Keywords
endovascular treatment - intracranial aneurysms - coil embolization - microcatheter
Introduction
With the recent development of endovascular treatment technology and devices, there
are more opportunities to treat intracranial aneurysms in previously challenging areas.
Paraclinoid aneurysms are one of the anatomically difficult aneurysms for endovascular
coil embolization. The paraclinoid aneurysms are generally defined as aneurysms that
arise from an ophthalmic segment of the internal carotid artery (ICA) between the
roof of the cavernous sinus and the origin of the posterior communicating artery.[1] Due to the sharp curve from the carotid siphon and the large caliber of the ICA
lumen, it is not always easy to maintain a stable microcatheter position while continuously
delivering the detachable coils into the aneurysm. Therefore, simple coiling of the
paraclinoid aneurysm using only microcatheter shaping can result in incomplete packing
or protrusion of the coils.[2]
Balloon- and stent-assisted coiling via a jailed microcatheter has been widely applied
in paraclinoid aneurysms. Both assist techniques are required to navigate two catheters
inside and beyond the aneurysm. We hypothesize that in a bent blood vessel, such as
a paraclinoid ICA, the catheter that was first guided tended to pass through the inside,
and the catheter that was guided later tended to pass through the outside. When the
microcatheter for coil insertion is placed outside the balloon or stent, the tip of
the microcatheter easily escapes from the aneurysmal dome to the ICA due to the balloon
inflation or stent deployment. We describe the results of experimental verification
and clinical experience regarding the order in which catheters are guided and the
positional relationship of catheters in the curved vessel.
Materials and Methods
Our hypothesis is shown in [Fig. 1]. When the balloon is first navigated around the aneurysmal neck and the microcatheter
navigated next into the aneurysm, the microcatheter tends to place outside the balloon.
Therefore, the tip of the microcatheter easily escapes from the aneurysmal dome to
the parent artery due to balloon inflation. On the other hand, if the order of navigating
the microcatheter and balloon is changed, the positional relationship tends to be
reversed. Therefore, inflating the balloon stabilizes the tip of the microcatheter
within the aneurysm.
Fig. 1 Here are schematic illustratings our hypothesis. The red arrows indicate the direction in which the catheter moves by balloon inflation. (A) When the balloon is first navigated around the aneurysmal neck and the microcatheter
is next navigated into the aneurysm, the microcatheter tends to place outside the
balloon. Therefore, the tip of the microcatheter easily escapes from the aneurysmal
dome due to balloon inflation. (B) If the order of navigating the microcatheter and the balloon is changed, the positional
relationship tends to be reversed. Hence, inflating the balloon stabilizes the tip
of the microcatheter within the aneurysm.
A silicone vascular aneurysmal model (FAIN Biomedical, Okayama, Japan) was prepared
([Fig. 2]). The diameter of the parent artery was 4 mm, the aneurysm was 5 × 5 mm, and the
neck size was 4 mm. The microcatheter was Phenom 17 preshaped 45 degrees (Medtronic,
Irvine, California, United States), and the balloon catheter was Hyperform 4 × 7 mm
(Medtronic). Colored water was used for balloon inflation to improve visibility. The
positional relationship was observed five times by exchanging the guidance order of
the microcatheter and the balloon catheter.
Fig. 2 Here are some pictures of the experiment. The black arrows indicate the aneurysm. The white arrowheads indicate the tip of the balloon. The white arrows indicate the tip of the microcatheter. (A) The balloon first and then the microcatheter was guided. The microcatheter was kicked
out by the inflated balloon. (B) The microcatheter first and then the balloon was guided. The microcatheter was pushed
up into the aneurysm by the inflated balloon.
Results
When the balloon was guided ahead of the microcatheter, the microcatheter passed outside
the balloon. After the inflation of the balloon, the tip of the microcatheter escaped
from the aneurysm to the parent artery ([Fig. 2A]). On the other hand, when the microcatheter was guided before the balloon, the microcatheter
passed inside the balloon. After the inflation of the balloon, the tip of the microcatheter
was pushed up into the aneurysm and stabilized ([Fig. 2B]). Similar results were obtained in all five sessions.
Representative Case
A 64-year-old woman was referred to our hospital due to incidentally found a right
ICA aneurysm. Cerebral angiography revealed an aneurysm (height 5.4 mm, length 4.1 mm,
and width 4.0 mm) at the right ICA paraclinoid portion projected posteriorly from
the inside of the curved ICA ([Fig. 3]). Under general anesthesia, a 6-F guiding catheter was advanced into the right ICA
through the right common femoral artery. At first, a TransForm SC occlusion balloon
catheter (Stryker Neurovascular, Kalamazoo, Michigan, United States) was navigated
distally through the aneurysm, and then a Headway 17 microcatheter (Terumo, Tokyo,
Japan), which was shaped with a hot air gun was navigated into the aneurysm. When
the balloon was inflated during coil delivery into the aneurysm, the tip of the microcatheter
was pushed out from the aneurysm by the balloon ([Fig. 3A]). The balloon was placed inside the parent artery rather than the microcatheter.
Therefore, the balloon catheter and its inside guidewire were once withdrawn at the
petrous portion of the ICA and navigated distally again. This time, the balloon was
placed outside the parent artery rather than the microcatheter. When the balloon was
inflated during coil delivery into the aneurysm, the tip of the microcatheter was
pushed up into the aneurysm by the balloon ([Fig. 3B]). Complete obliteration of the aneurysm was achieved with four detachable coils.
Fig. 3 Intraoperative images. The black arrows indicate the aneurysm. The white arrows indicate the tip of the microcatheter. (A) The balloon first and then the microcatheter was guided. The microcatheter was kicked
out by the inflated balloon. (B) The microcatheter first and then the balloon was guided. The microcatheter was pushed
up into the aneurysm by the inflated balloon.
Discussion
Balloon-assisted coil embolization has been used for aneurysms in various locations
and has also been applied in paraclinoid aneurysms.[3]
[4]
[5] Inflation of the balloon for the neck-remodeling might have a mechanical conflict
with the microcatheter in the aneurysm resulting in its displacement, especially in
the tight curve of the paraclinoid ICA. When the balloon is placed between the aneurysmal
neck and microcatheter, the balloon inflation may result in unexpected protrusion
of the microcatheter and coils, thereby leading to incomplete or impossible coiling
of the aneurysm. On the other hand, when the balloon is placed outside of the coil-delivering
microcatheter, the balloon inflation may result in stabilization of the microcatheter
for continuous coil insertion, thereby leading to complete coiling of the aneurysm.
Needless to say, more than one loop of the coil has to be deployed into the aneurysm,
before the balloon inflation to prevent unexpected aneurysmal injury by the microcatheter
movement.
If the aneurysmal neck is very wide, a neck-bridging stent may eventually be required.
The neck-bridging stent placement requires preceding microcatheter navigation to the
distal artery beyond the aneurysmal neck. When the stent delivery catheter is placed
between the aneurysmal neck and jailed coil inserting microcatheter, the stent deployment
may result in an unexpected kick out of the microcatheter. Once the microcatheter
in the aneurysmal dome is escaped to the parent artery, a subsequent trans-stent cell
approach may often be difficult. Unlike balloon-assisted coiling, stent-assisted coiling
has the disadvantage that it cannot be enforced repeatedly. On the other hand, when
the stent delivery catheter is placed outside of the coil-delivering microcatheter,
the stent deployment may result in stabilization of the microcatheter as well as the
balloon-assisted coiling.
In this study, there are some limitations. First, the number of our experiments was
quite small in the limited situation. The in vitro evaluation had been done only five
times using the same model. Our clinical experience was confirmed in only four cases,
including the presented representative cases. We had to evaluate in various in vitro
circumstances and various patients. Shaping of the tip of the microguidewire and catheter
may affect the course of tracing in curved vasculature. We believe that guiding the
coil-delivering microcatheter into the aneurysm first and then the balloon catheter
or stent delivery catheter distally involves the risk of aneurysmal rupture. Therefore,
it is safe to guide the coil delivery microcatheter to the site beyond the aneurysm,
and then guide the balloon or stent delivery catheter distally, and then pulls back
the microcatheter to navigate into the aneurysm ([Fig. 4]).
Fig. 4 Schematic drawings of our ideal procedure are showing. The coil delivery microcatheter
to the site beyond the aneurysm (A), then guides the balloon catheter distally (B), and then pulls back the microcatheter to navigate into the aneurysm (C).
We found the positioning of microcatheters changes depending on the order in which
the catheter is navigated to the curved vessel under both experimental and clinical
situations. It was considered extremely important for safe and reliable coil embolization
to realize the positional relationship of the catheters during the procedure.
