Vessel wall enhancement of intracranial aneurysms: fact or artifact?

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.

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.

Review Article Imaging Evaluation for the Size of Saccular Intracranial Aneurysm

BACKGROUND

In addition to evaluate the morphologic characteristics of intracranial aneurysms, the dimension of the aneurysm is an important parameter for selecting treatment strategies, determining follow-up period, and predicting the risk of rupture. High-resolution vessel wall imaging has an increasingly dominant role in measuring aneurysm size and assessing the risk of rupture accurately. The size of saccular intracranial aneurysm may play an important role as a predictor of the rupture risk. With the rapid improvement in radiological techniques, different noninvasive imaging methods have respective characteristics in saccular intracranial aneurysms (sIA) measurement and morphologic description. Although most studies believe that the larger the aneurysm, the higher the risk of rupture, there is still a synergistic effect of multiple factors (such as location, morphology, history of aneurysmal subarachnoid hemorrhage, and even patient factors) to explain the rupture of small aneurysms.

METHODS

A literature search was performed of intracranial aneurysm size and risk of rupture.

RESULTS

The specificity and sensitivity of different imaging methods for evaluating intracranial aneurysms varied based on sizes. Rupture risk of aneurysms was associated with multiple factors. A comprehensive assessment that considered aneurysm size in conjunction with other relevant factors would be helpful in guiding options of management.

CONCLUSIONS

Accurate measurement of the dimension of sIA is an important basis in the selection of appropriate treatment including intravascular intervention or surgical clipping, as well as for determining the follow-up cycles for conservative or postoperative treatment. A uniform definition of sIA size is recommended to facilitate the integration of similar studies and to accomplish rapid and effective screening of cases in sIA treatment.

Association Between Serum Homocysteine Concentration, Aneurysm Wall Inflammation, and Aneurysm Symptoms in Intracranial Fusiform Aneurysm

RATIONALE AND OBJECTIVES

The pathophysiology of fusiform intracranial aneurysm (FIA) involves inflammatory processes, and homocysteine plays a role in the inflammatory processes in the vessel wall. Moreover, aneurysm wall enhancement (AWE) has emerged as a new imaging biomarker of aneurysm wall inflammatory pathologies. To investigate the pathophysiological mechanisms of aneurysm wall inflammation and FIA instability, we aimed to determine the associations between the homocysteine concentration, AWE, and FIAs' related symptoms.

MATERIALS AND METHODS

We retrospectively reviewed the data of 53 patients with FIA who underwent both high-resolution magnetic resonance imaging and serum homocysteine concentration measurement. FIAs' related symptoms were defined as ischemic stroke or transient ischemic attack, cranial nerve compression, brainstem compression, and acute headache. The contrast ratio of the signal intensity of the aneurysm wall to the pituitary stalk (CRstalk) was used to indicate AWE. Multivariate logistic regression and receiver operating characteristic (ROC) curve analyses were performed to determine how well the independent factors could predict FIAs' related symptoms. Predictors of CRstalk were also investigated. Spearman's correlation coefficient was used to identify the potential associations between these predictors.

RESULTS

Fifty-three patients were included, of whom 23 (43.4%) presented with FIAs' related symptoms. After adjusting for baseline differences in the multivariate logistic regression analysis, the CRstalk (odds ratio [OR]=3.207, P = .023) and homocysteine concentration (OR=1.344, P = .015) independently predicted FIAs' related symptoms. The CRstalk was able to differentiate between FIAs with and without symptoms (area under the ROC curve [AUC]=0.805), with an optimal cutoff value of 0.76. The homocysteine concentration could also differentiate between FIAs with and without symptoms (AUC=0.788), with an optimal cutoff value of 13.13. The combination of the CRstalk and homocysteine concentration had a better ability to identify symptomatic FIAs (AUC=0.857). Male sex (OR=0.536, P = .018), FIAs' related symptoms (OR=1.292, P = .038), and homocysteine concentration (OR=1.254, P = .045) independently predicted the CRstalk.

CONCLUSION

A higher serum homocysteine concentration and greater AWE indicate FIA instability. Serum homocysteine concentration may be a useful biomarker of FIA instability; however, this needs to be verified in future studies.

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.

Molecular Magnetic Resonance Imaging of Aneurysmal Inflammation Using a Redox Active Iron Complex

OBJECTIVES

Inflammation plays a key role in driving brain aneurysmal instability and rupture, but clinical tools to noninvasively differentiate between inflamed and stable aneurysms are lacking. We hypothesize that imaging oxidative changes in the aneurysmal microenvironment driven by myeloid inflammatory cells may represent a noninvasive biomarker to evaluate rupture risk. In this study, we performed initial evaluation of the oxidatively activated probe Fe-PyC3A as a tool for magnetic resonance imaging (MRI) of inflammation in a rabbit model of saccular aneurysm.

MATERIALS AND METHODS

The difference in longitudinal relaxivity ( r1 ) in reduced and oxidized states of Fe-PyC3A was measured in water and blood plasma phantoms at 3 T. A rabbit saccular aneurysm model was created by endovascular intervention/elastinolysis with subsequent decellularization in situ. Rabbits were imaged at 4 weeks (n = 4) or 12 weeks (n = 4) after aneurysmal induction, when luminal levels of inflammation reflected by the presence of myeloperoxidase positive cells are relatively high and low, respectively, using a 3 T clinical scanner. Both groups were imaged dynamically using a 2-dimensional T1-weighted fast field echo pulse MRI sequence before and up to 4 minutes postinjection of Fe-PyC3A. Dynamic imaging was then repeated after an injection of gadobutrol (0.1 mmol/kg) as negative control probe. Rabbits from the 12-week aneurysm group were also imaged before and 20 minutes and 3 hours after injection of Fe-PyC3A using an axial respiratory gated turbo-spin echo (TSE) pulse sequence with motion-sensitized driven equilibrium (MSDE) preparation. The MSDE/TSE imaging was repeated before, immediately after dynamic acquisition (20 minutes postinjection), and 3 hours after injection of gadobutrol. Aneurysmal enhancement ratios (ERs) were calculated by dividing the postinjection aneurysm versus skeletal muscle contrast ratio by the preinjection contrast ratio. After imaging, the aneurysms were excised and inflammatory infiltrate was characterized by fluorometric detection of myeloperoxidase activity and calprotectin immunostaining, respectively.

RESULTS

In vitro relaxometry showed that oxidation of Fe-PyC3A by hydrogen peroxide resulted in a 15-fold increase of r1 at 3 T. Relaxometry in the presence of blood plasma showed no more than a 10% increase of r1 , indicating the absence of strong interaction of Fe-PyC3A with plasma proteins. Dynamic imaging with Fe-PyC3A generated little signal enhancement within the blood pool or adjacent muscle but did generate a transient increase in aneurysmal ER that was significantly greater 4 weeks versus 12 weeks after aneurysm induction (1.6 ± 0.30 vs 1.2 ± 0.03, P < 0.05). Dynamic imaging with gadobutrol generated strong aneurysmal enhancement, but also strong enhancement of the blood and muscle resulting in smaller relative ER change. In the 12-week group of rabbits, MSDE/TSE imaging showed that ER values measured immediately after dynamic MRI (20 minutes postinjection) were significantly higher ( P < 0.05) in the case of Fe-PyC3A (1.25 ± 0.06) than for gadobutrol injection (1.03 ± 0.03). Immunohistochemical corroboration using anticalprotectin antibody showed that leukocyte infiltration into the vessel walls and luminal thrombi was significantly higher in the 4-week group versus 12-week aneurysms (123 ± 37 vs 18 ± 7 cells/mm 2 , P < 0.05).

CONCLUSIONS

Magnetic resonance imaging using Fe-PyC3A injection in dynamic or delayed acquisition modes was shown to generate a higher magnetic resonance signal enhancement in aneurysms that exhibit higher degree of inflammation. The results of our pilot experiments support further evaluation of MRI using Fe-PyC3A as a noninvasive marker of aneurysmal inflammation.

Wall enhancement predictive of abnormal hemodynamics and ischemia in vertebrobasilar non-saccular aneurysms: a pilot study

Objective

To analyze how wall enhancement affects hemodynamics and cerebral ischemic risk factors in vertebrobasilar non-saccular intracranial aneurysms (VBNIAs).

Materials and methods

Ten consecutive non-saccular aneurysms were collected, including three transitional vertebrobasilar dolichoectasia (TVBD). A wall enhancement model was quantitatively constructed to analyze how wall enhancement interacts with hemodynamics and cerebral ischemic factors.

Results

Enhanced area revealed low wall shear stress (WSS) and wall shear stress gradient (WSSG), with high oscillatory shear index (OSI), relative residence time (RRT), and gradient oscillatory number (GON) while the vortex and slow flow region in fusiform aneurysms are similar to TVBD fusiform aneurysms. With low OSI, high RRT and similar GON in the dilated segment, the enhanced area still manifests low WSS and WSSG in the slow flow area with no vortex. In fusiform aneurysms, wall enhancement was negatively correlated with WSS (except for case 7¹, all p values  < 0.05, r = -0.52 ~ -0.95), while wall enhancement was positively correlated with OSI (except for case 5, all p values < 0.05, r = 0.50 ~ 0.83). For the 10 fusiform aneurysms, wall enhancement is significantly positively correlated with OSI (p = 0.0002, r = 0.75) and slightly negatively correlated with WSS (p = 0.196, r = -0.30) throughout the dataset. Aneurysm length, width, low wall shear stress area (LSA), high OSI, low flow volume (LFV), RRT, and high aneurysm-to-pituitary stalk contrast ratio (CRstalk) area plus proportion may be predictive of cerebral ischemia.

Conclusion

A wall enhancement quantitative model was established for vertebrobasilar non-saccular aneurysms. Low WSS was negatively correlated with wall enhancement, while high OSI was positively correlated with wall enhancement. Fusiform aneurysm hemodynamics in TVBD are similar to simple fusiform aneurysms. Cerebral ischemia risk appears to be correlated with large size, high OSI, LSA, and RRT, LFV, and wall enhancement.

Modern Imaging of Aneurysmal Subarachnoid Hemorrhage

In this review, we discuss the imaging of aneurysmal subarachnoid hemorrhage (SAH). We discuss emergency brain imaging, aneurysm detection techniques, and the management of CTA-negative SAH. We also review the concepts of cerebral vasospasm and delayed cerebral ischemia that occurs after aneurysm rupture and their impact on patient outcomes. These pathologies are distinct, and the use of multimodal imaging modalities is essential for prompt diagnosis and management to minimize morbidity from these conditions. Lastly, new advances in artificial intelligence and advanced imaging modalities such as PET and MR imaging scans have been shown to improve the detection of aneurysms and potentially predict outcomes early in the course of SAH.

Aneurysm wall enhancement, atherosclerotic proteins, and aneurysm size may be related in unruptured intracranial fusiform aneurysms

OBJECTIVE

This cross-sectional study aimed to investigate the associations between aneurysm wall enhancement (AWE), atherosclerotic protein levels, and aneurysm size in unruptured intracranial fusiform aneurysms (IFAs).

METHODS

Patients with IFAs underwent high-resolution magnetic resonance imaging (HR-MRI) and atherosclerotic protein examinations from May 2015 to December 2021 were collected. A CR_stalk (signal intensity [SI] of IFA wall/SI of pituitary stalk) > 0.60 was considered to indicate AWE. Atherosclerotic protein data was obtained from the peripheral blood. Aneurysmal characteristics included the maximal diameter of the cross-section (D_max), location, type of IFA, presence of mural thrombus, and mural clots. Statistical analyses were performed with univariate analysis, logistic regression analysis, and Spearman's correlation coefficient.

RESULTS

Seventy-one IFAs from 71 patients were included in the study. Multivariate analysis revealed statin use (OR = 0.189, p = 0.026) and apolipoprotein B (Apo-B) level (OR = 6.019, p = 0.026) were the independent predictors of AWE in IFAs. In addition, statin use (OR = 0.813, p = 0.036) and Apo-B level (OR = 1.610, p = 0.003) were also the independent predictors of CR_stalk. Additionally, we found that CR_stalk and AWE were significantly positively associated with D_max (r_s = 0.409 and 0.349, respectively; p < 0.001 and p = 0.003, respectively).

CONCLUSIONS

There may be correlations between AWE, atherosclerotic protein levels, and aneurysm size in patients with IFAs. Apo-B and statin use were independent predictors of AWE in IFAs, which have the potential to be new therapeutic targets for IFAs.

KEY POINTS

• There may be correlations between aneurysm wall enhancement, atherosclerotic protein levels in the peripheral blood, and aneurysm size in patients with intracranial fusiform aneurysms. • Apolipoprotein B and statin use were independent predictors of aneurysm wall enhancement in intracranial fusiform aneurysms.

Spontaneous internal carotid artery dissection in a child diagnosed by high resolution vessel wall MRI

Craniocervical dissection is one of the most common causes of stroke in children. Although the most common cause of dissection is trauma, spontaneous dissections in which no cause can be revealed may also occur. The diagnosis of this type of dissection in children can be challenging with the preferred non-invasive imaging methods (MRA, CTA). Intracranial vessel wall imaging is a promising novel method for identifying specific signs of dissection. We report an 11-year-old girl with spontaneous ICA dissection, whose diagnosis was confirmed by an MRI of the intracranial vessel wall. Vessel wall imaging has contributed substantially to the diagnosis and follow-up of this case.

The role of vessel wall imaging in determining the best treatment approach for coexisting aneurysms and subarachnoid hemorrhage

PURPOSE

The purpose of this study was to investigate the utilization of gadolinium enhancement on vessel wall imaging (VWI) in treatment decision-making for patients with two intracranial aneurysms presenting as a subarachnoid hemorrhage (SAH).

MATERIALS AND METHODS

We prospectively performed VWI using 3.0-Tesla (3T) magnetic resonance imaging (MRI) before treatment with endovascular coiling or surgical clipping in patients with one or two intracranial aneurysms. The VWI protocol includes three different scans: black blood (BB) T1-weighted, BB T2-weighted, TOF axial, and BB contrast-enhanced T1-weighted imaging. We analyzed all aneurysm ruptures both with and without gadolinium enhancement of the aneurysm wall.

RESULTS

Thirty-eight patients with 48 aneurysms were enrolled in this study. Of these patients, 28 had a single aneurysm (15 ruptured and 13 unruptured), and 10 had two aneurysms and SAH (9 patients with two aneurysms and 1 patient with three aneurysms). Of the 15 single ruptured aneurysms, 12 (80.0%) showed positive wall enhancement, whereas 2 of the 13 single unruptured aneurysms (15.4%) demonstrated positive wall enhancement. Ten patients with SAH and two aneurysms showed wall enhancement of a single aneurysm, and these aneurysms were treated first.

CONCLUSION

Gadolinium enhancement of an aneurysm wall on MRI was associated with aneurysm rupture. In patients with two aneurysms and SAH, this type of imaging can play an important role in determining the order of aneurysm treatment.

Vessel wall MR imaging in neuroradiology

Vessel wall MR imaging (VW-MRI) has been introduced into clinical practice and applied to a variety of diseases, and its usefulness has been reported. High-resolution VW-MRI is essential in the diagnostic workup and provides more information than other routine MR imaging protocols. VW-MRI is useful in assessing lesion location, morphology, and severity. Additional information, such as vessel wall enhancement, which is useful in the differential diagnosis of atherosclerotic disease and vasculitis could be assessed by this special imaging technique. This review describes the VW-MRI technique and its clinical applications in arterial disease, venous disease, vasculitis, and leptomeningeal disease.

Aneurysmal wall enhancement and hemodynamics: pixel-level correlation between spatial distribution

BACKGROUND

Inflammation and hemodynamics are interrelated risk factors for intracranial aneurysm rupture. This study aimed to identify the relationship between these risk factors from an individual-patient perspective using biomarkers of aneurysm wall enhancement (AWE) derived from high-resolution magnetic resonance imaging (HR-MRI) and hemodynamic parameters by four-dimensional flow MRI (4D-flow MRI).

METHODS

A total of 29 patients with 29 unruptured intracranial aneurysms larger than 4 mm were included in this prospective cross-sectional study. A total of 24 aneurysms had AWE and 5 did not have AWE. A three-dimensional (3D) vessel model of each individual aneurysm was generated with 3D time-of-flight magnetic resonance angiography (3D TOF-MRA). Quantification of AWE was sampled with HR-MRI. Time-averaged wall shear stress (WSS) and oscillatory shear index (OSI) were calculated from the 4D-flow MRI. The correlation between spatial distribution of AWE and hemodynamic parameters measured at pixel-level was evaluated for each aneurysm.

RESULTS

In aneurysms with AWE, the spatial distribution of WSS was negatively correlated with AWE in 100% (24/24) of aneurysms, though 2 had an absolute value of the correlation coefficient <0.1. The OSI was positively correlated with AWE in 91.7% (22/24) of aneurysms; the other 2 aneurysms showed a negative correlation with AWE. In aneurysms with no AWE, there was no correlation between WSS (100%, 5/5), OSI (80%, 4/5), and wall inflammation.

CONCLUSIONS

The spatial distribution of WSS was negatively correlated with AWE in aneurysms with AWE, and OSI was positively correlated with AWE in most aneurysms with AWE. While aneurysms that did not contain AWE showed no correlation between hemodynamics and wall inflammation.

Vessel wall imaging with advanced flow suppression in the characterization of intracranial aneurysms following flow diversion with Pipeline embolization device

BACKGROUND

High-resolution vessel wall MRI (VWI) is increasingly used to characterize intramural disorders of the intracranial vasculature unseen by conventional arteriography.

OBJECTIVE

To evaluate the use of VWI for surveillance of flow diverter (FD) treated aneurysms.

MATERIALS AND METHODS

Retrospective study of 28 aneurysms (in 21 patients) treated with a FD (mean 57 years; 14 female). All examinations included VWI and a contemporaneously obtained digital subtraction angiogram. Multiplanar pre- and post-gadolinium 3D, variable flip-angle T1 black-blood VWI was obtained using delay alternating nutation for tailored excitation (DANTE) at 3T. 3D time-of-flight MR angiography (MRA) was also carried out. Images were assessed for in-stent stenosis, aneurysm occlusion, presence and pattern/distribution of aneurysmal or parent vessel gadolinium enhancement.

RESULTS

The VWI-MRI was performed on average at 361±259 days after the intervention. Follow-up DSA was performed at 338±254 days postintervention. Good or excellent black-blood angiographic quality was recorded in 22/28 (79%) pre-contrast and 21/28 (75%) post-contrast VWI, with no cases excluded for image quality. Aneurysm enhancement was noted in 24/28 (85.7%) aneurysms, including in 79% of angiographically occluded aneurysms and 100% of angiographically non-occluded aneurysms. Enhancement of the stented parent-vessel wall occurred significantly more often when aneurysm enhancement was present (92% vs 33%, p=0.049).

CONCLUSION

Advanced VWI produces excellent depiction of FD-treated aneurysms, with robust evaluation of the parent vessel and aneurysm wall to an extent not achievable with conventional MRI/MRA. Gadolinium enhancement may, however, continue even after enduring catheter angiographic occlusion, confounding interpretation, and requiring cognizance of this potentially prolonged effect in such patients.

Activated Platelet-Homing Nanoplatform for Targeting Magnetic Resonance Imaging of Aneurysm-Related Thrombus in Rabbits

Thrombosis is closely related to the instability of intracranial aneurysm (IA), whose rupture is associated with high morbidity and mortality. It is difficult to detect an IA-related thrombus because traditional magnetic resonance imaging (MRI) and even contrast-enhanced MRI cannot clearly distinguish a thrombus from the surrounding tissues. Herein, a nanoplatform [(MFe₂O₄-ZnDPA nanoparticles (NPs)], consisting of Zn_0.4Co_0.6Fe₂O₄@Zn_0.4Mn_0.6Fe₂O₄ NPs for imaging and Zn(II)-bis(dipicolylamine) (ZnDPA) for thrombus targeting, is constructed to target an experimental aneurysm-related thrombus in rabbits via MRI. In vitro experiments including platelet safety evaluation primarily prove that MFe₂O₄-ZnDPA NPs with a high MRI transverse relaxation time (T₂) have good biocompatibility. MFe₂O₄-ZnDPA NPs could target a thrombus via the special interaction between ZnDPA and phosphatidylserine of activated platelets in the thrombus through MRI and Fe quantification assays. Moreover, after MFe₂O₄-ZnDPA NPs are injected into the ear vein of common carotid artery aneurysm model rabbits, MRI shows that MFe₂O₄-ZnDPA NPs could accumulate in the aneurysm-related thrombus from 0 to 15 min after injection and decrease in the next 45 min. Meanwhile, MFe₂O₄-ZnDPA NPs could decrease the MRI T₂ signal of the aneurysm-related thrombus to enhance the outline of the aneurysm. This study demonstrates that a nanoplatform can enhance the detection of an aneurysm-related thrombus as well as aneurysm itself to assist further treatment of IA.

Luminal enhancement in intracranial aneurysms: fact or feature?-A quantitative multimodal flow analysis

Purpose

Intracranial aneurysm (IA) wall enhancement on post-contrast vessel wall magnetic resonance imaging (VW-MRI) is assumed to be a biomarker for vessel wall inflammation and aneurysm instability. However, the exact factors contributing to enhancement are not yet clarified. This study investigates the relationship between luminal enhancement and intra-aneurysmal flow behaviour to assess the suitability of VW-MRI as a surrogate method for determining quantitative and qualitative flow behaviour in the aneurysm sac.

Methods

VW-MRI signal is measured in the lumen of three patient-specific IA flow models and compared with the intra-aneurysmal flow fields obtained using phase-contrast magnetic resonance imaging (PC-MRI) and computational fluid dynamics (CFD). The IA flow models were supplied with two different time-varying flow regimes.

Results

Overall, the velocity fields acquired using PC-MRI or CFD were in good agreement with the VW-MRI enhancement patterns. Generally, the regions with slow-flowing blood show higher VW-MRI signal intensities, whereas high flow leads to a suppression of the signal. For all aneurysm models, a signal value above three was associated with velocity values below three cm/s.

Conclusion

Regions with lower enhancements have been correlated with the slow and high flow at the same time. Thus, further factors like flow complexity and stability can contribute to flow suppression in addition to the flow magnitude. Nevertheless, VW-MRI can qualitatively assess intra-aneurysmal flow phenomena and estimate the velocity range present in the corresponding region.

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.

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.

Insights into the pathogenesis of cerebral fusiform aneurysms: high-resolution MRI and computational analysis

BACKGROUND

Intracranial fusiform aneurysms are complex and poorly characterized vascular lesions. High-resolution magnetic resonance imaging (HR-MRI) and computational morphological analysis may be used to characterize cerebral fusiform aneurysms.

OBJECTIVE

To use advanced imaging and computational analysis to understand the unique pathophysiology, and determine possible underlying mechanisms of instability of cerebral fusiform aneurysms.

METHODS

Patients with unruptured intracranial aneurysms prospectively underwent imaging with 3T HR-MRI at diagnosis. Aneurysmal wall enhancement was objectively quantified using signal intensity after normalization of the contrast ratio (CR) with the pituitary stalk. Enhancement between saccular and fusiform aneurysms was compared, as well as enhancement characteristics of fusiform aneurysms. The presence of microhemorrhages in fusiform aneurysms was determined with quantitative susceptibility mapping (QSM). Three distinct types of fusiform aneurysms were analyzed with computational fluid dynamics (CFD) and finite element analysis (FEA).

RESULTS

A total of 130 patients with 160 aneurysms underwent HR-MRI. 136 aneurysms were saccular and 24 were fusiform. Fusiform aneurysms had a significantly higher CR and diameter than saccular aneurysms. Enhancing fusiform aneurysms exhibited more enhancement of reference vessels than non-enhancing fusiform aneurysms. Ten fusiform aneurysms underwent QSM analysis, and five aneurysms showed microhemorrhages. Microhemorrhage-positive aneurysms had a larger volume, diameter, and greater enhancement than aneurysms without microhemorrhage. Three types of fusiform aneurysms exhibited different CFD and FEA patterns.

CONCLUSION

Fusiform aneurysms exhibited more contrast enhancement than saccular aneurysms. Enhancing fusiform aneurysms had larger volume and diameter, more enhancement of reference vessels, and more often exhibited microhemorrhage than non-enhancing aneurysms. CFD and FEA suggest that various pathophysiological processes determine the formation and growth of fusiform aneurysms.

Clinical Characteristics of Ruptured Intracranial Aneurysm in Patients with Multiple Intracranial Aneurysms

OBJECTIVE

It is difficult to correctly identify the ruptured aneurysm in patients with multiple intracranial aneurysms. Here, we investigated the clinical characteristics of ruptured intracranial aneurysms in such patients.

METHODS

We retrospectively analyzed 361 patients who underwent microsurgical clipping of ruptured intracranial aneurysms at our institution from 2012 to 2018. Patients' age, sex, Fisher group, World Federation of Neurosurgical Societies grade, size (neck width, depth, maximum diameter), location, and shape of intracranial aneurysm, and hemorrhage pattern on admission were reviewed.

RESULTS

In total, 266 patients (74%) had single intracranial aneurysms and 95 (26%) had multiple intracranial aneurysms. Eighty-nine of the 95 multiple intracranial aneurysms (94%) had irregular shape (P < 0.01). The median aspect ratios of ruptured and unruptured intracranial aneurysms were 2.2 ± 1.1 and 1.0 ± 0.4, respectively (P < 0.01). Twelve of 95 patients (13%) had ruptured intracranial aneurysms that were smaller than unruptured intracranial aneurysms. Among the 12 patients, the aspect ratios of ruptured intracranial aneurysms were greater than those of unruptured intracranial aneurysms (P < 0.01). Regarding morphologic characteristics, aspect ratio, maximum size, and irregular shape could be the useful predictive factors, but the greatest aspect ratio among patients with multiple aneurysms was the most predictive of an intracranial aneurysm rupture, after adjustment for aneurysmal size (adjusted odds ratio 217.82; 95% confidence interval 56.41-841.08).

CONCLUSIONS

The results of this study indicate that the aspect ratio is the most predictive factor of a ruptured intracranial aneurysm in patients with multiple intracranial aneurysms.

Performance of Aneurysm Wall Enhancement Compared with Clinical Predictive Scales: PHASES, ELAPSS, and UIATS

OBJECTIVE

To correlate the presence of objectively measured wall enhancement on high-resolution vessel wall imaging (HR-VWI) with the clinical predictive scales PHASES, ELAPSS, and UIATS.

METHODS

Patients with unruptured intracranial aneurysm (UIAs) prospectively underwent HR-VWI on a 3-T magnetic resonance imaging scanner at diagnosis. Aneurysmal wall enhancement was objectively quantified on T1 postcontrast magnetic resonance imaging using signal intensity values adjusted for the pituitary stalk to calculate a contrast ratio (CR_stalk). UIAs with CR_stalk ≥0.60 were considered "enhancing." Patients' demographics, comorbidities, and aneurysm morphology were reviewed to calculate PHASES, ELAPSS, and UIATS scores. Pearson coefficients were applied for statistical correlation. Univariable and multivariable logistic regressions were performed to assess for confounders.

RESULTS

One-hundred and twenty-three patients harboring 178 UIAs underwent HR-VWI. A total of 101 patients with 135 UIAs were analyzed. Enhancing UIAs were larger (8.4 ± 5.5 mm vs. 5.5 ± 2.3 mm; P < 0.001), had higher aspect ratio (2.3 ± 1.5 vs. 1.8 ± 0.7; P = 0.008), higher size ratio (3.0 ± 1.8 vs. 2.4 ± 1.1; P = 0.016), scored higher on PHASES (5.6 ± 3.9 vs. 4.4 ± 2.6; P = 0.04) and ELAPSS (19.4 ± 8.9 vs. 15.4 ± 7.3; P = 0.006) compared with nonenhancing UIAs. Treatment allocation as defined by UIATS was measured independently to enhancement status. No significant differences were found for UIATS between enhancing and nonenhancing UIAs (P = 0.63). Multivariable regression showed that size was the only independent factor significantly associated with UIA enhancement (odds ratio, 1.76; P = 0.005).

CONCLUSIONS

Enhancing UIAs score higher in PHASES and ELAPSS scales. This association is largely explained by aneurysm size, aspect, and size ratios. Morphologic UIA features should be accounted for in clinical predictive scales of aneurysm instability.

Regional Aneurysm Wall Enhancement is Affected by Local Hemodynamics: A 7T MRI Study

BACKGROUND AND PURPOSE

Aneurysm wall enhancement has been proposed as a biomarker for inflammation and instability. However, the mechanisms of aneurysm wall enhancement remain unclear. We used 7T MR imaging to determine the effect of flow in different regions of the wall.

MATERIALS AND METHODS

Twenty-three intracranial aneurysms imaged with 7T MR imaging and 3D angiography were studied with computational fluid dynamics. Local flow conditions were compared between aneurysm wall enhancement and nonenhanced regions. Aneurysm wall enhancement regions were subdivided according to their location on the aneurysm and relative to the inflow and were further compared.

RESULTS

On average, wall shear stress was lower in enhanced than in nonenhanced regions (P = .05). Aneurysm wall enhancement regions at the neck had higher wall shear stress gradients (P = .05) with lower oscillations (P = .05) than nonenhanced regions. In contrast, aneurysm wall enhancement regions at the aneurysm body had lower wall shear stress (P = .01) and wall shear stress gradients (P = .008) than nonenhanced regions. Aneurysm wall enhancement regions far from the inflow had lower wall shear stress (P = .006) than nonenhanced regions, while aneurysm wall enhancement regions close to the inflow tended to have higher wall shear stress than the nonenhanced regions, but this association was not significant.

CONCLUSIONS

Aneurysm wall enhancement regions tend to have lower wall shear stress than nonenhanced regions of the same aneurysm. Moreover, the association between flow conditions and aneurysm wall enhancement seems to depend on the location of the region on the aneurysm sac. Regions at the neck and close to the inflow tend to be exposed to higher wall shear stress and wall shear stress gradients. Regions at the body, dome, or far from the inflow tend to be exposed to uniformly low wall shear stress and have more aneurysm wall enhancement.

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.

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.

Radial Artery Graft for Giant Common Carotid Artery Pseudoaneurysm After Carotid Artery Stenting

BACKGROUND

We present a patient who underwent left superior temporal artery (STA)-to-right middle cerebral artery (MCA) bypass using a radial artery (RA) graft with resection of a giant right cervical common carotid artery (CCA) pseudoaneurysm after carotid artery stenting (CAS) and discuss the treatment strategy and surgical procedure in detail.

CASE DESCRIPTION

An 86-year-old male presented with sudden onset of altered consciousness and complete left hemiparesis. Magnetic resonance angiography and catheter angiography of the brain revealed occlusion of the right cervical ICA. Endovascular thrombectomy and stenting of the cervical segment of the ICA were performed. Thirty-two days after CAS, the patient developed a high fever and rapid swelling of the neck. Catheter angiography showed a giant right CCA pseudoaneurysm that had a fistula just proximal to the carotid stent, and the aneurysm extended to the neck entirely. Because of the expanding neck infection, stent placement long lesion, and lack of distal collateral flow on angiography, we performed aneurysm and stent removal and left STA-to-right MCA bypass using an RA graft. The harvested RA graft was anastomosed side to end to both the M2 segment of the right MCA and the left STA. Bypass patency was confirmed before neck exposure. The pseudoaneurysm and proximal portion area of the stent were resected. The patient recovered well postoperatively, and follow-up catheter angiography showed patency of the bypass.

CONCLUSIONS

Left STA-RA-right MCA bypass with aneurysm resection is a good treatment option for giant CCA pseudoaneurysms that occur after CAS.