Identification of Hostile Hemodynamics and Geometries of Cerebral Aneurysms: A Case-Control Study.

BACKGROUND AND PURPOSE: Hostile hemodynamic conditions and geometries are thought to predispose aneurysms for instability and rupture. This study compares stable, unstable, and ruptured aneurysms while controlling for location and patient characteristics. MATERIALS AND METHODS: The hemodynamics and geometries of 165 stable, 65 unstable, and 554 ruptured aneurysms were compared. Hemodynamics was modeled using image-based computational fluid dynamics. Case-control pairs were selected matching aneurysm location, patient age, and sex. Paired Wilcoxon tests were used to compare hemodynamic and geometric variables among different aneurysm groups. The pairing was repeated 100 times, and the combined P values were calculated and adjusted for multiple testing. RESULTS: Ruptured aneurysms had lower minimum wall shear stress (P = .03), higher maximum wall shear stress (P = .03), more concentrated (P = .03) and mean oscillatory shear stress (P = .03), higher maximum velocity (P = .03), and more complex flows (vortex core-line length, P = .03) than stable aneurysms. Similarly, unstable aneurysms had more concentrated shear stress (P = .04) and more complex flows (vortex core-line length, P = .04) than stable aneurysms. Compared with stable aneurysms, ruptured aneurysms were larger (size ratio, aneurysm size/vessel size, P = .03), more elongated (aspect ratio, P = .03), and irregular (nonsphericity index, P = .03). Similarly, unstable aneurysms were larger (size ratio, P = .04), more elongated (aspect ratio, P = .04), and irregular (bulge location, P = .04; area-weighted Gaussian curvature; P = .04) than stable aneurysms. No significant differences were found between unstable and ruptured aneurysms. CONCLUSIONS: Unstable and ruptured aneurysms have more complex flows with concentrated wall shear stress and are larger, more elongated, and irregular than stable aneurysms, independent of aneurysm location and patient sex and age.

Hemodynamic Characteristics of Ruptured and Unruptured Multiple Aneurysms at Mirror and Ipsilateral Locations.

BACKGROUND AND PURPOSE: Different hemodynamic patterns have been associated with aneurysm rupture. The objective was to test whether hemodynamic characteristics of the ruptured aneurysm in patients with multiple aneurysms were different from those in unruptured aneurysms in the same patient. MATERIALS AND METHODS: Twenty-four mirror and 58 ipsilateral multiple aneurysms with 1 ruptured and the others unruptured were studied. Computational fluid dynamics models were created from 3D angiographies. Case-control studies of mirror and ipsilateral aneurysms were performed with paired Wilcoxon tests. RESULTS: In mirror pairs, the ruptured aneurysm had more oscillatory wall shear stress (P = .007) than the unruptured one and tended to be more elongated (higher aspect ratio), though this trend achieved only marginal significance (P = .03, 1-sided test). In ipsilateral aneurysms, ruptured aneurysms had larger maximum wall shear (P = .05), more concentrated (P < .001) and oscillatory wall shear stress (P < .001), stronger (P < .001) and more concentrated inflow jets (P < .001), larger maximum velocity (P < .001), and more complex flow patterns (P < .001) compared with unruptured aneurysms. Additionally, ruptured aneurysms were larger (P < .001) and more elongated (P < .001) and had wider necks (P < .001) and lower minimum wall shear stress (P < .001) than unruptured aneurysms. CONCLUSIONS: High wall shear stress oscillations and larger aspect ratios are associated with rupture in mirror aneurysms. Adverse flow conditions characterized by high and concentrated inflow jets; high, concentrated, and oscillatory wall shear stress; and strong, complex and unstable flow patterns are associated with rupture in ipsilateral multiple aneurysms. In multiple ipsilateral aneurysms, these unfavorable flow conditions are more likely to develop in larger, more elongated, more wide-necked, and more distal aneurysms.

Angioarchitectures and Hemodynamic Characteristics of Posterior Communicating Artery Aneurysms and Their Association with Rupture Status.

BACKGROUND AND PURPOSE: Intracranial aneurysms originating at the posterior communicating artery are known to have high rupture risk compared with other locations. We tested the hypothesis that different angioarchitectures (ie, branch point configuration) of posterior communicating artery aneurysms are associated with aneurysm hemodynamics, which in turn predisposes aneurysms to rupture. MATERIALS AND METHODS: A total of 313 posterior communicating artery aneurysms (145 ruptured, 168 unruptured) were studied with image-based computational fluid dynamics. Aneurysms were classified into different angioarchitecture types depending on the location of the aneurysm with respect to parent artery bifurcation. Hemodynamic characteristics were compared between ruptured and unruptured aneurysms, as well as among aneurysms with different angioarchitectures. RESULTS: Angioarchitecture was associated with rupture (P = .003). Ruptured aneurysms had higher, more concentrated, and more oscillatory wall shear stress distributions (maximum wall shear stress, P < .001; shear concentration index, P < .001; mean oscillatory shear index, P < .001), stronger and more concentrated inflow jets (represented as Q, P = .01; inflow concentration index, P < .001), and more complex and unstable flow patterns (vortex core length, P < .001; proper orthogonal decomposition entropy, P < .001) compared with unruptured aneurysms. These adverse conditions were more common in aneurysms with bifurcation-type angioarchitectures compared with those with lateral or sidewall angioarchitectures. Interestingly, ruptured aneurysms also had lower normalized mean wall shear stress (P = .02) and minimum wall shear stress (P = .002) than unruptured aneurysms. CONCLUSIONS: High-flow intrasaccular hemodynamic characteristics, commonly found in bifurcation-type angioarchitectures, are associated with the posterior communicating artery aneurysm rupture status. These characteristics include strong and concentrated inflow jets, concentrated regions of elevated wall shear stress, oscillatory wall shear stress, lower normalized wall shear stress, and complex and unstable flow patterns.

Differences in Hemodynamics and Rupture Rate of Aneurysms at the Bifurcation of the Basilar and Internal Carotid Arteries.

BACKGROUND AND PURPOSE: Cerebral aneurysms in the posterior circulation are known to have a higher rupture risk than those in the anterior circulation. We sought to test the hypothesis that differences in hemodynamics can explain the difference in rupture rates. MATERIALS AND METHODS: A total of 117 aneurysms, 63 at the tip of the basilar artery (27 ruptured, 36 unruptured, rupture rate = 43%) and 54 at the bifurcation of the internal carotid artery (11 ruptured, 43 unruptured, rupture rate = 20%) were analyzed with image-based computational fluid dynamics. Several hemodynamic variables were compared among aneurysms at each location and between ruptured and unruptured aneurysms at each location. RESULTS: On average, aneurysms at the basilar tip had more concentrated inflow (P < .001), a larger inflow rate (P < .001), a larger maximum oscillatory shear index (P = .003), more complex flows (P = .033), and smaller areas under low wall shear stress (P < .001) than aneurysms at the bifurcation of the internal carotid artery. In general, ruptured aneurysms had larger inflow concentration (P = .02), larger shear concentration (P = .02), more complex flows (P < .001), and smaller minimum wall shear stress (P = .003) than unruptured aneurysms. CONCLUSIONS: High flow conditions, characterized by large and concentrated inflow jets, complex and oscillatory flow patterns, and wall shear stress distributions with focalized regions of high shear and large regions of low shear, are associated with aneurysm rupture, especially for basilar tip aneurysms. The higher flow conditions in basilar tip aneurysms could explain their increased rupture risk compared with internal carotid bifurcation aneurysms.

Effects of perianeurysmal environment during the growth of cerebral aneurysms: a case study.

BACKGROUND AND PURPOSE: The natural history of cerebral aneurysms is thought to be governed by multifactorial processes involving hemodynamics, biomechanics, mechanobiology, and perianeurysmal environment. The purpose of this study was to highlight the importance of considering the influence of contacts with perianeurysmal environment structures on the hemodynamics and geometric evolution of intracranial aneurysms. MATERIALS AND METHODS: A large aneurysm of the basilar artery in contact with bone and observed to grow during a 4-year follow-up period was selected for study. Anatomic models were constructed from longitudinal CTA images acquired at 1-year intervals during the observation period. Computational fluid dynamics simulations were carried out under pulsatile flow conditions to analyze the blood flow pattern and WSS distribution in the aneurysm during its evolution. RESULTS: The aneurysm was observed to grow against the bone, resulting in a geometric change of the proximal parent artery, which, in turn, induced substantial changes in the aneurysm hemodynamics. In particular, a region of elevated WSS created by the inflow streams was observed to shift locations around the place where the aneurysm enlarged in contact with the bone as the aneurysm progressed. In addition, a "notch" near the distal end of the aneurysm, away from the bone and subject to relatively high WSS, was observed to grow and, later, completely disappear. CONCLUSIONS: Contacts with perianeurysmal structures need to be considered and analyzed to assess whether they could exert a significant influence on the geometric evolution of each individual intracranial aneurysm and its hemodynamics.

Aneurysm rupture following treatment with flow-diverting stents: computational hemodynamics analysis of treatment.

BACKGROUND AND PURPOSE: Flow-diverting approaches to intracranial aneurysm treatment had many promising early results, but recent apparently successful treatments have been complicated by later aneurysm hemorrhage. We analyzed 7 cases of aneurysms treated with flow diversion to explore the possible rupture mechanisms. MATERIALS AND METHODS: CFD analysis of pre- and posttreatment conditions was performed on 3 giant aneurysms that ruptured after treatment and 4 successfully treated aneurysms. Pre- and posttreatment hemodynamics were compared including WSS, relative blood flows, vascular resistances, and pressures, to identify the effects of flow-diverter placements. RESULTS: Expected reductions in aneurysm velocity and WSS were obtained, indicating effective flow diversion from the sac into the parent artery, consistent with periprocedural observations. In each case with postaneurysm rupture, the result of flow diversion led to an increase in pressure within the aneurysm. This pressure increase is related to larger effective resistance in the parent artery from placement of the devices and, in 2 cases, the reduction of a preaneurysm stenosis. CONCLUSIONS: Flow-diversion devices can cause intra-aneurysmal pressure increases, which can potentially lead to rupture, especially for giant aneurysms. This relates both to changes in the parent artery configuration, such as reduction of a proximal stenosis, and to the flow diversion into higher resistance parent artery pathways combined with cerebral autoregulation, leading to higher pressure gradients. These may be important effects that should be considered when planning interventions. Potentially dangerous cases could be identified with angiography and/or patient-specific CFD models.

Association of hemodynamic characteristics and cerebral aneurysm rupture.

BACKGROUND AND PURPOSE: Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. This report describes a study of the associations between qualitative intra-aneurysmal hemodynamics and the rupture of cerebral aneurysms. MATERIALS AND METHODS: Two hundred ten consecutive aneurysms were analyzed by using patient-specific CFD simulations under pulsatile flow conditions. The aneurysms were classified into categories by 2 blinded observers, depending on the complexity and stability of the flow pattern, size of the impingement region, and inflow concentration. A statistical analysis was then performed with respect to the history of previous rupture. Interobserver variability analysis was performed. RESULTS: Ruptured aneurysms were more likely to have complex flow patterns (83%, P < .001), stable flow patterns (75%, P = .0018), concentrated inflow (66%, P = <.0001), and small impingement regions (76%, P = .0006) compared with unruptured aneurysms. Interobserver variability analyses indicated that all the classifications performed were in very good agreement-that is, well within the 95% CI. CONCLUSIONS: A qualitative hemodynamic analysis of cerebral aneurysms by using image-based patient-specific geometries has shown that concentrated inflow jets, small impingement regions, complex flow patterns, and unstable flow patterns are correlated with a clinical history of prior aneurysm rupture. These qualitative measures provide a starting point for more sophisticated quantitative analysis aimed at assigning aneurysm risk of future rupture. These analyses highlight the potential for CFD to play an important role in the clinical determination of aneurysm risks.

Wall motion estimation in intracranial aneurysms.

The quantification of wall motion in cerebral aneurysms is becoming important owing to its potential connection to rupture, and as a way to incorporate the effects of vascular compliance in computational fluid dynamics simulations. Most of papers report values obtained with experimental phantoms, simulated images or animal models, but the information for real patients is limited. In this paper, we have combined non-rigid registration with signal processing techniques to measure pulsation in real patients from high frame rate digital subtraction angiography. We have obtained physiological meaningful waveforms with amplitudes in the range 0 mm-0.3 mm for a population of 18 patients including ruptured and unruptured aneurysms. Statistically significant differences in pulsation were found according to the rupture status, in agreement with differences in biomechanical properties reported in the literature.

Blood-flow characteristics in a terminal basilar tip aneurysm prior to its fatal rupture.

BACKGROUND AND PURPOSE: The development and validation of methods to stratify the risk of rupture of cerebral aneurysms is highly desired because current treatment risks can exceed the natural risk of rupture. Because unruptured aneurysms are typically treated before they rupture, it is very difficult to connect the proposed risk indices to the rupture of an individual aneurysm. The purpose of this case study was to analyze the hemodynamic environment of a saccular aneurysm of the terminal morphology subtype that was imaged just before its rupture and to test whether the hemodynamic characteristics would designate this particular aneurysm as at high risk. MATERIALS AND METHODS: A patient-specific CFD model was constructed from 3DRA images acquired just hours before the aneurysm ruptured. A pulsatile flow calculation was performed, and hemodynamic characteristics previously connected to rupture were analyzed. RESULTS: It was found that the aneurysm had a concentrated inflow stream, small impingement region, complex intra-aneurysmal flow structure, asymmetric flow split from the parent vessel to the aneurysm and daughter branches, and high levels of aneurysmal WSS near the impaction zone. CONCLUSIONS: The hemodynamic characteristics observed in this aneurysm right before its rupture are consistent with previous studies correlating aneurysm rupture and hemodynamic patterns in saccular and terminal aneurysms. This study supports the notion that hemodynamic information may be used to help stratify the rupture risk of cerebral aneurysms.

Hemodynamics and bleb formation in intracranial aneurysms.

BACKGROUND AND PURPOSE: Intracranial aneurysms with irregular shapes and blebs or secondary outpouchings have been correlated with increased rupture risk. The purpose of this study was to investigate possible associations between the local hemodynamics and the formation of blebs in cerebral aneurysms. MATERIALS AND METHODS: Computational models of 20 cerebral aneurysms harboring 30 well-defined blebs were constructed from 3D rotational angiographies. Models representing the aneurysm before bleb formation were constructed by virtually removing the blebs from the anatomic models. Computational fluid dynamics simulations of the aneurysm before and after bleb formation were performed under pulsatile flows. Flow and WSS visualizations were used to analyze the local hemodynamics in the region of the aneurysm that developed the bleb. RESULTS: Most blebs (80%) occurred at or adjacent to the aneurysm region with the highest WSS before bleb formation, and near the flow impaction zone. Most blebs (83%) were found in regions of the aneurysm previously subjected to high or moderate WSS and progressed to low WSS states after the blebs were formed. Most blebs (77%) were aligned or adjacent to the inflow jet, whereas 17% were aligned with the outflow jet, and only 6% were not aligned with the flow direction. In addition, 90% of the aneurysms had maximal WSS higher than or similar to the WSS in the parent artery. CONCLUSIONS: Blebs form at or adjacent to regions of high WSS and are aligned with major intra-aneurysmal flow structures. Formation of blebs results in a lower WSS state with formation of a counter current vortex. These findings imply that locally elevated WSS could contribute to the focalized wall damage that formed these structures.

Hemodynamic patterns of anterior communicating artery aneurysms: a possible association with rupture.

BACKGROUND AND PURPOSE: The anterior communicating artery (AcomA) is a predilect location of aneurysms which typically carry higher rupture risks than other locations in the anterior circulation. The purpose of this study was to characterize the different flow types present in AcomA aneurysms and to investigate possible associations with rupture. MATERIALS AND METHODS: Patient-specific computational models of 26 AcomA aneurysms were constructed from 3D rotational angiography images. Bilateral images were acquired in 15 patients who had both A1 segments of the anterior cerebral arteries, and models of the whole anterior circulation were created by fusing the reconstructed left and right arterial trees. Computational fluid dynamics simulations were performed under pulsatile flow conditions measured on a healthy subject. Visualizations of flow velocity, instantaneous streamlines, and wall shear stress (WSS) were performed. These were analyzed for flow patterns, size of the impaction zone, and peak WSS and then correlations were made with prior history of rupture. RESULTS: Aneurysms with small impaction zones were more likely to have ruptured than those with large impaction zones (83% versus 63%). Maximum intra-aneurysmal WSS (MWSS) for the unruptured aneurysms ranged from 10 to 230 dyne/cm(2) (mean, 114 dyne/cm(2)) compared with ruptured aneurysms, which ranged from 35 to 1500 dyne/cm(2) (mean, 271 dyne/cm(2)). This difference in MWSS was statistically significant at 90% confidence levels (P = .10). CONCLUSIONS: Aneurysms with small impaction zones, higher flow rates entering the aneurysm, and elevated MWSS are associated with a clinical history of previous rupture.

Hemodynamics in a lethal basilar artery aneurysm just before its rupture.

BACKGROUND AND PURPOSE: Hemodynamics is thought to play an important role in the mechanisms of cerebral aneurysm initiation, progression, and rupture. The purpose of this study was to present a hemodynamic study of a cerebral aneurysm immediately before its rupture to assess whether previously identified hemodynamic characteristics would classify this aneurysm in the high-risk category. MATERIALS AND METHODS: A patient-specific computational fluid dynamics model was constructed from 3D rotational angiographic images acquired just hours before the aneurysm had ruptured. A pulsatile flow simulation was carried out, and the hemodynamics characterized by the concentration of the inflow jet, the size of the flow impingement region, and the complexity and stability of the flow pattern. RESULTS: We found that the aneurysm had a concentrated inflow jet that impacted onto a small region of the dome of the aneurysm and created a complex, unstable flow pattern. CONCLUSIONS: This study supports the proposition that hemodynamic characteristics derived from image-based computational models can be used to identify cerebral aneurysms at high risk for rupture.

Cement-embolic stroke associated with vertebroplasty.

Major neurologic morbidity and mortality with vertebroplasty are rare. We describe a 71-year-old woman who had a stroke approximately 30 minutes after vertebroplasty. Imaging revealed that bone cement had embolized to the left middle cerebral artery. Emergency embolectomy was attempted but was unsuccessful. This report emphasizes the need to be aware that intracranial embolization of polymethylmethacrylate can occur and describes management strategies to consider.

Flow-area relationship in internal carotid and vertebral arteries.

Subject-specific computational and experimental models of hemodynamics in cerebral aneurysms require the specification of physiologic flow conditions. Because patient-specific flow data are not always available, researchers have used 'typical' or population average flow rates and waveforms. However, in order to be able to compare the magnitude of hemodynamic variables between different aneurysms or groups of aneurysms (e.g. ruptured versus unruptured) it is necessary to scale the flow rates to the area of the inflow artery. In this work, a relationship between flow rates and vessel areas is derived from phase-contrast magnetic resonance measurements in the internal carotid arteries and vertebral arteries of normal subjects.

Patient-specific computational fluid dynamics modeling of anterior communicating artery aneurysms: a study of the sensitivity of intra-aneurysmal flow patterns to flow conditions in the carotid arteries.

BACKGROUND AND PURPOSE: The purpose of this study was to investigate the effects of unequal physiologic flow conditions in the internal carotid arteries (ICAs) on the hemodynamics of anterior communicating artery aneurysms. METHODS: Patient-specific computational fluid dynamics models of 2 cerebral aneurysms were constructed from bilateral 3D rotational angiograms. The flow dynamics of the aneurysm sac were analyzed under the effect of unequal mean flows, phase shifts, and waveforms between the ICAs. A total of 9 simulations were performed for each patient; cine flow velocity simulations and unsteady wall shear stress (WSS) maps were created for each flow condition. Time-dependent curves of average WSS magnitude over selected regions on the aneurysms were constructed. RESULTS: Mean flow unbalances in the feeding vessels tended to shift the regions of elevated WSS towards the dominating inflow jet and to change the magnitude of the WSS peaks. The overall qualitative appearance of the WSS distribution and velocity simulations was not substantially affected. Phase and waveform asymmetry increased the temporal complexity of the hemodynamic patterns and tended to destabilize the flow pattern. CONCLUSIONS: Differences in the relative phase and waveform shape in ICAs can significantly affect the complexity and stability of the hemodynamic force distributions. The magnitude of these effects is related to the geometry of the aneurysm and the feeding vessels. Conditions affecting the flow characteristics in the parent arteries of cerebral aneurysms with more than 1 avenue of inflow should be incorporated into flow models.

Computational fluid dynamics modeling of intracranial aneurysms: effects of parent artery segmentation on intra-aneurysmal hemodynamics.

PURPOSE: The purpose of this study is to show the influence of the upstream parent artery geometry on intraaneurysmal hemodynamics of cerebral aneurysms. METHODS: Patient-specific models of 4 cerebral aneurysms (1 posterior communicating artery [PcomA], 2 middle cerebral artery [MCA], and 1 anterior communicating artery [AcomA]) were constructed from 3D rotational angiography images. Two geometric models were constructed for each aneurysm. One model had the native parent vessel geometry; the second model was truncated approximately 1 cm upstream from the aneurysm, and the parent artery replaced with a straight cylinder. Corresponding finite element grids were generated and computational fluid dynamics simulations were carried out under pulsatile flow conditions. The intra-aneurysmal flow patterns and wall shear stress (WSS) distributions were visualized and compared. RESULTS: Models using the truncated parent vessel underestimated the WSS in the aneurysms in all cases and shifted the impaction zone to the neck compared with the native geometry. These effects were more pronounced in the PcomA and AcomA aneurysms where upstream curvature was substantial. The MCA aneurysm with a long M1 segment was the least effected. The more laminar flow pattern within the parent vessel in truncated models resulted in a less complex intra-aneurysmal flow patterns with fewer vortices and less velocity at the dome. CONCLUSIONS: Failure to properly model the inflow stream contributed by the upstream parent artery can significantly influence the results of intra-aneurysmal hemodynamic models. The upstream portion of the parent vessel of cerebral aneurysms should be included to accurately represent the intra-aneurysmal hemodynamics.

CT angiography in the rapid triage of patients with hyperacute stroke to intraarterial thrombolysis: accuracy in the detection of large vessel thrombus.

PURPOSE: The purpose of this work was to evaluate the accuracy of CT angiography (CTA) for the detection of large vessel intracranial thrombus in clinically suspected hyperacute (<6 h) stroke patients. METHOD: Forty-four consecutive intraarterial thrombolysis candidates underwent noncontrast CT followed immediately by CTA. Axial source and two-dimensional collapsed maximum intensity projection reformatted CTA images were rated for the presence or absence of large vessel occlusion. Five hundred seventy-two circle-of-Willis vessels were reviewed; arteriographic correlation was available for 224 of these. RESULTS: Sensitivity and specificity for the detection of large vessel occlusion were 98.4 and 98.1%; accuracy, calculated using receiver operating characteristic analysis, was 99%. Mean time for acquisition, reconstruction, and analysis of CTA images was approximately 15 min. CONCLUSION: CTA is highly accurate for the detection and exclusion of large vessel intracranial occlusion and may therefore be valuable in the rapid triage of hyperacute stroke patients to intraarterial thrombolytic treatment.

Posterior fossa decompression and clot evacuation for fourth ventricle hemorrhage after aneurysmal rupture: case report.

OBJECTIVE AND IMPORTANCE: Massive intraventricular hemorrhage due to aneurysmal rupture is associated with a dismal prognosis. An intraventricular clot causing fourth ventricle dilation can cause compression to the brainstem similar to other posterior fossa masses such as cerebellar hemorrhage or infarction. The presence of fourth ventricle dilation carries a very high risk of death within 48 hours. Neither ventricular drainage nor fibrinolytic infusion has been successful in eliminating clots of the fourth ventricle. Posterior fossa decompression and direct evacuation of the clot could have good results in relieving brainstem compression caused by the clot. CLINICAL PRESENTATION: A 45-year-old woman was admitted to our intensive care unit after experiencing an aneurysmal subarachnoid hemorrhage. The neurological examination at admission revealed that she was in Grade V according to the World Federation of Neurological Surgeons grading system, but brainstem reflexes were present. Computed tomographic scanning revealed a massive intraventricular hemorrhage, with fourth ventricle dilation caused by an intraventricular clot. Bilateral external ventricular drains were placed to relieve elevated intracranial pressure. Cerebral angiography revealed a 1-cm basilar tip aneurysm, which was embolized with Guglielmi detachable coils (Boston Scientific, Boston, MA) during the same procedure. INTERVENTION: Given the patient's poor neurological condition, it was decided that brainstem compression should be relieved. A posterior fossa decompressive craniectomy was performed immediately after coil therapy, with direct evacuation of the intraventricular clot. The patient experienced a clear improvement in the level of consciousness and has achieved a good neurological result at early follow-up. CONCLUSION: Dilation of the fourth ventricle by an intraventricular clot is a sign of brainstem compression that can be relieved by posterior fossa decompression and direct clot evacuation.

Combined surgical and endovascular techniques of flow alteration to treat fusiform and complex wide-necked intracranial aneurysms that are unsuitable for clipping or coil embolization.

OBJECT: Certain intracranial aneurysms, because of their fusiform or complex wide-necked structure, giant size, or involvement with critical perforating or branch vessels. are unamenable to direct surgical clipping or endovascular coil treatment. Management of such lesions requires alternative or novel treatment strategies. Proximal and distal occlusion (trapping) is the most effective strategy. In lesions that cannot be trapped, alteration in blood flow to the "inflow zone," the site most vulnerable to aneurysm growth and rupture, is used. METHODS: From 1991 to 1999 the combined neurosurgical-neuroendovascular team at the Massachusetts General Hospital (MGH) managed 48 intracranial aneurysms that could not be clipped or occluded. Intracavernous internal carotid artery aneurysms were excluded from this analysis. By applying a previously described aneurysm rupture risk classification system (MGH Grades 0-5) based on the age of the patient, aneurysm size, Hunt and Hess grade, Fisher grade, and whether the aneurysm was a giant lesion located in the posterior circulation, the authors found that a significant number of patients were at moderate risk (MGH Grade 2; 31.3% of patients) and at high risk (MGH Grades 3 or 4; 22.9%) for treatment-related morbidity. The lesions were treated using a variety of strategies--surgical, endovascular, or a combination of modalities. Aneurysms that could not be trapped or occluded were treated using a paradigm of flow alteration, with flow redirected from either native collateral networks or from a surgically performed vascular bypass. Overall clinical outcomes were determined using the Glasgow Outcome Scale (GOS). A GOS score of 5 or 4 was achieved in 77.1%, a GOS score of 3 or 2 in 8.3%, and death (GOS 1) occurred in 14.6% of the patients. Procedure-related complications occurred in 27.1% of cases; the major morbidity rate was 6.3% and the mortality rate was 10.4%. Three patients experienced aneurysmal hemorrhage posttreatment; in two patients this event proved to be fatal. Aneurysms with MGH Grades 0, 1, 2, 3, and 4 were associated with favorable outcomes (GOS scores of 5 or 4) in 100%, 92.8%, 71.4%, 50%, and 0% of instances, respectively. CONCLUSIONS: Despite a high incidence of transient complications, intracranial aneurysms that cannot be clipped or occluded require alternative surgical and endovascular treatment strategies. In those aneurysms that cannot safely be trapped or occluded, one approach is the treatment strategy of flow alteration.

Aneurysms of the lateral spinal artery: report of two cases.

OBJECTIVE AND IMPORTANCE: The goal of this report was to describe aneurysms arising from the lateral spinal artery. The locations of aneurysms contributing to subarachnoid hemorrhage (SAH) have been well characterized and are primarily in the circle of Willis or at the bifurcation points of the internal carotid artery or the vertebrobasilar system. Although the spinal arteries are also in direct communication with the subarachnoid space, aneurysms of these arteries that lead to SAH are rare. To date, only aneurysms of the anterior and posterior spinal arteries have been described. In this communication, we report two patients with aneurysms of the lateral spinal artery who presented with SAH. CLINICAL PRESENTATION: Review of our neurointerventional database from 1997 to the present revealed two patients with lateral spinal artery aneurysms. The medical records, as well as the operative and radiological findings, were reviewed for both patients. In both cases, the lateral spinal arteries were involved as collateral pathways for occlusive vertebral lesions, suggesting hemodynamic stress as a cause. INTERVENTION: Endovascular treatment was attempted in both cases and was successful in one; open surgery, with aneurysm resection, was performed in the other case. We review the vascular anatomic features of the spinal cord as they relate to the lateral spinal artery, as well as treatment options for lateral spinal artery aneurysms. CONCLUSION: Lateral spinal artery aneurysms are a rare cause of SAH. Both endovascular and surgical treatment options are available.