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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3733_Библиотеки_им_академика_М_И_Перельмана.pdf
any embolization procedure. Nontarget embolization is often an entirely
preventable complication of embolotherapy, but this requires both
recognition of this possibility and steps taken toward prevention.
During the course of many embolization procedures, the identification
of reflux during embolic agent administration is one sign used to determine if
the end of the procedure is near. For example, during uterine artery
embolization procedures to treat symptomatic fibroids, we allow for some
controlled reflux to determine the residual rate of flow in the uterine artery as
embolization progresses. For applications in which purposeful or
nonpurposeful reflux is going to occur, it is important for the position of the
delivery catheter to be well distal to any side branches that require protection
from reflux and nontarget embolization. This of course also requires close
and careful fluoroscopic monitoring during embolic agent delivery.
There are specific catheters that can be used as well when either the
embolic agent being used or the catheter position required for embolic agent
delivery is associated with significant risk for reflux and nontarget
embolization. For example, when ethanol is used for embolization, many
interventionalists will use a balloon catheter to prevent reflux. In this setting,
inflating the balloon during embolization slows the balloon to protect against
reflux and nontarget embolization by manually preventing backflow past the
inflated balloon. The Surefire Infusion System (Surefire Medical, Inc.,
Westminster, Colorado) can also be helpful in many situations to reduce this
risk. This catheter has an expandable cone-style tip that prevents reflux
around the expanded tip during embolic agent delivery (Fig. 12.2). This
expandable tip does collapse in the setting of forward flow, allowing for
native flow to help deliver a particulate or liquid embolic agent distally into a
target vascular bed. However, should reflux occur, the tip fully expands,
allowing for apposition against the vessel wall and prevention of retrograde
flow past the expandable tip. This particular catheter has been used more
frequently in the setting of radioembolization to optimize the delivery of
yttrium 90 microspheres and to prevent reflux into gastric and duodenal
vessels and subsequent ulcer formation as a result of this procedure.
12
TIPS AND TRICKS
• A thorough knowledge of vascular anatomy is critical before the
performance of any embolization procedure.
• For any embolization procedure, know what embolic agent is going to
be used so that an appropriate catheter can be selected for delivery of
that agent.
• Particulate embolic agents are best delivered through a microcatheter
with an inner lumen of 0.027 in. Use of a catheter with a smaller inner
diameter increases the risk for catheter occlusion.
• Nonselective angiography is recommended before selective
catheterization to optimize the catheterization technique and to ensure
that all involved vessels are embolized.
• When using a particulate embolic agent to embolize an abnormal
vascular bed, controlled reflux may help identify the angiographic end
point. Placing the catheter into a secondary branch within the target
vascular bed allows for reflux to occur into a more proximal but still
abnormal branch before the risk of nontarget embolization becomes
significant.
CONCLUSION
The successful performance of embolization procedures requires a welldeveloped knowledge base regarding normal vascular anatomy, the
indications for embolization, and the embolic agents used during these
procedures. It is important to remember, though, that experience with various
delivery catheters and catheterization techniques is just as important for
ensuring success in this area of interventional radiology.
REFERENCES
1. Van Ha TG. Use of the Interlock Fibered IDC Occlusion System in
clinical practice. Semin Intervent Radiol. 2008;25:3–10.
2. Arepally A, Osterman FA, Wakeman L. Pulmonary arteriovenous
malformations. In: Savader SJ, Trerotola SO, eds. Venous Interventional
Radiology with Clinical Perspectives. 2nd ed. New York, NY: Thieme
Medical Publishers; 2000:163–176.
3. Coldwell DM, Stokes KR, Yakes WF. Embolotherapy: agents, clinical
applications, and techniques. Radiographics. 1994;14:623–643.
4. Wang W, Li H, Tam MD. The Amplatzer Vascular Plug: a review of the
device and its clinical applications. Cardiovasc Intervent Radiol.
2012;35:725–740.
5. Pollak JS, White RI. The use of cyanoacrylate adhesives in peripheral
embolization. J Vasc Interv Radiol. 2001;12:907–913.
6. Kerber CW, Wong W. Liquid acrylic adhesive agents in interventional
neuroradiology. Neurosurg Clin N Am. 2000;11:85–99.
7. Guimaraes M, Wooster M. Onyx (ethylene-vinyl alcohol copolymer) in
peripheral applications. Semin Intervent Radiol. 2011;28:350–356.
8. Choe DH, Moon HH, Gyeong HK, et al. An experimental study of
embolic effect according to infusion rate and concentration of
suspension in transarterial particulate embolization. Invest Radiol.
1997;32:260–267.
9. Abada HT, Golzarian J. Gelatin sponge particles: handling
characteristics for endovascular use. Tech Vasc Interv Radiol.
2007;10:257–260.
10. Katsumori T, Kashara T. The size of gelatin sponge particles:
differences with preparation method. Cardiovasc Intervent Radiol.
2006;29:1077–1083.
11. Osuga K, Miyayama S, Yamagami T, et al. Porous gelatin particles for
hepatic arterial embolization—investigation of passage through current
microcatheters [in Japanese]. Gan To Kagaku Ryoho. 2007;34:59–64.
12. Rose SC, Kikolski SG, Chomas JE. Downstream hepatic arterial blood
pressure changes caused by deployment of the surefire antireflux
expandable tip. Cardiovasc Intervent Radiol. 2013;36:1262–1269.
II
Clinical Applications
C
Section A Intracranial and Spine
Embolization
13
Vascular Malformations
Moneeb Ehtesham • Imad S. Khan • J Mocco
entral nervous system arteriovenous malformations (AVMs) are
congenital anomalies generally consisting of an abnormal tangle of
thin-walled vessels (usually referred to as a nidus) located within the
brain or spinal cord receiving inflow from one or more large- to mediumsized arterial pedicles with subsequent direct outflow to one or more large
draining veins. Blood flowing through the nidus bypasses any normal
intervening capillary bed, thereby creating a high-flow arteriovenous shunt
which results in the presence of high-pressure arterialized blood in the
draining veins.1 When located intracranially, this pathologic state presents a
significant risk for devastating intracranial hemorrhage.
2,3
Additional
symptomatology can include seizures as well as cognitive or objective
neurologic deficits related to either ischemia or venous hypertension and
resultant cerebral or spinal cord edema.4 The primary goal of treating these
lesions is to eliminate the risk of hemorrhage. Furthermore, treatment can
successfully address the localized dysfunction created by presence of the
nidus by means of decreasing seizure frequency and/or preserving or
improving current neurologic function.
5,6
There are four main treatment approaches toward managing a patient
with an intracranial AVM: expectant observation, microsurgical resection,
endovascular embolization, and radiotherapy.7 In reality, when pursuing
treatment, many centers will use a combination of either embolization
followed by surgery or embolization with subsequent radiotherapy. The
evidence to support the efficacy of any specific combination of treatment
modalities is currently limited to small retrospective series and remains a
topic of controversy.
8–10
Regardless, the fundamental approach to any
treatment plan centers on appropriate patient selection followed by defining
an optimal plan for treatment for each specific patient.
PATIENT SELECTION
There is tremendous controversy regarding specific patient populations in
whom treatment of intracranial AVMs should be undertaken. This is
Unruptured Brain AVMs) trial, which was a prospective randomized
multicenter trial designed to compare outcomes in patients with unruptured
intracranial AVMs treated expectantly with medical management versus
surgical and/or endovascular intervention.
11–13
Early data reporting seems to
indicate a significantly higher adverse event rate in the surgical/endovascular
treatment group that led to early suspension of the study by the data safety
monitoring board.14 The full results of this study are still pending and will
provide important insight into appropriate patient selection in patients who
have not had a prior hemorrhage. In contrast, there is considerable (although
not universal) agreement that patients who present with an AVM-related
hemorrhage are generally candidates in whom therapy should be considered.
Data suggest that the rebleeding rate after AVM rupture is approximately 2%
to 4% per year and that each hemorrhage episode carries with it a 30% to
50% morbidity rate as well as a 10% risk for mortality.15 Seizure control in
patients with AVMs that have remained refractory to medical management
can also be improved with treatment of AVMs.
16
Assessment of the lesion’s angioarchitecture forms a second critical arm
when assessing a patient as part of the treatment planning process. To this
end, it is highly recommended that all patients with newly diagnosed
intracranial AVMs undergo a comprehensive cervicocerebral digital
subtraction angiogram as this allows for clear delineation of the vascular
anatomy of the AVM as well as its flow dynamics. The key aspects of an
AVM’s vascular anatomy include identifying all contributing arterial
pedicles, draining veins, any associated aneurysms, as well as collateral
circulation and any compensatory flow dynamics that are responsible for
perfusing normal neural tissue1 (Fig. 13.1). Furthermore, from the specific
regard of suitability for endovascular treatment, it is also important to
delineate potential impediments to accessing the nidus starting from aortic
arch disease, carotid bifurcation disease, tortuous extracranial or intracranial
carotid anatomy, as well as tortuous feeding pedicles. It is also critical to
determine whether arterial feeders to the nidus are either “end pedicles”
exclusively perfusing the lesion or, instead, are “en passage” with a
component of supply to normal neural tissue. In the latter situation,
endovascular embolization without sufficient superselective catheterization
can significantly jeopardize unaffected tissue and present a prohibitive risk
for treatment. Up to 50% of AVMs are associated with aneurysms.17 These
may either be intranidal or present on feeding arterial pedicles (flow-related).
It is generally recognized that the presence of such aneurysms presents a
higher risk of hemorrhage. More specifically, in patients presenting with
hemorrhage, these aneurysmal lesions require urgent treatment if there is any
suspicion based on anatomical distribution of the hemorrhage that they may
be the contributory lesion.
18,19
Finally, the flow dynamics through the lesion
also presents important considerations for treatment planning especially with
regard to endovascular therapy. Specifically, high-flow AVMs may harbor
fistulous connections between feeding arteries and draining veins, and it is
important to recognize these as their extent will affect the choice of embolic
material used and whether specific pedicles can be safely targeted for
embolization or not.
GOALS OF ENDOVASCULAR EMBOLIZATION
As detailed earlier, endovascular therapy represents only one of several
therapeutic modalities available for treating intracranial AVMs.20 It is
therefore critical that before deciding on a final treatment plan, a patient’s
history and angiographic anatomy (as delineated by a digital subtraction
angiogram) should be reviewed by a multidisciplinary team consisting of
neurointerventionalists, neurosurgeons, and radiation oncologists to allow for
formulation of an optimal course of therapy best suited to that particular
patient. In this regard, endovascular embolization can be incorporated as a
potent tool to either decrease flow to an AVM as a precursor to planned
surgical resection or as a means of decreasing nidus size to allow for more
focused stereotactic radiation. Rarely, and usually only in cases of small nidal
size, can embolization be used as a solitary curative modality. Therefore, the
goals of embolization will be determined by which additional treatment
methodologies are to be employed for that particular lesion. In the setting of
preoperative embolization, the ideal embolization strategy centers on
decreasing inflow into the nidus from the aspect of the lesion that will be
most difficult to access from the planned surgical corridor. In this setting, a
focused approach targeting catheterization via deep arterial pedicles that will
not be directly visible to the surgeon can result in improved intraoperative
visibility during microsurgical dissection and decreased blood loss. Similarly,
nidal penetration of embolic material helps to better delineate the nidus
during microsurgical dissection, and knowledge of the angiographic pattern
of embolization helps orient the surgeon particularly in the setting of large,
complex nidal resections.21 In certain situations, surgical resection may not
be feasible given the presence of eloquent neural tissue in close proximity to
the nidus. In these scenarios, targeted embolization of nidal segments
adjacent to eloquent regions can help decrease radiation exposure to
important functional neural tissue as stereotactic radiotherapy can be targeted
to the residual lesion with increased dose step-off between the radiation field
and adjacent eloquent tissue. If pursued, endovascular embolization can be
performed in a “staged” technique wherein specific portions of the nidus are
targeted (frequently via a distinct single feeding pedicle at each sitting).
When used, staged embolizations are felt to be safer as they decrease the total
radiation exposure in a single sitting and also minimize the likelihood of
overaggressive nidal embolization.
22
TECHNIQUES
Materials
Various materials have been used for embolotherapy in the setting of
endovascular AVM treatment. Of historical interest is the previous use of
liquid coils (essentially deliverable soft/coiled wires), detachable balloons for
proximal arterial pedicle occlusion, silastic pellets, silk sutures, and absolute
alcohol. The use of these diverse agents has now largely been supplanted by
the development of new liquid embolic agents. Key among these is the
cyanoacrylate polymer, Histoacryl Blue (N-butyl cyanoacrylate [NBCA];
Aesculap, Center Valley, Pennsylvania), and the DMSO-based liquid
precipitate, Onyx (Covidien, Irvine, California).20 NBCA is mixed with lowviscosity oil-based contrast medium (typically Ethiodol), and this mixture can