Microsurgical clipping for coil-extruded recurrent aneurysms: Case series and technical pearls

Abstract

Background:

Endovascular coil embolization is widely used for the treatment of intracranial aneurysms, offering minimally invasive access and favorable early outcomes. However, long-term durability remains a concern, with recurrences arising from coil compaction, sac regrowth, or incomplete occlusion. In rare instances, these failures present with coil extrusion, a technically demanding scenario that significantly limits endovascular retreatment options.

Methods:

We report three adult female patients with recurrent intracranial aneurysms involving the anterior communicating artery, middle cerebral artery bifurcation, and distal azygos anterior cerebral artery, all with imaging-confirmed coil extrusion following prior endovascular therapy. Recurrence occurred at 6 months, 10 years, and nearly 20 years, illustrating early, late, and very-late treatment failure. All patients underwent microsurgical clipping performed using neuronavigation, continuous neurophysiological monitoring, indocyanine green videoangiography, and intraoperative Doppler ultrasonography. Operative strategy, technical nuances, and intraoperative decision-making are described. A focused literature review was conducted to contextualize management strategies for this rare presentation.

Results:

Complete microsurgical reconstruction and aneurysm obliteration were achieved in all patients without coil extraction, bypass, procedure-related neurological morbidity, or mortality. Postoperative imaging confirmed stable clip placement and exclusion of the aneurysm sac. Despite the presence of coil extrusion and dense adhesions, meticulous microsurgical dissection combined with modern intraoperative adjuncts enabled safe and effective clip application without the need for coil removal.

Conclusion:

Coil extrusion is an uncommon but complex manifestation of aneurysm recurrence that may occur even decades after initial endovascular treatment and can affect a range of anterior circulation locations. This case series underscores the importance of lifelong imaging surveillance and demonstrates that, in carefully selected patients, microsurgical clipping remains a safe and definitive salvage strategy when guided by refined technique and contemporary intraoperative technologies.

INTRODUCTION

Intracranial aneurysms are encountered in approximately 3–5% of the adult population and remain a significant cause of morbidity and mortality when rupture occurs.[48] Preventive management is therefore critical in selected patients. Over the past two decades, endovascular coil embolization has emerged as the preferred treatment modality for many aneurysms owing to its minimally invasive nature and favorable short-term outcomes, particularly in elderly patients and those with surgically inaccessible lesions.[25] However, the long-term durability of coiling continues to be questioned, as recanalization rates of 15–30% have been reported, compared with recurrence rates of only 1–3% following microsurgical clipping.[4,49] Recurrence after coiling is most commonly attributed to coil compaction, incomplete initial occlusion, or aneurysm regrowth.[18,49] More rarely, coil-related complications such as migration or extrusion, defined as protrusion of coil loops beyond the aneurysm sac into the parent artery or subarachnoid space, pose unique clinical and surgical challenges.[1,16]

Recurrent aneurysms with coil extrusion are particularly complex.[55] Prior coil implantation leads to fibrosis of the aneurysm dome, adherence to adjacent neurovascular structures, and obliteration of normal dissection planes.[1] Extruded coil loops may herniate into the parent vessel or subarachnoid space, increasing the risk of thromboembolic events, distal flow compromise, or intraoperative rupture.[22] These altered anatomic conditions make endovascular re-intervention technically hazardous, as attempts at recoiling or flow diversion may be hindered by distorted sac architecture or the presence of protruding coils.[35] Recent reports underscore these risks: Rahme et al. described a ruptured recurrence in which coil protrusion precluded further endovascular therapy, necessitating open surgical salvage, while Zheng et al. demonstrated that dense scar tissue and coil entanglement demand meticulous microsurgical dissection to achieve safe neck reconstruction.[38,55]

High-resolution preoperative imaging, including 3D rotational angiography and vessel wall MRI (VWI), is essential to delineate coil position, parent vessel integrity, and neck remnants.[46] Intraoperatively, surgeons must contend with fragile, fibrosed aneurysm walls and coil-laden necks that obscure clip placement. Contemporary adjuncts such as neuronavigation, indocyanine green (ICG) videoangiography, micro-Doppler ultrasonography, and continuous neurophysiological monitoring are indispensable in mitigating the risks of these technically demanding procedures.[7]

When endovascular options are exhausted, as is often the case in coil extrusion, microsurgical clipping remains the most definitive salvage strategy, permitting direct visualization of the aneurysm neck, secure clip application, and exclusion of extruded coils if necessary. Several series have demonstrated high rates of complete occlusion (>90–95%) with acceptable morbidity, supporting the role of clipping as a durable solution for complex recurrences.[55] In this report, we present a case series of three patients with early, late, and very-late recurrence after coil embolization complicated by coil extrusion. Through these cases, we highlight the anatomical challenges encountered, technical strategies employed, and the enduring importance of open microsurgery in managing this difficult subset of aneurysms.

MATERIALS AND METHODS

We conducted a single-institution case series of three patients with recurrent intracranial aneurysms complicated by coil extrusion following prior endovascular embolization. All patients were treated surgically between 2024 and 2025 after multidisciplinary evaluation by a team including vascular neurosurgery, interventional neuroradiology, and neurology. The decision to pursue microsurgical clipping was guided by aneurysm morphology, clinical presentation, failure of prior endovascular therapy, and the presence of coil extrusion or unfavorable anatomy for repeat embolization.

All operations were performed via a standardized microsurgical technique under general anesthesia. Neuronavigation was used for trajectory planning and craniotomy localization. Continuous neurophysiological monitoring (somatosensory and motor evoked potentials) was employed to reduce the risk of ischemic or iatrogenic injury to eloquent structures. Arachnoid dissection was carried out under high magnification with careful mobilization of scarred planes and coil-adherent tissue. Coil masses were preserved in situ unless they directly obstructed safe clip application. Definitive aneurysm exclusion was achieved using straight, curved, or fenestrated clips as dictated by neck geometry.

Intraoperative ICG videoangiography and micro-Doppler ultrasonography were systematically performed after each clip placement to confirm complete aneurysm occlusion and parent vessel patency. Temporary proximal clipping was available as needed to facilitate safe neck reconstruction. Operative reports, perioperative imaging, and follow-up clinical assessments were reviewed for each patient. Outcomes of interest included surgical feasibility, completeness of aneurysm obliteration, preservation of adjacent vessels, perioperative complications, and neurological status at discharge and follow-up.

Finally, a focused literature review was performed to contextualize our institutional experience and to highlight technical strategies for microsurgical management of recurrent aneurysms with coil extrusion [Figure 1].

Figure 1:

Technical algorithm for microsurgical salvage of coil-extruded recurrent intracranial aneurysms: Proposed revised technical algorithm for the management of recurrent intracranial aneurysms with coil extrusion after endovascular treatment. The algorithm integrates morphological recurrence patterns, microsurgical feasibility assessment, and individualized reconstructive strategies. Red indicates an unfavorable/high-risk pathway in which endovascular retreatment is unsafe, has failed, or is anatomically unfavorable and microsurgical salvage is favored. Green indicates that endovascular retreatment remains feasible. Concepts adapted from Zheng et al. (Front Neurol 2021). C: Coil width, H: Compaction height, C/H: Coil width-to-compaction height ratio.

Surgical technique

• Exposure and dissection: Craniotomy and dural opening were tailored to aneurysm location using neuronavigation for accuracy. Microsurgical arachnoid dissection was performed under high magnification, with careful mobilization of scarred planes and adhesions from prior coil mass. Normal tissue planes were frequently absent, necessitating sharp dissection around coil-adherent dome tissue.

• Coil management: Previously implanted coils were left in situ unless they directly obstructed safe clip placement or compromised parent vessel patency. Extruded loops were mobilized only when required for exposure, avoiding unnecessary manipulation.

• Clip application: Definitive aneurysm occlusion was achieved using straight, curved, or fenestrated clips depending on aneurysm neck geometry. Temporary proximal clipping was selectively employed to reduce intraaneurysmal pressure and facilitate secure placement.

• Adjunctive intraoperative assessment: After each clip application, ICG videoangiography and micro-Doppler ultrasonography were performed to confirm aneurysm obliteration and parent vessel patency. Flow integrity was further validated by electrophysiological monitoring throughout the procedure.

• Closure: Hemostasis was ensured, and closure was performed in layers according to standard procedures. Patients were extubated in the operating room unless postoperative hemodynamic or neurological instability warranted transfer to the intensive care unit (ICU).

Retreatment decision-making and rupture-risk assessment

Retreatment decisions were made in a multidisciplinary conference involving vascular neurosurgery and interventional neuroradiology, integrating clinical presentation and serial vascular imaging. Recanalization was characterized using the modified Raymond–Roy occlusion classification (MRRC), with particular attention to the morphologic pattern of residual filling (e.g., neck remnant vs sac-type recanalization).[27] Retreatment was favored in cases demonstrating progressive angiographic worsening, interval aneurysm growth/new dome filling, or coil-mass instability (including extrusion/prolapse), as these features suggest persistent hemodynamic exposure of the aneurysm wall and reduced durability of further coil packing. This approach is consistent with reports showing that residual filling after treatment carries a low rupture risk in aneurysms that were unruptured at presentation but a higher rerupture risk when the aneurysm was ruptured at presentation, underscoring the importance of complete occlusion in the ruptured setting.[11,29,39] In addition, prior work suggests that sac-type recanalization (MRRC IIIb) is associated with higher rupture risk and should prompt consideration of early retreatment when feasible.[41,55]

Rationale for excluding repeat endovascular retreatment

In each case, repeat endovascular strategies were reviewed by neurointerventionalists, including repeat coiling (with or without adjunctive balloon or stent assistance) and reconstructive options such as flow diversion. A second endovascular approach was deferred when the recurrence was accompanied by coil extrusion/instability and unfavorable postcoiling geometry, as these factors reduce the likelihood of durable endovascular reconstruction and may increase thromboembolic or branch-compromise risk. While flow diversion has demonstrated favorable occlusion rates for selected previously coiled aneurysms, its use requires antiplatelet therapy and remains highly anatomy-dependent; distal or bifurcation lesions with incorporated branches and limited landing zones warrant careful selection and may be less suitable for a reconstructive endovascular solution.[26] Due to these characteristics mentioned, microsurgical treatment was chosen in the three cases presented. In addition to coil extrusion, several anatomical and hemodynamic features favored microsurgical treatment over flow diversion in our series. These included bifurcation anatomy with incorporated branch vessels, distal aneurysm location with limited landing zones, previously ruptured lesions requiring definitive immediate exclusion, and recurrent aneurysms with unstable coil masses extending beyond the aneurysm sac.

Furthermore, the requirement for dual antiplatelet therapy following flow diversion was considered less favorable in lesions where definitive mechanical reconstruction could be achieved surgically, with preservation of branch patency under direct visualization. In Cases 1 and 2, preoperative imaging demonstrated a residual neck segment relatively free of coils, permitting direct clip reconstruction without coil extraction. The main demographic, anatomical, radiological, and treatment characteristics of the three patients are summarized in Table 1. The rupture-risk profile, retreatment considerations, and anatomical factors influencing exclusion of repeat endovascular therapy in the present series are summarized in Table 2. The principal anatomical and technical factors favoring microsurgical salvage over repeat endovascular retreatment are summarized in Table 3.

Table 1:

Clinical, radiological, and surgical characteristics of recurrent intracranial aneurysms with coil extrusion.

Table 2:

Rupture-risk characterization and reasons for excluding repeat endovascular retreatment.

Table 3:

Technical factors favoring microsurgical salvage over repeat endovascular retreatment.

RESULTS

Case series

Case 1

A 38-year-old woman with a history of aneurysmal subarachnoid hemorrhage secondary to rupture of a bilobed anterior communicating artery (AComA) aneurysm underwent partial coil embolization in June 2024, achieving a Raymond–Roy Class II occlusion. Her initial recovery was uneventful, and she was discharged with routine surveillance recommendations. At 6-month follow-up, 3D cerebral angiography demonstrated coil compaction with extrusion beyond the aneurysm sac and a residual neck remnant. Given the unfavorable morphology and coil extrusion, the lesion was deemed unsuitable for further endovascular therapy. Following multidisciplinary discussion, microsurgical clipping was pursued [Figure 2].

Figure 2:

Preoperative and follow-up right internal carotid artery angiography of a previously coiled anterior communicating artery aneurysm. (a) Three-dimensional cerebral angiography demonstrating a bilobed saccular aneurysm of the anterior communicating artery. The white arrowhead indicates the original ruptured aneurysm. (b) Conventional cerebral angiography demonstrating partial coil embolization of the aneurysm. The black arrowhead indicates coils within the aneurysm sac. (c) Follow-up three-dimensional cerebral angiography revealing a residual aneurysm at the same location after previous embolization. The white arrowhead indicates the residual aneurysm. (d) Conventional cerebral angiography demonstrating coil compaction and extrusion beyond the aneurysmal dome. The black arrowhead indicates coil material extending beyond the original aneurysm dome, whereas the black arrow indicates coils remaining within the aneurysm sac.

A right-sided pterional craniotomy was performed under stereotactic neuronavigation. Intraoperatively, the aneurysm dome was found densely adherent to the frontal lobe with extruded coil loops projecting beyond the sac. Under continuous neurophysiological monitoring, meticulous arachnoid dissection was carried out to mobilize scarred tissue and expose the neck. Two straight clips (7 mm and 5 mm) were sequentially applied to reconstruct and secure the aneurysm neck. ICG videoangiography and micro-Doppler ultrasonography confirmed complete exclusion of the aneurysm and preserved patency of adjacent AComA perforators [Figure 3].

Figure 3:

Intraoperative views of a residual anterior communicating artery aneurysm previously treated with endovascular coiling. (a) Residual aneurysm dome following prior coil embolization. The black arrow indicates coil extrusion beyond the aneurysm dome, whereas the white arrow demonstrates coils incorporated within the aneurysm wall. (b) Definitive microsurgical exclusion of the residual aneurysm achieved with two straight clips measuring 5 mm and 7 mm. The white arrow indicates the aneurysm dome containing coils. (c) Indocyanine green fluorescence angiography confirming complete exclusion of the residual aneurysm. The white arrow indicates the aneurysm dome without contrast filling or residual flow. RON: Right optic nerve; LON: Left optic nerve; R A2: Right A2 segment of the anterior cerebral artery; L A2: Left A2 segment of the anterior cerebral artery.

The patient was extubated in the operating room and admitted to the neurocritical care unit for postoperative monitoring. Her recovery was uneventful; she remained neurologically intact and was discharged home on postoperative day 5. Outpatient neurovascular follow-up was arranged for long-term surveillance.

Case 2

A 60-year-old woman with a medical history of asthma, anxiety, and depression was diagnosed in 2015 with a ruptured saccular aneurysm at the bifurcation of the right middle cerebral artery (MCA). She underwent endovascular coil embolization, achieving complete occlusion (Raymond– Roy Class I). Initial postoperative angiography demonstrated durable exclusion of the aneurysm. However, serial follow-up studies revealed progressive coil compaction and subsequent extrusion beyond the aneurysm dome. By 2024, cerebral angiography confirmed a recurrent aneurysm at the previously treated site. Following multidisciplinary review, the patient was scheduled for microsurgical clipping [Figure 4].

Figure 4:

Preoperative and follow-up right internal carotid artery angiography of a previously coiled right middle cerebral artery bifurcation aneurysm. (a) Right internal carotid artery angiography demonstrating a saccular aneurysm of the right middle cerebral artery bifurcation. The arrowhead indicates the original ruptured saccular aneurysm. (b) Complete coil embolization of the aneurysm dome and neck. The arrowhead indicates coils within the aneurysm sac. (c) Follow-up angiography at 3 years demonstrating adequate coil compaction with preserved patency of the adjacent arterial branches. The arrowhead indicates compacted coils within the aneurysm sac. (d) Angiographic follow-up at 10 years revealing coil extrusion beyond the aneurysmal dome and residual aneurysm formation. The arrowhead indicates extruded coils beyond the aneurysm dome, whereas the arrow indicates the residual aneurysm. A1: A1 segment of the anterior cerebral artery; M1: M1 segment of the middle cerebral artery; M2: M2 segment of the middle cerebral artery.

A stereotactic right pterional craniotomy was performed with neuronavigation guidance. Intraoperatively, dense adhesions were encountered around the complex MCA bifurcation aneurysm with early branch incorporation, consistent with prior endovascular intervention. Under continuous neurophysiological monitoring, meticulous arachnoid dissection was performed to release the adhesions and expose the aneurysm neck. Two curved clips were sequentially applied across the neck to reconstruct the bifurcation and achieve complete aneurysm obliteration. ICG videoangiography and micro-Doppler ultrasonography confirmed complete exclusion of the aneurysm and preserved flow in all MCA branches [Figure 5].

Figure 5:

Intraoperative views of a residual saccular aneurysm of the right middle cerebral artery previously treated with endovascular coiling. (a) Residual saccular aneurysm of the right middle cerebral artery with coil extrusion beyond the aneurysmal dome. The arrow indicates extruded coils, whereas the arrowhead indicates the residual aneurysm dome. (b) Definitive microsurgical clipping performed using two curved clips, achieving complete exclusion of the residual aneurysm. The arrow indicates extruded coils adjacent to the clipped aneurysm. (c) Indocyanine green fluorescence angiography confirming complete exclusion of the residual aneurysm. The arrow demonstrates the absence of contrast filling within the residual aneurysm dome adjacent to the extruded coils. M1: M1 segment of the middle cerebral artery; M2: M2 segment of the middle cerebral artery.

The patient was extubated in the operating room and transferred to the ICU in stable condition. Neurological examination demonstrated intact orientation and no focal deficits. Postoperative computed tomography (CT) on day 1 revealed expected surgical changes without hemorrhage or infarction, and computed tomography angiography (CTA) confirmed occlusion with patency of adjacent MCA vessels. The patient was discharged home neurologically intact on postoperative day 4 with plans for routine outpatient neurovascular surveillance.

Case 3

A 66-year-old woman with a medical history of hypertension and hypothyroidism had previously undergone successful coil embolization of a ruptured azygos anterior cerebral artery (ACA) aneurysm in 2005 (Raymond–Roy Class I). She remained neurologically stable with long-term clinical follow-up. In early 2025, routine surveillance imaging demonstrated recanalization with deformation of the dome secondary to coil extrusion. Given the unfavorable morphology for reembolization and the associated risk of rerupture, the case was reviewed in a multidisciplinary conference including neurosurgery, neurology, and interventional neuroradiology. Microsurgical clipping was selected as the definitive management [Figure 6].

Figure 6:

Follow-up cerebral angiography at 20 years demonstrating a recurrent aneurysm of the azygos anterior cerebral artery with evidence of coil migration outside the aneurysmal sac. (a) Cerebral angiography demonstrating a residual aneurysm of the azygos anterior cerebral artery. The arrowhead indicates extruded coils outside the aneurysmal sac, whereas the black arrow indicates the residual aneurysm. The white arrow indicates the azygos anterior cerebral artery. (b) Magnified view of the same configuration for better characterization. The arrowhead indicates extruded coils outside the aneurysmal sac, whereas the black arrow indicates the residual aneurysm. The white arrow indicates the azygos anterior cerebral artery. (c) Three-dimensional cerebral angiography demonstrating dome deformation of the aneurysm caused by extruded coils. The arrowhead indicates the residual aneurysm, whereas the white arrow indicates the azygos anterior cerebral artery.

An anterior interhemispheric approach was performed with stereotactic neuronavigation and continuous intraoperative electrophysiological monitoring. Upon arachnoid dissection, extruded coils were identified as densely adherent to the surrounding frontal lobe parenchyma. Careful, high-magnification microdissection was undertaken to release adhesions and expose the aneurysm dome and neck. A right-angled fenestrated clip was applied across the aneurysm base, followed by a straight fenestrated clip positioned perpendicularly to reinforce closure and ensure stability. ICG videoangiography and micro-Doppler ultrasonography confirmed complete aneurysm exclusion with preserved flow in the bilateral A2 and A3 segments [Figure 7].

Figure 7:

Intraoperative photographs demonstrating the stepwise microsurgical dissection and clipping of a recurrent azygos anterior cerebral artery aneurysm with coil extrusion beyond the aneurysmal dome. (a) Microsurgical exposure of the residual aneurysm with coil extrusion beyond the dome. The arrowhead indicates the residual aneurysm, whereas the arrow indicates extruded coils. (b) Sequential application of a right-angled fenestrated clip for reconstruction of the aneurysm neck. The arrowhead indicates the residual aneurysm, whereas the arrow indicates extruded coils. (c) Application of a straight fenestrated clip achieving complete occlusion of the recurrent aneurysm. The arrowhead indicates the residual aneurysm dome. (d) Intraoperative indocyanine green video angiography confirming complete obliteration of residual aneurysmal flow. The arrowhead indicates the excluded aneurysm dome. Az: Azygos anterior cerebral artery. A3: A3 segment of the anterior cerebral artery; Az: Azygos anterior cerebral artery.

The patient was admitted to the ICU intubated for immediate postoperative observation. Noncontrast CT and CT angiography demonstrated complete aneurysm obliteration without hemorrhage or ischemic infarction. She was subsequently extubated without complications, remained neurologically intact, and was discharged home on postoperative day 5 with a plan for continued outpatient neurovascular surveillance.

DISCUSSION

Review of current literature

Pathophysiology and mechanisms of recurrence after coiling

Endovascular coil embolization has become the first-line treatment for many intracranial aneurysms due to its minimally invasive nature and favorable perioperative safety profile, particularly in elderly patients and those with surgically inaccessible lesions.[18,55] Despite these advantages, durability remains a limitation, with recurrence reported in 15–34% of coiled aneurysms[32,38] compared with recurrence rates of 1–3% after microsurgical clipping.[9]

Mechanisms of recurrence include coil compaction, aneurysm regrowth, fundal migration, and coil extrusion.[19,20,47] Coil compaction is often attributed to the “water-hammer effect,” pulsatile arterial flow, and thrombus resorption leading to gradual deformation of the coil mass.[8,17] By contrast, aneurysm regrowth reflects biological remodeling, with imaging studies suggesting that enlargement of the sac can independently drive recurrence, even in the absence of coil displacement.[6,19] Histopathological analyses of recurrent aneurysms following coiling have demonstrated chronic inflammatory changes, smooth muscle cell degradation, and adventitial remodeling, particularly in cases complicated by coil extrusion.[23,50] These pathological processes compromise aneurysm wall integrity and permit coil migration beyond the sac, as observed in all three cases in our series.

Clinical implications of coil extrusion

Coil extrusion is an uncommon and underrecognized phenomenon that may occur years or even decades after the index procedure. It reflects a fundamental failure of the aneurysm wall to heal, altering intra-aneurysmal hemodynamics and predisposing to delayed recurrence. For example, in our third case, an azygos ACA aneurysm remained stable for nearly 20 years before exhibiting late recurrence associated with dome deformation and coil extrusion.[50]

Clinically, extrusion may present with headache, new neurological deficits, or be incidentally detected on surveillance imaging. From a therapeutic standpoint, coil extrusion complicates re-embolization: distorted anatomy reduces achievable packing density and increases the risk of coil instability.[39] In such circumstances, microsurgical clipping often represents the only viable salvage strategy, permitting direct visualization and definitive exclusion of the aneurysm. From a cerebrovascular standpoint, recurrent aneurysms with coil instability or extrusion may also increase thromboembolic risk due to disturbed intra-aneurysmal flow dynamics and parent vessel interaction, further supporting consideration of definitive exclusion strategies in appropriately selected patients.

Role and technique of surgical clipping in recurrent aneurysms

Microsurgical clipping continues to provide a durable, definitive treatment in cases of recurrence, particularly those involving coil extrusion, large neck remnants, or unfavorable dome geometry.[42] However, previously coiled aneurysms pose unique technical challenges; adhesions, scarred tissue planes, and coil-laden domes necessitate meticulous microdissection and advanced intraoperative adjuncts.[52] In our experience, and consistent with prior literature, the combination of neuronavigation, intraoperative neurophysiological monitoring, ICG videoangiography, and micro-Doppler ultrasonography is indispensable for safe dissection and clip placement.

Several series confirm the safety and efficacy of clipping in this context. Daou et al. reported 97.3% complete occlusion in 111 patients with only 1.8% recurrence and 2.7% mortality.[9] Izumo et al. highlighted the utility of tandem and fenestrated clips when coil masses were densely compacted at the neck.[18] A meta-analysis by Petr et al. demonstrated that direct clipping without coil removal was associated with lower morbidity (5.0%) and superior outcomes compared with coil extraction or parent vessel occlusion.[34]

In smaller focused series, Panagiotopoulos et al. reported complete occlusion in all nine patients undergoing clipping for recurrent aneurysms after coiling, with no procedure-related morbidity and excellent functional outcomes (mRS 0–1 at follow-up).[33] Deshaies et al. described three patients managed with clipping and coil extraction, all with favorable outcomes and no complications.[10] While their approach differed from ours, which achieved complete obliteration without coil removal, both experiences underscore the versatility of microsurgical strategies and the need to tailor intervention to intraoperative findings.

Additional reports reinforce these principles. Nisson et al. emphasized the importance of individualized case selection, with microsurgical clipping offering durable results when recurrence involved unfavorable necks, regrowth, or extrusion.[31] Similarly, Wu et al. observed coil extrusion in 71% of previously coiled recurrent aneurysms and achieved high rates of complete exclusion through clipping, with or without coil removal, depending on operative anatomy.[52] Our own illustrative cases highlight these principles, demonstrating successful microsurgical clipping of recurrent aneurysms with coil extrusion and complete occlusion across different vascular territories [Figure 8].

Figure 8:

Six-month follow-up three-dimensional computed tomography angiography demonstrating successful microsurgical clipping with complete occlusion of previously embolized recurrent aneurysms associated with coil extrusion. (a) Complete closure of a recurrent anterior communicating artery aneurysm using two straight clips in a tandem configuration. (b) Complete occlusion of a recurrent middle cerebral artery aneurysm achieved using two curved clips. (c) Complete closure of a recurrent azygos anterior cerebral artery aneurysm using a right-angled fenestrated clip and a straight fenestrated clip. The yellow circles indicate the region of interest containing the treated recurrent aneurysm and corresponding microsurgical clip construct in each postoperative CTA reconstruction. Please add this information to the figure legend.

Patterns of coil extrusion and microsurgical implications

From a microsurgical perspective, coil extrusion may be conceptually categorized according to the predominant direction of coil migration and its impact on clip reconstruction. In our experience and review of the literature, three practical patterns can be recognized: (1) neck-directed extrusion, (2) extra-saccular extrusion beyond the aneurysm dome, and (3) bulky extrusion compromising parent vessel reconstruction.

Neck-directed extrusion may still permit direct clip reconstruction when an adequate residual neck remains relatively free of coils. In these cases, preoperative angiography frequently demonstrates a clipable neck remnant despite recurrence, allowing preservation of the coil mass in situ and minimizing the need for coil extraction.

By contrast, extra-saccular extrusion beyond the aneurysm dome often results in dense adhesions involving the arachnoid planes, parent vessels, perforators, and surrounding neurovascular structures. This pattern substantially increases operative complexity and requires meticulous sharp microsurgical dissection under high magnification to safely mobilize the aneurysm dome and expose the neck.

A third pattern involves bulky coil extrusion toward the parent artery or incorporated branches, where the coil mass may mechanically interfere with safe clip application or compromise vessel patency. In selected cases, partial coil mobilization or limited coil extraction may become necessary to achieve adequate neck reconstruction. Importantly, extra-saccular extrusion also reflects structural failure of the aneurysm wall and incomplete exclusion from the circulation. Persistent hemodynamic stress and coil instability may therefore contribute to progressive aneurysm enlargement and increased rerupture risk, favoring definitive microsurgical reconstruction when technically feasible.

Importance of long-term surveillance

The importance of long-term surveillance after endovascular treatment cannot be overstated. While the majority of recurrences occur within the first 2 years, delayed recanalization and coil extrusion have been documented even two decades after the index procedure, as exemplified by our third case. Current guidelines recommend follow-up imaging for aneurysms with incomplete occlusion, wide-neck morphology, or unusual hemodynamics.[15,36] However, there remains no consensus regarding the optimal duration, frequency, or imaging modality for surveillance.

Our findings support an individualized surveillance strategy, particularly in younger patients and in aneurysms treated with partial coiling, wide-neck geometry, or bifurcation configurations, all of which are established risk factors for recurrence.[19,36,47] Several studies suggest that sac regrowth is the dominant driver of recurrence, often independent of coil compaction or migration.[14,19,35] Although the risk of rebleeding after coiling is generally low, the potential for late recurrences underscores the need for lifelong imaging surveillance, especially in patients with high-risk anatomical features.[21,23]

Imaging advancements in planning and surveillance

Recent advances in imaging are reshaping both the surveillance of coiled aneurysms and the planning of microsurgical salvage. High-resolution VWI has emerged as a valuable adjunct for assessing aneurysm wall integrity. Enhancement of the aneurysm wall on VWI correlates with inflammation and instability; circumferential enhancement before treatment has been associated with higher rates of postcoiling recurrence, with odds ratios as high as 14 in some series.[13] In the follow-up of coiled aneurysms, persistent sac enhancement has been positively correlated with recanalization, particularly in cases with >3 mm dome recurrence.[23] These findings suggest that VWI may serve as an early biomarker for recurrence risk, enabling targeted surveillance and timely intervention.

Beyond VWI, four-dimensional flow MRI (4D-flow) provides noninvasive quantification of intra-aneurysmal hemodynamics and wall shear stress. By visualizing unstable flow patterns that predispose to coil compaction or sac regrowth, 4D-flow may function as a functional biomarker of recurrence risk and complement anatomic imaging.[43]

Dual-energy CT angiography (DE-CTA) has also demonstrated significant value in follow-up of coiled aneurysms. By improving delineation of contrast from metallic artifacts, DE-CTA achieves >90% sensitivity and specificity in detecting residual necks, compared with <10% sensitivity for conventional CTA.[51] This improved resolution enhances both long-term surveillance and preoperative planning for surgical salvage.

Together, these modalities enable neurosurgeons to stratify recurrence risk, refine surveillance protocols, and optimize surgical planning in cases of coil extrusion or complex regrowth. Their integration into clinical workflows may facilitate earlier identification of unstable aneurysms and improve preparedness for technically demanding salvage procedures.

When to transition from endovascular to open surgery

Determining the appropriate juncture to transition from endovascular therapy to microsurgical clipping requires a multifactorial assessment of aneurysm anatomy, recurrence pattern, and prior treatment history. While many recurrences can be managed with repeat endovascular treatment, certain morphologies are unfavorable for further reconstruction. Accordingly, retreatment selection often begins by weighing endovascular alternatives and their indications, durability, and risks relative to microsurgical clipping.

Flow diversion

Flow diversion has emerged as a prominent retreatment strategy after coiling, offering a reconstructive approach with high occlusion rates. Studies report complete obliteration in approximately 80–90% of previously coiled aneurysms treated with flow-diverting stents[24,26,54] with lower recurrence compared with repeat coiling.[26] This strategy is particularly useful for broad-neck and large recurrences that are difficult to secure with coiling, but it requires antiplatelet therapy and carries an approximate 5% risk of ischemic or hemorrhagic complications.[24] Compared with microsurgical clipping, flow diversion is less invasive and can achieve comparable mid-term occlusion[26] whereas clipping typically provides near-immediate definitive exclusion with minimal recurrence at the cost of craniotomy and potentially higher periprocedural morbidity in the retreatment setting.[28] These advantages are anatomy-dependent and may be attenuated in complex recurrences with coil instability or extrusion, where definitive mechanical exclusion with clips may be preferred.

Intrasaccular devices (WEBs)

Intrasaccular devices such as the Woven EndoBridge provide a stentless endovascular alternative for recurrent wide-neck bifurcation aneurysms. By directly filling the aneurysm, WEB avoids permanent stents and prolonged dual antiplatelet therapy.[28] Reported initial complete occlusion rates are lower than with clipping, with approximately 43% complete occlusion versus 96% with clipping in ruptured aneurysms, and 5–10% of treated aneurysms may require further treatment.[28,36,37,45] Nevertheless, recurrences after WEB are often manageable with additional endovascular therapy, particularly flow diversion or stent-assisted coiling (SAC).[5] Moreover, reported retreatment morbidity is low (approximately 5%).[5] However, WEB is limited to specific morphologies and may yield lower complete obliteration rates than clipping.[28] Thus, while WEB can be attractive in properly selected bifurcation lesions, microsurgical clipping remains the most definitive option when complete immediate exclusion is required or when endovascular reconstruction is constrained.

Stent-assisted coiling SAC

SAC is an established salvage strategy for recurrent aneurysms, using a stent scaffold to support coil packing and improve occlusion durability relative to coiling alone.[12] Recent series indicate that stent-assisted retreatment yields high aneurysm obliteration rates, with approximately 70–80% complete occlusion at follow-up, approaching microsurgical clipping. Drawbacks include the need for antiplatelet therapy and risks such as thrombosis or instent stenosis; overall complication rates remain low, with an incidence of 3–5%.[28] Anatomically, SAC can address recurrence patterns that include bifurcation aneurysms that may be poorly suited for flow diversion.[40] By contrast, clipping of previously coiled aneurysms, while definitively curative, can be technically demanding. In a single-center cohort of 39 patients (40 aneurysms), Shtaya et al. reported 5.1% permanent morbidity with no deaths or rebleeding and noted that coil-mass extraction was strongly associated with complications and unfavorable morphometrics, supporting coil removal only when unavoidable.[44] Taken together, these data support SAC as an effective, less invasive first-line retreatment for many recurrent aneurysms, while acknowledging that clipping remains a durable option when anatomy or prior implants preclude safe endovascular reconstruction.

Decision thresholds for transitioning to open surgery

The most common indications for microsurgical salvage after coiling include residual neck or neck regrowth (approximately 48%) and new dome enlargement (approximately 45%).[3] Wide-neck or bifurcation aneurysms with branch incorporation are particularly prone to anatomical constraints that limit endovascular options. Similarly, patients with multiple failed endovascular interventions are less likely to benefit from additional coiling and more likely to achieve durable exclusion through clipping.[9]

Coil extrusion represents a distinct marker of endovascular failure. Extruded coils signify structural wall breakdown and can cause mass effect, thromboembolic events, or cranial neuropathy when protruding into the subarachnoid space or parent artery.[2,16,53] Imaging evidence of coil loops extending beyond the aneurysm sac is therefore considered a strong indication for open surgery, since flow diversion in the setting of displaced coils carries high risk, especially in aneurysms located in distal arteries as in our three presented cases.

Microsurgical clipping in these contexts has consistently achieved rates of complete obliteration exceeding 90%, with procedure-related morbidity of 5–10% and low mortality.[3,9] Surgical complexity increases when coil extraction is required, as this is associated with higher rates of perioperative stroke; therefore, most authors recommend leaving coils in situ unless they obstruct safe clip placement.

Decision-making should balance the feasibility of further endovascular intervention against the risks and benefits of open surgery. Factors favoring microsurgical salvage include recurrent aneurysms with coil instability or extrusion, as well as complex neck morphology with branch or perforator incorporation, conditions that limit the durability and safety of further endovascular retreatment. Despite these principles, a standardized classification of recurrent aneurysms to guide retreatment algorithms remains needed.[33] Until then, management should rely on a multidisciplinary, individualized approach, with microsurgery reserved for cases where endovascular strategies cannot ensure long-term durability.

Contemporary case literature on coil extrusion

Several published reports have specifically examined microsurgical management of recurrent aneurysms with coil extrusion. These series consistently demonstrate that clipping, when performed with appropriate adjuncts, achieves high occlusion rates and low complication rates.[10,30,33,42] Representative contemporary series describing microsurgical treatment of recurrent aneurysms with coil extrusion after prior coiling are summarized in Table 4. Deshaies et al. reported three cases requiring coil extraction at the time of clipping; all patients achieved complete occlusion with no procedure-related morbidity.[10]

Table 4:

Summary of reported cases of recurrent aneurysms after coiling, with or without coil extrusion.

Wu et al. observed coil extrusion in 71% of previously coiled recurrent aneurysms, with durable occlusion achieved through clipping performed with or without coil removal depending on intraoperative findings.[52] Panagiotopoulos et al. described nine patients undergoing clipping for recurrences, including cases of extrusion, achieving 100% obliteration and excellent long-term outcomes (mRS 0–1).[33] Taken together, these reports affirm that microsurgical clipping is a safe and effective salvage strategy in coil extrusion, particularly when intraoperative adjuncts (ICG angiography, Doppler ultrasonography, and neuronavigation) are employed, and coil extraction is avoided unless strictly necessary. Our own series supports this evidence, with complete exclusion achieved in all patients without coil removal and no new neurological deficits.

Our experience demonstrates that microsurgical clipping remains an indispensable salvage option for recurrent aneurysms with coil extrusion, providing definitive exclusion when endovascular strategies are unsafe or ineffective. Across early, late, and very-late recurrences, meticulous microdissection, adjunctive intraoperative imaging, and modern monitoring enabled complete obliteration without coil extraction and with preservation of neurological function. These cases underscore two critical lessons: first, that lifelong surveillance is essential, as recurrence and extrusion may occur decades after treatment; and second, that precise operative strategy, prioritizing preservation of coils unless they obstruct safe clip placement, can minimize morbidity while ensuring durable outcomes.

In the context of growing reliance on endovascular therapy, this report reinforces the continuing relevance of microsurgery as a complementary and often definitive modality. Our proposed technical algorithm provides a structured framework to guide decision-making and operative planning, integrating imaging advancements, multidisciplinary evaluation, and technical pearls from both our cases and the contemporary literature. Ultimately, individualized patient selection, rigorous surveillance, and surgical preparedness are the cornerstones for optimizing outcomes in this uniquely challenging subset of recurrent aneurysms.

Technical pearls for microsurgical salvage after coil embolization

Several technical principles emerged consistently across our cases.

First, detailed preoperative angiographic analysis is essential to determine whether a residual neck relatively free of coils remains available for clip reconstruction. This assessment significantly influences the feasibility of clipping without coil extraction.

Second, preservation of the coil mass in situ should generally be prioritized whenever safe clip placement can be achieved. Coil extraction increases operative complexity and may increase the risk of parent vessel injury or intraoperative rupture.

Third, extra-saccular coil extrusion should alert the surgeon to the likely presence of dense adhesions involving the arachnoid planes and adjacent neurovascular structures. Sharp dissection under high magnification is frequently necessary, and aggressive traction should be avoided.

Fourth, intraoperative adjuncts including ICG videoangiography, micro-Doppler ultrasonography, neuronavigation, and neurophysiological monitoring are critical for confirming aneurysm exclusion and branch preservation during clip reconstruction.

Finally, retreatment strategy should remain individualized and multidisciplinary, integrating aneurysm morphology, recurrence pattern, branch incorporation, coil instability, and the feasibility of durable endovascular reconstruction.

Key take-home points

Coil extrusion is rare but clinically significant, and may occur even decades after initial coiling, underscoring the need for lifelong surveillance. Endovascular retreatment is often limited in cases of extrusion or wide-neck recurrence; microsurgical clipping provides a durable, definitive solution.

Meticulous microsurgical dissection with preservation of coils in situ (unless obstructing clip placement) reduces operative risk and facilitates safe reconstruction. Modern adjuncts neuronavigation, intraoperative neurophysiological monitoring, ICG videoangiography, and Doppler ultrasonography are essential to optimize safety and ensure parent vessel patency. Our proposed technical algorithm provides a structured framework for surgical salvage, integrating surveillance imaging, multidisciplinary evaluation, and intraoperative pearls to improve decision-making and outcomes.

CONCLUSION

Microsurgical clipping remains a critical salvage strategy for recurrent aneurysms complicated by coil extrusion, particularly when endovascular options are no longer feasible. Our case series highlights the technical challenges posed by scarred tissue planes and coil-adherent domes and demonstrates that complete and durable aneurysm exclusion can be achieved without coil removal, using meticulous microdissection and modern intraoperative adjuncts. Importantly, recurrence and extrusion may arise many years after initial treatment, underscoring the necessity for lifelong surveillance, especially in wide-neck, bifurcation, or partially coiled aneurysms. By integrating contemporary imaging modalities, multidisciplinary evaluation, and advanced microsurgical techniques, patient outcomes can be optimized even in this high-risk subset. The proposed technical algorithm provides a structured framework to guide surgical decision-making and operative execution. Ultimately, microsurgical clipping continues to play an indispensable role in the comprehensive management of complex, recurrent aneurysms and should remain part of the armamentarium of the modern vascular neurosurgeon.

Ethical approval:

The research/study was approved by the Institutional Review Board at Miami Neuroscience Center at Larkin IRB. Title: CNS, Neurosurgery Oncology and Vascular Neurology Outcomes Research number LCH-8-062021, dated November 1st, 2023.

Declaration of patient consent:

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given consent for their images and other clinical information to be reported in the journal. The patient understands that the patient’s names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

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