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Management strategies for intraprocedural coil migration during endovascular treatment of intracranial aneurysms
  1. Dale Ding,
  2. Kenneth C Liu
  1. Department of Neurosurgery, University of Virginia, Charlottesville, Virginia, USA
  1. Correspondence to Dr Kenneth C Liu, Division of Cerebrovascular and Skull Base Surgery, Department of Neurosurgery, University of Virginia Health System, P O Box 800212, Charlottesville, VA 22908, USA; kenneth.c.liu{at}


Migration of a coil during endovascular treatment of intracranial aneurysm occurs in 2–6% of cases. The consequences of coil migration vary significantly from minor flow alterations of the parent artery which are asymptomatic to thromboembolic occlusion of major intracranial vessels resulting in large territory infarcts. We performed a comprehensive literature review and identified 37 reported cases of migrated coil retrieval consisting of 10 case reports and six case series. Most of the aneurysms presented with rupture (65%) and were located in the anterior circulation (70%). The endovascular treatment approaches were coil embolization alone (57%), stent-assisted coiling (26%) and balloon remodeling (17%). Endovascular retrieval was performed with microwires, the Alligator Retrieval device, Merci devices, snares and stentrievers. There was a single report of microsurgical extraction following failed endovascular removal and three cases of coil fracture in which the coil fragments were secured to the vessel walls with stents.

  • Aneurysm
  • Coil
  • Complication
  • Device
  • Stroke

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Since the introduction of endovascular coil embolization for the treatment of intracranial aneurysms, numerous studies have repeatedly demonstrated that, for ruptured lesions, it possesses a level of safety and efficacy that is at least equivalent—if not superior—to microsurgical clipping.1–3 Coil migration is a significant intraprocedural complication during endovascular aneurysm treatment for which there is no standard management strategy.4 The reported rates of coil migration range from 2% to 6% and have not changed significantly over time since the inception of endovascular aneurysm treatment.5–8 Our objective is to summarize the current literature describing the management of intraprocedural coil migration including delineation of the circumstances in which coil migration arises and the specific devices used to retrieve migrated coils.


We performed a comprehensive literature search using PubMed from 1994 to 2013 to identify all reported cases in the English literature of retrieval techniques for protruded, displaced or migrated coils during endovascular embolization of intracranial aneurysms. Our search resulted in 10 single case reports and 6 case series, each comprising 2–14 cases, for a total of 37 cases reported in the literature. When available, the clinical presentation, aneurysm size and location, endovascular treatment strategy, technology used for retrieval and retrieval complications, if any, were noted. We categorized the retrieval methods into wire techniques, snare devices, retriever devices and ‘other’ retrieval techniques.


Wire techniques

Wire techniques were used in three cases. Standard et al9 used a dual guidewire technique with two Dasher 10 wires (Target Therapeutics, Fremont, California, USA) to retrieve an unraveled coil during the treatment of a ruptured 11 mm left anterior inferior cerebellar artery (AICA) aneurysm. More recently, Lee et al10 described two cases in which the authors fashioned wires into snares to retrieve displaced coils. The first case was a recurrent supraclinoid internal carotid artery (ICA) aneurysm previously treated with stent-assisted coiling. The final coil extruded from the aneurysm following deployment. After multiple unsuccessful attempts to retrieve the displaced coil with a Goose Neck snare (Microvena, White Bear Lake, Minnesota, USA), a microwire manually shaped like a pigtail was used to successfully retrieve the extruded coil. The second case was an unruptured 8 mm paraclinoid ICA aneurysm treated with the balloon remodeling technique. During placement of the final coil, the final 1 cm of the coil was unable to be inserted into the aneurysm. An attempt to withdraw the coil stretched it, thereby resulting in lodging of the coil in the aneurysm neck with the stretched proximal portion in the lumen of the parent vessel. An Xpedion balloon guidewire (MTI, Irvine, California, USA) with a J-shaped tip was used to remove the stretched coil.

Snare devices

Coil retrieval was performed with a snare device in nine cases. Watanabe et al11 described the first use of a loop snare to retrieve a migrated coil during treatment of a patient who presented with subarachnoid hemorrhage (SAH) and was found to have both basilar bifurcation and superior cerebellar artery (SCA) aneurysms. The basilar bifurcation aneurysm was treated uneventfully but, during coiling of the smaller 5 mm SCA aneurysm, the coil migrated into the basilar artery. After an initial failed attempt to remove the migrated coil with a Retriever-10 (Target Therapeutics), it was successfully evacuated with a Retriever-18 (Target Therapeutics). Prestigiacomo et al12 described the use of a 2 mm Goose Neck microsnare with a twist technique to retrieve a partially protruded coil which subsequently fractured during a failed attempt to withdraw it. The case involved a previously clipped left posterior inferior cerebellar artery (PICA) aneurysm which presented with a 10 mm recurrence and repeat rupture.

Koseoglu et al13 used a Goose Neck snare to retrieve a variety of fractured and intact foreign bodies including catheters, wires, stents and coils from multiple cardiovascular and cerebrovascular structures ranging from the superior vena cava to the middle cerebral artery (MCA). Although the case was not detailed, the authors reported a case of migrated coil during embolization of an unruptured left MCA aneurysm which was successfully retrieved with the Goose Neck snare. Fiorella et al14 described a monorail snare technique using a 2 mm Goose Neck snare advanced over a Prowler-14 microcatheter (Cordis Corp, Miami, Florida, USA) to retrieve a coil which had partially herniated outwards during stent-assisted coiling of an unruptured 10 mm left supraclinoid ICA aneurysm. The same technique was used by the authors to retrieve stretched coils in three other patients with unruptured aneurysms, two with supraclinoid ICA aneurysms treated with stent-assisted coiling and one patient with an MCA trifurcation aneurysm treated with coil embolization alone. Dinc et al15 used a 2 mm Goose Neck snare to retrieve migrated coils in two cases of aneurysmal SAH. The first case was a wide-necked MCA aneurysm treated with balloon remodeling, and the second case was a 2 mm distal anterior cerebral artery (ACA) aneurysm treated with a single coil.

Retriever devices

Retriever devices were used in a total of 21 cases. Zoarski et al16 reported two cases of ruptured 6 mm basilar bifurcation aneurysms who underwent endovascular treatment with intraprocedural herniation of the final coil into one of the posterior cerebral arteries. In both cases 2 mm and 4 mm Goose Neck snares failed to retrieve the herniated coils. A non-angled Retriever device (Target Therapeutics) was subsequently used to successfully remove the displaced coils in both cases. Henkes et al17 reported the first use of the Alligator Retrieval Device (Chestnut Medical Technologies, Menlo Park, California, USA). The Alligator is comprised of a 0.016 inch stainless steel insertion wire with precision grasping arms attached to its tip. The case was a previously ruptured 14 mm basilar bifurcation aneurysm with a 5 mm neck which was initially treated with coil embolization but partially recurred, necessitating retreatment. During Y-configuration stent-assisted coiling, a coil migrated from the aneurysm neck into the basilar bifurcation. The Alligator was used to successfully retrieve the migrated coil from the interstices of the two stents.

Vora et al18 described entanglement of a stent-coil construct while attempting to treat a ruptured 9 mm vertebrobasilar junction (VBJ) aneurysm. The authors used an L5 Merci Retriever (Concentric Medical, Mountain View, California, USA) to remove the stent-coil construct. Unfortunately, the aneurysm subsequently ruptured following extraction of the entangled stent and coil and the patient died. O'Hare et al19 used an X6 Merci Retriever (Concentric Medical) to remove an incompletely detached coil during treatment of a ruptured posterior communication artery (PCOM) aneurysm The first coil was at first unable to be detached but subsequently spontaneously detached during retraction from the aneurysm sac. The X6 Merci device was passed distally into the MCA and ensnared the displaced coil upon retraction on the third attempt.

Two case reports and a relatively large case series have described the use of stentriever devices for migrated coil retrieval.4 ,20 ,21 O'Hare et al21 reported a case of a ruptured wide-necked 13 mm PCOM aneurysm which was treated with the balloon remodeling technique. Deployment of the last coil displaced the previous coil into the ICA. In an attempt to secure the displaced coil with a Solitaire stent (ev3, Irvine, California, USA), the coil migrated distally into the MCA. Deployment of the stent ensnared the migrated coil and it was retracted in tandem with the stent. Hopf-Jensen et al20 described a similar case in which, during coiling of a ruptured 24 mm ophthalmic artery aneurysm, the final coil herniated out of the aneurysm sac and displaced proximally into the ICA. The displaced coil was successfully retrieved with a Solitaire stent. Leslie-Mazwi et al4 recently reported by far the largest series of coil retrieval interventions. Over a 44-month period in which 1125 aneurysms were treated, 14 patients (1.2%) had intraprocedural coil displacement requiring retrieval. All coil retrieval interventions were performed with stentriever devices, either the Solitaire stent or Catch Plus (Balt Extrusion, Montmorency, France), requiring a median of two passes. The cases included ruptured and unruptured aneurysms of diameter 4–28 mm in a wide range of locations including the ICA, MCA, ACA and basilar artery, treated by coil embolization alone or using the balloon remodeling technique. The details of each individual coil retrieval case were not described.

Other retrieval techniques

Methods of retrieval not including wire techniques, snares or retriever devices were used in four cases. While these salvage methods are suboptimal to successful coil retrieval by the aforementioned endovascular techniques, they warrant consideration when standard approaches to endovascular coil retrieval fail. Raftopoulos et al22 reported a case of a ruptured anterior communicating artery aneurysm which was initially treated with endovascular coiling. During coil embolization a coil unraveled and migrated distally into the MCA bifurcation. Due to the tortuosity of the carotid siphon, the authors were unable to retrieve the coil with an endovascular snare. The patient was therefore taken for microsurgical aneurysm clipping and intravascular coil retrieval. After obtaining vascular control and temporary clipping, a Rhoton 9 microhook (Codman/Johnson & Johnson, Raynam, Massachusetts, USA) was used to puncture the ACA and anchor the extruded coil. The coil was then removed from the vessel lumen and the opening was closed primarily. The patient had transient postoperative hemiparesis which resolved at 5 weeks follow-up.

Schutz et al23 reported three cases of coil fracture of a patient with a ruptured dorsal ICA aneurysm, another patient with a ruptured PCOM aneurysm and a last patient with ophthalmoplegia from a giant unruptured ICA aneurysm. The patients were treated with the balloon remodeling technique using a Hyperglide balloon (MTI), coil embolization only and Neuroform stent-assisted (Boston Scientific, Natick, Massachusetts, USA) coiling, respectively. In all three cases coil fracture followed initial stretching. Instead of retrieving the fractured fragments, the authors decided to fix the coil fragments to the vessel walls using Cerebrence stents (Medtronic, Minneapolis, Minnesota, USA) in the first two cases and a Neuroform stent in the third case.

Summary of cases

Excluding case series in which individual scenarios were not detailed, the endovascular approaches to aneurysm treatment were coil embolization only in 13 patients (56.5%), stent-assisted coiling in 6 patients (26.1%) and the balloon remodeling technique in 4 patients (17.4%). Aneurysm rupture was the clinical presentation in 15 patients (65.2%). The aneurysms were located in the anterior circulation in 16 cases (69.6%) and in the posterior circulation in 7 cases (30.4%). The only complication related to migrated coil retrieval was intraprocedural rupture of a VBJ aneurysm which resulted in the patient's death (4.5%).18 Table 1 summarizes the retrieval techniques, aneurysm locations and treatment approaches.

Table 1

Summary of case reports and series describing retrieval of migrated coils


Migration of detachable coils during endovascular embolization of intracranial aneurysms is a potentially serious intraprocedural complication. Protrusion, stretching, fracture or migration of a coil creates a thrombogenic nidus which may occlude proximal large-caliber vessels or shower emboli into smaller distal vasculature. Occlusion of the parent artery or major branches of distal vessels may result in a large territory infarct or death.

Incidence of coil migration

Since the published reports of coil retrieval techniques represent mostly novel or unique scenarios or techniques, the relatively small number of case reports and series is not an accurate reflection of the true incidence of coil migration, which is not trivial.5–8 In their initial report introducing endovascular treatment as an alternative to microsurgical clipping for intracranial aneurysm obliteration, Guglielmi et al7 reported coil migration in one of 43 cases (2.3%). In another early study, Casasco et al8 reported parent vessel occlusion from coil migration in four of 71 cases (5.6%) which resulted in death in two patients (2.8%) and moderate neurological deficit at long-term follow-up in the other two patients (2.8%).

After publication of the International Subarachnoid Aneurysm Trial (ISAT) sparked a paradigm shift in the treatment of intracranial aneurysms, the number of publications describing endovascular outcomes has grown exponentially.2 Henkes et al6 reported the results from endovascular treatment of 1811 aneurysms. There were 46 patients with coil migration (2.5%), with little difference between those with ruptured and those with unruptured aneurysms (2.4% vs 2.7%). However, only one patient with coil migration developed arterial thrombosis (0.1%). In a randomized trial of nearly 500 patients comparing hydrogel coils (HydroCoil; MicroVention, Aliso Viejo, California, USA) with bare platinum coils, White et al found a 6.0% rate of coil migration and 1.6% rate of parent artery occlusion in the HydroCoil cohort compared with a 4.0% rate of coil migration and 3.2% rate of parent artery occlusion in the bare platinum coil cohort. Therefore, despite a lower rate of coil migration in the bare platinum coil group, the proportion of patients who progressed to vessel occlusion was higher than in the HydroCoil group. Ultimately, the number of events in either treatment arm was inadequate to detect a statistical difference in coil migration.

While the vast majority of coil migration occurs during the procedure, there have been a few reports of delayed coil migration occurring after aneurysm treatment. Phatouros et al24 described four cases of post-procedural coil migration at time intervals 15 min (n=1), 2 months (n=1) and 6 months (n=2) following endovascular aneurysm treatment. Delayed coil migration resulted in arterial stenosis in three cases, which was asymptomatic in two patients and symptomatic in one patient. The symptomatic patient presented with a recurrent previously ruptured superior hypophyseal artery aneurysm which was treated with coil embolization. The patient developed focal neurological deficit 15 min after normal recovery due to distal coil migration into the MCA and ACA. After failed endovascular retrieval, the patient underwent microsurgical removal of the migrated coils but unfortunately suffered a large MCA distribution infarct. Gao et al25 reported a case of asymptomatic delayed coil migration 5 months after stent-assisted coiling of a PCOM aneurysm.

Management of intraprocedural coil migration

While intraprocedural coil migration typically precipitates during deployment of the final coil, it may also occur during the placement of the initial coil into a small aneurysm, following balloon deflation when coiling with the balloon remodeling technique, or as a result of displacement of a previous intrasaccular coil by the final coil.10 ,16 ,19–21 ,23 Wide-necked aneurysms are particularly prone to coil displacement despite adjuvant techniques such as balloon remodeling or stent placement.26 Most instances of minor coil migration, which may be classified as protrusion or prolapse, may be managed conservatively with anticoagulation or antiplatelet therapy.4

At our institution, a small degree of coil protrusion without angiographic evidence of thromboembolism or large vessel occlusion is typically treated with 24–48 h of anticoagulation with a heparin infusion followed by antiplatelet therapy for 6 months. If the aneurysm goes on to completely obliterate, the small amount of protruded coil will theoretically have been incorporated into the vessel wall by endothelialization. We have yet to see a late complication from conservative management of minor coil protrusion.

Unfortunately, not all instances of coil displacement are minor. Significant degrees of coil displacement, including stretching, fracture and migration, necessitate prompt intervention to avoid significant neurological morbidity and mortality from thromboembolic phenomena which may quickly ensue. From our review of the literature, we identified a wide variety of strategies for managing intraprocedural coil migration. Of the 37 cases of coil migration, a Goose Neck snare was successfully used for retrieval in eight cases (21.6%).12–15 In four cases (10.8%), initial use of a Goose Neck snare proved unsuccessful and required another approach including a custom-shaped microwire, non-angled Retriever device and microsurgical extraction.10 ,16 ,22 Raftopoulos et al22 demonstrated an elegant microsurgical solution to endovascular coil migration which did not result in long-term neurological morbidity. However, in the majority of cases, microsurgical removal of intravascular coils is associated with an extremely high risk of complications which outweighs the potential benefits.24


The incidence of intraprocedural coil migration during endovascular aneurysm treatment has remained relatively stagnant over time. Furthermore, the optimal management of coil migration is not standardized. Successful endovascular strategies for retrieval of migrated coils include utilization of wire techniques, snares, retriever devices and stentrievers. Occasionally, these endovascular approaches fail and salvage approaches such as microsurgical removal and stent fixation of fractured coil fragments may be employed. As endovascular technology for aneurysm occlusion continues to evolve, experience in migrated coil retrieval will remain crucial to the modern neurointerventionalist's repertoire.


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  • Contributors DD was involved in conception and design, analysis and interpretation of data, drafting the article, revising it critically for important intellectual content and final approval of the version to be published. KCL was involved in conception and design, analysis and interpretation of data, revising the article critically for important intellectual content and final approval of the version to be published.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.