Background
Renal artery pseudoaneurysm (RAP) is an uncommon but potentially life-threatening
condition that is often difficult to diagnose. Typically, RAPs are seen in patients
after renal biopsy, percutaneous nephrolithotomy, partial nephrectomy, or trauma.
Most of the time, small pseudoaneurysms are asymptomatic and thrombose spontaneously.[1] However, when they are symptomatic, patient can present with a pulsatile mass in
the pelvis, flank pain, renal dysfunction secondary to compression of artery branches
or shunting of blood, or hemorrhage from rupture. Although these lesions can be managed
surgically, renal artery embolization is preferred if they are amenable to embolization
to minimize the loss of normal renal parenchyma.[2]
[3] Spontaneous pseudoaneurysm of segmental renal artery is also a rare entity. Here
we present a case of asymptomatic spontaneous segmental RAP, which was diagnosed incidentally
and subsequently coil embolization was performed.
Case Presentation
A 28-year-old female was referred to the Department of Radiology for ultrasonography
(USG) of breast for mastalgia and routine USG of abdomen/pelvis. Her breast USG was
normal. In USG of the abdomen, there was a well-defined thin-walled cystic lesion
approximately 4.8 × 3 cm in size in the lower pole of the left kidney. On color Doppler
study, the lesion showed “to-and-fro” pattern of color flow within, giving rise to
the characteristic “yin–yang pattern,” highly suggestive of pseudoaneurysm. Computed
tomography (CT) renal angiography was performed, which showed a pseudoaneurysm with
a size of approximately 4.8 × 3.5 × 3.3 cm in the lower pole of the left kidney, arising
from the posterior segmental branch of the left renal artery ([Fig. 1]). There was no evidence of arteriovenous fistula. All other abdominopelvic organs,
as well as the aorta and rest of the arteries were normal.
Fig. 1 (a) Axial contrast computed tomography of abdomen and three-dimensional volume rendering
images. (b) A pseudoaneurysm in the lower pole of the left kidney arising from the posterior
segmental renal artery (arrows).
Clinical examination revealed no abnormality. Her blood pressure was 110/80 mm Hg
and her pulse was 62 beats per minute. Blood urea nitrogen was 14.1 mg/dL and serum
creatinine was 0.79 mg/dL. Hemoglobin was 14.3 g/dL, hematocrit was 46.1%, and platelets
were 2,22,000/μL. Prothrombin time was 11.0 seconds and activated partial thromboplastin
time was 34.2 seconds. On urine analysis, proteinuria and hematuria were not present
(0–2 red blood cells per high power field). She had caesarian section 3 years ago
for fetal distress, which was uneventful. There was no history of systemic illness,
hematuria, joint pain, skin rashes, recent fever, renal surgery, renal biopsy, or
abdominal trauma.
She was then planned for digital subtraction angiography (DSA) and coil embolization.
Selective renal angiogram revealed a large pseudoaneurysm in the lower pole of the
left kidney, arising from the posterior segmental branch of the left renal artery
([Fig. 2a]). The posterior segmental artery was selectively catheterized and 3 × 3 mm coil
was deployed at the distal part of the artery. Repeat renal angiogram after 1 minute
was performed, which revealed complete thrombosis of the distal part of the posterior
segmental artery with the absence of contrast opacification of the pseudoaneurysm
([Fig. 2b]). There were no intraoperative and postoperative complications. Repeat renal Doppler
USG was performed the next day, which showed complete absence of flow in the pseudoaneurysm,
with increased internal echogenicity suggesting thrombosis ([Fig. 3]). Her hospital stay was uneventful and she was discharged after 24 hours of hospital
stay.
Fig. 2 (a) Selective posterior segmental angiogram showing a large pseudoaneurysm arising from
posterior segmental artery in lower pole of left kidney. (b) Angiography after embolization using a coil shows a well-occluded feeding artery.
The absence of filling of the pseudoaneurysm with contrast material indicates successful
embolization.
Fig. 3 Follow-up color Doppler ultrasonography showing complete absence of flow in the pseudoaneurysm
along with increased echogenicity within indicating successful embolization and complete
thrombosis.
Discussion
RAP is a rare clinical entity that may occur after renal biopsy, renal surgery, renal
transplantation, penetrating trauma, or blunt renal trauma. Passage of blood from
a lacerated renal artery to the renal parenchyma leads to the formation of RAP.[1]
[2] After renal injury, combination of hypotension, coagulation, and pressure from the
surrounding tissues, such as the vascular adventitia, renal parenchyma, and Gerota's
fascia, result in temporary cessation of the bleeding. Later dissolution of the clot
and surrounding necrotic tissue results in recanalization between the intravascular
and extravascular space, which ultimately leads to formation of a pseudoaneurysm.
With restoration of normal blood flow in the artery, the pseudoaneurysm can grow in
size and eventually become unstable, with erosion into the surrounding perinephric
tissue.[3]
[4]
However, asymptomatic spontaneous RAP as in our case, without history of surgery,
renal biopsy, significant abdominal trauma, and systemic disease, is a very rare entity.
Previous trivial abdominal trauma may also be a predisposing factor for the development
of renal RAP and the patient may not elicit history of such minor event. Another cause
of spontaneous RAP can be vasculitides such as polyarteritis nodosa. Renal involvement
in polyarteritis nodosa often leads to arterial hypertension and ischemic nephropathy
with renal insufficiency. Imaging studies may show renal parenchymal infarcts with
stenoses and microaneurysms, which can rupture and cause hematomas. With subsequent
resolution of intrarenal hematoma, as in case of renal trauma, there is high chance
of developing pseudoaneurysms.[5]
Symptoms of RAP may include abdominal tenderness, abdominal mass, hematuria, hypertension,
and shock. Signs and symptoms of RAP may develop immediately after the insult or they
may be delayed.[6] Hematuria is the most common symptom associated with RAP and results from the erosion
of RAP into the adjacent renal collecting system; this may occur within 2 to 4 weeks
after the injury.[7] A meta-analysis including 13 studies of partial nephrectomy, which included a total
of 105 patients with RAP, showed that 102 (97%) patients were symptomatic at presentation.
The most common symptoms at presentation were gross hematuria, flank pain, and anemia,
with gross hematuria in 87.3% of patients. Along with hematuria, flank pain and anemia
were commonly reported, but only 5% of patients presented with all three symptoms.
RAP symptoms presented at a mean of postoperative day 14.9 (range: 1–90).[8]
However, patients can present with nonspecific symptoms and therefore RAP is incidentally
found. In one case, the patient presented with hematuria only, and arteriovenous fistula
and pseudoaneurysm were diagnosed 10 years after kidney allograft biopsy.[9] Asymptomatic RAP has also been detected 4 years after renal biopsy.[10]
Completely asymptomatic RAP without history of renal surgery or trauma is very rare
and even more difficult to diagnose. As in our case, the diagnosis was made incidentally
during routine USG of the abdomen and pelvis. Therefore, it is difficult to diagnose
an RAP without a high index of suspicion. These findings suggest that after renal
biopsy, renal surgery, or abdominal trauma, it is necessary to periodically evaluate
the kidney using imaging studies.
In fact, the diagnosis of RAP is challenging. Angiography has been the standard tool
for diagnosis. However, if the patient is stable, noninvasive tests such as contrast
medium-enhanced CT, color Doppler sonography, or magnetic resonance angiography should
be performed.[11] CT angiography has advantage of imaging of the entire urinary tract and is the technique
of choice for follow-up.[12] RAP is best seen on the arterial phase, which appears as a focal high attenuation
lesion with a density similar to that of the adjacent arterial vessels. RAP may also
be visible in the nephrographic phase, but may be missed when the adjacent renal parenchyma
is densely enhanced, masking the high density of the pseudoaneurysm. Due to washout
of contrast material from the pseudoaneurysm in pyelographic phase, RAP will not be
seen.[13]
Pseudoaneurysm resembles a cystic mass on sonography. The ultrasound findings may
not be sufficient to distinguish a hematoma from a pseudoaneurysm. Color Doppler sonography
is very useful and shows characteristic to-and-fro flow within the lesion. If imaging
findings are not conclusive and there is clinical suspicion of RAP, or the patient
is hemodynamically unstable, angiography should be undertaken. In addition to high
sensitivity in identifying RAP, the advantages of angiography include the potential
to achieve simultaneous endovascular management of RAP.[14] Embolization of RAP has been reported to have high success rates exceeding 90%.[4]
[14]
[15]
[16]
[17] The risk of rupture is estimated to be low, but is associated with a death rate
as high as 80%.[18]
Currently, no definite guidelines exist for the size at which an RAP should be repaired
in an asymptomatic patient. In general, aneurysms greater than 2 cm in diameter are
considered to have a high risk of rupture.[19] In fact, it has been reported that most pseudoaneurysms are small and asymptomatic
and sometimes resolve spontaneously.[20] However, growth of the pseudoaneurysm may occur rapidly. A previous report showed
diameter evolving from 17 to 30 mm within 2 months.[21] Another report demonstrated that a pseudoaneurysm was diagnosed at 30 mm, whereas
a CT scan performed 2 months before was normal.[22] Given that ruptures have also been reported in smaller aneurysms if left untreated,
it was decided that an intervention on the RAP would decrease the risk of ultimate
rupture.[23]
In our case, the size of the pseudoaneurysm was larger and was arising from a large
posterior segmental renal artery. Though asymptomatic, owing to its large size and
high risk of rupture, team of intervention radiologist and urosurgeons decided to
intervene in the pseudoaneurysm by percutaneous coil embolization.
Management methods of RAP are also a challenging issue, and a variety of treatment
modalities have been exploited so far.[7] Treatment of RAP can be by nephrectomy, open vascular surgery, or angiographic embolization,
depending on the patient's clinical condition. Surgical indications for repair include
overt ruptures, an aneurysm greater than 2 cm, renovascular hypertension, expansion
of the aneurysm, and evidence of renal damage.[7]
In general, angiographic embolization is the procedure of choice for management of
RAP due to its minimally invasive and selective nature and the maximal preservation
of renal parenchyma.[6] Renal artery embolization begins with a renal angiogram through a transfemoral approach.
Selective embolization of renal artery branches can be achieved by using microcatheters
inserted coaxially over a guidewire.[16] The embolization material should be chosen based on the patient's vascular anatomy
and the specific clinical indication or pathologic process necessitating the procedure.
Resorbable materials, coils, inert particles, and sclerosants (liquids) can be used,
depending on the clinical indication and vascular structure to be occluded.[16]
[17] Many case series and reports have shown that coil embolization is an effective method
for treating renal pseudoaneurysms following different cause with high success rates.[7]
[10]
[19]
[24]
[25]
[26]
[27] The general goal is to occlude the branch with hemorrhagic extravasation while sparing
surrounding branches to limit parenchymal damage.
However, embolization for the management of RAP appears to have some shortcomings
such as possible reflux of embolic material into the normal proximal vessel if the
distal branch has not been selectively cannulated and the risk of more generalized
ischemia resulting from thrombosis of a main feeding branch.[7]
[16]
[17] To overcome these limitations, treatment with covered stent grafts on RAP located
in branches of visceral arteries has been suggested.[14] In selected cases, the use of ultrasound-guided thrombin injection into an extracapsular
pseudoaneurysm following renal allograft biopsy can also be considered a treatment
option.[28]
Conclusion
In conclusion, we herein showed a case of a 28-year-old woman with spontaneous asymptomatic
segmental RAP diagnosed incidentally during routine USG of the abdomen, which was
later confirmed with CT renal angiography and DSA of the renal artery. RAP was treated
with percutaneous selective coil angioembolization of the posterior segmental renal
artery, and follow-up imaging showed successful resolution without evidence of complications.
Clinicians and radiologist need to bear in mind that even without history of major
renal trauma or surgery, renal pseudoaneurysm can occur in asymptomatic individuals.
Renal artery embolization is a minimally invasive technique for the diagnosis and
management of RAPs. Unlike other imaging modalities, such as CT and USG, angiography
not only demonstrates the anatomic location of pseudoaneurysms, but also allows the
interventional radiologist to quickly and effectively treat this potentially life-threatening
complication. Our cases demonstrate the efficacy of this technique.
