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ORIGINAL ARTICLE
Year : 2020  |  Volume : 15  |  Issue : 3  |  Page : 620-626

The exchange-free technique: A novel technique for enhancing surpass flow diverter placement


Department of Radiology, Faculty of Medicine, Hacettepe University, Ankara, Turkey

Date of Submission31-Dec-2019
Date of Acceptance18-Apr-2020
Date of Web Publication28-Aug-2020

Correspondence Address:
Prof. Anıl Arat
Department of Radiology, Faculty of Medicine, Hacettepe University, Hacettepe Mh. 06230 Ankara
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ajns.AJNS_374_19

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  Abstract 

Background: Following flow diverter placement, approximately 20% of intracranial aneurysms remain as residual aneurysms at 1 year. Device malapposition is a cause of residual aneurysms after flow diversion. We present a new and straightforward technique (exchange-free technique [EFT]) to enhance apposition of the surpass flow diverter (SFD), the only over-the-wire flow diverter currently available. Materials and Methods: We deployed laser-cut mini stents through the inner deployment catheter of the SFD. This maneuver was performed simply by withdrawing the micro-guidewire from its lumen and replacing it with a mini-stent (stents deliverable through microcatheters with inner diameter of 0.0165 inches), without a need to re-cross the deployed SFD or an exchange maneuver. All aneurysms in which this technique was utilized were retrospectively reviewed. Results: Twenty-eight patients (20 females) with 30 treated aneurysms were identified. The mean aneurysm diameter was 10.2 ± 6.6 mm. Technical success rate was 96.6% (29/30 aneurysms). There was no mortality or permanent morbidity related to the procedures. Except for the patient treated for an iatrogenic, surgery-related internal carotid artery pseudoaneurysm who died secondary to consequences of multiple surgeries, no cases of mortality or permanent morbidity were noted. Complete aneurysm occlusion rates were 78.2%, 82.1%, and 95.2% at 0–3, 3–6, and 9–12 months, respectively. None of the patients were re-treated. Conclusion: EFT is a simple and fast technique which was not associated with adverse effects in our series. The higher aneurysm obliteration rate obtained with EFT is probably the result of better wall apposition of the SFD.

Keywords: Aneurysm, endovascular treatment, flow diversion, flow diverter, stent


How to cite this article:
Ocal O, Arat A. The exchange-free technique: A novel technique for enhancing surpass flow diverter placement. Asian J Neurosurg 2020;15:620-6

How to cite this URL:
Ocal O, Arat A. The exchange-free technique: A novel technique for enhancing surpass flow diverter placement. Asian J Neurosurg [serial online] 2020 [cited 2020 Oct 24];15:620-6. Available from: https://www.asianjns.org/text.asp?2020/15/3/620/293741


  Introduction Top


Flow diverters are safe and effective in the treatment of cerebral aneurysms, including wide necked and fusiform aneurysms which have high recanalization rates with coiling. Complete aneurysm occlusion rates for different flow diverters in device-specific studies are reported to be between 56% and 71.4% at 3 months,[1],[2],[3] 66.6%–75% at 6 months,[1],[3],[4],[5],[6] and 77.8%–86.6% at 1 year follow-up.[1],[2],[4],[5] A variety of techniques have been proposed to increase the efficacy of flow diverters.[7] The most popular of these is adjunctive coiling and to a lesser extent, a combination of a flow diverter with the woven endobridge device.[8],[9] There are few reports about combined usage of stents with flow diverters,[10],[11],[12] and recently, it has been shown that this technique reduces the time needed for complete aneurysm occlusion.[13] In this article, we describe a new technique, the exchange-free technique (EFT) that not only enhances the wall apposition of the surpass flow diverter (SFD) but also, in selected cases, allows us to anchor the landing zones by pinning the device by means of a laser-cut stent directly placed through the unique delivery system of the SFD. EFT provides a fast and easy way to appose and pin the Surpass device without a need to re-cross the deployed flow diverter.


  Materials and Methods Top


Patients

This retrospective study was approved by the Ethics Committee of our University Hospital. Patient consent was not required since the study involved only a retrospective chart review of anonymous patient data. We evaluated all of our patients treated with a flow diverter between August 2015 and April 2018 and identified the patients who were treated with a Surpass device. Those patients in whom another stent was deployed during the same session was determined. Patients were excluded if a stent was deployed via a dedicated microcatheter (any other catheter except the inner catheter of Surpass delivery system) to appose the SFD (the “apposing stent”). A total of 28 patients with a mean age of 48.5 ± 15.5 (range 6–84 years) were identified. The age, sex, comorbidities, aneurysm location, size of the aneurysm, platelet inhibition level, adverse events and aneurysm occlusion of these patients were analyzed.

Devices

The SFD is a recently introduced flow diverter made of a cobalt-chromium alloy with integrated platinum wires to enhance visibility. The mesh density of the device is kept constant by increasing the number of wires as the diameter of the stent increases (e.g., 72 wires in 3–4 mm vs. 96 wires in 5 mm diameter). Its porosity is similar to its counterparts, whereas its mesh density is higher with 20–32 pores/mm2. The Surpass device is preloaded at the distal end of the delivery system, which is composed of inner (pusher) and outer (delivery) catheters. The delivery system of the Surpass device is a slightly larger version of the delivery system used in the Wingspan Stent (Stryker Neurovascular, Kalamazoo, MI, USA) in which the Wingspan stent is “sandwiched” between the outer delivery catheter and the approximately 2F inner delivery catheter. The outer diameter of the outer delivery catheter is 3.9 F at the proximal end and 3.7 F at the distal end. The inner delivery catheter, which we utilized in this study for stenting, has an outer diameter of approximately 2F, an inner diameter of 0.017 inch and is advanced over 0.014 inch microwire. The Surpass device is confined between the inner and outer catheters. It is deployed by unsheathing the outer 3.7 F catheter over the inner catheter, which is kept in place on the microwire. That is, there is no distal delivery wire. The device expands and conforms to the shape of the vasculature as it exits the lumen of the outer catheter. Meanwhile, the inner catheter moves distally over the microwire which is stationary. This delivery system is unique to SFD.

The Neuroform Atlas stent (Stryker, Kalamazoo, MI, USA) is a self-expanding, open cell, nitinol stent available in 2.5–4.5 mm diameters and 15–30 mm lengths. It has three radiopaque markers on each end. The stent is preloaded on the stent delivery wire and protected by an introducer sheath. All sizes of the Atlas stent can be delivered through a microcatheter with a 0.0165-inch inner diameter.

The Acclino stent (Acandis, Pforzheim, Germany) is a self-expanding, closed cell, nitinol stent. It also has three radiopaque markers on each end and is available in 3.5, 4.5, and 6.5 mm diameters and 15–35 mm lengths. While the stents with 3.5 and 4.5 mm diameters are deliverable through microcatheters with a 0.0165-inch inner diameter, the 6.5 mm diameter stents require microcatheters with a 0.021-inch inner diameter.

Antiplatelet therapy

Unruptured patients were started on a 300 mg acetylsalicylic acid and 75 mg clopidogrel (or 10 mg prasugrel) regimen at least 5 days before the intervention. Two patients, who were treated in the subacute phase of subarachnoid hemorrhage, were given a loading dose of 300 mg clopidogrel and 300 mg of aspirin 1 day before the procedure. One patient with an iatrogenic pseudoaneurysm was administered IV tirofiban during the procedure. The infusion was continued over the next 24 h, after which the patient was loaded with 300 mg clopidogrel. All patients, including the latter three, were then kept on 75 mg clopidogrel and 300 mg aspirin per day for 6 months. After a 6-month digital subtraction angiography (DSA) patients were maintained only on acetyl salicylic acid. Platelet inhibition was verified according to institutional protocol by the VerifyNow assay (Accumetrics, San Diego, CA, USA). Six patients who were resistant to clopidogrel were instead placed on a 10 mg/day prasugrel regimen.

Endovascular procedure

All treatments were performed under general anesthesia and systemic heparinization (activated clotting time >250 s) and using biplane flat panel DSA machines (Artis Zee Siemens, Erlangen, Germany). Both two-dimensional (2D) and 3D images were used to measure the parent artery and aneurysm sizes. For all procedures, a 6 F guiding sheath and a distal access catheter (AXS Catalyst 5; Stryker, Freemont, CA, USA or Navien; ev3 Neurovascular, Irvine, CA, USA) were advanced to the target parent artery via a femoral access. After catheterization, 2–5 ml of Nimodipine (Nimotop, Bayer, Newbury, Berkshire, UK, in 50 ml saline) was infused intraarterially. The Surpass device was deployed under fluoroscopic visualization, and proper vessel apposition was assessed with angiography and if necessary, with flat detector CT with intra-arterial contrast injection [Supplementary Digital Content 1 Figures 1[Additional file 1], Figure 2[Additional file 2], Figure 3[Additional file 3], Figure 4[Additional file 4], Figure 5[Additional file 5], Figure 6[Additional file 6], Figure 7[Additional file 7]]. The Surpass device was navigated across the aneurysm neck over a 0.014 microguidewire. Once the operator decided to place a stent within the flow diverter, the system was not withdrawn and only the microwire was removed. One of the mini stents mentioned above was directly advanced within the inner delivery catheter that was already in place, with its tip distal to the flow diverter. The stent was deployed through this catheter [Figure 1 [Additional file 8], Supplemental Digital Content 2 and Video 1, Supplemental Digital Content 3]. The stent was delivered directly through the pusher (inner) catheter, without a need for performing an exchange maneuver or using another microcatheter. The mini-stents were deployed in a manner to cover the whole flow diverter so that we can obtain an enhanced opening and apposition throughout the flow diverter. At times, this was not possible because the flow diverter spanned a long segment and it was not possible cover the whole device with a single stent. In these cases, as long as one end (either distal or proximal) was secure and well apposed, we opted to deploy the mini stent to cover the other end of the device which needed to be pinned by the mini stent. Follow-up angiograms and a final flat detector computed tomography (CT) were performed 30 min after stent deployment to check vessel wall apposition, patency of the parent vessel and intraluminal thrombus formation.
Figure 1: (a) Left internal carotid artery angiogram shows a supraclinoid aneurysm. Subtracted: Native image before (b) and after (c) contrast injection following deployment of the flow diverter show that the distal landing zone of the device is shorter than the diameter of the parent artery. (Arrow indicates distal end of the flow diverter) (d) angiogram after the deployment of a stent inside flow diverter demonstrates pinning of the device to the parent artery with good wall apposition (e) flat detector computed tomography image with intra-arterial contrast administration shows good wall apposition (f) follow-up angiogram obtained 6 months after the procedure shows complete occlusion of the aneurysm

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Follow-up imaging with computer tomography or magnetic resonance angiography and clinical evaluation were performed at 1–3 months. DSA was performed at 6 months. Noninvasive imaging and clinical follow-up was repeated at 9–12 months.


  Results Top


Patient and aneurysm characteristics

There were 30 aneurysms in 28 patients. Twenty patients (71.5%) were female and 8 (28.5%) were male. The mean aneurysm size diameter was 10.2 ± 6.6 mm (range 3–30 mm). Two of the 30 aneurysms were giant (>25 mm) and 12 were large (>10 mm). Twenty-five of 30 (83.3%) aneurysms were in the anterior circulation. Of these, 15 originated from the supraclinoid segment, 6 from the cavernous segment and 3 from the ophthalmic segment and 1 from the transitional segment of the internal carotid artery (ICA). Two of the 5 posterior circulation aneurysms were in the basilar trunk, one in the basilar apex, one in the V4 segment and the other was a fusiform aneurysm extending from the V4 segment of the vertebral artery to the basilar artery. There were 23 saccular aneurysms, 5 fusiform/dissecting aneurysms, one blister aneurysm and one pseudoaneurysm secondary surgical ICA injury. Four aneurysms were recurrent. Of these, 3 had previously been treated with coiling and the other one with another flow diverter. Three of the 30 aneurysms (including one with iatrogenic pseudoaneurysm) were ruptured and treated in the subacute phase.

Procedure characteristics

Our technical success rate (deployment of the stent inside flow diverter) was 96.6% (29/30). Loading of the stent into the inner catheter at the hub required special attention as the hub was not specifically designed for the passage of stents. However, once the device passed through the hub, there was no resistance to stent navigation. The only failure was secondary to ovalization of the inner catheter at a tortuous syphon which did not allow us to push an Acclino stent further. This stent was withdrawn, the aneurysm was bypassed with an Echelon 10 microcatheter (ev3 Endovascular, Plymouth, MN, USA) and the same stent was than deployed within the flow diverter. All patients were treated with a single surpass device except one patient who needed a second device due to incomplete neck coverage with one flow diverter. In two patients for whom a 40 mm length Surpass device was used, two stents were needed since the currently available stents have maximum lengths of 30–35 mm, which were not long enough to cover the whole length of the long flow diverter. In 23 patients, Atlas stents were used, and in 5 patients, Acclino stents were used. In only three patients, intrasaccular embolization was performed during the same session of flow diverter placement.

The stent was placed through the Surpass delivery system in the following situations:

  1. The device was deployed along a fusiform or wide neck aneurysm, in which re-crossing of the freshly deployed device was deemed to be risky due to concerns related to stent migration into the aneurysm due to short landing zone [Figure 2 [Additional file 9], Supplemental Digital Content 2][11]
  2. After the device was deployed, it was realized that the proximal or distal landing zone was less than ideal, i.e., distance <6 mm or less than the diameter of the parent artery, which is not an ideal deployment [Figure 1][14],[15]
  3. The proximal or distal landing zones were around artery bends, leading to device malapposition, a situation that does not respond well to balloon angioplasty [Figure 3 [Additional file 10], Supplemental Digital Content 2][15],[16]
  4. The distal end of the device was covering the origin of an intracranial major artery barely or partially, so that further expansion and apposition of the device would also lead to further shortening and subsequently unjailing of the specific arterial branch [Figure 4 [Additional file 11], Supplemental Digital Content 2]
  5. Previously placed endovascular devices which preclude the evaluation of optimal apposition (previously placed coils or stents) [Figure 5 [Additional file 12], Supplemental Digital Content 2].[17]


In two patients minimal clot formation was noted inside the flow diverter and successfully treated with immediate administration of a glycoprotein IIb/IIIa inhibitor. In another patient, guiding sheath related minor ICA dissection occurred during the procedure and was treated with a stent. All of the patients were discharged without neurological morbidity except the patient with surgical ICA injury.

Angiographic outcome

Except one patient, all of the patients had follow-up imaging. Two patients had only CT angiographic follow-up due to their reluctance to undergo a DSA procedure. Five patients did not receive the 3-months follow-up but did undergo the DSA procedure at 6 months. One-year follow-up was not due in 8 patients.

Complete aneurysm occlusion (100%) was achieved in 18/23 (78.2%) aneurysms at 3 months, 23/28 (82.1%) aneurysms at 6 months, and 20/21 (95.2%) aneurysms at 9 months to 1-year follow-up imaging. In a single patient, we were unable to appose flow diverter completely with the stent. This was because SFD foreshortened more than we expected, the Atlas stent was immediately deployed to prevent migration; however, the flow diverter remained too short to cover the neck of the aneurysm total. Another stent was not deployed due to the risk of device prolapse into aneurysm while crossing flow diverter with a catheter it segment could not cover the proximal part of the fusiform aneurysm. The patient refused further intervention and is currently being followed by MRA at 6 months' intervals without any change in the size and configuration of the residual aneurysm [Figure 2], Supplemental Digital Content 2].

No significant (≥50%) stenosis within the flow diverter or fish mouthing of the device was seen. None of the patients were retreated.

Complications

None of the patients had clinically significant thromboembolic or hemorrhagic complications after discharge. The patient with iatrogenic pseudoaneurysm was brought directly to the angiography suite from the operating room where she was having a transsphenoidal surgery. The patient had a lacerated ICA for which endovascular treatment was performed. After treatment and past the acute period, the patient underwent multiple transsphenoidal surgeries due to extensive involvement of the skull base with carcinoma. The patient died 53 days after the endovascular procedure secondary to postoperative sepsis. Otherwise, there were no permanent morbidity, mortality, or bleeding complications.


  Discussion Top


Flow diversion is an effective method for endovascular treatment of intracranial aneurysms. However, flow diversion does not lead to immediate aneurysmal occlusion and complete aneurysm occlusion rates at 6 months and 1 year are about 75%–85%.[1],[2],[4],[5],[18],[19] Residual aneurysms treated with flow diverters are still at a risk of rupture. Although the risk is, in general, small, it may be significant if there is residual opacification of the aneurysm dome on follow-up imaging.[20]

The factors involved in residual aneurysmal filling after flow diversion include malapposition,[21],[22],[23],[24],[25],[26] aneurysm size,[27] length of transition zone [28] and possibly strut thickness.[29] In a recently published animal study, apposition was more important than pore density as a predictor of aneurysm occlusion after flow diversion.[30] These data are clinically supported by the SCENT study which is a multi-center, prospective, non-randomized clinical study performed in 213 subjects. In this study, the total occlusion and residual aneurysm rates (Raymond-Roy grade 1 and 3) for optimally apposed and malapposed devices-based on core laboratory evaluation-were 79.2 versus 50% and 9.6 versus 41.2%.[26] This very striking difference shows the fundamental role of better apposition in the efficacy of the flow diverters. Suboptimal device apposition is not infrequent with braided devices at arterial bends, which leads to insufficient support and intimal overgrowth of the aneurysm neck due to lower metallic coverage.[16],[31] Apposition is critical not only for occlusion rates, but it also decreases that the rate of thromboembolic complications.[7],[14],[21] Incomplete apposition of the flow diverter to the vessel wall may cause distal embolic complications or delayed occlusions, even if the stenosis is not flow limiting.[14],[21] Six of the 7 malapposed flow diverters showed parent artery occlusion in a previous study [4] and in another experimental comparative study, correction of flow diverter malapposition in rabbits resulted in a statistically significant improvement in aneurysm occlusion rates.[21] It was also shown that incomplete stent apposition to the arterial wall can delay endothelial coverage of stent struts.[32],[33] However, even after balloon angioplasty of flow diverters, there may be residual malapposition,[10] which may be present in up to 1/3 of cases and may be detectable only with advanced imaging such as optical coherence tomography.[21] Although routine angioplasty of flow diverters may be considered given the difficulties of delineating all of the malappositions, animal research has shown that angioplasty in a properly apposed flow diverter may lead to malapposition and thus may be detrimental.[21] Balloon angioplasty of the flow diverter was also shown to cause microthrombi formation along the device as well as distal embolization, and it may lead to excessive flow diverter shortening with consequent migration of the device into the aneurysm.[15],[34] Finally, balloon angioplasty may not be effective for apposition of flow diverters when landing zones are at arterial bends.[17]

The EFT technique we describe is unique to the SFD, which tends to demonstrate a higher rate of malapposition at the expense of a high mesh density and a subsequent high rate of aneurysm occlusion.[35] The rate of use of adjunctive devices for better placement or apposition of the Surpass device was reported to be as high as 42% in the literature.[35] This possibly relates to the relatively bulky delivery system and the relatively stiffer device, which may result in intraprocedural findings-as listed above-that may necessitate the use of a stent or other adjunctive devices. The advantage of our technique is that it is quick and easy to perform and at least in our series, it did not result in neurologic morbidity. Our method has some technical advantages. First, it precludes the need to re-cross the flow diverter, which can potentially cause foreshortening or migration. Furthermore, especially if a larger stent is to be used to salvage device prolapse or foreshortening, an exchange maneuver will be needed for the larger microcatheters dedicated to these stents, increasing the risk of distal wire perforation. It is straightforward since the 2F inner catheter is already distal to the SFD once the device is deployed and the stent is deployed directly through this inner catheter, in a single step. This is associated with a decrease in the fluoroscopy time and the overall procedure time compared to placement of a balloon catheter or another flow diverter for better flow diverter apposition. Finally, placement of a laser cut stent also precludes fish-mouth formation during follow-up, which is a drawback, exclusively of the braided stent design.

The 5 conditions that prompted us to use EFT, as listed in the previous section, generally apply to large and fusiform aneurysms and to those aneurysms located close to arterial bends (e.g., carotid siphon). Such aneurysms tend to be complex aneurysms. Small aneurysms located on relatively straight segments are less likely to need EFT.

Laser-cut mini stents have a higher radial force compared to flow diverters and consequently enable better flow diverter wall apposition.[10],[15] We speculate that this translated into a higher occlusion rate in our series. Complete occlusion rates of commonly used flow diverters are reported to be around 66.6%–75% at 6 months.[1],[3],[4],[5],[6] Our technique was associated with a complete occlusion rate of 82.1% at 6 months and 95.2% at 9–12 months. Only one patient had residual filling at the end of 1 year due to suboptimal deployment of the flow diverter. Since the flow diverter foreshortened much more than we expected, the fusiform aneurysm remained only partially covered by the FD in its proximal segment. In the single case of failure of EFT, we tried to use an Acclino stent. None of those we treated with the Atlas stent resulted in failure. This may be due to the better flexibility of the latter stent.[36] In addition, due to the open-cell design of this stent, we believe it results in better wall apposition.

There are some drawbacks of this technique and we suggest that it should be limited only to those cases that need further endovascular manipulation to address an existing or potential problem with the deployment or apposition of the SFD such as those listed above in the previous section. The major disadvantages of the technique are cost and placement of an additional metallic device in the intracranial arteries that may become an issue in patients with recent subarachnoid hemorrhage. Cost is certainly an important issue when we compare the cost of a case treated with straightforward flow diversion to a case treated with EFT. However, this technique compares well with other adjunctive methods used for flow diversion. For instance, some authors prefer to perform coiling of the aneurysm sac to achieve occlusion rates as high as ours. Dense coiling is associated with increased cost and may also be associated with thrombus migration, occlusion of the flow diverter or mass effect.[37] In addition, some practitioners prefer to place telescopic flow diverters. A systematic review of flow diversion for intracranial aneurysms revealed that more than one diverter was used in 27% of the cases.[38] Similarly, in the PUFS trial, the number of flow diverters placed per aneurysm was three.[5] In another study using a single type of flow diverter, 63 of 77 aneurysms were treated with multiple flow diverters.[4] The mini-stents were used in this study are cheaper than flow diverters so the cost increase in our technique appears acceptable in comparison to telescoping flow diverters. The cost increase related to EFT is higher than balloon angioplasty which was used in as much as 42% of the cases in a recent study.[35] On the other hand, as discussed in detail above, balloon angioplasty is not an ideal a solution in situations for which this technique was used. As for the issue of increase the metallic ratio of the scaffold, it is probable that in patients with subarachnoid hemorrhage, additional placement of the stent may exacerbate a thrombotic event. In such cases, potential benefits and side effects of EFT should be considered in detail.

This study has a number of limitations. It is a retrospective study with a relatively small number of patients. In addition, due to the absence of a control arm, we certainly favor the use of this technique in selected situations, as listed in the results section, rather than routinely. Finally, neither the mini stents we used, nor the delivery system of the flow diverter is approved for this technique. Thus, the technique is an off-label use for both of these devices.


  Conclusion Top


The use of the inner catheter of the SFD to deploy laser cut stents to enhance wall apposition of this device was associated with a high and relatively early complete occlusion of the aneurysms. This EFT was simple to perform, safe and effective in our series. Although this technique may be used to improve the results of the Surpass device in selected situations, routine use of this technique cannot be recommended based on this study. We suggest that its use should be limited to those cases with imminent or potential problems related to the deployment or apposition of the SFD.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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