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January 2011
Renal Artery Aneurysm Embolization Using Microcatheters and Detachable Coils
A technical overview of one option for treating renal artery aneurysms that could also be applied to other visceral aneurysms and renal AVFs.
By Erin H. Murphy, MD; M. Zachary Arko; and Frank R. Arko, MD
Although renal artery aneurysms are the most common visceral artery aneurysm, they are relatively rare overall, accounting for < 1% of all aneurysms.1 Nonetheless, the incidence of this diagnosis is increasing as the use of cross-sectional imaging becomes more common. The current angiographic incidence ranges from 0.3% to 0.7%, with most discovered incidentally.2 These aneurysms are often complex and perihilar.
Renal arteriovenous fistulas (AVFs) are less common, with a prevalence of 0.04%. Most AVFs (70%) arise from a predisposing renal artery aneurysm that ruptures into the adjacent renal vein.3,4 Both renal aneurysms and AVFs may result in renovascular hypertension, thrombosis, flank pain, hematuria, and progressive arterial dilatation with a significant associated risk of rupture. Rupture may be associated with a mortality rate of up to 80%.5 The occurrence of any of these complications or an aneurysmal artery larger than 1.5 cm indicates the need for intervention. Surgical treatment requires resection with bypass; however, nephrectomy may be the only option in some cases.1-5
Endovascular techniques have been employed for the treatment of renal artery aneurysms and are becoming first-line therapies.6-10 Likewise, these options may be applied to AVFs.8,11 This article describes a technique for coiling of both renal artery aneurysms and AVFs with frameable detachable coils and reviews the advantages of this technique over other endovascular options.
CASE 1
A 57-year-old man presented with hypertension and
during the workup of a thoracic aneurysm was found to
have a 3-cm right renal artery aneurysm. The patient
underwent successful endovascular management of his thoracic aneurysm, and the right renal artery aneurysm
was repaired in a staged fashion. CTA showed a single left
renal artery that was widely patent without aneurysmal
dilatation or stenosis and a single right renal artery with a
widely patent origin. There was an aneurysm of the right
renal hilum that measured 22 X 21 X 20 mm, with minimal
calcification (Figure 1).
Presented with the options of coil embolization versus open repair of the aneurysm, the patient elected to undergo coil embolization. The left femoral artery was accessed under ultrasound guidance, and an aortogram was obtained (Figure 2). The right renal artery was accessed with a reversed curve catheter, and a 6-F Pinnacle Destination guiding sheath (Terumo Interventional Systems, Somerset, NJ) was advanced into the renal artery. A 2.4-F Progreat catheter (Terumo Interventional Systems) was then advanced into the aneurysm sac to allow for the placement of coils. With the aneurysm at the hilum of the renal artery, the use of detachable coils was used to allow for accurate placement and prevention of embolization. Multiple Azur coils (Terumo Interventional Systems) were placed into the aneurysm sac. A 20-mm X 50-cm framing coil was placed first followed by four 8-mm X 10-cm hydrocoils (Figure 3).
The patient was discharged home the same day without complications, and his follow-up CTA has showed that the renal artery aneurysm was completely excluded, with a well-perfused right kidney (Figure 4).
CASE 2
A 43-year-old man presented with a 3-cm right renal
artery aneurysm arising near the hilum of the kidney.
The aneurysm had been followed for 2 years, with
recent growth from 25 to 30 mm and was referred for
coil embolization of the aneurysm. The patient was otherwise asymptomatic. Aortography and selective
catheterization of the renal artery aneurysm was performed.
After this, a 7-F sheath was advanced into the
orifice of the renal artery, and a two-wire technique was
used to thrombose the wide-neck aneurysm. The first
0.014-inch wire was used to cross the aneurysm, and a
second 0.014-inch wire was placed into the aneurysm
sac itself. Then, a 4- X 2-mm balloon was passed across
the neck of the aneurysm. A Progreat catheter was
then placed into the aneurysm sac itself (Figure 5).
A 20-mm X 50-cm framing coil was placed first with
the balloon inflated. This was followed by five 8-mm
X 20-cm Azur coils, which achieved complete exclusion
of the aneurysm sac (Figure 6). Follow-up CTA at
6 months showed exclusion of the aneurysm sac with
normal kidney size and no flow into the aneurysm sac.
Noncontrast images show that the coils completely
exclude the aneurysm sac (Figure 7).
CASE 3
A 50-year-old woman was found to have a right renal
AVF via CTA. On selective renal angiogram, the flow
was so high that it was not possible to see the renal
angiogram, as all the flow was going through the AVF
(Figure 8). A 6-F Pinnacle Destination guiding sheath
was then placed within the right renal artery. A Progreat
catheter with coaxial wire was used to traverse the
lesion. A series of coils were placed into the AVF to slow
the flow. Multiple Azur coils (total of 12) (Figure 9) were
placed within the AVF with preservation of flow to the
kidney. A 6-month follow-up CTA showed normal function
of the kidney and exclusion of the flow (Figure 10).
Use of the detachable coils was beneficial in preventing
distal embolization and accurate positioning in the
high-flow AVF. The patient tolerated the procedure well
without any complications.
DISCUSSION
Indications for repair of renal artery aneurysms include
rupture, aneurysms larger than 1.5 cm, renovascular
hypertension, flank pain, hematuria, or the presence of
an AVF.1,2,5 Open repair with surgical exclusion and
bypass is considered the gold standard for treatment.
However, open repair is associated with the risks of general
anesthesia, as well as a 6% incidence of technical failure
with graft thrombosis, a 6% incidence of unplanned
nephrectomy, and a 0% to 4% procedure-related mortality
rate.1-5,9,10
Endovascular repair of renal artery aneurysms and AVFs has been associated with a decreased length of hospital stay, lower morbidity rates (including a lower incidence of nephrectomy), and lower mortality rates compared to open repair. At the same time, aneurysm-related outcomes are near equivalent to surgical interventions.9,10
Several options exist, including stenting, thrombogenic liquid injections, and coiling. Although successful results have been reported with each of these options, disadvantages exist for each approach.9,10 Covered stents may not be ideal for patients with disease near the renal hilum or major branch points. Thrombogenic liquids and coils have uncontrolled delivery, may be difficult to manipulate, and alternatively share the risks of embolization. When used in the extraparanchymal renal artery, major parenchyma may be at risk from these adverse consequences. In fact, most series reporting on these techniques describe the occurrence of major renal artery branch occlusions.9,10 Further, the use of traditional coils or thrombogenic liquids in the setting of renal AVF carries the risk of occlusive device embolization to pulmonary vasculature resulting in pulmonary embolism.8,11
The technique employed for our patients involved the use of superselective microcatheters as well as detachable peripheral hydrocoils. Because the goal for repair involves aneurysm or AVF exclusion without embolization or loss of renal parenchyma, this technique has several advantages. First, these catheter systems are both softer and more flexible than earlier versions, allowing more controlled and safer superselection of the thin-walled aneurysmal vessels. True detachable coils, such as the Azur coils, allow for controlled release, decreasing the risk of embolization, migration, and partial deployment in the main renal artery. These coils remain attached to the system until deliberately released. They can be positioned, confirmed angiographically, and then withdrawn and replaced if positioning is not ideal. The coil itself combines a platinum coil and an expandable hydrogel polymer, and these elements provide a stable and permanent platform for blood stasis, thrombus formation, and neointima formation. Full expansion of the hydrogel occurs within 20 minutes, and this results in greater filling and mechanical stability with fewer coils required.
The use of framing coils—larger coils to which the smaller coils are attached—is key to the safety and success of this technique. These larger coils stabilize the coil conglomerate within the aneurysm sac or AVF, preventing embolization and ensuring rapid coagulation and aneurysm or AVF exclusion. This advantage is of particular interest in high-flow AVFs, which may require temporary renal artery balloon occlusion to allow time for thrombosis with other techniques. Although some operators continue to use temporary balloon occlusion, even with framing detachable coils,7,8 we have not found this to be necessary, and we consider avoidance of this need a distinct advantage. The detachable Azur coils used in this series are released with an electrocurrent. The use of electrocurrent seems to advantageously prevent last-minute movement of the coils that may be associated with the mechanical release mechanisms of other similar coil designs. It has also been suggested that the electrocurrent may confer an additional thrombotic advantage.11
CONCLUSION
The techniques we have described have been successfully
reported in several case reports and small series
without loss of renal parenchyma.6,7 Our experience provides
further evidence that the use of microcoils and
detachable coils is a safe and effective means of treatment
for renal artery aneurysms and renal AVFs while
limiting the risks associated with other endovascular
techniques. The advantages demonstrated with these
techniques apply with equal ease to other types of visceral
artery aneurysms. As these techniques continue to
improve, it is likely that they will become the treatment
of choice for visceral artery aneurysm disease.
Erin H. Murphy, MD, is Chief Resident in General Surgery at the University of Texas Southwestern Medical Center in Dallas, Texas. She has disclosed that she holds no financial interest in any product or manufacturer mentioned herein.
M. Zachary Arko is a research assistant at the University of Texas Southwestern Medical Center in Dallas, Texas. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein.
Frank R. Arko, MD, is Chief of Endovascular Surgery and Associate Professor of Surgery at the University of Texas Southwestern Medical Center in Dallas, Texas. He has disclosed that he receives honoraria from Terumo Interventional Systems. Dr. Arko may be reached at (214) 645-0533; frank.arko@utsouthwestern.edu.
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