Endovascular treatment strategies for giant cerebral aneurysms: a narrative review

Introduction

Giant cerebral aneurysms (GCAs), defined as those ≥25 mm in diameter, are a rare but clinically significant subset of cerebral aneurysms, accounting for approximately 2–5% of all cases (1-3). GCAs can arise in any vascular territory, with each location presenting unique therapeutic challenges. They are slightly more common in older adults and show a female predominance. Despite their low prevalence, GCAs are associated with disproportionately high morbidity and mortality due to their aggressive natural history, high rupture risk, and mass effect on adjacent structures. Unlike smaller aneurysms, GCAs often present with progressive neurological symptoms such as cranial nerve palsy, seizures, or mass effect before rupture. Their pathogenesis involves complex vascular remodeling, thrombosis, hemorrhage, and altered hemodynamics. The annual rupture risk exceeds 6%, with untreated cases showing mortality rates as high as 65% within 2 years (4-7).

Key rupture predictors include aneurysm size, irregular morphology, anterior communicating artery location, smoking, and younger age (7-11). Among large (15–24 mm) and giant aneurysms, about 29% are classified as giant. Rupture risk is location-dependent, with posterior circulation GCAs showing a five-year cumulative rupture rate of ~50%, compared to ~40% in the anterior circulation (Table 1).

While traditional microsurgical options like clipping and bypass were historically used, advancements in neuroendovascular techniques have shifted the treatment paradigm. Flow diversion (FD) and parent artery occlusion (PAO) are now considered primary treatment modalities, enabling more personalized, anatomy-specific management. These techniques are especially valuable in aneurysms not amenable to vessel-preserving strategies or with complex morphology.

Treatment planning must consider aneurysm morphology (saccular, fusiform, or serpentine), wall characteristics (e.g., thrombosis, calcification), collateral circulation, and lesion stability indicators such as perianeurysmal edema, mural enhancement, or growth on serial imaging. Fusiform and serpentine aneurysms, which are often thrombosed and calcified, tend to cause symptoms from mass effect rather than rupture, particularly when located in the cavernous segment of the internal carotid artery (ICA)—where rupture is rare, and treatment focuses on symptom relief.

This review aims to synthesize current evidence on endovascular treatment strategies for GCAs, focusing on the efficacy, safety, and outcomes of FD, PAO, and adjunctive coiling. We highlight anatomical and morphological considerations across different vascular territories and compare endovascular approaches to microsurgical options where relevant. By systematically appraising the available literature—including multicenter studies, large case series, and illustrative reports—this review also seeks to identify current knowledge gaps and areas for future research and innovation in the management of complex intracranial aneurysms. We present this article in accordance with the Narrative Review reporting checklist (available at https://jni.amegroups.com/article/view/10.21037/jni-25-24/rc).

Methods

An extensive literature review was conducted using the advanced search feature of PubMed (https://pubmed.ncbi.nlm.nih.gov) to identify studies relevant to the endovascular management of large and giant intracranial aneurysms (Table 2). Search terms included combinations of keywords such as “Giant”, “Endovascular”, “Aneurysms”, “Cerebral”, “Flow Diversion”, and “Parent Artery Occlusion”. Additional site-specific searches were performed to distinguish aneurysms located in the anterior versus posterior circulation, and a separate targeted search strategy was used to identify studies related to giant serpentine aneurysms.

Priority was given to multicenter studies, randomized controlled trials, and large case series. However, select case reports were included when they provided novel insights into rare complications, technical nuances, or uncommon anatomical variants relevant to the treatment of giant aneurysms. The inclusion criteria favored studies reflecting contemporary treatment paradigms, with an emphasis on more recent publications to align with current clinical practice.

All included articles were reviewed in detail for study design, patient demographics, aneurysm characteristics, treatment strategies, clinical outcomes, and reported complications. The goal was to synthesize the current evidence on endovascular management, particularly FD, PAO, and adjunctive techniques, and to evaluate their use across different anatomical locations and aneurysm morphologies.

Discussion

Endovascular treatment strategies

GCAs can be classified based on morphology (saccular, fusiform, or serpentine), parent artery relationship (sidewall versus bifurcation), and anatomical location (anterior versus posterior circulation). Recent advancements in endovascular techniques—such as stent-assisted coiling, FD, and PAO—have expanded the therapeutic options for these challenging lesions, offering less invasive alternatives to traditional microsurgical approaches (2,13).

These endovascular methods have demonstrated favorable efficacy and safety profiles in both clinical studies and real-world experience, positioning them as frontline treatments for appropriately selected patients. However, the inherent complexity and variability of large and giant aneurysms necessitate careful consideration of individual anatomical and clinical factors. Broadly, endovascular strategies can be categorized into:

• Deconstructive approaches, which involve occlusion of the parent artery (e.g., PAO), and
• Reconstructive approaches, which aim to preserve the parent artery (e.g., FD and stent-assisted coiling).

PAO

PAO remains a durable and effective treatment for selected GCAs, particularly those involving the cavernous and supraclinoid ICA segments, where balloon occlusion test (BOT) demonstrates sufficient collateral circulation. Multiple studies have reported complete occlusion rates exceeding 90% with PAO, along with low retreatment rates and significant symptom relief. For example, Labeyrie et al. (14) reported a 91% aneurysmal retraction rate, 98% pain improvement, and 72% cranial nerve palsy improvement following PAO, while Bechan et al. (15) achieved 99% aneurysm occlusion with 76% showing shrinkage on follow-up MRI.

Comparative analyses show that PAO provides superior long-term occlusion compared to other endovascular techniques. A meta-analysis (16) comparing PAO without bypass to endovascular coiling for cavernous carotid aneurysms found significantly higher occlusion rates with PAO (93%) versus coiling (67%). Despite its durability, ischemic risk remains a consideration, particularly in patients with delayed venous phase filling on BOT. However, complication rates remain low with two studies reporting ischemic complications at 1.1% (15) and 5% (14) respectively with no procedure-related mortality over a median follow-up of three years.

When compared with other endovascular options like stent-assisted coiling (SAC) and FD, PAO maintains important advantages. Yan et al. (17) found that PAO was associated with lower retreatment rates (9.5%) than SAC (21.9%), and comparable rates to FD (11.5%). Though PAO had a slightly higher morbidity rate than coiling (7% vs. 3%), this difference was not statistically significant, indicating an overall favorable risk-benefit profile in appropriately selected patients (17). The same comparative study reported no significant difference in major complication rates between PAO (19.2%) and FD (16.4%), further supporting the role of PAO as a reliable treatment option (17).

FD with or without adjunctive coiling

FD has transformed the management of GCAs by reconstructing the parent artery and promoting progressive thrombosis especially in giant side wall aneurysms. The Pipeline Embolization Device (Medtronic, Minneapolis, MN, USA) is the most extensively studied, with occlusion rates of 70–90% (18-20), though morbidity is higher in posterior circulation lesions and when multiple devices are required. Adjunctive coiling has been introduced to accelerate thrombosis and reduce rupture risk (21). Several studies have shown improved outcomes with this approach: in one series, complete occlusion was achieved in 89% with FD plus coils versus 61.5% with FD alone (22), and Lin et al. reported 93.1% versus 74.7%, respectively (23). A meta-analysis confirmed these findings, showing improved occlusion rates with FD plus coiling (OR 1.59; 95% CI: 1.06–2.40; P=0.03) (21).

Each strategy carries distinct risks. FD alone may be associated with delayed rupture during the thrombosis phase while dense coiling may increase thromboembolic events (21). Still, adjunctive coiling reduces early rupture and retreatment rates, with device migration and foreshortening more common in FD-alone cases. Meta-analytic data reinforce this: early rupture was seen in 7% of FD-alone cases but 0% with FD plus coils (24). A systematic review of over 3,000 patients also found higher 6-month occlusion (83.5% vs. 69.2%) and lower retreatment (1.75% vs. 12.1%) with FD plus coiling, though complication rates for stroke (OR =1.66) and hemorrhage (OR =1.98) were higher. Importantly, mortality and functional outcomes did not differ significantly between the two strategies (25).

Compared with other endovascular options, FD plus coils provides a reconstructive, vessel-preserving strategy with superior durability. SAC shows lower occlusion (65.6%) and higher retreatment (21.9%) (25), while PAO remains highly effective but requires adequate collaterals and carries ischemic risk. FD alone may be sufficient for fusiform aneurysms in the anterior circulation with low rupture risk, but for large or giant saccular aneurysms with irregular morphology, FD plus coiling offers the best balance of early protection and long-term efficacy.

Site-specific treatment strategies

Anterior circulation

ICA giant aneurysms

Giant ICA aneurysms, particularly those located in the supraclinoid, paraclinoid, and cavernous segments, frequently present with mass effect, cranial neuropathies, and carry a substantial risk of rupture (Figure 1). While microsurgical approaches such as clipping and bypass were traditionally employed, endovascular techniques, especially PAO and FD, with or without adjunctive coiling, have become the mainstay of treatment. The choice of therapy is dictated by aneurysm morphology, the adequacy of collateral circulation, and clinical presentation.

Figure 1 Natural progression of giant ophthalmic internal carotid artery aneurysm. These images show the aggressive progression of a giant ICA ophthalmic aneurysm prior to availability of flow diverting devices. The initial non contrast CT (A) shows a calcified aneurysm wall with layered thrombus. The initial angiogram (B,C) shows the inflow jet just distal to the ophthalmic artery origin with filling of the central portion of the aneurysm. The patient had neurologically failed a balloon test occlusion and was therefore treated with primary coiling (D). Repeat angiogram at 5 months (E) shows a recurrence at the aneurysm neck with medial displacement of the coil mass into the thrombus. The patient was scheduled for repeat treatment but returned one year later with significant progression of the recurrence (F) and was re treated with additional coils (G) after which the aneurysm growth stabilized a CT scan (H) at 3-year shows the coil mass contained within the medial portion of the aneurysm without growth of the peripheral compartment. CT, computed tomography; ICA, internal carotid artery.

PAO has proven highly effective in patients who tolerate BOT. In a series of 146 patients, PAO achieved a 99% occlusion rate with only 1.1% morbidity and frequent resolution of cranial nerve symptoms (9). Long term occlusion in Japanese studies have been reported at 100% (26) and 92.4% (27) with higher cranial nerve recovery respectively. Another European series reported 91% aneurysm retraction, 98% pain relief, and 72% cranial nerve improvement, with a morbidity rate of 5% and no procedural deaths (8). A meta-analysis comparing PAO and coiling found PAO superior, with higher occlusion rates (93% vs. 67%) and lower retreatment rates (6% vs. 18%), albeit with slightly higher morbidity (7% vs. 3%) (11).

FD offers a reconstructive alternative that preserves the parent artery. In the IntrePED study (28) involving 63 giant aneurysms, complete occlusion was achieved in 72%, though the rates of procedure-related morbidity and mortality were 22.7% and 7.6%, respectively (28). Most complications, including ischemia (9%), hemorrhage (6%), and rupture (4.5%), occurred within the first 30 days post-procedure. Similar efficacy and safety rates have been reported from newer FD devices such as FRED (Microvention, Aliso Viejo, CA, USA) (29) with occlusion rate of 71% and ischemic and hemorrhagic complication rates of 6.7% and 8.9%, respectively. Comparative data reveal the highest occlusion rates with PAO (90.5%), followed by FD at 72.0% and SAC at 65.6%. Retreatment rates were lowest in the FD group (11.5% vs. 21.9%) (12). The addition of coiling to FD further improved occlusion rates and reduced retreatment, without a significant increase in complications (15).

Clinical considerations

• Patient selection, BOT results, aneurysm morphology, and presence of thrombus or calcification are key determinants of optimal strategy.
• PAO is ideal for giant ICA aneurysms (especially cavernous and paraclinoid) when BOT is tolerated, offering durable occlusion and symptom relief.
• FD preferably with coils, is preferred when parent artery preservation is essential, particularly in supraclinoid aneurysms.
• Surgical options are limited to cases with failed endovascular therapy or specific anatomical configurations.

Middle cerebral artery (MCA) giant aneurysms

Giant MCA aneurysms represent a particularly complex subset due to their intricate morphology, frequent thrombus burden, and involvement of major arterial branches. While microsurgical clipping has historically been the standard approach—owing to the MCA’s superficial location—advancements in endovascular techniques have expanded treatment options, particularly for surgically inaccessible lesions.

Recent comparative studies suggest no significant difference in clinical outcomes between microsurgical and endovascular modalities for ruptured giant fusiform MCA aneurysms. A review of 32 such patients showed similar aneurysm sizes, preoperative modified Rankin Scale (mRS) scores, and outcomes across both approaches (30).

Stent-assisted coiling has been effectively used for saccular bifurcation aneurysms, while PAO has demonstrated success in treating fusiform M2 lesions, provided BOT is negative (26). In a small series of 11 patients, PAO led to complete occlusion in all cases, and SAC showed good long-term durability, though one case required retreatment (26).

Flow diverters have emerged as a viable reconstructive solution for large and giant MCA aneurysms (Figure 2). In a multicenter study of 47 MCA aneurysms—including 10 giants—occlusion rates increased from 63% at midterm to 91% on final imaging. The overall morbidity and mortality were 8.6% and 2.1%, respectively (31). FD was particularly effective in dissecting, fusiform, or previously treated aneurysms, although its use in bifurcation aneurysms remains limited by risks of delayed rupture, incomplete occlusion, and thromboembolic complications, especially when multiple branches arise from the aneurysm dome (30,31).

Figure 2 The case is courtesy of Professor Pascal M. Jabbour from Thomas Jefferson University. The initial MRI examination (A) demonstrates a partially thrombosed serpentine aneurysm of the right middle cerebral artery. This was confirmed on selective catheter angiography (B,C). Endovascular treatment comprised on layering four overlapping flow diverting FRED (Microvention, Irvine, CA, USA) devices (D) and subsequent coiling through a jailed microcatheter (E). Follow up angiograms at six months (F,G) showed complete aneurysm exclusion with remodeling of the middle cerebral artery and preserved flow. FRED, Flow Redirection Endoluminal Device; MRI, magnetic resonance imaging.

Clinical considerations

• Treatment should be tailored to aneurysm morphology and branch involvement.
• SAC is suitable for saccular bifurcation aneurysms with favorable neck anatomy.
• PAO is effective for fusiform M2 lesions in patients with adequate collateral flow (negative BOT).
• FD is preferred for fusiform, dissecting, or previously treated aneurysms, but carries higher risk when multiple arterial branches originate from the dome.
• Microsurgical clipping remains an option in anatomically favorable or ruptured lesions.

Anterior cerebral artery (ACA) giant aneurysms

Giant ACA aneurysms pose technical challenges due to their frequent thrombus burden and proximity to critical perforators (Figure 3). Microsurgical clipping remains effective, particularly in cases of ruptured or calcified aneurysms. In a surgical series of 112 patients, complete occlusion was achieved in 90.5%, with favorable outcomes in 86.6%. However, ischemic complications occurred in 26%, largely due to perforator injury (27).

Figure 3 Giant anterior communicating artery aneurysm identified on a non-contrast CT (C) performed for headaches. An MRI examination (F) confirmed the presence of the giant anterior circulation aneurysm. The initial angiograms from the right (A) and left (B) internal carotid arteries show flow from both anterior cerebral arteries. The right anterior cerebral artery had broad involvement at the neck while the left anterior cerebral artery had a very narrow inflow. A microcatheter was placed in the aneurysm sac from the left side and a pipeline embolization device was placed across the right anterior cerebral artery covering the aneurysm neck (D,E). The control angiogram (G) demonstrated complete aneurysm occlusion which was stable on the 1-year angiogram (H) and the 3-year MRA (I). CT, computed tomography; MRA, magnetic resonance angiography; MRI, magnetic resonance imaging.

Endovascular approaches have shown mixed results. Coiling alone has demonstrated poor durability, with occlusion rates frequently below 50% and high recurrence rates (32). In a systematic review of giant anterior communicating artery aneurysms, only 16% underwent endovascular or combined treatment. Of these, SAC and adjunctive coiling were the most common techniques, but complex anatomy limited their use and reduced occlusion rates compared to microsurgical clipping (32).

FD, when feasible, has shown promise in achieving progressive thrombosis and reducing mass effect, especially in unruptured, non-calcified lesions (33). A meta-analysis of very large and giant anterior circulation aneurysms showed that FD was relatively safe, with a 17% complication rate—much lower than the 41% observed in the posterior circulation (24). Additionally, the use of adjunctive coiling with FD appeared to mitigate the risk of early rupture (0% vs. 7%) (24).

When microsurgical and endovascular treatments were directly compared, microsurgery achieved higher occlusion rates (85% vs. 67%), but favorable functional outcomes were slightly more common among endovascular patients (92% vs. 87%). Endovascular treatment also had a lower mortality rate (5.6%) (33).

Treatment decisions should be individualized based on aneurysm morphology, rupture status, anatomical location, and patient-specific factors. Microsurgical clipping is preferred in ruptured, calcified, or anatomically favorable aneurysms. FD—with or without adjunctive coiling—is better suited for unruptured, fusiform, or dissecting aneurysms where the risk to perforators is acceptable. In particularly complex cases, hybrid or staged approaches involving both surgical and endovascular strategies may be warranted.

Clinical considerations

• Microsurgical clipping is preferred for ruptured, calcified, or anatomically favorable aneurysms.
• FD with or without coiling is appropriate for unruptured, fusiform, or dissecting aneurysms where perforator risk is manageable.
• Endovascular treatment offers lower mortality and good functional outcomes, but durability may be less than surgery.
• Hybrid or staged approaches (bypass plus endovascular exclusion) may be considered for highly complex cases.

Posterior circulation giant aneurysms

Giant aneurysms in the posterior circulation present formidable therapeutic challenges due to their deep location, proximity to critical brainstem structures, and tendency for mass effect. Common sites include the vertebral artery (VA), basilar artery (BA), vertebrobasilar junction (VBJ), and posterior cerebral artery (PCA) (34,35). While posterior circulation aneurysms are uncommon (1–2% of intracranial aneurysms), a disproportionate number of them are giant in size (34,35). Insights from the Giant Intracranial Aneurysm Registry reveal that aneurysm volume—not simply brainstem displacement—is the principal determinant of neurologic deficit. Larger volumes were significantly associated with worse mRS scores (OR 1.13, P=0.04), whereas factors such as hydrocephalus, cranial nerve displacement, or partial thrombosis showed no independent correlation with poorer outcomes (36) (Figure 4).

Figure 4 The initial sagittal view from a CT angiogram (A) performed for headaches and dizziness shows a centrally thrombosed giant basilar apex aneurysm. This was confirmed by catheter angiogram (B) showing a wide necked centrally thrombosed basilar apex aneurysm incorporating the origins of the posterior cerebral arteries. Stage-1 stent assisted coiling was performed (C) without dense coil packing because of thromboembolic concern due to the presence of the large central thrombus. Angiogram at six months (D) demonstrated coil migration, thrombus resolution and and aneurysm recurrence. A second stent in a Y-configuration was placed with more dense aneurysm packing (E). Follow up angiogram at one year demonstrated coil compaction and aneurysm recurrence (G) which was retreated with coils (H). There was another recurrence at two years (I) with repeat treatment (J) following which the aneurysm stabilized. The patient however did develop mass effect (F) from the aneurysm and hydrocephalus that required ventricular shunting. CT, computed tomography.

Because microsurgical treatment in the posterior circulation is associated with high morbidity and mortality, endovascular approaches have become preferred in most series (34,35). In a literature review of 149 giant serpentine aneurysms, 33 (22.1%) were located in the posterior circulation. Among those, endovascular therapy was more often employed than surgery and was associated with a better clinical trajectory: 50 patients improved with endovascular therapy versus 23 with surgical intervention (37). In a 12-year retrospective series of 22 patients with giant posterior circulation aneurysms, PAO was used in 13 individuals and exhibited the most favorable safety profile—only one death and minimal morbidity (35). A broader review of 147 GSAs also showed that deconstructive endovascular techniques led to clinical improvement in over 55% of cases and were particularly effective in PCA aneurysms even when lesions exceeded 5 cm and caused midline shift (37).

FD has also been explored in posterior circulation GIAs and offers reconstructive potential for fusiform or dissecting lesions (Figure 5). In a cohort of 99 patients with 103 large or giant posterior circulation aneurysms, FD achieved complete occlusion in 74.1% of cases. Favorable clinical outcome (mRS 0–2) was achieved in 93.9% of patients, although overall mortality reached 6.1%, and 5.8% experienced major complications, including brainstem stroke and delayed aneurysm rupture. Lesions not involving side branches or located in the intradural segment of the VA were more likely to achieve complete occlusion (38). A smaller series by Limaye et al. also reported encouraging results using FD or SAC in posterior circulation GIAs, particularly in VA and PCA aneurysms. However, basilar artery aneurysms treated with flow reversal or telescoping stents had markedly higher morbidity and mortality (35). In basilar terminus aneurysms treated with coiling, progressive deformation and worsening curvature of the basilar artery over time have been observed, potentially due to the mechanical torque from coiled mass—especially in larger aneurysms—underscoring the challenges of coiling in this territory (39).

Figure 5 The initial CT angiogram (A) in a patient with dizziness and prior history of anterior communicating artery aneurysm clipping shows a a giant terminal sidewall basilar artery aneurysm. This was confirmed on catheter angiography from a right vertebral artery injection (B,C). Endovascular treatment comprised of flow diversion and light coil packing with placement of a pipeline embolization device from the left posterior cerebral artery to the proximal basilar artery and coil placement from a jailed microcatheter (D,E). No angioplasty of the flow diverter was performed. Control angiography (F,G) demonstrated reduced flow and stasis within the aneurysm. The patient presented three days later in a coma and a CT scan showed massive subarachnoid and intraventricular hemorrhage (H). An autopsy was performed (I) showing and intact aneurysm sac but a focal rent in the distal basilar artery adjacent to a plaque at the basilar artery bifurcation. The presumed hypothesis was slow stretching of a weakened basilar artery adjacent to the atheroma. CT, computed tomography.

Clinical considerations

Treatment selection for giant posterior circulation aneurysms depends heavily on location, aneurysm morphology, size, side branch involvement, and collateral status:

• PAO: first line in vertebral or PCA aneurysms with adequate collaterals; safe and highly effective.
• FD with adjunctive coiling is useful in anatomically complex or fusiform aneurysms where PAO is contraindicated.
• FD: suitable for fusiform or dissecting aneurysms not involving critical perforators or when parent vessel preservation is essential. Caution is warranted in basilar artery aneurysms and when multiple devices are required. Basilar artery truncal aneurysms carry the highest risk, and FD or telescoping stents should be approached cautiously with meticulous planning and close follow-up.
• SAC or coiling: may be considered in saccular aneurysms or where FD poses unacceptable risk.

While procedural risks remain non-negligible, endovascular treatment has significantly improved outcomes in this historically high-risk group.

Special consideration—giant serpentine aneurysms

Giant serpentine aneurysms (GSAs) are a distinct and rare subtype, defined by a large (≥25 mm), partially thrombosed aneurysm containing a tortuous intraluminal vascular channel with distinct inflow and outflow tracts. They constitute about 17.6% of all giant aneurysms and fewer than 0.1% of intracranial aneurysms (37,40,41). GSAs most commonly arise in the MCA, PCA, or posterior circulation (37,40,41). Unlike typical saccular aneurysms, hemorrhagic rupture is rare; patients more often present with mass effect, cranial neuropathies, brainstem compression, or ischemia (42).

Historically, surgical bypass and resection were attempted. However, early reports documented morbidity ranging from 30% to 35%, and the challenges of revascularization led clinicians toward more endovascular approaches (37,40,41). Cross-sectional imaging (MRI, CT) reveals the thrombosed core, perianeurysmal edema, and mass effect, while digital subtraction angiography delineates the functional serpentine lumen. Hemodynamic theories such as the Coandă effect—where flow tends to adhere to the vessel wall and promotes asymmetric thrombus layering—help explain the serpentine morphology in these lesions (43).

Today, PAO (with or without bypass) remains the mainstay of therapy for GSAs. A systematic review by Atallah et al. (n=83) found that PAO was the most commonly applied and effective strategy. Clinical improvement was documented in 66.7% of patients, with mortality of 5.1% and deterioration of 28.2%. Neurologic complications were more likely in patients presenting with seizures or visual disturbances, emphasizing the importance of early diagnosis and timely intervention. In a classic series by van Rooij et al., three GSAs in the ACA and MCA territories were successfully treated using endovascular intraluminal trapping (coils or glue) after BOT; all patients tolerated the occlusion and achieved good outcomes, reaffirming the role of PAO when adequate collateral circulation is present (44).

Although less commonly used, FD has shown promise in select GSAs, particularly when preserving the parent artery is desirable. In a single-center series of 13 patients, Tong et al. reported angiographic occlusion in 72.7% and favorable outcomes in 66.7% at 6 months. However, because GSAs already contain intraluminal thrombosis and variable flow, the use of FD must be judicious, especially in posterior circulation cases, as the risk of complications is higher than in saccular aneurysms (42).

Posterior circulation giant serpentine aneurysms tend to progress more aggressively than their anterior counterparts (Figure 6), with greater risk of enlargement, thrombosis, and ischemic complications (27). In such cases, deconstructive endovascular therapy frequently offers the most viable strategy. Treatment selection revolves around aneurysm location, morphology, side-branch involvement, and collateral status. PAO remains the primary option for vertebral or PCA aneurysms when collateral circulation is adequate, providing relatively safe and effective exclusion. FD, often with adjunctive coiling, becomes preferable when anatomical complexity or the need for vessel preservation contraindicates PAO. In basilar artery aneurysms, especially those involving the trunk, FD or telescoping stents must be approached with great caution and meticulous planning. SAC or conventional coiling may be considered in saccular aneurysms or when FD poses unacceptable risk. Although procedural risk remains non-trivial, modern endovascular therapy has considerably improved outcomes in this historically high-risk population.

Figure 6 A giant likely dissecting aneurysm of the left posterior cerebral artery is demonstrated on the initial angiogram (A,B). The patient presented with headaches without visual symptoms. The aneurysm underwent endovascular treatment with primary coiling. Loose coiling of the aneurysm sac was performed followed by closure of the inflow at the proximal posterior cerebral artery (C,D). The patient recovered without deficits due to pial collateral supply from the middle cerebral artery.

In managing GSAs, PAO remains the safest and most reliable first-line option when collateral flow is adequate. Flow diverters offer reconstructive capabilities but carry a greater risk in GSAs compared to saccular aneurysms and should be used only in carefully selected cases. Surgical strategies, including bypass or trapping, should be reserved for salvage situations or anatomically unfavorable lesions where endovascular methods are not feasible.

Clinical considerations

• PAO is safe and effective for GSAs with adequate collateral flow and should be considered first-line in non-eloquent territories.
• FDs offer reconstructive options but carry higher complication rates in GSAs compared to saccular aneurysms.
• Seizures and visual disturbances at presentation are predictive of worse postoperative outcomes and should prompt early, definitive management.
• Surgical options should be reserved for complex or salvage cases.

Limitations

This review has several limitations. First, most available evidence regarding endovascular treatment of large and giant intracranial aneurysms is derived from retrospective studies, single-center series, or registries, which are subject to inherent biases in patient selection, reporting, and follow-up. Randomized controlled trials comparing PAO, FD, and other reconstructive techniques are lacking, making direct comparisons across modalities challenging. Second, outcomes vary considerably depending on aneurysm morphology, anatomical location, and operator expertise, which limits the generalizability of reported results. Third, many studies report heterogeneous follow-up periods, and long-term durability of newer devices such as next-generation flow diverters remains incompletely defined. Finally, site-specific recommendations should be interpreted with caution, as most evidence comes from small subgroups rather than large, systematically studied populations.

Conclusions

The endovascular management of large and giant intracranial aneurysms has advanced significantly, yet challenges persist in balancing efficacy, safety, and long-term durability. Both PAO and FD—especially when combined with adjunctive coiling—play established roles, with treatment strategies tailored to aneurysm characteristics and individual patient risk profiles. Despite notable progress, procedural risks and anatomical complexities continue to necessitate careful planning and expert execution.

Looking forward, future innovations in device technology, hemodynamic modeling, and imaging-guided treatment planning hold great potential to further improve outcomes. Continued comparative research, including prospective multicenter studies, is essential to refine treatment algorithms and establish best practices for managing complex aneurysm subtypes. As endovascular tools and techniques evolve, the overarching goal remains to provide safer, more durable, and patient-centered care for this high-risk population.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editors (Tufail Patankar, Ricardo Hanel and Jeremy Lynch) for the series “Intracranial Aneurysms Current Status and Future Prospects” published in Journal of Neurointervention. The article has undergone external peer review.

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://jni.amegroups.com/article/view/10.21037/jni-25-24/rc

Peer Review File: Available at https://jni.amegroups.com/article/view/10.21037/jni-25-24/prf

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://jni.amegroups.com/article/view/10.21037/jni-25-24/coif). The series “Intracranial Aneurysms Current Status and Future Prospects” was commissioned by the editorial office without any funding or sponsorship. A.T.R. reports consulting fees received from Stryker Neurovascular, J&J Med Tech, Jacobs Institute. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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