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MRI plays an important role as a secondary test or problem-solving modality in the evaluation of adnexal lesions depicted at US. MRI has increased specificity compared with US, decreasing the number of false-positive diagnoses for malignancy and thereby avoiding unnecessary or over-extensive surgery in patients with benign lesions or borderline tumors, while women with possible malignancies can be expeditiously referred for oncologic surgical evaluation. The Ovarian-Adnexal Reporting and Data System (O-RADS) MRI Committee is an international collaborative effort formed under the direction of the American College of Radiology and includes a diverse group of experts on adnexal imaging and management who developed the O-RADS MRI risk stratification system. This scoring system assigns a probability of malignancy based on the MRI features of an adnexal lesion and provides information to facilitate optimal patient management. The widespread implementation of a codified reporting system will lead to improved interpretation agreement and standardized communication between radiologists and referring physicians. In addition, it will allow for high-quality multi-institutional collaborations-an important unmet need that has hampered the performance of high-quality research in this area in the past. This article provides guidelines on using the O-RADS MRI risk stratification system in clinical practice, as well as in the educational and research settings.

International audience; Background In acute ischemic stroke (AIS), fluid-attenuated inversion recovery (FLAIR) is used for treatment decisions when onset time is unknown. Synthetic FLAIR could be generated with deep learning from information embedded in diffusion-weighted imaging (DWI) and could replace acquired FLAIR sequence (real FLAIR) and shorten MRI duration. Purpose To compare performance of synthetic and real FLAIR for DWI-FLAIR mismatch estimation and identification of patients presenting within 4.5 hours from symptom onset. Materials and Methods In this retrospective study, all pretreatment and early follow-up ( .99). Conclusion Synthetic fluid-attenuated inversion recovery (FLAIR) had diagnostic performances similar to real FLAIR in depicting diffusion-weighted imaging-FLAIR mismatch and in helping to identify early acute ischemic stroke, and it may accelerate MRI protocols. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Carroll and Hurley in this issue.

Purpose To evaluate the association between dynamic contrast material-enhanced (DCE) and diffusion-weighted (DW) magnetic resonance (MR) imaging with pathologic complete response after preoperative combined chemotherapy and radiation therapy for cervical carcinoma and evaluate the risk of local recurrence. Materials and Methods The institutional ethics committee approved the study and waived the requirement to obtain informed consent. The study comprised 52 patients with locally advanced carcinoma, treated first with combined chemotherapy and radiation therapy, who underwent MR imaging before final surgery between June 2011 and July 2015. Three radiologists evaluated conventional, DW, and DCE MR images to identify a complete response. The standard of reference was surgical-pathologic findings. Results An initial increase in signal intensity on DCE MR images that was greater in the cervical lesion than in the myometrium was defined as time-signal intensity curve type B and showed a significant association with incomplete response (P = .0004). DCE MR imaging parameters (ie, maximum slope enhancement, area under the gadolinium concentration-time curve during the first 90 seconds after gadolinium injection [AUGC90], and volume transfer constant [Ktrans]) and a low signal intensity on apparent diffusion coefficient (ADC) maps were significantly associated with an incomplete response (P = .027, P = .041, P = .037, and P = .032, respectively). A mean ADC of 0.0014 m2/sec or less (hazard ratio [HR] = 8.3), low ADC signal intensity (HR = 7.3), high signal intensity at DW imaging (HR = 7.1), and time-signal intensity curve type B (HR = 4.3) were associated with earlier recurrence (P 0.9) and the following parameters: AUGC90, Ktrans, and maximum slope enhancement (intraclass correlation coefficient, >0.9). Conclusion DCE MR imaging parameters, especially the time-signal intensity curve, and DW imaging are associated with complete response and incomplete response and could potentially help oncologists with management decisions. Moreover, DCE and DW MR imaging could help oncologists accentuate the follow-up for patients with a high risk of local recurrence to assess for recurrence. © RSNA, 2017 Online supplemental material is available for this article.

To retrospectively evaluate the diagnostic performance of magnetic resonance (MR) imaging for the diagnosis of adnexal torsion in a series of patients with an equivocal adnexal mass at ultrasonography (US) in the context of acute or subacute pelvic pain.The institutional ethics committee approved the study and waived informed consent. All patients with acute or subacute pelvic pain who were undergoing MR examination for the exploration of an equivocal adnexal mass (January 2007 to December 2012) with surgical exploration or clinical and radiologic follow-up of at least 3 months were retrospectively included (n = 58). The prospective interpretations were recorded. Additionally, three radiologists who were blinded to the clinical, US, and surgical data retrospectively and independently reviewed MR images. Features associated with adnexal torsion were identified by using univariate and recursive partitioning multivariate analysis.Twenty-two patients (38%) had a diagnosis of adnexal torsion. The accuracy of MR imaging at the time of prospective interpretation was 80.6% (25 of 31 patients) and 85.1% (23 of 27 patients) in acute and subacute torsion, respectively. The accuracy of image interpretation by each retrospective reader was 83.9% (26 of 31 patients), 90.3% (28 of 31 patients), and 83.9% (26 of 31 patients) in the context of acute pelvic pain and 92.6% (25 of 27 patients), 88.9% (24 of 27 patients), and 81.5% (22 of 27 patients) in the context of subacute pelvic pain for readers 1, 2, and 3, respectively. At multivariate analysis, the whirlpool sign (odds ratio = 6.5 [95% confidence interval: 1.36, 31.0], P = .01) and a thickened tube (10 mm) (odds ratio = 8.2 [95% confidence interval: 1.2, 56.8], P = .03) were associated with adnexal torsion, with substantial interreader agreement (κ = 0.71-0.84 and 0.82-0.86, respectively). The presence of adnexal hemorrhagic content was associated with nonviable ovaries in seven of 10 patients (70%) and with viable ovaries in 12 of 45 patients (27%) (P = .009).MR imaging is an accurate technique for the diagnosis of adnexal torsion in patients who have an adnexal mass with acute or subacute pelvic pain.

Purpose To identify wall enhancement patterns on vessel wall MRI that discriminate between stable and unstable unruptured intracranial aneurysm (UIA). Materials and Methods Patients were included from November 2012 through January 2016. Vessel wall MR images were acquired at 3 T in patients with stable (incidental and nonchanging over 6 months) or unstable (symptomatic or changing over 6 months) UIA. Each aneurysm was evaluated by using a four-grade classification of enhancement: 0, none; 1, focal; 2, thin circumferential; and 3, thick (1 mm) circumferential. Inter- and intrareader agreement for the presence and the grade of enhancement were assessed by using κ statistics and 95% confidence interval (CI). The sensitivity, specificity, and negative and positive predictive values of each enhancement grade for differentiating stable from unstable aneurysms was compared. Results The study included 263 patients with 333 aneurysms. Inter- and intrareader agreement was excellent for both the presence of enhancement (κ values, 0.82 [95% CI: 0.67, 0.99] and 0.87 [95% CI: 0.7, 1.0], respectively) and enhancement grade (κ = 0.92 [95% CI: 0.87, 0.95]). In unruptured aneurysms (n = 307), grade 3 enhancement exhibited the highest specificity (84.4%; 233 of 276; 95% CI: 80.1%, 88.7%; P = .02) and negative predictive value (94.3%; 233 of 247) for differentiating between stable and unstable lesions. There was a significant association between grade 3 enhancement and aneurysm instability (P.0001). Conclusion In patients with intracranial aneurysm, a thick (1 mm) circumferential pattern of wall enhancement demonstrated the highest specificity for differentiating between stable and unstable aneurysms. © RSNA, 2018.

Purpose To propose and validate a modified pediatric intracerebral hemorrhage (PICH) (mPICH) score and to compare its association with functional outcome to that of the original PICH score. Materials and Methods Data from prospectively included patients were retrospectively analyzed. Consecutive patients with nontraumatic PICH who had undergone clinical follow-up were included. The study population was divided into a development cohort (2008-2012, n = 100) and a validation cohort (2013-2016, n = 43). An mPICH score was developed after variables associated with poor outcome were identified at multivariate analysis (King's Outcome Scale for Childhood Head Injury score5a) in the development cohort. The accuracy of the score for prediction of poor outcome was evaluated (sensitivity, specificity). Discrimination and calibration of associations between the mPICH score and poor outcome cohorts were assessed (C statistics, Hosmer-Lemeshow test). Results The mPICH score assessed as follows: brain herniation, four points; altered mental status, three points; hydrocephalus, two points; infratentorial PICH, two points; intraventricular hemorrhage, one point; PICH volume greater than 2% of total brain volume, one point. An mPICH score greater than 5 was associated with severe disability or worse, with sensitivity of 97% (95% confidence interval [CI]: 83%, 100%) and specificity of 61% (95% CI: 49%, 73%). The C statistic was 0.81 (95% CI: 0.73, 0.89). In the validation cohort, sensitivity and specificity were 95.2% (95% CI: 76%, 99%) and 77% (95% CI: 55%, 92%), respectively. There was no significant difference between the observed and predicted risks of poor outcome (P = .46). Conclusion An mPICH score was developed as a simple clinical and imaging grading scale for acute prognosis in patients with PICH.

Editor: We were pleased to read the very interesting article in the September 2015 issue of Radiology by Dr Nougaret and colleagues (1), who underlined that the major clinical challenge in endometrial cancer staging is to select the patients who are most likely to benefit from lymphadenectomy. This is particularly relevant in patients with type 1 endometrial cancer, as patients with type 2 cancer do require systematic pelvic and para-aortic lymphadenectomy (2). Moreover, tumor size and lymphovascular space involvement (LVSI) have no impact on survival in patients with type 2 endometrial cancer (3,4). Therefore, it is of particular interest to determine the contribution of magnetic resonance (MR) imaging in a homogeneous population of patients with type 1 endometrial cancer (59 of 70 patients in this study). In these patients with type 1 cancer, European Society for Medical Oncology (ESMO) guidelines state that patients with low or intermediate risk of recurrence who exhibit LVSI should be considered a high-risk group (2). In the study by Dr Nougaret and colleagues, a very high percentage of patients underwent para-aortic lymph node sampling (89%), which is commonly indicated in high-risk patients, who typically have comprised less than one-quarter of patients with early stage disease in previous retrospective studies (3,5). Moreover, in this study, there was a high level of LVSI (50% vs 20%–30% in previous studies) (3,5). Thus, it would be very helpful to understand in which ESMO category the patients in this study were initially classified and in how many cases the new MR imaging criteria evaluated would have modified management. Second, in their study, Dr Nougaret and colleagues conclude that the different MR pulse sequences were equal in the evaluation of tumor size because nonsignificant differences were found. Did the authors have a sufficient study size to draw this conclusion? For that issue, the measurement of the concordance between size at histologic and MR examination would have been helpful. Is this histologic information available? Finally, Dr Nougaret and colleagues compared the accuracy of a number of MR pulse sequences in the evaluation of myometrial invasion. It is surprising that the authors did not compare T2and diffusion-weighted pulse sequences with a high-spatial-resolution T1-weighted pulse sequence, which is considered as a standard in European guidelines (6). Moreover, the number of premenopausal and menopausal patients and the presence of benign uterine-associated abnormalities would be useful to discuss in the assessment of myometrial invasion.

To report subgroup analyses of an updated systematic review on endovascular treatment of intracranial unruptured aneurysms (UAs); to compare types of embolic agents, adjunct techniques, and newer devices; and to identify potential risk factors for poor outcomes.Meta-Analysis of Observational Studies in Epidemiology and Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were used to prepare this article, and the literature was searched with PubMed and with EMBASE and Cochrane databases. Six eligibility criteria (procedural complications rates; at least 10 patients; saccular, nondissecting UAs; original study published in English or French between January 2003 and July 2011; methodological quality score6 [modified Strengthening and Reporting of Observational Studies in Epidemiology criteria]; a study published in a peer-reviewed journal) were used. End points included procedural mortality and unfavorable outcomes (death or modified Rankin Scale, Glasgow Outcome Scale, or World Federation of Neurosurgeons Scale at 1 month scores, all2). A fixed-effects model (Mantel-Haenszel) was used for pooled estimates of mortality and unfavorable outcomes; a random-effects model (DerSimonian-Laird) was used in case of heterogeneity.Ninety-seven studies with 7172 patients (26 studies published July 2008 through July 2011) were included. Sixty-nine (1.8%) of 7034 patients died (fixed-effect weighted average; 99% confidence interval [CI]: 1.4%, 2.4%; Q value, 55.0; I(2) = 0%). Unfavorable outcomes, including death, occurred in 4.7% (242 of 6941) of patients (99% CI: 3.8, 5.7; Q value, 128.3; I(2) = 26.8%). Patients treated after 2004 had better outcomes (unfavorable outcome, 3.1; 99% CI: 2.4, 4.0) than patients treated during 2001-2003 (unfavorable outcome, 4.7%; 99% CI: 3.6%, 6.1%; P = .01) or in 2000 and before (unfavorable outcome, 5.6%; 99% CI: 4.7%, 6.6%; P.001). Significantly higher risk was associated with liquid embolic agents (8.1%; 99% CI: 4.7%, 13.7%) versus simple coil placement (4.9%; 99% CI: 3.8%, 6.3%; P = .002). Unfavorable outcomes occurred in 11.5% (99% CI: 4.9%, 24.6%) of patients treated with flow diversion.Procedure-related poor outcomes occurred (4.7% of patients), risks decreased, and liquid embolic agents and flow diversion were associated with higher risks.

To determine the value of adding conventional imaging (mammography and ultrasonography [US]) to nonmasslike enhancement (NMLE) analysis with breast magnetic resonance (MR) imaging for predicting malignancy and for building an interpretation model incorporating all imaging modalities.The institutional ethics committees approved the study and granted a waiver of informed consent. In 115 women (mean age, 48.3 years; range, 21-76 years; 56 malignant, 12 high-risk, and 63 benign lesions), 131 NMLE lesions were analyzed. Two independent readers first classified MR images by using descriptive Breast Imaging Reporting and Data System (BI-RADS) criteria (BI-RADS classification with MR images alone [BI-RADS(MR)]) and later repeated this classification, adding information from conventional imaging (BI-RADS classification with combination of MR images and conventional images [BI-RADS(MR+Con)]). Lesion diagnosis was established with surgical histopathologic findings (n = 68), percutaneous biopsy results (n = 25), or 2 years of stability at MR imaging (n = 38). Receiver operating characteristic curves were built to compare BI-RADS(MR) with BI-RADS(MR+Con). A multivariate interpretation model was constructed and validated in a distinct cohort of 44 women.Values for inter- and intraobserver agreement, respectively, were better for BI-RADS(MR+Con) (κ = 0.847 and 0.937) than for BI-RADS(MR) (κ = 0.748 and 0.861). For both readers, the areas under the receiver operating characteristic curve (AUCs) for diagnosis of malignancy were also superior when BI-RADS(MR+Con) (AUC = 0.91 [reader 1] and 0.93 [reader 2]) was compared with BI-RADS(MR) (AUC = 0.84 [reader 1] and 0.87 [reader 2]) (P.05). An interpretation model combining conventional imaging with MR imaging criteria showed very good discrimination (AUC = 0.89 [training set] and 0.90 [validating set]).Adding conventional imaging to NMLE lesion characterization at breast MR imaging improved the diagnostic performance of radiologists, and the interpretation model used offers good accuracy with the potential to optimize the reproducibility of NMLE analysis at MR imaging.

To retrospectively determine the value of adding perfusion-weighted (PW) and diffusion-weighted (DW) sequences to a conventional magnetic resonance (MR) imaging protocol to differentiate benign from malignant tumors.The institutional ethics committee approved this retrospective study and waived the requirement to obtain informed consent. MR images in 87 women (age range, 25-87 years) who underwent imaging before surgery for complex adnexal masses-excluding endometriomas and cystic teratomas-were analyzed. Conventional morphologic, perfusion, and diffusion MR criteria of malignancy were recorded. Three independent observers reviewed images in four steps: conventional MR images alone, conventional MR images and PW images combined, conventional MR images and DW images combined, and conventional, PW, and DW MR images combined. Receiver operating characteristic curve analysis was performed to compare the results of the readings. A recursive partitioning model was built to establish a multivariate decision tree.There was almost perfect agreement for lesion characterization regardless of the reader experiment or step considered (κ = 0.811-0.929). Area under the receiver operating characteristic curve values were higher for conventional and DW images combined, conventional and PW images combined, and conventional, DW, and PW images combined compared with conventional MR images alone (P.05). For all readers, the accuracy of conventional, PW, and DW imaging combined was higher than that of conventional MR imaging alone for benign masses (P.01) but not for malignant masses (P = .24). The addition of both PW and DW images led to a correct change in the diagnosis in 19% (11 of 57 patients), 23% (13 of 57 patients), and 24% (14 of 57 patients) of cases for readers 1, 2, and 3, respectively, with no incorrect changes. Conventional, PW, and DW MR imaging criteria were combined to generate a decision tree giving an accuracy of 95%.The addition of PW and DW sequences to a conventional MR imaging protocol improved the diagnostic accuracy in the characterization of complex adnexal masses.

To retrospectively evaluate the diagnostic performance of dynamic contrast material-enhanced magnetic resonance (MR) imaging for the characterization of ovarian epithelial tumors, by using histologic findings as the reference standard, and to correlate dynamic contrast-enhanced MR imaging findings with angiogenesis biomarkers.Ethics committee approval was obtained, with waiver of informed consent. Patients consented to having their data used for future retrospective research. Forty-one women (age range, 22-73 years) with 48 epithelial ovarian tumors underwent dynamic contrast-enhanced MR imaging before surgical excision. In case of bilateral tumors (n = 7), only the most complex tumor was analyzed. Thus, 41 tumors (12 benign, 13 borderline, and 16 invasive) were examined with dynamic contrast-enhanced MR imaging and immunohistochemical methods. Dynamic contrast-enhanced MR imaging parameters (enhancement amplitude [EA], time of half rising [T(max)], and maximal slope [MS]) were analyzed according to histopathologic findings, microvessel density, pericyte coverage index (PCI), and vascular endothelial growth factor receptor 2 (VEGFR-2) expression. Statistical analyses were performed by using Kruskal-Wallis, Fisher exact, and Spearman tests and receiver operating curve analysis.EA was higher for invasive tumors than for benign (P.001) and borderline (P.05) tumors. T(max) was longer for benign tumors than for borderline (P.05) and invasive (P.01) tumors. MS was steeper for invasive tumors than for benign (P.001) and borderline (P.001) tumors. PCI was lower in invasive tumors than in borderline (P.05) and benign (P.05) tumors. Microvessels showed stronger immunohistochemical VEGFR-2 expression in invasive tumors than in benign or borderline tumors (P.05). MS correlated with a lower PCI (r = -0.34, P = .04) and stronger VEGFR-2 expression by using both epithelial (r = 0.41, P.01) and endothelial (r = 0.66, P.001) cells.The early enhancement patterns of ovarian epithelial tumors on dynamic contrast-enhanced MR images can help distinguish among benign, borderline, and invasive tumors and were found to correlate with tumoral angiogenic status.

To assess the efficacy of endovascular treatment (EVT) of intracranial aneurysms for recurrence, bleeding, and de novo aneurysm formation at long-term follow-up (10 years after treatment) with magnetic resonance (MR) angiography and to identify risk factors for recurrence through a prospective study and a systematic review of the literature.Clinical examinations and 3-T MR angiography were performed prospectively 10 years after EVT of intracranial aneurysms in a single institution. Ethics committee approval and informed consent were obtained. PubMed, EMBASE, and Cochrane databases were searched to identify studies in which authors reported bleeding and/or aneurysm recurrence rates in patients who received follow-up more than 10 years after EVT. Univariate and multivariate subgroup analyses were performed to identify risk factors (midterm MR angiographic results, aneurysm characteristics, retreatment within 5 years).In the prospective study, sac recanalization occurred between midterm and long-term MR angiography in 16 of 129 (12.4%) aneurysms. Grade 2 classification on the Raymond scale at midterm MR angiography (relative risk [RR], 4.16; 99% confidence interval [CI]: 2.12, 8.14) and retreatment within 5 years (RR, 4.67; 99% CI: 1.55, 14.03) were risk factors for late recurrence. In the systematic review (15 cohorts, 2773 patients, 2902 aneurysms), bleeding, aneurysm recurrence, and de novo lesion formation rates were, respectively, 0.7% (99% CI: 0.2%, 2.7%; I(2), 0%; one of 694 patients), 11.4% (99% CI: 7.0%, 18.0%; I(2), 21.6%), and 4.1% (99% CI: 1.7, 9.4%; I(2), 54.1%). Raymond grade 2 initial result (RR, 7.08; 99% CI: 1.24, 40.37; I(2), 82.6%) and aneurysm size greater than 10 mm (RR, 4.37; 99% CI: 1.83, 10.44; I(2), 0%) were risk factors for late recurrence.EVT of intracranial aneurysm is effective for prevention of long-term bleeding, but recurrences occur in a clinically relevant percentage of patients, a finding that may justify follow-up of selected patients for 10 years or more, such as patients with aneurysms larger than 10 mm or classified as Raymond grade 2 at midterm MR angiography.

To assess the feasibility of a selective flow-tracking cartographic procedure applied to four-dimensional (4D) flow imaging and to demonstrate its usefulness in the characterization of dural arteriovenous fistulas (DAVFs).Institutional review board approval was obtained, and all patients provided written informed consent. Eight patients (nine DAVFs) underwent 3.0-T magnetic resonance (MR) imaging and digital subtraction angiography (DSA). Imaging examinations were performed within 24 hours of each other. 4D flow MR imaging was performed by using a 4D radial phase-contrast vastly undersampled isotropic projection reconstruction pulse sequence with an isotropic spatial resolution of 0.86 mm (5 minutes 35 seconds). Two radiologists independently reviewed images from MR flow-tracking cartography and reported the location of arterial feeder vessels and the venous drainage type and classified DAVFs according to the risk of rupture (Cognard classification). These results were compared with those at DSA. Quadratic weighted κ statistics with their 95% confidence intervals (CIs) were used to test intermodality agreement in the identification of arterial feeder vessels, draining veins, and Cognard classification.Interreader agreement for shunt location on MR images was perfect (κ = 1), with good-to-excellent interreader agreement for arterial feeder vessel identification (κ = 0.97; 95% CI = 0.92, 1.0), and matched in all cases with shunt location defined at DSA. There was good-to-excellent agreement between MR cartography and DSA in the definition of the main feeding arteries (κ = 0.92; 95% CI = 0.83, 1.0), presence of retrograde flow in dural sinuses (κ = 1), presence of retrograde cortical venous drainage (κ = 1), presence of venous ectasia (κ = 1), and final Cognard classification of DAVFs (κ = 1, standard error = 0.35).MR selective flow-tracking cartography enabled the noninvasive characterization of cranial DAVFs.

To construct and undertake preliminary validation of a magnetic resonance (MR) imaging scoring system designed for use in pelvic MR imaging performed for characterization of adnexal masses that were indeterminate at ultrasonography (US).The institutional ethics committee approved this retrospective study and granted a waiver of informed consent. The study population comprised 394 women who underwent MR imaging between January 1, 2008, and October 30, 2010, for characterization of 497 adnexal masses that were seen at US. Then, masses were chronologically divided into a training set (329 masses) and a validating set (168 masses). Two radiologists who were blinded to the clinical findings retrospectively evaluated MR imaging criteria for characterization of adnexal masses. In the training set, the positive likelihood ratio (PLR) of malignancy and κ values were calculated for each criterion. The reference standard was surgical pathologic findings or findings at imaging follow-up of at least 1 year. On the basis of the PLR and multivariate analysis, a five-category MR scoring system called the ADNEX MR SCORING system was created and was subsequently tested by six readers with the validating set.There was almost perfect agreement (κ0.80) for each MR imaging feature except for grouped septa (κ = 0.558) and thickened regular septa (κ = 0.555). The classification was accurate in both the training set (area under the receiver operating characteristic [ROC] curve [AUC] = 0.981 for reader 1 and 0.961 for reader 2) and the validating set (AUC = 0.964 for reader 1 and 0.943 for reader 2). ROC curve analysis demonstrated that the optimal cutoff point was an ADNEX MR score of 3; an ADNEX MR score of 4 or higher was associated with malignancy with a sensitivity of 93.5% (58 of 62) and a specificity of 96.6% (258 of 267).In this study, a reproducible and accurate MR imaging scoring system that has the potential to improve patient care was developed and tested. Multicenter prospective validation of the score is warranted.http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13121161/-/DC1.

To report an updated, systematic review of medical literature from January 2003 to July 2008, on endovascular treatment (EVT) of intracranial unruptured aneurysms (UAs) (a) to assess the morbidity and case fatality rate of EVT of UAs, (b) to understand how bias can affect results, and (c) to estimate the efficacy of EVT by using reported digital subtraction angiographic (DSA) results and clinical follow-up events.This article was prepared in accordance with the Meta-Analysis of Observational Studies in Epidemiology and Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The literature was searched by using PubMed and the EMBASE and Cochrane Library databases. Eligibility criteria were (a) explicit procedural mortality and morbidity rates; (b) at least 10 patients; (c) saccular, intradural, nondissecting UAs; (d) original study published in English or French between January 2003 and July 2008; and (e) a methodological quality score higher than 6, according to Strengthening the Reporting of Observational Studies in Epidemiology criteria. End points included procedural mortality and morbidity, defined as a modified Rankin scale score of 3-6 at 1 month, and efficacy, estimated by using immediate and follow-up digital subtraction angiographic results, as well as delayed hemorrhagic events.Seventy-one studies were included. Procedural unfavorable outcome was found in 4.8% (random-effect weighted average; 189 of 5044) of patients (99% confidence interval [CI]: 3.9%, 6.0%). Immediate angiographic results showed satisfactory occlusion in 86.1% (2660 of 3089) of UAs. Recurrences were shown in 321 (24.4%) of 1316 patients followed up for 0.4-3.2 years. Retreatment was performed in 9.1% (random-effect weighted average; 166 of 1699) of patients (99% CI: 6.2%, 13.1%). The annual risk of bleeding after EVT was 0.2% (random-effect weighted average; nine of 1395) of patients (99% CI: 0.1%, 0.3%), but clinical follow-up was short, limited to the first 6 months for 76.7% (n = 1071) of reported patients.EVT of UAs can be performed with relative safety. The efficacy of treatment as compared with observation has not been rigorously documented.