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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3900_Библиотеки_им_академика_М_И_Перельмана
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Abstract Patients presenting with coexistent abdominal aortic aneurysm and
renal ectopia or fusion abnormalities present a technical challenge to the vas-
cular surgeon at the time of aortic aneurysm repair. The most common of these
unusual renal conditions is horseshoe kidney, thought to occur in 0.25% of the
population. Associated abnormalities in the number and distribution of renal
arteries occur in three quarters of these patients and abnormalities of the renal
collecting systems are also common. Because the renal blood supply may be
asymmetric, division of the renal isthmus to allow aortic aneurysm exposure
may be hazardous. Improvements in preoperative imaging modalities have fa-
cilitated the preoperative awareness of the aberrant renal anatomy. While en-
dovascular aortic aneurysm exclusion may be feasible in some patients with
appropriate renal anatomy and normal preoperative renal function, the sacrifice
of renal arterial perfusion and the nephrotoxicity associated with contrast re-
quirements may preclude this approach for others. However, using current open
surgical techniques, including retroperitoneal exposure and renal preservation
methods, safe aortic aneurysm repair with preservation of renal perfusion is
now possible in the majority of patients with acceptable surgical risk.
Keywords
Aneurysm , Aorta , Horseshoe kidney , Renal ectopia , Renal fusion
Background and Prevalence
Renal artery abnormalities, which can potentially complicate the repair of
abdominal aortic aneurysms, are the most common congenital renal anomaly
occurring in 25–40% of kidneys.
1
These are usually easily handled by the expe-
rienced vascular surgeon when encountered during abdominal aortic aneurysm
repair. However, congenital anomalies of the upper urinary tract are much less
common and can pose substantial technical challenges at the time of aneurysm
repair, especially if their presence is not anticipated. Although upper urinary
tract anomalies influencing abdominal aortic aneurysm repair have been gener-
ally categorized as those involving renal ascent, fusion, and rotation, they may
also commonly be associated with coexisting anomalies of renal vasculature and
Chapter 18
Management of Abdominal Aortic
Aneurysms in Patients with Renal
Ectopia and Renal Fusion
Patrick J. O’Hara
G. Upchurch and E. Criado (eds.) Aortic Aneurysms, Contemporary Cardiology
DOI: 10.1007/978-1-60327-204-9_18, © Humana Press, a part of
Springer Science + Business Media, LLC 2009
263
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264 P.J. O
,
Hara
the collecting system (Table 1 ).
2
The reported prevalence of renal ectopia ranges
from 1 in 500 to 1 in 1200 in autopsy series, while horseshoe kidney is the most
common renal fusion anomaly occurring in 0.25% of the population.
2
Embryology
A review of the normal embryological development of the upper urinary tract
is useful to allow visualization of the anatomic changes that may occur during
abnormal development and provide perspective as to how they influence the
approach to aortic reconstruction.
Three early kidneys, called the pronephros, the mesonephros, and the
metanephros, develop from the mesoderm during the initial life of the embryo.
The first two of these early structures regress, but by approximately the fourth
week of gestation, the metanephros differentiates into the definitive fetal kid-
ney, which forms in the sacral region. In this primitive single structure, a pair
of uerteric buds develops and interacts with the metanephric mesenchyme to
form a pair of fetal kidneys. It is thought that, during this process, the collect-
ing system develops from each ureteric bud and the nephrons develop from
the metanephric mesenchyme through reciprocal interaction. Between the
sixth and ninth weeks of gestation, the two kidneys rotate and ascend from the
pelvis to their usual anatomic position in the right and left side of the lumbar
region, just below the adrenal glands. As the kidneys ascend, they receive their
blood supply through a series of paired arteries arising in sequence from the
primitive aorta and which degenerate as the kidneys migrate. The final result
is usually a single pair of renal arteries, one for each kidney.
3
Classification
Congenital anomalies of the kidneys and upper urinary tracts are categorized accord-
ing to those resulting from problems with number, ascent, and rotation (Table 1 ),
2
as
well as those resulting from problems with renal form and ascent (Table 2 ).
2
All can
be associated with abnormalities in the renal vasculature as well as abnormalities
Table 1 Renal anomalies infrequently
complicating aortic aneurysm repair.
2
Agenesis
Unilateral
Bilateral
Ascent
Simple ectopia
Cephalad renal ectopia
Thoracic kidney
Rotation
Ventral
Dorsal
Lateral
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Chapter 18 Management of Abdominal Aortic Aneurysms in Patients with Renal Ectopia 265
in the collecting system but the problems with renal form and ascent are the most
troublesome for the vascular surgeon during aortic aneurysm repair.
If the kidney completely fails to ascend and remains in the pelvis, it is
known as a pelvic kidney. However, if the renal ascent is only partially com-
plete, the resulting kidney is known as an ectopic kidney. Because rotation
is linked to ascent, pelvic and ectopic kidneys are usually also associated
with some degree of malrotation. If the metanephric mass fails to separate
in response to the development of two ureteric buds, a variety of fusion
abnormalities may result, such as the development of a discoid or lump kid-
ney (Table 2 ).
3
If one kidney fuses to the contralateral kidney and the fused
kidneys ascend to the opposite side, crossed fused renal ectopia results. If the
aorta, the normal ascent of the fused renal mass may be blocked by the inferior
mesenteric artery, resulting in the formation of a horseshoe kidney (Fig. 1 ).
3
Because the primitive renal unit fails to rotate medially, horseshoe kidneys and
other forms of renal ectopia are often associated with abnormalities of the col-
lecting system, such as the presence of multiple ureters, lying anterior to the
renal isthmus in the case of horseshoe kidney, or a common renal pelvis, which
can lie anterior to the abdominal aorta and, consequently, can complicate the
exposure of an associated abdominal aortic aneurysm from the midline or
transverse, transperitoneal approach.
4,
5
Horseshoe kidneys are also often asso-
ciated with multiple, abnormally located renal arteries (Fig. 2 ).
4,
6
This feature
probably arises because of disturbances in the appearance and regression of
the sequential pairs of renal arteries that form during the normal ascent and
rotation of the developing horseshoe kidney in the embryo. Only about one
Table 2 Renal anomalies frequently complicating aortic
aneurysm repair.
2
Crossed renal ectopia without fusion
Solitary
Bilateral
Crossed renal ectopia with fusion
Inferior ectopic kidney
S-shaped (sigmoid) kidney
Lump kidney
L-shaped kidney
Disc kidney
Superior ectopic kidney
Horseshoe kidney
Table 3 Cold renal perfusate composition used by author.
1000 cc Ringer’s lactate
1 ampoule (18 g) mannitol
500 mg methylprednisolone
2000 units heparin
Chill to 3°C
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266 P.J. O
,
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third of horseshoe kidneys have renal arteries in the usual anatomic position
but the remaining two thirds have either single or multiple arteries (Fig. 3 ).
While the isthmus of a horseshoe kidney may occasionally be a fibrous band
that might be amenable to division, more commonly it is composed of a thick
ribbon of renal parenchyma (Fig. 4 ). Division of this thick parenchyma may be
hazardous since the arterial distribution of the kidney is segmental with poor
collateralization between the segments and the blood supply to the isthmus
may be asymmetric and unpredictable arising from one side or the other.
4,
5
As
a result, exposure and division of the isthmus in this setting carries a risk of
Fig. 1 Diagrammatic representation of horseshoe kidney anomaly and its relationship
to the abdominal aorta. (Reprinted with permission from O’Hara et al.
4
)
Fig. 2 3-Dimensional reconstruction of a CT image of an abdominal aortic aneurysm
and coexistent horseshoe kidney. Note the multiple aberrant renal arteries (arrows)
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Chapter 18 Management of Abdominal Aortic Aneurysms in Patients with Renal Ectopia 267
Fig. 3 Diagram of renal arterial patterns found in 19 patients with aortic aneurysms
and coexistent horseshoe kidneys. (a) Four common patterns each found in more
than one patient. (b and c) Seven uncommon patterns each found in a single patient.
(Reprinted with permission from O’Hara et al.
4
)
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268 P.J. O
,
Hara
Fig. 3 (continued)
Fig. 4 CT scan demonstrating horseshoe kidney overlying a small abdominal aortic
aneurysm. Note the isthmus ( arrow ) containing renal parenchyma and collecting
system overlying the aorta. Division at this point would be hazardous
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Chapter 18 Management of Abdominal Aortic Aneurysms in Patients with Renal Ectopia 269
renal infarction, hydronephrosis, or possible urine leak or from an injury to the
collecting system, a complication that may lead to subsequent graft infection,
since approximately 13% of patients with horseshoe kidney are reported to
have chronic urinary infection.
6
Diagnosis and Imaging
Most would agree that it is best for the surgeon to be aware of the presence
of coexistent horseshoe kidney or renal ectopia prior to the time of abdominal
aortic aneurysm repair because its presence has the potential to substantially
complicate the procedure whether either an open or an endovascular approach is
utilized to repair the aneurysm. During an open aneurysm repair, an experienced
surgeon could probably define most of the anomalous anatomy, but clearly more
operative time would be required and the procedure would likely entail more
potential for injury. Furthermore, it might not be possible to completely deter-
mine the arterial and collecting system anatomy with certainty or gain adequate
exposure for safe aneurysm repair from the anterior, transperitoneal approach.
Depending on the arterial distribution (Fig. 3 ) encountered, endovascular aneu-
rysm exclusion with the current commercially available endografts may not be
feasible without sacrifice of substantial renal parenchyma.
On physical examination of the abdomen, the size of an abdominal aortic
aneurysm may be overestimated in the presence of a coexistent horseshoe
kidney because of the presence of the renal mass overlying the aneurysm.
Interestingly, ultrasonography is usually able to correctly estimate the size
of the associated aneurysm but was only able to demonstrate the associated
horseshoe kidney in a minority of patients. In our own series, preoperative
ultrasonography was interpreted to demonstrate the horseshoe kidney in only
38% (5/13) of the patients in whom it was obtained (Fig. 5 ),
4
a finding also
reported by others.
7
Angiography was only able to demonstrate the presence
Fig. 5 Ultrasound examination of the abdominal aorta with horseshoe kidney (arrow)
anterior to the aortic aneurysm. (Reprinted with permission from O’Hara et al.
4
)
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270 P.J. O
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of the horseshoe kidney in about two thirds of the patients in our own series,
but it has been a useful tool to delineate the aberrant arterial anatomy when
the presence of the renal anomaly is known (Fig. 6 ).
4
Currently, MRI scanning
or, preferentially, CT scanning with three-dimensional image reconstruction
is the most useful diagnostic imaging method for the detection of horseshoe
kidney or renal ectopia and for planning an optimal treatment strategy for
coexistent abdominal aortic aneurysm repair (Fig. 7 ). In our own experi-
ence, which was collected over a span of 31 years, horseshoe kidney was
recognized preoperatively in 84% (16/19) of patients and discovered intra-
operatively in the remaining 3 (16%).
4
However, in the current era, because
of the liberal use of CT or MRI scanning, it would be unusual not to have
the diagnosis of coexistent horseshoe kidney available preoperatively, even
for urgent procedures, provided that the patient is stable enough to undergo
preoperative scanning.
Therapy
Open Repair
The technical aspects of the management of anomalous renal arteries have
evolved to the point that open abdominal aortic aneurysm repair in the presence
of coexistent horseshoe kidney, with preservation of the renal blood supply,
collecting system and renal mass, is virtually always feasible, provided that the
patient is an acceptable surgical risk. Two approaches transperitoneal and left
retroperitoneal are used, and each has inherent advantages. The first abdominal
aortic aneurysm repair in the presence of horseshoe kidney was performed at
the Mayo Clinic in 1956.
8
For this procedure, a transperitoneal approach was
utilized and no arterial or venous anomalies were encountered. The aneurysm
Fig. 6 Transfemoral aortogram of a patient with an abdominal aortic aneurysm and
coexistent horseshoe kidney. (Reprinted with permission from O’Hara et al.
4
)
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Chapter 18 Management of Abdominal Aortic Aneurysms in Patients with Renal Ectopia 271
was replaced with an aortic homograft that was tunneled posterior to the isth-
mus of the horseshoe kidney. In our own experience, however, this normal
pattern of renal arteries was encountered in only 26% of patients with coex-
istent abdominal aortic aneurysm and horseshoe kidney whereas anomalous
renal arteries were encountered in the remaining 74%
4
(Fig. 3 ), findings also
reported by other investigators.
2,
6
Early in our experience, transperitoneal
exposure through a midline incision was used and the aortic graft was tunneled
through the aneurysm sac behind the isthmus. Often in the past, this exposure
was chosen because the presence of a horseshoe kidney was not appreciated
prior to abdominal aortic aneurysm repair. Perhaps the single advantage of
this approach is that it offers better exposure of the distal right common iliac
artery than does the left retroperitoneal approach, especially in an obese patient.
Anomalous renal arteries must be reconstructed with either reimplantation or
bypass but the exposure through the transperitoneal approach is sometimes less
than ideal, especially if the aberrant renal arteries arise from the aorta or iliac
arteries directly posterior to the horseshoe kidney (Fig. 8 ). Furthermore, if the
length of the renal artery is inadequate to reach the graft after the aneurysm
is decompressed, the renal bypass grafts required for reconstruction are often
difficult to construct and to position in order to minimize the risk of kinking
when performed from the transperitoneal approach.
4,
5
Division of the isthmus
to facilitate access to the underlying aortic aneurysm has been reported but is
probably hazardous because of the risk of ischemia or injury to the anomalous
collecting system.
4,
5
Fig. 7 ( a ) 3-Dimensional reconstruction of a CT image of an abdominal aortic aneurysm and coexistent horseshoe
kidney. Note the multiple aberrant renal arteries ( arrows ). ( b ) CT scan demonstrating horseshoe kidney overlying
an abdominal aortic aneurysm. Note the isthmus ( arrow ) containing renal parenchyma overlying the aorta
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272 P.J. O
,
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From a practical perspective, given the advances in preoperative imaging
techniques using CT or MR scanning, the diagnosis of coexistent horseshoe
kidney is rarely unsuspected prior to elective, or even emergency, abdominal
aortic aneurysm repair. For these reasons we, and others, have advocated a
Fig. 8 Diagram of surgical exposure and reconstruction options. ( a ) Transperitoneal exposure through a midline
abdominal incision with Dacron graft placed beneath renal isthmus and renal branches reconstructed by implan-
tation or bypass grafting. ( b ) Retroperitoneal exposure through a low left thoracoabdominal incision. Dacron
graft placed within the aneurysm sac and renal arterial branches reconstructed by implantation. (Reprinted with
permission from O’Hara et al
4)
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