Growth and Rupture Risk of Small Unruptured Intracranial Aneurysms: A Systematic Review

Management of Tiny Unruptured Intracranial Aneurysms: A Comparative Effectiveness Analysis

Importance

Unruptured intracranial aneurysms (UIAs) are relatively common in the general population and are being increasingly diagnosed; a significant proportion are tiny (≤3 mm) aneurysms. There is significant heterogeneity in practice and lack of clear guidelines on the management of incidental, tiny UIAs. It is important to quantify the implications of different management strategies in terms of health benefits to patients.

Objective

To evaluate the effectiveness of routine treatment (aneurysm coiling) vs 3 strategies for imaging surveillance compared with no preventive treatment or routine follow-up of tiny UIAs.

Design, Setting, and Participants

A decision-analytic model-based comparative effectiveness analysis was conducted from May 1 to June 30, 2017, using inputs from the medical literature. PubMed searches were performed to identify relevant literature for all key model inputs, each of which was derived from the clinical study with the most robust data and greatest applicability. Analysis included 10 000 iterations simulating adult patients with incidental detections of UIAs 3 mm or smaller and no history of subarachnoid hemorrhage.

Interventions

The following 5 management strategies for tiny UIAs were evaluated: annual magnetic resonance angiography (MRA) screening, biennial MRA screening, MRA screening every 5 years, aneurysm coiling and follow-up, and no treatment or preventive follow-up.

Main Outcomes and Measures

A Markov decision model for lifetime rupture was constructed from a societal perspective per 10 000 patients with incidental, tiny UIAs. Outcomes were assessed in terms of quality-adjusted life-years. Probabilistic, 1-way, and 2-way sensitivity analyses were performed.

Results

In this analysis of 10 000 iterations simulating adult patients with a mean age of 50 years, the base-case calculation shows that the management strategy of no treatment or preventive follow-up has the highest health benefit (mean [SD] quality-adjusted life-years, 19.40 [0.31]). Among the management strategies that incorporate follow-up imaging, MRA every 5 years is the best strategy with the next highest effectiveness (mean [SD] quality-adjusted life-years, 18.05 [0.62]). The conclusion remains robust in probabilistic and 1-way sensitivity analyses. No routine follow-up remains the optimal strategy when the annual growth rate and risk of rupture of growing aneurysms are varied. When the annual risk of rupture of nongrowing UIAs is less than 1.7% (0.23% in base case scenario), no follow-up is the optimal strategy. If annual risk of rupture is more than 1.7%, coiling should be performed directly.

Conclusions and Relevance

Given the current literature, no preventive treatment or imaging follow-up is the most effective strategy in patients with aneurysms that are 3 mm or smaller, resulting in better health outcomes. More aggressive imaging surveillance for aneurysm growth or preventive treatment should be reserved for patients with a high risk of rupture. Given these findings, it is important to critically evaluate the appropriateness of current clinical practices, and potentially determine specific guidelines to reflect the most effective management strategy for patients with incidental, tiny UIAs.

Incidental Microaneurysms During Microvascular Surgery: Incidence, Treatment, and Significance

BACKGROUND

Although new imaging tools have been developed for the detection of smaller aneurysms, angiographically negative microaneurysms are still encountered during cerebral microsurgery. Currently, only limited information regarding incidence and efficacy of treatment of these microaneurysms is available.

METHODS

We investigated the incidence and treatment of incidental microaneurysms (IMAs) in the last 5 years. IMAs are unidentifiable and invisible on preoperative angiography, but are detected during microvascular surgery. The inclusion criteria were aneurysm cases treated with microsurgery via transsylvian approaches, and those undergoing preoperative digital subtraction angiography.

RESULTS

This study enrolled 484 surgical cases (248 cases of subarachnoid hemorrhage and 236 cases of unruptured aneurysms) in 460 patients, and 33 tiny aneurysms were found in 31 operative cases (6.4% incidence per operation). The most typical type was located on another branching site of the middle cerebral artery found during neck clipping of the middle cerebral artery bifurcation aneurysm. A patient with multiple aneurysms presented a statistically significant risk (375/78 vs. 15/16; P < 0.001) of IMA identification. IMAs were treated by clipping and wrapping in 18 and 15 cases, respectively, without complications.

CONCLUSIONS

This study revealed a 6.4% incidence of IMAs; however, this could be underestimated because of the limited range of inspection. Early detection of an IMA through careful inspection during microvascular surgery could be beneficial, especially in patients with multiple aneurysms.

Cost-Effectiveness of Computed Tomography Angiography in Management of Tiny Unruptured Intracranial Aneurysms in the United States

Background and Purpose—

Our study aims to evaluate the cost-effectiveness of computed tomography angiography (CTA) for surveillance of tiny unruptured intracranial aneurysms and the impact of CTA radiation-induced brain tumor on the overall effectiveness of CTA.

Methods—

A Markov decision model was constructed from a societal perspective starting with patients 30-, 40-, or 50-year-old, with incidental detection of unruptured intracranial aneurysm ≤3 mm and no prior history of subarachnoid hemorrhage. Five different management strategies were assessed (1) annual CTA surveillance, (2) biennial CTA, (3) CTA follow-up every 5 years, (4) coiling and subsequent magnetic resonance imaging follow-up, and (5) annual CTA surveillance for the first 2 years, followed by every 5-year CTA follow-up. Probabilistic, 1-way, and 2-way sensitivity analyses were performed.

Results—

The base case calculation shows every 5-year CTA follow-up to be the most cost-effective strategy, and the conclusion remains robust in probabilistic sensitivity analysis. It remains the dominant strategy when the annual rupture risk of nongrowing unruptured intracranial aneurysms is smaller than 2.66% or the rupture risk in growing aneurysms is <57.4%. The radiation-induced brain cancer risk is relatively low, and sensitivity analysis shows that the radiation-induced cancer risk does not influence the conclusions unless the risk exceeds 663-fold of the base case values.

Conclusions—

Given the current literature, every 5-year CTA imaging follow-up is the cost-effective strategy in patients with aneurysms ≤3 mm, resulting in better health outcomes and lower healthcare spending. Patients with aneurysms at high risk of rupture might need more aggressive management.

Prediction of Aneurysm Stability Using a Machine Learning Model Based on PyRadiomics-Derived Morphological Features

Background and Purpose- Discrimination of the stability of intracranial aneurysms is critical for determining the treatment strategy, especially in small aneurysms. This study aims to evaluate the feasibility of applying machine learning for predicting aneurysm stability with radiomics-derived morphological features. Methods- Morphological features of 719 aneurysms were extracted from PyRadiomics, of which 420 aneurysms with Maximum3DDiameter ranging from 4 mm to 8 mm were enrolled for analysis. The stability of these aneurysms and other clinical characteristics were reviewed from the medical records. Based on the morphologies with/without clinical features, machine learning models were constructed and compared to define the morphological determinants and screen the optimal model for predicting aneurysm stability. The effect of clinical characteristics on the morphology of unstable aneurysms was analyzed. Results- Twelve morphological features were automatically extracted from PyRadiomics implemented in Python for each aneurysm. Lasso regression defined Flatness as the most important morphological feature to predict aneurysm stability, followed by SphericalDisproportion, Maximum2DDiameterSlice, and SurfaceArea. SurfaceArea (odds ratio [OR], 0.697; 95% CI, 0.476-0.998), SphericalDisproportion (OR, 1.730; 95% CI, 1.143-2.658), Flatness (OR, 0.584; 95% CI, 0.374-0.894), Hyperlipemia (OR, 2.410; 95% CI, 1.029-5.721), Multiplicity (OR, 0.182; 95% CI, 0.082-0.380), Location at middle cerebral artery (OR, 0.359; 95% CI, 0.134-0.902), and internal carotid artery (OR, 0.087; 95% CI, 0.030-0.211) were enrolled into the final prediction model. In terms of performance, the area under curve of the model reached 0.853 (95% CI, 0.767-0.940). For unstable aneurysms, Compactness1 (P=0.035), Compactness2 (P=0.036), Sphericity (P=0.035), and Flatness (P=0.010) were low, whereas SphericalDisproportion (P=0.034) was higher in patients with hypertension. Conclusions- Morphological features extracted from PyRadiomics can be used for aneurysm stratification. Flatness is the most important morphological determinant to predict aneurysm stability. Our model can be used to predict aneurysm stability. Unstable aneurysm is more irregular in patients with hypertension.

Management of Unruptured Intracranial Aneurysms in Older Adults: A Cost-effectiveness Analysis

Background Unruptured intracranial aneurysms (UIAs) are relatively common and are being increasingly diagnosed, with a significant proportion in older patients (˃ 65 years old). Serial imaging is often performed to assess change in size or morphology of UIAs since growing aneurysms are known to be at high risk for rupture. However, the frequency and duration of surveillance imaging have not been established. Purpose To evaluate the cost-effectiveness of routine treatment (aneurysm coil placement) versus four different strategies for imaging surveillance of UIAs in adults older than 65 years. Materials and Methods A Markov decision-analytic model was constructed from a societal perspective. Age-dependent input parameters were obtained from published literature. Analysis included adults older than 65 years, with incidental detection of UIA and no prior history of subarachnoid hemorrhage. Five different management strategies for UIAs in older adults were evaluated: (a) annual MR angiography, (b) biennial MR angiography, (c) MR angiography every 5 years, (d) coil placement and follow-up, and (e) limited MR angiography follow-up for the first 2 years after detection only. Outcomes were assessed in terms of quality-adjusted life-years (QALYs). Probabilistic, one-way, and two-way sensitivity analyses were performed. Results Imaging follow-up for the first 2 years after detection is the most cost-effective strategy (cost = $24 572, effectiveness = 13.73 QALYs), showing the lowest cost and highest effectiveness. The conclusion remains robust in probabilistic and one-way sensitivity analyses. Time-limited imaging follow-up remains the optimal strategy when the annual growth rate and rupture risk of growing aneurysms are varied. If annual rupture risk of nongrowing aneurysms is greater than 7.1%, coil placement should be performed directly. Conclusion Routine preventive treatment or periodic, indefinite imaging follow-up is not a cost-effective strategy in all adults older than 65 years with unruptured intracranial aneurysms. More aggressive management strategies should be reserved for patients with high risk of rupture, such as those with aneurysms larger than 7 mm and those with aneurysms in the posterior circulation. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Cloft in this issue.

MR Angiography Screening and Surveillance for Intracranial Aneurysms in Autosomal Dominant Polycystic Kidney Disease: A Cost-effectiveness Analysis

Background Autosomal dominant polycystic kidney disease (ADPKD) affects one in 400 to one in 1000 individuals; 10%-11% of these individuals have intracranial aneurysms. The frequency and patterns of screening for intracranial aneurysms have not been defined. Purpose To evaluate different MR angiography screening and surveillance strategies for unruptured intracranial aneurysms in patients with ADPKD. Materials and Methods A Markov decision-analytic model was constructed accounting for both costs and outcomes from a societal perspective. Five different management strategies were evaluated: (a) no screening for intracranial aneurysm, (b) one-time screening with annual MR angiography follow-up in patients with intracranial aneurysm, (c) MR angiographic screening every 5 years with endovascular treatment in detected intracranial aneurysm, (d) MR angiography screening every 5 years with annual MR angiography follow-up in patients with intracranial aneurysm, and (e) MR angiography screening every 5 years with biennial follow-up in patients with intracranial aneurysm. One-way, two-way, and probabilistic sensitivity analyses were performed. Results Base case calculation shows that MR angiography screening of patients with ADPKD every 5 years and annual follow-up in patients with detected intracranial aneurysm is the optimal strategy (cost, $19 839; utility, 25.86 quality-adjusted life years), which becomes more favorable as the life expectancy increases beyond 6 years. The conclusion remains robust in probabilistic and one-way sensitivity analyses. When the prevalence of intracranial aneurysms is greater than 10%, annual rupture risk is 0.35%-2.5%, and the rate of de novo aneurysm detection is lower than 1.8%, MR angiography screening every 5 years with annual MR angiography follow-up is the favorable strategy. Conclusion Screening for intracranial aneurysms with MR angiography in patients with autosomal dominant polycystic kidney disease is cost-effective. Repeat screening every 5 years should be performed after a negative initial study. Annual surveillance MR angiography is optimal in patients with detected, incidental intracranial aneurysm, and treatment may be considered in patients with growing, high-risk aneurysms. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Anzai in this issue.

Risk of Radiation-Induced Cancer From Computed Tomography Angiography Use in Imaging Surveillance for Unruptured Cerebral Aneurysms

Background and Purpose- Although computed tomography angiography (CTA) is an excellent, noninvasive imaging modality for surveillance of intracranial aneurysms, radiation concerns have been cited to restrict its use in surveillance imaging. The goal of this study was to estimate distributions of radiation-induced central nervous system cancer incidence from CTA surveillance for intracranial aneurysms, and the impact of frequency and duration of surveillance imaging using follow-up CTAs. Methods- Simulation-modeling approach was performed using data on CTA associated radiation risk. We used the Radiation Risk Assessment Tool, based on the data using the BEIR VII report (BEIR VII). Each CTA was assigned as a separate exposure event. Men and women, respectively, starting surveillance imaging at 30, 40, and 50 years and receiving annual CTAs were considered as separate subgroups. As a comparison, we also calculated the radiation-induced cancer risk in the same groups of patients but receiving CTAs every 2 and 5 years, respectively. Results- CTA-associated excess cancer risk per exposure increases relatively more rapidly with the first 10 exposures and plateaus after the 44th exposure. On average, per CTA incurs ≈0.0026% in excess lifetime cancer risk. Receiving CTA follow-up at a younger age, more frequent follow-up, longer surveillance period, and men are the major factors contributing to an elevated excess lifetime risk. In the highest risk group, male patient receiving annual CTA follow-ups from the age of 30 years, the excess lifetime risk is 0.115% at the age of 81 years. Conclusions- Radiation-induced brain cancer incidence associated with unruptured intracranial aneurysm surveillance strategies using CTA is low relative to the risk for aneurysmal rupture. Further cost-effectiveness/utility analyses might help assess this risk in the context of aneurysmal ruptures prevented by surveillance imaging.

Racial and Ethnic Disparities in Treatment Outcomes of Patients with Ruptured or Unruptured Intracranial Aneurysms

OBJECTIVE

The aim of this study is to examine how health outcomes varied by treatment selection and race/ethnicity among hospitalized US patients with ruptured or unruptured IAs.

METHODS

A retrospective cohort study was conducted using a sample of 62,224 hospital discharges from the 2002-2012 Nationwide Inpatient Sample. Logistic regression models evaluated treatment selection as predictor of in-hospital survival (IHS: "yes," "no") and length of stay (LOS ≤ 7 days, > 7 days), overall and across racial/ethnic groups, taking hospital- and patient-level confounders into account, while stratifying by IA rupture status.

RESULTS

Compared to surgical clipping, endovascular coiling was associated with better IHS, after controlling for confounders. Compared to surgical clipping, LOS ≤ 7 days was less likely in patients with combination of treatments and more likely among patients with endovascular coiling as well as balloon- or stent-assisted coiling. Observed relationships varied significantly by race and ethnicity for IHS, but not for LOS ≤ 7 days. Whereas combination of treatments were associated with worse IHS than surgical clipping among Blacks alone, endovascular coiling was associated with better IHS than surgical clipping among White and Other racial/ethnic subgroups. These relationships were for the most part consistent among patients with and without IA rupture.

CONCLUSIONS

Racial and ethnic subgroups of IA patients experienced differential IHS by treatment selection, irrespective of IA rupture status. Prospective cohort studies are needed to further elucidate these racial and ethnic disparities, while collecting data on IA size, location, and morphology as well as Hunt and Hess grade for ruptured IA.

Management of Small Unruptured Intracranial Aneurysms: A Survey of Neuroradiologists

BACKGROUND AND PURPOSE

The long-term history and management of unruptured intracranial aneurysms is not well understood. Our aim was to determine current practice patterns in the management of unruptured intracranial aneurysms, especially regarding imaging surveillance for conservatively managed aneurysms of this type.

MATERIALS AND METHODS

An on-line survey was designed to examine physician practice and preference regarding the management of small unruptured intracranial aneurysms (≤7 mm in diameter). The survey was circulated to members of the American Society of Neuroradiology. Participation was voluntary, and all responses were anonymous.

RESULTS

A total of 227 individual survey responses were obtained and included in the analysis with 54.6% (124/227) from diagnostic neuroradiologists (practicing >50% neuroradiology) and one-third (29%) from neurointerventional radiologists. One hundred seventy-three of 227 responded that routine, periodic imaging surveillance would be appropriate for conservatively managed unruptured intracranial aneurysms, and 84% of respondents recommended surveillance frequency of at least once a year. Fifty-nine percent favored indefinite, life-long follow-up for small unruptured intracranial aneurysms, and a similar number of respondents favored noncontrast MR angiography for aneurysm follow-up. Significant heterogeneity was found in size measurements used to assess aneurysms and criteria used to define growth on surveillance imaging.

CONCLUSIONS

The natural history of intracranial aneurysms is not well-understood. A large proportion of incidentally detected, unruptured aneurysms are small (<7 mm). The survey results show significant heterogeneity in practice even among neuroradiologists and underlies the need to standardize imaging practice. Further studies are needed to assess the optimal frequency and duration of surveillance imaging for unruptured intracranial aneurysms. The criteria used to measure aneurysms and define growth on imaging also need to be standardized.