Stent-Assisted Occlusion of Cerebral Aneurysms

D.V. Svistov, D.V. Kandyba, A.V. Savello

Department of Neurosurgery, Military Medical Academy, Saint Petersburg, Russia

 

Introduction

The last fifteen years are characterized by active development of an alternative trend of interventions for intracranial aneurysms with applying detachable coils [6]. The main goal of such operations is dense filling of an aneurysm cavity with coil loops, which should be as maximum as possible. It allows to prevent blood penetration into an aneurysm cavity, necessary for forming a stable thrombus in an aneurysm lumen with its subsequent substitution by a connective-tissue cicatrix within several weeks after operation [3]. An aneurysm neck, blocked by interlaced coils, is gradually isolated by a collagen membrane, which inner side is covered with a layer of neointima. This process is promoted by a new generation of biodegrading coils [16].

The long term practice has resulted in indications for endovascular obliteration of aneurysms with coils. They include a ratio between a dome and neck of 2:1 and more, as well as a neck diameter of less than 4-5 mm.

Aneurysms with a wide neck (a dome/neck ratio of less than 2.0 and a neck diameter of more than 4-5 mm) are a serious problem. In spite of continuous improvement of surgical technique and instruments, their total occlusion is difficult to perform, which conditions a high risk of recanalization, growth and repeated hemorrhage. According to the data of dynamic angiographic monitoring, a rate of aneurysm recanalization after occlusion with GDS coils varies from 16.8% up to 33.6% [18, 21]. A neck size is an important independent predictive factor of recanalization. Unified data [17, 18] demonstrate, that during the first year after occlusion a recanalization rate in narrow-neck and wide-neck aneurysms is 16% and 37% respectively. As for a recanalization rate of large and giant aneurysms, it is 87% and 90% respectively [7]. Immediate results of endovascular obliteration of “problematic” aneurysms are improved by use of such special methods, as temporary occlusion of a parent vessel by a balloon-catheter, reconstruction of an artery lumen with a stent, aneurysm obliteration with liquid copolymers (Onyx, HELP), etc. [2, 3, 14-16]. Stent implantation into a parent vessel at a neck level, favors coils retention in a dome; besides, it prevents protrusion of their loops into a lumen of a parent artery, ensuring vessel patency. The present article describes the first experience of endovascular stent-assisted occlusion of wide-neck and fusiform aneurysms.

Materials and Methods

There were 9 patients with cerebral aneurysms, operated in the Clinic of Neurosurgery in June 2004 - April 2005 with use of stents. Saccular and fusiform aneurysms were watched in 7 (big and giant aneurysms – 5, small aneurysms – 2) and 2 cases respectively. Subarachnoid hemorrhages (1-3 episodes) were suffered by 5 patients (saccular aneurysms – 4, fusiform ameurysms – 1); the rest cases had unruptured aneurysms. All operations were performed in a posthemorrhagic period and a satisfactory state of patients in accordance with recommendations of stent manufacturers. Aneurysms of the carotid region, in particular of ophthalmic and paraclinoid segments of ICA, were most frequent (n=4).

Information on the patients’ state and aneurysm morphology is given in Table 1. Selection of patients for stent-assisted embolization was carried out with taking into account peculiarities of aneurysm anatomy, which demanded use of assisting means. It meant, that the majority of cases had wide-neck aneurysms (more than 4 mm) and/or a dome/neck ratio of 2.0 or less. All the patients and their relatives were informed about peculiarities of a forthcoming operation. While selecting patients, we paid great attention to accessibility of a lesion zone, possibility of placing a system of stent delivery into a parent artery segment. All the cases underwent diagnostic and 3D rotation angiography for precise measurement of an aneurysm size and volume, a parent artery diameter and a length of a lesion area. It was necessary for determining a stent size, a diameter and length of coils.

Table 1

Basic Information on the Patients and Morphology of Intracranial Aneurysms

A Case (N)

Age

H&H

Localization

An Aneurysm Type

An Aneurysm Size (mm)

A Neck Size (mm)

A Dome/Neck Ratio

1

52

I

ICA, C2 segment relapse

Saccular

17 ´ 16 ´ 16

5

3.0

2

44

I

ICA, C2 segment relapse

Saccular

25 ´ 10 ´ 12

6

2.0

3

26

0

BA

Saccular

7 ´ 6 ´ 6

6

1.0

4

35

0

PCoA-PCA, Đ1 segment

Saccular

21 ´ 18 ´ 18

10

2.0

5

57

0

ICA, Ñ2 segment

Saccular

6 ´ 5.4 ´ 4.5

5.4

1.2

6

45

I

BA, bifurcation

Saccular

24 ´ 21 ´ 19

12

2.0

7

25

II

ICA, Ñ3 segment

Saccular

18 ´ 9 ´ 8

6

1.5

8

45

I

BA

Fusiform

30 ´ 12 ´ 10

-

-

9

44

0

VA

Fusiform

27 ´ 9 ´ 9

-

-

A preoperative preparation included prescription of antiaggregating drugs (PlavixÒ and AspirinÒ in a dose 75 mg and 300 mg respectively once a day 3-4 days before an operation). Local anesthesia under conditions of intravenous sedation was used. Intraoperative heparinization (100 U per 1 kg of body weight) was carried out. In case of ruptured aneurysms heparin was administered after introduction of the first coil into an aneurysm dome. Antiaggregants were given in a postoperative period too (4-6 weeks). Low-molecular types of heparin were prescribed in some cases.

We used two types of self-expanding stents: LEO (BALT Extrusion, France) and Neuroform2 (Boston Scientific, USA). A stent size was chosen in the following way: its diameter was to exceed a diameter of a parent vessels in its widest part by 0.5 mm. As for its length, it was to overlap a neck area by 5 mm. A stent of a little bit larger size would be better, than that of an insufficient size. In spite of a permanent radial effect, caused by a stent on an artery wall during its expanding, we did not observe any significant change of an artery caliber. Implantation did not provoke manipulation spasm of a vessel either.

The 6F guide was used for implantation in all cases. It should be mentioned, that the LEO stent is supplied without a guiding catheter (Vasco), whose diameter varies from 3F up to 5F, depending on a stent diameter. The delivering microcatheter was inserted through a microguide and placed at the level of an aneurysm neck so, that its distal marker corresponded to a desirable position of the stent’s distal end. Then the microcatheter was washed, the microguide was pulled out and the stent, loaded into a guiding device, was introduced. A pusher, connected with the stent by a locking device, was used for its advancement inside the microcatheter. When the stent reached the microcatheter butt-end, the delivering system was straightened and the locking valves of Y-shaped connectors loosened. Then the stent was introduced into an artery with the help of the pusher. The microcatheter sank spontaneously in a proximal direction, freeing the stent segments. In case of excessive distal migration the stent with its delivering system was brought down to a desirable level and its freeing was continued by conflicting movements of the pusher and microcatheter. The pusher rotation by 1/3 of a circle was necessary to free the stent within an artery lumen. The LEO stent is made of braided nitinol wires and has a form of a stocking. Thanks to it, it can be brought down to the delivering device and removed at any stage of implantation (Fig.1). The stent is marked by two platinum threads along its whole length; thus, it can be visualized both in a folded and expanded state without any difficulty.

The Neuroform2 stent is supplied in the 2.8F delivering microcatheter. We performed catheterization of a parent vessel with a microcatheter (standard 14). Then an exchangeable microguidewire (Transcend 14, 300 cm) was introduced and delivered into distal segments of vasculature, avoiding an aneurysm. After it the microcatheter was replaced by a coaxial system, assembled beforehand and consisting of the delivering microcatheter, carrying the stent, and the stabilizing (supporting) 2F microcatheter, inserted into the first one. After placing the stent in a desirable position, it was freed by bringing the delivering microcatheter down and using the immovable stabilizing microcatheter as a support. After the stent implantation one can use the microguidewire, left within its and artery’s lumen, for aneurysm catheterization. Bringing down, removal of the partially implanted Neuroform2 stent is impossible. The stent has radiopaque markers at proximal and distal butt-ends only (4 markers at each end). Thus, its visualization in fluoroscopic examination is difficult. A general view of the stent is represented in Fig.2.

Implantation of the stents of both types is characterized by one common rule, i.e. their distal and proximal butt-ends should be located in straight parts of arteries. One should avoid their placement in T-shaped bifurcations and sharp bends of arteries. As for our experience, in case of saccular aneurysms the stent implantation along a microguide was followed by aneurysm catheterization with a microcatheter (Prowler Plus-4, Vasco 18+-1, SL-10-1) and its occlusion with a necessary number of coils (TruFill DCS-5, TruFill Orbit-2, MDS Pression-2, Matrix-1, GDC-1). When possible, embolization was continued till there was no filling of an aneurysm by a contrast medium; besides, we tried to pack an aneurysm with coils up to 30% of its volume. The principle of the method of stent-assisted aneurysm embolization is shown in an animation (Video 1, Video 2, Video 3).

Results

The information on types of surgical interventions and their results is given in Table 2.

Stent implantation (10 – LEO, 1 – Neuroform2) did not cause serious difficulties in any single case. Staged treatment was carried out in three patients. Endovascular interventions, performed during previous admissions (5-24 months ago), consisted in aneurysm embolization with detachable coils without using assisting methods. Control examinations revealed aneurysm recanalization (case 1) or its growth (cases 2, 6); thus, stent implantation with simultaneous (case 2) or delayed (cases 1, 6) embolization was made. One-stage stent implantation and aneurysm embolization were performed in 2 patients (cases 3, 5). Subtotal embolization with coils was followed by stent implantation in 1 patient (case 4). There was one patient, in whom stent implantation and embolization were performed on the next day after prior embolization with coils, which was conditioned by diagnosed recanalization of a proximal lobe of a bilobular aneurysm (case 7). Stent-in-stent implantation only was used in 2 patients with fusiform aneurysms (cases 8, 9).

Table 2

Intervention Types, Applied Stents and Obtained Results

A Case (N)

Interventions

A Stent Type

A Stent Size

A Type of Aneurysm Occlusion

An Outcome according to mRs [18]

1

Coil/Stent/Coil

LEO

3.5 ´ 18

A

1

2

Coil/Stent+Coil

LEO

5.5 ´ 30

A

1

3

Stent+Coil

LEO

4.5 ´ 25

A

0

4

Coil+Stent

LEO

2.5 ´ 12

A

1

5

Stent+Coil

Neuroform2

4.5 ´ 15

A

0

6

Coil/Stent/Coil

LEO

4.5 ´ 25

B

5

7

Coil/Stent+Coil

LEO

4.5 ´ 25

B

2

8

Stent+Stent

LEO

4.5 ´ 502

-

1

9

Stent+Stent

LEO

5.5 ´ 302

-

0

Isolated stent implantation (case 1, 6) in saccular aneurysms had no effect on their size in 1-5 months. On the contrary, one could observe its increase in an aneurysm of the ICA ophthalmic segment (case 1). Total occlusion of saccular aneurysms (type A) with coils was achieved in 5 cases; filling of a neck (type B) was observed in 2 patients. Embolization was always completed by application of coils with a diameter of 2 mm, which was 2 and more times smaller, than an angiographic neck. Thus, presence of the stent net in a neck area allowed to complete embolization in compliance with principles of embolization of a narrow-neck aneurysms. In cases of fusiform aneurysms, we did not perform aneurysm embolization with coils, as an operation was aimed at isolation of its wall from a lumen for preventing hemorrhage. Control angiographic examinations were carried out on the 1-7th day of stay in hospital. Stable occlusion of an aneurysm and/or an artery patency were watched in all the patients. A final result of operations can be estimated only on the basis of delayed control examinations, which have not been carried out yet.

Clinical Cases

Primary Stenting and Embolization of Aneurysms

Case 3: Female patient K., aged 26, had an incidental aneurysm of a basilar artery trunk, which had been diagnosed during an outpatient examination (Fig.3). Rotation angiography showed a wide-neck aneurysm (6.0 mm); a dome/neck ratio was 1.0. A preoperative preparation (PlavixÒ and AspirinÒ in a dose of 75 mg/day and 300 mg/day respectively) was followed by implantation of the self-expanding LEO stent into the basilar artery. A distal butt-end of the stent was placed below the SCAs. One-stage embolization with TruFill DCS coils was performed. A postoperative course was uneventful.

Case 5: Female patient K., aged 57, was admitted with complaints of periodical headache. An outpatient examination revealed an unruptured aneurysm of an ophthalmic segment of the left ICA (Fig.4). Left-side carotid angiography and rotation angiography (Video 4) were indicative of a wide-neck aneurysm (5.5 mm); a dome/neck ratio was 1:1. A preoperative preparation was followed by implantation of the self-expandable Neuroform2 stent into sub-supraclinoid segments of the ICA and embolization of the aneurysm with the Matrix coils (Boston Scientific). A postoperative course was uneventful. Control MRI-examination, carried out a month after operation, demonstrated no signs of blood flow in the aneurysm cavity.

Stenting and Embolization of Recurrent Aneurysms

Case 2: Female patient N., aged 44, suffered spontaneous SAH in February 2002. An angiographic examination showed a giant aneurysm of the left ICA (Fig.5). Its total embolization with free and mechanically detachable coils (FIB, MDS, BALT Extrusion) was performed in March 2002. A control angiographic examination, carried out in September 2004, was indicative of the aneurysm growth, because of widening of its neck. The neck width was two times greater than the maximum size of the dome, so it was decided to use a stent for the aneurysm occlusion. Implantation of the LEO stent (5.5´30), total embolization of the aneurysm with TruFill DCS coils (Cordis) were performed. There were no complications postoperatively.

Case 6: Female patient A., aged 47, had spontaneous SAH in summer of 2000. An angiographic examination failed to reveal its source. The results of MRI- and angiographic examinations, carried out in March 2003, demonstrated a giant aneurysm of the basilar artery (Fig.6). Its partial embolization with detachable MDS coils (BALT) was made in March 2003. There was augmentation of general symptoms of the brain disorder in December 2004. Cerebral angiography revealed a considerable growth of the aneurysm, compaction of coils along a posterior-external outline of the aneurysm. The Leo stent (4.5´25) was implanted. A control angiographic examination, carried out in 4 weeks, was indicative of no dynamics. The aneurysm was occluded with MDS-Pression coils (BALT) and TruFill DCS coils (Cordis). There was augmentation of focal symptoms postoperatively, caused by ischemic stroke in the left PCA despite its patency.

Stenting of Fusiform Aneurysms

Case 9: Male patient Zh., aged 44, had a fusiform aneurysm of the left VA, diagnosed during an outpatient examination. Its size was determined with left-side vertebral rotation angiography (Fig.7, Video 5). A preoperative preparation was followed by stent-in-stent implantation. Two LEO stents were implanted into V4 segment of the left VA. There was marked stagnation of a contrast substance between the stent net and arterial wall in the area of widening. A postoperative course was uneventful.

Complications

A risk of thromboembolic and other complications was conditioned by implantation of a foreign body into a vascular bed. They were watched in 4 patients and had a symptomatic character in 2 of them.

The stent migration was observed in 2 cases.

As for case 8, migration took place during implantation of the third stent into a fusiform aneurysm of the basilar artery. It resulted in its thrombosis and acute uncomplicated SAH (Fig.8, Video 6).

There was a distal displacement of the stent during an attempt to catheterize the aneurysm with a microcatheter (case 1). It was likely to be caused by equal diameters of the stent and artery; thus, a radial stress was insufficient for its stable position.

Thrombosis of a parent artery was observed after the stent implantation in 2 patients (case 4, 6). It was connected with an imperfect preoperative medication.

The stent implantation in a female patient with a large aneurysm of the left PCoA-PCA (Fig.9) was performed after its subtotal embolization (type B) with coils. Acute thrombosis of the stent and aneurysm was diagnosed on the next day during a control angiographic examination. The thrombus was located within the stent limits. There were no neurologic disorders, caused by it, due to a developed system of cortex collaterals between the MCA and PCA.

Transient neurologic disorders were observed in a female patient with a giant aneurysm after stenting the bifurcation area of the basilar artery (case 6). The stent was placed in an area of branching of the basilar artery into its right P1 segment. In spite of an adequate preparation and heparinization there was augmentation of common cerebral symptoms 30 min after operation. It was caused by a parietal thrombus in the bifurcation area. The artery was recanalized after intraarterial fibrinolysis of 1 500000 U of streptokinase. Neurologic symptoms regressed.

Thus, despite an insufficient experience of using stents for treatment of patients with aneurysms, it should be noted, that a satisfactory clinical-and-morphologic result was obtained in 8 out of 9 cases. There was only one case of undesirable occlusion of a fusiform aneurysm. There were no fatal outcomes, conditioned by the stent implantation and aneurysm embolization. Verified thromboembolic complications, connected with implantation of the stent and coils, were observed in 4 patients. However, persistent deficit was typical of one case only (11.1%).

Discussion

Endovascular surgery of wide-neck aneurysms is a serious clinical problem. Despite development of 3D coils, total occlusion of such aneurysms is rather rare due to a risk of protrusion of its loops into a lumen of a parent artery. Balloon-assisted embolizaton has been proposed as a means of preventing this complication [15]. Simultaneous use of two catheters, one of which carries a nondetachable balloon, predetermines considerable technical difficulties of a procedure.

A rate of total balloon-assisted embolization of aneurysms varies from 67% up to 83%; failures are watched in 23% of cases. Balloon inflation at a neck level can lead to a growth of pressure within an aneurysm. Its sudden changes can provoke an aneurysm rupture, watched in 5% of cases [20].

One more alternative is stent implantation at a neck level with subsequent catheterization of an aneurysm through its mesh. Medical literature contains a limited number of reports on use of coronary balloon-expandable stents with these purposes [9].

We used nitinol self-expanding stents of two manufactures in our series. Interesting as it may seem, but we have not found any information on application of the LEO stent (BALT Extrusion) both in current literature and Internet. All the reports are devoted only to the Neuroform2 stents (Boston Scientific). Main clinical data on use of self-expanding stents in surgery of aneurysms are given in Table 3.

Table 3

Use of Self-Expanding Stents in Surgery of Aneurysms

Authors

A Number of Cases

Technical Success
(%)

Technical difficulties
(%)

Aneurysm Occlusion of A+B Type (%)

Complications/ Mortality
(%)

Lylyk P. et al., 2005 [20]

46

92

31

No data

8.6 / 2.1

Sani S. et al., 2005 [28] *

10

100

10

No data

0 / 0

Li Y.X. et al., 2004 [17]

8

87.5

25

50

12.5 / 12.5

Jabbour P. et al., 2004 [14]

32

100

No data

75

6.3 / 0

Benitez R.P. et al., 2004 [4]

48

85.7

No data

81.6

10.7 / 8.9

Fiorella D. et al., 2004 [7]

19

77.3

52.6

35.3

10.5 / 5.3

Wanke I. et al., 2003 [31]

4

100

100

100

0 / 0

Our data

9

100

11.1

77.8

11.1 / 0

* - the Neuroform2 Treo stent

The main conclusions, given in the above repots, are rather optimistic:

The rest reports contain mainly description of cases from practice. D. Lopes et al. [12] dwell on morphologic changes in an arterial wall, observed 4 months after stenting an aneurysm of the ICA supraclinoid segment. They included thickening of intima in an area, which was proximal in relation to the stent, its integration into an inner layer of the artery with moderate hyperplasia of intima. There was vegetation of connective tissue within the aneurysm with its spread to the neck area, though a central part of the dome was filled with masses, resembling a thrombotic substance. D. Fiorella et al. [5] describe development of late in-stent stenosis after intervention for an unruptured aneurysm.

The analysis of reports, devoted to stent-assisted endovascular surgery of aneurysms, allows to conclude: according to preliminary data, immediate results of stent-assisted occlusion of wide-neck aneurysms are much better despite rather frequent technical difficulties, encountered during its placement. The main problems, demanding solution in the nearest future, are improvement of navigation properties of the stent delivery system, improvement of its radial stability especially in implantation within an area of a vessel’s sharp bend, increase of density of stent cells at a neck level. Achievement of this goal has been promoted by development of the Neuroform2 Treo stent, which meets the above demands partially.

Medical literature of today contains no data on use of the LEO stent in surgery of aneurysms, though it is the only stent of this class, authorized for use and available in Russia. We consider it appropriate to present a table, comparing main technical and operating characteristics of the stents of two manufacturers, which will allow beginners to form an opinion on drawbacks and advantages of this or that system (Table 4).

Table 4

Comparison of the LEO Stent (BALT) with the Neuroform2 Stent (Boston Scientific)

 

LEO

Neuroform2

The stent length, mm

12-18-20-25-30-35-40-50-60-75-80-95

10-15-20-30

The stent diameter, mm

2.5-3.5-4.5-5.5-6.5-7.5

2.5-3.0-3.5-4.0-4.5

The mesh size

2.1F-2.4F-3.0F-3.5F-4.0F-5.0F
It depends on the stent diameter

2.0-2.5F
It does not depend on the stent diameter

Configuration of the stent cells

Closed cell

Open cell

Shortening of the stent after placing

It depends on an artery diameter

1.8-5.4%

Possibility of reloading into a delivering device and replacing

Yes
(when less than 90% of the stent length is freed)

No

Visualization

Two platinum threads along the whole length of the stent

4 markers on each butt-end

Accessibility of an artery segment after the stent implantation

Necessity of repeated catheterization with a microguide

An exchangeable microguide is left in the stent lumen after its implantation

A delivering catheter

Vasco 21-28-35
It depends on the stent diameter

2.8F
It does not depend on the stent diameter

Thus, both devices have positive and negative features, which determine their operating characteristics.

Conclusion

Intracranial stents as an assisting method in intracranial interventions for wide-neck aneurysms, can be necessary in 20% of patients with this pathology.

Stent implantation should be preceded by thorough preoperative drug therapy, individual planning of an operation with precise morphologic estimation of an area of a vascular bed lesion. Isolated stent implantation in saccular aneurysms does not cause a considerable effect on local hemodynamics in a neck area; thus, it cannot be recommended as an independent method of treatment.

Despite technical difficulties, connected with stent implantation, complications, which manifest clinically, are a rare phenomenon. As a whole, treatment results are favorable.

LITERATURE

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