Abstract Flow diverting devices (FDDs) have revolutionized the treatment of morphologically complex intracranial aneurysms such as wide-necked, giant, or fusiform aneurysms. Although FDDs are extremely effective, they carry a small yet significant risk of intraprocedural complications. As the implementation of these devices increases, the ability to predict and rapidly treat complications, especially those that are iatrogenic or intraprocedural in nature, is becoming increasingly more necessary. Our objective in this paper is to provide a descriptive summary of the various types of intraprocedural complications that may occur during FDDs deployment and how they may best be treated. A systematic and qualitative review of the literature was conducted using electronic databases MEDLINE and Google Scholar. Searches consisted of Boolean operators “AND” and “OR” for the following terms in different combinations: “aneurysm,” “endovascular,” “flow diverter,” “intracranial,” and “pipeline.” A total of 94 papers were included in our analysis; approximately 87 of these papers dealt with periprocedural endovascular (mainly related to FDDs) complications and their treatment; 7 studies concerned background material. The main categories of periprocedural complications encountered during deployment of FDDs are failure of occlusion, parent vessel injury and/or rupture, spontaneous intraparenchymal hemorrhage, migration or malposition of the FDDs, thromboembolic or ischemic events, and side branch occlusion Periprocedural complications occur mainly due to thromboembolic events or mechanical issues related to device deployment and placement. With increasing use and expanding versatility of FDDs, the understanding of these complications is vital in order to effectively manage such situations in a timely manner. Flow diverting devices, Pipeline, Aneurysms, Complications, Parent vessel ABBREVIATIONS ABBREVIATIONS CCF carotid cavernous fistula DIC distal intermediate catheter FDD flow diverting device ICA internal carotid artery ICH intracranial haemorrhage IPH intraparenchymal haemorrhage MCA middle cerebral artery PED Pipeline Embolization Device PITA Pipeline for the Intracranial Treatment of Aneurysm PFT platelet function testing Flow diverting devices (FDDs) have revolutionized the treatment of morphologically complex intracranial aneurysms such as wide-necked, giant, or fusiform aneurysms.1-3 Although alternative techniques for treating complex intracranial aneurysms such as balloon-assisted coiling and stent-assisted coiling have traditionally been employed, efficacy rates are lower than expected and recanalization rates tend to be relatively high.4-7 FDDs have the benefit of carrying minimal risk of aneurysm recurrence and have overall morbidity and mortality complication rates that are comparable to existing endovascular strategies.2,8 Flow diversion has typically been utilized to treat large or giant-necked intracranial aneurysms but recently has been used for several “off-label” purposes such as blister aneurysms and fusiform aneurysms.9 FDDs work primarily on 2 principles: (1) reduction of flow into the aneurysmal sac leading to thrombosis and (2) provision of a scaffold to promote neo-intimal growth and parent vessel reconstruction.10-12 Over 6 to 12 mo, aneurysmal thrombosis and progressive endothelialization will result in shrinkage/collapse of the aneurysm and reconstruction of the parent vessel.2,13-15 Although FDDs are extremely valuable in treating morphologically complex aneurysms, they carry a small yet significant risk of intraprocedural complication and require a skilled operator for safe deployment. As these devices are increasingly used, the ability to predict and rapidly treat complications is vital, especially those that are iatrogenic or intraprocedural in nature. Our primary purpose in this paper is to provide a descriptive summary of the various types of intraprocedural complications that may occur and how they may best be treated. METHODS A systematic and qualitative review of the literature for pertinent peer-reviewed articles was completed. Electronic databases MEDLINE and Google Scholar were surveyed using Boolean operators “AND” and “OR” for the following search terms in different combinations: “aneurysm,” “endovascular,” “flow diverter,” “intracranial,” and “pipeline.” Query methodology and results (including article title, abstract, full text, bibliographies, and articles citing them) were comprehensively reviewed by 3 authors. Any case reports, case series, observational cohorts, or clinical trials were included if they pertained to complications of FDD deployment or management of FDDs deployment-related complications in any form. Articles addressing usage of FDDs in any condition besides intracranial aneurysms were excluded. Additionally, articles concerning subsequent postprocedural events such as intraparenchymal hemorrhage (IPH), delayed aneurysmal rupture, and nonocclusion were excluded. Potential disputes concerning article selection were resolved by conference of the 3 authors with final arbitration authority being held by the senior author. RESULTS A total of 94 papers were included in our analysis; approximately 87 of these papers dealt with periprocedural endovascular (mainly related to FDDs) complications and their treatment. Seven of the studies concerned background material and are ancillary to explaining points made in the paper. Periprocedural complications of FDD deployment may increase morbidity and must be prevented when possible and detected/rapidly managed if they occur. The main categories of periprocedural complications may be grouped into failure of occlusion, parent vessel injury (including both perforation and arterial dissection), IPH, migration or malposition of the FDD, thromboembolic or ischemic events, and side branch occlusion. Failure of Occlusion Failure of aneurysm occlusion following FDD deployment has been reported to occur in approximately 20% of cases.16-18 Several reasons have been hypothesized for the observed failure of occlusion by FDDs. In a study examining factors related to occlusion failure of Pipeline Embolization Devices (PEDs; ev3/Chestnut Medical, Medtronic Inc, Dublin, Ireland), Shapiro et al18 found that fusiform aneurysm morphology, decreasing dome-neck ratio, and the presence of a preexisting stent were statistically significantly associated with failure of aneurysm occlusion. Additionally, other postulated contributing mechanisms of nonocclusion include device malapposition to the parent vessel wall, inadequate coverage of the aneurysm neck, and incorporation of a branch vessel into the aneurysm fundus. Another potential contributing factor of failure of occlusion by FDDs is the presence of the target aneurysm in a persistent fetal type posterior communicating artery.17 In the case of failure of occlusion, endosaccular treatment options are limited by the presence of the FDD; a second FDD may be deployed or surgical clipping may be necessary.19 Parent Vessel Injury—Intracranial Hemorrhage Due to Vessel Perforation Intracranial hemorrhage (ICH) has been reported in approximately 2% of cases secondary to either vessel perforation or balloon remodeling of incompletely expanded FDD. Clinical consequences range from mild to disastrous depending on the nature of the injury. Arterial perforation and parent artery injury during FDD deployment generally have superior outcomes compared to vascular ruptures during attempted angioplasty of incompletely expanded devices.13,20-23 Arterial perforation may be best avoided by gentle intra-arterial manipulation of the FDD and vigilance in avoiding placing the distal tip of the delivery wire into angulated and/or small vessels.24 In cases of cavernous or paraclinoid internal carotid artery (ICA) aneurysms, several operators choose to initially unsheath the FDD in the distal middle cerebral artery, thus avoiding inadvertent penetration of middle cerebral artery (MCA) lenticulostriate perforators or more proximal branches by the distal tip of the delivery wire. The FDD is then retracted proximally into the landing zone for ultimate deployment. A balloon test occlusion may be warranted prior to attempted deployment of an FDD if intraprocedural difficulties are expected based on vascular anatomy.25 Rapid discernment and management of arterial perforation is essential to minimize damage. Arterial perforation may be detected by the prototypical signs of acute ICH, such as an abrupt increase in intracranial pressure, or a sudden rise in systemic blood pressure with simultaneous bradycardia. Following the perforation, the minimum number of angiographic runs necessary should be performed to confirm extravasation of contrast as well as location of the perforation; any excess runs may waste crucial time and lead to excess deposition of contrast material in the subarachnoid space.26 In the event of iatrogenic ICH, neutralization of heparin effect is achieved with a dose of 1 mg protamine sulfate/100 units of heparin. Because of the relatively short half-life of intravenously administered heparin (approximately 30 to 60 min), the dose of protamine sulfate is calculated by estimating the amount of heparin remaining in the plasma at the time that reversal is required. If more than 30 min have elapsed since the administration of heparin, 0.5 mg intravenous protamine sulfate per 100 units of heparin should be given.26 Antiplatelet medications may be countered with platelet transfusions and strict control of blood pressure is advised.27 In the De Vries et al21 case study of 37 patients using the Surpass Flow Diverter (Stryker Neurovascular, Kalamazoo, Michigan), an isolated case of a wire perforation in the MCA prior to FDD deployment resulted in a subarachnoid hemorrhage.21 The patient was successfully managed with reversal of antiplatelet agents and heparin, and subsequently suffered no clinical sequelae.21 The aforementioned conservative therapies may be sufficient if the perforation is relatively small and the FDD has not yet been deployed. If clinical evidence of elevated intracranial pressure manifests, this should be managed rapidly with surgical intervention such as ventriculostomy and placement of an external ventricular drain or decompressive hemicraniectomy. Additionally, proper sedation and concurrent burst suppression may lower intracranial pressure, prevent seizures, and reduce the cerebral metabolic demand for oxygen.28 In certain scenarios, particularly in perforation of the aneurysm itself, some neurointerventionalists recommend leaving the perforating device in place as it may prevent further extravasation from the puncture site, and may actually cause more damage upon withdrawal.26 As a temporizing measure, an endovascular balloon may be prepared and inflated within the target vessel to stop the extravasation. In cases of perforated aneurysms, a second microcatheter may be utilized to treat the ruptured aneurysm, if the FDD has not yet excluded endosaccular access to the aneurysm, while the first microcatheter remains in place.29 Parent artery sacrifice generally is only considered as a last resort, with clinical outcome being determined by the affected vessel and the presence of collateral vascular supply to the affected area. Penetration of the distal MCA by the distal wire tip during deployment of a Silk Flow Diverter (Balt Extrusion, Montmorency, France) was reported in 1 case out of a series by Pistocchi et al.22 Immediate occlusion of the injured parent artery via coil embolization was accomplished without resulting adverse clinical consequences. Sometimes, open surgical intervention may be required. Out of 31 patients treated in the Pipeline for the Intracranial Treatment of Aneurysms (PITA) trial, Nelson et al13 reported a case of vascular rupture that required open surgical intervention; an attempt to use angioplasty to increase flow in an unsuccessfully deployed PED (ev3/Chestnut Medical, Medtronic Inc) resulted in rupture of the ICA, requiring surgical ligation and resulting in an extensive left hemispheric infarct.13,30 Parent Vessel Injury—Carotid Cavernous Fistula Due to Vessel Perforation If the lesion being treated involves the cavernous ICA, deployment of the FDD and subsequent vessel damage could result in the development of a direct carotid cavernous fistula (CCF). Although uncommon, spontaneous development of a direct CCF following deployment of an FDD has been reported in both acute and subacute timeframes. Treatment of a CCF resulting from FDD deployment could be accomplished via transvenous embolization, parent artery sacrifice, or operative methods such as surgical ligation. Transarterial embolization techniques in the context of a direct CCF resulting from FDD deployment tend to be of limited efficacy because the physical obstruction of the device restricts access to the area via catheter. In a few cases, further use of flow diversion has been employed successfully, mostly combined with the concomitant use of transvenous embolization.30-35 Currently, evidence is lacking to support an optimal course of treatment of direct CCFs related to FDD deployment. Balloon test occlusion of the ipsilateral ICA should be considered in preparing a treatment plan. Following balloon test occlusion, other techniques such as tranvenous treatment, parent artery sacrifice, surgical ligation, and perhaps even further flow diversion should be considered. Parent Vessel Injury—Arterial Dissection Arterial dissection is another type of vessel injury that may occur due to deployment of an FDD. In a study of the Surpass Flow Diverter (Stryker Neurovascular), De Vries et al21 reported 2 iatrogenic cervical ICA dissections. Further flow diversion was used to treat 1 of these cases; however, the other ICA dissection was missed during the procedure and eventually became occluded.21 Spontaneous intracranial arterial dissections are typically managed with antiplatelet therapy and in the majority of cases, do not lead to strokes.36,37 Although a general consensus on treatment of dissection caused by FDDs has not been established, the use of FDDs to treat these dissections should be given consideration. FDD use in intracranial aneurysmal dissections has been shown to be efficacious in several studies and is becoming increasingly popular.38 Until more definitive data regarding the efficacy of FDD treatment in arterial dissection are published, these FDD-induced dissections should be treated based on displayed symptoms, historical data, the degree of stenosis, operator preference, as well as other relevant factors. Hemorrhagic Complications IPH can follow deployment of an FDD. This complication is poorly understood, but when IPH does arise, it usually happens within a week of FDD deployment, ipsilateral to the FDD, though usually remote to the FDD.39,40 The rate at which these complications occur is less than 10%, and the prognosis of this complication varies widely, ranging from favorable to death.39,41-43 While the pathophysiology of this complication is not well understood, some causes and associations have been identified. One potential cause of IPH following FDD deployment is the embolization of foreign materials.44,45 A genetic component may be implicated; 1 study found that the development of IPH was associated with the degree to which patients respond to P2Y12 receptor antagonists, such as clopidogrel.46 Cruz et al39 proposed that the vascular reconstruction following FDD placement eventually reduces arterial compliance. However, the imaging required to test this hypothesis is not yet available.39 Treatment for IPH specifically following FDD deployment has not been established, but as with all cases of IPH, treatment is usually supportive. Maldeployment of FDDs: Incomplete Expansion, Migration, and Prolapse Deployment of an FDD necessitates a sequence of maneuvers to properly implant the device into a vessel.47 Learning these maneuvers typically takes 35 to 40 cases, during which time the risk for specific mechanical complications associated with deployment may be increased. These complications include suboptimal deployment and overt technical failure. Even under the best circumstances, FDDs often have a higher risk of failure during deployment than traditional self-expanding devices because of an expected foreshortening that occurs during deployment. When combined with the difficult or tortuous vascular anatomy that FDDs are typically employed in treating, this foreshortening often results in an increased risk of device failure. The 2 most common technical events reported with Flow Diverting Devices are suboptimal or incomplete device expansion and proximal device migration.15,20,25,35,47-52 Another less common adverse technical event reported is prolapse of an FDD into the aneurysm sac.23,48,50,53 Operators should be familiar with these common intraprocedural technical events as well as the appropriate corrective maneuvers to remediate them. In some cases, rapid and inventive action may be required to correct them.54 To achieve the best results, the following criteria should be considered in selecting an FDD: (1) the diameter of the selected FDD should match the diameter of the proximal parent vessel; (2) due to an anticipated foreshortening of approximately 50% to 60% (depending on the nominal expanded FDD size and parent vessel diameter), the length of the FDD should be at least 6 mm longer than the aneurysm neck; (3) 2 to 3 mm of the device should cover the proximal and distal ends of the parent artery surrounding the treated lesion, preferably in a straight segment to better anchor the device. Anticipation of foreshortening of an FDD may lead to avoidance of maldeployment complications, and is important for the operator to be aware of. Foreshortening of an FDD is highly dependent on the nominal size of the FDD relative to the diameter of the parent vessel. A sizing mismatch between the FDD and the parent vessel invariably leads to substantial heterogeneity in metal coverage, porosity across the aneurysm neck, and the amount of foreshortening of the FDD.55 This factor has led to the purposeful selection of oversized FDD in cases where decreased flow diversion across perforator vessels is desired, such as in cases of fusiform basilar artery aneurysms.56 Because an FDD is typically deployed from distally to proximally, if the distal end fails to expand, the entire catheter and delivery system may be removed as a single element. If, however, the device is fully unsheathed and the proximal end fails to expand the device that cannot be easily removed, other steps must be taken to ensure complete proximal expansion. A technique known as “wagging” in which the microcatheter and delivery wire together are advanced and withdrawn may aid in device deployment around arterial curvatures. Additionally, bumping the proximal end of the FDD with a microcatheter after deployment may induce further expansion.57 Another maneuver that can aid in completing device expansion is pushing a microwire with a J-tip through the FDD. Though potentially helpful, execution of these auxiliary procedures is not without risk, and may incur vascular injury or foreshortening/migration of the FDD.25,47,51,54,58 Normal deployment, expansion, and apposition to the vessel of an FDD are linked to the distal/forward movement of the coil tip and delivery wire. If the delivery wire or coil tip cannot move forward due to anatomical or mechanical problems, the FDD may become stretched and may even completely fail to deploy. In such cases, a technique described by Lin et al47 involving unsheathing the FDD in a distal intermediate catheter (DIC) may be utilized.47 This technique involves first passing a DIC over the microcatheter up until the unopened portion of the FDD. The delivery wire is subsequently completely unsheathed within the DIC, releasing the FDD from the delivery wire. A line diagram representation of the technique is depicted in Figure. Thereafter, the FDD may be completely unsheathed independently from the delivery wire via wagging of the DIC and microcatheter back and forth.47 FIGURE. View largeDownload slide Diagram of the technique described by Lin et al47—deployment of the FDD in a DIC. A, Initial partial deployment of the FDD through the delivery Marksman catheter (Penumbra, Alameda, California). A distal obstruction blocks distal movement of the delivery wire. B, A Navien (Covidien Vascular Therapies, Mansfield, Massachusetts) DIC is advanced over the Marksman catheter up until the portion of deployed FDD. C, The FDD is unsheathed within the Navien DIC by pulling the Marksman backwards. D, With the FDD fully unsheathed, the delivery wire may be withdrawn. The FDD may now be fully deployed with the Marksman acting as the “pusher,” with a “wagging” motion back and forth to enhance unsheathing. FIGURE. View largeDownload slide Diagram of the technique described by Lin et al47—deployment of the FDD in a DIC. A, Initial partial deployment of the FDD through the delivery Marksman catheter (Penumbra, Alameda, California). A distal obstruction blocks distal movement of the delivery wire. B, A Navien (Covidien Vascular Therapies, Mansfield, Massachusetts) DIC is advanced over the Marksman catheter up until the portion of deployed FDD. C, The FDD is unsheathed within the Navien DIC by pulling the Marksman backwards. D, With the FDD fully unsheathed, the delivery wire may be withdrawn. The FDD may now be fully deployed with the Marksman acting as the “pusher,” with a “wagging” motion back and forth to enhance unsheathing. If the previously mentioned techniques of “wagging,” bumping, or intra-DIC deployment result in inadequate expansion of the FDD, balloon angioplasty may be utilized. Balloon angioplasty for suboptimally expanded PEDs (ev3/Chestnut Medical, Medtronic Inc) has been cited as being successfully used in “a few instances” in the Pipeline for Uncoilable or Failed Aneurysms study by Becske et al.15 Use of balloon angioplasty was also cited as being used by Burrows et al20 in 2 patients with incompletely expanded PEDs (ev3, Medtronic Inc) as well as in a prospective study by McAuliffe et al.35 Despite the existing evidence for balloon angioplasty's success in the literature, caution should be used in executing this technique as it bears a risk of vessel rupture, thrombosis, and possibly device migration and/or prolapse.24,59,60 When utilizing balloon angioplasty, it is recommended that the balloon be placed entirely inside the device when inflated rather than just the proximal portion as an increased chance of arterial injury exists in the latter scenario.24 In 1 case, balloon angioplasty of the proximal portion of a Silk FDD (Balt Extrusion) that had been deployed through a previously implanted Solitaire AB stent (Covidien, Medtronic Inc) resulted in rupture of the parent artery (the MCA) and ultimately fatal hemorrhage.23 In cases where anterograde access through the ICA to a constricted FDD is not possible, retrograde access has been shown to be feasible. Navarro described a case in which a PED (ev3, Medtronic Inc) failed to expand and was accessed in a retrograde fashion with an Excelsior SL-10 microcatheter (Stryker Neurovascular) via the contralateral anterior communicating artery. Balloon angioplasty was undertaken with a Hyperform balloon (ev3, Medtronic Inc) and was utilized to successfully expand the PED.25 Proximal or distal device migration with or without concurrent prolapse is another common adverse technical event. In a case review by Burrows et al,20 proximal device (PED, ev3, Medtronic Inc) prolapse occurred 12 times out of 100 cases and was cited as the most common adverse event in the review.20 Two cases of device (PED, ev3, Medtronic Inc) migration were also seen in a prospective study of 54 patients by McAuliffe et al.35 Device migration may not always be deleterious if the aneurysm neck is still covered well enough. More problematic is the possibility of distal prolapse into the aneurysm neck, directing flow into the aneurysm dome and increasing the chance of rupture. Device migration may be caused by several factors, which include but are not limited to (1) greater foreshortening than expected, resulting in shrinkage and the so called “accordion effect”; (2) vertical positioning in the ICA may result in gravitational forces pulling the device downward; (3) wide differences between the diameter of inflow and outflow vessels at the proximal and distal ends of the FDD may cause a squeezing force distal to the FDD and push the device backwards (ie “watermelon seeding effect”;61 (4) possible displacement during re-navigation of the FDD after failure to recapture the delivery wire;62 (5) deformation and twisting of the FDD, a phenomenon of a device that was possibly stretched, particularly during deployment around severely tortuous curvatures. The PED is particularly vulnerable to the phenomenon of spontaneous migration and deformity because it is a low-porosity stent, which facilitates the transmission of a force exerted at one end of the device to the other end.61 Management of FDD migration, prolapse, foreshortening, and/or deformity may be accomplished using additional devices to complete coverage of the aneurysm neck and divert blood flow away from the aneurysmal sac. Many of the following techniques may be necessary for initial access in implantation of an FDD; however, we also discuss them here because comprehension of these techniques is very important in the intraprocedural salvage of a migrated FDD, especially if migration diverts flow toward the aneurysm sac. A J-shaped guidewire can be passed through a migrated device into the distal ICA and further FDD deployment may be used to cover the aneurysm neck and complete parent vessel reconstruction.61 When FDD migration occurs intraprocedurally and multiple FDDs are being utilized, it is critical to retain distal access until the parent vessel has been fully reconstructed. While greatly desired, the direct path across the aneurysm neck may not always be achievable, particularly in the case of a giant intracranial aneurysm. In these scenarios, “traversing the dome” (threading the microcatheter into the aneurysm sac) can be helpful in attaining a foothold in the distal parent artery of the aneurysm.59 In this technique, a microwire is threaded into the aneurysmal sac, traversing the interior of the sac, and then out of the sac far into a distal vessel, followed by the tracking of the microcatheter over the wire. Thereafter, the microwire is retracted just proximal to the aneurysm loop and the microcatheter is pulled backward, causing the loop of microcatheter to straighten out. After the loop has been removed from within the aneurysm, and a distal foothold has been obtained, the desired FDD may be easily deployed. If the microcatheter within the aneurysmal sac cannot be unlooped despite being advanced quite far into a distal artery, an anchor technique with balloons and/or retrievable stents may be used to secure the distal end of the microcatheter. A Solitaire FR stentriever (ev3, Medtronic Inc) or a Hyperglide angioplasty balloon (ev3, Medtronic Inc) can be tracked within the microcatheter until it is distal to the aneurysm neck. The balloon or stentriever can then be deployed, anchoring the distal portion of the microcatheter and allowing for retraction and unlooping of the looped portion of the microcatheter without loss of distal arterial access.63,64 If the proximal portion of an FDD has migrated into the aneurysmal sac and cannot be recatheterized using an anterograde approach, a retrograde or “transcirculation rescue” approach may be attempted utilizing the contralateral anterior communicating artery or the basilar artery through the posterior communicating artery.53,61 A microwire more proximally in the parent vessel or in the aneurysm is then locked by a snare loop so that the microcatheter can regain access to the distal vessel through “flossing.” Additional devices can then be deployed. When an FDD has migrated and is unable to be repositioned, it may need to be removed to avoid obstruction of parent vessel flow. Recent release of the second-generation PED, named Pipeline Flex (ev3/Covidien, Medtronic Inc), has made removal largely unnecessary as the proximal end is positioned on a pad that allows for resheathing of the device when it is up to 90% deployed. Despite the advances with the PFED’s resheathability, understanding other removal techniques is important as many other devices do not have this inherent capability. Two primary techniques exist for removal of a partially deployed device (a fully deployed one may not be removed) that are known as “corking” and “pseudo-corking.” In the technique known as “corking” the pusher wire is withdrawn until the protective/capture coil engages the proximal portion of the FDD still within the microcatheter and traps it against the wall of the microcatheter. The microcatheter, pusher wire, and FDD then may be removed as a single unit.65 One potential problem with this approach is that if a majority of the FDD has already been deployed, the friction of the vessel wall against the device may cause excess traction on the pusher wire and result in its fracture. In the event of a fractured pusher wire, the technique known as pseudo-corking may be used. A DIC is advanced over the microcatheter containing the partially deployed FDD until the tips are aligned as to provide maximum support. The microcatheter is then pushed forward forcefully to “jam” into the proximal end of the partially deployed FDD. The microcatheter (and now frictionally attached FDD) is withdrawn into the DIC and then the entire entity is removed as a single unit.47,66 In last resorts, if tolerated, parent vessel sacrifice or surgical ligation may be an auxiliary treatment strategy in FDD migration. Thromboembolic and Ischemic Complications Symptomatic thromboembolic and ischemic complications in association with flow diversion have been reported as occurring at a rate of 2% to 8% and include intradevice thrombosis and large vessel, perforator, or side branch occlusion.15,20,41,67-69 These rates are similar to the thromboembolic complication rates experienced with coil embolization.70-72 Several strategies may be used to prevent thromboembolic and ischemic complications. Patients must be treated with dual-antiplatelet therapy when having an FDD implanted, which is not difficult due to the elective or semi-elective nature of the procedure. This factor predominantly limits use of FDD in the treatment of ruptured intracranial aneurysms.1 The continued usage of dual-antiplatelet therapy is based on the protocols of the original prospective studies in which FDDs were first clinically tested (Pipeline for Uncoilable or Failed Aneurysms [PUFS] and Pipeline Embolization Device for the Intracranial Treatment of Aneurysms [PITA]) trials.13,15 Recent data from a study on flow diversion in patients on dual-antiplatelet therapy (Aspirin 325 + Plavix [Bristol-Myers Squibb/Sanofi Pharmaceuticals, Bridgewater, New Jersey] 75 mg daily) who were Plavix hyporesponders (Platelet Reactivity Units [PRU] ≥ 200) found an 8% rate of transient neurological deficit in patients, but no permanent neurological deficit.73 This finding suggests that requirements for stringent dual-antiplatelet therapy may be exaggerated. Additionally, new innovations such as flow diverters with a phosphorylcholine coating (Shield Technology by Medtronic Inc) decrease thrombogenicity and may modify the requirement for dual-antiplatelet therapy in the future.74 Platelet function testing (PFT) prior to deployment of an FDD remains controversial; there are numerous conflicting studies supporting and disputing its efficacy.75 More definitive evidence is required to draw conclusions concerning the clinical utility of PFT prior to FDD. In addition to dual-antiplatelet therapy, angiography should be performed regularly to check for patency of the parent artery, device, and perforator side branches. Lastly, intraprocedural use of heparinization and the ready availability of glycoprotein IIb/IIIa receptor antagonists are crucial. In the event that a periprocedural thrombus forms in an FDD, 2 main strategies may be used: chemical thrombolysis and mechanical thrombectomy. Conservative measures such as blood pressure elevation and intravascular volume expansion that have long been the standard for treating periprocedural thromboembolic complications may be implemented alongside chemical and mechanical clot disruption.76,77 Intraprocedural thrombosis, whether within a newly positioned FDD or within a vessel proximal or distal to the FDD, must be recognized and managed in a timely manner. Acute thrombosis may initially present as a focus of diminished opacification, which may progressively increase in size or prominence on subsequent angiograms. Other early angiographic signs of acute in-device thrombus formation include progressive stagnation of blood flow in covered side branches, occlusion of covered side branches, excessive stagnation of blood flow in the target aneurysm, as well as occlusion of the target aneurysm.78 In any case where acute thrombus formation is recognized and treated, strict radiographic follow-up is necessary in order to confirm subsequent resolution. Some authors have suggested repeating serial angiograms every 10 min until angiographic resolution of thrombus is comfortably obtained. Due to the platelet-rich nature of acute thrombi (also known as “white thrombi”), antiplatelet medications tend to be better suited for intraprocedural thrombus treatment than fibrinolytics.79,80 These medications are robust inhibitors of platelet aggregation and cross-linking and thus are particularly appropriate for periprocedural thrombus disruption. The 3 currently FDA-approved glycoprotein IIb/IIIa receptor antagonists are abciximab (ReoPro, Ely Lily, Indianapolis, Indiana), epitifibatide (Integrilin, Millenium Pharmaceuticals, Cambridge, Massachusetts), and tirofiban (Aggrastat, Medicure Pharma, Somerset, New Jersey). Abciximab is the most widely reported of the 3 to be used for neuroendovascular thromboembolic rescue therapy intraprocedurally.20,21 Abciximab may be administered either intravenously or intra-arterially, beginning with a rapid bolus at a weight-based dose of 0.25 mg/kg, followed by a continuous maintenance infusion of 125 μg/kg/min (to a maximum of 10 mg/min) for 12 h.81 In a small retrospectively reviewed series of cases, Song et al79 noted enhanced thrombolysis when abciximab was delivered intra-arterially rather than when it was administered intravenously. Considering these data and our own clinical experience, we concur with these results and recommend delivery of abciximab intra-aterially via catheter at or within an obstructing thrombus.24 The 2 main complications associated with administration of abciximab are thrombocytopenia and paradoxical drug-induced platelet activation. Paradoxical drug-induced platelet activation carries an associated risk of thromboembolic complications and may be seen when lower than adequate levels of platelet inhibition have been achieved.82 To reduce this risk, partial dosing of abciximab should be avoided. Because thrombocytopenia is a complication of abciximab administration, careful monitoring of platelet levels should be undertaken before and after use.83 Another risk associated with abciximab and all other GP IIb/IIIa inhibitors is ICH, especially in patients undergoing endovascular treatment of ruptured aneurysms.84 Inhibition of platelets following abciximab may persist for days following administration, but may be promptly reversed by platelet transfusion. This reversibility may explain abciximab's relative preference by clinicians in the setting of neuroendovascular procedures.85 Epitifibatide and tirofiban are GP IIb/IIIa inhibitors that may be used alternatively to abciximab. Both have relatively short durations of action, with epitifibatide having a half-life of 2 to 4 h and tirofiban having one of 1.5 to 2 h. Epitifibatide and tirofiban are cleared renally and in nonrenally impaired patients, the platelet inhibitory effects of the drugs should be insignificant several hours after infusion discontinuation.85 If patients are renally impaired, doses must be adjusted.83 One disadvantage of using eptifibatide and tirofiban is that platelet infusion will not reverse their antiplatelet effect as remaining drug in the circulation will inactivate any transfused platelets.83 Intra-arterial fibrinolytics may also be used to treat intra-arterial thrombus formation during endovascular aneurysm treatment. Agents such as recombinant tissue plasminogen activator and urokinase are well suited for this application due to their short half-lives.86,87 Theoretically, due to the platelet-rich nature of acute thrombi, fibrinolytic agents may not be as effective as GP IIb/IIIa inhibitors at thrombus disruption. Additionally, fibrinolytics carry a risk of ICH (as GP IIb/IIIa inhibitors do), which limits their use in the setting of ruptured aneurysm treatment. In cases of device or parent artery occlusion, Cronqvist et al87 described a technique in which mechanical disruption is used to dislodge thrombus material and create a greater surface area for an antiplatelet or thrombolytic drug to act upon. An acutely thrombosed FDD may theoretically be recanalized utilizing mechanical thrombectomy. De Vries et al21 reported success with this approach in 1 case out of a case series utilizing the Surpass flow diverter (Stryker Neurovascular) but did not delineate the exact details.21 More studies may be required to examine the safety of mechanical thrombectomy with regard to the appropriate choice of mechanical thrombectomy device, the risk of downstream embolization, and the theoretical risk of disrupting the flow-diverting construct. In the event of endoluminal stenosis of an FDD, angioplasty may be used to treat the stenosis.88 Side Branch and Perforator Occlusion Although a potentially serious and deleterious complication, side branch occlusion appears to be quite rare and is usually clinically silent.89 One prospective study of PEDs (ev3, Medtronic Inc) reported a rate of 1.4% (2 out of 140 cases), while other smaller case series, reports, and reviews have reported higher rates.21,68,89,90 It is believed that side branch occlusion may occur more often when multiple (2 or more) FDDs overlap with one another at the origin of a branching artery; this phenomenon is likely due to a decrease in device porosity between the parent vessel and branch artery that results from overlapping devices.1 The posterior circulation, particularly the basilar artery, appears to be a more common location for occlusion of side branches and perforators.90-93 In a prospective case study by De Vries et al21 utilizing the Surpass Flow Diverter (Stryker Neurovascular) involving 37 patients, 4 out of 15 patients (31%) with covered posterior communicating arteries showed absence of anterograde flow at 6-mo follow-up while only 2 out of 15 patients (15%) with covered ophthalmic arteries showed absence of anterograde flow.21 Luckily, the patients with absence of anterograde flow in both the ophthalmic artery group and posterior communicating artery groups were neurologically asymptomatic.21 Another review by Phillips et al92 examining the safety of PEDs (ev3, Medtronic Inc) in treatment of posterior circulation aneurysms came to similar conclusions concerning the elevated incidence of perforator occlusions in the posterior circulation. Of 21 patients who were treated with flow diversion for basilar artery aneurysms, 3 (14%) developed perforator infarctions following treatment leading to permanent neurological disability.92 The increased incidence of occlusion of perforators in the posterior circulation has been explained by the demanding eloquence of the vertebrobasilar system as well as its differential embryological origins.92,94 Additionally, perforator diameter in the vertebrobasilar circulation is small enough that perforators may not even be visible on DSA which increases the risk of inadvertent occlusion.92,95 Symptomatic posterior circulation perforator occlusion may also be more common due to the lack of collateral circulation present in the vascular territories supplied by small perforators. This is in contrast to the anterior circulation, which demonstrates more robust collateralization. In a study of 19 patients with ICA aneurysms treated with PEDs (ev3, Medtronic Inc), follow-up angiography revealed that 4 (21%) patients had occlusion of the ophthalmic artery while 2 (11%) had slowed anterograde flow. These patients experienced no visual changes or clinical symptoms, presumably due to the collateral circulation to this artery via the external carotids.96,97 Besides preprocedural preparation with antiplatelets, prevention of side branch occlusion may be best accomplished by sparing use of flow-diverting devices in the stent construct. If a side branch is occluded due to an FDD despite prophylactic measures, IA abciximab has been demonstrated to be of use in recanalization.68 CONCLUSION FDDs have transformed the treatment of previously difficult-to-manage aneurysms. These devices divert flow away from an aneurysm into its parent vessel, permit reconstruction of the affected parent vessel, and provide a platform for new endothelialization. Given the novelty of these devices, the rate of intraprocedural complication and management of these complications is just beginning to be realized. With increasing use and the expanding versatility of FDD, the understanding of these complications is critical in order to effectively manage them. Periprocedural complications occur mainly due to thromboembolic events or mechanical issues related to device deployment and placement. The main categories of periprocedural complications seen in deployment of FDDs are failure of occlusion, parent vessel injury and/or rupture, IPH, migration or malposition of the FDD, thromboembolic or ischemic events, and side branch occlusion. Failure of occlusion occurs in approximately 20% of cases and may be further managed with another FDD or surgical clipping. Intraprocedural vessel rupture and hemorrhage is best managed with immediate reversal of anticoagulation and then further treatment with conventional angiographic techniques such as tranvenous coagulation, parent artery sacrifice, and further flow diversion. IPH can occur in up to 10% of those who receive FDDs, and treatment is usually supportive. Migration or malposition of FDDs necessitates several special techniques of microcatheter manipulation as well as possible removal using specific endovascular techniques. Thromboembolic events are best managed with GP IIb/IIIa antagonists, with fibrinolytic agents being a less favored treatment. Mechanical thrombectomy in the treatment of thromboembolic complications related to FDD deployment holds promise and should be investigated further for safety and efficacy. Intraprocedural side branch occlusion may be best prevented with conservative use of FDDs and pretreatment with antiplatelet agents, but if it occurs IA abciximab may be used to attempt to recanalize the occluded side branch. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Szikora I, Berentei Z, Kulcsar Z et al. Treatment of intracranial aneurysms by functional reconstruction of the parent artery: the budapest experience with the pipeline embolization device. Am J Neuroradiol . 2010; 31( 6): 1139- 1147. Google Scholar CrossRef Search ADS PubMed 2. Lylyk P, Miranda C, Ceratto R et al. Curative endovascular reconstruction of cerebral aneurysms with the pipeline embolization device: the buenos aires experience. Neurosurgery . 2009; 64( 4): 632- 343. Google Scholar CrossRef Search ADS PubMed 3. Fischer S, Vajda Z, Aguilar Perez M et al. 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Chinese: Hailiang Tang, MD Department of Neurosurgery Huashan Hospital Fudan University Shanghai, China Chinese: Hailiang Tang, MD Department of Neurosurgery Huashan Hospital Fudan University Shanghai, China Close English: Roberto Jose Diaz, MD, PhD Department of Neurological Surgery University of Miami Miller School of Medicine Miami, Florida English: Roberto Jose Diaz, MD, PhD Department of Neurological Surgery University of Miami Miller School of Medicine Miami, Florida Close French: Michael Bruneau, MD, PhD Department of Neurosurgery Erasme Hospital Brussels, Belgium French: Michael Bruneau, MD, PhD Department of Neurosurgery Erasme Hospital Brussels, Belgium Close Italian: Daniele Bongetta, MD Department of Neurosurgery Fondazione IRCCS Policlinico San Matteo Pavia, Italy Italian: Daniele Bongetta, MD Department of Neurosurgery Fondazione IRCCS Policlinico San Matteo Pavia, Italy Close Portuguese: Eduardo Carvalhal Ribas, MD Neurosurgery Department Hospital das Clínicas University of São Paulo Medicine School (HC-FMUSP), and Hospital Israelita Albert Einstein São Paulo, Brazil Portuguese: Eduardo Carvalhal Ribas, MD Neurosurgery Department Hospital das Clínicas University of São Paulo Medicine School (HC-FMUSP), and Hospital Israelita Albert Einstein São Paulo, Brazil Close Spanish: Carlos E. Alvarez, MD Department of Neurosurgery Instituto del Cerebro y la Columna Vertebral Lima, Peru Spanish: Carlos E. Alvarez, MD Department of Neurosurgery Instituto del Cerebro y la Columna Vertebral Lima, Peru Close Russian: Sergei Kim Department of Pediatric Neurosurgery Novosibirsk Federal Centre of Neurosurgery Novosibirsk, Russia Russian: Sergei Kim Department of Pediatric Neurosurgery Novosibirsk Federal Centre of Neurosurgery Novosibirsk, Russia Close Korean: Tae Gon Kim, MD Division of Vascular Section Department of Neurosurgery Bundang CHA Hospital Seongnam, Republic of Korea Korean: Tae Gon Kim, MD Division of Vascular Section Department of Neurosurgery Bundang CHA Hospital Seongnam, Republic of Korea Close Greek: Andreas Zigouris, MD Department of Neurosurgery University Hospital of Ioannina Ioannina, Greece Greek: Andreas Zigouris, MD Department of Neurosurgery University Hospital of Ioannina Ioannina, Greece Close Copyright © 2018 by the Congress of Neurological Surgeons
Operative Neurosurgery – Oxford University Press
Published: Mar 22, 2018
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