Blood Flow Mimicking Aneurysmal Wall Enhancement: A Diagnostic Pitfall of Vessel Wall MRI Using the Postcontrast 3D Turbo Spin-Echo MR Imaging Sequence

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.

Optimizing timing for quantification of intracranial aneurysm enhancement: a multi-phase contrast-enhanced vessel wall MRI study

OBJECTIVES

Aneurysm wall enhancement (AWE) on high-resolution contrast-enhanced vessel wall MRI (VWMRI) is an emerging biomarker for intracranial aneurysms (IAs) stability. Quantification methods of AWE in the literature, however, are variable. We aimed to determine the optimal post-contrast timing to quantify AWE in both saccular and fusiform IAs.

MATERIALS AND METHODS

Consecutive patients with unruptured IAs were prospectively recruited. VWMRI was acquired on 1 pre-contrast and 4 consecutive post-contrast phases (each phase was 9 min). Signal intensity values of cerebrospinal fluid (CSF) and aneurysm wall on pre- and 4 post-contrast phases were measured to determine the aneurysm wall enhancement index (WEI). AWE was also qualitatively analyzed on post-contrast images using previous grading criteria. The dynamic changes of AWE grade and WEI were analyzed for both saccular and fusiform IAs.

RESULTS

Thirty-four patients with 42 IAs (27 saccular IAs and 15 fusiform IAs) were included. The changes in AWE grade occurred in 8 (30%) saccular IAs and 6 (40%) in fusiform IAs during the 4 post-contrast phases. The WEI of fusiform IAs decreased 22.0% over time after contrast enhancement (p = 0.009), while the WEI of saccular IAs kept constant during the 4 post-contrast phases (p > 0.05).

CONCLUSIONS

When performing quantitative analysis of AWE, acquiring post-contrast VWMRI immediately after contrast injection achieves the strongest AWE for fusiform IAs. While the AWE degree is stable for 36 min after contrast injection for saccular IAs.

CLINICAL RELEVANCE STATEMENT

The standardization of imaging protocols and analysis methods for AWE will be helpful for imaging surveillance and further treatment decisions of patients with unruptured IAs.

KEY POINTS

Imaging protocols and measurements of intracranial aneurysm wall enhancement are reported heterogeneously. Aneurysm wall enhancement for fusiform intracranial aneurysms (IAs) is strongest immediately post-contrast, and stable for 36 min for saccular IAs. Future multi-center studies should investigate aneurysm wall enhancement as an emerging marker of aneurysm growth and rupture.

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.

The relationship between symptomatic status and aneurysm wall enhancement characteristics of single unruptured intracranial aneurysm

OBJECTIVE

We aimed to analyze the aneurysm wall enhancement (AWE) characteristics of a single unruptured intracranial aneurysm (UIA) and observe the relationship between the symptoms of a single UIA and the aneurysm wall.

METHODS

In our hospital, 85 patients diagnosed with a single UIA using computed tomography angiography (CTA) were retrospectively analyzed. The patients were divided into symptomatic and asymptomatic groups, including 46 asymptomatic and 39 symptomatic aneurysms. High-resolution magnetic resonance imaging of the vascular wall (HR-MR-VWI) was utilized to ascertain the presence, degree, and extent of AWE and thick-wall enhancement. In addition to AWE characteristics, morphological parameters of aneurysms, such as maximal size, shape, height, neck width, aspect ratio (AR), and size ratio (SR), were scanned using CTA. The differences in the parameters of a single UIA between the two groups were compared. An investigation explored the correlation between the symptom status of a single UIA and AWE.

RESULTS

We observed a correlation between symptom status and maximal size, height, and neck width for a single UIA, the presence or absence of AWE, and the levels and boundaries of AWE and thick-wall reinforcement. This study found that the AWE range was independently correlated with symptom status in the multivariate regression analysis.

CONCLUSION

A larger AWE range was an independent risk factor for the onset of symptoms in a single UIA.

Advanced cross-sectional imaging of cerebral aneurysms

While the rupture rate of cerebral aneurysms is only 1% per year, ruptured aneurysms are associated with significant morbidity and mortality, while aneurysm treatments have their own associated risk of morbidity and mortality. Conventional markers for aneurysm rupture include patient-specific and aneurysm-specific characteristics, with the development of scoring systems to better assess rupture risk. These scores, however, rely heavily on aneurysm size, and their accuracy in assessing risk in smaller aneurysms is limited. While the individual risk of rupture of small aneurysms is low, due to their sheer number, the largest proportion of ruptured aneurysms are small aneurysms. Conventional imaging techniques are valuable in characterizing aneurysm morphology; however, advanced imaging techniques assessing the presence of inflammatory changes within the aneurysm wall, hemodynamic characteristics of blood flow within aneurysm sacs, and imaging visualization of irregular aneurysm wall motion have been used to further determine aneurysm instability that otherwise cannot be characterized by conventional imaging techniques. The current manuscript reviews conventional imaging techniques and their value and limitations in cerebral aneurysm characterization, and evaluates the applications, value and limitations of advanced aneurysm imaging and post-processing techniques including intracranial vessel wall MRA, 4D-flow, 4D-CTA, and computational fluid dynamic simulations.

Improved Blood Suppression of Motion-Sensitized Driven Equilibrium in High-Resolution Whole-Brain Vessel Wall Imaging: Comparison of Contrast-Enhanced 3D T1-Weighted FSE with Motion-Sensitized Driven Equilibrium and Delay Alternating with Nutation for Tailored Excitation

BACKGROUND AND PURPOSE

High-resolution vessel wall MR imaging is prone to slow-flow artifacts, particularly when gadolinium shortens the T1 relaxation time of blood. This study aimed to determine the optimal preparation pulses for contrast-enhanced high-resolution vessel wall MR imaging.

MATERIALS AND METHODS

Fifty patients who underwent both motion-sensitized driven equilibrium and delay alternating with nutation for tailored excitation (DANTE) preparation pulses with contrast-enhanced 3D-T1-FSE were retrospectively included. Qualitative analysis was performed using a 4-grade visual scoring system for black-blood performance in the small-sized intracranial vessels, overall image quality, severity of artifacts, and the degree of blood suppression in all cortical veins as well as transverse sinuses. Quantitative analysis of the M1 segment of the MCA was also performed.

RESULTS

The qualitative analysis revealed that motion-sensitized driven equilibrium demonstrated a significantly higher black-blood score than DANTE in contrast-enhanced 3D-T1-FSE of the A3 segment (3.90 versus 3.58, P < .001); M3 (3.72 versus 3.26, P = .004); P2 to P3 (3.86 versus 3.64, P = .017); the internal cerebral vein (3.72 versus 2.32, P < .001); and overall cortical veins (3.30 versus 2.74, P < .001); and transverse sinuses (2.82 versus 2.38, P < .001). SNR_lumen, contrast-to noise ratio_wall-lumen, and SNR_wall in the M1 vessel were not significantly different between the 2 preparation pulses (all, P > .05).

CONCLUSIONS

Motion-sensitized driven equilibrium demonstrated improved blood suppression on contrast-enhanced 3D-T1-FSE in the small intracranial arteries and veins compared with DANTE. Motion-sensitized driven equilibrium is a useful preparation pulse for high-resolution vessel wall MR imaging to decrease venous contamination and suppress slow-flow artifacts when using contrast enhancement.

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.

Image-Quality Assessment of 3D Intracranial Vessel Wall MRI Using DANTE or DANTE-CAIPI for Blood Suppression and Imaging Acceleration

BACKGROUND AND PURPOSE

3D intracranial vessel wall MRI techniques are time consuming and prone to artifacts, especially flow artifacts. Our aim was to compare the image quality of accelerated and flow-suppressed 3D intracranial vessel wall MR imaging techniques relative to conventional acquisitions.

MATERIALS AND METHODS

Consecutive patients undergoing MR imaging had conventional postcontrast 3D T1-sampling perfection with application-optimized contrasts by using different flip angle evolution (SPACE) and either postcontrast delay alternating with nutation for tailored excitation (DANTE) flow-suppressed or DANTE-controlled aliasing in parallel imaging results in higher acceleration (CAIPI) flow-suppressed and accelerated T1-SPACE sequences performed. The sequences were evaluated using 4- or 5-point Likert scales for overall image quality, SNR, extent/severity of artifacts, motion, blood suppression, sharpness, and lesion assessment. Quantitative assessment of lumen and wall-to-lumen contrast ratios was performed.

RESULTS

Eighty-nine patients were included. T1-DANTE-SPACE had significantly better qualitative ratings relative to T1-SPACE for image quality, SNR, artifact impact, arterial and venous suppression, and lesion assessment (P < .001 for each, respectively), with the exception of motion (P = .16). T1-DANTE-CAIPI-SPACE had significantly better image quality, lesion assessment, arterial and venous blood suppression, less artifact impact, and less motion compared with T1-SPACE (P < .001 for each, respectively). The SNR was higher with T1-SPACE compared with T1-DANTE-CAIPI-SPACE (P < .001). T1-DANTE-CAIPI-SPACE showed significantly worse lumen (P = .005) and wall-to-lumen contrast ratios (P = .001) compared with T1-SPACE, without a significant difference between T1-SPACE and T1-DANTE-SPACE. T1-DANTE-CAIPI-SPACE scan time was 5:11 minutes compared with 8:08 and 8:41 minutes for conventional T1-SPACE and T1-DANTE-SPACE, respectively.

CONCLUSIONS

Accelerated postcontrast T1-DANTE-CAIPI-SPACE had fewer image artifacts, less motion, improved blood suppression, and a shorter scan time, but lower qualitative and quantitative SNR ratings relative to conventional T1-SPACE intracranial vessel wall MR imaging. Postcontrast T1-DANTE-SPACE had superior SNR, blood suppression, higher image quality, and fewer image artifacts, but slightly longer scan times relative to T1-SPACE.

Imaging Modalities for Intracranial Aneurysm: More Than Meets the Eye

Intracranial aneurysms (IA) are often asymptomatic and have a prevalence of 3 to 5% in the adult population. The risk of IA rupture is low, however when it occurs half of the patients dies from subarachnoid hemorrhage (SAH). To avoid this fatal evolution, the main treatment is an invasive surgical procedure, which is considered to be at high risk of rupture. This risk score of IA rupture is evaluated mainly according to its size and location. Therefore, angiography and anatomic imaging of the intracranial aneurysm are crucial for its diagnosis. Moreover, it has become obvious in recent years that several other factors are implied in this complication, such as the blood flow complexity or inflammation. These recent findings lead to the development of new IA imaging tools such as vessel wall imaging, 4D-MRI, or molecular MRI to visualize inflammation at the site of IA in human and animal models. In this review, we will summarize IA imaging techniques used for the patients and those currently in development.

Vessel Wall MR Imaging in the Pediatric Head and Neck

Vessel wall MR imaging (VWI) is a technique that progressively has gained traction in clinical diagnostic applications for evaluation of intracranial and extracranial vasculopathies, with increasing use in pediatric populations. The technique has shown promise in detection, differentiation, and characterization of both inflammatory and noninflammatory vasculopathies. In this article, optimal techniques for intracranial and extracranial VWI as well as applications and value for pediatric vascular disease evaluation are discussed.

Pseudo-Enhancement in Intracranial Aneurysms on Black-Blood MRI: Effects of Flow Rate, Spatial Resolution, and Additional Flow Suppression

BACKGROUND

Vessel-wall enhancement (VWE) on black-blood MRI (BB MRI) has been proposed as an imaging marker for a higher risk of rupture and associated with wall inflammation. Whether VWE is causally linked to inflammation or rather induced by flow phenomena has been a subject of debate.

PURPOSE

To study the effects of slow flow, spatial resolution, and motion-sensitized driven equilibrium (MSDE) preparation on signal intensities in BB MRI of patient-specific aneurysm flow models.

STUDY TYPE

Prospective.

SUBJECTS/FLOW ANEURYSM MODEL/VIRTUAL VESSELS

Aneurysm flow models based on 3D rotational angiography datasets of three patients with intracranial aneurysms were 3D printed and perfused at two different flow rates, with and without Gd-containing contrast agent.

FIELD STRENGTH/SEQUENCE

Variable refocusing flip angle 3D fast-spin echo sequence at 3 T with and without MSDE with three voxel sizes ((0.5 mm)³ , (0.7 mm)³ , and (0.9 mm)³ ); time-resolved with phase-contrast velocity-encoding 3D spoiled gradient echo sequence (4D flow MRI).

ASSESSMENT

Three independent observers performed a qualitative visual assessment of flow patterns and signal enhancement. Quantitative analysis included voxel-wise evaluation of signal intensities and magnitude velocity distributions in the aneurysm.

STATISTICAL TESTS

Kruskal-Wallis test, potential regressions.

RESULTS

A hyperintense signal in the lumen and adjacent to the aneurysm walls on BB MRI was colocalized with slow flow. Signal intensities increased by a factor of 2.56 ± 0.68 (P < 0.01) after administering Gd contrast. After Gd contrast administration, the signal was suppressed most in conjunction with high flows and with MSDE (2.41 ± 2.07 for slow flow without MSDE, and 0.87 ± 0.99 for high flow with MSDE). A clear result was not achieved by modifying the spatial resolution .

DATA CONCLUSIONS

Slow-flow phenomena contribute substantially to aneurysm enhancement and vary with MRI parameters. This should be considered in the clinical setting when assessing VWE in patients with an unruptured aneurysm.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Quantitative analysis of unruptured intracranial aneurysm wall thickness and enhancement using 7T high resolution, black blood magnetic resonance imaging

BACKGROUND

This study was performed to quantify intracranial aneurysm wall thickness (AWT) and enhancement using 7T MRI, and their relationship with aneurysm size and type.

METHODS

27 patients with 29 intracranial aneurysms were included. Three-dimensional T1 weighted pre- and post-contrast fast spin echo with 0.4 mm isotropic resolution was used. AWT was defined as the full width at half maximum on profiles of signal intensity across the aneurysm wall on pre-contrast images. Enhancement ratio (ER) was defined as the signal intensity of the aneurysm wall over that of the brain parenchyma. The relationships between AWT, ER, and aneurysm size and type were investigated.

RESULTS

7T MRI revealed large variations in AWT (range 0.11-1.24 mm). Large aneurysms (>7 mm) had thicker walls than small aneurysms (≤7 mm) (0.49±0.05 vs 0.41±0.05 mm, p<0.001). AWT was similar between saccular and fusiform aneurysms (p=0.546). Within each aneurysm, a thicker aneurysm wall was associated with increased enhancement in 28 of 29 aneurysms (average r=0.65, p<0.05). Thicker walls were observed in enhanced segments (ER >1) than in non-enhanced segments (0.53±0.09 vs 0.38±0.07 mm, p<0.001).

CONCLUSION

Improved image quality at 7T allowed quantification of intracranial AWT and enhancement. A thicker aneurysm wall was observed in larger aneurysms and was associated with stronger enhancement.

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.

The diagnostic contribution of intracranial vessel wall imaging in the differentiation of primary angiitis of the central nervous system from other intracranial vasculopathies

PURPOSE

The aim of this study is to demonstrate the diagnostic effect of VWI in differentiating PACNS from other vasculopathies and its role in post-treatment follow-up in PACNS patients in this study.

METHODS

In this prospective study, we included patients with clinical suspicion of PACNS who presented with new-onset ischemic events and had significant intracranial large vessel stenosis on DSA or MRA. VWI was performed on all patients. The imaging findings and final diagnoses were recorded. Control VWI was performed on patients with PACNS diagnosis after at least 3 months of treatment, and the change in findings was also evaluated.

RESULTS

Twenty-three patients were included in the study had a median age of 40 (range 12-58). The most common clinical manifestations were focal neurologic deficits. According to the initial clinical evaluation, 10 patients (43.5%) were classified as PACNS and 13 patients (56.5%) as indeterminate for PACNS. After incorporating the VWI findings, the diagnosis of PACNS was confirmed in all clinically diagnosed PACNS patients. Concentric wall thickening and contrast enhancement were statistically significant in the PACNS group (p <0.001). According to concentric thickening and VWE features, sensitivity and specificity in distinguishing PACNS and other vasculopathies were 95.2%, 75% and 95.2%, 68.8%, respectively. Vessel wall enhancement regressed in 7 of 9 patients during a median follow-up period of 8 months (range 5.5-11.5) in PACNS patients who followed up.

CONCLUSION

VWI seems a new and useful imaging method in the differential diagnosis of PACNS and might be a useful adjunct for post-treatment follow-up.

Risk factors and treatment approach for subarachnoid hemorrhage in a patient with nine intracranial aneurysms

Introduction. In about one-third of the patients with aneurysmal subarachnoid bleeding, multiple intracranial aneurysms are confirmed. Risk factors such as female gender, smoking, hypertension, and age over 60 tend to be associated with multiple aneurysms. In this paper, we also discuss family predisposition and the treatment approach for multiple cerebral aneurysms. Case outline. Here, we present a case of a female patient, 64-year-old, with spontaneous subarachnoid hemorrhage that had nine intracranial aneurysms. The patient was treated for hypertension for a longer period, excessive smoker, and two of her nearest members of the family died from intracranial bleeding. The patient was fully conscious, without any neurological impairment. Subarachnoid bleeding was diffuse and nor brain-computer tomography finding nor digital subtraction angiography couldn't suggest the source or location of bleeding among nine presented aneurisms. Magnet resonance imaging had to be done, and the T1W fast spin-echo sequence showed a 9 mm large ruptured an aneurysm at the basilar tip, after contrast application, beside others. Three days after insult endovascular embolization was done and two basilar aneurysms were excluded from the circulation, including the one that bled. Conclusion. The patient had the majority of risk factors for multiple intracranial aneurysms. Knowledge of the family predisposition of multiple intracranial aneurysms allowed us to make proper diagnostics of a patient's descendant and reveal a new patient.

Qualitative and Quantitative Wall Enhancement on Magnetic Resonance Imaging Is Associated With Symptoms of Unruptured Intracranial Aneurysms

BACKGROUND AND PURPOSE

Aneurysmal wall enhancement (AWE) on vessel wall magnetic resonance imaging (VW-MRI) has been described as a new imaging biomarker of unstable unruptured intracranial aneurysms (UIAs). Previous studies of symptomatic UIAs are limited due to small sample sizes and lack of AWE quantification. Our study aims to investigate whether qualitative and quantitative assessment of AWE can differentiate symptomatic and asymptomatic UIAs.

METHODS

Consecutive patients with UIAs were prospectively recruited for vessel wall magnetic resonance imaging at 3T from October 2014 to October 2019. UIAs were categorized as symptomatic if presenting with sentinel headache or oculomotor nerve palsy directly related to the aneurysm. Evaluation of wall enhancement included enhancement pattern (0=none, 1=focal, and 2=circumferential) and quantitative wall enhancement index (WEI). Univariate and multivariate analyses were used to identify the parameters associated with symptoms.

RESULTS

Two hundred sixty-seven patients with 341 UIAs (93 symptomatic and 248 asymptomatic) were included in this study. Symptomatic UIAs more frequently showed circumferential AWE than asymptomatic UIAs (66.7% versus 17.3%, P<0.001), as well as higher WEI (median [interquartile range], 1.3 [1.0-1.9] versus 0.3 [0.1-0.9], P<0.001). In multivariate analysis, both AWE pattern and WEI were independent factors associated with symptoms (odds ratio=2.03 across AWE patterns [95% CI, 1.21-3.39], P=0.01; odds ratio=3.32 for WEI [95% CI, 1.51-7.26], P=0.003). The combination of AWE pattern and WEI had an area under the curve of 0.91 to identify symptomatic UIAs, with a sensitivity of 95.7% and a specificity of 73.4%.

CONCLUSIONS

In a large cohort of UIAs with vessel wall magnetic resonance imaging, both AWE pattern and WEI were independently associated with aneurysm-related symptoms. The qualitative and quantitative features of AWE can potentially be used to identify unstable intracranial aneurysms.

Multimodal validation of focal enhancement in intracranial aneurysms as a surrogate marker for aneurysm instability

Purpose

Circumferential enhancement on MR vessel wall imaging has been proposed as a biomarker of a higher risk of rupture in intracranial aneurysms. Focal enhancement is frequently encountered in unruptured aneurysms, but its implication for risk stratification and patient management remains unclear. This study investigates the association of focal wall enhancement with hemodynamic and morphological risk factors and histologic markers of wall inflammation and degeneration.

Methods

Patients with an unruptured middle cerebral artery aneurysm who underwent 3D rotational angiography and 3T MR vessel wall imaging showing focal wall enhancement were included. Hemodynamic parameters were calculated based on flow simulations and compared between enhanced regions and the entire aneurysm surface. Morphological parameters were semiautomatically extracted and quantitatively associated with wall enhancement. Histological analysis included detection of vasa vasorum, CD34, and myeloperoxidase staining in a subset of patients.

Results

Twenty-two aneurysms were analyzed. Enhanced regions were significantly associated with lower AWSS, lower maxOSI, and increased LSA. In multivariate analysis, higher ellipticity index was an independent predictor of wall enhancement. Histologic signs of inflammation and degeneration and higher PHASES score were significantly associated with focal enhancement.

Conclusion

Focal wall enhancement is colocalized with hemodynamic factors that have been related to a higher rupture risk. It is correlated with morphological factors linked to rupture risk, higher PHASES score, and histologic markers of wall destabilization. The results support the hypothesis that focal enhancement could serve as a surrogate marker for aneurysm instability.

Wall enhancement on black-blood MRI is independently associated with symptomatic status of unruptured intracranial saccular aneurysm

OBJECTIVE

This study aims to investigate whether aneurysm wall enhancement (AWE) is independently associated with symptomatic status of unruptured intracranial aneurysms (UIAs).

METHODS

One hundred thirty-nine consecutive patients (67 male, mean age 58 ± 11 years) with 79 symptomatic and 87 asymptomatic UIAs were imaged using black-blood MRI pre- and post-gadolinium contrast administration and 3D DSA. Symptoms related to aneurysms were identified including cranial nerve deficits and headache. AWE grade and area were characterized, and aneurysm size was measured on DSA. Multivariate binary logistic regression analysis was used to identify factors associated with symptoms. Further subgroup analysis was performed for aneurysms size < 10 mm.

RESULTS

Symptomatic UIAs had significantly larger aneurysm size (11.2 ± 6.2 mm vs. 6.4 ± 3.3 mm), enhancement grade (1.3 ± 0.6 vs. 0.4 ± 0.6), enhancement area (2.0 ± 0.9 vs. 0.4 ± 0.7), and higher prevalence of thick enhancement (39% vs. 3%) compared with asymptomatic UIAs, all p < 0.001. In multivariate analysis, only AWE area (odds ratio [OR] 6.9, 95% confidence interval [4.0, 11.7]) was independently associated with symptoms. AWE area had an area under curve (AUC) value of 0.888, with 72.2% sensitivity and 92.0% specificity for symptoms, which was superior to aneurysm size (AUC of 0.771, with 75.9% sensitivity and 65.5% specificity). In the subgroup analysis of aneurysms smaller than 10 mm (n = 118), AWE area (OR, 7.0, p < 0.001) remained the only independent risk factor associated with symptoms.

CONCLUSIONS

Larger AWE area is independently associated with symptomatic UIAs, which may provide additional value to guide UIA management and improve patient outcomes.

KEY POINTS

• Symptomatic intracranial aneurysms are larger and more often demonstrate significant wall enhancement than asymptomatic aneurysms. • Larger wall enhancement area is independently associated with symptomatic intracranial aneurysm.

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.

Magnetic resonance vessel wall imaging in cerebrovascular diseases

Cerebrovascular diseases manifest as abnormalities of and disruption to the intracranial vasculature and its capacity to carry blood to the brain. However, the pathogenesis of many cerebrovascular diseases begins in the vessel wall. Traditional luminal and perfusion imaging techniques do not provide adequate information regarding the differentiation, onset, or progression of disease. Intracranial high-resolution MR vessel wall imaging (VWI) has emerged as an invaluable technique for understanding and evaluating cerebrovascular diseases. The location and pattern of contrast enhancement in intracranial VWI provides new insight into the inflammatory etiology of cerebrovascular diseases and has potential to permit earlier diagnosis and treatment. In this report, technical considerations of VWI are discussed and current applications of VWI in vascular malformations, blunt cerebrovascular injury/dissection, and steno-occlusive cerebrovascular vasculopathies are reviewed.

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.

Vessel wall enhancement of intracranial aneurysms: fact or artifact?

OBJECTIVE

For patients with subarachnoid hemorrhage (SAH) and multiple intracranial aneurysms, it is often challenging to identify the ruptured aneurysm. Some investigators have asserted that vessel wall imaging (VWI) can be used to identify the ruptured aneurysm since wall enhancement after contrast agent injection is presumably related to inflammation in unstable and ruptured aneurysms. The aim of this study was to determine whether additional factors contribute to aneurysm wall enhancement by assessing imaging data in a series of patients.

METHODS

Patients with symptoms of SAH who subsequently underwent VWI in the period between January 2017 and September 2018 were eligible for study inclusion. Three-dimensional turbo spin-echo sequences with motion-sensitized driven-equilibrium preparation pulses were acquired using a 3-T MRI scanner to visualize the aneurysm wall. Identification of the ruptured aneurysm was based on aneurysm characteristics and hemorrhage distributions on MRI. Complementary imaging data (CT, DSA, MRI) were used to assess potential underlying enhancement mechanisms. Additionally, aneurysm luminal diameter measurements on MRA were compared with those on contrast-enhanced VWI to assess the intraluminal contribution to aneurysm enhancement.

RESULTS

Six patients with 14 aneurysms were included in this series. The mean aneurysm size was 5.8 mm (range 1.1–16.9 mm). A total of 10 aneurysms showed enhancement on VWI; 5 ruptured aneurysms showed enhancement, and 1 unruptured but symptomatic aneurysm showed enhancement on VWI and ruptured 1 day later. Four unruptured aneurysms showed enhancement. In 6 (60%) of the 10 enhanced aneurysms, intraluminal diameters appeared notably smaller (≥ 0.8 mm smaller) on contrast-enhanced VWI compared to their appearance on multiple overlapping thin slab acquisition time of flight (MOTSA-TOF) MRA and/or precontrast VWI, suggesting that enhancement was at least partially in the aneurysm lumen itself.

CONCLUSIONS

Several factors other than the hypothesized inflammatory response contribute to aneurysm wall enhancement. In 60% of the cases in this study, enhancement was at least partially caused by slow intraaneurysmal flow, leading to pseudo-enhancement of the aneurysm wall. Notwithstanding, there seems to be clinical value in differentiating ruptured from unruptured aneurysms using VWI, but the hypothesis that we image the inflammatory cell infiltration in the aneurysm wall is not yet confirmed.

Insufficient slow-flow suppression mimicking aneurysm wall enhancement in magnetic resonance vessel wall imaging: a phantom study

OBJECTIVE

MR vessel wall imaging (VWI) is increasingly performed in clinical settings to support treatment decision-making regarding intracranial aneurysms. Aneurysm wall enhancement after contrast agent injection is expected to be related to aneurysm instability and rupture status. However, the authors hypothesize that slow-flow artifacts mimic aneurysm wall enhancement. Therefore, in this phantom study they assess the effect of slow flow on wall-like enhancement by using different MR VWI techniques.

METHODS

The authors developed an MR-compatible aneurysm phantom model, which was connected to a pump to enable pulsatile inflow conditions. For VWI, 3D turbo spin echo sequences—both with and without motion-sensitized driven equilibrium (MSDE) and delay alternating with nutation for tailored excitation (DANTE) preparation pulses—were performed using a 3-T MR scanner. VWI was acquired both before and after Gd contrast agent administration by using two different pulsatile inflow conditions (2.5 ml/sec peak flow at 77 and 48 beats per minute). The intraluminal signal intensity along the aneurysm wall was analyzed to assess the performance of slow-flow suppression.

RESULTS

The authors observed wall-like enhancement after contrast agent injection, especially in low pump rate settings. Preparation pulses, in particular the DANTE technique, improved the performance of slow-flow suppression.

CONCLUSIONS

Near-wall slow flow mimics wall enhancement in VWI protocols. Therefore, VWI should be carefully interpreted. Preparation pulses improve slow-flow suppression, and therefore the authors encourage further development and clinical implementation of these techniques.

Wall enhancement of intracranial saccular and fusiform aneurysms may differ in intensity and extension: a pilot study using 7-T high-resolution black-blood MRI

PURPOSE

To evaluate and compare wall enhancement patterns in saccular and fusiform intracranial aneurysms using high-resolution black-blood MRI at 7 T.

METHODS

Thirty-one patients with 32 unruptured intracranial aneurysms (21 saccular and 11 fusiform) underwent 7-T black-blood MRI. Aneurysm wall enhancement (AWE) was categorized as follows: no wall enhancement (NWE), focal wall enhancement (FWE), and uniform wall enhancement (UWE). The degree of enhancement was scored as follows: 0 (no enhancement), 1 (signal intensity (SI) of the aneurysm wall less than that of the pituitary infundibulum), and 2 (equal to that of the pituitary infundibulum). The chi-squared test was used to compare the AWE pattern and degree between saccular and fusiform aneurysms.

RESULTS

In saccular aneurysms, 12/21 (57%) enhanced. Of these, 9 showed FWE (5 grade 1 and 4 grade 2), and 3 showed UWE (2 grade 1 and 1 grade 2). In fusiform aneurysms, 11/11 (100%) enhanced. Of these, 1 showed FWE and 10 showed UWE. All fusiform aneurysms had grade-2 enhancement. Fusiform aneurysms had more extensive and higher SI AWE than saccular aneurysms (p < 0.01) despite having a similar size (6.9 ± 3.0 mm vs. 8.0 ± 2.9, p = 0.23). For saccular aneurysm, larger aneurysm size was correlated with higher degree of enhancement with Pearson's r = 0.64 (p = 0.002).

CONCLUSION

Intracranial fusiform aneurysms had enhancement of higher SI and that covered a more extensive area than saccular aneurysms, which might indicate differences in vessel wall pathology.

KEY POINTS

• Intracranial aneurysm wall enhancement can be reliably characterized by 7-T black-blood MRI. • AWE in intracranial fusiform aneurysms presents over a larger surface area and with greater signal intensity as compared with that in saccular aneurysms, which might indicate differences in pathology. • Stronger signal intensity of AWE correlates with the aneurysm size in saccular aneurysms.

Intracranial Aneurysm Wall Enhancement Associated with Aneurysm Rupture: A Systematic Review and Meta-analysis

RATIONALE AND OBJECTIVES

Aneurysm wall enhancement (AWE) on magnetic resonance vessel wall imaging has been proposed as an imaging marker of aneurysm wall inflammation and instability. We performed a systematic review and meta-analysis to summarize the association between AWE and aneurysm rupture.

MATERIALS AND METHODS

We performed a comprehensive literature search of studies evaluating the association between AWE and aneurysm rupture. We abstracted the following study data: study design, patient demographics, aneurysm characteristics, MRI protocols, and AWE assessment. We performed meta-analysis using a random-effects model. Study heterogeneity was assessed by using the Cochrane Q and I² statistic, and publication bias was examined by using the Begg-Mazumdar test.

RESULTS

Five studies with 492 subjects met eligibility for systematic review. We found a significant positive overall association between AWE and aneurysm rupture, with an odds ratio (OR) of 34.26 (95% confidence interval [CI] 10.20-115.07, p < 0.001). No significant heterogeneity (Q = 5.38, p = 0.25; I² = 26%) or publication bias (p = 1.000) was present. In the separate analysis of circumferential AWE and aneurysm rupture, we identified marked heterogeneity across studies (Q = 21.23, p < 0.001; I² = 86%). Further subgroup analysis considering the effect of aneurysm size showed that the strength of association between circumferential AWE and aneurysm rupture was significant in small aneurysms (<7 mm), with an OR of 26.12 (95% CI 6.11-111.75, p < 0.001), but limited in large aneurysms (OR = 0.56, 95% CI [0.21, 1.44], p = 0.23).

CONCLUSION

AWE on magnetic resonance vessel wall imaging is significantly and independently associated with aneurysm rupture and may become a promising imaging marker to predict aneurysm behavior and identify high-risk aneurysms.

Utility of intracranial high-resolution vessel wall magnetic resonance imaging in differentiating intracranial vasculopathic diseases causing ischemic stroke

PURPOSE

High-resolution vessel wall imaging (HRVWI) by MRI is a novel noninvasive imaging tool which provides direct information regarding vessel wall pathologies. The utility of HRVWI in differentiating various intracranial vasculopathies among ischemic stroke is still evolving.

METHODS

Consecutive ischemic stroke/TIA patients within 2 weeks of symptom onset between January 2016 to December 2017, with symptomatic vessel stenosis of 50% or more/occlusion on baseline luminal imaging studies were recruited into the study. Stroke subtypes were classified as per TOAST classification initially on the basis of luminal imaging findings alone and subsequently after incorporation of HRVWI findings as well.

RESULTS

Forty-nine subjects were recruited into the study. The median age of the population was 42 years (range 11 to 75) with 69% being males. Incorporation of HRVWI findings classified 38.8% subjects into intracranial atherosclerotic disease (ICAD), 32.6% as stroke of other determined aetiology (ODE) (inflammatory vasculopathy [IVas] being the major subgroup [81.2%]) and 28.6% into stroke of undetermined aetiology (UE). HRVWI enabled a diagnostic reclassification in an additional 47.3% among the baseline UE category as against luminal imaging findings alone. ICAD was likelier to have eccentric vessel wall thickening, eccentric vessel wall enhancement and T2 juxtaluminal hyperintensity with surrounding hypointensity (P < 0.001), while IVas were more likely to exhibit concentric vessel wall thickening with homogenous enhancement (P < 0.001).

CONCLUSION

HRVWI is a useful noninvasive adjunctive tool in the diagnostic evaluation of intracranial vasculopathies, with maximum benefit in ICAD and IVas subtypes.