Renal arteries can easily be identified on CT-angiography,
even lesser arteries like segmentary branches can also be seen.
Despite detection of vessels inferior to 2mm is limited,
CT-angiography can reach 100% sensitivity using 3D reconstructions and MIP to identify main renal arteries.
Furthermore,
3D and MIP have demonstrated 100% sensitiviy in detection of polar arteries.
Multiple renal arteries constitute the most common anatomical variant of the renal vasculature according to its clinical relevance,
and they are presente in barely 30% of the population.
Multiple renal arteries are unilateral in 30% of patients,
and bilateral in 10%.
(FIGURE 2).
They usually have their origin at aorta or iliac arteries,
from D11 to L4 (FIGURE 3)(FIGURE 4).
They may even originate in thoracic aorta,
lumbar or mesenteric arteries.
Other rare origins of renal arteries have been described: celiac trunk,
common iliac or frenic arteries.
Despite renal arteries usually travel through hilum to supply both renal poles,
sometimes there are polar arteries with own aortic origin which directly supply a renal pole,
with no hilar input.
These vascular variants should be considered as “multiple renal arteries”; terms like “extra”,
“aberrant”,
or “accessory”,
which are frequently used,
should be avoided because these vessels are,
in fact,
terminal segmentary branches,
with no asnatomosis between them.
So that,
these vessels correspond to segmentary vessels from an only renal artery.
Even the term“supernumerary” should be avoided,
it can lead to think that this vessel´s function is superfluous.
Therefore,
this terminology suggests that a possible injury to these arteries has no repercussion over kidney parenchyma,
meanwhile exclusion of this arteries can lead to ischemia.
Every ectopy,
malrotation or anomalous development of the kidney uses to be bounded to renal vascular variants (FIGURE 5). Patients with horseshoe kidney can present even a common artery for both kidneys.
According to Sampaio & Passos,
nomenclature used to categorize renal arteries is (FIGURE 7):
a. Hilar artery: aortic branch with renal hilar input.
b. Extra-hilar artery: it originates in main renal artery and has an extrahilar input (usually superior pole).
c. Superior polar artery: aortic branch with superior polar input.
d. Inferior polar artery: aortic branch with inferior polar input.
e. Early bifurcation: renal artery with short trunk,
shorter than 1cm prior to its ramification.
According to ramification level,
hilar renal artery refers to those arteries which divide at hilum,
and extra-hilar are those segmentary arteries originated at the trunk of the renal artery,
prior to its division,
with superior or inferior polar input instead of hilum (FIGURE 8)(FIGURE 9).
Multiple renal arteries are cathegorized according to its course as polar (which directly penetrate to superior or inferior poles) or hilar arteries (arteries with an hilar input).
Incidence of superior polar arteries is clearly superior to inferior; both around 15% and 3%,
respectively.
Correct nomination of renal arteries before explant is important.
In cases of multiple renal arteries,
hilar arteries (not polar ones) are nominated in order of their appearence in abdominal aorta,
from craneal to caudal,
as: R1,
R2,
R3,
etc.
Early bifurcation is a normal variant described as an artery shorter than 1,5-2 cm from aortic wall origin until its division(FIGURE 10).
An early bifurcation can be considered as multiple supply from a surgical point of view.
At least,
1cm of main renal artery is necessary to reach a safety artery ligation and anastomosis, with no risk of stenosis.
Clinical importance of inferior polar arteries has been highlighted in many publications because of secondary development of hydronefrosis due to their presence.
Polar renal arteries can potentially compress proximal ureter and/or ureteropelvic junction.
Anatomical variants of renal arteries should be ketpt in mind not only in renal transplant or nefrectomies,
but also in abdominal interventions as EVAR (Endovascular Aortic Repair).
EVAR has a higher rate of technical success in those aneurysms classified as infrarrenal aortic aneurysms.
But this is not the only predictive factor of clinical relevance: presence of multiple renal arteries should be mentioned to avoid non-intentioned artery exclusion by endovascular graft.
If a renal polar artery is excluded,
in this cases there will be renal ischemia of the territory supplied by this artery what consequently may have repercusion over renal function or arterial pressure; but with scarce impact.