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BLOOD RHEOLOGY To analyze blood fl ow and stresses that develop in it, and its interaction with the blood constituents, we traditionally consider blood as a continuously deformable continuum in motion. Using this approach, we can characterize blood as a Newtonian fl uid (in which the fl uid deforms linearly as a function of the stress imposed) or a non-Newtonian fl uid (in which the fl uid deforms nonlinearly as a function of the stress). The Newtonian behavior of blood fl ow is relevant to most of the larger arteries in the vasculature. However, blood possesses a unique non-Newtonian viscosity behavior, which becomes apparent when it fl ows through the smaller vessels, such as arterioles and capillaries. This behavior is also observed when blood fl ow forms vortical structures, as may be found in fl ow through cardiovascular prostheses or in cardiovascular disease processes such as stenoses and aneurysms ( 1 ). In analyzing other aspects of hemodynamics such as the apparent reduction of viscosity and the migratory tendency of blood cells in the smaller scale vessels (i.e., the microcirculation), it is found that blood may be treated as a suspension of cells in plasma. The non-Newtonian behavior exhibited by whole blood is due to fi brinogen molecules on the surface of red blood cells (RBC) that cause them to stack together in the rouleaux formation. This phenomenon is most pronounced during pregnancy, under pathological conditions, and when a large number of fi brinogen molecules are present on RBC surfaces. Such aggregation of cells in arterioles and small arteries is responsible for blood’s deviation from Newtonian behavior ( 1 ). From a mechanics point of view, this behavior is a combination of Bingham and pseudoplastic fl uid characteristics. That is, it has a yield stress; however even above this yield stress, the shear stress to shear rate relationship is nonlinear ( Fig. 1 ). A well-accepted, heuristic non-Newtonian model of blood is the Casson model. This behavior is most apparent in shear rates that are below 20 s −1 , with the region 20–100 s −1 being the transition region. Above a shear rate of 100 s −1 blood behaves as a Newtonian fl uid. However, in the non-Newtonian range, the shear stress does not exceed the yield stress in the central core fl ow region, and the core is merely carried along by the fl uid in the annular region. Thus, the central core has a fl at velocity profi le (plug fl ow), which is carried by the annular region surrounding it, sustaining the bulk of the shear stress ( 1 ). As blood consists of various kinds of cells such as erythrocytes (RBC), white blood cells (WBC or leukocytes), and platelets (thrombocytes) suspended in plasma, there is often a need to analyze its rheological properties in relation to its nature and to its cell-suspension properties. RBCs outnumber the other cells and assume major AQ01

Rupture of a cerebral arteriovenous malformation can result in devastating hemorrhage with a possibility of serious neurological injury or death. Endovascular embolization is an important adjunct in the treatment of cerebral arteriovenous malformations, and in a small number of cases may provide definitive treatment. Currently available embolic agents have several shortcomings, including the possibility of recanalization, adhesiveness to the endovascular microcatheter and suboptimal handling at the time of surgical resection. Onyx is an ethylene vinyl alcohol copolymer dissolved in dimethyl sulfoxide that was approved by the US FDA in July 2005 as an embolic agent for brain arteriovenous malformations. Although long-term follow-up is limited, this agent appears to offer several advantages over the other available embolic agents for the endovascular management of arteriovenous malformations and other vascular lesions.

Object The authors describe a novel concept for brain mapping in which an endovascular approach is used, and they demonstrate its feasibility in animal models. The purpose of endovascular brain mapping is to delineate clearly the nonfunctional brain parenchyma when a craniotomy is performed for resection. The nonfunctional brain will be stained with sharp visual margins, differentiating it from the functional, nonstained brain. The authors list four essential criteria for developing an ideal endovascular mapping agent, and they describe seven potential approaches for accomplishing a successful endovascular brain map. Methods Four Sprague–Dawley rats and one New Zealand white rabbit were used to determine initial feasibility of the procedure. The animals were anesthetized, and the internal carotid artery was catheterized. Four potential brain mapping agents were infused into the right hemisphere of the five animals. Afterward, the brains were removed and each was analyzed both grossly and histologically. Fluorescein and FD&C Green No. 3 provided good visual clarity and margins, but required blood–brain barrier (BBB) manipulation. Tantalum particles enabled avoidance of BBB manipulation, but provided inadequate visual clarity, probably because of their size. A Sudan black “cocktail” provided excellent clarity and margins despite remaining in the brain capillaries. Conclusions This is a novel application of the endovascular approach, and has broad potential for clinical neurosurgical brain mapping. The animal models in this study establish the feasibility of the procedure. However, further study is required to demonstrate safety, minimize toxicity, investigate stain durability, and improve the characteristics of potential mapping agents. The authors are planning to conduct future studies for identification of mapping agents that do not require BBB manipulation or vascular occlusion.

We describe a novel technique of using fluorescent silica nanoparticles (FSNPs) to detect over-expressed folate receptors, as typical for certain malignancies (metastatic adenocarcinoma, pituitary adenoma and others). Using Stober's method with some modification, 135 nm size FSNPs were synthesized by a hydrolysis and co-condensation reaction of tetraethylorthosilicate (TEOS), fluorescein labeled (3-aminopropyl)triethoxysilane (APTS) and a water-dispersible silane reagent, (3-trihydroxysilyl)propyl methylphosphonate (THPMP) in the presence of ammonium hydroxide catalyst. Folic acid (folate) was covalently attached to the amine modified FSNPs by a carbodiimide coupling reaction. The characterization of folate-FSNPs was performed using a variety of spectroscopic (UV-VIS and fluorescence), microscopic (transmission electron microscopy, TEM) and light scattering techniques. Folate conjugated FSNPs were then targeted to human squamous cancer cells (SCC-9). Laser scanning confocal images successfully demonstrated the labeling of SCC-9 cells and the efficacy of FSNP based detection system.

Ultra-small (3.1 nm) multifunctional CdS:Mn/ZnS core−shell semiconductor quantum dots (Qdots), which possess fluorescent, radio-opacity, and paramagnetic properties, have been shown here. To demonstrate in vivo bioimaging capability, a rat was administered endovascularly with Qdots conjugated with a TAT peptide. The labeling efficacy of these Qdots was demonstrated on the basis of the histological analysis of the microtome sliced brain tissue, clearly showing that TAT-conjugated Qdots stained brain blood vessels.

Background Intraoperative angiography for neurovascular disease has gained wide acceptance as a useful tool. There are few published cases of intraoperative angiography performed in the prone or three-quarter prone position, and the transradial approach has not previously been described for this situation. Methods We retrospectively reviewed our last 177 consecutive cases of intraoperative angiography performed for neurovascular disease. Of these cases, 21 were performed in the prone or three-quarter prone position. Two different approaches were used: (1) a previously described extended femoral sheath approach (13 cases) and (2) a newly described transradial approach (8 cases). Results All 21 intraoperative angiograms were successfully completed in the prone or three-quarter prone position. This enabled us to make additional surgical adjustments when necessary or to conclude the operation. One complication, a dissection of the brachial artery, occurred during one intraoperative angiographic procedure. Conclusions Intraoperative angiography can be performed in the prone or three-quarter prone position with good efficacy and safety. The transfemoral route has the advantage of familiarity but has disadvantages of poor sterility at access site, possible kinking or thrombosis of the sheath, and possible skin injury while resting on the tubing during long procedures. The transradial route has advantages of continuous access to the entry site throughout the surgical procedure and ease of catheterization of vertebral arteries for occipital and suboccipital lesions. However, the transradial route has the disadvantage of working from an unfamiliar approach, especially for spinal arteriovenous malformations.

Water-in-oil (w/o) microemulsion synthesis of 70 nm size monodisperse TAT (a cell penetrating peptide, CPP) conjugated, FITC (fluorescein isothiocyanate) doped silica nanoparticles (TAT-FSNPs) is reported; human lung adenocarcinoma (A549) cells (in vitro) and rat brain tissue (in vivo) were successfully labeled using TAT-FSNPs.

Object. The safety and efficacy of Gd as an intraarterial contrast agent for pediatric neuroendovascular procedures were investigated. Methods. The authors retrospectively reviewed data regarding pediatric neuroendovascular procedures performed during a 1-year period. Seventeen procedures involving the use of gadodiamide in nine pediatric patients were identified. All angiographic images were of diagnostic quality but usually required minimal postimage processing. In time-consuming cases, the use of gadodiamide allowed the procedure to continue when the dosage of iodinated contrast approached a toxicity level and would have otherwise prompted termination of the procedure. This likely reduced the total number of procedures necessary. No adverse events due to the intraarterial use of gadodiamide were identified. Conclusions. Gadodiamide appears to be a safe and effective contrast agent for pediatric patients.

Object. The cortical arteries arising from the main trunk of the middle cerebral artery, proximal to its bifurcation or trifurcation, are called “early branches.” The purpose of this study was to characterize these early branches. Methods. The early branches were characterized according to their sites and patterns of origin, diameters, and relative proximity to the internal carotid artery bifurcation, as well as the course and area of supply of their cortical branches based on an examination of 50 hemispheres. Special attention was directed to the perforating arteries that arose from the early branches and entered the anterior perforated substance. The anatomical findings were compared with data obtained from 109 angiograms. Conclusions. Early branches directed to the temporal and frontal lobes were found in 90 and 32% of the hemispheres, respectively. The early branches that arose more proximally from the M1 segment were larger than those arising distally. Lenticulostriate arteries arose from 81% of the early frontal branches (EFBs) and from 48% of the early temporal branches (ETBs). An average of two cortical arteries arose from the EFBs and 1.3 from the ETBs, the most common of which supplied the temporopolar and orbitofrontal areas. Although the microsurgical anatomy of the early branches demonstrates abundant diversity, they can be classified into clearly defined patterns based on anatomical features. These patterns can prove helpful in evaluating angiographic data and in planning an operative procedure.

Traditional minimally-invasive endovascular procedures like coiling are inadequate for the effective treatment of may wide-necked, fusiform aneurysms and arteriovenous fistulae (AVF) in the brain. An endovascular approach of placing a covered microstent across the intracranial aneurysm neck and AVE rent is promising. Unlike bare stents (stent without cover), covered microstents will have the capability of completely preventing blood flow into the aneurysm cavity of AVF rent. The strategy will restore normal vessel morphology and blood flow.Copyright © 2003 by ASME

Introduction Outcomes studies utilize patient reported outcome (PRO) measurements to assess treatment effectiveness but can lack direct clinical meaning. Minimum clinical important difference (MCID) is a tool which measures the critical threshold needed to achieve clinicallyrelevant treatment effectiveness. MCID remains uninvestigated for Percutaneous Stereotactic Rhizotomy (PSR), a common surgical procedure for Trigeminal Neuralgia (TN). We aimed to determine MCID for the most commonly used PRO measures of pain after PSR: Visual Analog Scale (VAS) and Barrow Neurological Institute Pain Scale (BNI-PS).

Object. The authors report their experience with carotid artery stent placement (CASP) in patients with concomitant carotid artery (CA) and coronary artery (CorA) diseases. Methods. In a review of 320 consecutive patients who underwent CASP, the authors identified 49 with severe CorA disease in addition to significant CA stenosis, who had undergone CASP before planned CorA bypass grafting (CorABG). The average age of these 49 patients was 68 years. In 39 patients (80%) the New York Heart Association functional classification grade was IV and in 10 the grade was III. In 26 patients 50% or greater stenosis of the left main CorA was found. Seventeen patients (35%) suffered from either significant hemodynamic contralateral CA stenosis (> 60% stenosis; eight patients) or contralateral CA occlusion (nine patients). Sixteen patients (33%) had symptomatic CA disease. No cerebrovascular events occurred during CorABG. Four patients (8%) died of cardiac arrest and one patient (2%) suffered a major stroke within 30 days after the CorABG procedure. No patient experienced clinically significant recurrent CA stenosis during the study period (average clinical follow-up period 27 months). Conclusions. Carotid artery stent placement should be considered as an alternative for the management of concomitant CA and CorA diseases. These preliminary results support the feasibility and durability of CASP in the population studied.

Object. The risks associated with carotid endarterectomy (CEA) are increased in the presence of contralateral carotid artery (CA) occlusion. The 30-day stroke and death rate for patients in the North American Symptomatic Carotid Endarterectomy Trial (NASCET) who had contralateral CA occlusion was 14.3%. The authors analyze their experience with angioplasty and/or stent placement in patients with contralateral CA occlusion to determine the safety and efficacy of endoluminal revascularization in this subgroup.Methods. Twenty-six procedures were evaluated in 23 patients with high-grade CA stenosis and contralateral CA occlusion. The first 15 procedures were evaluated retrospectively, and the next 11 prospectively. All patients had severe medical comorbidities and were considered too high risk for CEA, even without considering the contralateral occlusion. Clinical follow-up review was performed an average of 18 months later (median 15 months).Conclusions. The average ipsilateral CA stenosis according to NASCET criteria was 78% preprocedure and 5% postprocedure. There were no changes in neurological or functional outcome immediately postoperatively in any patient. The 30-day postoperative stroke and death rates were zero. However, there was one symptomatic femoral hematoma that resolved without surgery. At follow up, there were three patients who had suffered stroke or death. One patient died secondary to respiratory arrest at 2 months; one died secondary to prostate carcinoma at 12 months; and one patient experienced a minor stroke contralateral to the treated artery at 41 months. Despite the substantial preoperative risk factors in patients in this series, the 30-day stroke and death rate for angioplasty and/or stent placement appears to be lower than that of CEA in patients with contralateral occlusions.

Object. Treatment consisting of percutaneous transluminal angioplasty (PTA) and stent placement has recently been proposed as an alternative to surgical reexploration in patients with recurrent carotid artery stenosis following endarterectomy. The authors retrospectively reviewed their experience after performing 25 procedures in 21 patients to assess the safety and efficacy of PTA with or without stent placement for carotid artery restenosis.Methods. The mean interval between endarterectomy and the endovascular procedures was 57 months (range 8–220 months). Seven arteries in five patients were treated by PTA alone (including bilateral procedures in one patient and repeated angioplasty in the same vessel in another). Early suboptimum results and recurrent stenosis in some of these initial cases prompted the authors to combine PTA with stent placement in the treatment of 18 arteries over the past 3 years. No major periprocedural deficits (neurological or cardiac complications) or death occurred. There was one periprocedural transient neurological event, and in one patient a pseudoaneurysm of the femoral artery (at the access site) required surgical repair. In the 16 patients who each underwent at least 6 months of follow-up review, no neurological events ipsilateral to the treated artery had occurred after a mean follow-up period of 27 months (range 6–57 months). Three of five patients who underwent PTA alone developed significant (> 50%) asymptomatic restenoses that required repeated angioplasty in one and PTA with stent placement in two patients. Significant restenosis (55%) was observed in only one of the vessels treated by combined angioplasty and stent placement.Conclusions. Endovascular PTA and stenting of recurrent carotid artery stenosis is both technically feasible and safe and has a satisfactory midterm patency. This procedure can be considered a viable alternative to surgical reexploration in patients with recurrent carotid artery stenosis.

OBJECTIVE: Interpretation of angioarchitecture during embolization of intracranial arteriovenous malformations (AVMs) is critical to optimizing results. We describe an adjunctive technique to aid in the interpretation of AVM embolization and improve safety. METHODS: In the past 100 consecutive patients who underwent AVM embolization by a single surgeon (RAM), each AVM nidus was selectively catheterized and microangiography was performed. After the microcatheter contrast exited the AVM, a guiding catheter angiogram was performed during the same digital run. The microangiogram was digitally superimposed on the guiding catheter angiogram to delineate important landmarks such as the nidus perimeter, draining veins, and microcatheter tip, which were then drawn on the digital subtraction angiographic monitor with a marking pen in two orthogonal views. RESULTS: Important landmarks were continually visualized during the embolization procedure despite subtracted fluoroscopy ("blank" roadmap). These techniques qualitatively helped to: 1) appreciate the overall size and morphology of the nidus, 2) clearly visualize the safe limits of the embolic injection within the nidus perimeter, 3) clearly visualize draining patterns to help avoid premature venous embolization, 4) decipher small draining veins from arteries, 5) continuously monitor the location and status of the microcatheter tip, and 6) increase the confidence of the surgeon during prolonged embolic injections. CONCLUSION: The double injection technique with marking pen demarcation of the nidus perimeter, venous drainage, and microcatheter tip position was qualitatively useful in every case.

Objective and importance Endovascular stents have been successfully used in the treatment of fusiform and dissecting aneurysms of the peripheral circulation and extracranial carotid and vertebral arteries. Technical limitations related to the inability to navigate the stent and the delivery system through tortuous vascular segments has limited their application with intracranial lesions. Availability of new flexible and pliable stent systems might overcome these difficulties. Clinical presentation A 49-year-old woman presented with a dissecting pseudoaneurysm of the horizontal portion of the petrous internal carotid artery that increased in size, as revealed by serial angiographic studies. Intervention The aneurysm was treated by deploying a new flexible stent across the aneurysm neck and by then packing the aneurysm sac with Guglielmi detachable coils that were delivered by a microcatheter positioned through the stent struts into the aneurysm lumen. Conclusion New flexible stents can be used to treat intracranial internal carotid artery aneurysms in difficult-to-access areas, such as the horizontal petrous segment. The stent may disrupt the aneurysm inflow tract, thereby inducing stasis and facilitating intra-aneurysmal thrombosis. In addition, the stent acts as an endoluminal scaffold to prevent coil herniation into the parent artery, which allows tight packing of even wide-necked and irregularly shaped aneurysms. The stent may also serve as a matrix for endothelial growth. We think this new generation of flexible stents and the use of this described technique will usher in the next era of endovascular management of intracranial aneurysms.

✓ Guglielmi detachable coil (GDC) treatment for complicated cerebral aneurysms is an attractive option that has become widely accepted in recent years. This technique is usually considered only if the patient harbors an aneurysm that is not a good candidate for surgical clipping. However, the definition of “surgical candidate” varies among institutions, and many patients worldwide are being treated with GDCs as primary therapy. Although most centers currently perform follow-up angiography at 6 months to 1 year, others do not routinely perform it after an initially good result. The authors present a case that indicates longer follow up may be necessary and illustrates some of the pitfalls of GDC treatment. This 56-year-old man presented to the emergency room with a Hunt and Hess Grade II subarachnoid hemorrhage and was found to have a wide-necked basilar apex aneurysm. Because of associated medical comorbidities, it was decided to treat the aneurysm with endovascular techniques. The patient did well on follow-up angiography at 1 year postprocedure. However, at approximately 2 years follow up, the aneurysm was demonstrated to have dramatically recanalized and regrown, requiring open surgical intervention. Endovascular coiling was insufficient to treat this aneurysm and complicated definitive surgical management because a large coil mass had been placed in the operative field. It can be inferred from this case that angiographic follow up of these types of lesions may be beneficial up to 2 years after GDC treatment.

TAT (a cell penetrating peptide)-conjugated CdSratioMn/ZnS quantum dots (Qdots), intra-arterially delivered to a rat brain, rapidly (within a few minutes) labeled the brain tissue without manipulating the blood-brain-barrier (BBB). Qdot loading was sufficiently high that it allowed a gross fluorescent visualization of the whole rat brain using a low power hand-held UV lamp. Histological data clearly showed that TAT-conjugated Qdots migrated beyond the endothelial cell line and reached the brain parenchyma. Qdots without TAT did not label the brain tissue confirming the fact that TAT peptide was necessary to overcome the BBB. The present study clearly demonstrated the possibility of delivering a large amount of Qdot-based imaging agents to the brain tissue.

Following the favorable results obtained in the treatment of coronary artery disease, combined angioplasty and stenting has been advocated for the treatment of carotid artery stenosis as well. Although widespread application of angioplasty and stenting for carotid artery disease is neither indicated nor recommended, it may be a viable alternative therapy for select patients who are high-risk patients for surgery. The results of early series have suggested that endoluminal revascularization in these high-risk patients can be performed with an acceptable degree of safety. Although the incidence of death and major stroke rates following angioplasty and stenting procedures compares favorably with surgery, results of more recent clinical series have suggested that the incidence of perioperative transient neurological events and minor strokes may be higher than suggested by earlier reports, especially in patients with recent neurological symptoms and “unstable” plaques. In this article, the authors review the current potential indications for and preliminary results of angioplasty and stenting and describe their procedural technique. In addition, potential applications of stenting to intracranial thromboocclusive carotid artery disease are reviewed.

Percutaneous transluminal angioplasty (PTA) and stenting has recently been proposed as an alternative to surgical reexploration in patients with recurrent carotid artery stenosis following endarterectomy. The authors retrospectively reviewed their experience after performing 25 procedures in 21 patients to assess the safety and efficacy of PTA with or without stenting for carotid artery restenosis. The mean interval between endarterectomy and the endovascular procedure was 57 months (range 8-220 months). Seven arteries in five patients were treated by PTA alone (including bilateral procedures in one patient and repeated angioplasty in the same vessel in another). Early suboptimum results and recurrent stenosis in some of these initial cases prompted the authors to combine PTA with stenting in the treatment of 18 arteries over the past 3 years. No major periprocedural deficits (neurological or cardiac complications) or death occurred. There was one periprocedural transient neurological event. A pseudoaneurysm of the femoral artery (at the access site) required surgical repair. In the 16 patients who each underwent at least 6 months of follow-up review, no neurological events ipsilateral to the treated artery had occurred after a mean follow-up period of 27 months (range 6-57 months). Three of five patients who underwent PTA alone developed significant (> 50%) asymptomatic restenoses that required repeated angioplasty in one and PTA with stenting in two patients. Significant restenosis (55%) was observed in only one of the vessels treated by combined angioplasty with stenting. Endovascular PTA and stenting of recurrent carotid artery stenosis is both technically feasible and safe and has a satisfactory midterm patency. This procedure can be considered a viable alternative to surgical reexploration in patients with recurrent carotid artery stenosis.

Object.Successful therapeutic embolization of arteriovenous malformations (AVMs) of the brain with liquid polymers (glues) requires precise knowledge of highly variable AVM structure and flow velocities and transit times of blood through the AVM nidus. The goal of this study was to improve AVM flow measurement and visualization by the substitution of the insoluble Ethiodol (ethiodized oil) contrast agent for the soluble contrast media normally used in angiographic studies.Methods.Before enbucrilate embolization of 24 AVM feeding pedicles in 13 patients, standard contrast medium was superselectively injected into each target pedicle, followed by infusion of 20 µl of Ethiodol microdroplets. Transport of contrast material was assessed using high-speed biplane pulsed digital subtraction angiography (DSA) operating at 15 frames per second.The mean blood flow transit times through AVMs after administration of Ethiodol were found to be approximately half as long as in those measured after injection of soluble contrast materials (0.22 ± 0.10 seconds compared with 0.46 ± 0.19 seconds [mean ± standard deviation]; p < 0.0001). The discrete Ethiodol microdroplets travel with the core flow, more closely approximating the dynamic behavior of enbucrilate, allowing the AVM structure to be traced with high spatial and temporal resolution. There were no inadvertent vessel occlusions or pulmonary complications related to the use of Ethiodol for DSA.Conclusions.Because of diffusion and convection, forces that decrease concentration, visualization of the contrast front is reduced, often resulting in deceptively long transit times when soluble contrast materials are used. Overestimation may prove dangerous when planning embolizations. The Ethiodol droplet DSA method provides accurate transit time measurements and precise, detailed, and dynamic AVM visualization. Further development of this method will improve the safety and precision of AVM treatments.

Results of previous in vitro and in vivo experimental studies have suggested that the placement of a porous stent within the parent artery across the aneurysm neck may hemodynamically uncouple the aneurysm from the parent vessel, leading to thrombosis of the aneurysm. For complex wide-necked aneurysms, a stent may also aid the packing of the aneurysm with Guglielmi detachable coils (GDCs) by acting as a rigid scaffold that prevents coil herniation into the parent vessel. Recently, improved stent system delivery technology has allowed access to the tortuous vascular segments of the intracranial system. The authors report here the intracranial stenting of aneurysms involving different segments of the internal carotid artery (ICA) and the vertebral artery (VA). Four patients with intracranial aneurysms located at the petrous, cavernous, and paraclinoid segments of the ICA and at the VA proximal to the origin of the posterior inferior cerebellar artery, respectively, were treated since January 1998. In three of these patients, stent placement across the aneurysm neck was followed by GDC placement, accomplished via a microcatheter through stent mesh. In one patient, the aneurysm was treated solely by stenting. No periprocedural complications were observed, and at follow up, no patient was found to have suffered symptoms referable to aneurysm growth or thromboembolic complications. More than 90% occlusion of the aneurysm was achieved in the three cases treated by stenting and GDC placement. One of these patients underwent 6-month follow-up angiography that did not reveal any in-stent stenosis. In the case treated solely by stent placement, no evidence of aneurysm thrombosis was observed either immediately postprocedure or on follow-up angiography performed 24 hours later. A new generation of flexible stents can be used to treat intracranial aneurysms in difficult-to-access areas such as the proximal intracranial segments of the ICA or the VA. The stent allows tight coil packing even in the presence of a wide-necked, irregularly shaped aneurysm and may provide an endoluminal matrix for endothelial growth. Although convincing experimental evidence suggests that stent placement across the aneurysm neck may by itself promote intraluminal thrombosis, the role of this phenomenon in clinical practice may be limited at present by the high porosity of currently available stents.