The significant impact of framing coils on long-term outcomes in endovascular coiling for intracranial aneurysms: how to select an appropriate framing coil

Risk factors for recanalization after coil embolization for cerebral aneurysms: importance of the first coil and prediction model

BACKGROUND

Endovascular coil embolization for cerebral aneurysms is a well-established treatment; however, postoperative recanalization remains a risk. This study aimed to clarify risk factors for cerebral aneurysm recanalization after coil embolization and to develop a predictive model for assessing risks.

METHODS

This retrospective study included patients with cerebral saccular aneurysms who underwent initial coil embolization at our hospital in Tokyo, Japan between 2012 and 2023. The following cases were excluded: follow-up of <1 year, re-treatment and use of bioactive coils. Outcomes included aneurysm characteristics and postoperative Raymond-Roy Occlusion Classification (RROC). Univariate and multivariate Cox proportional hazards models were used to identify independent predictors. A simplified risk score was constructed using LASSO logistic regression and β-coefficients from multivariable analysis. Internal validity was assessed by bootstrap resampling. External validation was performed using an independent cohort and model performance was evaluated in terms of discrimination and calibration.

RESULTS

Among the 150 patients with aneurysms, 79 were analyzed after applying exclusion criteria. Multivariate analysis identified four independent predictors of recanalization: rupture status, aneurysm size ≥7 mm, RROC without class I, and first volume embolization ratio <8 %. These variables were incorporated into an integer-based risk score ranging from 0 to 7. The model demonstrated strong discrimination in the internal validation cohort (C-statistic: 0.89), which remained acceptable in the external validation cohort (C-statistic: 0.81, 95 % CI: 0.74-0.89). Risk stratification showed increasing recanalization rates of 1.8 %, 13.5 %, and 41.5 % in low- (0-2), intermediate- (3-4), and high-risk (5-7) groups, respectively. Calibration in the external cohort showed slight overestimation of risk in high-score patients.

CONCLUSION

This study identified four significant risk factors for recanalization after coil embolization and proposed a practical, externally validated risk score. The model provides clinically relevant risk stratification and may support individualized follow-up strategies.

Simplified volume embolization ratio calculation method in endovascular coiling for unruptured cerebral aneurysms

ObjectiveVolume embolization ratio (VER) is an important factor involved in recurrence rates in endovascular coiling for cerebral aneurysms. However, there is no method to clearly understand it during surgery. We report our simplified aneurysm VER calculation method and discuss the outcomes.MethodsWe performed treatment by calculating the aneurysm volume and coil length using the formula D(length of coil inserted to achieve 100% packing in cm) = 2 V(aneurysm volume in mm3). The volume and VER calculated by our simplified method were denoted as simplified volume (sV) and simplified VER (sVER). The volume and VER were also calculated by the application Angiosuite Neuro Edition, which were denoted as aV and aVER. The volume of the coil calculated by Angiosuite Neuro Edition divided by sV was called simplified Angiosuite VER (saVER). Comparisons were made between the averages of sVER and aVER, and sVER and saVER. Postoperative follow-up was performed by magnetic resonance angiography (MRA) or DSA 3 or 6, and 12 months, and Raymond Roy occlusion classification (RROC) was evaluated.ResultsT-test results were not significantly different between sVER and aVER (P = 0.06) or sVER and saVER (P = 0.9) ( Table 2), the difference in VER due to the calculation method was within the margin of error. Eight of the 18 patients had improved RROC at 12 months, and there were no cases of worsening of the score.ConclusionSimplified calculation method for VER which can be performed in real time and clinically acceptable approximation without the need for a smartphone app.

Interdependence of First-coil and Global volume embolization ratios (VERs) calculated by Sim&Size in predicting aneurysm occlusion outcomes

BackgroundCoil embolization is a standard therapeutic approach for intracranial aneurysms. Recurrence risk during follow-up is not negligible, with inadequate packing density identified as a potential risk factor. This study aims to identify patient- and procedure-related factors contributing to recurrence.MethodsWe retrospectively enrolled consecutive patients with unruptured intracranial aneurysms treated only with coils between January 2021 and December 2022. Aneurysms were included if 3D-rotational angiography and follow-up imaging were available. For each patient, the volume embolization ratio (VER) was computed using Sim&Size® (Sim&Cure, France) for both the framing coil (First-coil VER) and the entire coiling procedure (Global VER). Patient demographics and aneurysm characteristics were also recorded. Follow-up imaging classified patients into adequate- or inadequate-occlusion groups. Multivariate analyses assessed independent factors associated with recurrence.ResultsSeventy-nine unruptured aneurysms from 79 patients were included. At follow-up, n = 69 (87%) demonstrated adequate occlusion, defined as modified Raymond-Roy classification I-II. Adequate- and inadequate-occlusion groups differed in First-coil (13.5 ± 5.5% vs 7.1 ± 4.0% respectively, P = .002) and Global VER (24.5 ± 6.8% vs 17.3 ± 5.7% respectively, P = .004). Posterior aneurysm location (P = .013), aneurysm height (P = .007), and neck diameter (P = .018) were significantly associated with recurrence. In multivariate analysis, Global- (P = .029) and First-coil VER (P = .025) remained significant risk factors for recurrence, with their interaction term being statistically significant as well (P = .020).ConclusionsFirst-coil and Global VER computed using Sim&Size® are predictive of aneurysm occlusion at follow-up. These results highlight the potential value of virtual simulation in optimizing coil packing density to improve mid- to long-term occlusion outcomes.

A deep-learning system to help make the surgical planning of coil embolization for unruptured intracranial aneurysms

BACKGROUND

Coil embolization is a common method for treating unruptured intracranial aneurysms (UIAs). To effectively perform coil embolization for UIAs, clinicians must undergo extensive training with the assistance of senior physicians over an extended period. This study aimed to establish a deep-learning system for measuring the morphological features of UIAs and help the surgical planning of coil embolization for UIAs.

METHODS

Preoperative computational tomography angiography (CTA) data and surgical data from UIA patients receiving coil embolization in our medical institution were retrospectively reviewed. A convolutional neural network (CNN) model was trained on the preoperative CTA data, and the morphological features of UIAs were measured automatically using this CNN model. The intraclass correlation coefficient (ICC) was utilized to examine the similarity between the morphologies measured by the CNN model and those determined by experienced clinicians. A deep neural network model to determine the diameter of first coil was further established based on the CNN model within the derivation set (75% of all patients) using neural factorization machines (NFM) model and was validated using a validation set (25% of all patients). The general match ratio (the difference was within ± 1 mm) between the predicted diameter of first coil by model and that used in practical scenario was calculated.

RESULTS

One-hundred fifty-three UIA patients were enrolled in this study. The CNN model could diagnose UIAs with an accuracy of 0.97. The performance of this CNN model in measuring the morphological features of UIAs (i.e., size, height, neck diameter, dome diameter, and volume) was comparable to the accuracy of senior clinicians (all ICC > 0.85). The diameter of first coil predicted by the model established based on CNN model and the diameter of first coil used actually exhibited a high general match ratio (0.90) within the derivation set. Moreover, the model performed well in recommending the diameter of first coil within the validation set (general match ratio as 0.91).

CONCLUSION

This study presents a deep-learning system which can help to improve surgical planning of coil embolization for UIAs.

Packing density and the angiographic results of coil embolization of intracranial aneurysms: A systematic review and meta-analysis

BACKGROUND

Endovascular coil embolization (ECE) for intracranial aneurysms has been proven as an effective minimally invasive treatment. However, the aneurysm recanalization after coiling is a serious complication of this technique. Among all the proposed factors associated with recanalization, the impact of packing density (PD) is still controversial.

OBJECTIVE

To clarify the role of PD in the aneurysm recanalization following ECE, via conducting a systematic review and meta-analysis.

METHODS

A systematic literature search was conducted using PubMed, Scopus, Embase, and Web of Science databases, until November 28, 2022, by adhering to the Preferred Reporting Items for Systematic Review and Meta-Analyses statement guidelines. Considering the eligibility criteria, all the studies reporting the outcomes of interest were included. Data elements of interest were extracted and analyzed using R software version 4.2.1.

RESULTS

The pooled analysis of the 17 eligible papers revealed a 29% higher PD of the nonrecanalized aneurysms (ROM = 1.29, 95% confidence interval [CI] = 1.18-1.40, p < 0.001), even after removing outlier studies to reduce heterogeneity. However, the pooled estimates from multivariable regression models within nine included studies showed no significant effect of PD on recanalization odds when incorporated into a multivariable model with other predictors (odds ratio [OR] = 0.93, 95% CI = 0.84-1.02, p = 0.126), even after removing outlier studies.

CONCLUSION

The current literature does not support PD as a significant predictor of aneurysm treatment outcomes, especially with adjusting for other variables. This finding necessitates further prospective multicenter studies with a larger sample size to overcome the current methodological shortcomings.

Association of circumferential aneurysm wall enhancement with recurrence after coiling of unruptured intracranial aneurysms: a preliminary vessel wall imaging study

OBJECTIVE

Recent histopathological studies of unruptured intracranial aneurysms (UIAs) have confirmed that aneurysm wall enhancement (AWE) on MR vessel wall imaging (VWI) is related to wall degeneration with in vivo inflammatory cell infiltration. Therefore, pretreatment aneurysm wall status on VWI may be associated with recurrence after endovascular treatment.

METHODS

VWI with gadolinium was performed on 67 consecutive saccular UIAs before endovascular treatment between April 2017 and June 2021. The mean (range) follow-up period after treatment was 24.4 (6-54) months. AWE patterns were classified as circumferential AWE (CAWE), focal AWE (FAWE), and negative AWE (NAWE). The authors retrospectively investigated the relationship between aneurysm recurrence and AWE patterns, as well as conventional risk factors.

RESULTS

Sixty-seven patients with 67 saccular UIAs were eligible for the present study. AWE patterns were as follows: 10 CAWE (14.9%), 20 FAWE (29.9%), and 37 NAWE (55.2%). Follow-up MRA detected aneurysm recurrence in 18 of 69 cases (26.1%). Univariate analysis identified maximum diameter (mean ± SD 5.8 ± 2.2 mm in patients with stable aneurysms vs 7.7 ± 3.8 mm in those with unstable aneurysms, p = 0.02), aspect ratio (1.4 ± 0.5 vs 1.1 ± 0.4, p < 0.01), aneurysm location in posterior circulation (4.1% vs 27.8%, p < 0.01), volume embolization ratio (29.6% ± 7.8% vs 25.2% ± 6.1%, p = 0.02), and AWE pattern (p = 0.04) as significant predictive factors of recurrence. Among the 3 AWE patterns, CAWE was significantly more frequent in the unstable group, but no significant differences in stability of the treated aneurysms were observed with the FAWE and NAWE patterns. In multivariate logistic regression analysis, CAWE pattern (OR 14.2, 95% CI 1.8-110.8, p = 0.01) and volume embolization ratio ≥ 25% (OR 8.6, 95% CI 2.1-34.3, p < 0.01) remained as significant factors associated with aneurysm stability after coiling.

CONCLUSIONS

VWI before coiling provides novel insights into the stability of treated aneurysms. Aneurysms with the CAWE pattern on VWI before coiling may be less stable after treatment.

The first coil embolization ratio is the key factor for retreatment for unruptured cerebral aneurysms

Background

In coil embolization, a high volume embolization ratio prevents recanalization that may require retreatment. However, patients with a high volume embolization ratio may also require retreatment. Patients with inadequate framing with the first coil may experience recanalization of the aneurysm. We analyzed the relationship between embolization ratio of the first coil and recanalization requiring retreatment.

Methods

We reviewed data from 181 patients with unruptured cerebral aneurysms who underwent initial coil embolization between 2011 and 2021. We retrospectively analyzed the correlation between neck width, maximum aneurysm size, width, aneurysm volume, volume embolization ratio of the framing coil (first volume embolization ratio [1^st VER]), and final volume embolization ratio (final VER) of cerebral aneurysms in patients and their retreatment.

Results

Recanalization requiring retreatment was observed in 13 patients (7.2%). The factors related to recanalization were neck width, maximum aneurysm size, width, aneurysm volume, and 1^st VER, but not the final VER. Multivariate analysis of the five factors showed a significant difference in the 1^st VER (P = 0.002). The cutoff value for recanalization was a 1^st VER of 5.8%. There were 162 cases with a VER ≥ 20% or higher, and the same analysis yielded similar results.

Conclusion

The 1^st VER was significantly correlated with recanalization of cerebral aneurysms requiring retreatment. In coil embolization of unruptured cerebral aneurysms, it is important to achieve an embolization rate of at least 5.8% using a framing coil to prevent recanalization.

Porous Media Computational Fluid Dynamics and the Role of the First Coil in the Embolization of Ruptured Intracranial Aneurysms

Background: The objective of our project was to identify a late recanalization predictor in ruptured intracranial aneurysms treated with coil embolization. This goal was achieved by means of a statistical analysis followed by a computational fluid dynamics (CFD) with porous media modelling approach. Porous media CFD simulated the hemodynamics within the aneurysmal dome after coiling. Methods: Firstly, a retrospective single center analysis of 66 aneurysmal subarachnoid hemorrhage patients was conducted. The authors assessed morphometric parameters, packing density, first coil volume packing density (1st VPD) and recanalization rate on digital subtraction angiograms (DSA). The effectiveness of initial endovascular treatment was visually determined using the modified Raymond–Roy classification directly after the embolization and in a 6- and 12-month follow-up DSA. In the next step, a comparison between porous media CFD analyses and our statistical results was performed. A geometry used during numerical simulations based on a patient-specific anatomy, where the aneurysm dome was modelled as a separate, porous domain. To evaluate hemodynamic changes, CFD was utilized for a control case (without any porosity) and for a wide range of porosities that resembled 1–30% of VPD. Numerical analyses were performed in Ansys CFX solver. Results: A multivariate analysis showed that 1st VPD affected the late recanalization rate (p < 0.001). Its value was significantly greater in all patients without recanalization (p < 0.001). Receiver operating characteristic curves governed by the univariate analysis showed that the model for late recanalization prediction based on 1st VPD (AUC 0.94 (95%CI: 0.86–1.00) is the most important predictor of late recanalization (p < 0.001). A cut-off point of 10.56% (sensitivity—0.722; specificity—0.979) was confirmed as optimal in a computational fluid dynamics analysis. The CFD results indicate that pressure at the aneurysm wall and residual flow volume (blood volume with mean fluid velocity > 0.01 m/s) within the aneurysmal dome tended to asymptotically decrease when VPD exceeded 10%. Conclusions: High 1st VPD decreases the late recanalization rate in ruptured intracranial aneurysms treated with coil embolization (according to our statistical results > 10.56%). We present an easy intraoperatively calculable predictor which has the potential to be used in clinical practice as a tip to improve clinical outcomes.

Evaluation of Contact Force between Aneurysm Model and Coil for Embolization of Intracranial Aneurysms

Objective

To ensure safe coil embolization for intracranial aneurysms, it is important to investigate the contact force between the coil and the aneurysm wall. However, it is unclear how the catheter tip position and the diameter of the secondary loop of the coil influence the contact force. In this study, we measured the contact force between a coil and an aneurysm biomodel under different conditions.

Methods

A commercially available coil was inserted through a microcatheter into a silicone rubber aneurysm model at a constant speed (1 mm/s) using an automatic stage, and the contact force between the coil and the aneurysm wall was measured by a force sensor attached on the aneurysm model. The inner diameter of the spherical aneurysm was 5 mm. The effects of varying the position of the catheter tip (near dome, center, near neck) and the diameter of the secondary coil (4.5 mm) were evaluated.

Results

When the catheter tip was inserted more deeply into the aneurysm (especially near the dome), the contact force increased. The contact force also increased as the secondary coil diameter was increased with the catheter tip near and in the center of the dome.

Conclusion

These results suggest that the catheter tip position and the secondary coil diameter affect the contact force. In particular, the contact force should be considered large with the catheter tip near the dome to ensure safe coil deployment.

Three-dimensional aneurysm volume measurements show no correlation between coil packing density and recurrence

Objective

Endovascular treatment is the mainstay therapy for brain aneurysms. About 15% of patients need re-treatment within six months due to early recanalization. In this study, we investigate risk factors associated with treatment failure.

Methods

This retrospective cohort study includes endovascularly treated aneurysm cases between July 2012 and December 2015 at the University of California Davis Medical Center with pre-treatment and early post-treatment imaging. Thin cut 3D aneurysm volume rendering was used for morphologic analyses. Univariate and bivariate analyses were conducted to evaluate differences between patients and clinical factors by treatment failure.

Results

Of the 50 patients who met the inclusion criteria, 41 (82.0%) were female, with an average age of 61 years. Most aneurysms were on the anterior communicating artery (40%) or posterior communicating artery (22.0%), and 34 (68%) aneurysms were ruptured. Early treatment failure was observed in 14 (28.0%) of endovascularly treated patients. Raymond-Roy class (RRC) was significantly associated with treatment failure (p = 0.0052), with 10 out of the 14 cases (71.4%) with early recanalization having an RRC of 3. Coil packing density did not associate with aneurysm recanalization (p = 0.61).

Conclusion

In our single institution series, patient characteristics, aneurysm characteristics, or coil packing density did not affect early aneurysm recanalization. RRC was the best predictor of early recanalization; however, further confirmation with additional studies are required. Although this study focused on early treatment failure, late recanalization has been shown with longer follow up. Further investigation into factors associated with late treatment failure will need further investigation. New intrasaccular devices and flow diverters will also likely play a role in reducing recurrence in the future as these treatments gain usage.

Efficacy of a 14-coil for Framing in Coil Embolization of Small Cerebral Aneurysms

Objective

The purpose of this study was to demonstrate the efficacy of a 14-coil (Target XL) for framing in coil embolization of small cerebral aneurysms.

Methods

Between January 2017 and December 2018, 46 patients underwent coil embolization of a small cerebral aneurysm that was less than 5 mm in maximum diameter. They were categorized into 26 patients in whom only 10-coils were used and 20 in whom Target XL was used for framing. The volume embolization rate (VER) and recanalization rate were compared between the two groups.

Results

Although there were two patients in whom Target XL was replaced with a 10-coil for framing, no adverse events associated with the use of Target XL were noted. The mean VER of the first framing coil was significantly higher in aneurysms that were framed with Target XL than in those framed with a 10-coil (Target XL 22.6 ± 4.5%, 10-coil 17.9 ± 8.4%; p = 0.03). Furthermore, the mean VER at the end of the procedure was significantly higher in aneurysms with Target XL used for framing than in those embolized using only 10-coils (14-coil: 36.8 ± 7.8%, 10-coil: 32.0 ± 6.5%; p = 0.03). No recanalization was observed in aneurysms for which Target XL was used for framing, whereas five aneurysms embolized using only 10-coils were recanalized.

Conclusion

Target XL may be safe and feasible as a framing coil in coil embolization of small cerebral aneurysms, which may result in a high VER, low recanalization rate, and good outcome.

Importance of the First Coil in the Embolization of Intracranial Aneurysms : A Case Control Study

PURPOSE

Endovascular therapy for the treatment of cerebral aneurysms has a higher incidence of rebleeding and a lower occlusion rate than microsurgical clipping. This study investigated whether first coil volume packing density (1st VPD) and first loop diameter of the first coil (1st LD) are associated with recanalization after endovascular coiling.

METHODS

The study included 174 initial saccular aneurysm cases from 2010 to 2015. Between the recanalization and non-recanalization groups, we compared age, sex, aneurysm location, rupture occurrence, shape, maximum aneurysm size, neck width, dome-to-neck ratio, aneurysm volume, coil volume, VPD, 1st VPD, 1st LD, relation of the first loop diameter of the first coil and the maximum aneurysm size (RLAS), types of assistance techniques, and the Raymond scale score at initial and follow-up angiography.

RESULTS

Recanalization occurred in 41 cases (23.6%). The factors associated with recanalization were irregular shape, maximum aneurysm size, neck width, dome-to-neck ratio, aneurysm volume, VPD, 1st VPD and 1st LD smaller than the maximum aneurysm size. The cut-off values for aneurysmal recanalization were 92%, 11% and 37% for RLAS, 1st VPD and VPD, respectively.

CONCLUSION

The 1st VPD and 1st LD were associated with aneurysmal recanalization after embolization. These factors provide a helpful index for coil programming.

Experimental study of the characteristics of various types of filling coils for intracranial aneurysm embolisation

Background In endovascular embolisation for an intracranial aneurysm, after framing coil deployment, soft coils (often called filling coils) are usually selected to fill inside the cage of previous coils. Various kinds of filling coils are available, although each coil has its own characteristics. Understanding their differences to ensure proper coil selection is important to achieve successful embolisation. The purpose of this study was to investigate the characteristics of various filling coils. Materials and methods The authors developed a radiolucent coil to evaluate the performance of coils under conditions simulating the course of embolisation. Experimental embolisation was performed by using a silicone aneurysm filled with radiolucent coils. Indices including area, circularity, centroid position and coefficient of variation were investigated by analysing the figures of the filling coils after being inserted into the radiolucent coil under fluoroscopy. Results The characteristics of each coil depended on the coil design. The helical coil had the highest circularity and centroid position scores and lowest area score. Therefore, it tended to develop a compacted mass. The low shape-memory coil had the lowest circularity, second-highest centroid position and highest coefficient of variation scores. Therefore, it tended to develop irregularly shaped distribution with low reproducibility. Complex coils generally had higher area and circularity scores. Therefore, they tended to provide a balanced distribution with relatively expanded mass and less small compartmentation. Conclusions The evaluated characteristics of various filling coils should be useful for appropriate selection of filling coils.

Optimal first coil selection to avoid aneurysmal recanalization in endovascular intracranial aneurysmal coiling

BACKGROUND

Aneurysmal recanalization is a problem with endovascular coiling and one of its risk factors is the low volume embolization ratio (VER). The first coil VER (1st VER) is believed to be critical for obtaining a high VER. The main objective of this study was to evaluate factors potentially useful for selecting the optimal 1st VER for endovascular coiling.

METHODS

609 initial saccular aneurysmal treatments performed between January 2010 and December 2014 at our institution were included in this retrospective study. Attempted procedures, retreatment cases, intraoperative rupture cases, and stent-assisted coiling cases were excluded. Age, sex, aneurysm location, ruptured aneurysm, aneurysm shape, neck size, maximum aneurysm size, dome-to-neck ratio, aneurysm volume, procedure, immediate Raymond scale score, 1st VER, and VER between the recanalization groups and non-recanalization groups were compared.

RESULTS

The factors related to recanalization were ruptured aneurysms, neck width, maximum aneurysm size, aneurysm volume, procedure, 1st VER, and VER. The cut-off values for aneurysm recanalization were a 1st VER of 10.0% and a VER of 33.0%. The maximum average VER of normal size aneurysms was found in the groups with a 1st VER of 17.5-20.0%.

CONCLUSIONS

1st VER was found to be a helpful index for estimating aneurysmal recanalization after coil embolization. The target 1st VER was 17.5-20.0% for obtaining a higher VER and avoiding recanalization.