Comparative effectiveness of carotid revascularization therapies: evidence from a National Hospital Discharge Database

BACKGROUND AND PURPOSE

Clinical equipoise of carotid revascularization therapies remains controversial. We sought to determine whether adverse outcomes after carotid endarterectomy (CEA) or carotid angioplasty and stenting (CAS) were similar using propensity score-matched analysis of retrospective data from a large hospital discharge database.

METHODS

All CEA and CAS cases were identified from the 2006 to 2011 Premier Perspective Database and subjected to 1:1 propensity score matching using 33 clinical covariates associated with carotid revascularization. A primary composite end point of peri- or postoperative mortality, stroke, or acute myocardial infarction and a modified composite end point excluding acute myocardial infarction were used to compare our findings with recent prospective controlled trials. Multivariate regression and Cox-proportional hazard ratio survival analysis were performed to compare revascularization therapy outcomes.

RESULTS

After 1:1 propensity score matching, 24 004 (12 002 CEA and CAS) asymptomatic and 3506 (1753 CEA and CAS) symptomatic procedures were included. The risk of the primary composite end point was significantly higher after CAS than CEA in both asymptomatic (odds ratio, 1.40 [1.19-1.65]; P<0.0001) and symptomatic (odds ratio=2.31 [1.78-3.00]; P<0.0001) presentations, irrespective of age (P=0.28) or sex (P=0.35). Similar findings were observed using the modified composite end point for both asymptomatic (odds ratio, 1.49 [1.25-1.78]; P<0.0001) and symptomatic (odds ratio, 3.02 [2.25-4.07]; P<0.0001) presentations. Acute myocardial infarction risk was not significantly different between revascularization therapies, regardless of clinical presentation (P=0.71 and 0.24).

CONCLUSIONS

Among individuals undergoing carotid artery revascularization from a large sample of US hospitals, CAS was associated with higher risk of perioperative mortality, stroke, and unfavorable discharges compared with CEA for all ages and clinical presentations.

Analysis of flow changes in side branches jailed by flow diverters in rabbit models

Understanding the flow alteration in side branches during flow diversion treatment of cerebral aneurysms is important to prevent ischemic complications and improve device designs. Flow diverters were placed in the aorta of four rabbits crossing the origin of side arteries. Subject-specific computational models were constructed from 3D angiographies and Doppler ultrasounds (DUSs). Flow simulations were run before and after virtually deploying the flow diverters, assuming distal resistances remained unchanged after treatment. All jailed arteries remained patent angiographically 8 weeks after treatment. The computational models estimated decreases compared to pretreatment in the mean flow rates between 2% and 20% and in peak flow rates between 5% and 36%. The major changes were observed during systole. Flow patterns did not exhibit recirculation zones before treatment. Implantation of the flow diverters altered the flow structure only locally near the device wires. No major recirculation regions were created or destroyed. Flow diverters seem safe with respect to perforator or side branch occlusion. Relatively small changes in flow rates through jailed arteries are expected, even for moderate to large degrees of coverage of their origins. These results seem consistent with previous clinical experiences where no or very few complications related to perforator occlusion have been reported.

Analysis of hemodynamics and aneurysm occlusion after flow-diverting treatment in rabbit models

BACKGROUND AND PURPOSE

Predicting the outcome of flow diversion treatment of cerebral aneurysms remains challenging. Our aim was to investigate the relationship between hemodynamic conditions created immediately after flow diversion and subsequent occlusion of experimental aneurysms in rabbits.

MATERIALS AND METHODS

The hemodynamic environment before and after flow-diversion treatment of elastase-induced aneurysms in 20 rabbits was modeled by using image-based computational fluid dynamics. Local aneurysm occlusion was quantified by using a voxelization technique on 3D images acquired 8 weeks after treatment. Global and local voxel-by-voxel hemodynamic variables were used to statistically compare aneurysm regions that later thrombosed to regions that remained patent.

RESULTS

Six aneurysms remained patent at 8 weeks, while 14 were completely or nearly completely occluded. Patent aneurysms had statistically larger neck sizes (P = .0015) and smaller mean transit times (P = .02). The velocity, vorticity, and shear rate were approximately 2.8 times (P < .0001) larger in patent regions-that is, they had larger "flow activity" than regions that progressed to occlusion. Statistical models based on local hemodynamic variables were capable of predicting local occlusion with good precision (84% accuracy), especially away from the neck (92%-94%). Predictions near the neck were poorer (73% accuracy).

CONCLUSIONS

These results suggests that the dominant healing mechanism of occlusion within the aneurysm dome is related to slow-flow-induced thrombosis, while near the neck, other processes could be at play simultaneously.

Rescue treatment of thromboembolic complications during endovascular treatment of cerebral aneurysms: a meta-analysis

BACKGROUND AND PURPOSE

Intraprocedural thrombus formation during endovascular treatment of intracranial aneurysms is often treated with glycoprotein IIb/IIIa inhibitors and, in some instances, fibrinolytic therapy. We performed a meta-analysis evaluating the safety and efficacy of GP IIb/IIIa inhibitors compared with fibrinolysis. We also evaluated the safety and efficacy of abciximab, an irreversible inhibitor, compared with tirofiban and eptifibatide, reversible inhibitors of platelet function.

MATERIALS AND METHODS

We performed a comprehensive literature search for studies on rescue therapy for intraprocedural thromboembolic complications with glycoprotein IIb/IIIa inhibitors or fibrinolysis during endovascular treatment of intracranial aneurysms. We studied rates of periprocedural stroke/hemorrhage, procedure-related morbidity and mortality, immediate arterial recanalization, and long-term good clinical outcome. Event rates were pooled across studies by using random-effects meta-analysis.

RESULTS

Twenty-three studies with 516 patients were included. Patients receiving GP IIb/IIIa inhibitors had significantly lower perioperative morbidity from stroke/hemorrhage compared with those treated with fibrinolytics (11.0%; 95% CI, 7.0%-16.0% versus 29.0%; 95% CI, 13.0%-55.0%; P = .04) and were significantly less likely to have long-term morbidity (16.0%; 95% CI, 11.0%-21.0% versus 35.0%; 95% CI, 17.0%-58.0%; P = .04). There was a trend toward higher recanalization rates among patients treated with glycoprotein IIb/IIIa inhibitors compared with those treated with fibrinolytics (72.0%; 95% CI, 64.0%-78.0% versus 50.0%; 95% CI, 28.0%-73.0%; P = .08). Patients receiving tirofiban or eptifibatide had significantly higher recanalization rates compared with those treated with abciximab (83.0%; 95% CI, 68.0%-91.0% versus 66.0%; 95% CI, 58.0%-74.0%; P = .05). No difference in recanalization was seen in patients receiving intra-arterial (77.0%; 95% CI, 66.0%-85.0%) or intravenous GP IIb/IIIa inhibitors (70.0%; 95% CI, 57.0%-80.0%, P = .36).

CONCLUSIONS

Rescue therapy with thrombolytic agents resulted in significantly more morbidity than rescue therapy with glycoprotein IIb/IIIa inhibitors. Tirofiban/eptifibatide resulted in significantly higher recanalization rates compared with abciximab.

Periprocedural and mid-term technical and clinical events after flow diversion for intracranial aneurysms

OBJECT

Flow diversion has emerged as a promising treatment alternative for cerebral aneurysms. As a new device, treatment-related events and complications are currently being characterized.

METHODS

Data on 100 consecutive procedures with the intention to use flow diversion were prospectively collected and analyzed retrospectively.

RESULTS

Ninety-five aneurysms were treated in 93 patients during 100 consecutive procedures in which the intention was to treat an intracranial aneurysm with flow diversion. Death occurred in 1% and permanent morbidity in 1%. However, periprocedural technical complications occurred in 35% of the procedures and included proximal device migration in 12%, incomplete device expansion in 9%, catheter-induced vasospasm in 6%, and artery perforation from the wire in 3%. Perioperative clinical events were seen in 28% (thromboembolism and access site complications were the most common, being observed in 6.5% of patients). Worsened extraocular motility was seen in 5.4% and resolved in 4/5 patients. Mean clinical follow-up was 17 months. There were no late clinical or technical issues resulting in permanent deficits, although one patient suffered worsening ataxia. Overall, using very strict angiographic criteria, complete angiographic obliteration was 50% at 6 months and 69% after 1 year.

CONCLUSIONS

Flow diversion for intracranial aneurysms is a safe and effective treatment. Technical and clinical events are common in the perioperative period. Careful perioperative care and proper management of technical and clinical events encountered is key to achieving low morbidity and mortality. Late clinical events can occur but are unlikely to result in permanent complications.

Racial and health insurance disparities of inpatient spine augmentation for osteoporotic vertebral fractures from 2005 to 2010

BACKGROUND AND PURPOSE

Vertebroplasty and kyphoplasty are frequently utilized in the treatment of symptomatic vertebral body fractures. While prior studies have demonstrated disparities in the treatment of back pain and care for osteoporotic patients, disparities in spine augmentation have not been investigated. We investigated racial and health insurance status differences in the use of spine augmentation for the treatment of osteoporotic vertebral fractures in the United States.

MATERIALS AND METHODS

Using the Nationwide Inpatient Sample from 2005 to 2010, we selected all discharges with a primary diagnosis of vertebral fracture (International Classification of Diseases-9 code 733.13). Patients who received spine augmentation were identified by using International Classification of Diseases-9 procedure code 81.65 for vertebroplasty and 81.66 for kyphoplasty. Patients with a diagnosis of cancer were excluded. We compared usage rates of spine augmentation by race/ethnicity (white, black, Hispanic, and Asian/Pacific Islander) and insurance status (Medicare, Medicaid, self-pay, and private). Comparisons among groups were made by using χ(2) tests. A multivariate logistic regression analysis was fit to determine variables associated with spine augmentation use.

RESULTS

A total of 228,329 patients were included in this analysis, of whom 129,206 (56.6%) received spine augmentation. Among patients with spine augmentation, 97,022 (75%) received kyphoplasty and 32,184 (25%) received vertebroplasty; 57.5% (92,779/161,281) of white patients received spine augmentation compared with 38.7% (1405/3631) of black patients (P < .001). Hispanic patients had significantly lower spine augmentation rates compared with white patients (52.3%, 3777/7222, P < .001) as did Asian/Pacific Islander patients (53.1%, 1784/3361, P < .001). The spine augmentation usage rate was 57.2% (114,768/200,662) among patients with Medicare, significantly higher than that of those with Medicaid (43.9%, 1907/4341, P < .001) and those who self-pay (40.2%, 488/1214, P < .001).

CONCLUSIONS

Our findings demonstrate substantial racial and health insurance-based disparities in the inpatient use of spinal augmentation for the treatment of osteoporotic vertebral fracture.

Endovascular treatment of anterior communicating artery aneurysms: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Endovascular therapy has become an acceptable alternative to traditional clipping for the management of intracranial aneurysms. However, a limited number of studies have examined outcomes and complications specific to embolization of anterior communicating artery aneurysms.

MATERIALS AND METHODS

A systematic review of the literature was conducted with the use of multiple data bases to identify reports on endovascular treatment of anterior communicating artery aneurysms between 1994 and 2012. Angiographic results, clinical outcomes, and complication rates were pooled across studies by using random-effects meta-analysis with subgroup analysis of outcomes by rupture status and time trend stratification.

RESULTS

Fourteen studies, consisting of 1552 treated anterior communicating artery aneurysms, were included in this meta-analysis. The rate of immediate and long-term complete and near-complete angiographic occlusion was 88% (95% CI = 81-93%) and 85% (95% CI = 78-90%), respectively. Intraprocedural rupture rate was 4% (95% CI = 3-6%). The re-bleeding rate was 2% (95% CI = 1-4%) and the retreatment rate was 7% (95% CI = 5-12%). Morbidity or mortality caused by perioperative stroke occurred at a 3% (95% CI = 2-6%) rate. Overall procedure-related morbidity and mortality were 6% (95% CI = 4-8%) and 3% (95% CI = 2-4%), respectively. Outcomes did not differ between ruptured and unruptured aneurysms, nor did outcomes change over time, though these latter subanalyses were relatively underpowered.

CONCLUSIONS

Endovascular therapy for anterior communicating artery aneurysms is associated with a high rate of complete angiographic occlusion. However, the procedure-related permanent morbidity and mortality are not negligible for aneurysms in this location.

Early basal ganglia hyperperfusion on CT perfusion in acute ischemic stroke: a marker of irreversible damage?

BACKGROUND AND PURPOSE

CT perfusion scans are often used in acute stroke evaluations. We aimed to assess the outcome of areas of basal ganglia hyperperfusion on CTP in patients with acute ischemic stroke.

MATERIALS AND METHODS

We retrospectively reviewed the medical records and brain imaging of 139 patients presenting with acute stroke who underwent CTP for consideration of endovascular recanalization. Hyperperfusion was assessed qualitatively and defined as a matched region of increased cerebral blood flow and cerebral blood volume. CTA was used to locate arterial occlusion. Follow-up imaging was used to determine whether regions of hyperperfusion at baseline became infarcted or developed hemorrhage. Angiographic imaging was assessed to determine the presence or absence of early venous opacification.

RESULTS

Six patients (4.3%) demonstrated hyperperfusion in the basal ganglia of the affected side (4 in the lenticular nucleus and 2 in the caudate). In all cases, the area of hyperperfusion ultimately proved to be infarcted. All patients had received intravenous thrombolysis before the CTP. CTA at the time of CTP showed middle or distal M1 occlusion but patency of the proximal M1 and A1 segments. Intracranial hemorrhage was noted in 2 of these 6 patients at follow-up.

CONCLUSIONS

Acute basal ganglia hyperperfusion in patients with stroke may indicate nonviable parenchyma and risk of hemorrhagic conversion.

Immunoglobulin G4-related disease of the orbit: imaging features in 27 patients

BACKGROUND AND PURPOSE

Immunoglobulin G4-related disease is a systemic fibroinflammatory process of unknown etiology, characterized by tissue infiltration by immunoglobulin G4 plasma cells. The purpose of this study was to retrospectively identify the spectrum of imaging features seen in immunoglobulin G4-related disease of the orbit.

MATERIALS AND METHODS

This study included 27 patients with biopsy-proved immunoglobulin G4-related disease of the orbit and either a CT or MR imaging of the orbits. These CT or MR imaging examinations were evaluated for the following: extraocular muscle size, extraocular muscle tendon enlargement, lacrimal gland enlargement, infiltrative process in the orbital fat (increased attenuation on CT or abnormal signal on MR imaging), infraorbital nerve enlargement, mucosal thickening in the paranasal sinuses, and extension of orbital findings intracranially.

RESULTS

Extraocular muscles were enlarged in 24 of 27 (89%) patients, 21 (88%) bilaterally. In 32 of 45 (71%) affected orbits, the lateral rectus was the most enlarged muscle. In 26 (96%) patients, the tendons of the extraocular muscles were spared. Nineteen (70%) patients had lacrimal gland enlargement. Twelve (44%) patients had an infiltrative process within the orbital fat. Infraorbital nerve enlargement was seen in 8 (30%) patients. Twenty-four (89%) patients had sinus disease. Cavernous sinus or Meckel cave extension was seen in 3 (11%) patients.

CONCLUSIONS

In patients with extraocular muscle enlargement, particularly when the tendons are spared and the lateral rectus is the most enlarged, and even more so when other noted findings are present, immunoglobulin G4-related disease should be a leading differential consideration, even over more commonly known etiologies of extraocular muscle enlargement.

Percutaneous closure devices do not reduce the risk of major access site complications in patients undergoing elective carotid stent placement

PURPOSE

To examine the risk of femoral access site complications in patients undergoing carotid stent placement who were treated with a closure device compared with patients who were not treated with a closure device.

MATERIALS AND METHODS

A national, multihospital patient database, the Premier Perspective database, was used to identify patients hospitalized for carotid stent placement from 2006-2011. To reduce potential selection bias, a propensity score was generated for each patient using relevant clinical variables. Propensity score adjustment via 1:1 matching was performed on patients who did and did not receive a closure device. Primary outcomes were minor femoral access site complications and major complications requiring procedural intervention. Secondary outcomes included in-hospital mortality, stroke, and blood transfusion.

RESULTS

Among 12,287 patients who underwent carotid stent placement at 217 hospitals, 6,398 (52%) received a closure device on the day of the procedure. After propensity score matching, patients who received a closure device had a lower likelihood of minor access site complications (4.2% vs 5.4%; odds ratio = 0.77; 95% confidence interval, 0.55-0.93; P = .0071) compared with patients who did not receive a closure device; however, this difference was small and likely not clinically relevant. Both groups had a similar risk of major access site complications (P = .32), in-hospital mortality (P = .0520), and stroke (P = .31).

CONCLUSIONS

Use of a closure device was not associated with a substantially reduced risk of major adverse events after carotid stent placement and was associated with only a small improvement in minor access site complications.

Abstract W MP34: Safety and Efficacy of Hydrosoft Coils in the Treatment of the Aneurysm Neck: Preliminary Results From the GEL THE NEC Registry

Background and Purpose: The HydroSoft coil was developed to be placed along the aneurysm neck to enhance intracranial aneurysm healing. In order to better understand the safety and efficacy of Hydrosoft coils in treating the aneurysm neck, the GEL THE NEC multicenter registry was developed. We report immediate angiographic and clinical results of this prospective registry.

Methods: The GEL THE NEC study was undertaken at 30 centers in 5 countries. Patients aged 21-90 years with a ruptured or unruptured aneurysm 3-15 mm in size were eligible for enrollment. For each patient the following data were obtained: demographics and comorbidities, aneurysm geometry, use of adjunctive devices, immediate angiographic outcomes, and early (<30 days) adverse events. Postoperative anatomic results were graded by on-site neuroradiologists using the Modified Raymond Scale (Raymond 1=complete obliteration of aneurysm including the neck, Raymond 2=contrast filling the neck of the aneurysm without opacification of the aneurysm sac, Raymond 3=contrast filling the sac of the aneurysm). Predictors of good angiographic outcome were studied using chi-squared and t-tests.

Results: A total of 571 patients with 571 aneurysms have been treated thus far in the study (196 ruptured, 375 unruptured). HydroSoft coils were successfully deployed in 549 (96.3%) of these patients. Adjunctive devices were used in 307 cases (53.8%) (212 balloon assistance, 89 stent). Aneurysmal occlusion rates were the following: 261 patients (47.3%) exhibited Raymond 1 occlusion, 257 patients (47.0%) had Raymond 2, and 29 patients (5.3%) had Raymond 3. Early post-operative stroke occurred in 10 patients (1.8%). Aneurysm perforation occurred in 11 patients (1.9%). Coil prolapse/migration occurred in 8 patients (1.4%). Early post-operative death occurred in 3 patients, all of whom presented with SAH (0.5%). Small aneurysm neck size was a significant predictor of good angiographic outcome (P=0.0003).

Conclusions: Endovascular treatment of intracranial aneurysms with HydroSoft coils resulted in high rates of satisfactory occlusion (94.3%) and low rates of major clinical complications. Aneurysm neck size was a significant predictor of angiographic outcomes.

Risk of intravenous contrast material-mediated acute kidney injury: a propensity score-matched study stratified by baseline-estimated glomerular filtration rate

PURPOSE

To determine the effect of baseline estimated glomerular filtration rate (eGFR) on the causal association between intravenous iodinated contrast material exposure and subsequent development of acute kidney injury (AKI) in propensity score-matched groups of patients who underwent contrast material-enhanced or unenhanced computed tomography (CT).

MATERIALS AND METHODS

This retrospective study was HIPAA compliant and institutional review board approved. All patients who underwent contrast-enhanced (contrast material group) or unenhanced (non-contrast material group) CT between 2000 and 2010 were identified and stratified according to baseline eGFR by using Kidney Disease Outcomes Quality Initiative cutoffs for chronic kidney disease into subgroups with eGFR of 90 or greater, 60-89, 30-59, and less than 30 mL/min/1.73 m(2). Propensity score generation and 1:1 matching of patients were performed in each eGFR subgroup. Incidence of AKI (serum creatinine [SCr] increase of ≥0.5 mg/dL [≥44.2 μmol/L] above baseline) was compared in the matched subgroups by using the Fisher exact test.

RESULTS

A total of 12 508 propensity score-matched patients with contrast-enhanced and unenhanced scans met all inclusion criteria. In this predominantly inpatient cohort, the incidence of AKI significantly increased with decreasing baseline eGFR (P < .0001). However, this incidence was not significantly different between contrast material and non-contrast material groups in any eGFR subgroup; for the subgroup with eGFR of 90 or greater (n = 1642), odds ratio (OR) was 0.91 (95% confidence interval [CI]: 0.38, 2.15), P = .82; for the subgroup with eGFR of 60-89 (n = 3870), OR was 1.03 (95% CI: 0.66, 1.60), P = .99; for the subgroup with eGFR of 30-59 (n = 5510), OR was 0.94 (95% CI: 0.76, 1.18), P = .65; and for the subgroup with eGFR of less than 30 mL/min/1.73 m(2) (n = 1486), OR was 0.97 (95% CI: 0.72, 1.30), P = .89.

CONCLUSION

Diminished eGFR is associated with an increased risk of SCr-defined AKI following CT examinations. However, the risk of AKI is independent of contrast material exposure, even in patients with eGFR of less than 30 mL/min/1.73 m(2).

Treatment of cavernous sinus aneurysms with flow diversion: results in 44 patients

BACKGROUND AND PURPOSE

Aneurysms of the cavernous segment of the ICA are difficult to treat with standard endovascular techniques, and ICA sacrifice achieves a high rate of occlusion but carries an elevated level of surgical complications and risk of de novo aneurysm formation. We report rates of occlusion and treatment-related data in 44 patients with cavernous sinus aneurysms treated with flow diversion.

MATERIALS AND METHODS

Patients with cavernous segment aneurysms treated with flow diversion were selected from a prospectively maintained data base of patients from 2009 to the present. Demographic information, treatment indications, number/type of flow diverters placed, outcome, complications (technical or clinical), and clinical/imaging follow-up data were analyzed.

RESULTS

We identified 44 patients (37 females, 7 males) who had a flow diverter placed for treatment of a cavernous ICA aneurysm (mean age, 57.2; mean aneurysm size, 20.9 mm). The mean number of devices placed per patient was 2.2. At final angiographic follow-up (mean, 10.9 months), 71% had complete occlusion, and of those with incomplete occlusion, 40% had minimal remnants (<3 mm). In symptomatic patients, complete resolution or significant improvement in symptoms was noted in 90% at follow-up. Technical complications (which included, among others, vessel perforation in 4 patients, groin hematoma in 2, and asymptomatic carotid occlusion in 1) occurred in approximately 36% of patients but did not result in any clinical sequelae immediately or at follow-up.

CONCLUSIONS

Our series of flow-diversion treatments achieved markedly greater rates of complete occlusion than coiling, with a safety profile that compares favorably with that of carotid sacrifice.

Pretreatment advanced imaging in patients with stroke treated with IV thrombolysis: evaluation of a multihospital data base

BACKGROUND AND PURPOSE

CT angiography, CT perfusion, and MR imaging have all been advocated as potentially useful in treatment planning for patients with acute ischemic stroke. We evaluated a large multihospital data base to determine how the use of advanced imaging is evolving in patients treated with intravenous thrombolysis.

MATERIALS AND METHODS

Patients with acute ischemic stroke receiving IV thrombolytic therapy from 2008 to 2011 were identified by using the Premier Perspective data base. Mortality and discharge to long-term care rates were compared following multivariate logistic regression between patients who received head CT only versus those who received CTA without CT perfusion, CT perfusion, or MR imaging.

RESULTS

Of 12,429 included patients, 7305 (59%) were in the CT group, 2359 (19%) were in the CTA group, 848 (7%) were in the CTP group, and 1917 (15%) were in the MR group. From 2008 to 2011, the percentage of patients receiving head CT only decreased from 64% to 55%, while the percentage who received cerebral CT perfusion increased from 3% to 8%. The use of CT angiography and MR imaging marginally increased (1%-2%). Outcomes were similar between CT only and advanced imaging patients, except discharge to long-term care was slightly more frequent in the CTP group (OR = 1.17 [95% CI, 0.96-1.43]; P = .0412) and MR group (OR = 1.14 [95% CI, 1.01-1.28]; P = .0177) and mortality was lower in the MR group (OR = 0.64 [95% CI, 0.52-0.79]; P < .0001).

CONCLUSIONS

Use of advanced imaging is increasing in patients treated with IV thrombolysis. While there were differences in outcomes among imaging groups, the clinical effect of advanced imaging remains unclear.

Adaptive grid generation in a patient-specific cerebral aneurysm

Adapting grid density to flow behavior provides the advantage of increasing solution accuracy while decreasing the number of grid elements in the simulation domain, therefore reducing the computational time. One method for grid adaptation requires successive refinement of grid density based on observed solution behavior until the numerical errors between successive grids are negligible. However, such an approach is time consuming and it is often neglected by the researchers. We present a technique to calculate the grid size distribution of an adaptive grid for computational fluid dynamics (CFD) simulations in a complex cerebral aneurysm geometry based on the kinematic curvature and torsion calculated from the velocity field. The relationship between the kinematic characteristics of the flow and the element size of the adaptive grid leads to a mathematical equation to calculate the grid size in different regions of the flow. The adaptive grid density is obtained such that it captures the more complex details of the flow with locally smaller grid size, while less complex flow characteristics are calculated on locally larger grid size. The current study shows that kinematic curvature and torsion calculated from the velocity field in a cerebral aneurysm can be used to find the locations of complex flow where the computational grid needs to be refined in order to obtain an accurate solution. We found that the complexity of the flow can be adequately described by velocity and vorticity and the angle between the two vectors. For example, inside the aneurysm bleb, at the bifurcation, and at the major arterial turns the element size in the lumen needs to be less than 10% of the artery radius, while at the boundary layer, the element size should be smaller than 1% of the artery radius, for accurate results within a 0.5% relative approximation error. This technique of quantifying flow complexity and adaptive remeshing has the potential to improve results accuracy and reduce computational time for patient-specific hemodynamics simulations, which are used to help assess the likelihood of aneurysm rupture using CFD calculated flow patterns.

Cellular mechanisms of aneurysm occlusion after treatment with a flow diverter

PURPOSE

To characterize the progression of healing across aneurysm necks following treatment with a flow diverter in a rabbit aneurysm model.

MATERIALS AND METHODS

With institutional animal care and use committee approval, saccular aneurysms were created in 20 rabbits and treated with flow diverters. On days 1, 3, and 7 and weeks 4 and 8 after implantation, the aneurysm and the device-implanted vessel were harvested. En face staining of the gross specimen was performed for endothelial cells, endothelial progenitor cells, smooth muscle cells, and inflammatory cells.

RESULTS

The parent artery segments covered by the flow diverters were completely devoid of endothelial cells at 1 and 3 days but had completely reendothelialized by 7 days. At all time points, the struts along the patent portions of the aneurysm necks harbored scattered tissue islands composed exclusively of inflammatory cells. At 4 and 8 weeks, all samples contiguous with the tissue along the parent arteries had translucent tissue present along the occluded segments of the aneurysm neck. The vast majority of endothelial cells were contiguous with the parent artery and had smooth muscle cells underlying them. Endothelial progenitor cells were not observed along the neck of any aneurysm. Aneurysm closure was noted only when complete or nearly complete endothelialization over the device struts was present.

CONCLUSION

The initial event following flow diversion treatment is adherence of clusters of inflammatory cells across the aneurysm neck. Endothelialization is relatively delayed and derived exclusively from cells in the adjacent parent artery.