The correlation of cerebral arteriovenous malformation flow measured by quantitative MR angiography on MR-detected arteriovenous malformation microhemorrhage.

OBJECTIVE: The objective of this study was to assess the relationship of arteriovenous malformation (AVM) blood flow measured by quantitative MR angiography (QMRA) in nonruptured AVMs with MR-detected microhemorrhage. METHODS: All patients with unruptured AVMs who received baseline QMRA and gradient echo or susceptibility-weighted MRI were retrospectively reviewed (2004-2022). Imaging data, clinical history, and AVM angioarchitectural and flow features were collected and assessed. AVM flow was calculated from the difference of flow within primary arterial feeders from their contralateral counterparts. A review of the MR images determined the presence of microhemorrhages. Analysis of descriptive statistics, chi-square test, and binomial logistic regression were performed. RESULTS: Of 634 patients with cerebral AVMs at a single center, 89 patients met the inclusion criteria (54 with microhemorrhage and 35 without microhemorrhage). The calculated AVM flow was significantly higher in the group with a microhemorrhage (447.9 ± 193.1 ml/min vs 287.6 ± 235.7 ml/min, p = 0.009). In addition, the presence of venous anomaly, arterial ectasia, and diffuse nidus was significantly associated with microhemorrhage (p = 0.017, p = 0.041, and p = 0.041, respectively). Binary logistic regression found that higher flow predicted the presence of microhemorrhage (OR 1.002, 95% CI 1.000-1.004; p = 0.031). The highest AVM flow quartile significantly predicted the presence of venous anomaly (OR 3.840, 95% CI 1.037-14.213; p = 0.044), diffuse nidus (OR 6.800, 95% CI 1.766-25.181; p = 0.005), and arterial ectasia (OR 13.846, 95% CI 1.905-122.584; p = 0.018). CONCLUSIONS: This study represents the first to examine the association between flow measurements on QMRA with microhemorrhage in unruptured AVMs. Higher AVM flow, venous anomaly, arterial ectasia, and diffuse AVM nidus were related to a higher likelihood of AVM microhemorrhage. Higher AVM flow was present in AVMs with venous anomalies, a diffuse nidus, and arterial ectasia, indicating a possible interaction between these angioarchitectural findings, AVM flow, and microhemorrhage. These findings suggest a relationship between higher AVM flow and the risk of microhemorrhage.

Approaches to ventriculoperitoneal shunt scalp erosion: countersinking into the calvarium. Illustrative case.

BACKGROUND: Ventriculoperitoneal shunting (VPS) is a standard procedure for the treatment of hydrocephalus, and the management of its complications is common in the practice of pediatric neurosurgery. Shunt exposure, though a rare complication, can occur because of thin, fragile skin, a young patient age, protuberant hardware, poor scalp perfusion, and a multitude of other patient factors. OBSERVATIONS: The authors report a complex case of VPS erosion through the scalp in a young female with Pfeiffer syndrome treated with external ventricular drainage, empirical antibiotics, and reinternalization with countersinking of replaced shunt hardware into the calvarium to prevent internal skin pressure points, reduce wound tension, and allow wound healing. LESSONS: Recessing the shunt hardware, or countersinking the implant, into the calvarium is a simple technique often used in functional neurosurgical implantation surgeries, providing a safe surgical strategy to optimize wound healing in select cases in which the skin flap is unfavorable.

Quantitative Blood Flow Reduction in Selective Embolization of Intranidal Fistula of Cerebral Arteriovenous Malformations: Case Series.

BACKGROUND AND OBJECTIVES: Arteriovenous malformations (AVMs) are often associated with high-flow intranidal fistulas (INFs). Although INF embolization has been suggested to provide higher reduction of total AVM flow compared with regular pedicle embolization, this effect has not previously been quantified. The aim of this study was to characterize the effect of AVM INF embolization on total AVM flow. METHODS: This study is an Institutional Review Board-approved, retrospective case series of patients from 2010 to 2022 with AVMs, both with and without INFs, who underwent quantitative magnetic resonance angiography and endovascular embolization. RESULTS: Twenty patients accounted for 35 separate embolization sessions: 13 patients with INFs underwent a total 21 embolizations and 12 patients without INFs had 14 embolizations. No significant differences were found between groups on age, sex, laterality, drainage pattern, and Spetzler-Martin grade. However, AVMs with INFs were larger than the control group (12.7 vs 8.37 cm 3 , P = .049). Baseline pre-embolization AVM flow significantly differed between AVM with INF vs control groups (522 vs 320 cc/min, P = .005). Similarly, postembolization AVM flow also differed between AVM with INF and control groups (392 vs 224 cc/min, P = .008), with a larger decrease in flow per vessel per embolization session within the AVM INF group compared with controls (101.5 vs 33.2 cc/min, P < .001). Repeated measure analysis of variance showed significant differences pre-embolization and postembolization AVM flow between those with INFs vs controls ( P < .001). CONCLUSION: This study represents the first to examine the effect of INF embolization on total AVM flow. AVMs with INFs showed higher baseline flow, and targeted embolization toward INFs significantly lowered AVM flow in comparison with controls without INFs. The results of this study emphasize the importance of recognizing the presence of INFs within AVMs and their embolization to reduce AVM flow as part of a multistep management paradigm.

Preoperative embolization of brain arteriovenous malformation and efficacy in intraoperative blood loss reduction: a quantitative study.

BACKGROUND: Embolization of brain arteriovenous malformations (bAVMs) is often used as adjuvant therapy to microsurgical resection to reduce the high-risk features of bAVMs such as large size and high flow. However, the effect of preoperative embolization on surgical performance and patient outcome has shown mixed results. Heterogeneity in treatment goals, selection criteria, and unpredictable changes in bAVM hemodynamics after partial embolization may account for these uncertain findings. In this study we use an objective quantitative technique to assess the impact of preoperative embolization on intraoperative blood loss (IBL). METHODS: Patients with bAVM treated with microsurgical resection only or in combination with preoperative embolization from 2012 to 2022 were retrospectively reviewed. Patients were included if quantitative magnetic resonance angiography was performed prior to any treatment. Correlation of baseline bAVM flow, volume, and IBL was evaluated between the two groups. Additionally, bAVM flow prior to and after embolization was compared. RESULTS: Forty-three patients were included, 31 of whom required preoperative embolization (20 had more than one session). Mean bAVM initial flow (362.3 mL/min vs 89.6 mL/min, p=0.001) and volume (9.6 mL vs 2.8 mL, p=0.001) were significantly higher in the preoperative embolization group; flow decreased significantly after embolization (408.0 mL/min vs 139.5 mL/min, p<0.001). IBL was comparable between the two groups (258.6 mL vs 141.3 mL, p=0.17). Linear regression continued to show a significant difference in initial bAVM flow (p=0.03) but no significant difference in IBL (p=0.53). CONCLUSION: Patients with larger bAVMs who underwent preoperative embolization had comparable IBL to those with smaller bAVMs undergoing only surgical treatment. Preoperative embolization of high-flow bAVMs facilitates surgical resection, reducing the risk of IBL.

Vessel wall imaging and quantitative flow assessment in arteriovenous malformations: A feasibility study.

INTRODUCTION: Cerebral arteriovenous malformations (AVMs) carry a rupture rate of 2-3% per year. Several architectural factors may influence rupture rate, and a recently theorized model of AVMs describes the influence of vessel wall inflammation. A novel imaging modality, vessel wall imaging (VWI), has been developed to view inflammatory processes in vessel wall foci but has not yet been examined in AVMs, which is the aim of this study. METHODS: This retrospective review studies prospectively collected data on patients with ruptured and unruptured AVMs between 2019 and 2021. Inclusion criteria included adult patients (≥18 years) with radiographically diagnosed AVM who underwent VWI. Charts were reviewed for medical history, clinical presentation, hospital course, discharge condition, and follow-up. Angioarchitectural features, blood flow, and VWI were compared in patients with and without hemorrhagic patients. RESULTS: Nine patients underwent VWI, mean age 37.7 ± 9.9 years. Four presented with hemorrhage (44.4%). Seven (77.7%) received glue embolization and 6 (66.7%) underwent surgical resection. All patients (4/4) with a history of hypertension presented with hemorrhage (p = 0.0027). Size and Spetzler-Martin grade were not associated with hemorrhage (p = 0.47, p = 0.59). Net AVM flow was higher in patients presenting with hemorrhage, although nonsignificant (p = 0.19). With VWI, 3 (75%) hemorrhagic AVMs showed visible nidus and draining veins, and all three demonstrated positive post-contrast wall enhancement in at least one of their draining veins; conversely, of fivenonhemorrhagic AVMs, only 2 (40%) demonstrated post-contrast wall enhancement in any draining vein (p = 0.090). CONCLUSION: This pilot study successfully demonstrated capture of venous walls in AVMs using VWI. In this study, draining vein enhancement occurred more often in hemorrhagic AVM and in those with higher venous volumetric flow.

Brain arteriovenous malformation flow after stereotactic radiosurgery: Role of quantitative MRA.

BACKGROUND: Stereotactic radiosurgery (SRS) is a current therapeutic option for treatment of arteriovenous malformations (AVMs) located in deep or eloquent brain regions. Obliteration usually occurs in a delayed fashion, with an expected latency of 3-5 years. Here, we assess how AVM flow correlates with volume before and after SRS treatment. METHODS: Patients with supratentorial AVM treated with SRS at our institution between 2012-2022 were retrospectively reviewed. Patients were included if Quantitative Magnetic Resonance Angiography (QMRA) study was performed at baseline and at least at the first follow-up. Correlation between AVM flow and volume before and after treatment was evaluated. AVM flow and volume were additionally assessed for obliteration using the non-parametric receiver operating characteristic (ROC) curve. RESULTS: Twelve patients with radiologic follow-up imaging were included. Eight patients presented AVM rupture, one of which occurred after radiosurgical treatment. Three patients underwent embolization prior SRS. Mean AVM initial volume was 3.8 cc (0.1-12.4 cc), mean initial flow 174 ml/min (11-604 ml/min), both variables showed progressive reduction at follow-up (range 3-57 months); and flow decreased with volume reduction (p < 0.001). Area under the ROC was 0.914 for both AVM flow and volume with obliteration (p = 0.019). CONCLUSIONS: AVM flow significantly decreased after SRS treatment, reflecting volume reduction. Baseline AVM flow and volume both predicted obliteration. QMRA provides additional non-invasive information to monitor patients after radiosurgical treatment.

Impact of cerebral aneurysm size on distal intracranial hemodynamics and changes following flow diversion.

BACKGROUND: The impact of cerebral aneurysm size on distal intracranial hemodynamics such as arterial pressure and Pulsatility Index is not completely understood, either before or after flow diversion. OBJECTIVE: The aim of the study is to assess the impact of aneurysm size on distal Pulsatility Index and pressure before and after flow diversion. METHODS: From December 2015, prospective measurement of middle cerebral artery pressure and Pulsatility Index was performed in consecutive patients with unruptured cerebral aneurysms in the cavernous to communicating segments of the internal carotid artery, which were treated with single flow diversion. Pressure and Pulsatility Index were recorded at the M1-segment ipsilateral to the cerebral aneurysm. Ratio of middle cerebral artery to radial arterial pressure (pressure ratio) was calculated to control for variations in systemic blood pressure. Correlations between aneurysm size and pressure ratio and Pulsatility Index were assessed before and after treatment. RESULTS: A total of 28 aneurysms were treated. The mean aneurysm size was 7.2 mm. Aneurysm size correlated linearly with systolic pressure ratio (1% pressure ratio increase per mm aneurysm size increase, P = 0.002, r2 = 0.33), mean pressure ratio (0.6% per mm, P = 0.03, r2 = 0.17) and Pulsatility Index (5% Pulsatility Index increase per mm, P = 0.003, r2 = 0.43). After flow diversion, aneurysm size preserved a linear correlation with the systolic pressure ratio (1% per mm, P = 0.004, r2 = 0.28), but not with the mean pressure ratio (0.4% per mm, P = 0.15, r2 < 0.1) or Pulsatility Index (0.3% per mm, P = 0.78, r2 < 0.1). CONCLUSION: Aneurysm size affects distal hemodynamics: patients with larger aneurysms have increased systolic and mean pressure ratio, and increased Pulsatility Index. After flow diversion, mean pressure ratio and Pulsatility Index no longer associate with the aneurysm size, suggesting an effect of the flow diversion also on distal intracranial hemodynamics.

Predictors of Poor Outcome Despite Successful Mechanical Thrombectomy of Anterior Circulation Large Vessel Occlusions Within 6 h of Symptom Onset.

Background and Purpose: Successful reperfusion is a significant predictor of a good clinical outcome after mechanical thrombectomy (MT). However, some patients have a poor clinical outcome even with successful reperfusion. We aimed to study factors that predict a poor clinical outcome (90-day modified Rankin Scale ≥ 3) in patients with anterior circulation large vessel occlusion (LVO) treated by successful MT within 6 h of symptom onset. Methods: We performed a retrospective review of a prospectively maintained MT database of all patients who underwent MT within 6 h of symptom onset for an anterior circulation LVO at our institution from May 2016 to June 2018. Uni- and multivariable analyses were performed to identify predictors of poor outcome. Results: A total of 56 patients met the criteria for inclusion in this study. A poor outcome occurred in 31 (55.4%) patients. On univariate analysis, compared to patients with good clinical outcome, patients with poor outcome had higher mean baseline NIHSS scores (23.3 vs. 13.8, P < 0.001), were more likely to have internal carotid artery (ICA) occlusions (38.7 vs. 8%, P = 0.008), and had a higher incidence of distal clot migration (DCM) (48.4 vs. 8%, P = 0.028). Age, gender, other baseline clinical characteristics, MT technique, and incidence of hemorrhagic transformation did not differ between the two cohorts. On multivariable regression analysis, baseline NIHSS score [OR; 1.3, 95%CI [1.11-1.52], P = 0.001], site of occlusion (ICA) [OR; 8.9, 95%CI [1.3-60.9], P = 0.026], and DCM [OR; 5.77, 95%CI [1.09-30.69], P = 0.04] were independent predictors of poor outcome at 90-days. Conclusion: Baseline NIHSS score, ICA occlusion, and DCM are independent predictors of a poor outcome after MT for anterior circulation LVO performed within 6 h of symptoms onset.

Operative Nuances of Blind Catheterization of Occluded Sinuses Using Negative Road Map Technique: 2-Dimensional Operative Video.

Dural arteriovenous fistula (DAVF) are often treated with endovascular transvenous embolization. DAVFs though, are often associated with intracranial venous sinus occlusion, which limits the transvenous route. Here, we present the operative nuances of blind catheterization of an occluded dural venous sinus in 2 different cases with DAVF. First case is a 72-yr-old patient with indirect right carotid-cavernous fistula associated with an occluded inferior petrosal sinus, with severe orbital congestion. Second patient is a 79-yr-old patient with a new external carotid to a trapped transverse sinus fistula (Cognard IIA + B), extensive cortical venous reflux in the setting of an occluded sigmoid sinus. In both cases, the transarterial route was limited because of small arterial feeders thus, after obtaining patients' consent, we performed transvenous sacrifice of the isolated sinus. In both cases, the occluded sinus was transvenously blindly retrograde probed using a 0.035 inch Terumo Glidewire (Terumo Medical Corporation, Somerset, New Jersey). Once the occluded segment was probed, a dark roadmap was acquired with the wire in place. This created a negative roadmap once the guidewire is removed. This negative roadmap is used to navigate the microcatheter-microwire into the isolated sinus. In the first case, the cavernous sinus and the superior ophthalmic veins were sacrificed with coils. In the second patient, the entrapped left transverse sinus was embolized using Onyx. In both cases, complete occlusion of the fistula was attained. In this neuroendovascular video, we demonstrate the nuances of blind catheterization of an occluded sinus using a negative roadmap technique as guidance for the micro-catheterization. Institutional Review Board approved. Patient consent not required due to retrospective nature of manuscript, based on medical chart and imaging reviews, anonymized in the video.

Risk Factors for Distal Clot Migration during Mechanical Thrombectomy of Anterior Circulation Large Vessel Occlusion.

INTRODUCTION: Distal clot migration (DCM) is a known complication of mechanical thrombectomy (MT), but neither risk factors for DCM nor ways of how it might affect clinical outcomes have been extensively studied to date. METHODS: To identify risk factors for and outcomes in the setting of DCM, the records of all patients with acute ischemic stroke due to anterior circulation large vessel occlusion (LVO) treated with MT at a single center between May 2016 and June 2018 were retrospectively reviewed. Uni- and multivariable analyses were performed to evaluate predictors of DCM and good functional outcome (90-day modified Rankin Scale; mRS 0-2). RESULTS: A total of 65 patients were included, DCM was identified in 22 patients (33.8%). Patients with DCM had significantly higher pre-procedural intravenous tissue plasminogen activator (IV-tPA) administration (81.8 vs. 53.5%, p = 0.03), stentrievers thrombectomy (95.5 vs. 62.8%, p = 0.006), and longer median puncture to recanalization time (44 [34-97] vs. 30 [20-56] min, p = 0.028) as compared to group with non-DCM. Also, they had lower rates of Thrombolysis in Cerebral Infarction (TICI) 2b/3 recanalization (p = 0.002), higher median National Institutes of Health Stroke Scale (NIHSS) scores at discharge (p = 0.01), and lower rates of 90-day mRS (0-2; 18.2 vs. 48.8%; p = 0.016). On subgroup analysis, patients with middle cerebral artery occlusions who underwent MT with stentrievers <40 mm in length had a higher risk of DCM (p = 0.026). On multivariable analysis, IV-tPA administration (OR; 5.019, 95% CI [1.319-19.102], p = 0.018) and stentrievers thrombectomy (OR; 10.031, 95% CI [1.090-92.344]; p = 0.04) remained significant predictors of DCM. Baseline NIHSS score (OR; 0.872, 95% CI [0.788-0.965], p = 0.008) and DCM (OR; 0.250, 95% CI [0.075-0.866], p = 0.03) were independent predictors of 90-day mRS 0-2. CONCLUSION: In patients undergoing MT for anterior circulation LVO, DCM is associated with lower rates of TICI 2b/3 recanalization and worse functional outcomes at 90 days. IV-tPA administration and MT with short stentrievers are independent predictors of DCM development.

2D parametric contrast time-density analysis for the prediction of complete aneurysm occlusion at six months' post-flow diversion stent.

OBJECTIVE: Indications for the treatment of cerebral aneurysms with flow diversion stents are expanding. The current aneurysm occlusion rate at six months ranges between 60 and 80%. Predictability of complete vs. partial aneurysm occlusion is poorly defined. Here, we evaluate the angiographic contrast time-density as a predictor of aneurysm occlusion rate at six months' post-flow diversion stents. METHODS: Patients with unruptured cerebral aneurysms proximal to the internal carotid artery terminus treated with single flow diversion stents were included. 2D parametric parenchymal blood flow software (Siemens-Healthineers, Forchheim, Germany) was used to calculate contrast time-density within the aneurysm and in the proximal adjacent internal carotid artery. The area under the curve ratio between the two regions of interests was assessed at baseline and after flow diversion stents deployment. The area under the curve ratio between completely vs. partially occluded aneurysms at six months' follow-up was compared. RESULTS: Thirty patients with 31 aneurysms were included. Mean aneurysm diameter was 8 mm (range 2-28 mm). Complete occlusion was obtained in 19 aneurysms. Younger patients (P = 0.006) and smaller aneurysms (P = 0.046) presented higher chance of complete obliteration. Incomplete occlusion of the aneurysm was more likely if the area under the curve contrast time-density ratio showed absolute (P = 0.001) and relative percentage (P = 0.001) decrease after flow diversion stents deployment. Area under ROC curve was 0.85. CONCLUSION: Negative change in the area under the curve ratio indicates less contrast stagnation in the aneurysm and lower chance of occlusion. These data provide a real-time analysis after aneurysm treatment. If validated in larger datasets, this can prompt input to the surgeon to place a second flow diversion stents.

Role of Resistivity Index Analysis in the Prediction of Hemodynamically Significant Venous Sinus Stenosis in Patient With Idiopathic Intracranial Hypertension.

BACKGROUND: The resistivity index (RI) in cerebral venous sinus stenosis (VSS) has not been studied in patients with idiopathic intracranial hypertension (IIH). OBJECTIVE: To evaluate the role of RI measured by quantitative magnetic resonance venogram (QMRV) as a noninvasive tool in the diagnosis of venous hypertension associated with VSS in IIH. METHODS: Retrospective evaluation of 13 consecutive IIH patients who underwent venous sinus stenting at our institution between 2013 and 2018.Patients' demographics, clinical presentation, cerebral mean venous sinus pressure (MVP), and RI both pre- and poststenting were recorded. The baseline RI was also compared to a control group. RESULTS: Among 13 patients of IIH, 11 had unilateral VSS in dominant sinus, whereas 2 had bilateral VSS. RI was significantly higher in IIH patients compared to the control group in the superior sagittal (SSS) and transverse sinuses (TS) (0.21 vs 0.11, P = .01 and 0.22 vs 0.13, P = .03, respectively). The MVP (in mm Hg) decreased significantly after venous sinus stenting in the SSS (41.9 to 22.5, P < .001) and TS (39.4 to 19.5, P < .001), which was also associated with a significant reduction of the RI (0.22 vs 0.17, P < .01 in SSS and 0.23 vs 0.17, P = .03 in TS) poststenting. CONCLUSION: RI calculated using QMRV can serve as a noninvasive tool to aid in the diagnosis of hemodynamically significant VSS. The study had a small sample size, and larger multicenter studies would be required to validate the results further.

Intracranial venous sinus stenosis: hemodynamic assessment with two-dimensional parametric parenchymal blood flow software on digital subtraction angiography.

OBJECTIVE: Intracranial venous sinus stenosis (IVSS) is the most common finding associated with idiopathic intracranial hypertension. A pressure gradient >8-10 mm Hg across the stenosis is considered hemodynamically significant, and typically responds to endovascular stent treatment. Here we assess the venous hemodynamics with two-dimensional (2D) parametric parenchymal blood flow software (Siemens-Healthineers, Forchheim, Germany) and its ability to predict significant IVSS. METHODS: Patients with IVSS treated at our institution between 2013 and 2018 were retrospectively reviewed. Measurements of contrast transit time on DSA were calculated with 2D parametric parenchymal blood flow software. Values were obtained proximally and distally to the stenotic region. Venous Stenosis Index (VSI) was defined as the ratio of the area under the curve (AUC) in the pre-stenotic vessel to the AUC in the post-stenotic vessel. VSI was compared between the stenotic and control groups at baseline, and before and after stent deployment in the stenotic group. The accuracy of VSI was assessed using the non-parametric receiver operating characteristic (ROC) curve. RESULTS: 11 patients with IVSS treated with venous stent deployment were included. Patients in the control group were similar in age, gender, and absence of major comorbidities. VSI in the IVSS group was significantly higher at baseline compared with the control group (1.42 vs 0.97, p=0.01). Area under the ROC was 0.82. After stent deployment, VSI decreased significantly compared with baseline (1.04 vs 1.42, p<0.01). CONCLUSION: 2D parametric parenchymal blood flow software is a useful tool which can accurately evaluate significant hemodynamic venous stenosis without intracranial catheterization, added radiation exposure, additional contrast injection, and periprocedural risks.

Correlation Between Laminar Wall Shear Stress and Growth of Unruptured Cerebral Aneurysms: In Vivo Assessment.

BACKGROUND: Cerebral aneurysm growth is significantly associated with aneurysm rupture, but risk factors for aneurysm growth are not well characterized. It is believed that altered intracranial hemodynamics may contribute to the pathophysiology of aneurysm growth, but these mechanisms are not fully understood. OBJECTIVE: Here, we assess the correlation between growth of unruptured cerebral aneurysms over time and average laminar shear stress on the wall of the parent vessel proximal to the aneurysm. METHODS: Patients with unruptured, untreated cerebral aneurysms followed over time at our institution between 2005 and 2017 were retrospectively reviewed. Patients were included if at least 1 quantitative magnetic resonance angiography study was performed at baseline and follow-up. The nonparametric Wilcoxon-Mann-Whitney test was used to compare mean parent vessel-laminar wall shear stress (PV-LWSS) proximal to the aneurysm in growing versus stable aneurysms. Change in PV-LWSS over time was evaluated using the 1-way repeated measures analysis of variance test. RESULTS: Thirty-three patients with 45 total aneurysms were included (63% female, mean age 60 years). Four patients presented with aneurysm growth over time. Unstable aneurysms had significantly higher PV-LWSS compared with stable aneurysms at the time of first diagnosis (29.3 vs. 13.1 dynes/cm2, P = 0.02) and at 1-year follow-up (25.8 vs. 12.3 dynes/cm2, P = 0.05). CONCLUSIONS: The subset of unruptured cerebral aneurysms that demonstrate growth over time has a significantly higher mean PV-LWSS than stable aneurysms, as measured by quantitative magnetic resonance angiography. This information at the time of diagnosis may help predict future aneurysm growth, stratify rupture risk, and identify those aneurysms that should undergo prophylactic treatment.