Article ID: 24-00021
Introduction: Renal arteries vary in their number and arrangement. Accessory renal arteries (ARA), termed by various names in the literature, can arise from different arterial sources and may be single, double, or multiple. Understanding these variations is essential for various medical procedures.
Aim: To determine the presence of ARA in the cadavers of South Indian origin and their origin and termination and to discuss its relevant clinical anatomy.
Materials and Methods: This descriptive study utilized 36 adult cadavers of South Indian origin aged between 50 and 80 years. The ARA observed were classified according to their origin and termination. The Chi-square test was used to determine the variation in the distribution of accessory arteries between the sides.
Results: Among the 72 kidneys examined, 27.7% had ARA, with a left-sided preponderance. Most accessory arteries had an aortic origin and hilar or superior polar termination. Various forms of accessory arteries were observed, including those entering the anterior surface of the kidney, a rare phenomenon.
Conclusion: The incidence of accessory arteries supplying the kidney emphasizes the importance of understanding renal vascular anatomy for clinical practice. Anatomical variations play a crucial role in selecting donors for renal transplantation and during various renal interventional procedures.
The kidneys are excretory organs that receive blood supply from renal arteries. Renal arteries transport approximately 20% of the heart’s output to nourish the kidneys, constituting less than 1% of the entire body weight. In 70% of cases, a solitary renal artery provides each kidney with blood1). It’s frequent to observe variations in both the number and configuration of these renal arteries.
Renal perfusion is completely dependent on the renal arteries, which are specific for each renal segment. If a kidney is supplied by multiple arteries, the dominant or main renal artery is identified as the one with the largest diameter, reaching into the hilum of the respective kidney, while all other renal arteries are classified as accessory. In the literature, these accessory arteries are referred to by various names such as supplementary, additional, multiple, extra, supernumerary, anomalous, and aberrant renal arteries2).
Accessory renal arteries (ARA) can originate from either the renal artery or the aorta. Additionally, they may arise from various other arteries, including the thoracic aorta, celiac artery, inferior phrenic artery, gonadal artery, superior mesenteric artery, inferior mesenteric artery, common iliac artery, external iliac artery, and internal iliac artery. These ARA may exist singly, in pairs, or in multiples2).
The traditional way of further classifying ARA was based on their origin and termination. There are five categories, namely, aortic hilar, aortic upper polar, renal upper polar, aortic lower polar, and renal lower polar2). Anatomical variations seen in renal vasculature have serious clinical implications during radio-diagnostic procedures, endoscopic surgeries, renal vascular interventions, and treating renal hypertension.
This study aims to determine the presence of ARA in the cadavers utilized for routine dissection purposes and their origin, their entry into the renal substance, and to discuss its relevant clinical anatomy.
Ethical Approval was obtained from the Institutional Human Ethics Committee (No. IHEC-II/0235/22 dated 10.08.2022). Adult cadavers dissected for undergraduate teaching in the anatomy department constituted the study material. Thirty-six embalmed adult cadavers of South Indian origin, aged between 50 and 80 years, were used in this descriptive study. All anterior abdominal structures were excised to allow free access to the posterior body wall. Components of the urogenital system, including the kidneys along with the suprarenal gland and ureters, were identified. The abdominal aorta, renal artery, and its branches, inferior vena cava, renal vein and its tributaries, along with the supra renal vessels, were dissected.
ClassificationThe artery arising from the aorta with the largest diameter and reaching the renal hilum is considered the main renal artery, and all other arteries reaching the kidney were regarded as ARA. Branches of the main renal artery reaching the kidney other than the hilum were also considered ARA. Branches arising from the main renal artery and reaching the hilum are considered hilar ARA if they are in addition to and proximal to the normal segmental branches. Among the various classification methods, we have adopted the method used by Merklin and Michels3) and Budhiraja et al.4):
i. ARA arising from the aorta
ii. ARA arising from the main renal artery
iii. ARA arising from other arteries
All 72 kidneys underwent an examination to identify any ARA. If found, they were classified according to the above-mentioned classification system. Additional information about the ARA, such as their location, number, origin, and entry point into the kidney, was carefully observed and documented.
Statistical analysisA descriptive analysis was conducted, and categorical variables were presented as frequencies and percentages. The Chi-square test was employed to assess the differences in the distribution of ARA between the right and left sides (p<0.05).
Out of the 72 samples examined, ARA were found in 20 kidneys (27.7%), with 8 (40%) occurring on the right side and 12 (60%) on the left side. The distribution of single (Fig. 1A), double (Fig. 1B), or triple (Fig. 1C) accessory arteries and their respective sides is shown in Table 1. In this study, ARA were more commonly observed on the left side, with single accessory arteries (60%) being the most prevalent, followed by double (20%) and triple (20%) accessory arteries. Triple ARA were exclusively observed on the left side. Despite the higher occurrence of accessory arteries on the left side, this difference did not reach statistical significance when compared to the right side (Chi-Square statistic = 1.4, p = 0.49).
Kidney specimens with one, two, and three ARA. 1A: Right kidney with hilar accessory renal artery arising from the aorta. 1B: Right kidney with double accessory renal artery. One superior polar arising from the main renal artery, and one inferior polar arising from the abdominal aorta. 1C: Left kidney with two ARA arising from the main renal artery and one arising from the inferior supra renal artery.
HARA-Hilar accessory renal artery, RMRA-Right main renal artery, IVC-Inferior vena cava, AA-Abdominal aorta. RK-Right kidney, LRA-Left renal artery, IPA-inferior polar artery, SPA-superior polar artery, RRA-Right main renal artery, LMRA-Left main renal artery, CT-Common trunk, ARA-Accessory renal artery, ISRA-Inferior supra renal artery, LK-Left kidney, SRG-Supra renal gland.
ARA-Number and side of occurrence.
*(χ2 = 1.4, p= 0.49)
Every accessory renal artery originated from either the aorta (62.4%) or the main renal arteries (37.6%), with none originating from other sources reported earlier.
Termination of ARAARA displayed diverse forms of entry into the kidneys. The configurations observed in this study were Hilar (Fig. 1A), Superior polar, Inferior polar, Superior and inferior polar (Fig. 1B), and Hilar and polar (Table 2). Among these types, hilar and superior polar were the most common type observed (25%). Table 3 includes information on both the origin and termination of the accessory arteries observed in this study.
In this investigation, an uncommon occurrence of two ARA entering the anterior aspect of the kidney was observed. Specifically, a left kidney with triple ARA was identified, featuring a hilar artery and a superior polar artery, both stemming from the left renal artery. Additionally, it exhibited a third accessory artery originating from the abdominal aorta above the main renal artery, which then entered the anterior surface of the renal parenchyma. This third accessory artery also supplied a branch to the left suprarenal gland (Fig. 2A). Right kidney possessing a double accessory renal artery was also noted on another cadaver. It included a hilar accessory artery emerging from the right renal artery, along with another accessory artery originating from the aorta and entering the kidney’s anterior surface (Fig. 2B).
Different types of termination of the ARA.
Origin and Termination of ARA in comparison with Budhiraja et al.4)
Kidney specimens with ARA entering the anterior aspect of the kidney and ARA coursing anterior to inferior vena cava. 2A: Left kidney with third ARA entering the anterior surface of the kidney. Inset provides a schematic representation of the 3 ARA. 2B: Right kidney showing ARA entering the anterior surface of the kidney. 2C: Right pre-caval accessory renal artery, with testicular artery arising from the main renal artery.
AA-Abdominal aorta, LK-Left kidney, ISRA-Inferior supra renal artery, SPA-Superior polar artery, LSG-Left supra renal gland, LRA-Left renal artery, RK-Right kidney, HARA-Hilar accessory renal artery, RRA-Right renal artery, RRV-Right renal vein, LRV-Left renal vein, IVC-Inferior vena cava, SPA-ARA entering anterior surface of kidney, SMA-Superior mesenteric artery, SRG-Supra renal gland, TA-Testicular artery, TV-Testicular vein.
Out of the 36 right kidneys examined, two were discovered to have ARA originating from the aorta, which traveled in front of the inferior vena cava (referred to as pre-caval ARA). These additional arteries were observed entering the hilum of the right kidneys. Furthermore, one of the kidneys possessing the precaval accessory renal artery also had the right testicular artery branching off from the right main renal artery (Fig. 2C).
Studies on Nigerian5), Colombian6), Western Indian7), and South African8) populations showed incidences of ARA at 24.5%, 24.9%, 24.99%, and 27.7% respectively. A retrospective CT angiographic study conducted by Palmieri et al.9) on the Brazilian population showed the highest incidence at 61.5%. In this study, among the 72 kidneys examined, the occurrence rate of ARA was 27.7%, aligning with previous research findings except for Palmieri et al.9) The notable disparity in occurrence rates suggests a substantial variation in the presence of ARA among different ethnic groups. A study done on kidney donors showed that 51% of donors had renal arterial variations, with 38% having an accessory renal artery10).
In agreement with the general observation, our study revealed a higher prevalence of ARA on the left side (60%). However, Budhiraja et al.4) and Jamkar et al.7) reported a predominance on the right side. Pradhay et al.11) noted that the discrepancy in the occurrence of ARA between sides was not statistically significant (p = 0.193).
The occurrence of a single accessory artery was more common than double, triple, or multiple ARA. Our study found 12 (60%) kidneys with a single artery, four kidneys with double (20%), and triple or multiple (20%) ARA. Pradhay et al.11) reported that 18 out of 100 kidneys had ARA, with 88.8% and 11.2% being single and double ARA, respectively.
In our study, the most prevalent type of accessory renal artery observed was the hilar and superior polar variant, accounting for 25% of cases. This finding contrasts with those reported by Saldarriaga et al. and Budhiraja et al., where the incidence of hilar ARA was more prevalent (12.1%) than other types of termination4,6). Conversely, Famurewa et al. documented a higher occurrence of the inferior polar type (5.5%) than other types of termination5).
The results of our current study have been juxtaposed with those of a study conducted in North India by Budhiraja et al.4) as outlined in Table 3. In both investigations, ARA predominantly originated from the aorta, with the hilar variant being the most prevalent type. Regarding polar arteries, the superior polar type was more frequent than the inferior polar type. Notably, accessory arteries terminating on the anterior surface were not reported in the North Indian study.
In our current investigation, we noted two ARA entering the kidney’s anterior surface without traversing through the hilum or medial border towards the poles. Despite numerous studies examining ARA, none of them have documented the existence of ARA entering the kidney’s anterior surface.
The presence of an accessory renal artery originating from the aorta on the right side holds particular significance, as it may travel in front of the inferior vena cava, potentially causing compression. In our study, only two specimens (2.7%) exhibited the hilar type of pre-caval accessory renal artery (Fig. 2C), which was a lower occurrence compared to findings reported by Famurewa et al. (4.5%), Srivastava et al. (5.48%), and Gupta et al. (6%)5,12,13). Additionally, Bouali et al. noted that 11 kidneys (9.1%) had precaval renal arteries, with 10 featuring precaval lower polar accessory arteries, while one kidney had both the right main renal artery and an accessory renal artery passing anterior to the inferior vena cava14).
Factors contributing to the development of ARAThe embryological basis put forth by Felix in 1912 is the widely accepted theory related to the formation of ARA. The urogenital organs receive blood supply from nine sets of mesonephric arteries originating from the aorta. These arteries extend towards the mesonephric fold, where their terminal branches create a network known as the rete arteriosum urogenitale. By the time the embryo reaches 18 millimeters in size, this network intersects with vessels entering the renal sinus, establishing a linkage between the aorta and mesonephric arteries. These mesonephric arteries gradually form three groups: cranial group (comprising the first two pairs), middle group (consisting of the third and fourth pairs, including the left fifth artery), and caudal group (fifth and sixth arteries on the right side and sixth and ninth arteries on the left side). These groups collectively offer vascular support to the developing kidneys. The renal artery originates from the middle group, whereas the other branches undergo regression. Retention of the remaining pairs within the middle group leads to the formation of ARA, typically found between the eleventh thoracic and fifth lumbar vertebral levels2,15).
A 64-slice CT study conducted on 167 Turkey patients found that the main renal arteries were significantly smaller in kidneys with ARA than in kidneys without accessory arteries (p<0.001)16). This observation can be substantiated by Hagen-Poiseuille’s law, which describes the pressure drop along a cylindrical tube as proportional to its length and inversely proportional to its radius (ΔP = 8 μLQ/πR4)17). The hypothesis of reduced blood flow through small-caliber principal renal arteries during development inducing the formation of ARA needs further research.
In addition to the embryological basis, genetic factors, hemodynamic shear force, and various chemical factors such as transcription factors (FOXD1, TBX18) and medication also play a vital role in the regulation of renal vasculature development2). Mouse models with Foxd1 gene knockout or with ablation of Foxd1-positive cells showed replacement of the main renal artery with multiple arteries branching from the aorta and entering the renal capsule centripetally in addition to structural abnormalities18). Medication during pregnancy affecting the renin-angiotensin system or mutation of the renin-angiotensin gene results in renal vascular abnormalities that are incompatible with life19).
Clinical implicationsIn general, ARA do not produce any symptoms and are only diagnosed during screening, diagnostic, or surgical procedures. These arteries, whether hilar or polar, act like segmental end arteries and can cause ischemia when blocked. Their presence increases complications during diagnostic and surgical procedures. ARA are associated with a higher incidence of stenosis, hypertension, and thrombosis2). Early consideration of ARA may improve the success rate of renal denervation therapy in hypertensive patients20).
The origin and course of the right accessory renal artery are significant, as it might stem from a lower point and traverse in front of the inferior vena cava. This anomalous course could potentially compress the inferior vena cava during procedures like endovascular embolization and stent placement. Additionally, the existence of an inferior polar artery in front of the renal pelvis could cause blockage of the ureter, resulting in dilation of the renal pelvis, hydronephrosis, and subsequent renal infection2). In the past, polar artery ligation was employed in the treatment of hydronephrosis, resulting in segmental renal ischemia and ureteral necrosis. Polar arteries are prone to accidental injuries when surgeons are dissecting the fat in the renal poles.
A recent research investigation involving renal cell carcinoma patients revealed a notable association between the presence of ARA and the occurrence of renal cell carcinoma. The study found that the presence of ARA in the kidney affected with clear cell renal cell carcinoma and the tumor size was significantly associated with higher grades based on the Fuhrman grading system. This system typically determines the grade by postoperative pathological examination of the tumor. The presence of ARA was shown to be a significant predictor of high-grade carcinoma.21).
The presence of ARA holds great significance in renal transplantation. The rise in laparoscopic kidney donor procedures emphasizes the importance of vascular anatomy in surgical assessment. During living donor medical assessment, imaging with 64-slice multidetector computerized tomography is routinely employed to determine vascular abnormalities, including small capsular and polar arteries.
Normally, a kidney with long renal vessels branching near the renal hilum is preferred for harvest. Therefore, the left kidney, whether with a single or two renal arteries, is routinely harvested from a live kidney donor. However, if there are multiple accessory arteries, a right nephrectomy may be the best alternative. In the case of a donor with multiple anatomical variations, the donor is left with a more normal kidney, and the one with variations will be harvested. The presence of multiple ARA in a living or deceased donor complicates the transplantation workup. The donor arteries have to be anastomosed separately or with each other before being anastomosed to the recipient’s artery22). Failure of reanastomosis of accessory arteries with the recipient arteries leads to segmental blood loss and ischemic injury to the transplanted kidney. Despite these facts, successful transplantation using a kidney with two renal arteries was performed. However, it was reported to have postoperative complications and a poor prognosis22).
The presence of polar arteries further increases challenges during renal transplantation. When polar arteries are lost during harvesting, it results in ischemia of the concerned segment and necrosis of the ureter. The failure rate also escalates as they can cause urinary leakage and renal vessel thrombosis2). In the present study, the observed frequency of superior polar and inferior polar ARA is higher than Budhiraja et al.4). This observation seeks extra caution during renal transplant surgeries.
In this study, it was found that 27.7% of the South Indian population had ARA. These arteries typically originated from the aorta and ended either at the hilum or the superior pole of the kidney, with no difference in occurrence between the left and right sides. ARA entering the anterior surface of the kidney, a rare phenomenon, was observed in two kidneys. Advanced imaging technology allows for early detection of ARA, enabling clinicians to warn individuals about potential risks such as renal artery stenosis, hypertension, and renal cell carcinoma. The observed anatomical variations in renal arteries are crucial for donor selection in renal transplantation, as well as for procedures like renal denervation therapy, endovascular embolization, and stent placement surgeries.
The authors extend sincere gratitude to the altruistic individuals who generously contributed their bodies to anatomical research and education.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
The authors have no relevant financial or non-financial interests to disclose.
The data that support the findings of this study are available on request from the corresponding author.
