Sidewall Aneurysms Research Articles

“Waffle Cone” Technique for Intra/Extra-Aneurysmal Stent Placement for the Treatment of Complex and Wide-Necked Bifurcation Aneurysm

Endovascular treatment of intracranial aneurysms by coiling has become an accepted alternative to surgical clipping (1). In cases of wide-necked and sidewall aneurysms, selective embolization is difficult because of the risk of coil protrusion into the parent vessel. The use of three-dimensional coils, stents (2), and balloon remodeling have all aided the attempt to adequately manage such lesions. However, compared with sidewall aneurysms, bifurcation aneurysms are more challenging from an endovascular standpoint. Because of their specific anatomy and hemodynamics, the tendency to recur and rerupture is higher. Several authors have reported successful treatment of these complex and wide-necked bifurcation aneurysms by using Yconfigured dual stent-assisted coil embolization (3,4), the double microcatheter technique (5), a more compliant balloon remodeling technique (6), the TriSpan neck-bridge device (7), or the waffle cone technique (8).We describe two cases of widenecked bifurcation aneurysms in which the waffle cone technique was used for coil embolization. The waffle cone technique was first described in 2006; however, the small number of published cases and the lack of follow-up prevent one from assessing this technique's durability and the probability of recanalization.We report the cases of two patients harboring unruptured wide-necked bifurcation aneurysms that were treated and followed-up for six months.

A novel endovascular clip system for the treatment of intracranial aneurysms: technology, concept, and initial experimental results

The authors describe a novel device for the endovascular treatment of intracranial aneurysms, the endovascular clip system (eCLIPs). Descriptions of the device and its delivery system as well as the results of flow model tests and the treatment of experimental aneurysms are provided. The eCLIPs comprises a flexible hybrid implantable device (an anchor and a covered leaf) and a balloon catheter delivery system, designed to be positioned and activated in the parent vessel in such a way that the covered portion will abut the aneurysm neck. The eCLIPs was subjected to testing in glass, elastomeric, and cadaveric flow models to determine its navigability, orientation, and activation compared with commercially available stents. In a second experiment, 8 carotid artery sidewall aneurysms in swine were treated using eCLIPs. The degree of occlusion was observed on angiography immediately following and 30 days after device activation, and a histological analysis was performed at 30 days. The device could navigate tortuous glass models and human cadaveric vessels. Compared with commercially available stents, the eCLIPs performed well. It could be navigated, oriented, and activated easily and reliably. With regard to the 8 porcine experimental aneurysms, immediate postactivation angiograms confirmed complete occlusion of 4 lesions and near occlusion of the other 4. Angiographic follow-up at 30 days postactivation showed occlusion of all 8 aneurysms and patency of all parent vessels. Histopathological analysis revealed aneurysm healing, with smooth-muscle cells growing across the lesion neck to allow reendothelialization. Aneurysm occlusion with a single extrasaccular endovascular device has potential advantages. The authors believe that eCLIPs may prove to be a useful tool in the endovascular treatment of cerebral aneurysms. The system should reduce risks associated with coiling, procedure time, costs, and radiation exposure. The device satisfactorily occluded 8 experimental sidewall aneurysms. The observed healing pattern is similar to that seen after microsurgical clipping.

Asymmetric Vascular Stent

Intracranial aneurysm (IA) treatment through hemodynamic modification with novel stent designs is a burgeoning area of research. We present a feasibility study for a new low-porosity patch-containing stent designed to treat intracranial aneurysms. The device is deployed so the patch covers the aneurysm neck ensuring strong flow diversion away from the aneurysm while keeping a low probability of occlusion of perforating vessels. We created 17 side-wall aneurysms in 6 dogs, 2 per carotid artery if animal size permitted. Twelve proximal aneurysms were treated with AVSs: 5 distal aneurysms were untreated, serving as controls against self-thrombosis; 7 treated aneurysms were fully-covered; and 5 were partially-covered. After 4 weeks, a final angiogram was performed and aneurysms were explanted. Angiograms acquired pre- and posttreatment and at 4-week follow-up were analyzed quantitatively using normalized time-density curves (NTDC). Cone-beam micro-CT and histological specimen analysis were then performed. Posttreatment, NTDC average peaks dropped to 45% of initial values for the partially-covered aneurysms and 78% for the fully-covered aneurysms. Cone-beam micro-CT imaging performed at 4 weeks posttreatment showed partial thrombosis in 4 of 5 partially-covered aneurysms and complete thrombosis in all fully-covered aneurysms. Histology revealed neointimal coverage of all asymmetrical patch regions and thrombus formation in both fully- and partially-covered aneurysms. Four-week follow-up was not done for 1 animal (2 controls, 2 treated) that expired because of groin hemorrhage and for another animal (1 aneurysm) with an occluded carotid. We demonstrate aneurysmal blood flow diversion using a new low-porosity patch-containing asymmetrical vascular stent in a canine side-wall aneurysm model. Overall results are encouraging and support continued AVS development.

Impact of aneurysmal geometry on intraaneurysmal flow: a computerized flow simulation study

This study was performed to assess the effect of aneurysm geometry on parameters that may have an impact on the natural history of intracranial aneurysms, such as intraaneurysmal flow pressure and shear stress. Flow was simulated in 21 randomly selected aneurysms using finite volume modeling. Ten aneurysms were classified as side-wall aneurysms, with either single-sided or circumferential involvement of the parent artery wall, and 11 as bifurcation aneurysms (symmetric or asymmetric), with an axis either perpendicular or parallel to the parent artery. The flow patterns were classified as either jet or vortex types (with regular or irregular vortex flow). Pressures and shear stresses were characterized as evenly or unevenly distributed over the aneurysm wall and neck. All side-wall and four of the bifurcation aneurysms with a perpendicular axis had a vortex type flow pattern and seven bifurcation aneurysms with a parallel axis (four symmetric and two asymmetric) had a jet flow pattern. Jet type flow was associated with an uneven pressure distribution in seven out of seven aneurysms. Vortex type flow resulted in an even pressure distribution in five out of six aneurysms with an irregular flow pattern and six out of eight with a regular flow pattern. No firm relationship could be established between any geometrical type and shear stress distribution. Only 1 of 14 aneurysms with a perpendicular axis, but 4 of 7 aneurysms with a parallel axis, had ruptured. Aneurysm geometry does have an impact on flow conditions. Aneurysms with a main axis parallel to the parent artery have a tendency to have a jet flow pattern and uneven distribution of unsteady pressure. These aneurysms may have a higher rate of rupture as than those with a main axis perpendicular to the parent artery.

Effects of stent porosity on hemodynamics in a sidewall aneurysm model

Computation and experiment have been complementarily performed to study the fluid flow inside a stented lateral aneurysm anchored on the straight parent vessel. The implicit solver was based on the time-dependent incompressible Navier–Stokes equations of laminar flow. Solutions were generated by a cell-center finite-volume method that used second-order upwind and second-order center flux difference splitting for the convection and diffusion term, respectively. The second-order Crank–Nicolson method was used in the time integration term. Experimental techniques used were flow visualization (FV) and particle tracking velocimetry (PTV). Experimentally, the straight afferent vessel had an inner diameter 10 mm. The diameters of the aneurysmal orifice, neck, and fundus were 14, 10, and 15 mm, respectively, and the distance between the orifice and dome measured 20 mm. A 30 mm long helix-shaped stent was tested. Four stent porosities of 100%, 70%, 50%, and 25% were examined. Volume-flow rate waveform of a cerebral artery was considered with a maximum Reynolds number of 250 and Womersley number of 3.9. Results are presented in terms of the pulsatile main and secondary flow velocity vector fields, the volume inflow rates into the aneurysm, and the wall shear stress (WSS) and wall pressure at the aneurysm dome. Some comparisons of computed results with the present FV and PTV results and with the data available from the literature are also made. The maximum flow velocity inside the aneurysm ostium and the WSS in the dome region at the peak flow can, respectively, be suppressed to less than 5% of the parent vessel bulk velocity (or 20% of the unstented case) and 8% of the unstented case if the stent porosity is smaller than 40% (about the porosity of the two-layer stents). In general, the three-layer stents seem not as effective as the two-layer stents in reducing the magnitude of aneurysm inflow rate and WSS.

Noninvasive Measurement of Intra-Aneurysmal Pressure and Flow Pattern Using Phase Contrast with Vastly Undersampled Isotropic Projection Imaging

Currently, more reliable parameters to predict the risk of aneurysmal rupture are needed. Intra-aneurysmal pressure gradients and flow maps could provide additional information regarding the risk of rupture. Our hypothesis was that phase contrast with vastly undersampled isotropic projection reconstruction (PC-VIPR), a novel 3D MR imaging sequence, could accurately assess intra-aneurysmal pressure gradients in a canine aneurysmal model when compared with invasive measurements. A total of 13 surgically created aneurysms in 8 canines were included in this study. Pressure measurements were performed in the parent vessel, aneurysm neck, and 5 regions within the aneurysmal sac with a microcatheter. PC-VIPR sequence was used to obtain cardiac-gated velocity measurements in a region covering the entire aneurysm. The velocity and pressure gradient maps derived from the PC-VIPR data were then coregistered with the anatomic DSA images and compared with catheter measurements. In 7 of the bifurcation aneurysms, the velocity flow maps demonstrated a recirculation flow pattern with a small neck-to-dome pressure gradient (mean, +0.5 mm Hg). In 1 bifurcation aneurysm, a flow jet extending from the neck to the dome with significantly greater pressure gradient (+50.2 mm Hg) was observed. All sidewall aneurysms had low flow in the sac with intermediate pressure gradients (mean, +8.3 mm Hg). High statistical correlation existed between PC-VIPR aneurysmal pressures and microcatheter pressure measurements (R = 0.82, P < .01). PC-VIPR can provide anatomic as well as noninvasive quantitative and qualitative hemodynamic information in the canine aneurysm model. The PC-VIPR intra-aneurysmal pressure measurements correlated well with catheter measurements.

Comparison of platinum and first-generation Matrix coils in under-packed canine side-wall aneurysms: evaluation of progressive thrombosis

There is much speculation in reference to the occurrence and mechanisms of progressive aneurysm occlusion after treatment with bioactive coils. However, to our knowledge, there are no studies documenting the impact on progressive occlusion in aneurysms that are intentionally under-packed. A total of 24 experimental side-wall aneurysms were created in canine common carotid arteries. Of these 24, 9 were treated with Guglielmi detachable coils (GDC) and 15 with first-generation Matrix (Matrix1) coils to packing densities of 22% or less. Angiograms were obtained immediately after treatment and again at the time of explant at 2 weeks, 8 weeks, or 12 weeks, and were graded utilizing the Raymond scale. At the time of the final angiography and explant all aneurysms were histologically processed and evaluated. At the conclusion of initial coiling, near or complete occlusion was achieved in 7 of the 15 aneurysms (47%) treated with Matrix1 coils and in 2 of the 9 (22%) treated with GDC. Of the aneurysms that were incompletely occluded, six of eight (75%) treated with Matrix1 coils and two of seven (29%) treated with GDC showed progressive thrombosis at explant. Histopathological analysis demonstrated that the aneurysms treated with Matrix1 coils had increased fibrocellular tissue and inflammation, with less histological recanalization or vascular spaces, relative to those treated with GDC. Experimental wide-necked side-wall canine aneurysms suboptimally treated with first-generation Matrix1 coils had a higher incidence of progressive occlusion and on histological analysis showed evidence of more advanced thrombus organization than did those treated with GDC.

PRELIMINARY INVESTIGATION OF CALCIUM ALGINATE GEL AS A BIOCOMPATIBLE MATERIAL FOR ENDOVASCULAR ANEURYSM EMBOLIZATION IN VIVO

We sought to expand our assessment of calcium alginate as an embolic agent in an aneurysm model in swine that survived from 30 to 90 days. The objective of this study was to assess the biocompatibility and stability of calcium alginate in aneurysms in vivo. Ten models were created from a venous pouch sutured to the carotid artery, simulating flow to a side-wall aneurysm. Eight swine received complete embolizations, and two were less than 50% embolized to be used as controls. Alginate and calcium chloride were injected from concentric-tube microcatheters to form a mass that filled the aneurysm pouch. Angiography and histology verified complete aneurysm occlusion and neck healing up to 90 days in eight swine. Both control animal aneurysms ruptured within 8 days. No animals showed evidence of downstream calcium alginate gel propagation. A minor bioactive response to the alginate gel was noted at 30 days, and fibrous tissue grew over the aneurysm orifice, sealing off the defect. No degenerative or inflammatory response was observed. At 90 days, moderate fibrous tissue surrounded the alginate. Tissue growth across the aneurysm neck remained complete and stable with no signs of neointimal growth into the parent vessel. Calcium alginate was an effective endovascular occlusion material that filled the aneurysm and provided an effective template for tissue growth across the aneurysm neck after 30 days and up to 90 days. Complete filling of the aneurysm with calcium alginate ensures stability, biocompatibility, and optimal healing for up to 90 days in swine.

Hydrogel-coated and platinum coils for intracranial aneurysm embolization compared in three experimental models using computerized angiographic and histologic morphometry

Angiographic and histologic results of hydrogel-coated (HydroCoil®) and platinum coil-treated canine sidewall, canine bifurcation, and rabbit elastase aneurysms (2–52 weeks follow-ups) were quantified by computer-assisted morphometry. Angiograms were analyzed using density determination to differentiate embolic mass and contrast medium filling. Aneurysm total and occluded areas, embolic material and red thrombus areas were determined from images of surface stained, plastic embedded ground sections. Long-term stable occlusion was observed in all three models with the use of hydrogel-coated coils. However, platinum coils were as effective only in the canine sidewall model. With the use of hydrogel-coated coils, a two-fold increase in the volumetric filling of the aneurysm sac resulted in improved outcomes.

The Influence of Aneurysm Configuration on Intra-Aneurysmal Pressure and Flow

Aneurysm rupture may occur in conjunction with swift pressure increases like heavy lifting. We therefore investigated the transmission of pressure waves as well as local flow rates in various types of experimental aneurysms and their parent arteries. 0.014-inch guidewires containing a combined pressure and thermistor sensor were inserted into both the dome and the parent artery of idealized silicone aneurysms mounted in a pulsatile flow phantom. Intravascular pressure and thermodilution responses to injections of room-temperatured normal saline at a rate of 5cc.s(-1) over two seconds were recorded simultaneously at both sites. Flow was evaluated semiquantitatively applying the thermodilution principle. We found that the propagation of pressure was attenuated at the dome of the aneurysms compared to their respective parent arteries. This difference was more distinct in side-wall aneurysms than in bifurcational aneurysms. The attenuation of traveling pressure in the aneurysm was most effective at low systemic pressures. The intraaneurysmal flow rate was unique, always lower than in the respective parent arteries and highly dependent on the configuration of the aneurysm.We observed considerably higher flow rates in bifurcational aneurysms compared to side-wall aneurysms. Bifurcational aneurysms were hence characterized by a relatively high pressure transmission and high flow rates which may represent a stimulus for enlargement of untreated aneurysms and promote coil compaction in endovascularly treated lesions.

Volume Changes of Experimental Carotid Sidewall Aneurysms Due to Embolization with Liquid Embolic Agents: A Multidetector CT Angiography Study

Iodine-containing polyvinyl alcohol polymer (I-PVAL) is a novel precipitating liquid embolic that allows for artifact-free evaluation of CT angiography (CTA). As accurate aneurysm volumetry can be performed with multidetector CTA, we determined volumes of experimental aneurysms before, immediately after, and 4 weeks after embolization of 14 porcine experimental carotid sidewall aneurysms with this liquid embolic. An automated three-dimensional software measurement tool was used for volumetric analysis of volume-rendering CTA data. Furthermore, intra-aneurysmal pressure changes during liquid embolization were measured in four silicone aneurysms and potential polymer volume changes within 4 weeks were assessed in vitro. Liquid embolic injection was performed during temporary balloon occlusion of the aneurysm neck, resulting in a mean occlusion rate of 98.3%. Aneurysms enlarged significantly during embolization by 61.1 +/- 28.9%, whereas a significant shrinkage of 5.6 +/- 2.7% was observed within the follow-up period. Histologic analysis revealed an inflammatory foreign body reaction with partial polymer degradation. In silicone aneurysm models, intra-aneurysmal pressure remained unchanged during liquid embolic injection, whereas balloon inflation resulted in a mean pressure increase of 31.2 +/- 0.7%. No polymer shrinkage was observed in vitro. The aneurysm enlargement noted was presumably due to pressure elevation after balloon inflation, which resulted in dilatation of the weak venous wall of the newly constructed aneurysm--another shortcoming of this experimental aneurysm model. The volume decrease after 4 weeks expressed partial polymer degradation.

Cerebral Mycotic Aneurysms Treated with a Neuroform Stent: Technical Case Report

We describe the first documented endovascular treatment of proximal intracranial mycotic aneurysms by a self-expanding, flexible, dedicated, intracranial Neuroform stent. Treatment with this stent rapidly obliterated the aneurysms, eliminated the need for additional coiling, and maintained the patency of the parent arteries. A 47-year-old male patient with infective endocarditis presented with ischemic stroke and minimal subarachnoid hemorrhage. Cerebral angiography demonstrated a fusiform aneurysm of the supraclinoid segment of the left internal carotid artery and horizontal segment of the left middle cerebral artery, with superimposing side-wall focal aneurysms. Despite antibiotic therapy, the focal aneurysms progressively enlarged, as demonstrated on a subsequent cerebral angiogram at Day 11. A 4-mm x 2-cm Neuroform stent was deployed along the fusiform aneurysm of the left supraclinoid internal carotid artery and the horizontal middle cerebral artery M-1 segment encompassing the focal side-wall aneurysms with preserved patency of the parent arterial segments. Endovascular stent placement can be an effective treatment for proximal intracranial mycotic aneurysms that fail to respond to medical therapy.

Predictors of Angiographic Changes in Neck Remnants of Ruptured Cerebral Aneurysms Treated With Guglielmi Detachable Coils

The angiographic changes in neck remnants of ruptured cerebral aneurysms treated with Guglielmi detachable coils (GDCs) were evaluated in the acute stage to analyze the important radiological and clinical factors. The clinical and radiological data of 37 patients with a residual neck of a ruptured cerebral aneurysm treated with GDC were reviewed. The angiographic changes on follow-up angiography were classified into three groups: recanalization of the neck remnant, progressive thrombosis, and unchanged. The effects of the clinical and angiographic findings, such as patient age, follow-up period, type of aneurysm (terminal type or side wall type), dome diameter, neck size, dome/neck ratio, obliteration rate, and volume embolization ratio were investigated. Recanalization of the neck remnant was observed in 18 of 37 cases, progressive thrombosis in nine, and unchanged in 10. The type of aneurysm, dome diameter, neck size, and volume embolization ratio were correlated with changes in the neck remnant. The aneurysm dome diameter and type of aneurysm were independent predictive factors for the recanalization of neck remnants on follow-up angiography. Dome diameter of less than 4.5 mm and volume embolization ratio of more than 31% in side wall aneurysms were likely to lead to progressive thrombosis.

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

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

Method to Quantify Flow Reduction in Aneurysmal Cavities of Lateral Wall Aneurysms Produced by Stent Implants Used for Flow Diversion

Stent implants placed across the neck of cerebral aneurysms are capable of reducing aneurysmal flow when coils are not used for filling the aneurysms. It is important to evaluate the effects of flow reduction caused by stent implants used for the treatment of cerebral aneurysms. Subtracted vortex centers path line method (SVC method) is one of the image post processing methods employed for quantitative flow measurement. We developed a modified SVC method by employing Cinematic Angiography (25 frames/s) and digital video recording (30 frames/s) with a commercial digital camera.We successfully compared the flow effectiveness using a tubular silicon model with a sidewall aneurysm. The result suggests that our modified SVC method is useful for a comparative examination of the effect of aneurysmal flow reduction caused by stent implants.

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

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

Contrast settling in cerebral aneurysm angiography

During angiography, blood flow is visualized with a radiopaque contrast agent, which is denser than blood. In complex vasculature, such as cerebral saccular aneurysms, the density difference may produce an appreciable gravity effect, where the contrast material separates from blood and settles along the gravity direction. Although contrast settling has been occasionally reported before, the fluid mechanics behind it have not been explored. Furthermore, the severity of contrast settling in cerebral aneurysms varies significantly from case to case. Therefore, a better understanding of the physical principles behind this phenomenon is needed to evaluate contrast settling in clinical angiography. In this study, flow in two identical groups of sidewall aneurysm models with varying parent-vessel curvature was examined by angiography. Intravascular stents were deployed into one group of the models. To detect contrast settling, we used lateral view angiography. Time-intensity curves were analysed from the angiographic data, and a computational fluid dynamic analysis was conducted. Results showed that contrast settling was strongly related to the local flow dynamics. We used the Froude number, a ratio of flow inertia to gravity force, to characterize the significance of gravity force. An aneurysm with a larger vessel curvature experienced higher flow, which resulted in a larger Froude number and, thus, less gravitational settling. Addition of a stent reduced the aneurysmal flow, thereby increasing the contrast settling. We found that contrast settling resulted in an elevated washout tail in the time-intensity curve. However, this signature is not unique to contrast settling. To determine whether contrast settling is present, a lateral view should be obtained in addition to the anteroposterior (AP) view routinely used clinically so as to rule out contrast settling and hence to enable a valid time-intensity curve analysis of blood flow in the aneurysm.

Evaluation of the Stability of Small Ruptured Aneurysms with a Small Neck after Embolization with Guglielmi Detachable Coils: Correlation between Coil Packing Ratio and Coil Compaction

Because it is difficult to predict the compaction of Guglielmi detachable coils (GDCs) after endovascular surgery for aneurysms, we studied the relationship between the coil packing ratio and compaction. Here, we propose a simple method for the preoperative estimation of coil compaction. Using follow-up angiograms, we studied the timing and degree of coil compaction in small terminal and side-wall aneurysms with narrow necks. We studied 62 patients with acute ruptured intracranial aneurysms that were small (<10 mm), had a small neck (<4 mm), and were coil embolized with GDC-10s. The aneurysmal volume was calculated using the equation V = 4/3pi(a/2) x (b/2) x (c/2), where a, b, and c are the aneurysmal height, length, and width in millimeters, respectively. The coil volume was calculated using the equation V = pi(p/2)2 x l x 10, where p represents the GDC-10 coil diameter (0.25 mm) and l is the coil length. We recorded the maximum prospective coil length, L, as that corresponding with the volume of packed coils occupying 30% of the aneurysmal volume. Therefore, L was calculated as L (cm) = 0.3 x a x b x c, and the coil packing ratio was expressed as packed coil length/L x 100. Angiographic follow-up studies were generally performed at 3 months and 1 and 2 years after endovascular surgery. We considered coil compaction exceeding 2 mm as major compaction and recorded minor compaction when it was less than 2 mm of the empty reappeared space in the embolized aneurysm. Aneurysmal location was recorded as terminal or side wall. Of the 62 patients, 16 (25.8%) manifested angiographic coil compaction (10 minor and 6 major compactions); the mean coil packing ratio was 51.9 +/- 13.4%. The mean coil packing ratio in the other 46 patients was 80.5 +/- 20.2%, and the difference was statistically significant (P < 0.01). In all 6 patients with major compaction, the mean packing ratio was less than 50% and all underwent re-embolization after a mean of 24.9 +/- 1.1 months. The 10 patients with minor compaction were conservatively treated, and the degree of compaction did not change during a mean period of 24 months. We detected 93.8% of the compactions within 12 months of coil placement. The aneurysm was of the terminal type in 5 of the 6 patients with major coil compaction. In patients who underwent embolization with GDC-10s of aneurysms that were small and had a small neck, the optimal coil packing ratio could be identified with the formula 0.3 x a x b x c. The probability of coil compaction was significantly higher when the coil packing ratio was less than 50%. To detect coil compaction after embolization, follow-up angiograms must be examined regularly for at least 12 months. To detect major coil compaction in patients with terminal type aneurysms, angiographic follow-up should not be shorter than 24 months.

Impact of Stent Design on Intra-Aneurysmal Flow

In addition to providing a skeleton for vessel reconstruction, stent implantation as used for cerebral aneurysm treatment can induce flow redirection, thus reducing vortical flow velocities within the aneurysm cavity. Further, stent characteristics such as strut size, porosity and cell shape influence the changes in intra-aneurysmal flow by analog simulations. The purpose of this computer simulation study was to visualize the flow pattern over the entire neck area of a side wall aneurysm while changing the stent parameters. A 3-D computer model aneurysm was constructed to have a parent artery of 5 mm diameter and an aneurysm of 10 mm diameter. The distance between the midline of main artery and center point of the aneurysm was 6.8 mm, providing a neck length of 5 mm, a width of 3.6 mm, and a neck area of 14 mm 2. The simulations were carried out with a Finite Element Method based flow simulation package. The incompressible Navier-Stokes equation was solved for a steady flow with a mean speed of 290 mm/s, steady viscosity of 3.83 cp, and density of 1.0 g/cm3. Two parallel stent struts (dimensions: 100 mum m 100 mum m 2.0 mm) were introduced into the plane of the aneurysm neck. The fraction of the aneurysm neck cross-section occupied by the stent was 2.83% in all cases. The velocity distribution through the neck of the aneurysm was calculated for three different choices of separation between the struts for each of two orientations of the struts (parallel and perpendicular) relative to the vessel axis. The flow pattern in the aneurysm was composed of an inflow zone at the distal neck and of an outflow zone at the proximal neck. The placement of stent struts at the aneurysm neck resulted in a decrease in the mean speed in the aneurysm. The degree of reduction and the distribution of flow through the neck did depend on the orientation of the stent struts. The struts, when placed parallel or perpendicular to the parent vessel axis affected the mean speed through the aneurysm neck differently.

Endovascular treatment of intracranial aneurysms: comparative evaluation in a terminal bifurcation aneurysm model in dogs

The authors investigated whether HydroCoils decreased coil compaction and aneurysm recanalization in a canine model of a large, wide-necked, high-flow bifurcation aneurysm. Eleven experimental aneurysms were created. Two aneurysms were untreated (Group 1); three were treated with standard platinum coils (Guglielmi Detachable Coils; Group 2); and six were treated with platinum framing coils and filling HydroCoils (Group 3). Comparative angiographic and histopathological data were analyzed at 2 weeks and again at 3 months. At 3 months, the Group 1 aneurysms remained patent without spontaneous thrombosis. After coil placement the percentage of aneurysm filling by volume ranged from 59 to 90% (mean 75.4%) for Group 3 (HydroCoil-treated) and 34.3 to 48.9% (mean 39.6%) for Group 2 (GDC-treated) (p < 0.05). At 14 days, two of the three Group 2 aneurysms exhibited coil compaction and aneurysm recanalization at the neck; in both cases the condition worsened at 3 months. At 14 days and 3 months, five of the six Group 3 aneurysms were 100%, and one of six was 90% occluded and remained stable. At 3 months, the neointima of the aneurysm neck was significantly thicker in the Group 3 lesions, which had been treated by HydroCoils (0.329 +/- 0.191 mm), than in Group 2 lesions, which had been treated with GDCs (0.026 +/- 0.018 mm) (p < 0.001). No thrombus formation occurred in Group 2; however, in two of the six aneurysms in Group 3, thrombus formed at the coil-neck interface. The experimental canine bifurcation aneurysm model overcomes the limitations of side-wall aneurysm models. In this model, HydroCoils resulted in significantly denser coil packing, less follow-up coil compaction, and thicker neointimal tissue at the neck of the lesion. HydroCoils also appeared more thrombogenic at the aneurysm neck-parent artery interface.