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H. Henkes
1, 2
J. Reinartz
1
H. Preiss
1
E. Miloslavski
1
M. Kirsch
3
D. Kühne
2
Endovascular Treatment of Small Intracranial
Aneurysms: Three Alternatives to Coil Occlusion
Abstract
cular treatment strategies may provide solutions for these chal−
lenging lesions.
Introduction: Small intracranial aneurysms with a fundus dia−
meter of 2 ± 3 mm may rupture and are therefore potential tar−
gets for an endovascular approach in treatment. Currently avail−
able coil technology is less than optimal for the treatment of an−
eurysms within this size range. Even the smallest coils are some−
times too large. If such a minute coil can be introduced into a
small aneurysm, the hemodynamic effect and the induced
thrombosis are frequently inadequate to occlude the aneurysm
sufficiently from the parent artery circulation. Methods: Three
technical alternatives for the endovascular treatment of small in−
tracranial aneurysms not suitable for coil occlusion are illustrat−
ed with the following three case descriptions. Results: Stent
grafts are usable for the intracranial internal carotid artery and
for the V4 segment. The stiffness of the stent and the high expan−
sion pressures are the two major drawbacks. Coaxial deployment
of two or more self−expanding porous stents can result in suffi−
cient redirection of the blood flow to induce aneurysmal throm−
bosis. Deployment of multiple stents, however, may require sev−
eral treatment sessions in order to allow for the integration of
the stents into the vessel wall from session to session. A regular
microcatheter can block aneurysmal inflow in aneurysms with a
very narrow neck. This allows the occlusion of the aneurysm
with an appropriate amount of highly concentrated, rapidly
polymerizing glue. Polymer emboli may result from excessive or
rapid glue injection. Conclusion: The available coil technology
has inherent limitations in the treatment of very small intracra−
nial aneurysms. Liquid embolic agents and stent−based extrasac−
Key words
Aneurysm ¥ endovascular ¥ embolization ¥ coil ¥ stent ¥ stent graft ¥
neuroform ¥ histoacryl ¥ NBCA
Introduction
The success of endovascular coil occlusion is currently limited in
treating very small and giant aneurysms. Most difficulties ob−
served in the treatment of giant aneurysms are related to recur−
rent aneurysm perfusion, due to coil compaction and/or coil mi−
gration into the intra−aneurysmal thrombus. Both issues are well
addressed by meticulous follow−up examinations and eventual
retreatments.
65
In aneurysms with a fundus diameter of 2 ± 3 mm, the initial en−
dovascular treatment may be more dangerous and less efficient
than in midsize aneurysms. The currently available microcath−
eters and microguidewires allow for precise catheterization of
small aneurysms and are therefore less of a risk factor. Existent
coil technology, however, has not been adapted to the specific
requirements of small aneurysms. With our experience, it is
commonly found that even the smallest and softest available
coils are sometimes too large and/or too stiff for this specific pur−
Affiliation
1
Robert Janker Klinik, Bonn, Germany
2
Klinik für Radiologie und Neuroradiologie, Alfried Krupp Krankenhaus, Essen, Germany
3
Institut für Diagnostische Radiologie und Neuroradiologie, Universitätsklinikum Greifswald
der Ernst−Moritz−Arndt−Universität, Greifswald, Germany
Correspondence
Priv.−Doz. Dr. med. Hans Henkes ¥ Neuroradiologie und Radiologie ¥ Robert Janker Klinik ¥ Villenstrasse 4 ± 8 ¥
53129 Bonn ¥ Germany ¥ Tel.: +49/201/434/41602 ¥ Fax: +49/201/434/2375 ¥ E−mail: HHHenkes@aol.com
Bibliography
Minim Invas Neurosurg 2006; 49: 65±69
Georg Thieme Verlag KG Stuttgart ¥ New York
DOI 10.1055/s−2005−919150
ISSN 0946−7211
pose. If the attempt to introduce such a coil into an aneurysm is
successful, the isolation of the aneurysm and subsequent throm−
bosis are frequently incomplete, and rupture or rerupture may
result.
Subsequent angiography confirmed the obliteration of the an−
eurysm with normal opacification of the ophthalmic artery pre−
sent (Fig. 1b). The procedure was tolerated well and the patient
was discharged home 19 days later without any demonstrated
neurological deficit. Follow−up angiography 6 months later con−
firmed the obliteration of the aneurysm. In the meantime, the
ophthalmic artery had thrombosed. Ophthalmologic examina−
tion confirmed normal visual acuity of the left eye.
Based on an institutional experience of more than 2,700 intracra−
nial aneurysms treated by coil occlusion, it is the purpose of this
paper to present alternative endovascular treatment strategies.
These alternatives might be contemplated in case of failure or
anticipated difficulty of conventional coil occlusion.
Case 2 (stent−in−stent)
This 28−year−old female experienced a subarachnoid hemor−
rhage on September 1, 2001. Angiography showed an aneurysm
of the right ICA at the origin of the posterior communicating ar−
tery (Fig. 2a). She underwent an operation for this aneurysm on
September 5, 2001. Postoperative angiography, however, re−
vealed an aneurysm remnant with a diameter of 2 mm adjacent
to the applied clip (Fig. 2b). Neither coil occlusion nor stent graft
deployment was considered promising. The aneurysm appeared
too small to accept a coil. The vasculature in this young lady was
quite irritable and we feared a risk of severe vasospasm or dis−
section related to the attempt of introducing a stent graft. After
routine premedication with a loading dose of 500 mg ASA and
300 mg Clopidogrel, the first endovascular procedure was carried
out on July 9, 2004. Under controlled heparinization an X−celera−
tor_10 guidewire was introduced into the right MCA. Via this
wire a Neuroform2 Treo stent (3.5 mm/20 mm) was inserted
and deployed over the residual aneurysm. The filling of the an−
eurysm appeared unchanged on immediate DSA (Fig. 2b). Fol−
low−up angiography on September 11, 2004 revealed a slightly
reduced size of the aneurysm remnant. A second Neuroform2
Treo stent (4.5 mm/15mm) was deployed within the first stent
on September 11, 2004. This second procedure was carried out
in essentially the same way as the first treatment. Eight weeks
after the first treatment session, the previously inserted stent ap−
peared completely integrated into the vessel wall. The struts of
this first stent did not interfere with the insertion of the micro−
guidewire or the Neuroform2 stent catheter. Aneurysm filling
was insignificantly reduced immediately after the second stent
deployment (Fig. 2c). Both procedures were tolerated well with−
out neurological sequelae. The patient has been kept on 100 mg
ASA orally since the last procedure, while the intake of Clopido−
grel was discontinued in November 2004. Angiographic follow−
up on December 8, 2004 showed the complete thrombosis of
the aneurysm without any evidence of angiographically visible
intimal hyperplasia within the stent (Fig. 2d).
Illustrative Cases
66
Case 1 (stent graft)
This 47−year−old male presented with severe headache and was
diagnosed as having a subarachnoid hemorrhage on July 7, 2004.
Cerebral angiography revealed an aneurysm of the left internal
carotid artery at the origin of the superior hypophyseal artery
with a diameter of both the fundus and neck of 2 mm. On July
10, 2004 an attempt at surgical clipping of this aneurysm was un−
dertaken with an anterior pterional approach and failed because
the aneurysm was not sufficiently visible and reachable. The pa−
tient was referred to us for endovascular treatment. On July 17,
2004 the procedure was carried out under general anesthesia.
Injection of the left ICA via a 6F guiding catheter confirmed size
and location of the aneurysm as previously known (Fig. 1a).
Under controlled heparinization, all possible efforts to catheter−
ize the aneurysm with sufficient stability failed. We therefore
decided to seal the aneurysm with a stent graft. For this purpose,
a Choice PT extra support microguidewire (Boston Scientific) was
introduced into the left middle cerebral artery through an Eche−
lon_14 microcatheter (MTI). In order to prevent vasospasm dur−
ing the insertion of the stent graft, 2 mg glycerol trinitrate were
slowly injected into the ICA via the guiding catheter. A 3.5 mm/
12 mm stent graft (Abbott) was introduced without difficulty
until reaching the level of the aneurysm orifice. At this point of
the procedure, 500 mg Aspisol (intravenously) and 300 mg
Clopidogrel (gastric tube) were given. The stent graft was
deployed by primary balloon inflation with 10 atm in the select−
ed position. The stent graft was also found to be covering the
origin of the ophthalmic artery. In order to both preserve the pa−
tency of the ophthalmic artery and to completely cover the an−
eurysm, the deflated balloon was slightly advanced more distally
and reinflated in the distal half of the stent graft with 16 atm.
Fig. 1 Ruptured small aneurysm of the left
ICA/superior hypophyseal artery (a). At−
tempts at surgery and coil occlusion both
failed to occlude the aneurysm. Treatment
was finally accomplished by deploying a
stent graft into the left ICA, sealing the an−
eurysm neck and leaving the origin of the
ophthalmic artery patent (b). A comparison
of a and b reveals a significant straightening
of the ICA and a displacement of the ACA
and MCA, related to the stiffness of the im−
planted stent graft.
Henkes H et al. Endovascular Treatment of Small Intracranial º Minim Invas Neurosurg 2006; 49: 65 ± 69
Fig. 2 Ruptured aneurysm of the right ICA
at the origin of the posterior communicat−
ing artery, preoperative angiogram (a).
Postoperative angiography showed an an−
eurysm remnant after partial clipping. De−
ployment of a first (b) and a second Neuro−
form stent (c) did not immediately change
the filling of the aneurysm. Angiography 3
months after deployment of the second
stent revealed complete thrombosis of the
aneurysm (d).
Case 3 (intrasaccular polymer glue injection)
This 39−year−old female experienced a subarachnoid hemor−
rhage on April 22, 2003. Angiography revealed a large, ruptured
aneurysm of the left ICA at the origin of the posterior communi−
cating artery, a small left paraophthalmic aneurysm and an even
smaller aneurysm of the left ICA at the origin of the superior hy−
pophyseal artery. The large aneurysm was occluded with coils at
another institution on April 23, 2003 and required retreatment
due to coil packing on November 13, 2003. Further angiographic
follow−up on June 8, 2004 showed a significant reperfusion. On
July 21, 2004 a Neuroform2 stent (4.5 mm/20 mm) was deployed
into the distal segment of the left ICA, followed by coil occlusion
of the PcomA aneurysm on October 20, 2004. During this treat−
ment session an attempt at catheterizing the paraophthalmic an−
eurysm had failed. After a completely frank discussion of all pos−
sible options for the untreated paraophthalmic aneurysm, the
patient opted for another endovascular attempt. At this time, a
heat−shaped Echelon_14 microcatheter was inserted without
difficulty into the aneurysm using a SilverSpeed_14 guidewire.
Stabilization of the microcatheter was substantially facilitated
by the Neuroform2 stent, which bridged both aneurysms. Injec−
tion of the ICA with the microcatheter in the paraophthalmic an−
eurysm showed no opacification of the aneurysmal sac (Fig. 3b).
The attempt to introduce a small coil (2 mm/15 mm mini com−
67
Fig. 3 Small unruptured paraophthalmic
aneurysm of the right internal carotid ar−
tery, with a small aneurysm of the superior
hypophyseal artery and a previously rup−
tured, large aneurysm at the origin of the
posterior communicating artery, which had
been coil treated (a). Flow in and out the
paraophthalmic aneurysm was interrupted
after a microcatheter had been introduced
into the aneurysm orifice (b). Injection of a
small amount of polymer glue obliterated
the aneurysm fundus, leaving an aneurysm
neck remnant behind (c). Angiography 7
months later showed complete occlusion of
the paraophthalmic aneurysm (d).
Henkes H et al. Endovascular Treatment of Small Intracranial º Minim Invas Neurosurg 2006; 49: 65 ± 69
plex, Cordis; NXT 2 mm/10 mm soft, MTI) failed. It became evi−
dent that the space provided by the aneurysm sac was too small
to allow a circular configuration of the coil loops. After gentle
flushing of the microcatheter with a 40 % glucose solution,
< 0.1 ml of a homogeneous Histoacryl (Braun Aesculap)/Lipiodol
(Guerbet) solution of equal parts was injected into the hub of the
microcatheter. The liquid embolic agent was very gently ad−
vanced within the microcatheter by slow injection of 40 % glu−
cose solution. Under non−pulsed fluoroscopy the distal end of
the microcatheter was observed. The injection was terminated
as soon as the radiopaque Histoacryl/Lipiodol column appeared
in the field of view. Then the continued propagation of the glue
column was decelerated by applying negative pressure to the
syringe. A small volume of Histoacryl/Lipiodol detached slowly
from the distal tip of the microcatheter and stayed within the an−
eurysm. After two seconds the microcatheter was abruptly with−
drawn. The Histoacryl/Lipiodol remained unchanged within the
aneurysm. Immediate angiography showed a minor neck rem−
nant (Fig. 3c). Follow−up angiography 7 months after the final
treatment confirmed the complete obliteration of the paraoph−
thalmic aneurysm and showed the small aneurysm of the super−
ior hypophyseal artery essentially unchanged (Fig. 3d). With re−
spect to the size and the unfortunate angle between ICA and an−
eurysm, no further attempt at endovascular treatment was un−
dertaken until now. Treatment with a new hemodynamically ac−
tive device, which will soon be available, was discussed with the
patient as a future option.
originating adjacent to the target aneurysm, however, are a con−
cern. Currently the only available device suitable for intracranial
vessels is the Jomed StentGraft (Abbott), which is premounted on
a balloon. This stent is very stiff and rigid and the recommended
expansion pressure of 16 atm requires precise sizing. In general,
this stent is certainly a last resort and not a first choice of neuro−
vascular aneurysm treatment.
The self−expanding nitinol stent Neuroform (Boston Scientific)
was originally developed as an adjunctive device to allow coil oc−
clusion of wide−necked aneurysms. This stent is very flexible and
deployment is atraumatic [4]. Experimental data have revealed
that a single porous stent will significantly reduce flow into an
underlying aneurysm [5, 6]. The hemodynamic effect of the co−
axial deployment of two Neuroform stents will vary depending
on the resultant overlapping effect of the stent struts. This can
hardly be influenced by the operator. Intimal hyperplasia has
been reported after the deployment of Neuroform stents [7, 8].
In our patient a certain degree of intimal hyperplasia, not appar−
ent angiographically, may have contributed to the complete oc−
clusion of the aneurysm. The major drawback of the treatment
strategy described in this patient is the unpredictable efficacy. It
may last several weeks if not months from the first treatment
until the occlusion of the target aneurysm.
Several liquid embolic agents have been proposed for the endo−
vascular treatment of intracranial aneurysms, including n−BCA
[9], cellulose acetate polymer (CAP) [10 ± 12], and ethylene vinyl
alcohol copolymer dissolved in dimethyl sulfoxide (Onyx
, MTI)
[13]. Only Onyx
had been developed as a commercial product.
The use of liquid embolic agents has been justified by the search
for a more complete and lasting aneurysm occlusion. Despite
good initial results, aneurysms filled with Onyx may show reper−
fusion [14,15]. These procedures turned out to be substantially
more demanding than conventional coil occlusion. Escape of the
embolic agent out of the aneurysm sac into the parent artery is
one of the major risks. The currently available n−BCA polymer
glues Histoacryl
(Braun/Aesculap) and Glubran2
(GEM) are
far from ideal for the use in aneurysm treatment. Apparent ad−
vantages are their low viscosity, high radiopacity and short poly−
merization time on contact with blood. Radiopacity and modifi−
cation of polymerization is, for both substances, achieved by
adding Lipiodol
(Guerbet). The resulting delay in polymeriza−
tion is, however, variable and to a certain degree unpredictable.
There would certainly be a space in the neuroendovascular pro−
duct assortment for optimized polymer glue. Adding an inert
radiopaque compound to the liquid embolic agent and modify−
ing the polymerization time by an independently added agent
might be one of several possible solutions [16]. Prevention of
the escape of the embolic agent from the aneurysm sac can be
achieved in different ways. Balloon sealing was established for
the use of Onyx. In our case the microcatheter isolated the aneu−
rysm from the parent artery. Alternative methods might be con−
sidered under certain circumstances. Transient circulatory “ar−
rest” for 10±15 sec can be achieved by the intravenous injection
of adenosine [17]. A significant reduction of blood circulation
within the aneurysmal sac is caused by the insertion of even a
small number of coils [18]. Coil occlusion, stent deployment and
polymer injection are therefore potentially synergistic methods.
Discussion
68
The treatment of a very small aneurysm is clearly indicated if an
intracranial hemorrhage can be attributed to it. A previous he−
morrhage from another aneurysm also justifies treatment. In
the case of a small unruptured aneurysm, we explain the indica−
tion criteria to the patient [1]. Our final recommendation, how−
ever, also takes individual aspects such as patient age, medical
condition, and extent of atherosclerotic changes of extra− and in−
tracranial vessels and aneurysm geometry into account. The di−
lemma of recommending conservative or proactive treatment to
a patient with an unruptured intracranial aneurysm can hardly
be solved on the basis of statistic numbers [2]. The microsurgical
and endovascular treatment risks vary in relation to many indivi−
dual factors. The risk of future rupture is even more difficult to
anticipate. The wall of unruptured aneurysms with identical an−
giographic appearance may at surgery be found to be very thin
and fragile or thick and robust. One might assume that this is a
more predictive feature for rupture than any other.
The three methods of endovascular aneurysm treatment des−
cribed above clearly constitute “off−label−use” for all involved
products. All patients were informed and had agreed in advance
to the potential use of medical products which are not certified
for this specific purpose. Apart from that, German law provides
the option of using medical products “off−label” for the sake of
the patient, if the physician in charge is convinced that there is
no feasible alternative at hand (“Heilversuch”).
Covered stents or stent grafts are intuitively an exquisite concept
for the treatment of intracranial side wall aneurysms [3]. Vessels
Henkes H et al. Endovascular Treatment of Small Intracranial º Minim Invas Neurosurg 2006; 49: 65 ± 69
In summary, very small intracranial aneurysms remain a chal−
lenge for endovascular treatment and the three methods of treat−
ment described in this paper are rather preliminary efforts than
final solutions.
8
Lopes D, Sani S. Histological postmortem study of an internal carotid
artery aneurysm treated with the Neuroform stent. Neurosurgery
2005; 56: 416
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Teng MM, Chen CC, Lirng JF, Chen SS, Lee LS, Chang T. n−Butyl 2−cya−
noacrylate for embolization of carotid aneurysm. Neuroradiology
1994; 36: 144 ± 147
10
Macdonald RL, Mojtahedi S, Johns L, Kowalczuk A. Randomized com−
parison of Guglielmi detachable coils and cellulose acetate polymer
for treatment of aneurysm in dogs. Stroke 1998; 29: 478 ± 485
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Henkes H et al. Endovascular Treatment of Small Intracranial º Minim Invas Neurosurg 2006; 49: 65 ± 69
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