Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3733_Библиотеки_им_академика_М_И_Перельмана.pdf
Balloon Remodeling
The use of balloon remodeling, first described by Moret and colleagues10 in
1997, involves the temporary inflation of a balloon across the neck of an
aneurysm, allowing for coil deployment into aneurysms with unfavorable
neck-to-dome ratios.4 As coils are inserted, a stable 3-D coil structure forms,
thereby holding the coil mass within the aneurysm in cases in which coil
herniation into the parent vessel is a primary concern. An advantage of coil
introduction with adjunctive balloon use is that the microcatheter is
stabilized, preventing premature kickback and need to reaccess. However,
there are two drawbacks: first, as the microcatheter is firmly pinned within
the aneurysm, it prevents recoil when excessive pressure is applied on a
deployed coil, thereby directing the pressure to the aneurysm dome,
potentially contributing to perforation; and second, balloon inflation leads to
cessation of antegrade flow, potentially risking ischemia. Balloon inflation
leads to local anterograde flow arrest in the territory involved. The other
well-described risks of balloon remodeling include perforator occlusion,
parent vessel dissection or rupture, and promotion of thromboemboli.
3,11–13
The available evidence is conflicting with respect to use of balloon
remodeling in aneurysm coil embolization and rates of ischemic
complications, with some studies reporting a higher incidence
4,12,14–16
and
others reporting an equal or decreased incidence compared to unassisted
coiling.
13,17–20
Balloon inflation can be performed intermittently, allowing
reperfusion of the distal vascular territory in addition to unconstrained
manipulation of the microcatheter within the aneurysm itself, even after
coiling has been initiated. Although there are risks to the use of balloons, the
most dreaded is aneurysm perforation; the benefit of having a balloon ready
and available to achieve immediate flow arrest and to continue coiling to
aneurysm occlusion in a controlled fashion is a significant advantage.
Balloon remodeling is a very useful adjunct in the hands of an experienced
operator but should be employed cautiously in the uninitiated (Fig. 14.5).
Stent-Assisted Coiling
The technique of stent-assisted coiling in the clinical setting was first
described in 1997.21 Soon after, the availability of new flexible, selfexpanding intracranial stents allowed for increasing application of this
technique and observation of its benefits. Stents have been quickly adopted as
promising adjuncts with potential mechanical, hemodynamic, and biologic
properties, imparting an advantage over coil embolization alone.22 Stent
deployment provides mechanical support to prevent coil prolapse, and it may
serve as a conduit to divert flow and provide a scaffold for endothelial growth
and vessel healing.
22–24
In addition, an implanted stent may incur subtle
changes in the parent vessel–aneurysm geometry, imparting significant
hemodynamic alterations which change the inflow substantially.
A stent may be deployed across the aneurysm neck followed by
microcatheter selection of the aneurysm through the twines of the stent, or the
aneurysm can be selected first with the microcatheter and the stent deployed
across the neck and microcatheter (jailing technique). The jailing strategy has
the advantage of affixing or “pinning” the microcatheter between the outer
confines of the stent and the lining of the parent vessel. This achieves a more
stable, although somewhat locked-in, microcatheter position within the
aneurysm and minimizes the risk of premature kickback of the microcatheter
out of the aneurysm during coil deployment. A second strategy is the “coil
through,” in which a stent is first fully deployed across the aneurysm neck
and then the aneurysm is catheterized by navigating through the tines of the
stent. This method allows for relatively unrestricted movement of the
microcatheter, allowing it to paint back and forth with the introduction of
coils; however, at times, depending on anatomy, it may be difficult to
traverse a newly deployed stent. The microcatheter may get caught up on the
stent tines and there is risk of the stent migrating distally. Third, the “coil–
stent” technique involves an unassisted coil embolization to completion,
immediately followed by stent deployment, potentially to capitalize on the
biologic benefit of vascular remodeling or to constrain a prolapsed coil loop.
Last, the “balloon stent” method involves a stent placement after completion
of a balloon-assisted embolization.
The advantage of employing a stent to bridge the neck of an aneurysm,
as opposed to balloon remodeling, is that it does not involve flow arrest in the
parent vessel. A disadvantage is that it requires permanent placement of the
device and a minimum antiplatelet regimen of at least 3 months. Most
aneurysms treated with stent-assisted coiling are geometrically complex and
pose a technical challenge. Since the first clinical applications in the late
1990s, several studies have proven stent-assisted coiling to be a feasible, safe,
and effective method of embolization
25–34
of aneurysms previously believed
to be not amenable to coiling (Fig. 14.6).
Stent Reconstruction
Despite all these device advancements and the refinement of technical
nuances by experienced operators, broad-necked aneurysms arising at
bifurcations that incorporate the daughter vessel origins remain a formidable
challenge to endovascular treatment. This is perhaps best exemplified by the
difficulty in treating middle cerebral artery bifurcation aneurysms but also
those at the basilar apex and carotid terminus. At vascular bifurcations, a
stent can be used to stabilize a coil mass within an aneurysm while protecting
the parent vessel and the daughter vessel at greatest risk. When the aneurysm
neck incorporates the origins of both daughter vessels and there is a
significant risk of coil herniation into either vessel, a single stent, even with
balloon remodeling as an adjunct, may not be sufficient.
The “Y-stent” technique
35–40
involves the passage of a second stent
through the interstices of the first deployed stent. Y-stent reconstruction
enables the endovascular management of otherwise complex, wide-necked
cerebral aneurysms by providing two critical functions: support for the coil
mass and preservation of the daughter vessels. The open-cell design of the
Neuroform stent as the initial placed stent allows this construct to be possible
because the first stent deployed can expand at its interstices to accommodate
the second self-expanding stent. Y-stent using a closed-cell design stent at the
first stent, although technically feasible, results in undesirable synching of the
second deployed stent because of its constrained interstices. The initial shortand midterm results using the Y-configuration technique are promising.
39,40
Although many of the aneurysms displayed residual filling at initial
treatment, some were found to have spontaneous thrombosis on angiographic
follow-up. These results have been considered satisfactory because the
technique addresses aneurysms for which there are otherwise no viable
treatment options. However, there are several concerns regarding the longterm effects in patients harboring the Y-configured reconstruction. The longer
term effects of having two overlapping stents in the distal basilar as well as
the junction of the Y in which there is considerable intraluminal stent overlap
not amenable to endothelization without the scaffolding provided by adjacent
intima are unknown. In addition, this reconstruction is technically
demanding. Navigating through the first stent with either a 0.021-in (closedcell) or 0.027-in (open-cell) microcatheter to prepare to deliver the second
stent of the construct can be difficult and result in stent migration. Initial
microcatheter selection and reaccessing of the aneurysm during coiling
following Y stenting can also pose a challenge. Indeed, there are many steps
required to successfully achieve Y-stent reconstruction, each with possibility
of technical complications.
Stent Delivery through Balloon Catheter
Balloon-remodeling and stent assistance techniques may be used in
combination to capitalize on the benefits that each affords. This “balloon–
stent” method involves stent placement after completion of a balloon-assisted
embolization. The drawback to this sequential technique is that employing
currently available stent delivery systems requires either a 0.021-in or a
0.027-in microcatheter system; the coil mass achieved during balloon
remodeling must be crossed before stent deployment. This additional
maneuver introduces the potential risk of coil disruption, especially when
there is coil loop prolapse or herniation into the parent vessel, which may
lead to thromboembolic or ischemic complications. In addition, this step may
add fluoroscopy and procedure time, especially when access to the lesion is
challenging.
We described the first report of a novel technique for “balloon stenting,”
which incorporates the use of two novel devices.41 The Scepter C is a new
temporary occlusion balloon system that has a dual coaxial lumen catheter
attached to a low-inflation pressure compliant balloon. The design
accommodates a steerable 0.014-in guidewire through a 0.0165-in inner
lumen. The LVIS is a novel neurovascular self-expanding retrievable stent
system which is composed of a single nitinol round braided wire and double
helix tantalum strands in addition to radiopaque tantalum proximal and distal
markers to assist full-length visualization. It is a compliant, closed-cell
system which is retrievable up to 80% deployment and provides 15% surface
area coverage. The commercially available LVIS stent is 0.021-in
microcatheter compatible. However, the LVIS Jr. stent is 0.017-in
microcatheter compatible, allowing it to be delivered by the Scepter C
balloon catheter system. We have found this technique to be safe and
feasible, reducing both the number of steps involved in this technique and the
opportunities for mechanical coil-related complications.
Flow Diversion
Stents were recognized to impart flow diversion properties on aneurysm
inflow, spurring the introduction of flow diversion stents. Flow-diverting
stents are constructed of lower porosity with higher device surface area
coverage at the aneurysm neck. By shunting flow preferentially down the
parent vessel and away from the aneurysm, it promotes conditions leading to
progressive aneurysm thrombosis and eventual vessel remodeling (Fig. 14.7).
Theoretically, even small-caliber perforating vessels, which are covered
by the flow diverter, will remain patent due to the siphoning effect of the
distal territory they irrigate. Aneurysms have no such downstream outflow
and will thrombose. Flow diversion has been used effectively in the treatment
of fusiform and giant aneurysms. Disadvantages include the inability to cross
the stent with a microcatheter for treatment of recurrences, reports of
perforator occlusions leading to strokes, as well as reported cases of delayed
aneurysmal rupture and subacute and remote intracerebral hemorrhage.
Pushing the Envelope
Despite these technologic advances, broad-based aneurysms continue to pose
a formidable challenge for endovascular treatment, which requires creative
solutions.
41–46
As long as there are complex aneurysms that require treatment
and highly skilled neurointerventionalists who are knowledgeable about the
devices available and motivated to treat them, devices will be used in an offlabel fashion in an attempt to address the unmet needs of adjuncts.
Retrievable, closed-cell design stents can be partially deployed across an
aneurysm neck and then recaptured following stent-assisted coil
embolization, thereby incorporating the benefits of balloon remodeling
without the drawbacks of parent vessel occlusion and without permanent
stent implantation. A stent may also be deployed with its distal extent aimed
at the aperture of the aneurysm to support a coil mass rather than across the
neck along the long axis of the parent vessel, the so-called waffle cone
technique.
47,48
In the treatment of a fusiform aneurysm, stents can be
deployed in parallel in the so-called double-barrel technique.47 Aneurysms
incorporating two daughter vessels have been addressed, employing two
simultaneously inflated balloons after selecting the aneurysm with a
microcatheter (“kissing balloon” technique). Last, to promote thrombosis and
occlusion of fusiform aneurysms, some operators advocate jailing a
microcatheter with a flow-diverting stent to capture the benefits of flow
diversion and coil embolization in one strategy.
CLINICAL APPLICATIONS
At our institution, we tend to use a fair amount of primary coiling and balloon
remodeling. We prefer the use of the balloon as an adjunctive device over
stents as balloons are temporary implants, obviating the need for long-term
dual antiplatelet therapy. Also, in the setting of subarachnoid hemorrhage
where antiplatelet therapy is contraindicated, balloons allow for the treatment
of complex, wide-necked aneurysms without the use of stents. Ultimately, the
choice of how to coil, balloon remodel, or perform a stent-assisted coiling is
up to the primary operator. The risks/benefits of each technique must be
weighed against not only the anatomy and geometry of the aneurysm but also
the operator’s comfort level with each technique.
Preoperative Planning
Elective patients are pretreated with dual antiplatelet therapy regardless if
stenting is planned to mitigate the risk of thromboembolic complications.
Ideally, patients are given a 600 mg clopidogrel and 650 mg acetylsalicylic
acid (ASA) load the night before a coiling procedure. Alternatively, a 5-day
loading regiment may be used: 75 mg clopidogrel and 325 mg ASA daily
starting 5 days before the procedure. For patients where a stent or
endoluminal device is planned, clopidogrel and ASA response assays may be
performed. At this time, a decision should be made regarding how to
approach the aneurysm. Will primary coiling suffice? Will there be a need for
an adjunctive device or will newer technologies such as flow-diverting stents
or newer intrasaccular devices be used? These decisions will determine
access devices and microcatheter selection on the day of operation.
We perform all embolization procedures under general anesthesia. All
patients are systemically anticoagulated: Elective patients receive a bolus
dose of 5,000 units of heparin, whereas subarachnoid hemorrhage patients
receive 3,000 units bolus dose. After placement of the first coil, patients are
titrated to an activated clotting time (ACT) of 2 to 2.5 times their ACT
baseline.