The kidneys are known for their varied anatomical spectrum in regard to parenchyma, vasculature and collecting system. During the embryonic development kidneys are irrigated by multiple feeding vessels. Arterial variations are attributed to failure of some of those arteries to regress.[1]
The clinical importance of arterial variations is both medical and surgical. Renal arteries are end arteries without anastomotic connections, therefore their involvement by different pathological conditions such as atherosclerosis, fibromuscular dysplasia, dissection may lead to ischemic nephropathy and functional deterioration. There is no consensus among practitioners on the role of ARA in the pathogenesis of arterial hypertension. Typically, they are small-caliber vessels with lower perfusion pressure which leads to increased renin secretion from the parenchyma irrigated by ARA and activation of the renin-angiotensin system and hypertension.[15] Moreover, their stenosis or occlusion due to atherosclerosis may additionally contribute to the development and worsening of hypertension.[16] Some researchers consider them a factor for diminished response in radiofrequency renal denervation.[27]
From a surgical perspective, it is well known that crossing inferior polar ARA is an etiological factor for extrinsic ureteropelvic junction compression and hydronephrosis in children with reported incidence 11–25%.[5, 13] With the advances in laparoscopic and robot-assisted surgery, vascular preoperative evaluation is essential for the planning of number of abdominal and pelvic surgical interventions, thus, lowering the risk of iatrogenic injury.[28] Although ARA are an undesirable factor in transplantation and are associated with higher rate of complications, recent studies report similar short and long term outcomes in multiple and single renal artery grafts.[9, 30] Furthermore, it is important to report ED because sufficient arterial length is needed to ensure safe vascular anastomosis.
Presence of ARA and their origin location is also important during surgical or endovascular treatment of abdominal aortic aneurysms. Although data is inconsistent, some researchers report higher incidence of acute kidney injury and long term worsening of renal function after sealing of ARA.[26]
The difference in occurrence of anatomic variations is not only population but also region-based.[4] Our study shows higher number of anatomic renal arterial variations compared to most previously published results. Only 46.3% of the patients exhibited classic renal arterial anatomy. Similar to other studies, the most common variation was the presence of ARA, discovered in 41.2% of our subjects (n = 231).[11, 14, 20] These results are higher than the average reported frequency of 10–30% in other studies.[3, 10, 18] The variability of the results could be attributed to the size of the study group, method of data collection and classification and regional differences. According to laterality, published results are inconsistent. Some researchers report higher prevalence on the right side [24] and others on the left [14] but without significant difference. Our results demonstrated that ARA are more common on the left side in comparison to the right side (25.5% vs. 24.3% respectively) without reaching statistical significance. In our study, similar to most researchers greater proportion of males exhibited presence of ARA.[17] However, statistically significant difference between genders was not observed. Contrary to our results Sośnik stated significantly greater occurrence of ARA in males.[22]
The occurrence frequency of hilar ARA (72.6%) in our study was remarkably higher compared to polar ARA (15.2% superior polar ARA and 12.2% inferior polar ARA). Similar to our results Çınar et al. described greater frequency of hilar ARA (84.5%) compared to polar ARA (15.5%) and greater proportion of superior than inferior polar ARA.[7] One study by Johnson et al. also report higher prevalence of hilar ARA compared to polar ARA. However, ARA entering the kidney through the lower pole were more common in comparison to superior polar ARA.[14]
In our study, the most common site of both main and accessory renal arteries origin was the abdominal aorta between the level of L1 and L2 vertebrae. These findings are consistent with the classical teaching and previously published data reporting that 94–95% of the main renal arteries and 78–80% of ARA arise from the aorta at the L1-L2 level.[11, 18] Similar to our results Natsis states that the majority of right main renal arteries originate at the level of L1 and the majority of left main renal arteries- at the level of L2, while the most common level described by Palmieri is the L1-L2 intervertebral disk on both sides.[18, 19] ARA exhibit bigger range and more inferior ostium location compared to the main renal arteries. In the current study, both the main and accessory renal arteries on the left showed lower ostium position compared to the contralateral side, coinciding with previous literature reports.[11, 18] Three main renal arteries (0.3%) and eleven ARA (3.4%) did not arise from the aorta. The most common origin arteries were the common iliac arteries. One left main renal artery showed a very rare variant and originated from a common trunk with the median sacral artery. One left ARA arose from the left internal iliac artery. The renal arteries are known to originate from the iliac arteries, superior and inferior mesenteric arteries, contralateral renal artery, lumbar artery or the thoracic aorta. The variations in the ostium location and number of renal arteries are commonly encountered together with other concomitant genitourinary anomalies such as horseshoe or ectopic kidney.[10]
The prevalence of ED in the literature ranged between 4-35.9%.[8, 25] The frequency of 21.7% in our study could be considered moderate and aligns with previously published data. The majority of the studies do not establish a significant association between ED and laterality, although it was more prevalent on the right side.[6, 17, 25] However, according to our findings, ED is significantly more common on the right- 12.8% vs. 8.9%, p = 0.035. With respect to gender, two studies report significantly higher ED occurrence in males.[6, 11] On the other hand Kumaresan et al. report higher prevalence in females but without statistical significance.[17] However, in our study the rates of early bifurcation were similar between genders- 21.3% in males and 21.5% in females. Discrepancies in branching pattern could be attributed to regional differences, the methodology of data sampling and the adopted definition of ED in each study, which often varies between studies.
Traditionally, right-sided renal arteries pass behind the IVC. The reported prevalence of precaval course of the renal arteries is 4.5–9.17%[2, 8]. It is important to acknowledge precaval renal arteries because their presence has been associated with asymmetrical obstruction of the renal collecting system although the incidence of symptomatic hydroneprhosis is still unknown.[29] In the present study 6.9% of the right renal arteries had a precaval course which is in agreement with other studies. Similar to the studies of Yeh et al. and Bouali et al. the overwhelming majority of the precaval renal arteries were accessory.[2, 29] Precaval course was noted in only 0.5% of the main renal arteries and in 30% of ARA and significant difference was determined (p < 0.001). Precaval course of a single and main artery was found in one patient which is a very rare variant, and only few cases are described in literature.[29]