Circumferential wall enhancement in evolving intracranial aneurysms on magnetic resonance vessel wall imaging

Does it stable? Intracranial aneurysm wall enhancement might be the warning signals: a meta-analysis of observational studies

Magnetic resonance vessel wall imaging (MR-VWI) is an emerging imaging technology used to assess the progressive risk of unruptured intracranial aneurysms (UIAs). Unlike the standard evaluation model, MR-VWI is still debatable. This study aims to further define the potential relationship between aneurysm wall enhancement (AWE) and aneurysm stability. Using "intracranial aneurysm", "magnetic resonance", and "enhancement" as keywords, relevant studies were systematically searched in PubMed, Embase, and Cochrane, and the qualified studies were enrolled for further analysis. There were 13 case-control studies, 4 cohort studies, and 2,678 cases of intracranial aneurysms included in the meta-analysis. It was shown that AWE was correlated with intracranial aneurysm rupture (OR = 35.90, 95% CI: 15.58 to 82.75, p < 0.001), growth (OR = 6.69, 95% CI: 2.69 to 16.63, p < 0.001), and presence of symptoms (OR = 14.46, 95% CI: 9.07 to 23.05, p < 0.001). This finding had a high diagnostic value, but the correlation was probably not independent of aneurysm size. The pooled relative risks of the follow-up studies revealed that the risk of UIA progression was approximately 3.33 times higher with AWE than without AWE (RR = 3.33, 95% CI: 2.33 to 4.78, p < 0.001). In addition, the pooled results demonstrated that quantitative indices of VWI enhancement were equally linked with aneurysm stability (OR = 19.61, 95% CI: 10.63 to 36.17, p < 0.001). AWE is an effective imaging method to assess the stability of UIAs, and it can be a marker for the prophylactic treatment of small unruptured intracranial aneurysms in the future, which remains to be validated by prospective studies with large samples.

Gadolinium-enhanced intracranial aneurysm wall imaging and risk of aneurysm growth and rupture: a multicentre longitudinal cohort study

OBJECTIVES

In patients with an unruptured intracranial aneurysm, gadolinium enhancement of the aneurysm wall is associated with growth and rupture. However, most previous studies did not have a longitudinal design and did not adjust for aneurysm size, which is the main predictor of aneurysm instability and the most important determinant of wall enhancement. We investigated whether aneurysm wall enhancement predicts aneurysm growth and rupture during follow-up and whether the predictive value was independent of aneurysm size.

MATERIALS AND METHODS

In this multicentre longitudinal cohort study, individual patient data were obtained from twelve international cohorts. Inclusion criteria were as follows: 18 years or older with ≥ 1 untreated unruptured intracranial aneurysm < 15 mm; gadolinium-enhanced aneurysm wall imaging and MRA at baseline; and MRA or rupture during follow-up. Patients were included between November 2012 and November 2019. We calculated crude hazard ratios with 95%CI of aneurysm wall enhancement for growth (≥ 1 mm increase) or rupture and adjusted for aneurysm size.

RESULTS

In 455 patients (mean age (SD), 60 (13) years; 323 (71%) women) with 559 aneurysms, growth or rupture occurred in 13/194 (6.7%) aneurysms with wall enhancement and in 9/365 (2.5%) aneurysms without enhancement (crude hazard ratio 3.1 [95%CI: 1.3-7.4], adjusted hazard ratio 1.4 [95%CI: 0.5-3.7]) with a median follow-up duration of 1.2 years.

CONCLUSIONS

Gadolinium enhancement of the aneurysm wall predicts aneurysm growth or rupture during short-term follow-up, but not independent of aneurysm size.

CLINICAL RELEVANCE STATEMENT

Gadolinium-enhanced aneurysm wall imaging is not recommended for short-term prediction of growth and rupture, since it appears to have no additional value to conventional predictors.

KEY POINTS

• Although aneurysm wall enhancement is associated with aneurysm instability in cross-sectional studies, it remains unknown whether it predicts risk of aneurysm growth or rupture in longitudinal studies. • Gadolinium enhancement of the aneurysm wall predicts aneurysm growth or rupture during short-term follow-up, but not when adjusting for aneurysm size. • While gadolinium-enhanced aneurysm wall imaging is not recommended for short-term prediction of growth and rupture, it may hold potential for aneurysms smaller than 7 mm.

Imaging of Intracranial Aneurysms: A Review of Standard and Advanced Imaging Techniques

The treatment of intracranial aneurysms is dictated by its risk of rupture in the future. Several clinical and radiological risk factors for aneurysm rupture have been described and incorporated into prediction models. Despite the recent technological advancements in aneurysm imaging, linear length and visible irregularity with a bleb are the only radiological measure used in clinical prediction models. The purpose of this article is to summarize both the standard imaging techniques, including their limitations, and the advanced techniques being used experimentally to image aneurysms. It is expected that as our understanding of advanced techniques improves, and their ability to predict clinical events is demonstrated, they become an increasingly routine part of aneurysm assessment. It is important that neurovascular specialists understand the spectrum of imaging techniques available.

Vertebral artery wall inflammation suspected as the cause of cryptogenic ischemic stroke developing during the recovery period of COVID-19

Coronavirus disease-2019 (COVID-19) can cause acute ischemic stroke (AIS) due to large vessel occlusion (LVO). Some cases of COVID-19-related LVO are known to be resistant to mechanical thrombectomy and have different characteristics from non-COVID-19-related LVO. Inflammation of the occluded arterial wall is suspected as one of the causes of such differences, but the exact mechanism is not fully understood. A 52-year-old man suffered from AIS due to left vertebral artery (VA) occlusion during the recovery period after mild COVID-19. Successful recanalization of the left VA was achieved with antithrombotic therapy, but a late and reversible edematous lesion appeared in part of the brainstem adjacent to the left VA, with abnormal enhancement in both the left VA wall and medulla oblongata on postcontrast magnetic resonance imaging. We suggest that the left VA wall inflammation, induced by COVID-19, caused the ischemic stroke and extended to the brainstem, and an incidental thrombosed unruptured aneurysm of the left VA accelerated these changes. This case provides the first evidence of LVO after COVID-19 in which the pathological conditions in the brainstem adjacent to the affected artery could be observed with neuroimaging and inflammation of the arterial wall was indirectly confirmed. Physicians should be aware that unconventional ischemic stroke may develop in some patients during the recovery period after COVID-19.

MR Imaging of the Cerebral Aneurysmal Wall for Assessment of Rupture Risk

The evaluation of unruptured intracranial aneurysms requires a comprehensive and multifaceted approach. The comprehensive analysis of aneurysm wall enhancement through high-resolution MRI, in tandem with advanced processing techniques like finite element analysis, quantitative susceptibility mapping, and computational fluid dynamics, has begun to unveil insights into the intricate biology of aneurysms. This enhanced understanding of the etiology, progression, and eventual rupture of aneurysms holds the potential to be used as a tool to triage patients to intervention versus observation. Emerging tools such as radiomics and machine learning are poised to contribute significantly to this evolving landscape of diagnostic refinement.

Hemodynamic nature of black-blood enhancement in long-term coiled cerebral aneurysms

PURPOSE

Vessel wall imaging (VWI) with black-blood (BB) technique can demonstrate aneurysmal enhancement preluding to growth/rupture in treatment-naive cerebral aneurysms. Interestingly, recent works showed that BB enhancement may also occur in endovascularly treated aneurysms, though its meaning is controversial. Hypothesizing a flow-related mechanism of BB enhancement, we explored its relationship with incomplete occlusion status and coil packing density at DSA.

METHODS

We analyzed the subjects undergoing 3T MRI between January 2017 and October 2020 for a previous aneurysmal coiling. All the MRI studies included pre- and post-contrast 3D BB sequences. The presence of intra-aneurysmal pre-contrast BB signal was assessed. BB enhancement (when present) was classified as follows: (1) enhancement at the neck, (2) intrasaccular/intra-coil enhancement, and (3) peripheral enhancement. Coil packing density and aneurysmal occlusion status (according to the modified Raymond-Roy classification, MRRC) were determined on post-treatment DSA and compared with BB findings using generalized linear mixed-effect model and ANOVA. Significant p values were <0.05.

RESULTS

Forty-eight aneurysms from 44 patients were eligible for analysis. Pre-contrast BB signal was observed in 50% of the aneurysms and showed a relationship with baseline aneurysmal size. BB enhancement was detectable in 31 aneurysms (65%), being significantly associated with incomplete aneurysmal occlusion and reduced coil packing density at DSA.

CONCLUSION

BB enhancement of coiled aneurysms is related with increasing degrees of post-coiling aneurysmal remnants and with loose coil packing density at DSA. This supports a hemodynamic interpretation of BB enhancement in long-term coiled aneurysms.

High resolution vessel-wall imaging for peripheral aneurysms in adult moyamoya disease: a report of three cases

Peripheral aneurysms in patients with moyamoya disease have been reported to be hazardous owing to their rupture-prone nature. High-resolution vessel wall imaging has recently emerged as a useful modality for evaluating intracranial aneurysmal status. We present the vessel-wall imaging of peripheral aneurysms in three patients with moyamoya disease. Strong circumferential wall enhancement was observed in ruptured peripheral aneurysms. Peripheral aneurysms were located at the connection point between the single main stem and the multiple medullary tributaries of the choroidal anastomosis. Using high-resolution vessel-wall imaging, we identified the characteristics of peripheral aneurysms in patients with moyamoya disease.

Three-dimensional aneurysm wall enhancement in fusiform intracranial aneurysms is associated with aneurysmal symptoms

Background and purpose

Aneurysm wall enhancement (AWE) in high-resolution magnetic resonance imaging (HR-MRI) is a potential biomarker for evaluating unstable aneurysms. Fusiform intracranial aneurysms (FIAs) frequently have a complex and curved structure. We aimed to develop a new three-dimensional (3D) aneurysmal wall enhancement (AWE) characterization method to enable comprehensive FIA evaluation and to investigate the ability of 3D-AWE to predict symptomatic FIA.

Methods

We prospectively recruited patients with unruptured FIAs and received 3 T HR-MRI imaging from September 2017 to January 2019. 3D models of aneurysms and parent arteries were generated. Boundaries of the FIA were determined using 3D vessel diameter measurements. D_max was the greatest diameter in the cross-section, while L_max was the length of the centerline of the aneurysm. Signal intensity of the FIA was normalized to the pituitary stalk and then mapped onto the 3D model, then the average enhancement (3D-AWE_avg), maximum enhancement (3D-AWE_max), enhancement area (AWE_area), and enhancement ratio (AWE_ratio) were calculated as AWE indicators, and the surface area of the entire aneurysm (A_area) was also calculated. Areas with high AWE were defined as those with a value >0.9 times the signal intensity of the pituitary stalk. Multivariable logistic regression analyses were performed to determine independent predictors of aneurysm-related symptoms. FIA subtypes were defined as fusiform, dolichoectasia, and transitional. Differences between the three FIA subtypes were also examined.

Results

Forty-seven patients with 47 FIAs were included. Mean patient age was 55 ± 12.62 years and 74.5% were male. Twenty-nine patients (38.3%) were symptomatic. After adjusting for baseline differences in age, hypertension, L_max, and FIA subtype, the multivariate logistics regression models showed that 3D-AWE_avg (odds ratio [OR], 4.029; p = 0.019), 3D-AWE_max (OR, 3.437; p = 0.022), AWE_area (OR, 1.019; p = 0.008), and AWE_ratio (OR, 2.490; p = 0.045) were independent predictors of aneurysm-related symptoms. D_max and A_area were larger and 3D-AWE_avg, 3D-AWE_max, AWE_area, and AWE_ratio were higher with the transitional subtype than the other two subtypes.

Conclusion

The new 3D AWE method, which enables the use of numerous new metrics, can predict symptomatic FIAs. Different 3D-AWE between the three FIA subtypes may be helpful in understanding the pathophysiology of FIAs.

Qualitative and quantitative wall enhancement associated with unstable intracranial aneurysms: a meta-analysis

Background

Unstable intracranial aneurysms (UIAs) are more likely to rupture and cause serious consequences. Evaluating the stability of unruptured aneurysms facilitates clinical management stratification.

Purpose

To compare and evaluate the predictive performance of qualitative and quantitative wall enhancement (aneurysmal wall enhancement [AWE], circumferential aneurysmal wall enhancement [CAWE], wall enhancement ratio [WER]) on high-resolution magnetic resonance imaging (MRI) of the vessel wall to predict the presence of UIA.

Material and Methods

Original articles describing the depiction of aneurysmal wall enhancement on 3.0-T or 1.5-T high-resolution vessel wall imaging were retrieved from the Web of Science, Medline/PubMed, the Cochrane Library, and EMBASE databases up to 15 February 2022. The combined sensitivity, specificity, and summary area under the receiver operating characteristic curve (AUC) were calculated, and meta-regression analysis was performed.

Results

In total, 12 original articles involving 1619 intracranial aneurysms (IAs) were included. The combined sensitivity and specificity of AWE, CAWE, and WER were 91% and 67%, 59% and 83%, and 86% and 75%, respectively, in the diagnosis of UIA. The summary AUC values of these items were, in order from high to low, 0.88 (WER), 0.84 (AWE), and 0.77 (CAWE), and the differences among them were significant ( z = 2.976, P = 0.003 and z = 2.950, P = 0.003). The meta-regression analysis identified average size and 2D/3D magnetic imaging technology as possible sources of heterogeneity.

Conclusion

Qualitative and quantitative wall enhancement showed moderate accuracy in predicting UIA, and WER had the highest accuracy among them in this meta-analysis. Two covariates were found to explain the heterogeneity.

Wall enhancement in unruptured posterior communicating aneurysms with oculomotor nerve palsy on magnetic resonance vessel wall imaging

OBJECTIVE

Recent MR vessel wall imaging studies of unruptured intracranial aneurysms (UIAs) have revealed that aneurysm wall enhancement (AWE) can be an indicator for aneurysm evolution; however, the degree of AWE among different types of evolving UIAs has yet to be clarified. The authors assessed the degree of AWE in unruptured posterior communicating artery (PcomA) aneurysms with oculomotor nerve palsy (ONP), which may be a subgroup of evolving UIAs with rapid enlargement and high rupture risk.

METHODS

The degree of AWE was analyzed in 35 consecutive evolving PcomA aneurysms (19 with and 16 without ONP). UIAs were considered to be evolving when showing growth or ONP. A 3D T1-weighted fast spin echo sequence was obtained after contrast media injection, and the contrast ratio of the aneurysm wall against the pituitary stalk (CRstalk) was calculated as the indicator of AWE. The CRstalk in evolving UIAs with ONP was compared with that in UIAs without ONP.

RESULTS

The CRstalk was significantly higher in evolving UIAs with ONP than in those without ONP (0.85 vs 0.57; p = 0.006). In multivariable analysis, the CRstalk remained a significant indicator for ONP presentation in evolving UIAs (OR 6.13, 95% CI 1.21-31.06).

CONCLUSIONS

AWE was stronger in evolving PcomA aneurysms with ONP than in those without ONP, suggesting the potential utility of AWE for risk stratification in evolving UIAs. The degree of AWE can be a promising indicator of a rupture-prone UIA, which can be useful information for the decision-making process in the treatment of UIAs.

Topographical Analysis of Aneurysm Wall Enhancement With 3-Dimensional Mapping

BACKGROUND

Aneurysm wall enhancement has been identified as a potential biomarker for aneurysm instability. Enhancement has been determined by different approaches on 2D multiplanar views. This study describes a new method to quantify enhancement through 3D heatmaps and histograms.

METHODS

A custom algorithm was developed using orthogonal probes extending from the aneurysm lumen into the wall to create 3D heatmaps and histograms of wall enhancement on 7T-MRI. Three quantitative metrics for general, specific, and focal wall enhancement were generated from the histograms.

RESULTS

Thirty-two aneurysms were analyzed and classified based on 3D heatmaps and histograms. Larger aneurysms were more enhancing (Spearman's r=0.472, p=0.006), and had more heterogeneous enhancement (Spearman's r=0.557, p<0.001) than smaller aneurysms. Patterns of enhancement differed between saccular, fusiform, and thrombosed aneurysms. Fusiform aneurysms were larger (p=0.015) and had more heterogenous enhancement compared to saccular aneurysms. Fusiform aneurysms had more areas of focal enhancement (p<0.001) and right skewed histograms (p=0.003).

CONCLUSIONS

The 3D analysis of aneurysm wall enhancement provides topographic data of the entire aneurysm wall. New metrics developed based on this method showed that large and fusiform aneurysms have heterogenous enhancement.

Neutrophil-to-Lymphocyte Ratio Is Associated With Circumferential Wall Enhancement of Unruptured Intracranial Aneurysm

Background and Purpose

Neutrophil-lymphocyte ratio (NLR) predicts clinical outcomes in patients with stroke. Aneurysm wall enhancement (AWE) on high-resolution vessel wall magnetic resonance imaging (HR-VWI) is an inflammation marker for intracranial aneurysm (IA). This study aims to evaluate the association of NLR as a peripheral blood inflammatory marker with circumferential AWE in patients with IA.

Methods

We analyzed data of consecutive patients harboring IAs between September 2017 and December 2021 at our institution. The peripheral blood inflammatory indicators were compared between patients with ruptured and unruptured IAs. The presence of circumferential AWE in unruptured IA was identified and quantitatively measured using the aneurysm-to-pituitary stalk contrast ratio (CRstalk) on HR-VWI. We used the optimal cutoff value of 0.5 for CRstalk to differentiate circumferential AWE in unruptured IAs. We assessed the relationship of clinical, laboratory, and radiological characteristics with circumferential AWE and CRstalk ≥0.5 in unruptured IAs.

Results

The study group was composed of one hundred and twenty-five patients with 142 IAs. NLR level at admission was significantly higher in patients with ruptured IAs than those with unruptured IAs (7.55 vs. 1.81; P < 0.001). AWE on HR-VWI was present in 30 patients with unruptured IAs (38.5%), including 12 with focal AWE and 18 with circumferential AWE. NLR (odds ratio (OR), 2.168; 95% CI, 1.149–4.088) and size (odds ratio, 1.370; 95% CI, 1.126–1.667) were independently associated with circumferential AWE in unruptured IA. NLR was also independently associated with circumferential AWE in small unruptured IA (<7 mm). Furthermore, NLR level at admission was associated with CRstalk ≥.5 in patients with unruptured IA. The optimal cutoff value of NLR for circumferential AWE was 1.86.

Conclusion

NLR is a valuable peripheral blood inflammatory marker is more often in the rupture status of IA and was associated with circumferential AWE on HR-VWI in unruptured IA.

Circumferential wall enhancement with contrast ratio measurement in unruptured intracranial aneurysm for aneurysm instability

BACKGROUND

Aneurysm wall enhancement on high-resolution vessel wall imaging (HR-VWI) may represent vessel wall inflammation for unruptured intracranial aneurysms (UIAs). Further evidence for the role of circumferential aneurysm wall enhancement (CAWE) in evaluating the instability of UIAs is required, especially in small aneurysms (<7 mm).

METHODS

We analyzed patients with saccular UIAs who prospectively underwent HR-VWI on a 3.0 T MRI scanner in our center from September 2017 to August 2021. The presence of AWE was identified and quantitatively measured using the aneurysm-to-pituitary stalk contrast ratio (CRstalk) with maximal signal intensity value. The PHASES and ELAPSS scores were used to assess the risk of aneurysm rupture and growth. We evaluated the association of CAWE and CRstalk value with intracranial aneurysm instability.

RESULTS

One hundred patients with 109 saccular UIAs were included in this study. Eighty-three UIAs (76.1%) had a size smaller than 7 mm. PHASES and ELAPSS scores were significantly higher in UIAs with CAWE than in UIAs without CAWE (p < .01). The association of CAWE with PHASES and ELAPSS scores remained in small UIAs (<7 mm). The optimal cutoff value of CRstalk for CAWE was 0.5. PHASES and ELAPSS scores were significantly higher in UIAs with CRstalk ≥0.5 than in UIAs with CRstalk <0.5 (p < .01).

CONCLUSIONS

CAWE on HR-VWI is a valuable imaging marker for aneurysm instability in UIAs. CRstalk value ≥0.5 may be associated with a higher risk of intracranial aneurysm rupture and growth.

Quantitative assessment of microstructural evolution of intracranial aneurysm wall by vessel wall imaging

PURPOSE

This study aimed to evaluate new quantitative parameters of aneurysm wall enhancement (AWE) on magnetic resonance vessel wall imaging (VWI) in differentiating between the stable and evolving unruptured intracranial aneurysms (UIAs).

METHODS

Thirty-eight consecutive patients with UIAs (27 stable and 11 evolving) underwent VWI with contrast-enhanced 3D T1 volume isotropic turbo spin echo acquisition. The voxel-based enhancement maps were created using pre- and post-contrast images. The aneurysmal lumen with signal suppression by black-blood method was segmented. Then, one voxel outer and inner layers of the lumen contour were automatically segmented. The shape features of the aneurysms and AWE of the two layers were compared between stable and evolving groups.

RESULTS

The shape features, including aneurysm volume, surface, and compacity were significantly different between the stable and evolving groups (P = 0.024, 0.028, and 0.033, respectively). Stable and evolving groups also differed significantly in the AWE at the union of outer and inner layers of the aneurysm wall (P = 0.0082) but not in that of the outer or inner layer alone. Multivariate logistic regression analysis revealed significant differences in aneurysm volume, surface, and AWE at the union of outer and inner layers between the two groups (P = 0.0029, 0.0092, and 0.0033, respectively). Receiver operating characteristics curve analysis revealed that the area under the curve of the logistic regression model was 0.89.

CONCLUSION

Quantitative combined analysis of aneurysm shape features and AWE of the union of outer and inner layers were effective for differentiating between stable and evolving UIAs.

Aneurysm risk metrics and hemodynamics are associated with greater vessel wall enhancement in intracranial aneurysms

Vessel wall enhancement (VWE) in contrast-enhanced magnetic resonance imaging (MRI) is a potential biomarker for intracranial aneurysm (IA) risk stratification. In this study, we investigated the relationship between VWE features, risk metrics, morphology and hemodynamics in 41 unruptured aneurysms. We reconstructed the IA geometries from MR angiography and mapped pituitary stalk-normalized MRI intensity on the aneurysm surface using an in-house tool. For each case, we calculated the maximum intensity (CRstalk) and IA risk (via size and the rupture resemblance score (RRS)). We performed correlation analysis to assess relationships between CRstalk and IA risk metrics (size and RRS), as well as each parameter encompassed in RRS, i.e. aneurysmal size ratio (SR), normalized wall shear stress (WSS) and oscillatory shear index. We found that CRstalk had a strong correlation (Pearson correlation coefficient, PCC = 0.630) with size and a moderate correlation (PCC = 0.472) with RRS, indicating an association between VWE and IA risk. Furthermore, CRstalk had a weak negative correlation with normalized WSS (PCC = -0.320) and a weak positive correlation with SR (PCC = 0.390). Local voxel-based analysis showed only a weak negative correlation between normalized WSS and contrast-enhanced MRI signal intensity (PCC = -0.240), suggesting that if low-normalized WSS induces enhancement-associated pathobiology, the effect is not localized.

An Image-Based Workflow for Objective Vessel Wall Enhancement Quantification in Intracranial Aneurysms

BACKGROUND

VWE in contrast-enhanced magnetic resonance imaging (MRI) is a potential biomarker for the evaluation of IA. The common practice to identify IAs with VWE is mainly based on a visual inspection of MR images, which is subject to errors and inconsistencies. Here, we develop and validate a tool for the visualization, quantification and objective identification of regions with VWE.

METHODS

N = 41 3D T1-MRI and 3D TOF-MRA IA images from 38 patients were obtained and co-registered. A contrast-enhanced MRI was normalized by the enhancement intensity of the pituitary stalk and signal intensities were mapped onto the surface of IA models generated from segmented MRA. N = 30 IAs were used to identify the optimal signal intensity value to distinguish the enhancing and non-enhancing regions (marked by an experienced neuroradiologist). The remaining IAs (n = 11) were used to validate the threshold. We tested if the enhancement area ratio (EAR-ratio of the enhancing area to the IA surface-area) could identify high risk aneurysms as identified by the ISUIA clinical score.

RESULTS

A normalized intensity of 0.276 was the optimal threshold to delineate enhancing regions, with a validation accuracy of 81.7%. In comparing the overlap between the identified enhancement regions against those marked by the neuroradiologist, our method had a dice coefficient of 71.1%. An EAR of 23% was able to discriminate high-risk cases with an AUC of 0.7.

CONCLUSIONS

We developed and validated a pipeline for the visualization and objective identification of VWE regions that could potentially help evaluation of IAs become more reliable and consistent.

Semiautomated 3D mapping of aneurysmal wall enhancement with 7T-MRI

Aneurysm wall enhancement (AWE) after the administration of contrast gadolinium is a potential biomarker of unstable intracranial aneurysms. While most studies determine AWE subjectively, this study comprehensively quantified AWE in 3D imaging using a semi-automated method. Thirty patients with 33 unruptured intracranial aneurysms prospectively underwent high-resolution imaging with 7T-MRI. The signal intensity (SI) of the aneurysm wall was mapped and normalized to the pituitary stalk (PS) and corpus callosum (CC). The CC proved to be a more reliable normalizing structure in detecting contrast enhancement (p < 0.0001). 3D-heatmaps and histogram analysis of AWE were used to generate the following metrics: specific aneurysm wall enhancement (SAWE), general aneurysm wall enhancement (GAWE) and focal aneurysm wall enhancement (FAWE). GAWE was more accurate in detecting known morphological determinants of aneurysm instability such as size ≥ 7 mm (p = 0.049), size ratio (p = 0.01) and aspect ratio (p = 0.002). SAWE and FAWE were aneurysm specific metrics used to characterize enhancement patterns within the aneurysm wall and the distribution of enhancement along the aneurysm. Blebs were easily identified on 3D-heatmaps and were more enhancing than aneurysm sacs (p = 0.0017). 3D-AWE mapping may be a powerful objective tool in characterizing different biological processes of the aneurysm wall.

Intracranial aneurysm wall enhancement as an indicator of instability: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Aneurysm wall enhancement (AWE) of intracranial aneurysms on magnetic resonance imaging has been described in previous studies as a surrogate marker of instability. With this study, an updated literature overview and summary risk estimates of the association between AWE and different specific outcomes (i.e., rupture, growth or symptomatic presentation) for both cross-sectional and longitudinal studies are provided.

METHODS

The PRISMA guideline was followed and a search was performed of PubMed and Embase to 1 January 2021 for studies that reported on AWE and aneurysm instability. In cross-sectional studies, AWE was compared between patients with stable and unstable aneurysms. In longitudinal studies, AWE of stable aneurysms was assessed at baseline after which patients were followed longitudinally. Risk ratios were calculated for longitudinal studies, prevalence ratios for cross-sectional studies and then the ratios were pooled in a random-effects meta-analysis. Also, the performance of AWE to differentiate between stable and unstable aneurysms was evaluated.

RESULTS

Twelve studies were included with a total of 1761 aneurysms. In cross-sectional studies, AWE was positively associated with rupture (prevalence ratio 11.47, 95% confidence interval [CI] 4.05-32.46) and growth or symptomatic presentation (prevalence ratio 4.62, 95% CI 2.85-7.49). Longitudinal studies demonstrated a positive association between AWE and growth or rupture (risk ratio 8.00, 95% CI 2.14-29.88). Assessment of the performance of AWE showed high sensitivities, mixed specificities, low positive predictive values and high negative predictive values.

CONCLUSIONS

Although AWE is positively associated with aneurysm instability, current evidence mostly supports the use of its absence as a surrogate marker of aneurysm stability.

Segmentation of aneurysm wall enhancement in evolving unruptured intracranial aneurysms

OBJECTIVE

Morphological changes in unruptured intracranial aneurysms (UIAs) are an imaging marker of aneurysm instability. Recent studies have indicated the ability of MR vessel wall imaging (VWI) to stratify unstable UIAs based on a correlation with histopathological aneurysm wall inflammation. In the present study the authors investigated the relationships between aneurysm growth patterns and the segmentation of aneurysm wall enhancement (AWE) in VWI.

METHODS

A total of 120 aneurysms with serial angiography from a follow-up period of at least 2 years (mean 65 months, range 24-215 months) were assessed by VWI. Two readers independently evaluated the patterns of morphological changes (stable, whole sac expansion, and secondary aneurysm formation) and the segmentation of AWE (no, focal, and circumferential AWE). The contrast enhancement ratio of the aneurysm wall versus the pituitary stalk (CRstalk) was calculated for the quantitative assessment of AWE. Statistical analyses were performed to investigate the relationships between AWE patterns and patient baseline profiles, aneurysm characteristics, and morphological modifications.

RESULTS

Forty-one of 120 UIAs (34%) exhibited aneurysm growth (whole sac expansion in 19 and secondary aneurysm formation in 22). AWE was detected in 35 of 120 UIAs (focal AWE in 25 and circumferential AWE in 10). The maximum diameter of, irregularities in, and morphological modifications in aneurysms were associated with the segmentation of AWE. Focal AWE correlated with secondary aneurysm formation, and circumferential AWE correlated with whole sac expansion. In focal AWE, CRstalk was significantly higher in secondary aneurysm formation than in stable UIAs. UIAs without AWE (categorized as no AWE) correlated with aneurysm stability.

CONCLUSIONS

The segmentation of AWE was associated with aneurysm growth scenarios and may provide a novel insight into the evaluation of unstable UIAs.

Decreased contrast enhancement on high-resolution vessel wall imaging of unruptured intracranial aneurysms in patients taking aspirin

OBJECTIVE

Inflammation plays an integral role in the formation, growth, and progression to rupture of unruptured intracranial aneurysms (UIAs). Animal and human studies have suggested that, due to its antiinflammatory effect, aspirin (ASA) may decrease the risks of growth and rupture of UIAs. High-resolution vessel wall imaging (HR-VWI) has emerged as a noninvasive method to assess vessel wall inflammation and UIA instability. To the authors' knowledge, to date no studies have found a significant correlation between patient use of ASA and contrast enhancement of UIAs on HR-VWI.

METHODS

The University of Iowa HR-VWI Project database was analyzed. This database is a compilation of data on patients with UIAs who prospectively underwent HR-VWI on a 3T Siemens MRI scanner. The presence of aneurysmal wall enhancement was objectively defined using the aneurysm-to-pituitary stalk contrast ratio (CRstalk). This ratio was calculated by measuring the maximal signal intensity in the aneurysmal wall and the pituitary stalk on postcontrast T1-weighted images. Data on aneurysm size, morphology, and location and patient demographics and comorbidities were collected. Use of ASA was defined as daily intake of ≥ 81 mg during the previous 6 months or longer. Univariate and multivariate logistic regression analyses were performed to determine factors independently associated with increased contrast enhancement of UIAs on HR-VWI.

RESULTS

In total, 74 patients harboring 96 UIAs were included in the study. The mean patient age was 64.7 ± 12.4 years, and 60 patients (81%) were women. Multivariate analysis showed that age (OR 1.12, 95% CI 1.05-1.19), aneurysm size ≥ 7 mm (OR 21.3, 95% CI 4.88-92.8), and location in the anterior communicating, posterior communicating, and basilar arteries (OR 10.7, 95% CI 2.45-46.5) were significantly associated with increased wall enhancement on HR-VWI. On the other hand, use of ASA was significantly associated with decreased aneurysmal wall enhancement on HR-VWI (OR 0.22, 95% CI 0.06-0.83, p = 0.026).

CONCLUSIONS

The study results establish a correlation between use of ASA daily for ≥ 6 months and significant decreases in wall enhancement of UIAs on HR-VWI. The findings also demonstrate that detection of wall enhancement using HR-MRI may be a valuable noninvasive method for assessing aneurysmal wall inflammation and UIA instability.

Objective quantification of contrast enhancement of unruptured intracranial aneurysms: a high-resolution vessel wall imaging validation study

OBJECTIVE

High-resolution vessel wall imaging (HR-VWI) has emerged as a valuable tool in assessing unruptured intracranial aneurysms (UIAs). There is no standardized method to quantify contrast enhancement of the aneurysm wall. Contrast enhancement can be objectively measured as signal intensity (SI) or subjectively adjudicated. In this study, the authors compared the different methods to quantify wall enhancement of UIAs and determined the sensitivity and specificity of each method as a surrogate of aneurysm instability. They also compared SI quantification between scanners from different manufacturers.

METHODS

The University of Iowa HR-VWI Project database was analyzed. This database compiles patients with UIAs who prospectively underwent HR-VWI using a 3T MRI scanner. The mean and maximal SI values of the aneurysm wall, pituitary stalk, and genu of the corpus callosum were used to compare 3 different measurement methods: 1) aneurysm enhancement ratio AER = (SIwall post - SIwall pre)/SIwall pre; 2) aneurysm-to-pituitary stalk contrast ratio CRstalk = SIwall post/SIstalk post; and 3) aneurysm enhancement index AEI = ([SIwall post/SIbrain post] - [SIwall pre/SIbrain pre])/(SIwall pre/SIbrain pre) (where "pre" indicates precontrast images and "post" indicates postcontrast images). Size ≥ 7 mm was used as a surrogate of aneurysm instability for receiver operating characteristic (ROC) curve analysis. To determine if the objective quantification of SI varies among scanners from different manufacturers, 9 UIAs underwent the same HR-VWI protocol using a 3T General Electric (GE) scanner and a 3T Siemens scanner. Three UIAs also underwent a third scanning procedure on a unit with a different magnet strength (7T GE).

RESULTS

Eighty patients with 102 UIAs were included in the study. The mean age was 64.5 ± 12.2 years, and 64 (80%) patients were women. UIAs ≥ 7 mm had significantly higher SIs than smaller UIAs (< 7 mm): AER = 0.82 vs 0.49, p < 0.001; CRstalk = 0.84 vs 0.61, p < 0.001; and AEI = 0.81 vs 0.48, p < 0.001. ROC curves demonstrated optimal sensitivity of 81.5% for CRstalk ≥ 0.60, 75.9% for AEI ≥ 0.50, and 74.1% for AER ≥ 0.49. Intermanufacturer correlation between 3T GE and 3T Siemens MRI scanners for CRstalk using mean and maximal SI values was excellent (Pearson coefficients > 0.80, p < 0.001). A similar correlation was identified among the 3 UIAs that underwent 7T imaging.

CONCLUSIONS

CRstalk using maximal SI values was the most reliable objective method to quantify enhancement of UIAs on HR-VWI. The same ratios were obtained between different manufacturers and on scans obtained using magnets of different strengths.

Basilar artery dissection with rupture 6 years after accidental detection: A case report

Background:

Chronic basilar artery dissection (BAD) is a rare pathology, and only a few reports have been mentioned in the literature. The imaging features of chronic BAD, especially those that develop into a subarachnoid hemorrhage (SAH), are unknown.

Case Description:

We report a unique case of a chronic BAD with a split intimal flap that developed into an SAH. A 74-year-old man was diagnosed with BAD. After considering all treatment options, conservative treatment was selected for the patient. We continued imaging follow-up of the patient in our outpatient clinic once a year. The BA gradually dilated and the internal flap split. The patient and his family refused surgical treatment; therefore, conservative treatment was continued. Six years and 2 months from the first diagnosis, he developed a massive SAH and died.

Conclusion:

In the case of this patient, the weakened condition of the internal elastic lamina may have caused dissection of the intimal flap between the intima and media. Furthermore, the dissection may have developed and connected the true lumen to the pseudolumen and induced BA rupture. Thereby, split of the internal flap could be a risk factor for rupture in chronic BAD.

Qualitative and Quantitative Wall Enhancement Analyses in Unruptured Aneurysms Are Associated With an Increased Risk of Aneurysm Instability

Objective

Intracranial aneurysm wall enhancement (AWE) is independently associated with unstable aneurysms. However, a quantitative analysis of wall enhancement is lacking. This study aims to investigate the relationship between qualitative and quantitative wall enhancement indices (WEIs), traditional risk factors for aneurysms, and clinical ELAPSS/PHASES scores in a large cohort of intracranial saccular aneurysms.

Materials and Methods

In this cross-sectional study, a total of 174 patients (mean age 60.4 ± 9.5 years; 53% women) with 248 asymptomatic unruptured intracranial aneurysms underwent pre- and post-contrast black-blood magnetic resonance imaging (MRI). The extent of AWE was defined as non-AWE (pattern 0), focal AWE (pattern 1), or circumferential AWE (pattern 2). WEI was calculated using wall signal intensities on pre- and post-contrast images. Predicted 3- and 5-year growth risk and 5-year rupture risk were obtained from ELAPSS and PHASES scores, respectively. Uni- and multivariate analyses were conducted to explore the relationship between AWE characteristics, risk-related factors, and aneurysm instability.

Results

Aneurysm size [odds ratio (OR), 1.3; 95% confidence interval (CI), 1.2-1.4; P < 0.001], non-internal carotid artery/middle cerebral artery location (OR, 1.9; 95% CI, 1.0-3.6; P = 0.045), and irregular shape (OR, 2.4; 95% CI, 1.2-4.5; P = 0.009) were independently associated with AWE. For aneurysms with AWE, the estimated 3- and 5-year growth risk (25.3 ± 13.0% and 38.0 ± 17.4%) and the 5-year rupture risk (3.9 ± 5.2%) were 1.9-3.3 times higher than those for aneurysms without AWE (12.8 ± 9.1%, 20.3 ± 13.0%, and 1.2 ± 1.6%, respectively; all P < 0.001). Larger areas and higher WEIs of enhancement positively correlated with aneurysm size (r = 0.43 and 0.38, respectively), 3- and 5-year growth risk, and 5-year rupture risk (r = 0.49 and 0.40, r = 0.49 and 0.40, r = 0.36 and 0.24, respectively; all P < 0.001). In sum, a larger aneurysm size, non-internal carotid artery/middle cerebral artery location, and irregular shape were independently associated with AWE. Larger areas and higher WEIs were associated with an increased risk of aneurysm growth and rupture. These findings suggest that quantitative AWE metrics should be considered in future large-scale longitudinal studies to evaluate their value in aneurysm risk management.

Management of unruptured incidentally found intracranial saccular aneurysms

Unruptured intracranial saccular aneurysms occur in 3-5% of the general population. As the use of diagnostic medical imaging has steadily increased over the past few decades with the increased availability of computed tomography (CT) and magnetic resonance imaging (MRI), so has the detection of incidental aneurysms. The management of an unruptured intracranial saccular aneurysm is challenging for both patients and physicians, as the decision to intervene must weigh the risk of rupture and resultant subarachnoid hemorrhage against the risk inherent to the surgical or endovascular procedure. The purpose of this paper is to provide an overview of factors to be considered in the decision to offer treatment for unruptured intracranial aneurysms in adults. In addition, we review aneurysm and patient characteristics that favor surgical clipping over endovascular intervention and vice versa. Finally, the authors propose a novel, simple, and clinically relevant algorithm for observation versus intervention in unruptured intracranial aneurysms based on the PHASES scoring system.

Lack of Baseline Intracranial Aneurysm Wall Enhancement Predicts Future Stability: A Systematic Review and Meta-Analysis of Longitudinal Studies

BACKGROUND

The utility of vessel wall MR imaging in identifying unstable intracranial aneurysms has been suggested but remains controversial.

PURPOSE

Our aim was to provide further insight into the potential relationship between aneurysm wall enhancement on initial vessel wall imaging and aneurysm instability at follow-up.

DATA SOURCES

Our sources were PubMed, Scopus, the Web of Science, and the Cochrane Central Register of Controlled Trials.

STUDY SELECTION

We searched for English language studies that reported the presence of vessel wall enhancement of unruptured intracranial aneurysms on baseline vessel wall imaging studies with longitudinal follow-up of aneurysm status.

DATA ANALYSIS

Aneurysms were grouped into "stable" and "unstable" groups at follow-up on the basis of growth, symptomatic manifestation, or rupture. The association of each group with aneurysm wall enhancement on initial vessel wall imaging was determined.

DATA SYNTHESIS

Three studies constituting 407 aneurysms were included. Aneurysms with wall enhancement were at higher risk of being unstable at follow-up (risk ratio = 3.6; 95% confidence interval, 1.7-7.5). The sensitivity of aneurysm wall enhancement on vessel wall imaging was 74.3% (95% CI, 56.7%-87.5%), specificity was 58.3% (95% CI, 53.1%-63.4%), positive predictive value was 14.4% (95% CI, 11.8%-17.4%), negative predictive value was 96.0% (95% CI, 93.2%-97.7%), and the overall accuracy of the test was 59.7% (95% CI, 54.8%-64.5%).

LIMITATIONS

Only 3 studies were identified for inclusion in this analysis. More longitudinal studies of vessel wall imaging and aneurysm progression are needed.

CONCLUSIONS

The lack of wall enhancement may be a predictor of aneurysm stability. The utility of vessel wall imaging in detecting unstable aneurysms requires more data.

Magnetic resonance vessel wall imaging predicts morphological deterioration in unruptured intracranial artery dissection

OBJECTIVE

The mechanism involved in progression of unruptured intracranial artery dissection (IAD) is poorly understood. We investigated the relationship between contrast enhancement of dissecting lesions on magnetic resonance vessel wall imaging (MR-VWI) and unruptured IAD progression on the hypothesis that this finding might predict its instability.

METHODS

A total of 49 unruptured IADs were investigated retrospectively. Three-dimensional T1-weighted fast spin-echo sequences were obtained before and after injection of contrast medium, and the dissecting lesion/pituitary stalk contrast enhancement ratio (CR_stalk) was calculated. Unruptured IAD progression was defined as morphological deterioration; progressive dilatation or stenosis. The relations between unruptured IAD progression and potential risk factors were statistically investigated.

RESULTS

Morphological deterioration was demonstrated in eleven of 49 unruptured IADs (22 %). The CR_stalk value and male predominance was significantly higher in progressed IADs than stable ones (1.0 vs. 0.65; p = 0.0035, 82% vs 37%; p= 0.015, respectively). On stepwise multivariable logistic regression analysis, the CR_stalk value was independently associated with unruptured IAD progression with odds ratio of 102.5 (95% CI, 2.59-4059, P=0.0013). The optimal cutoff value of CR_stalk to estimate IADs with progression was 0.87 (sensitivity, 0.82; specificity, 0.74). Multimodalic images showed contrast enhancement on VWI corresponded to residual stagnant flow in dissecting lesions.

CONCLUSIONS

Quantitative analysis of contrast enhancement on VWI could predict instability of unruptured IADs. Contrast enhancement in dissecting lesions would be a clue to understand the mechanism of unruptured IAD progression.

Determinants of the Presence and Size of Intracranial Aneurysms in the General Population: The Rotterdam Study

Supplemental Digital Content is available in the text.

The prevalence of unruptured intracranial aneurysms (UIAs) in the adult population is ≈3%. Rupture of an intracranial aneurysm can have devastating consequences, which emphasizes the importance of identification of potentially modifiable determinants for the presence and size of UIAs. Our aim was to study the association of a broad spectrum of potential determinants with the presence and size of UIAs in a general adult population.

Quantitative Susceptibility Mapping and Vessel Wall Imaging as Screening Tools to Detect Microbleed in Sentinel Headache

Background: MR-quantitative susceptibility mapping (QSM) can identify microbleeds (MBs) in intracranial aneurysm (IA) wall associated with sentinel headache (SH) preceding subarachnoid hemorrhage. However, its use is limited, due to associated skull base bonny and air artifact. MR-vessel wall imaging (VWI) is not limited by such artifact and therefore could be an alternative to QSM. The purpose of this study was to investigate the correlation between QSM and VWI in detecting MBs and to help develop a diagnostic strategy for SH. Methods: We performed a prospective study of subjects with one or more unruptured IAs in our hospital. All subjects underwent evaluation using 3T-MRI for MR angiography (MRA), QSM, and pre- and post-contrast VWI of the IAs. Presence/absence of MBs detected by QSM was correlated with aneurysm wall enhancement (AWE) on VWI. Results: A total of 40 subjects harboring 51 unruptured IAs were enrolled in the study. MBs evident on the QSM sequence was detected in 12 (23.5%) IAs of 11 subjects. All these subjects had a history of severe headache suggestive of SH. AWE was detected in 22 (43.1%) IAs. Using positive QSM as a surrogate for MBs, the sensitivity, specificity, positive predictive value, and negative predictive value of AWE on VWI for detecting MBs were 91.7%, 71.8%, 50%, and 96.6%, respectively. Conclusions: Positive QSM findings strongly suggested the presence of MBs with SH, whereas, the lack of AWE on VWI can rule it out with a probability of 96.6%. If proven in a larger cohort, combining QSM and VWI could be an adjunctive tool to help diagnose SH, especially in cases with negative or non-diagnostic CT and lumbar puncture.

Vessel wall magnetic resonance imaging in intracranial aneurysms: Principles and emerging clinical applications

Intracranial high-resolution vessel wall magnetic resonance imaging is an imaging paradigm that complements conventional imaging modalities used in the evaluation of neurovascular pathology. This review focuses on the emerging utility of vessel wall magnetic resonance imaging in the characterization of intracranial aneurysms. We first discuss the technical principles of vessel wall magnetic resonance imaging highlighting methods to determine aneurysm wall enhancement and how to avoid common interpretive pitfalls. We then review its clinical application in the characterization of ruptured and unruptured intracranial aneurysms, in particular, the emergence of aneurysm wall enhancement as a biomarker of aneurysm instability. We offer our perspective from a high-volume neurovascular center where vessel wall magnetic resonance imaging is in routine clinical use.

Lessons from Vessel Wall Imaging of Intracranial Aneurysms: New Era of Aneurysm Evaluation beyond Morphology

Recent basic studies have clarified that aneurysmal wall inflammation plays an important role in the pathophysiology of intracranial aneurysms. However, it remains an interdisciplinary challenge to visualize aneurysm wall status in vivo. MR-vessel wall imaging (VWI) is a current topic of advanced imaging techniques since it could provide an additional value for unruptured intracranial aneurysms (UIAs) risk stratification. With regard to ruptured intracranial aneurysms, VWI could identify a ruptured aneurysm in patients with multiple intracranial aneurysms. Intraluminal thrombus could be a clue to interpret aneurysm wall enhancement on VWI in ruptured intracranial aneurysms. The interpretation of VWI findings in UIAs would require much caution. Actually aneurysm wall enhancement in VWI was significantly associated with consensus morphologic risk factors. However, aneurysmal wall with contrast enhancement oftentimes associated with atherosclerotic, degenerated and thickened wall structure. It remains ill defined if thin wall without wall enhancement (oftentimes invisible in VWI) could be actually safe or look over wall vulnerability. We reviewed currently available studies, especially focusing on VWI for intracranial aneurysms and discussed the clinical utility of VWI.

Vessel wall imaging in intracranial aneurysms

High-resolution vessel wall imaging (HR-VWI) is becoming a useful tool in the characterization and identification of unstable unruptured brain aneurysms. However, it has not been validated for clinical use. The current evidence on HR-VWI techniques for characterization of brain aneurysms is described in this review. Specific imaging approaches such as aneurysm wall contrast enhancement, MRI-quantitative susceptibility mapping, and 7T MRI are described in detail.

Macrophage Imaging of Intracranial Aneurysms

Considered with a poor outcome of subarachnoid hemorrhage due to rupture of intracranial aneurysms (IAs), treatment interventions to prevent rupture of the lesions are mandatory for social health. As treatment option is limited to surgical manipulations, like microsurgical clipping, endovascular coiling or deployment of flow diverter, and these surgical interventions have a potential risk of complications in nature, a proper selection of rupture-prone IAs among ones incidentally found is essential. Today, a rupture risk in each case is estimated by several factors like patient characteristics and morphological ones of each lesion. However, unfortunately, an IA without treatment sometimes unexpectedly ruptures resulting in a devastating outcome or an IA surgically treated is turned out to have a thick wall. To achieve more efficient treatment interventions, the development of a novel diagnostic modality is required. Here, mainly through the accumulation of experimental findings, the crucial contribution of macrophage-mediated chronic inflammatory responses to IA progression have been revealed, making macrophage being a promising target for a diagnosis. If we could non-invasively visualize accumulation of macrophages in lesions, this imaging technique ‘macrophage imaging’ may enable a qualitative evaluation of IAs to stratify rupture-prone ‘dangerous’ lesions among many stable ones. Thereby, a development of macrophage imaging makes an indication of surgical interventions being more accurate and also greatly facilitates a development of a novel medical therapy if used as a surrogate marker.