branch, which divide into segmental arteries that supply the renal vascular segments.][7][8] This study presents two cases of anatomical variation of the renal and gonadal vessels that are not only of interest to academics but are also of importance in daily practice, as much for correct interpretation of radiological exams as for local surgical interventions.

CASE DESCRIPTIONS
During routine dissection of the abdominal region, vascular variations were found in supply to the right kidney in two adult human cadavers.These case reports were prepared at the Laboratory of Human Anatomy of the Santa Marcelina Medical School and were approved by the Ethics Committee, process nº 6.147.298/2023.

Case 1
A triple atypical variation of right kidney vascularization was found in a 37-year-old male cadaver.During access to the right renal lodge, we observed duplication of the renal vein in two smaller caliber veins that emerged from the real hilum of the kidney and drained directly into the inferior vena cava.They were both anterior to the renal pelvis and the right renal artery, one being superior and the other inferior to the renal artery.The right inferior renal vein opened into the vena cava at the same level as the left renal vein, while the superior renal vein opened at a point slightly above the left renal vein.Moreover, we observed that the right gonadal vein, which usually ends directly into the inferior vena cava, instead flowed into the inferior right renal vein near its entry point in the inferior vena cava.In addition to these venous variations, an accessory renal artery was found emerging from the anterior aspect of the abdominal aorta just above the origin of the inferior mesenteric artery, crossing anteriorly to the inferior vena cava, and entering the right hilum of the kidney anteriorly and inferiorly to the inferior renal vein and renal pelvis (Figure 1).

Case 2
In this case, we observed a vascular variation in a 57-year-old male cadaver.The right gonadal vein opened inferiorly at the exact point of junction of the right renal vein with the inferior vena cava.The renal vein was not duplicated.We also observed an accessory renal artery emerging from the anterior aspect of the abdominal aorta slightly above the origin of the inferior mesenteric artery, crossing anterior of the inferior vena cava, and entering the hilum of the kidney anteriorly and inferiorly to the right renal vein and renal pelvis (Figure 2).
There were no variations in the vessels leading to the left kidney in either case or any other vascular abnormalities found during dissection of the abdominal cavities.

DISCUSSION
][10][11][12] Accessory arteries are the most common and account for a third of these cases, generally arising from the aorta below the main renal artery. 5,8Accessory renal arteries are differentiated into hilar and polar arteries.[10][11][12] We present two cases in which an accessory renal artery was observed.Such variations can be explained by the embryological development of kidneys and gonads from the intermediate mesoderm of the mesonephric crest and vascularization of both organs from the lateral mesonephric branches of the dorsal aorta. 13,14ccessory arteries do not constitute duplication of vessels, but rather one or more segmental arteries (terminal branches) are each exclusively responsible for a portion of the kidney. 4,6Therefore, if an accessory artery is damaged, the part of the kidney supplied by it will likely become ischemic. 1,13se of kidneys from living donors with multiple renal arteries has been discouraged due to the increased risk to the donor of obtaining a mutual aortic cuff, the technical difficulty of completing multiple arterial anastomoses, prolonged ischemia time, and poorly controlled hypertension from segmental allograft alterations. 1 In addition to the possibility of nutcracker syndrome, in which compression of the left renal vein is caused by the superior mesenteric artery. 4s with arteries, the causes of variation in the origin, course, and branches of the renal and gonadal veins can be attributed to embryological origin. 2,14Development of the renal and gonadal veins is often closely related to the inferior vena cava.Embryogenesis of these veins involves the development, regression, anastomosis, and replacement of three pairs of venous channels: the posterior cardinal, subcardinal, and supracardinal veins.Anastomosis between the supracardinal and subcardinal veins, which occurs bilaterally, forms the renal segment of the inferior vena cava.The gonadal vein develops from the caudal part of the subcardinal vein and drains into the suprasubcardinal anastomosis.On the right side, this suprasubcardinal anastomosis and a small portion of the sub-cardinal vein are incorporated into the formation of the inferior vena cava.Thence, the right gonadal vein usually drains into the inferior vena cava. 2,15,16n the two cases presented here, there was only variation in the venous drainage pattern on the right side, a variation that appears to be less common.According to a study presented by Baptista-Silva et al. 8 that analyzed 342 cases of variation in the renal vein, only 6.4% of the cases occurred on the right side, about a third of which had a duplicated renal vein with just a single case of tributary gonadal vein.The authors reported that the variation in syntopy of a single vein is much more common (61.29%), while three or more renal veins are found less commonly (9.7%).Cicek et al. 5 found slightly higher rates of multiple right-sided renal veins, at 28.2%, in a retrospective study of 1,859 voluntary donors during an 11-year follow-up.
Furthermore, variation in the venous drainage pattern of the gonadal veins was noted in both cases, but with different patterns.The differences in regular testicular venous drainage patterns probably explain the fact that 95% of varicoceles occur on the left side, where the gonadal vein is a few centimeters higher than the right and performs two bends at two right angles to flow into the inferior vena cava.On the other hand, the right testicular vein ends directly in the inferior vena cava at an acute angle, indicating higher hemodynamic pressure in the left testicular vein than in the right. 17n the first case, we noted that the gonadal vein opened directly into the right renal vein at a 90° angle.This variation was also described in a case report by Nayak. 18Ahlberg et al. 19 observed this type of variation in only 8.3% of cases in 84 autopsies performed and Asala et al. 20 observed it only twice (1.3%) in 150 cadavers studied.If we extrapolate the knowledge of the hemodynamic resistance that occurs on the left side, this type of variation may result in right-sided or bilateral varicocele, as documented by Zini et al. 21n the second case, the gonadal vein ended obliquely at the point of junction of the renal vein with the inferior vena cava; we did not find similar reports in the literature.In this case, we can only assume that the oblique termination of the vein, although unusual, does not seem to offer the same hemodynamic resistance described in the previous case, since the retrograde flow through this vein tends to be lower due to its position about the inferior vena cava.
The origin and course of the vessels to the kidneys must be carefully identified to preserve normal blood flow and to prevent possible anatomical variations from becoming clinically complex abnormalities. 3,4Radiologists, vascular surgeons, urologists, and oncologists should be familiar with anatomical variations to provide an accurate diagnosis during preoperative studies.

Figure 2 .
Figure 2. Anterior view of the right kidney and its blood vessels from Case 2. RK = Right kidney; IVC = Inferior vena cava; AA = abdominal aorta; RRV = Right renal vein; RRA = Right renal artery; ARA = Accessory renal artery; IMA = Inferior mesenteric artery; RU = Right ureter; RGV = Right gonadal vein; (*) point where the right gonadal vein empties at the junction of the right renal vein and the inferior vena cava.