Diagnostic Performance of Ultrafast Brain MRI for Evaluation of Abusive Head Trauma

BACKGROUND AND PURPOSE:MR imaging with sedation is commonly used to detect intracranial traumatic pathology in the pediatric population. Our purpose was to compare nonsedated ultrafast MR imaging, noncontrast head CT, and standard MR imaging for the detection of intracranial trauma in patients with potential abusive head trauma.MATERIALS AND METHODS:A prospective study was performed in 24 pediatric patients who were evaluated for potential abusive head trauma. All patients received noncontrast head CT, ultrafast brain MR imaging without sedation, and standard MR imaging with general anesthesia or an immobilizer, sequentially. Two pediatric neuroradiologists independently reviewed each technique blinded to other modalities for intracranial trauma. We performed interreader agreement and consensus interpretation for standard MR imaging as the criterion standard. Diagnostic accuracy was calculated for ultrafast MR imaging, noncontrast head CT, and combined ultrafast MR imaging and noncontrast head CT.RESULTS:Interreader agreement was moderate for ultrafast MR imaging (κ = 0.42), substantial for noncontrast head CT (κ = 0.63), and nearly perfect for standard MR imaging (κ = 0.86). Forty-two percent of patients had discrepancies between ultrafast MR imaging and standard MR imaging, which included detection of subarachnoid hemorrhage and subdural hemorrhage. Sensitivity, specificity, and positive and negative predictive values were obtained for any traumatic pathology for each examination: ultrafast MR imaging (50%, 100%, 100%, 31%), noncontrast head CT (25%, 100%, 100%, 21%), and a combination of ultrafast MR imaging and noncontrast head CT (60%, 100%, 100%, 33%). Ultrafast MR imaging was more sensitive than noncontrast head CT for the detection of intraparenchymal hemorrhage (P = .03), and the combination of ultrafast MR imaging and noncontrast head CT was more sensitive than noncontrast head CT alone for intracranial trauma (P = .02).CONCLUSIONS:In abusive head trauma, ultrafast MR imaging, even combined with noncontrast head CT, demonstrated low sensitivity compared with standard MR imaging for intracranial traumatic pathology, which may limit its utility in this patient population.

The incidence of abusive head trauma (AHT) in the United States from 2000 to 2009 was 39.8 per 100,000 children younger than 1 year of age and 6.8 per 100,000 children 1 year of age.¹ The outcomes of patients with AHT are worse than those of children with accidental traumatic brain injury, including higher rates of mortality and permanent disability from neurologic impairment.^2–5 The diagnosis of AHT is frequently not recognized when affected patients initially present to a physician, and up to 28% of children with a missed AHT diagnosis may be re-injured, leading to permanent neurologic damage or even death.⁶ Because neuroimaging plays a central role in AHT, continued improvement in neuroimaging is necessary.Common neuroimaging findings of AHT include intracranial hemorrhage, ischemia, axonal injury, and skull fracture, with advantages and disadvantages for both CT and MR imaging for the detection of AHT.⁷ A noncontrast head CT (nHCT) is usually the initial imaging study in suspected AHT due to its high sensitivity for the detection of acute hemorrhage and fracture and the high level of accessibility from the emergency department, and it can be performed quickly and safely without the need for special monitoring equipment.^8,9 The disadvantages of CT include ionizing radiation, particularly in children, and the reduced sensitivity in detecting microhemorrhages, axonal injury, and acute ischemia compared with MR imaging.¹⁰MR imaging is frequently performed in AHT and adds additional information in 25% of all children with abnormal findings on the initial CT scan.¹¹ Brain MR imaging can also be useful for identifying bridging vein thrombosis, differentiating subdural fluid collections from enlarged subarachnoid spaces, characterizing the signal of subdural blood, and demonstrating membrane formation within subdural collections.^12–16 Brain MR imaging findings have correlated with poor outcomes associated with findings on diffusion-weighted imaging and susceptibility-weighted imaging in AHT; however, disadvantages of MR imaging continue to include the need for sedation in children and compatible monitoring equipment.^17–22 Although there is greater accessibility of CT compared with MR imaging, the availability of MR imaging is relatively high and imaging techniques that allow neuroimaging in patients with potential AHT without sedation would be valuable, particularly given the potential adverse effects of sedation on the developing brain.^23,24A potential solution for diagnostic-quality brain MR imaging without sedation in AHT is the use of ultrafast MR imaging (ufMRI) sequences, also termed “fast MR imaging,” “quick MR imaging,” or “rapid MR imaging.” Ultrafast MR imaging uses pulse sequences that rapidly acquire images, potentially reducing motion artifacts and the need for sedation. ufMRI has been most commonly used in pediatric neuroradiology for the evaluation of intracranial shunts in children with hydrocephalus, and most of the reported ufMRI brain protocols include only multiplanar T2-weighted HASTE sequences.^25–34 Consequently, previously reported limitations of ufMRI in detecting intracranial hemorrhage is primarily due to the lack of blood sensitive sequences.³⁵Recently, an ufMRI protocol incorporating sequences in addition to T2 sequences has been reported in pediatric patients with trauma.³⁶ This study did not compare findings with those of a standard MR imaging (stMRI) and included a wider age range of pediatric patients, so the value of ufMRI in pediatric abusive head trauma remains uncertain.³⁶ Therefore, the purpose of our study was to evaluate an ufMRI brain protocol performed without sedation for feasibility in terms of scanning time and diagnostic value as well as diagnostic accuracy compared with nHCT and stMRI of the brain for the detection of intracranial traumatic pathology in patients with suspected AHT.     

Delayed ipsilateral parenchymal hemorrhage following flow diversion for the treatment of anterior circulation aneurysms

BACKGROUND AND PURPOSE:The PED is a flow-diverting stent designed for the treatment of cerebral aneurysms. We report 4 cases of delayed ipsilateral IPH following the technically successful treatment of anterior circulation aneurysms with the PED.MATERIALS AND METHODS:Clinical and imaging data from all patients undergoing aneurysm treatment with the PED at 2 institutions were analyzed to assess the incidence of delayed IPH after treatment with the PED.RESULTS:A total of 66 patients (47 anterior circulation) with cerebral aneurysms underwent treatment with a PED between January 2008 and November 2010. Four patients experienced delayed periprocedural IPH, all after the treatment of anterior circulation aneurysms (8.5%, 4/47). The aneurysm size ranged from 5 to 21 mm. All IPHs occurred within the cerebral hemisphere, ipsilateral to the treated aneurysm, and were anatomically remote from the treated aneurysms. All procedures were uncomplicated, and patients emerged from general anesthesia at neurologic baseline. The hemorrhages became clinically evident between 1 and 6 days after the procedure. Two patients had unfavorable outcomes (mRS scores, 4 and 6).CONCLUSIONS:Delayed IPH may occur after the treatment of anterior circulation aneurysms with flow diverters. This complication does not seem to be restricted to a specific aneurysm subtype and does not seem to be related to an intraprocedural complication or solely attributable to DAT.

Flow diverters have recently received full European Conformity Mark approval for commercialization within the European Union and FDA approval for their use within the United States. To date, the reported periprocedural and midterm follow-up results have been extremely impressive,^1–5 with very high rates of complete aneurysm occlusion and relatively low rates of postoperative morbidity and mortality. However, as more experience is accrued, their potential limitations and optimal applications are becoming increasingly evident.^6–12We report 4 cases of delayed ipsilateral IPH following the treatment of anterior circulation aneurysms with the PED.     

Fellows' Journal Club: Brain MRI Findings in Neurologically Asymptomatic Patients with Infective Endocarditis

BACKGROUND AND PURPOSE:Neurologic complications in infective endocarditis are frequent and affect patient prognosis negatively. Additionally, detection of asymptomatic lesions by MR imaging could help early management of this condition. The objective of our study was to describe MR imaging characteristics of cerebral lesions in a neurologically asymptomatic population with infective endocarditis.MATERIALS AND METHODS:One hundred nine patients at the acute phase of a definite or possible infective endocarditis according to the Duke modified criteria and without neurologic manifestations according to the NIHSS were prospectively included. Each patient underwent cerebral MR imaging and MRA within 7 days of admission.RESULTS:MR imaging showed abnormalities in 78 patients (71.5%). Acute ischemic lesions (40 patients, 37%) and cerebral microbleeds (62 patients, 57%) were the most frequent lesions. Eight patients had an acute SAH, 3 patients had brain microabscesses, 3 had a small cortical hemorrhage, and 3 had a mycotic aneurysm. Acute ischemic lesions mostly appeared as multiple small infarcts disseminated in watershed territories (25/40, 62.5%) and as lesions of different ages (21/40, 52.5%). Cerebral microbleeds were preferentially distributed in cortical areas (362/539 cerebral microbleeds, 67%). No significant correlation was found among lesions, in particular between acute ischemia and cerebral microbleeds.CONCLUSIONS:Occult cerebral lesions, in particular cerebral microbleeds and acute ischemic lesions, are frequent in infective endocarditis. The MR imaging pattern of acute small infarcts of different ages predominating in watershed territories and cortical cerebral microbleeds may represent a surrogate imaging marker of infective endocarditis.

Infective endocarditis is associated with symptomatic neurologic complications in 20%–40% of cases.^1–4 Among symptomatic complications, ischemic stroke is the most common manifestation, whereas hemorrhagic stroke, brain abscess, cerebral hemorrhage or SAH, and mycotic aneurysms are less frequent.² Symptomatic cerebral complications are one of the main prognostic factors in infective endocarditis (IE)^5–8 because they are significantly associated with a 3-month mortality rate.^2,3,9,10 Symptomatic neurologic complications are difficult to predict and prevent because they mostly occur in the early phase of IE and have been reported as the presenting symptom of the disease in up to 47% of cases.²Asymptomatic cerebral lesions revealed by systematic cerebral CT and/or MR imaging have been recently reported, but their impact on patient care and prognosis has not been completely assessed.^8,11–13 Our group showed that detection of cerebral asymptomatic lesions influenced diagnostic decisions in cases of suspected IE.^14,15The purposes of the present study were to extensively describe MR imaging characteristics of cerebral lesions in a neurologically asymptomatic population at the acute phase of IE, to prospectively report their respective frequencies, and to assess correlations between different MR imaging features.     

Brain Parenchymal Signal Abnormalities Associated with Developmental Venous Anomalies in Children and Young Adults

BACKGROUND AND PURPOSE:Abnormal signal in the drainage territory of developmental venous anomalies has been well described in adults but has been incompletely investigated in children. This study was performed to evaluate the prevalence of brain parenchymal abnormalities subjacent to developmental venous anomalies in children and young adults, correlating with subject age and developmental venous anomaly morphology and location.MATERIALS AND METHODS:Two hundred eighty-five patients with developmental venous anomalies identified on brain MR imaging with contrast, performed from November 2008 through November 2012, composed the study group. Data were collected for the following explanatory variables: subject demographics, developmental venous anomaly location, morphology, and associated parenchymal abnormalities. Associations between these variables and the presence of parenchymal signal abnormalities (response variable) were then determined.RESULTS:Of the 285 subjects identified, 172 met inclusion criteria, and among these subjects, 193 developmental venous anomalies were identified. Twenty-six (13.5%) of the 193 developmental venous anomalies had associated signal-intensity abnormalities in their drainage territory. After excluding developmental venous anomalies with coexisting cavernous malformations, we obtained an adjusted prevalence of 21/181 (11.6%) for associated signal-intensity abnormalities in developmental venous anomalies. Signal-intensity abnormalities were independently associated with younger subject age, cavernous malformations, parenchymal atrophy, and deep venous drainage of developmental venous anomalies.CONCLUSIONS:Signal-intensity abnormalities detectable by standard clinical MR images were identified in 11.6% of consecutively identified developmental venous anomalies. Signal abnormalities are more common in developmental venous anomalies with deep venous drainage, associated cavernous malformation and parenchymal atrophy, and younger subject age. The pathophysiology of these signal-intensity abnormalities remains unclear but may represent effects of delayed myelination and/or alterations in venous flow within the developmental venous anomaly drainage territory.

Developmental venous anomalies (DVAs) are frequently identified on routine MR imaging of the brain with contrast. DVAs are typically considered normal variants of venous development and usually have no associated imaging findings. However, a subset of DVAs has been associated with findings such as cavernous malformations (CMs),^1–3 thrombosis with subsequent venous infarction,^4–8 lobar atrophy,⁹ T2 and FLAIR signal-intensity abnormalities,^9,10 and SWI hypointensities.¹¹ Signal abnormalities can occur in the drainage territory of DVAs and may produce diagnostic uncertainty with regard to the significance and relationship to presenting symptoms. Signal abnormalities on MR imaging have been described in 12.5%¹⁰ to 28.3%⁹ of DVAs in adults, with an increasing prevalence with older age. While well described in adults, this relationship has not been investigated in children, to our knowledge. The MR imaging appearance of the brain in children is quite different from that in adults during myelination, and the effect of DVAs on regional brain maturation has not been studied.The most commonly proposed etiologies for parenchymal abnormalities associated with DVAs are chronic venous hypertension/insufficiency leading to ischemia or microhemorrhage.^9–12 Although the effect of brain maturation is unknown, on the basis of these pathophysiologic mechanisms, we hypothesized that parenchymal abnormalities would be less common in children compared with adults. This study was performed to test this hypothesis and to investigate clinical factors and DVA characteristics associated with parenchymal signal abnormalities in children and young adults.     

Inflow Jet Patterns of Unruptured Cerebral Aneurysms Based on the Flow Velocity in the Parent Artery: Evaluation Using 4D Flow MRI

BACKGROUND AND PURPOSE:Inflow jet characteristics may be related to aneurysmal bleb formation and rupture. We investigated the visualization threshold on the basis of the flow velocity in the parent artery to classify the inflow jet patterns observed on 4D flow MR imaging.MATERIALS AND METHODS:Fifty-seven unruptured aneurysms (24 bifurcation and 33 sidewall aneurysms) were subjected to 4D flow MR imaging to visualize inflow streamline bundles whose velocity exceeded visualization thresholds corresponding to 60%, 75%, and 90% of the maximum flow velocity in the parent artery. The shape of the streamline bundle was determined visually, and the inflow jet patterns were classified as concentrated, diffuse, neck-limited, and unvisualized.RESULTS:At the 75% threshold, bifurcation aneurysms exhibited a concentrated inflow jet pattern at the highest rate. At this threshold, the inflow jets were concentrated in 13 aneurysms (group C, 22.8%), diffuse in 18 (group D, 31.6%), neck-limited in 11 (group N, 19.3%), and unvisualized in 15 (group U, 26.3%). In 16 (28.1%) of the 57 aneurysms, the inflow jet pattern was different at various thresholds. Most inflow parameters, including the maximum inflow velocity and rate, the inflow velocity ratio, and the inflow rate ratio, were significantly higher in groups C and D than in groups N and U.CONCLUSIONS:The inflow jet pattern may depend on the threshold applied to visualize the inflow streamlines on 4D flow MR imaging. For the classification of the inflow jet patterns on 4D flow MR imaging, the 75% threshold may be optimal among the 3 thresholds corresponding to 60%, 75%, and 90% of the maximum flow velocity in the parent artery.

The inflow jets of cerebral aneurysms have been characterized as flow structures composed of strongly directed inflow with higher speeds than in other parts of the aneurysm.^1,2 Computational fluid dynamics analyses by using human cerebral aneurysm models suggested that inflow jets may be related to bleb formation and aneurysmal rupture.^3–5 Cebral et al³ reported that most blebs formed at sites where the inflow jet impacted the aneurysmal wall, and they qualitatively classified the inflow jets of ruptured and unruptured cerebral aneurysms into concentrated and diffuse inflow jets.^3–5 They found that most ruptured aneurysms featured concentrated inflow jets, while diffuse inflow jets tended to be seen in unruptured aneurysms.^4,5 This finding suggests that bleb formation and aneurysm rupture may be attributable to a degenerative change in the aneurysm wall exposed to the increased hemodynamic stress exerted by the inflow jet. Therefore, the assessment of inflow jet patterns and quantitative estimation of the inflow hemodynamics may contribute to a more precise prediction of the risk for bleb formation and aneurysm rupture.Computational fluid dynamics analysis uses human aneurysm models based on a number of assumptions and approximations regarding blood properties, vessel wall compliance, and flow conditions.^3–8 For the quantitative evaluation of the hemodynamics in real human cerebral aneurysms, 4D flow MR imaging, which is based on time-resolved 3D cine phase-contrast MR imaging techniques, has been used.^9–20 In this study, we investigated the visualization threshold on the basis of the flow velocity in the parent artery to classify the inflow jet patterns of unruptured cerebral aneurysms on 4D flow MR imaging. We applied different thresholds to visualize the inflow streamlines, evaluated the inflow jet patterns, and examined the relationship between the inflow jet pattern and the inflow hemodynamics.     

Parent Artery Curvature Influences Inflow Zone Location of Unruptured Sidewall Internal Carotid Artery Aneurysms

BACKGROUND AND PURPOSE:Future aneurysmal behaviors or treatment outcomes of cerebral aneurysms may be related to the hemodynamics around the inflow zone. Here we investigated the influence of parent artery curvature on the inflow zone location of unruptured sidewall internal carotid artery aneurysms.MATERIALS AND METHODS:In 32 aneurysms, the inflow zone location was decided by 4D flow MR imaging, and the radius of the parent artery curvature was measured in 2D on an en face image of the section plane corresponding to the aneurysm orifice.RESULTS:The inflow zone was on the distal neck in 10 (group 1, 31.3%), on the lateral side in 19 (group 2, 59.4%), and on the proximal neck in 3 (group 3, 9.4%) aneurysms. The radius in group 1 was significantly larger than that in group 2 (8.3 mm [4.5 mm] versus 4.5 mm [1.9 mm]; median [interquartile range]; P < .0001). All 7 aneurysms with a radius of >8.0 mm were in group 1. All 18 aneurysms with a radius of <6.0 mm were in group 2 or 3. In two group 3 aneurysms, the inflow zone was located in a part of the neck extending beyond the central axis of the parent artery.CONCLUSIONS:The inflow zone locations of sidewall aneurysms can be influenced by the parent artery curvature evaluated in 2D on an en face image of the section plane corresponding to the aneurysm orifice.

The hemodynamics around the inflow zone of cerebral aneurysms may be a principal cause of growth,^1–4 bleb formation resulting in rupture,^1,2,5–8 and regrowth following clipping surgery or endovascular coiling.^9–13 These sequelae are possibly related to the increased wall shear stress on the aneurysmal wall surrounding the inflow zone.^2–6,14 Therefore, both identification of the exact location of the inflow zone and evaluation of the hemodynamics around this area may contribute to predicting future aneurysmal behaviors or obtaining good treatment outcomes.¹⁵ Previous studies have estimated that neck width and geometric relationship between an aneurysm and the parent artery are dominant factors in the determination of the inflow zone location.^1,14,16–194D flow MR imaging based on time-resolved 3D cine phase-contrast MR imaging techniques was recently used to evaluate the hemodynamics of cerebral aneurysms^20–24 and to identify the inflow zone of cerebral aneurysms.¹⁵ However, no previous studies have examined the correlation between the distribution of the inflow zone on the section plane corresponding to the aneurysm orifice and aneurysm morphology or the parent artery curvature in patient-specific imaging analysis, to our knowledge. Here we investigated the influence of morphologic factors or the parent artery curvature on the inflow zone location identified by using 4D flow MR imaging in unruptured sidewall ICA aneurysms.     

Rupture-Associated Changes of Cerebral Aneurysm Geometry: High-Resolution 3D Imaging before and after Rupture

BACKGROUND AND PURPOSE:Comparisons of geometric data of ruptured and unruptured aneurysms may yield risk factors for rupture. Data on changes of geometric measures associated with rupture are, however, sparse, because patients with ruptured aneurysms rarely have undergone previous imaging of the intracranial vasculature. We had the opportunity to assess 3D geometric differences of aneurysms before and after rupture. The purpose of this study was to evaluate possible differences between prerupture and postrupture imaging of a ruptured intracranial aneurysm.MATERIALS AND METHODS:Using high-quality 3D image data, we generated 3D geometric models before and after rupture and compared these for changes in aneurysm volume and displacement. A neuroradiologist qualitatively assessed aneurysm shape change, the presence of perianeurysmal hematoma, and subsequent mass effect exerted on aneurysm and parent vessels.RESULTS:Aneurysm volume was larger in the postrupture imaging in 7 of 9 aneurysms, with a median increase of 38% and an average increase of 137%. Three aneurysms had new lobulations on postrupture imaging; 2 other aneurysms were displaced up to 5 mm and had changed in geometry due to perianeurysmal hematoma.CONCLUSIONS:Geometric comparisons of aneurysms before and after rupture show a large volume increase, origination of lobulations, and displacement due to perianeurysmal hematoma. Geometric and hemodynamic comparison of series of unruptured and ruptured aneurysms in the search for rupture-risk-related factors should be interpreted with caution.

Unruptured intracranial aneurysms are found in approximately 3% of the population.¹ Once they are detected, the decision for preventive treatment has to be weighed against the risk of rupture, with inherent high case fatality and morbidity.² Prediction of rupture of intracranial aneurysms remains poor, with size as the most important risk factor. However, not all large aneurysms would rupture if left untreated; whereas small aneurysms, which are often left untreated, do sometimes rupture during follow-up. Better predictors are, therefore, needed. Intra-aneurysmal hemodynamic characteristics may have predictive value.^3,4Computational fluid dynamics have been applied to simulate hemodynamic flow patterns in the aneurysm and surrounding vessels to relate hemodynamic characteristics with aneurysmal rupture risk.^4,5 Several studies indeed found differences in flow patterns between ruptured and unruptured aneurysms.^3,4,6 However, if one compares ruptured with unruptured aneurysms, the potential changes of the aneurysm geometry before, during, or after rupture itself are neglected.The rupture of the aneurysm may result in shape changes of the aneurysm due to changes in the aneurysmal sac. These changes potentially alter the aneurysmal or perianeurysmal geometry and its related hemodynamic patterns. It is, therefore, pivotal to know whether changes before, during, or shortly after rupture of aneurysms in themselves affect aneurysm geometry and aneurysm hemodynamics; and if so, what these changes are. Such data are difficult to collect because high-quality images of intracranial aneurysms before and after rupture are rare. We had the opportunity to assess changes in aneurysm geometry associated with rupture in a series of 9 patients by using advanced image registration of high-quality 3D imaging data performed before and after rupture.     

Visual Outcomes with Flow-Diverter Stents Covering the Ophthalmic Artery for Treatment of Internal Carotid Artery Aneurysms

BACKGROUND AND PURPOSE:Flow-diverting stents can be used to treat intracranial aneurysms that are not amenable to treatment with coils. We analyzed ophthalmic consequences due to coverage of the origin of the ophthalmic artery by flow-diverting stents for the treatment of internal carotid artery aneurysms.MATERIALS AND METHODS:From April 2009 to April 2013, the clinical and angiographic outcomes of all 28 patients treated for aneurysms with flow-diverting stents covering the origin of the ophthalmic artery were prospectively collected. The origin of the ophthalmic artery in relation to the target aneurysm was classified by using a 4-type classification. A complete ophthalmic examination was performed by a single ophthalmologist 48 hours before and 1 week after covering the ophthalmic artery.RESULTS:Ophthalmic artery patency was normal at the end of endovascular treatment in 24/28 cases (85.7%). With extensive ophthalmic examinations, 11 patients (39.3%) showed new ophthalmic complications. Patients with the ophthalmic artery originating from the aneurysm sac were at high risk for retinal emboli (4/5, 80%). Patients with the ophthalmic artery originating from the inner curve of the carotid siphon were at high risk for optic nerve ischemic atrophy (3/4, 75%).CONCLUSIONS:This prospective study shows that covering the ophthalmic artery with a flow-diverting stent is not without potential complications. Ophthalmic complications can occur but are often not diagnosed. The anatomic disposition of the ophthalmic artery in relation to the carotid siphon and aneurysm should be clearly understood because some configurations have a higher risk. When not required, covering of the ophthalmic artery by flow-diverting stents should be avoided.

Flow-diverting stents (FDSs) are commonly used for the endovascular reconstruction of a segmentally diseased parent vessel and treatment of large-neck intracranial aneurysms, which can be difficult to reconstruct with coils, even when used with large-cell stents.^1–6 FDSs aim to maintain normal blood flow through parent and branch vessels while disrupting flow into the aneurysm, causing thrombosis, and eventually sealing the aneurysm ostium through neointimal proliferation across the device struts.^6–8 Good angiographic and clinical results have been achieved in small series.^4–6,9–12One issue concerning intracranial aneurysm treatment by an FDS is the patency of the perforating arteries and side branches covered by the device.¹³ FDSs are designed to provide sufficient coverage across the aneurysm neck to exclude the lesion from circulation but to be porous enough to preserve the patency of any branch vessels covered by the construct through the interstices between the device strands.¹³ The flow into the regional perforators and branch arteries is governed by different factors from those that drive flow into an aneurysm, and the patency of the perforators is maintained by a suction effect due to lower pressure in those branches.¹⁴ This has been studied with histologic evaluation of the Pipeline Embolization Device (PED; Covidien, Irvine, California) in rabbit aorta, demonstrating rounded funnel-like defects into the homogeneous sheet of neoendothelium on the FDS in regard to the orifices of the regional branches.¹⁵This pressure gradient may, however, be less important in vessels that have robust competitive collateral flow.¹⁵ This is most frequently seen when constructs are built over the ophthalmic artery, which occasionally becomes occluded when covered by multiple devices.⁸ In these situations, competitive collateral flow from the external carotid artery may create a “flow equalization point,” resulting in slow flow or proximal occlusion of the ophthalmic artery because of its retrograde supply from the external carotid artery circulation.^15,16 Recently, a study evaluated the patency rate of the ophthalmic artery with standard digital subtraction angiography and any change in angiographic flow in the artery immediately after FDS placement across the arterial inlet for the treatment of 20 proximal ICA aneurysms.¹⁷ This study assessed 21% of ophthalmic artery occlusions and 11% of ophthalmic arteries with slow antegrade flow. In this small, retrospective series, no visual worsening was observed in case of flow change in the ophthalmic artery, but only 5 patients had a detailed ophthalmic examination.¹⁷ Because small visual field amputations due to ischemic lesions can be easily underdiagnosed and they are often asymptomatic, it appears mandatory to explore ophthalmic disorders with a complete examination to identify even small deficits.In this study, we analyzed ophthalmic consequences due to coverage of the ophthalmic artery by the implantation of an FDS covering the origin of the ophthalmic artery for the treatment of terminal ICA aneurysms. This analysis focuses on the anatomy of the origin of the ophthalmic artery in relation to the target aneurysm.     

Increased Facet Fluid Predicts Dynamic Changes in the Dural Sac Size on Axial-Loaded MRI in Patients with Lumbar Spinal Canal Stenosis

BACKGROUND AND PURPOSE:Axial-loaded MR imaging, which simulates the spinal canal in a standing position, demonstrates reductions of the dural sac cross-sectional area in patients with lumbar spinal canal stenosis. However, there has been no useful conventional MR imaging finding for predicting a reduction in the dural sac cross-sectional area on axial-loaded MR imaging. Previous studies have shown that increased facet fluid is associated with the spinal instability detected during positional changes. The purpose of this study was to analyze the correlations between facet fluid and dynamic changes in the dural sac cross-sectional area on axial-loaded MR imaging.MATERIALS AND METHODS:In 93 patients with lumbar spinal canal stenosis, the dural sac cross-sectional area was measured by using axial images of conventional and axial-loaded MR imaging. Changes in the dural sac cross-sectional area induced by axial loading were calculated. The correlation between the facet fluid width measured on conventional MR imaging and the change in dural sac cross-sectional area was analyzed. The change in the dural sac cross-sectional area was compared between the intervertebral levels with and without the facet fluid width that was over the cutoff value determined in this study.RESULTS:The dural sac cross-sectional area was significantly smaller on axial-loaded MR imaging than on conventional MR imaging. The facet fluid width significantly correlated with the change in the dural sac cross-sectional area (r = 0.73, P < .001). The change in the dural sac cross-sectional area at the intervertebral level with the facet fluid width over the cutoff value was significantly greater than that at the other level.CONCLUSIONS:The increased facet fluid on conventional MR imaging is highly predictive of the dynamic reduction of dural sac cross-sectional area detected on axial-loaded MR imaging in the clinical assessment of lumbar spinal canal stenosis.

MR imaging is widely used for the clinical assessment of degenerative lumbar spinal diseases. In evaluating the severity of spinal canal narrowing, the dural sac cross-sectional area (DCSA) is frequently measured by using axial MR images.^1–6 However, conventional MR imaging is performed with the patient in the supine position, and the DCSA may be larger in this position than in the standing position.^3,4,7 Hence, conventional MR imaging carries a risk of underestimating the severity of spinal canal narrowing.^3,8Recently, the clinical usefulness of axial-loaded MR imaging for assessing patients with lumbar spinal canal stenosis (LSCS) has been reported.^3,4 With axial-loaded MR imaging, physiologically normal weight-bearing conditions in the upright position can be simulated by using a compression device with the patient in the supine position. Axial-loaded MR imaging may induce a significant reduction in the DCSA and potentially show additional imaging findings that cannot be acquired on conventional MR imaging.^3,4,6,8 The DCSA on axial-loaded MR imaging has been reported to correlate with the severity of clinical symptoms in patients with LSCS.⁹ Furthermore, previous studies have demonstrated that a dynamic decrease in the DCSA induced by axial loading increases the diagnostic specificity of spinal canal narrowing and influences the indications for surgical treatment.^4,8,10,11 Therefore, evaluating the degree of spinal canal narrowing on axial-loaded MR imaging is beneficial for achieving a more accurate diagnosis and selecting the optimal treatment. However, no reliable imaging findings on conventional MR imaging predict the dynamic reduction in the DCSA.Many previous studies have shown that the morphology of the facet joints is associated with the segmental motion and instability of the lumbar spine detected during positional changes in the patient.^12–15 Most interesting, recent studies have suggested that increased fluid signals in the facet joint on conventional MR images predict instability of the lumbar spine.^16–19 Therefore, in the present study, we hypothesized that increased facet fluid signals on conventional MR images may be correlated with significant changes in the DCSA on axial-loaded MR images because the lumbar spinal canal is more likely to be affected by axial loading if the lumbar spine is unstable.To the best of our knowledge, no previous studies have investigated the correlation between the facet fluid width and dynamic changes in the DCSA induced by axial loading. The purpose of this study was thus to analyze the correlation between the facet fluid width and dynamic changes in the DCSA detected by using axial-loaded MR imaging in patients with LSCS.     

Generalized versus Patient-Specific Inflow Boundary Conditions in Computational Fluid Dynamics Simulations of Cerebral Aneurysmal Hemodynamics

BACKGROUND AND PURPOSE:Attempts have been made to associate intracranial aneurysmal hemodynamics with aneurysm growth and rupture status. Hemodynamics in aneurysms is traditionally determined with computational fluid dynamics by using generalized inflow boundary conditions in a parent artery. Recently, patient-specific inflow boundary conditions are being implemented more frequently. Our purpose was to compare intracranial aneurysm hemodynamics based on generalized versus patient-specific inflow boundary conditions.MATERIALS AND METHODS:For 36 patients, geometric models of aneurysms were determined by using 3D rotational angiography. 2D phase-contrast MR imaging velocity measurements of the parent artery were performed. Computational fluid dynamics simulations were performed twice: once by using patient-specific phase-contrast MR imaging velocity profiles and once by using generalized Womersley profiles as inflow boundary conditions. Resulting mean and maximum wall shear stress and oscillatory shear index values were analyzed, and hemodynamic characteristics were qualitatively compared.RESULTS:Quantitative analysis showed statistically significant differences for mean and maximum wall shear stress values between both inflow boundary conditions (P < .001). Qualitative assessment of hemodynamic characteristics showed differences in 21 cases: high wall shear stress location (n = 8), deflection location (n = 3), lobulation wall shear stress (n = 12), and/or vortex and inflow jet stability (n = 9). The latter showed more instability for the generalized inflow boundary conditions in 7 of 9 patients.CONCLUSIONS:Using generalized and patient-specific inflow boundary conditions for computational fluid dynamics results in different wall shear stress magnitudes and hemodynamic characteristics. Generalized inflow boundary conditions result in more vortices and inflow jet instabilities. This study emphasizes the necessity of patient-specific inflow boundary conditions for calculation of hemodynamics in cerebral aneurysms by using computational fluid dynamics techniques.

It has been estimated that the prevalence of intracranial aneurysms in the adult population is between 1% and 5%.¹ Although most aneurysms go undetected, acute rupture resulting in subarachnoid hemorrhage is associated with high morbidity and fatality rates.^2,3 Ruptured aneurysms are treated by coiling or clipping to prevent rebleed. The indication for preventive treatment of unruptured aneurysms is, however, not straightforward.^4,5 The risk of treatment has to be carefully balanced against the risk of rupture. At present, rupture-risk assessment of unruptured intracranial aneurysms and the decision to treat or wait and scan are mainly based on size, location, and growth of the aneurysm.⁶ It is, however, clear that the predictive value of these characteristics is limited.^1,6–8 It is therefore crucial to search for additional and more predictive parameters for aneurysm rupture risk assessment.Aneurysmal hemodynamics, in particular wall shear stress (WSS) and vortex instability, have been proposed as additional risk factors for aneurysm growth and rupture.^9,10 It has been shown that the combination of vortex instability and high or low WSS within the aneurysm is more prevalent in ruptured cases.^11–13In many studies, computational fluid dynamics (CFD) is used to simulate aneurysmal hemodynamics. CFD is traditionally performed by using generalized inflow boundary conditions based on typical flow rates in a healthy adult.^14–27 Recently, several studies have replaced these generalized inflow boundary conditions by patient-specific velocity measurements in the vessels proximal to the aneurysm.^{10,12,28–32} In these studies, either 2D phase-contrast MR imaging (PC-MR imaging) or transcranial Doppler sonography was used to measure the flow. So far, only 3 studies have compared patient-specific with generalized inflow boundary conditions in a total of 14 aneurysms.^28–30 Evidently, the necessity of using patient-specific inflow boundary conditions has not been elucidated to the full extent. In this study, we assessed the effects of patient-specific inflow boundary conditions in a group of 36 patients.     

Reduction of Oxygen-Induced CSF Hyperintensity on FLAIR MR Images in Sedated Children: Usefulness of Magnetization-Prepared FLAIR Imaging

BACKGROUND AND PURPOSE:Oxygen-induced CSF hyperintensity on FLAIR MR imaging is often observed in sedated children. This phenomenon can mimic leptomeningeal pathology and lead to a misdiagnosis. The purpose of this study was to investigate whether magnetization-prepared FLAIR MR imaging can reduce oxygen-induced CSF hyperintensity and improve image quality compared with conventional (non-magnetization-prepared) FLAIR MR imaging.MATERIALS AND METHODS:Bloch simulation for magnetization-prepared and non-magnetization-prepared FLAIR sequences was performed for tissue contrast. We retrospectively reviewed 85 children with epilepsy who underwent MR imaging under general anesthesia with supplemental oxygen (41 with non-magnetization-prepared FLAIR and 44 with magnetization-prepared FLAIR). CSF hyperintensity was scored from 0 to 3 points according to the degree of CSF signal intensity and was compared between the 2 sequences. The contrast-to-noise ratios among GM, WM, and CSF were evaluated to assess general image quality from both sequences. To assess the diagnostic accuracy for hemorrhage, we reviewed an additional 25 patients with hemorrhage.RESULTS:Bloch simulation demonstrated that CSF hyperintensity can be reduced on magnetization-prepared FLAIR compared with non-magnetization-prepared FLAIR. CSF hyperintensity scores were significantly lower in magnetization-prepared FLAIR than in non-magnetization-prepared FLAIR (P < .01). The contrast-to-noise ratios for GM-WM, GM-CSF, and WM-CSF were significantly higher in magnetization-prepared FLAIR than in non-magnetization-prepared FLAIR (P < .05). Hemorrhage was clearly demarcated from CSF hyperintensity in the magnetization-prepared group (100%, 12/12) and non-magnetization-prepared group (38%, 5/13).CONCLUSIONS:Magnetization-prepared 3D-FLAIR MR imaging can significantly reduce oxygen-induced CSF artifacts and increase the tissue contrast-to-noise ratio beyond the levels achieved with conventional non-magnetization-prepared 3D-FLAIR MR imaging.

MR imaging is the diagnostic tool of choice in pediatric neurologic diseases because it has no ionizing radiation and is noninvasive. However, sedation is unavoidable if suitable MR images are sought because pediatric patients usually do not cooperate during long-duration scans.CSF hyperintensity on FLAIR MR images is frequently encountered in sedated children.^1–5 These artifacts cause a diagnostic dilemma because they can mimic hemorrhage, infection, and leptomeningeal seeding metastasis, which are all known to generate hyperintense CSF signals on FLAIR MR images.^6–9 Initially, CSF hyperintensity was attributed to anesthetic-induced T1-shortening, protein redistribution due to changes in the intravascular membrane permeability, hyperdynamic CSF pulsation due to altered vascular tone, and supplemental oxygen during anesthesia.^2–4,10 However, several studies have revealed that the most plausible cause of hyperintense CSF artifacts in FLAIR imaging is the administration of supplemental oxygen during anesthesia.^1,2,4,5,10Oxygen is a weak paramagnetic substance, which has 2 unpaired electrons that can cause a moderate increase in the T1 relaxation rate.^11,12 Studies have shown that the diffusional transfer of oxygen from blood to CSF and a consequent FLAIR MR signal increase depend on the inhaled oxygen concentration^1,2,4,13 and oxygen delivery methods.^3,103D-FLAIR imaging is based on the 3D TSE imaging technique that modulates a refocusing flip angle at the TSE echo-train to maintain relatively steady signal levels during a long train of echo signals, which can provide improved image sharpness, helpful in detecting small structures. Consequently, the relaxation-induced image blurring, partial volume effect, and specific absorption rate can be reduced allowing high-resolution 3D data acquisition at isotropic voxels during clinically feasible scan durations.¹⁴ 3D-FLAIR also provides increased SNR and reduces CSF pulsation artifacts compared with 2D FLAIR.^5,15–18 In magnetization-prepared (MP) 3D-FLAIR imaging, a dedicated magnetization preparation is implemented before typical inversion recovery, followed by TSE imaging, which is known to reduce unwanted T1-weighting and image TR.^19,20 Therefore, the purpose of this study was to compare magnetization-prepared 3D-FLAIR imaging with conventional (non-MP) 3D-FLAIR imaging in terms of the ability to reduce oxygen-induced CSF hyperintensity and improve image quality in sedated pediatric patients.     

Temporal evolution of susceptibility artifacts from coiled aneurysms on MR angiography: an in vivo canine study

BACKGROUND AND PURPOSE:Intracranial aneurysms treated by coiling have a risk for recurrence, requiring surveillance imaging. MRA has emerged as an attractive technique for postcoiling aneurysm imaging. Previous research has evaluated MR imaging artifacts of the coil mass in vitro. Our aim in this study was to evaluate MR imaging artifacts of coiled aneurysms in vivo with time.MATERIALS AND METHODS:Four sidewall aneurysms were created in each of 4 dogs. Aneurysms were embolized receiving only 1 type of coils. After embolization, the animals were transferred to MR imaging, which included axial 3D TOF MRA (TEs, 3.5, 5, and 6.9 ms), phase-contrast MRA, and coronal CE-MRA. MR imaging studies were repeated at 1, 4, 6, 8, 14, and 28 weeks. We calculated an OEF: OEF = V_A/V_CM, where the numerator represents the volume of the MR imaging artifacts and the denominator is the true volume of the coil mass measured by 3D RA.RESULTS:OEFs were largest immediately after embolization and showed a gradual decay until approximately 4 weeks, when there was stabilization of the size of the artifacts. By 4 weeks, there was mild coil compaction (average coil mass volume decrease of 7.8%); however, the OEFs decreased by 25% after 4 weeks (P < .001).CONCLUSIONS:MR imaging susceptibility artifacts change with time, being maximal in the postembolization setting and decaying until 4 weeks. The clinical implications of this study are that baseline MRA for comparison with future imaging should be acquired at a minimum of 1 week after the procedure.

Endovascular procedures are increasingly being used for the treatment of intracranial aneurysms. In this setting, coiling has evolved with new devices and technologies achieving better outcomes.¹ Nevertheless, recurrence due to coil compaction and/or aneurysm regrowth still remains a limitation of the method, and long-term imaging follow-up is a requirement.^2–5DSA is an invasive procedure that involves risks for permanent neurologic deficits ranging from 0% to 5.7%^6–8 and also exposure to ionizing radiation, which has been recently regarded with increasing concern, especially in this subset of patients who receive high doses from diagnostic work-up and treatment procedures.⁹ CTA is very effective in detecting aneurysms; however, the beam-hardening and streak artifacts limit its use as a posttreatment imaging method.¹⁰ Recently, MRA has become a viable option for noninvasive follow-up. 3D-TOF and CE-MRA offer a noninvasive high-resolution alternative to DSA for postembolization surveillance due to its high flow sensitivity and lack of ionizing radiation. Other advantages include comfort, convenience for the patient, and cost reduction.^10–13 Often, a baseline MRA within 1 week of coiling is acquired for future comparison. This timeframe is presumably based on the hospital admission of the patient.With MR imaging, it is possible to obtain information on aneurysm residual patency or recanalization and parent vessel abnormalities. The coil mass produces magnetic susceptibility or blooming artifacts that can obscure visualization of these parameters and subsequent interpretation. Shorter TE techniques can be used to reduce susceptibility-induced signal-intensity loss from the coil mass.^14,15 Previous research into MR imaging artifacts has been conducted mostly in vitro,^16–19 but the dynamic characteristics of a functional vascular system cannot be fully simulated. Plastic or vascular replicas have little MR imaging signal intensity compared with the arterial wall. Most important, the signal intensity from the aneurysm healing process—the acute thrombosis and thrombus organization—are not evaluated. Therefore, implantation and imaging of these devices in animal models are desirable. Our aim in this study was to evaluate the MR imaging artifacts of the coiled aneurysms in an animal model in different MRA sequences, with time.     

Identification of the Inflow Zone of Unruptured Cerebral Aneurysms: Comparison of 4D Flow MRI and 3D TOF MRA Data

BACKGROUND AND PURPOSE:The hemodynamics of the inflow zone of cerebral aneurysms may be a key factor in coil compaction and recanalization after endovascular coil embolization. We performed 4D flow MR imaging in conjunction with 3D TOF MRA and compared their ability to identify the inflow zone of unruptured cerebral aneurysms.MATERIALS AND METHODS:This series comprised 50 unruptured saccular cerebral aneurysms in 44 patients. Transluminal color-coded 3D MRA images were created by selecting the signal-intensity ranges on 3D TOF MRA images that corresponded with both the luminal margin and the putative inflow.RESULTS:4D flow MR imaging demonstrated the inflow zone and yielded inflow velocity profiles for all 50 aneurysms. In 18 of 24 lateral-projection aneurysms (75%), the inflow zone was located distally on the aneurysmal neck. The maximum inflow velocity ranged from 285 to 922 mm/s. On 4D flow MR imaging and transluminal color-coded 3D MRA studies, the inflow zone of 32 aneurysms (64%) was at a similar location. In 91% of aneurysms whose neck section plane angle was <30° with respect to the imaging section direction on 3D TOF MRA, depiction of the inflow zone was similar on transluminal color-coded 3D MRA and 4D flow MR images.CONCLUSIONS:4D flow MR imaging can demonstrate the inflow zone and provide inflow velocity profiles. In aneurysms whose angle of the neck-section plane is obtuse vis-a-vis the imaging section on 3D TOF MRA scans, transluminal color-coded 3D MRA may depict the inflow zone reliably.

Although endovascular coil embolization has become a major tactic to address cerebral aneurysms, recanalization or recurrence, which may result in rebleeding, are important problems. Recanalization was reported in 6.1%–39.8% of patients who had undergone endovascular treatment,^1–6 and a meta-analysis found that 20.8% of treated aneurysms recurred.³ The rate of rerupture after endovascular treatment for ruptured aneurysms has ranged from 0.11% to 5.3%,^1,4,6 and the rupture rate in the first year after coil embolization was reported as 2.5%⁷ and 2.2%.⁸ Because hemodynamics acting on the aneurysmal inflow zone may play a key role in the development of coil compaction or recanalization after endovascular coil embolization, the aneurysmal inflow zone must be packed densely to preserve the durability of aneurysm obliteration and to prevent rerupture.^9–15The inflow through the aneurysmal neck into the dome can be seen on 3D TOF MRA images.^13,16,17 Satoh et al,^16,17 who used conventional 3D TOF MRA techniques to select threshold ranges based on the signal intensity of the volume-rendering data, determined the spatial signal-intensity distribution in aneurysms. They developed transluminal color-coded 3D MRA (TC 3D MRA) to improve visualization of the aneurysmal inflow. More recently, 4D flow MR imaging based on time-resolved 3D cine phase-contrast MR imaging techniques was used to evaluate the hemodynamics of cerebral aneurysms.^18–27 However, 4D flow MR imaging requires additional time for data acquisition, and TC 3D MRA may be a convenient alternative to 4D flow MR imaging for identifying the aneurysmal inflow zone.Here, we compared the ability of 4D flow MR imaging and TC 3D MRA to identify the inflow zone of cerebral aneurysms.     

Silk Flow-Diverter Stent for the Treatment of Intracranial Aneurysms: A Series of 58 Patients with Emphasis on Long-Term Results

BACKGROUND AND PURPOSE:The Silk flow-diverter stent is increasingly used to treat complex intracranial aneurysms including wide-neck, fusiform aneurysms. Sparse data are available concerning long-term results of this technique. We report our 5-year experience with Silk stent treatment of intracranial aneurysms.MATERIALS AND METHODS:A retrospective review of our prospectively maintained database identified all patients treated by the Silk stent in 2 institutions. Clinical charts, procedural data, and angiographic results were reviewed.RESULTS:Between July 2009 and May 2014, we identified 58 patients with 70 intracranial aneurysms. Endovascular treatment was successful in 93% of patients with 32 treated with the first-generation Silk stent and 26 with the new Silk+ stent. Mean follow-up in 47 patients was 22 months. Despite an 11% delayed complication rate, overall permanent neurologic morbidity was 5.5%. All complications were seen with the first-generation Silk stent. There was no procedure-related mortality. Long-term anatomic results showed 73% with complete occlusion, 16% with neck remnants, and 11% with incomplete occlusion. No recanalization or retreatment was performed. The midterm intrastent stenosis rate was 57%, of which 60% improved or disappeared, 28% were stable, and 12% led to vessel occlusion. Seventy-four percent of stenosis and all vessel occlusions occurred with the first-generation Silk stent.CONCLUSIONS:Endovascular treatment of complex intracranial aneurysms with the Silk stent is an effective therapeutic option. Despite a high rate of delayed complications with the first-generation stents, the current Silk+ stent appears safer. This treatment achieves a high rate of adequate and stable occlusion at long-term follow-up.

Endovascular treatment is now the first-intention treatment for both ruptured and unruptured intracranial aneurysms.^1–4 However, endovascular treatment of complex intracranial aneurysms (wide-neck and fusiform) remains technically challenging. On the other hand, aneurysm coil recanalization is an important issue in endovascular therapy, with approximately 20% of coiled aneurysms recanalized and 10% retreated.⁵ As previously shown, wide-neck aneurysms are highly prone to recanalization.⁶These relative limitations of standard coiling have contributed to the development of new endovascular approaches, including balloon-assisted coiling, stent-assisted coiling, flow diversion, and flow disruption. Flow-diverter stents have been developed, and they offer the potential of aneurysm occlusion related to flow disruption. Recently, several flow-diverter stents, such as the Silk flow diverter (Balt Extrusion, Montmorency, France), have been released, and short- and midterm results have been published.^7–15 Notwithstanding the early promise of these devices, important shortcomings have been reported. First, delayed complications, either hemorrhagic or thromboembolic, are not uncommon; second, the flow-diverter stent tolerance might be considered poor because of the relatively high rates of intrastent stenosis and parent artery occlusion (PAO) during follow-up.^7–15 To the best of our knowledge, sparse data are available about the long-term results of this technique, including stability of aneurysm occlusion and stent tolerance. These data are mandatory to define the place of flow-diverter stents in the therapeutic armamentarium of intracranial aneurysms. Therefore, the aim of our study was to report our 5-year experience with Silk stent treatment of intracranial aneurysms with an emphasis on long-term results.     

Correlation of Prenatal and Postnatal MRI Findings in Schizencephaly

BACKGROUND AND PURPOSE:Schizencephaly is a rare malformation of the brain characterized by a gray matter–lined defect extending from the pial surface to the lateral ventricles. The purpose of this study was to correlate imaging findings of schizencephaly and associated anomalies on fetal and postnatal MR imaging and assess possible changes that may occur from the prenatal-to-postnatal state.MATERIALS AND METHODS:A retrospective review of subjects with schizencephaly who had both pre- and postnatal MR imaging was performed. Subject age, cleft type, number, location, and features of the defects and associated anomalies were recorded. Normalized dimensions of the defect and ipsilateral ventricle were measured and correlated to changes in the clefts between pre- and postnatal imaging.RESULTS:Ten subjects with 18 clefts (8 bilateral) were included. Most defects (83%) were open on prenatal MR imaging, but 47% of those were found to have subsequently closed on postnatal imaging. Evidence of prior hemorrhage was seen in 83%. Prenatal MR imaging detected all cases of an absent septum pellucidum but detected a fraction of gross polymicrogyria and missed all cases of optic nerve hypoplasia. The normalized ipsilateral ventricular and inner and middle width dimensions of the defects were significantly decreased at postnatal imaging (P < .05). The widths of the defects, ventricular width, and presence of hemorrhage were not predictors of closure of prenatally diagnosed open defects (P > .05).CONCLUSIONS:In our series, nearly half of prenatally open schizencephaly defects had closed on postnatal imaging. Prenatal MR imaging was only able to demonstrate some of the associated anomalies.

Schizencephaly is a rare malformation of the central nervous system characterized by a gray matter–lined defect extending from the pial surface to the lateral ventricles. The etiology of schizencephaly is poorly understood; however, it appears to be heterogeneous.^1–3 The presence of gray matter lining the defects, distinguishing schizencephaly from porencephaly, is usually ascribed to the damage to the radial glial cell fibers or to the molecules that promote neuronal migration and timing during pregnancy.^2,4 Despite early reports of the association of schizencephaly and mutations of the EMX2 homeobox gene,⁵ this association has not been verified in further studies.⁶ The common pathophysiology of injury is frequently ascribed to a vascular disruption, hypoxia-ischemia, and/or prenatal infection at critical time points during neuronal development,^1–3 though there are some reports favoring schizencephaly as a developmental disorder.^7–9Classically, schizencephaly has been divided into “closed” or “closed-lip” defects, in which the walls appose one another within the defect, and “open” or “open-lip” defects, in which CSF fills the defect all the way from the lateral ventricle to the overlying subarachnoid space.¹⁰ Open lesions have been further subclassified as small or large according to size of the defect.¹⁰ These classifications have prognostic significance because it has been shown that a small, unilateral closed defect without involvement of the motor cortex can be associated with seizures but otherwise normal development.¹⁰ The prognosis is poorer with open and bilateral defects.^2,10,11 Associated anomalies, such as optic nerve hypoplasia, absence of the septum pellucidum, and other migrational abnormalities, will also adversely affect the prognosis.^2,9,12,13MR imaging was reported to prenatally diagnose schizencephaly as early as 1989.¹⁴ On the basis of the current literature, the imaging appearance of schizencephaly on fetal MR imaging is considered identical to that in postnatal MR imaging.² The purpose of this study was to correlate imaging findings of schizencephaly and associated anomalies on fetal and postnatal MR imaging and to assess the possible changes that may occur from the prenatal-to-postnatal state on MR imaging.     

In Vitro Evaluation of Intra-Aneurysmal,Flow-Diverter-Induced Thrombus Formation: A Feasibility Study

BACKGROUND AND PURPOSE:Intracranial aneurysm treatment by flow diverters aims at triggering intra-aneurysmal thrombosis. By combining in vitro blood experiments with particle imaging velocimetry measurements, we investigated the time-resolved thrombus formation triggered by flow diverters.MATERIALS AND METHODS:Two test setups were built, 1 for particle imaging velocimetry and 1 for blood experiments, both generating the same pulsatile flow and including a silicone aneurysm model. Tests without flow diverters and with 2 different flow-diverter sizes (diameter: 4.5 and 4.0 mm) were performed. In the blood experiments, the intra-aneurysmal flow was monitored by using Doppler sonography. The experiments were stopped at 3 different changes of the spatial extent of the signal.RESULTS:No thrombus was detected in the aneurysm model without the flow diverter. Otherwise, thrombi were observed in all aneurysm models with flow diverters. The thrombi grew from the proximal side of the aneurysm neck with fibrin threads connected to the flow diverter and extending across the aneurysm. The thrombus resulting from the 4.0-mm flow diverter grew along the aneurysm wall as a solid and organized thrombus, which correlates with the slower velocities near the wall detected by particle imaging velocimetry. The thrombus that evolved by using the 4.5-mm flow diverter showed no identifiable growing direction. The entire thrombus presumably resulted from stagnation of blood and correlates with the central vortex detected by particle imaging velocimetry.CONCLUSIONS:We showed the feasibility of in vitro investigation of time-resolved thrombus formation in the presence of flow diverters.

Intracranial aneurysm treatment by flow diverters (FDs) aims at blood clotting in the aneurysm, triggered by the reduction or elimination of intra-aneurysmal blood flow. This therapeutic approach offers an alternative treatment for larger wide-neck aneurysms, in which coil embolization is associated with high recurrence.^1,2 Otherwise, a longer delay to complete intra-aneurysmal thrombosis and documented cases of postprocedural bleeding^3–5 suggest that the FD-driven mechanism of thrombus formation is considerably different from that using coils. In previous studies, it has been hypothesized that aneurysm rupture occurring in patients after treatment with FDs is a consequence of uncontrolled flow-driven clot formation resulting in thrombus-associated autolysis⁴ or mural destabilization of the aneurysm wall due to thrombus evolution.⁶The influence of FDs on hemodynamic properties was investigated in several in vitro experiments by particle imaging velocimetry (PIV). Especially, the influence of the geometry of the aneurysm,^7,8 the stent porosity,^7,9–12 the number of stents, and the stent material^8,13 on intra-aneurysmal velocity fields was extensively studied. All investigations were performed with water-glycerol mixtures as a blood analog fluid. The use of a transparent fluid is inevitable because PIV is an optical method, but it forestalls the possibility of investigate clotting effects. Therefore, because the thrombus-growing process influences the flow behavior, PIV investigations only represent the flow conditions directly after the insertion of FDs.The goal of our study was the in vitro investigation of time-resolved formation of thrombi triggered by FDs. Although biologic mechanisms, triggered by the aneurysm wall, are not depicted in the new in vitro model, the location and shape of thrombus during the forming and growing process, as well as the composition of the thrombus, were investigated for 2 different FD configurations. Moreover, we correlated the results with PIV measurements.     

Associations between Cerebral Embolism and Carotid Intraplaque Hemorrhage during Protected Carotid Artery Stenting

BACKGROUND AND PURPOSE:Carotid artery stent placement in patients with intraplaque hemorrhage remains controversial because of the incidence of cerebral embolism after the procedure. The purpose of this study is to determine if intraplaque hemorrhage is a significant risk factor for cerebral embolism during carotid artery stent placement.MATERIALS AND METHODS:This prospective study assessed 94 consecutive patients with severe carotid stenosis. These patients underwent preprocedural carotid MR imaging and postprocedural DWI after carotid artery stent placement. Intraplaque hemorrhage was defined as the presence of high signal intensity within the carotid plaque that was >200% of the signal from the adjacent muscle on MPRAGE. We then analyzed the incidence of postprocedural ipsilateral ischemic events on DWI and primary outcomes within 30 days of carotid artery stent placement.RESULTS:Forty-three patients (45.7%) had intraplaque hemorrhage on an MPRAGE image. There was no significant difference in the incidence of postprocedural ipsilateral ischemic events and primary outcomes between the intraplaque hemorrhage and non–intraplaque hemorrhage group. However, postprocedural ipsilateral ischemic events were more frequently observed in the symptomatic group (17/41 [41.5%]) than in the asymptomatic group (8/53 [15.1%]; P = .005).CONCLUSIONS:Intraplaque hemorrhage was not a significant risk factor for cerebral embolism during carotid artery stent placement in patients with severe carotid stenosis. Symptomatic patients should receive more careful treatment during carotid artery stent placement because of the higher risk of postprocedural ipsilateral ischemic events.

Extracranial carotid artery stenosis is considered a causative factor in 20%–30% of all strokes.^1–3 Large randomized clinical trials showed that carotid endarterectomy is superior to carotid artery stent placement (CAS) for the management of carotid artery stenosis.^4–6 Other randomized clinical trials showed that CAS and carotid endarterectomy offer similar efficacy.⁷ Although indications for CAS remain controversial, CAS has emerged as a less-invasive treatment that requires shorter hospital times than carotid endarterectomy.Some studies found a relationship between the baseline presence of carotid intraplaque hemorrhage (IPH) and the development of ischemic stroke in previously asymptomatic and symptomatic patients.^8–10 IPH is associated with plaque progression and, consequently, induces luminal narrowing. Thus, IPH may serve as a measure of risk for the development of future ischemic stroke. The risk of cerebral embolism after CAS in patients with IPH is controversial. Yoshimura et al¹¹ reported that a high-intensity signal on TOF MRA indicates that carotid plaques are at high risk for cerebral embolism during stent placement. However, Yoon et al¹² reported that protected CAS seems to be safe in patients with severe carotid stenosis and IPH. This study did not perform DWI to evaluate ipsilateral ischemic lesions. In addition, these studies used TOF imaging to detect IPH. Alternative techniques proposed for more accurate detection of IPH include heavily T1-weighted techniques, such as the MPRAGE sequence. Ota et al¹³ reported that the MPRAGE sequence demonstrated higher diagnostic capability in detecting IPH when compared with conventional T1-weighted sequences or TOF sequences.We prospectively designed the study with the following inclusion criteria: 1) preoperative multicontrast carotid plaque MR; 2) protected CAS; 3) postprocedural imaging, including DWI and noncontrast CT within 24 hours; and 4) clinical outcomes after 30 days. The aim of this study was to determine whether IPH is a significant risk factor for cerebral embolism during CAS.     

Intraplaque Hemorrhage and the Plaque Surface in Carotid Atherosclerosis: The Plaque At RISK Study (PARISK)

BACKGROUND AND PURPOSE:An important characteristic of vulnerable plaque, intraplaque hemorrhage, may predict plaque rupture. Plaque rupture can be visible on noninvasive imaging as a disruption of the plaque surface. We investigated the association between intraplaque hemorrhage and disruption of the plaque surface.MATERIALS AND METHODS:We selected the first 100 patients of the Plaque At RISK study, an ongoing prospective noninvasive plaque imaging study in patients with mild-to-moderate atherosclerotic lesions in the carotid artery. In carotid artery plaques, disruption of the plaque surface (defined as ulcerated plaques and/or fissured fibrous cap) and intraplaque hemorrhage were assessed by using MDCTA and 3T MR imaging, respectively. We used a χ² test and multivariable logistic regression to assess the association between intraplaque hemorrhage and disrupted plaque surface.RESULTS:One hundred forty-nine carotid arteries in 78 patients could be used for the current analyses. Intraplaque hemorrhage and plaque ulcerations were more prevalent in symptomatic compared with contralateral vessels (hemorrhage, 38% versus 11%; P < .001; and ulcerations, 27% versus 7%; P = .001). Fissured fibrous cap was more prevalent in symptomatic compared with contralateral vessels (13% versus 4%; P = .06). After adjustment for age, sex, diabetes mellitus, and degree of stenosis, intraplaque hemorrhage was associated with disrupted plaque surface (OR, 3.13; 95% CI, 1.25–7.84) in all vessels.CONCLUSIONS:Intraplaque hemorrhage is associated with disruption of the plaque surface in patients with a carotid artery stenosis of <70%. Serial studies are needed to investigate whether intraplaque hemorrhage indeed increases the risk of plaque rupture and subsequent ischemic stroke during follow-up.

The need to identify patients with mild-to-moderate carotid artery stenosis and an increased stroke risk who might benefit from surgical treatment has shifted research interest from assessment of the degree of carotid stenosis to assessment of vulnerable plaque characteristics.¹ Vulnerable plaques are atherosclerotic plaques more prone to rupture and are associated with a higher risk for thromboembolism and ischemic stroke.^2,3 Intraplaque hemorrhage is an important characteristic of the vulnerable plaque.⁴ Prevalence of intraplaque hemorrhage has been shown to be higher in symptomatic than in asymptomatic lesions.⁵ Moreover, the presence of intraplaque hemorrhage in carotid artery disease is associated with an increased risk of cerebral ischemic events.^6–8The pathophysiologic mechanism leading to intraplaque hemorrhage is a topic of debate. However, a common viewpoint is that small leaky neovessels in the atherosclerotic plaques are a likely source of intraplaque hemorrhage.^5,9,10 The presence of intraplaque hemorrhage is thought to initiate several biologic processes like phagocytosis and local inflammation, leading to the release of proteolytic enzymes, deposition of free cholesterol and subsequently plaque growth, plaque destabilization, and possible plaque rupture.^5,9–12 Plaque rupture can be visible on imaging as a disruption of the atherosclerotic plaque surface (plaque ulceration and/or a fissured fibrous cap).^13,14 A previous study reported that plaque ulceration on CTA was useful for the prediction of intraplaque hemorrhage on MR imaging in a broad group of symptomatic patients referred for carotid artery imaging.¹⁵ Ulcerated plaques themselves are independently associated with an increased risk of ipsilateral ischemic events as well.^16,17The aim of the current study was to investigate the association between intraplaque hemorrhage, as assessed on MR imaging, and disruption of the plaque surface, assessed on MDCTA, in symptomatic patients with a carotid artery stenosis of <70%.     

Double Inversion Recovery MR Sequence for the Detection of Subacute Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE:The diagnosis of subacute subarachnoid hemorrhage is important because rebleeding may occur with subsequent life-threatening hemorrhage. Our aim was to determine the sensitivity of the 3D double inversion recovery sequence compared with CT, 2D and 3D FLAIR, 2D T2*, and 3D SWI sequences for the detection of subacute SAH.MATERIALS AND METHODS:This prospective study included 25 patients with a CT-proved acute SAH. Brain imaging was repeated between days 14 and 16 (mean, 14.75 days) after clinical onset and included MR imaging (2D and 3D FLAIR, 2D T2*, SWI, and 3D double inversion recovery) after CT (median delay, 3 hours; range, 2–5 hours). A control group of 20 healthy volunteers was used for comparison. MR images and CT scans were analyzed independently in a randomized order by 3 blinded readers. For each subject, the presence or absence of hemorrhage was assessed in 4 subarachnoid areas (basal cisterns, Sylvian fissures, interhemispheric fissure, and convexity) and in brain ventricles. The diagnosis of subacute SAH was defined by the presence of at least 1 subarachnoid area with hemorrhage.RESULTS:For the diagnosis of subacute SAH, the double inversion recovery sequence had a higher sensitivity compared with CT (P < .001), 2D FLAIR (P = .005), T2* (P = .02), SWI, and 3D FLAIR (P = .03) sequences. Hemorrhage was present for all patients in the interhemispheric fissure on double inversion recovery images, while no signal abnormality was noted in healthy volunteers. Interobserver agreement was excellent with double inversion recovery.CONCLUSIONS:Our study showed that the double inversion recovery sequence has a higher sensitivity for the detection of subacute SAH than CT, 2D or 3D FLAIR, 2D T2*, and SWI.

Nontraumatic subarachnoid hemorrhage accounts for 3% of all strokes, and 85% are related to a ruptured intracranial aneurysm.¹ CT is highly sensitive for the diagnosis of SAH at the acute stage.² However, clinical symptoms may be atypical and result in delayed admission. In such patients, the diagnosis of subacute SAH is important because rebleeding may occur with subsequent life-threatening intracranial hemorrhage.³When performed several days after symptom onset, CT does not appear reliable for the diagnosis of SAH^4,5 and is outperformed by brain MR imaging in this setting.⁶ Indeed, FLAIR MR imaging is more sensitive than CT for SAH detection at both acute^7–9 and subacute¹⁰ stages. 3D FLAIR is even more specific than 2D FLAIR by reducing flow-related artifacts, which are known to provide false-positive findings on 2D FLAIR.¹¹ Nevertheless, SAH can still be misdiagnosed by using FLAIR imaging due to the time interval after onset¹² or artifacts.^13,14 T2* gradient-echo sequences are useful for subacute or chronic SAH depiction.^6,15,16 Susceptibility-weighted imaging uses tissue magnetic-susceptibility differences to generate a unique contrast, based on a 3D flow-compensated gradient-echo sequence.¹⁷ Previous studies have suggested that SWI could accurately detect small amounts of SAH and intraventricular hemorrhage (IVH).^18–20 A recent study focusing on the detection of microbleeds also demonstrated that SWI had a greater sensitivity for blood products than the conventional T2* sequence.²¹ However, no study available compares the diagnostic performance of T2* and SWI for the detection of spontaneous SAH, to our knowledge.Double inversion recovery (DIR) MR imaging is useful for the detection of cortical lesions.^22–24 This technique is based on a 3D turbo spin-echo acquisition with variable refocusing flip angles (BrainView, Philips Healthcare, Best, the Netherlands; Cube, GE Healthcare, Milwaukee, Wisconsin; SPACE, Siemens, Erlangen, Germany). DIR includes 2 inversion recovery pulses designed for the suppression of both CSF and normal white matter.²⁴ Data are still not available on the value of 3D DIR for the detection of SAH. The purpose of our study was to determine the sensitivity of the 3D DIR sequence compared with CT, 2D and 3D FLAIR, 2D T2*, and 3D SWI sequences for the detection of subacute SAH.