Clinical implications and radiographic characteristics of the relation between giant intracranial aneurysms of the posterior circulation and the brainstem.

BACKGROUND: Giant intracranial aneurysms of the posterior circulation (GPCirA) are rare entities compressing the brainstem and adjacent structures. Previous evidence has shown that the amount of brainstem shift away from the cranial base is not associated with neurological deficits. This raises the question whether other factors may be associated with neurological deficits. METHODS: All data were extracted from the Giant Intracranial Aneurysm Registry, an international multicenter prospective study on giant intracranial aneurysms. We grouped GPCirA according to the mass effect on the brainstem (lateral versus medial). Brainstem compression was evaluated with two indices: (a) brainstem compression ratio (BCR) or diameter of the compressed brainstem to the assumed normal diameter of the brainstem and (b) aneurysm to brainstem ratio (ABR) or diameter of the aneurysm to the diameter of the compressed brainstem. We examined associations between neurological deficits and GPCirA characteristics using binary regression analysis. RESULTS: Twenty-eight GPCirA were included. Twenty GPCirA showed medial (71.4%) and 8 lateral compression of the brainstem (28.6%). Baseline characteristics did not differ between the groups for patient age, aneurysm diameter, aneurysm volume, modified Rankin Scale (mRS), motor deficit (MD), or cranial nerve deficits (CND). Mean BCR was 53.0 in the medial and 54.0 in the lateral group (p = 0.92). The mean ABR was 2.9 in the medial and 2.3 in the lateral group (p = 0.96). In the entire cohort, neither BCR nor ABR nor GPCirA volumes were associated with the occurrence of CND or MD. In contrast, disability (mRS) was significantly associated with ABR (OR 1.94 (95% CI 1.01-3.70; p = 0.045) and GPCirA volumes (OR 1.21 (95% CI 1.01-1.44); p = 0.035), but not with BCR. CONCLUSION: In this cohort of patients with GPCirA, neither the degree of lateral projection nor the amount of brainstem compression predicted neurological deficits. Disability was associated only with aneurysm volume. When designing treatment strategies for GPCirA, aneurysm laterality or the amount of brainstem compression should be viewed as less relevant while the high risk of rupture of such giant lesions should be emphasized. TRIAL REGISTRATION: The registry is listed at clinicaltrials.gov under the registration no. NCT02066493.

Brain herniations into arachnoid granulations: about 68 cases in 38 patients and review of the literature.

INTRODUCTION: Brain herniations (BH) into arachnoid granulations (AG) in dural venous sinuses and calvarium have rarely been reported in the literature. METHODS: MRIs of 38 patients with BH into AG (BHAG) were retrospectively analyzed. Locations of BHAG, gyrus/lobe of the herniated brain, parenchymal abnormalities of the BH, and clinical and radiological conditions with raised intracranial pressure were recorded. RESULTS: Sixty-eight BHAG were found, by order of frequency, in the occipital squama (OS), transverse sinus (TS), lateral lacuna of the superior sagittal sinus (LLSSS), and straight sinus (SS), with cerebellar tissue being the most frequently involved in BHAG (94.5 % of OS, 55 % of TS, 100 % SS BHAG). Multiple BHAG were found in 58 % of the patients (up to five per patient). Parenchymal signal and structural changes (SSCG) were observed in 46 % of BHAG (100 % were cerebellar). Three patients had pseudotumor cerebri (PTCS); one patient had only MRI signs of PTCS. Twenty-one percent of patients had intracranial conditions susceptible of increasing cerebrospinal fluid (CSF) pressure other than PTCS. CONCLUSIONS: BHAG occurred in the OS, TS, LLSSS, and the SS. SSCG of the herniated cerebellum were frequent and possibly result from tethering/strangulation in the AG. No symptoms could be clearly attributed to BHAG, though in three cases of PTCS, TS BHAG could have contributed to sustaining the raised CSF pressure. Various factors are probably involved in the development of BHAG including normal pia-arachnoid bridges between the brain surface and the AG, hydrodynamic constrains on the brain and AG, and, in some cases, increased intracranial pressure.

Changes in volume of giant intracranial aneurysms treated by surgical strategies other than direct clipping.

BACKGROUND: Giant intracranial aneurysms (GIA) are often not eligible for direct clip occlusion. Surgical alternatives include partial clip occlusion or the placement of a cerebrovascular bypass or the combination of both. These alternative indirect strategies are expected to lead to a decrease in GIA volume over time rather than instantaneously. To examine whether this is the case, we analyzed follow-up imaging results 1 year after surgery. METHODS: We retrospectively screened the prospective GIA Registry's imaging database for anterior circulation GIA treated by surgical strategies other than direct clipping. We measured pre- and 1-year post-treatment GIA volume, lateral ventricle volume (LVV), and mid-line shift (MLS) in 19 cases. RESULTS: After a mean follow-up of 466 days (standard deviation ±171) GIA volumes decreased from 9.6 cm(3) (interquartile range (IQR) 6.1-14.1) to 4.3 cm(3) (IQR 2.9-5.7; p < 0.01). Ipsilateral LVV increased from 8.6 cm(3) (IQR 6.4-24.9) to 16.0 cm(3) (IQR 9.1-27.2; p < 0.01) while contralateral LVV increased from 10.3 cm(3) (IQR 7.3-20.1) to 11.7 cm(3) (IQR 8.2-19.4; p = 0.02). MLS changed from 0.1 mm (IQR -1.9 to 2.0) to -0.9 mm (IQR -1.8 to 0.4; p = 0.03). The decrease in GIA volume correlated with the increase in ipsilateral LVV (rs = 0.60; p = 0.01) but not with the changes in MLS (rs = 0.41; p = 0.08). CONCLUSIONS: In our patient cohort, surgical strategies other that direct clipping for the treatment of anterior circulation GIA lead to a significant decrease in GIA volume over time. The resulting decrease in mass effect was more sensitively monitored by the measurement of changes in ipsilateral LVV than changes in MLS. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov . Unique identifier: NCT02066493.

A new-generation, low-permeability flow diverting device for treatment of saccular aneurysms.

OBJECTIVES: We report a preclinical comparative study of a 96-strand braided flow diverter. METHODS: The 96-strand braided device was compared with the currently commercially available flow diverter with 48 strands. The devices were implanted across the neck of 12 elastase-induced aneurysms in New Zealand White rabbits and followed for 1 and 3 months (n = 6 respectively). Aneurysm occlusion rates, parent artery stenosis and patency of jailed branch occlusions were assessed by angiography, histology and scanning electron microscopy studies. RESULTS: It was feasible to navigate and implant the 96-strand device over the aneurysm orifice in all cases. At follow-up two aneurysms in the 48-strand vs. one in the 96-strand group were not occluded. This aneurysm from the 96-strand group however had a tracheal branch arising from the sac and showed a reverse remodelling of the vascular pouch at 3 months. In the occluded aneurysms, the parent artery was always completely reconstructed and the aneurysm orifice was sealed with neointimal tissue. No in-stent stenosis or jailed branch artery occlusion was observed. CONCLUSIONS: The 96-strand flow diverter proved to be safe, biocompatible and haemodynamically effective, induced stable occlusion of aneurysms and led to reverse remodelling of the parent artery. KEY POINTS: • Flow diversion has been introduced to improve endovascular treatment of cerebral aneurysms • A new low-permeability flow diverter is feasible for parent artery reconstruction. • The Silk 96 flow diverter appears effective at inducing aneurysm healing. • The covered branches remained patent at follow-up.

Multisociety consensus quality improvement guidelines for intraarterial catheter-directed treatment of acute ischemic stroke, from the American Society of Neuroradiology, Canadian Interventional Radiology Association, Cardiovascular and Interventional Radiological Society of Europe, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of NeuroInterventional Surgery, European Society of Minimally Invasive Neurological Therapy, and Society of Vascular and Interventional Neurology.

PURPOSE: In this international multispecialty document, quality benchmarks for processes of care and clinical outcomes are defined. It is intended that these benchmarks be used in a quality assurance program to assess and improve processes and outcomes in acute stroke revascularization. MATERIALS AND METHODS: Members of the writing group were appointed by the American Society of Neuroradiology, Canadian Interventional Radiology Association, Cardiovascular and Interventional Radiological Society of Europe, Society of Cardiac Angiography and Interventions, Society of Interventional Radiology, Society of NeuroInterventional Surgery, European Society of Minimally Invasive Neurological Therapy, and Society of Vascular and Interventional Neurology. The writing group reviewed the relevant literature from 1986 through February 2012 to create an evidence table summarizing processes and outcomes of care. Performance metrics and thresholds were then created by consensus. The guideline was approved by the sponsoring societies. It is intended that this guideline be fully updated in 3 years. RESULTS: In this international multispecialty document, quality benchmarks for processes of care and clinical outcomes are defined. These include process measures of time to imaging, arterial puncture, and revascularization and measures of clinical outcome up to 90 days. CONCLUSIONS: Quality improvement guidelines are provided for endovascular acute ischemic stroke revascularization procedures.

Multisociety consensus quality improvement guidelines for intraarterial catheter-directed treatment of acute ischemic stroke, from the American Society of Neuroradiology, Canadian Interventional Radiology Association, Cardiovascular and Interventional Radiological Society of Europe, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of NeuroInterventional Surgery, European Society of Minimally Invasive Neurological Therapy, and Society of Vascular and Interventional Neurology.

PURPOSE: In this international multispecialty document, quality benchmarks for processes of care and clinical outcomes are defined. It is intended that these benchmarks be used in a quality assurance program to assess and improve processes and outcomes in acute stroke revascularization. MATERIALS AND METHODS: Members of the writing group were appointed by the American Society of Neuroradiology, Canadian Interventional Radiology Association, Cardiovascular and Interventional Radiological Society of Europe, Society of Cardiac Angiography and Interventions, Society of Interventional Radiology, Society of NeuroInterventional Surgery, European Society of Minimally Invasive Neurological Therapy, and Society of Vascular and Interventional Neurology. The writing group reviewed the relevant literature from 1986 through February 2012 to create an evidence table summarizing processes and outcomes of care. Performance metrics and thresholds were then created by consensus. The guideline was approved by the sponsoring societies. It is intended that this guideline be fully updated in 3 years. RESULTS: In this international multispecialty document, quality benchmarks for processes of care and clinical outcomes are defined. These include process measures of time to imaging, arterial puncture, and revascularization and measures of clinical outcome up to 90 days. CONCLUSIONS: Quality improvement guidelines are provided for endovascular acute ischemic stroke revascularization procedures.

Flow diversion treatment: intra-aneurismal blood flow velocity and WSS reduction are parameters to predict aneurysm thrombosis.

BACKGROUND: To evaluate the haemodynamic changes induced by flow diversion treatment in cerebral aneurysms, resulting in thrombosis or persisting aneurysm patency over time. METHOD: Eight patients with aneurysms at the para-ophthalmic segment of the internal carotid artery were treated by flow diversion only. The clinical follow-up ranged between 6 days and 12 months. Computational fluid dynamics (CFD) analysis of pre- and post-treatment conditions was performed in all cases. True geometric models of the flow diverter were created and placed over the neck of the aneurysms by using a virtual stent-deployment technique, and the device was simulated as a true physical barrier. Pre- and post-treatment haemodynamics were compared, including mean and maximal velocities, wall-shear stress (WSS) and intra-aneurysmal flow patterns. The CFD study results were then correlated to angiographic follow-up studies. RESULTS: Mean intra-aneurysmal flow velocities and WSS were significantly reduced in all aneurysms. Changes in flow patterns were recorded in only one case. Seven of eight aneurysms showed complete occlusion during the follow-up. One aneurysm remaining patent after 1 year showed no change in flow patterns. One aneurysm rupturing 5 days after treatment showed also no change in flow pattern, and no change in the maximal inflow velocity. CONCLUSIONS: Relative flow velocity and WSS reduction in and of itself may result in aneurysm thrombosis in the majority of cases. Flow reductions under aneurysm-specific thresholds may, however, be the reason why some aneurysms remain completely or partially patent after flow diversion.

Effect of aging on elastin functionality in human cerebral arteries.

BACKGROUND AND PURPOSE: Aging affects elastin, a key component of the arterial wall integrity and functionality. Elastin degradation in cerebral vessels is associated with cerebrovascular disease. The goal of this study is to assess the biomechanical properties of human cerebral arteries, their composition, and their geometry, with particular focus on the functional alteration of elastin attributable to aging. METHODS: Twelve posterior cranial arteries obtained from human cadavers of 2 different age groups were compared morphologically and tested biomechanically before and after enzymatic degradation of elastin. Light, confocal, and scanning electron microscopy were used to analyze and determine structural differences, potentially attributed to aging. RESULTS: Aging affects structural morphology and the mechanical properties of intracranial arteries. In contrast to main systemic arteries, intima and media thicken while outer diameter remains relatively constant with age, leading to concentric hypertrophy. The structural morphology of elastin changed from a fiber network oriented primarily in the circumferential direction to a more heterogeneously oriented fiber mesh, especially at the intima. Biomechanically, cerebral arteries stiffen with age and lose compliance in the elastin dominated regime. Enzymatic degradation of elastin led to loss in compliance and stiffening in the young group but did not affect the structural and material properties in the older group, suggesting that elastin, though present in equal quantities in the old group, becomes dysfunctional with aging. CONCLUSIONS: Elastin loses its functionality in cerebral arteries with aging, leading to stiffer less compliant arteries. The area fraction of elastin remained, however, fairly constant. The loss of functionality may thus be attributed to fragmentation and structural reorganization of elastin occurring with age.

Effect of flow diverter porosity on intraaneurysmal blood flow.

BACKGROUND AND PURPOSE: Growth and rupture, the two events that dominate the evolution of an intracranial aneurysm, are both dependent on intraaneurysmal flow. Decrease of intraaneurysmal flow is considered an attractive alternative for treating intracranial aneurysms by minimally invasive techniques. Such modification can be achieved by inserting stents or flow diverters alone. In the present paper, the effect of different commercial and innovative flow diverters' porosity was studied in intracranial aneurysm models. MATERIAL AND METHODS: Single and stent-in-stent combination of Neuroform II as well as single and stent-in-stent combination of a new innovative, low-porosity, intracranial stent device (D1, D2, D1 + D2) were inserted in models of intracranial aneurysms under shear-driven flow and inertia-driven flow configurations. Steady and pulsating flow rates were applied using a blood-like fluid. Particle image velocimetry was used to measure velocity vector fields in the aneurysm midplane along the vessel axis. Flow and vorticity patterns, velocity and vorticity magnitudes were quantified and their value compared with the same flows in absence of the flow diverter. RESULTS: In absence of flow diverters, a solid-like rotation could be observed in both shear-driven and inertia-driven models under steady and pulsatile flow conditions. The flow effects due to the insertion of low-porous devices such as D1 or D2 provoked a complete alteration of the flow patterns and massive reduction of velocity or vorticity magnitudes, whereas the introduction of clinically adopted high-porous devices provoked less effect in the aneurysm cavity. As expected, results showed that the lower the porosity the larger the reduction in velocity and vorticity within the aneurysm cavity. The lowest-porosity device combination (D1 and D2) reached an averaged reduction of flow parameters of 80% and 88% under steady and pulsatile flow conditions, respectively. The reduction in mean velocity and vorticity was much more significant in the shear-driven flows as compared to the inertia-driven flows. CONCLUSION: Although device porosity is the main parameter influencing flow reduction, other parameters such as device design and local flow conditions may influence the level of flow reduction within intracranial aneurysms.

Subtracted vortex centers path line method with cinematic angiography for measurement of flow speed in cerebral aneurysms.

BACKGROUND AND PURPOSE: The assessment of blood flow speed by imaging modalities is of increasing importance for endovascular treatment, such as stent implantation, of cerebral aneurysms. The subtracted vortex centers path line method (SVC method) utilizes image post-processing for determining flow quantitatively. In current practice, intra-aneurysmal flow in an in vitro model is visualized by laser sheet translumination and digitally recorded. In this study, we applied this method to cinematic angiography (CA), which is the preferred imaging method for endovascular interventions, to analyse hemodynamic changes. The SVC method was applied to the images and compared with results of the slipstream line method with colored fluid. METHODS: A transparent tubular model was constructed of silicone which included an aneurysm 10 mm in diameter and having a 5 mm neck on a straight parent artery with a diameter of 3.5 mm. The model was integrated into a pulsatile circulation system. By CA, successive images at 25 frames/s with injection of contrast were obtained. RESULTS AND CONCLUSION: Rotating vortexes of contrast, which advanced along the wall of the aneurysm, were observed in successive images of the aneurysm cavity. This phenomenon was also observed in the successive images with the slipstream line method. The speed of the vortex center was calculated and the results show that the vortex speed of CA was the same as that under the slipstream line method. This indicates the possibility of applying the SVC method to medical imaging equipment for analysis of the flow in aneurysms containing stent.

Giant intracranial aneurysms of the posterior circulation and their relation to the brainstem: analysis of risk factors for neurological deficits.

OBJECTIVE: Giant posterior circulation aneurysms (GPCirAs) usually cause substantial mass effect on the brainstem, which may lead to neurological deficits. So far, there has been no systematic investigation of factors associated with such deficits in GPCirA. The authors aim to examine the risk factors for cranial nerve deficit (CND), motor deficit, and disability in patients with GPCirA. METHODS: Using MR images obtained in 30 patients with unruptured GPCirA, the authors examined GPCirA volume, presence of hydrocephalus or partial thrombosis (PT) of the aneurysm, and the degree of brainstem displacement measured by the distance between the McRae line and the tip of the GPCirA (∆MT). They evaluated associations between these factors and neurological deficits. RESULTS: Thirty GPCirAs in 30 patients were included. The prevalence of CNDs was 50%. Patients with CNDs significantly differed from those without CNDs in terms of age (mean 51.0 years [SD 15.0 years] vs 69.0 years [SD 21.0 years], p = 0.01) and in ∆MT (median 50.7 mm [IQR 39.2-53.9 mm] vs 39.0 mm [IQR 32.3-45.9 mm], p = 0.02). The prevalence of motor deficits was 33.3%. Patients with motor deficits showed a larger ∆MT (median 50.5 mm [IQR 40.8-54.6 mm]) compared with those without (∆MT: median 39.1 mm [IQR 32.8-50.5 mm], p = 0.04). GPCirA volume was larger in patients with poor modified Rankin Scale (mRS) scores (median 14.9 cm3 [IQR 8.6-18.7 cm3]) than in those with mRS scores of 0-2 (median 6.8 cm3 [IQR 4.4-11.7 cm3], p = 0.03). After adjusting for patient age and the occurrence of hydrocephalus or PT, the authors found that higher degrees of disability were significantly associated with aneurysm volume (OR 1.13, 95% CI 1.0-1.3; p = 0.04), but not with ∆MT. The occurrence of CND or motor deficit was not associated with any of the examined variables. There was no correlation between GPCirA volume and ∆MT (rs = 0.01, p = 0.96). The prevalence of neurological deficits did not differ between GPCirA at the basilar apex, the basilar trunk, the vertebrobasilar junction, or the vertebral artery. CONCLUSIONS: In this study, the neurological condition of the patients was associated only with GPCirA volume and not with the degree of brainstem displacement, the occurrence of PT or hydrocephalus, or the exact location of the GPCirA. These findings highlight the clinical relevance of GPCirA volume and suggest that factors such as brainstem displacement or PT should play less of a role when finding arguments for or against treatment of GPCirA.Clinical trial registration no.: NCT02066493 (clinicaltrials.gov).

Cardiovascular effects of selected water-miscible solvents for pharmaceutical injections and embolization materials: a comparative hemodynamic study using a sheep model.

Generally, organic water-miscible solvents are used intravascularly (both intravenously and intra-arterially) for preparing two types of formulations, namely, pharmaceutical injections of poorly soluble drugs and precipitating liquid embolic polymeric materials for the minimally invasive treatment of aneurysms, arteriovenous malformations, or tumors, by arterial route. Although several of such solvents have been used in both drug delivery and interventional radiology, their safety profile is a concern. In particular, there is a lack of comparative investigations of their cardiovascular effects when injected intra-arterially. We selected 13 non-aqueous water-miscible solvents based on their capacity to solubilize drugs or embolic polymeric materials, and on their described use, at least diluted with water, in pharmaceutical formulations. Their in vivo hemodynamic toxicity in male adult sheep after infra-renal aorta catheterization has been estimated with respect to the arterial and venous pressures, as well as the heart rate. Saline solution was used as a control. Three different volumes (0.1, 0.5, and 1.0 mL) were infused rapidly. An increase in arterial pressure and concomitant decrease in venous pressure, which we considered as signs of a cardiovascular toxicity, were observed to a differing extent for all organic solvents. Changes in heart rate were negligible. Based on the intensity of arterial pressure change after a 1-mL infusion, a classification of the toxicity of the solvents following intra-arterial infusion is proposed: Solvents devoid of significant cardiovascular toxicity: dimethyl isosorbide (DMI), Glycofurol 75, polyethylene glycol 200 (PEG 200), diglyme. Solvents with moderate cardiovascular toxicity: tetrahydrofurfuryl alcohol (THFA), ethanol, acetone, Solketal, glycerol formal, dimethyl sulfoxide (DMSO). Solvents with marked cardiovascular toxicity: propylene glycol, ethyl lactate, N-methyl-2-pyrrolidone (NMP). Emphasis is put on the relative character of the proposed ranking and on the lack for certain solvents, at least in the open literature, of data pertaining at other forms of toxic effects (e.g., undesirable pharmacological action, carcinogenicity, teratogenicity, mutagenicity, and irritating and sensitizing properties), all factors that have to be considered when selecting a proper solvent.

Intrinsically radiopaque iodine-containing polyvinyl alcohol as a liquid embolic agent: evaluation in experimental wide-necked aneurysms.

OBJECT: To evaluate iodine-containing polyvinyl alcohol (I-PVA) as a precipitating liquid embolic agent, implant characteristics--including radiopacity, setting behavior, and biocompatibility--were studied in an aneurysm model in swine. METHODS: Twelve broad-based carotid artery (CA) sidewall aneurysms were surgically constructed in six pigs. Iodine-containing polyvinyl alcohol dissolved in dimethyl sulfoxide (DMSO) was injected during temporary balloon occlusion bridging the aneurysm neck. Control angiography as well as multidetector row computerized tomography (CT) angiography was performed after 4 weeks. Harvested aneurysms were investigated histopathologically and by 3-tesla high-field magnetic resonance (MR) imaging. The mean degree of aneurysm occlusion achieved was 96%. In two aneurysms a minimal protrusion of I-PVA into the CA lumen was observed. During one embolization, leakage of the liquid embolic agent due to DMSO-induced damage of the microcatheter resulted in CA occlusion. Aneurysms embolized with I-PVA could be discriminated clearly from the parent artery on CT angiograms because there was no beam-hardening artifact. High-field MR imaging allowed a detailed depiction of the liquid embolic distribution within the aneurysm. Histologically, a mild to moderate inflammatory response was found in successfully embolized aneurysms, and the polymer mass was frequently covered by a membrane of fibroblasts and endothelial cells. CONCLUSIONS: Iodine-containing polyvinyl alcohol is a ready-to-use liquid embolic agent clearly visible under fluoroscopy; additives are not required. The setting behavior allows for controlled delivery in aneurysm cavities. Histological studies performed 4 weeks after embolization revealed no sign of toxic tissue response to the liquid embolic agent. Overall, I-PVA exhibits interesting implant characteristics in that radiopaque admixtures are not necessary, thus allowing for artifact-free evaluation of treated aneurysms by using CT and MR angiography.

Change in aneurysmal flow pulsatility after flow diverter treatment.

MOTIVATION: Treatment of intracranial aneurysms with flow diverters (FDs) has recently become an attractive alternative. Although considerable effort has been devoted to understand their effects on the time-averaged or peak systolic flow field, no previous study has analyzed the variability of FD-induced flow reduction along the cardiac cycle. METHODS: Fourteen saccular aneurysms, candidates for FD treatment because of their morphology, located on the internal carotid artery were virtually treated with FDs and pre- and post-treatment blood flow was simulated with CFD techniques. Common hemodynamic variables were recorded at each time step of the cardiac cycle and differences between the untreated and treated models were assessed. RESULTS: Flow pulsatility, expressed by the pulsatility index (PI) of the velocity, significantly increased (36.0%; range: 14.6-88.3%) after FD treatment. Peak systole velocity reduction was significantly smaller (30.5%; range: 19.6-51.0%) than time-averaged velocity reduction (43.0%; range: 29.1-69.8%). No changes were observed in the aneurysmal pressure. CONCLUSIONS: FD-induced flow reduction varies considerably during the cardiac cycle. FD treatment significantly increased the flow pulsatility in the aneurysm.

Influence of stent properties on the alteration of cerebral intra-aneurysmal haemodynamics: flow quantification in elastic sidewall aneurysm models.

OBJECTIVES: Stent implantation across the neck of cerebral aneurysms may induce intra-aneurysmal flow reduction, and consequently saccular thrombosis and vessel wall repair. To analyse the influence of different stent parameters on such flow reduction, we studied the flow changes in vascular models, induced by a series of stents. METHODS: Two different neck-sized elastic sidewall aneurysm models were connected to a circulatory loop. Twenty different stents were introduced in both models to analyse the effect of their parameters, such as porosity, filament diameter and permeability. Flow patterns were visualized by using glass particles and laser sheet translumination. The digitally recorded data were transferred for computer analysis. The changes of the vortex velocity for each stent model combination were investigated and statistically evaluated. RESULTS: Intra-aneurysmal flow analysis showed dispersion of the vortices of a variable degree, and velocity reduction of 30% mean in model 1 and 49% mean in model 2. By statistical analysis three groups of stents ('best', 'medium', 'worst') were identified, according to their haemodynamic efficacy. No correlations were observed between the haemodynamic performance of the stents and the porosity, filament diameter and permeability values separately. The stent effects were on average more important in the large-necked than in the small-necked aneurysm model. DISCUSSION: Stent implantation induces intra-aneurysmal loss of vortex coherence and flow reduction. The analysed stent parameters show complex interrelationship, including also stent 'design'. The difference in the haemodynamic efficacy of the individual stents between the two models raises the question of 'stent positioning effects'.

Development of a polyvinyl alcohol hydrogel for temperature measurement by MRI.

This paper describes the development of a Polyvinyl alcohol hydrogel (PVA-H) model for calibration and measurement of temperature using image contrast on MRI using DMSO/H_2O as a solvent to alter the freezing and melting points of PVA-H. Tissues exposed to temperature changes above 41 degrees C or below 0 degrees C exhibit increasingly extensive and irreversible damage, depending on the exposure duration. MR images can provide a map of temperature if there is sufficient tissue signal. To evaluate treatment principles using temperature changes (hyperthermia, cryotherapy), a model simulating tissue may be useful to provide a reproducible test environment. PVA-H is water soluble and can be seen on MRI. It can be used to construct complicated shapes such as vascular structure, soft tissues, and so on. Therefore, PVA-H can be useful to measure temperatures and assume the distribution of temperature under treatment. In this paper, we applied PVA-H as a temperature detector and calibrated temperature from image contrast. The results exhibit good capability as a temperature detector not only of high temperature (around 41 degrees C), but also of low temperature (as low as -23 degrees C).

Effect of aneurysm and ICA morphology on hemodynamics before and after flow diverter treatment.

BACKGROUND: Flow diverter (FD) treatment aims to slow down blood flow inside the aneurysm and increase the average time that blood resides in the aneurysm. OBJECTIVE: To investigate the relationship between vessel and aneurysm morphology and their influence on the way in which braided FDs change intra-aneurysmal hemodynamics. MATERIALS AND METHODS: Twenty-three patient-specific intracranial aneurysm models at the supraclinoid segment of the internal carotid artery were studied. Vessel and aneurysm morphology was quantified and blood flow was modeled with computational fluid dynamics simulations. The relation between morphologic variables and the hemodynamic variables, WSS (wall shear stress) and totime (ratio between the aneurysm volume and inflow at the aneurysm neck), was assessed statistically. RESULTS: Intra-aneurysmal flow was less dependent on the vessel than on aneurysm morphology. In summary, after treatment with a FD, a greater aneurysm flow reduction and redirection to the vessel main stream should be expected for (a) aneurysms located further away from the curvature peak, (b) aneurysms on the inner side of the bend, (c) aneurysms with no proximal stenosis, and (d) larger aneurysms. CONCLUSIONS: Although the change in intra-aneurysmal hemodynamics after FD treatment strongly depends on the morphology of the aneurysm, the hemodynamic effect of a FD is also linked to the parent vessel morphology and the position and orientation of the aneurysm with respect to it.

Cervical sympathetic block to reverse delayed ischemic neurological deficits after aneurysmal subarachnoid hemorrhage.

BACKGROUND AND PURPOSE: The purpose of the present study was to evaluate the feasibility and safety of a locoregional cervical sympathetic block to improve cerebral perfusion in patients suffering from cerebral vasospasm after aneurysmal subarachnoid hemorrhage. METHODS: Nine consecutive patients with symptoms of delayed ischemic deficits, induced by angiographically confirmed cerebral vasospasm, were treated with the injection of locoregional anesthesia to block the ascending cervical sympathetic chain at the level of the superior cervical ganglion. Neurological status was recorded before and after the procedure, and cerebral angiography was performed before and after the procedure. RESULTS: No complications occurred in this short series. The procedure appeared to be simple and safe. Horner's signs appeared within 12+/-0.1 minutes and lasted for an average of 6.3+/-4 hours. In all patients, improved cerebral perfusion was detected at the confirmatory angiography but without change in vessel caliber. One patient died of the complications of the initial hemorrhage, and 2 died of the consequences of the severe vasospasm despite maximal medical treatment. In all the other cases, the neurological status promptly returned to normal within 48 hours after the locoregional treatment. CONCLUSIONS: Patients with mild to moderate symptoms seem to benefit greatly from transient ipsilateral cervical sympathetic block. This simple technique may be helpful when used as an adjunct to the standard therapy to improve cerebral perfusion.

Anatomically shaped internal carotid artery aneurysm in vitro model for flow analysis to evaluate stent effect.

BACKGROUND AND PURPOSE: Stent implantation alone might not be sufficient to produce definitive treatment of cerebral aneurysms. Therefore, extended experimental work is needed to improve results. We show the feasibility of using an in vitro anatomically shaped elastic model for flow evaluation before and after stent implantation. METHODS: Based on human vascular casting, an anatomic elastic internal carotid artery model, including an aneurysm on the supraclinoid portion, was manufactured. The model was connected to a circulatory loop to simulate physiological flow. After visualization of the flow by using glass particles and laser sheet translumination, the digitally recorded data were transferred for computer analysis. Intra-saccular flow pattern changes and the vortex velocity reduction induced by the stent were investigated qualitatively and quantitatively. RESULTS: The distal neck of the aneurysm behaved as a flow divider. Therefore, it was directly exposed to the hemodynamic stress. Inside the sac, a well-defined vortex formed and progressed along the wall toward the proximal neck. After stent implantation this pattern changed significantly; the vortex appeared more dispersed and its residence time increased. The velocity reduction was 32%. Velocity peak was observed close to the distal neck in both cases. CONCLUSION: In vitro anatomic elastic models are feasible for flow evaluation with laser sheet translumination. In our model, stent implantation resulted in hemodynamic changes that might favor the exclusion of the aneurysm from the circulation and can prevent regrowth of the aneurysmal sac.