Blood flow in cerebral aneurysms: comparison of phase contrast magnetic resonance and computational fluid dynamics--preliminary experience.

PURPOSE: Computational fluid dynamics (CFD) simulations are increasingly used to model cerebral aneurysm hemodynamics. We investigated the capability of phase contrast magnetic resonance imaging (pcMRI), guided by specialized software for optimal slice definition (NOVA, Vassol Inc.) as a non-invasive method to measure intra-aneurysmal blood flow patterns in-vivo. In a novel approach, these blood flow patterns measured with pcMRI were qualitatively compared to the ones calculated with CFD. MATERIALS AND METHODS: The volumetric inflow rates into three unruptured cerebral aneurysms and the temporal variations of the intra-aneurysmal blood flow patterns were recorded with pcMRI. Transient CFD simulations were performed on geometric models of these aneurysms derived from 3D digital subtraction angiograms. Calculated intra-aneurysmal blood flow patterns were compared at the times of maximum and minimum arterial inflow to the ones measured with pcMRI and the temporal variations of these patterns during the cardiac cycle were investigated. RESULTS: In all three aneurysms, the main features of intra-aneurysmal flow patterns obtained with pcMRI consisted of areas with positive velocities components and areas with negative velocities components. The measured velocities ranged from approx. +/- 60 to +/- 100 cm/sec. Comparison with calculated CFD simulations showed good correlation with regard to the spatial distribution of these areas, while differences in calculated magnitudes of velocities were found. CONCLUSION: CFD simulations using inflow boundary conditions measured with pcMRI yield main features of intra-aneurysmal velocity patterns corresponding to intra-aneurysmal measurements performed with pcMRI. Thus, pcMRI may become a valuable complementary technique to CFD simulations to obtain in-vivo reference data for the study of aneurysmal hemodynamics. More data is needed to compare and fully explore the capabilities of both methods.

Relationships and redundancies of selected hemodynamic and structural parameters for characterizing virtual treatment of cerebral aneurysms with flow diverter devices.

BACKGROUND AND PURPOSE: To quantify the relationship and to demonstrate redundancies between hemodynamic and structural parameters before and after virtual treatment with a flow diverter device (FDD) in cerebral aneurysms. METHODS: Steady computational fluid dynamics (CFD) simulations were performed for 10 cerebral aneurysms where FDD treatment with the SILK device was simulated by virtually reducing the porosity at the aneurysm ostium. Velocity and pressure values proximal and distal to and at the aneurysm ostium as well as inside the aneurysm were quantified. In addition, dome-to-neck ratios and size ratios were determined. Multiple correlation analysis (MCA) and hierarchical cluster analysis (HCA) were conducted to demonstrate dependencies between both structural and hemodynamic parameters. RESULTS: Velocities in the aneurysm were reduced by 0.14m/s on average and correlated significantly (p<0.05) with velocity values in the parent artery (average correlation coefficient: 0.70). Pressure changes in the aneurysm correlated significantly with pressure values in the parent artery and aneurysm (average correlation coefficient: 0.87). MCA found statistically significant correlations between velocity values and between pressure values, respectively. HCA sorted velocity parameters, pressure parameters and structural parameters into different hierarchical clusters. HCA of aneurysms based on the parameter values yielded similar results by either including all (n=22) or only non-redundant parameters (n=2, 3 and 4). CONCLUSION: Hemodynamic and structural parameters before and after virtual FDD treatment show strong inter-correlations. Redundancy of parameters was demonstrated with hierarchical cluster analysis.

Quantitative comparison of hemodynamic parameters from steady and transient CFD simulations in cerebral aneurysms with focus on the aneurysm ostium.

OBJECTIVE: To quantitatively compare hemodynamics simulated with steady-state and transient computational fluid dynamics (CFD) simulations in cerebral aneurysms with single inflow, with focus at the aneurysm ostium. METHODS: Transient and steady-state CFD simulations were performed in 10 cerebral aneurysms. Distributions and average values for pressure, helicity, vorticity, and velocity were qualitatively compared at proximal and distal parent artery locations, at the ostium plane, and in the aneurysm, and scaling factors between the two kinds of simulations were determined. Relative inflow and outflow areas at the ostium were compared, as were average inflow and outflow velocities. In addition, values for the pressure-loss coefficient (PLC), a recently introduced parameter to assess aneurysm rupture risk, were compared for both kinds of simulation. RESULTS: Distributions of hemodynamic parameters had a similar shape but were lower for transient than for steady-state simulations. Averaged scaling factors over cases and anatomical locations showed differences for hemodynamic parameters (0.485 ± 0.01 for pressure, 0.33 ± 0.02 for helicity, 0.58 ± 0.06 for vorticity and 0.56 ± 0.04 for velocity). Good agreement between ratios of inflow and outflow areas at the aneurysm ostium was obtained (Pearson correlation coefficient >0.97, p<0.001) and for the PLC (linear regression slope 0.73 ± 0.14, R(2)=0.75). CONCLUSIONS: Steady-state simulations are a quick alternative to transient simulation for visualizing and quantifying inflow and outflow areas at the aneurysm ostium, potentially of value when planning flow diverter treatment and for quantifying the PLC, a potential indicator of aneurysm rupture.

Giant serpentine aneurysms: radiographic features and endovascular treatment.

PURPOSE: To describe the characteristic CT, MR, and angiographic features of giant serpentine aneurysms and discuss their endovascular treatment. METHODS: Thirteen patients with giant serpentine aneurysms were studied at our institution in the last 3 years. They all underwent CT and MR studies as well as cerebral angiography. More recently, some of the patients were studied with MR angiography. Seven patients had endovascular occlusion of the giant serpentine aneurysms, 3 with N-butyl cyanoacrylate, 2 with Guglielmi detachable coils, and 2 with detachable balloons. RESULTS: Giant serpentine aneurysms mimic cerebral neoplasms on CT and MR studies; they are often associated with mass effect and adjacent edema, and they enhance with contrast medium. The cerebral angiogram shows a residual irregular lumen of the partially clotted aneurysm, which continues into normal branches supplying the distal arterial territory. Six patients were treated successfully with an endovascular approach consisting of complete and permanent occlusion of the parent artery. CONCLUSION: Giant serpentine aneurysms from a subgroup of large intracranial aneurysms that have specific CT, MR, and angiographic features, which should be recognized before their treatment. The endovascular treatment of the aneurysm consists of permanent occlusion of the parent artery.

Aneurysms of the posterior cerebral artery: classification and endovascular treatment.

BACKGROUND AND PURPOSE: We present a retrospective review of our experience in the endovascular treatment of posterior cerebral artery (PCA) aneurysms. We detail the anatomic location of these aneurysms, the technique of endovascular treatment, morphologic results, and clinical outcome. We also discuss the segmental anatomy of the PCA as it relates to the various neurologic deficits that may result from occlusion of the parent artery. METHODS: From 1993 to 1998, 20 patients (12 female, eight male; mean age, 44 yrs) harboring a PCA aneurysm were treated via an endovascular approach. One patient had two aneurysms, comprising a total of 21 lesions. Fourteen (66%) of 21 aneurysms were saccular in nature, five (24%) were giant serpentine aneurysms, and two (10%) were posttraumatic. All aneurysms were treated using Guglielmi detachable coils (GDC) either by selective obliteration of the aneurysm sac or by parent artery occlusion. RESULTS: Fourteen (66%) of the 21 aneurysms were successfully treated with preservation of the parent artery. In the remaining seven (33%), the parent artery was permanently occluded. The overall complication rate in this series was 15%, with a permanent morbidity rate of 10% and a 0% mortality rate. CONCLUSION: Aneurysms of the PCA are rare compared with other locations in the intracranial circulation. Saccular PCA aneurysms can be treated effectively, by use of GDC, to obliterate the aneurysm yet preserve the parent artery. Fusiform and giant serpentine aneurysms of the PCA can effectively be treated by permanent occlusion of the parent artery; in these cases, thorough knowledge of the PCA segmental anatomy is crucial in order to select the site of occlusion and to avoid major neurologic deficits.

De novo development of an aneurysm: case report.

A case of the de novo formation of an aneurysm in a young woman is presented. At age 13 years, she had a spontaneous subarachnoid hemorrhage. Cerebral angiography showed an aneurysm of the bifurcation of the left internal carotid artery and a small aneurysm of the left anterior choroidal artery. At surgery, the aneurysm of the internal carotid artery was clipped, and the aneurysm of the left anterior choroidal artery was wrapped with muslin. Thirteen years later, the patient had another subarachnoid hemorrhage. Cerebral arteriography showed four aneurysms that had developed at previously angiographically normal sites. This case suggests that young patients with aneurysms might benefit from follow-up angiography in search of late aneurysm formation.

Elimination of a cirsoid aneurysm of the scalp by direct percutaneous embolization with thrombogenic coils. Case report.

Cirsoid aneurysms of the scalp are notoriously difficult lesions to manage. The authors report a patient in whom a large traumatic cirsoid aneurysm of the scalp was eliminated using a combined neurosurgical and interventional neuroradiological approach. Transarterial embolization was utilized to reduce arterial blood supply to the fistula. Thrombogenic Gianturco spring coils were then introduced via direct percutaneous puncture of the aneurysm. The aneurysm thrombosed and the multiple tortuous scalp vessels disappeared. One month after embolization, a small area of skin necrosis over the aneurysm necessitated surgical excision of the lesion. The thrombosed aneurysm was easily resected with minimal blood loss. Percutaneous embolization with thrombogenic coils in this case was a safe and effective ablative technique.

Enlargement of basilar artery aneurysms following balloon occlusion--"water-hammer effect". Report of two cases.

Two patients with distal basilar aneurysms were treated with intra-aneurysmal balloon occlusion. After apparently successful therapy, follow-up angiograms demonstrated aneurysm enlargement with balloon migration distally in the sac. Geometric mismatch between the base of the balloons and the aneurysm neck together with transmitted pulsation through the 2-hydroxyl-ethylmethacrylate (HEMA)-filled balloon directly contributed to aneurysm enlargement. In this report, the authors discuss the problems of progressive aneurysm enlargement due to a "water-hammer effect" and the possibility of hemorrhage following subtotal occlusion.

Modified encephaloduroarteriosynangiosis as a surgical treatment of childhood moyamoya disease: report of five cases.

Moyamoya disease is an idiopathic disorder characterized by progressive occlusion of the internal carotid and anterior and middle cerebral arteries, with formation of an extensive abnormal collateral circulation at the base of the brain. Many neurosurgical procedures have been designed to bypass these occluded vessels. The results of one of these procedures, modified encephaloduroarteriosynangiosis was reviewed in five children followed for 3 1/2 to 19 1/2 years. Modified encephaloduroarteriosynangiosis performed unilaterally in one and bilaterally in four of the children, appeared to halt neurologic deterioration, despite angiographic progression, in four of the five children.

The influence of anulotomy selection on disc competence. A radiographic, biomechanical, and histologic analysis.

STUDY DESIGN: This study analyzed the radiographic, biomechanical, and histologic attributes of three commonly used anulotomy techniques. OBJECTIVES: This study defined the propensity of the anulus fibrosus to heal after discectomy and correlated biomechanical differences between subgroups of the motion segments studied. SUMMARY OF BACKGROUND DATA: No previous report that compares the influence of anulotomy selection on disc competence exists. METHODS: Anulotomies were performed on the anterolateral aspects of the lumbar discs of 54 adult goats. The goats were randomly assigned to one of three subgroups containing 18 animals. In subgroup A, a full-thickness anular window was excised. In subgroup B, a full-thickness cruciate anulotomy was accomplished. In subgroup C, a full-thickness anulotomy was developed by inserting a trocar, 2.5 mm in diameter, into the disc. RESULTS: Histologic analysis revealed that primary anular healing did not occur in any specimen. The anulotomy tracts in subgroup C (trocar) were consistently narrower than those of subgroups A and B. Discography demonstrated the presence of severe and early disc degeneration with subgroup A (anular window), a finding not observed within the trocar anulotomy group. Biomechanical testing demonstrated increased resistance to pull out by the trocar anulotomy group at 4 weeks, as well as increased torsional stiffness of the motion segment when compared to both window and cruciate anulotomy. CONCLUSIONS: The authors conclude that attempts should be made to minimize injury to the anulus fibrosus during the performance of discectomy.

A case of Pott's disease in a 20-year-old military dependent.

Tuberculous spondylitis (Pott's disease) is an uncommon complication of Mycobacterium tuberculosis infection that may have serious consequences if the diagnosis is missed or delayed. A case of tuberculous spondylitis in a military dependent is presented. Clinical presentation, radiologic findings, laboratory findings, and treatment are discussed.

In-vivo quantification of wall motion in cerebral aneurysms from 2D cine phase contrast magnetic resonance images.

PURPOSE: The quantification of wall motion in cerebral aneurysms is of interest for the assessment of aneurysmal rupture risk, for providing boundary conditions for computational simulations and as a validation tool for theoretical models. MATERIALS AND METHODS: 2D cine phase contrast magnetic resonance imaging (2D pcMRI) in combination with quantitative magnetic resonance angiography (QMRA) was evaluated for measuring wall motion in 7 intracranial aneurysms. In each aneurysm, 2 (in one case 3) cross sections, oriented approximately perpendicular to each other, were measured. RESULTS: The maximum aneurysmal wall distention ranged from 0.16 mm to 1.6 mm (mean 0.67 mm), the maximum aneurysmal wall contraction was -1.91 mm to -0.34 mm (mean 0.94 mm), and the average wall displacement ranged from 0.04 mm to 0.31 mm (mean 0.15 mm). Statistically significant correlations between average wall displacement and the shape of inflow curves (p-value < 0.05) were found in 7 of 15 cross sections; statistically significant correlations between the displacement of the luminal boundary center point and the shape of inflow curves (p-value < 0.05) were found in 6 of 15 cross sections. CONCLUSION: 2D pcMRI in combination with QMRA is capable of visualizing and quantifying wall motion in cerebral aneurysms. However, application of this technique is currently restricted by its limited spatial resolution.

Risk factors associated with major cerebrovascular complications after intracranial stenting.

BACKGROUND: There are limited data on the relationship between patient and site characteristics and clinical outcomes after intracranial stenting. METHODS: We performed a multivariable analysis that correlated patient and site characteristics with the occurrence of the primary endpoint (any stroke or death within 30 days of stenting or stroke in the territory of the stented artery beyond 30 days) in 160 patients enrolled in this stenting registry. All patients presented with an ischemic stroke, TIA, or other cerebral ischemic event (e.g., vertebrobasilar insufficiency) in the territory of a suspected 50-99% stenosis of a major intracranial artery while on antithrombotic therapy. RESULTS: Cerebral angiography confirmed that 99% (158/160) of patients had a 50-99% stenosis. In multivariable analysis, the primary endpoint was associated with posterior circulation stenosis (vs anterior circulation) (hazard ratio [HR] 3.4, 95% confidence interval [CI] 1.2-9.3, p = 0.018), stenting at low enrollment sites (< 10 patients each) (vs high enrollment site) (HR 2.8, 95% CI 1.1-7.6, p = 0.038), < or = 10 days from qualifying event to stenting (vs > or = 10 days) (HR 2.7, 95% CI 1.0-7.8, p = 0.058), and stroke as a qualifying event (vs TIA/other) (HR 3.2, 95% CI 0.9-11.2, p = 0.064). There was no significant difference in the primary endpoint based on age, gender, race, or percent stenosis (50-69% vs 70-99%). CONCLUSIONS: Major cerebrovascular complications after intracranial stenting may be associated with posterior circulation stenosis, low volume sites, stenting soon after a qualifying event, and stroke as the qualifying event. These factors will need to be monitored in future trials of intracranial stenting.

The NIH registry on use of the Wingspan stent for symptomatic 70-99% intracranial arterial stenosis.

BACKGROUND: The Warfarin-Aspirin Symptomatic Intracranial Disease (WASID) trial showed that patients with symptomatic 70% to 99% intracranial arterial stenosis are at particularly high risk of ipsilateral stroke on medical therapy: 18% at 1 year (95% CI = 3% to 24%). The Wingspan intracranial stent is another therapeutic option but there are limited data on the technical success of stenting and outcome of patients with 70% to 99% stenosis treated with a Wingspan stent. METHODS: Sixteen medical centers enrolled consecutive patients treated with a Wingspan stent in this registry between November 2005 and October 2006. Data on stenting indication, severity of stenosis, technical success (stent placement across the target lesion with <50% residual stenosis), follow-up angiography, and outcome were collected. RESULTS: A total of 129 patients with symptomatic 70% to 99% intracranial stenosis were enrolled. The technical success rate was 96.7%. The mean pre and post-stent stenoses were 82% and 20%. The frequency of any stroke, intracerebral hemorrhage, or death within 30 days or ipsilateral stroke beyond 30 days was 14.0% at 6 months (95% CI = 8.7% to 22.1%). The frequency of >or=50% restenosis on follow-up angiography was 13/52 (25%). CONCLUSION: The use of a Wingspan stent in patients with severe intracranial stenosis is relatively safe with high rate of technical success with moderately high rate of restenosis. Comparison of the event rates in high-risk patients in Warfarin-Aspirin Symptomatic Intracranial Disease (WASID) vs this registry do not rule out either that stenting could be associated with a substantial relative risk reduction (e.g., 50%) or has no advantage compared with medical therapy. A randomized trial comparing stenting with medical therapy is needed.

Transvenous occlusion of a dural cavernous sinus fistula using a new expandable hydrogel-platinum coil (hydrocoil(r)).

SUMMARY: Hydrogel-coated platinum coils (Hydrocoils(R)) are currently under clinical investigation for their efficacy to improve anatomic results of endovascular occlusion of cerebral aneurysms. A case is presented in which this new expandable coil type was added to bare platinum coils in order to accelerate the transvenous occlusion of a dural cavernous sinus fistula (DCSF). A 53-year-old woman presenting with mild left-sided eye redness and diplopia due to a DCSF (type D) underwent transvenous occlusion using bare platinum coils (Trufill(R)) and hydrogel coated coils (Hydrocoil(R)). After successful catherization of the cavernous sinus, bare platinum coils were densely packed and eventually combined with Hydrocoils(R) which resulted in immediate and complete occlusion of the fistula. No technical or clinical complication occurred. The new expansile hydrogel-coated platinum coil (Hydrocoil(R)) can be successfully combined with bare platinum coils to accelerate transvenous occlusion of an AV-shunting lesion. Controlled volume expansion after deployment of this device offers potential benefits for occlusion of dural arteriovenous fistulas in other locations or for parent vessel occlusions in the treatment of giant or large complex aneurysms.