Keywords
horseshoe kidney - anomaly - artery - vein - anatomy
Introduction
Kidneys are oval-shaped organs that are situated in the retroperitoneum, on the posterior
abdominal wall, one on each side of the vertebral column, at the level of the T12-L3
vertebrae. They have a reddish-brown color and are ∼ 10 cm long, 5 cm wide, and 2.5
cm thick. The right kidney is located ∼ 2.5 cm lower than the left kidney, probably
because of the liver. The lower pole of the right kidney is approximately one finger
width above the iliac crest.[1]
Horseshoe kidney is the most common congenital malformation of the urinary system,
and it combines three anatomical variations: ectopia, poor rotation, and vascular
change.[2] In most of the cases, the fusion occurs through the lower renal poles with the formation
of an isthmus of fibrous tissue that crosses the median line, which prevents the kidney
from ascending from the pelvis to the abdominal cavity due to the presence of the
inferior mesenteric artery, at the level of the third to the fifth lumbar vertebrae.
Due to this fact, they do not rotate 90° anteriorly, which damages the arteriovenous
formation, giving rise to numerous accessory vessels.[2]
[3]
[4]
This malformation has a prevalence of 0.25% (1 in 400 births) and a higher rate in
males (2:1 or 3:1). The arrangement of the arteries and veins in the renal hilum varies
considerably, which can compress the ureters and cause urinary lithiasis in up to
41% of the cases.[5]
[6] The anomalous anatomical position predisposes to a greater risk of blunt injuries.[3] In addition, the horseshoe kidney has also been related to a greater propensity
to neoplasias, such as Wilms tumor, and to systemic malformations, such as Turner
syndrome.[7]
The blood supply to the horseshoe kidney is varied, with the arteries originating
from branches of the aorta, from the inferior mesenteric artery, or from the iliac
artery.[8] The identification of the anatomical variations of the renal arteries is of extreme
importance for the performance of surgical procedures involving the renal arteries
in order to prevent reckless lesions during surgery. This study cooperate especially
in surgical interventions, as well as in renal transplants and radiological studies.[9]
[10]
[11]
The objective of the present study is to report the arteriovenous pattern found in
the renal hilum in a case of horseshoe kidney.
Materials and Methods
A conventional retroperitoneal dissection was performed in a corpse, fixed for 2 years
in formalin, of a 64-year-old adult female, brown skin color, legally belonging to
the Anatomy Laboratory of Unicastelo, Fernandópolis, state of São Paulo, Brazil, with
causa mortis related to uterine cancer.
Results
Horseshoe kidney ([Fig. 1]) was detected, with a union pattern at the lower extremities formed by an isthmus
with a concavity facing upwards. The right kidney was 5.69 cm long, 3.62 cm wide,
and had an average thickness of 2.68 cm. The left kidney was 11.65 cm long, 5.02 cm
wide, and had an average thickness of 2.82 cm. The distance between the 2 upper poles
was 9 cm, with a convex margin of 37 cm, and a concave margin of 19.5 cm. The ureters
originated from an anomalous and extruded renal pelvis; however, with a normal path
and topography ([Fig. 1]).
Fig. 1 Right anterior aspect of the horseshoe kidney (green arrow: renal pelvis; red arrows:
larger renal calyces; black arrow: abdominal part of the ureter).
In a comparison with the usual pattern of renal arterial supply ([Fig. 2]), the following variations could be observed ([Figs. 3] to [6]): single right superior polar segmental artery with right posterior artery; double
left superior polar segmental arteries originating from the renal artery (one in each
renal face); renal isthmus artery originating from the posterior aspect of the abdominal
aorta; and a vein from the renal isthmus opening into the left common iliac vein.
Fig. 2 Renal arterial pattern.
Fig. 3 Blood supply found in a case of horseshoe kidney.
Fig. 4 Presence of right superior polar segmental artery (red arrow) in posterior view,
after the dislocation of the horseshoe kidney.
Fig. 5 Presence of two left superior polar segmental arteries (red arrows) in horseshoe
kidney.
Fig. 6 Detection of the artery (red arrow) and of the vein (black arrow) of the renal isthmus
in a case of horseshoe kidney.
Discussion
Horseshoe kidneys are asymptomatic and are usually detected at random. However, they
are subject to a series of complications as a result of poor drainage, which may lead
to clinical symptoms.[3]
[12] These complications include hydronephrosis secondary to obstruction of the ureteral
junction, infection and renal calculi, increased incidence of malignancy (especially
Wilms tumor and transitional cell carcinoma), and increased susceptibility to trauma.[3]
[12]
[13] Glomerulonephritis is another complication, with immunoglobulin A nephropathy being
the most common in horseshoe kidneys.[13]
The most probable explanation for the formal genesis of the anomaly of the present
case is the fusion of the two caudal poles during a period in which two renal sketches
were very close, mainly at the lower poles. As a result, the mesodermal tissue among
the methanephrons disappears or does not carry out its normal development. For reasons
that are not yet determined, the lower poles of the kidneys are close to merge. This
merge explains the successive stop of rotation along the longitudinal axis.[7]
[12]
The blood supply is, in most cases, anomalous, being composed of several accessory
vessels.[3] This variation was classified in different ways and is important for surgical programming.[14]
Conclusion
Horseshoe kidney is a congenital anomaly whose arteries can originate from branches
of the aorta, from the inferior mesenteric artery, or from the iliac artery. Its veins
drain into the renal vein, into the inferior vena cava, or into the iliac veins. Although
it may be associated with hydronephrosis and nephroblastoma, no reports were found
in the literature regarding the correlation between horseshoe kidney and uterine cancer,
which highlights the importance of the hilar vascular pattern of the reported case.
