Intraaneurysmal flow changes affected by clip location and occlusion magnitude in a lateral aneurysm model

In order to study the flow dynamic changes inside an aneurysm sac due to the partial occlusion of the aneurysm neck, velocity fields were measured using a particle image velocitimeter (PIV) in in vitro aneurysm models under the physiological flow waveform. Lateral aneurysm models arising from the curved parent vessel with different occlusion ratios and sites-e.g. no clip, 50% proximal and distal clip, and 75% proximal and distal clip-were tested. Reduced inflow and intraaneurysmal velocities may provide a better hemodynamic environment for aneurysm embolization. Comparing inflow rates and averaged intraaneurysmal velocities in the proximal and the distal clip model, they were lower in the distal clip model in cases of 50% neck occlusion, but they were lower in the proximal clip model in cases of 75% occlusion. These results suggest that clipping sites for reduced inflow and intraaneurysmal flow velocities may differ for different residual neck sizes. Less effective inflow blocking in the 75% distally clipped model may be due to the curvature of the parent artery. Therefore, not only the residual neck size and clipping site but the geometry of parent vessel significantly affect the flow fields inside the aneurysm, and subsequently the success of the aneurysm treatment.     

Development of a novel endothelial cell-seeded endovascular stent for intracranial aneurysm therapy

The metallic stent has been widely used in endovascular treatment of intracranial aneurysms and arterial stenosis. Endothelialization at the neck of the aneurysm or stenotic lesion after stent deployment plays a pivotal role in preventing aneurysm recurrence, as well as local thrombus formation and restenosis. To deliver autologous endothelial cells and to promote the endothelialization on the luminal wall of the parent artery, we established an endothelial cell-seeded intracranial stent device. Endothelial cells were isolated from canine jugular vein and identified by FACS assay and immunohistochemistry. We demonstrated that the seeded endothelial cells formed a confluent endothelial layer on the stent's surface. After being brushed with 100 dyne/cm(2) of shear stress, we found that this endothelial layer remained intact for at least 48 h on the heparinized polymer coated stent, rather than the poly-lactic-acid coated stent (p < 0.05). The results suggest that an autologous endothelial cell-seeded stent may be a feasible and optimal tool for endothelial delivery during stenting and may overcome some limitations of the traditional bare stent in the treatment of intracranial aneurysms and arterial stenosis.     

颅内前循环动脉瘤夹闭术的显微外科技术

目的 总结我院自2004年以采采用显微神经外科手术治疗的104例颅内前循环动脉瘤的经验，探讨颅内前循环动脉瘤夹闭术的显微手术技巧，以期进一步提高该病的临床治疗效果。方法 104例颅内前循环动脉瘤病人中，1例胼周动脉瘤采用前纵裂入路，1例后交通合并胼周动脉瘤采用翼点和前纵裂的联合入路，其余部位的动脉瘤均采用改盘翼点入路。手术采用显微外科技术解剖脑池，锐性分离瘤颈并夹闭之。术中采用控制性降压、栽瘤动脉临时阻断和动脉瘤体翻转等技术以防止破裂出血和误夹正常血管。结果 104例手术病人中，102例成功夹闭瘤颈，2例采用了动脉瘤包裹术。术后病人恢复盘好78例，轻残17倒，重残6例，植物生存2例。死亡1例。结论 采用显微外科技术夹闭动脉瘤颈是治疗颅内前循环动脉瘤的根本方法；术中采用控制性降压、载瘤动脉临时阻断和动脉瘤体翻转等技术以防止破裂出血和误夹正常血管。可以提高颅内前循环动脉瘤的手术治疗效果。     

带生物膜跨血管包裹性动脉瘤夹的研制与应用

对于栓塞和手术夹闭均困难的动脉瘤,外部包裹是最后的选择.但理想的包裹材料和方法至今未取得突破性进展.本文介绍一种带生物膜跨血管包裹性动脉瘤夹,在夹闭瘤颈的同时包裹瘤囊,成功地解决了包裹材料不理想与包裹技术设备不完善等两大方面问题,是治疗颅内难治性动脉瘤的有效方法.     

CFD modeling of blood flow following coil embolization of aneurysms

In case of coil embolization of a giant or a multilobular aneurysm, it is difficult to fill an aneurysm sac completely with coils, therefore, partial blocking of an aneurysm sac is inevitable. Blood flow characteristics, which may influence embolization process of an aneurysm, are affected by the locations of coils for partially blocked aneurysms. Blood flow fields inside an aneurysm are also influenced by the geometry of a parent vessel. In order to suggest the coil locations effective for aneurysm embolization, the blood flow fields of lateral aneurysm models were analyzed for different coil locations and parent vessel geometries. Flow rate into an aneurysm sac from a parent vessel (inflow rate) and wall shear stress were also calculated. Inflow rates were smaller and low wall shear regions were larger in the distal neck blocked model comparing to the dome blocked models. In the distal neck blocked model, inflow volume was smaller by 31% (straight parent vessel model) and 34% (curved parent vessel model) comparing to other models. The time averaged values of normalized low wall shear regions were 4% and 12% greater in the distal neck blocked models with a straight and a curved parent vessel, respectively. Since smaller inflow and low wall shear stress provide hemodynamic environment promoting thrombus embolization, distal neck should be the effective coil location for aneurysm embolization.     

Long-Term Clinical and Angiographic Outcomes of Wrap-Clipping Strategies for Unclippable Cerebral Aneurysms

Purpose

To evaluate the efficacy and stability of the wrap-clipping methods as a reconstructive strategy in the treatment of unclippable cerebral aneurysms.

Materials and Methods

Twenty four patients who had undergone wrap-clipping microsurgery were retrospectively reviewed. Type and morphology of the treated aneurysm, utilized technique for wrap-clip procedure, and clinical outcome with angiographic results at their last follow-up were evaluated.

Results

Of 24 patients, eleven patients had internal carotid artery (ICA) blister-like aneurysms, three had dissecting type aneurysms, and ten had fusiform aneurysms. The follow-up period for the late clinical and angiographic results ranged from 10 to 75 months (mean 35 months). Wrap-clipping was performed in eleven, wrap-holding clipping was in ten, and combination of wrap-clip and wrap-holding clip was in three cases. At the last angiographic follow-up study, twelve aneurysms (50%) were found to have completely healed, and nine aneurysms (38%) were at least stable. However, wrap-holding clip for the elongated blister type of ICA aneurysm was found failed, leading to fatal rebleeding in one case, and two cases of combination of wrap-clip-wrap-holding clip revealed delayed branch occlusion and marked regrowing, respectively.

Conclusion

Wrap-clipping strategy could be an easy and safe alternative for unclippable aneurysms. The wrapped aneurysm mostly disappeared, or at least remained stationary, after a long-term period. However, surgeons should be aware of that the wrapped aneurysm might become worse. Therefore, follow-up surveillance for an extended period should be mandatory.     

Three-Dimensional Geometrical Characterization of Cerebral Aneurysms

The risk of rupture of cerebral aneurysms has been correlated with the size of the aneurysm sac. It is conceivable that geometrical shape, not just size may also be related to aneurysm rupture potential. Further, aneurysm shape may also be a factor in deciding on treatment modalities, i.e., to clip or coil. However, our ability to make use of available information on aneurysm shape remains poor. In this study, methods were developed to quantify the seemingly arbitrary three-dimensional geometry of the aneurysm sac, using differential and computational geometry techniques. From computed tomography angiography (CTA) data, the three-dimensional geometry of five unruptured human cerebral aneurysms was reconstructed. Various indices (maximum diameter, neck diameter, height, aspect ratio, bottleneck factor, bulge location, volume, surface area, Gaussian and mean curvatures, isoperimetric ratio, and convexity ratio) were utilized to characterize the geometry of these aneurysm surfaces and four size-matched hypothetical control aneurysms. The physical meanings of various indices and their possible role as prognosticators for rupture risk and presurgical planning were discussed.     

Kissing anterior communicating artery aneurysms: diagnostic dilemma and management issues

Kissing aneurysms are unusual and relatively rare types of multiple intracranial arterial aneurysms. When located on the anterior communicating artery (ACoA), kissing aneurysms pose considerable diagnostic difficulty on preoperative conventional angiogram. Special angiographic views or 3D rotational angiogram are needed to make the correct diagnosis and to avoid interpreting them as multilobed or bilobed saccular aneurysms on preoperative conventional angiogram. Treatment of these aneurysms, either by clipping or coiling, needs to be individualized. Unique problems which need to be addressed during surgical clipping are high risk of rupture due to dense adhesions between the kissing aneurysms, requirement of at least two clips in a narrow working area, the aneurysm that needs to be clipped first and interference of the first clip with application of subsequent clips. The authors present a case of a 63-year-old male who had kissing ACoA aneurysms managed successfully by clipping.     

Circumferential wrapping and clipping with temporalis fascia for treatment of unclippable intracranial aneurysms

We utilized a clip-reinforced wrapping technique using temporalis fascia for treating unclippable aneurysms in 14 patients. Herein, we describe a modification of the clip- reinforced wrapping technique and report on the results. An appropriately sized strip of temporalis fascia is passed around the aneurysms with cuts made to accommodate perforating arteries. After applying fibrin glue, the aneurysm clip is positioned to secure the circumferential wrapping. Of the 14 patients, 4 (29%) were unclippable microbleb, 4 (29%) were wall defect, 3 (21%) were imperfect clipping due to the complexity of the aneurysm, 2 (14%) were bleb at the base of the aneurysm and 1 (7%) was a fusiform aneurysm. Multiple aneurysms were found in 6 (43%) patients and half (50%) of the 14 patients had MCA aneurysms. Postoperative angiography demonstrated no narrowing of parent arteries or enlargement of the aneurysms. No subsequent bleeding was observed during the 1 year follow-up period. These results suggest that circumferential wrapping-clipping with temporalis fascia and biological glue provides an alternative and safe method of treatment for unclippable intracranial aneurysms.     

Blood flow dynamics in patient-specific cerebral aneurysm models: the relationship between wall shear stress and aneurysm area index

Hemodynamics plays an important role in the progression and rupture of cerebral aneurysms. The temporal and spatial variations in wall shear stress (WSS) within the aneurysmal sac are hypothesized to be correlated with the growth and rupture of the aneurysm. The current work describes the blood flow dynamics in 34 patient-specific models of saccular aneurysms located in the region of the anterior and posterior circulation of the circle of Willis. The models were obtained from three-dimensional rotational angiography image data and blood flow dynamics was studied under a physiologically representative waveform of inflow. The three-dimensional continuity and momentum equations for unsteady laminar flow were solved with commercial software using non-structured fine grid sizes. The vortex structure, the wall pressure, and the WSS showed large variations, depending on the morphology of the artery, size of the aneurysm, and form. A correlation existed between the mean WSS on the aneurysmal sac for lateral unruptured and ruptured aneurysms with an aneurysm surface index, which is defined as the ratio between the aneurysm area and the artery area at model inlet, respectively.     

Giant aneurysms not amenable to direct treatment by ligation of the carotid artery

Surgical treatment of giant aneurysms are a challenge. Optimal treatment for an intracranial aneurysm is the direct approach, and also clipping the neck of the aneurysm and preservation of the parent vessel. These surgical procedures are not always possible to carry out even with state-of-the-art in neurological surgery. This is the case for giant aneurysms. Carotid ligation remains a good alternative for ophthalmic, intercavernous sinus, and giant aneurysms of the internal carotid artery. We present two patients with unclippable carotid artery aneurysms, one in the intercavernous sinus, and the other in the internal carotid. These were treated by progressive ligature of the carotid artery at the neck. The ligation was done after angiographic and CT scan evaluation. Tolerance to carotid occlusion was evaluated by electroencephalogram and somatosensory evoked potential monitoring, and the procedure was undertaken gradually. Outcome of the two patients was gradual improvement of oculomotor nerve palsy and decrease of ocular pain. These results of treatment and favorable evolution suggest that this treatment is a useful alternative in the management of unclippable carotid aneurysm. Acute or long-term complications were not observed.     

Patient-specific flow analysis of brain aneurysms at a single location: comparison of hemodynamic characteristics in small aneurysms

The purpose of this study is to examine and compare the hemodynamic characteristics of small aneurysms at the same anatomical location. Six internal carotid artery-ophthalmic artery aneurysms smaller than 10 mm were selected. Image-based computational fluid dynamics (CFD) techniques were used to simulate aneurysm hemodynamics. Flow velocity and wall shear stress (WSS) were also quantitatively compared, both in absolute value and relative value using the parent artery as a baseline. We found that flow properties were similar in ruptured and unruptured small aneurysms. However, the WSS was lower at the aneurysm site in unruptured aneurysms and higher in ruptured aneurysms (P < 0.05). Hemodynamic analyses at a single location with similar size enabled us to directly compare the hemodynamics and clinical presentation of brain aneurysms. The results suggest that the WSS in an aneurysm sac can be an important hemodynamic parameter related to the mechanism of brain aneurysm growth and rupture.     

Changes of flow characteristics by stenting in aneurysm models: influence of aneurysm geometry and stent porosity

An endovascular technique using a stent has been developed and successfully applied in the treatment of wide neck aneurysms. A stent can facilitate thrombosis in the aneurysm pouch while maintaining biocompatible passage of the parent artery. Insertion of the stent changes the flow characteristics inside the aneurysm pouch, which can affect the intra-aneurysmal embolization process. The purpose of this study is to clarify the velocity and wall shear stress changes that are caused by stenting in fusiform and lateral aneurysm models. We used a flow visualization technique that incorporated a photochromic dye in order to observe the flow fields and measure the wall shear rates. The intra-aneurysmal flow motion was significantly reduced in the stented aneurysm models. Coherent inflow along the distal wall of the aneurysm was diminished and inflow was distributed along the pores of the stent wall in the stented models. Also, sluggish intra-aneurysmal vortex motion was well maintained in the stented aneurysm models during the deceleration phase. A less porous stent generally reduced the intraneurysmal fluid motion further, but the porosity effect was not significant. The magnitude and pulsatility of the wall shear rate were reduced by stenting, and the reductions were more significant in the lateral aneurysm models compared to the fusiform aneurysm models. The hemodynamic changes that were observed in our study can help explain the efficacy of in vivo thrombus formation caused by stenting. © 2002 Biomedical Engineering Society. PAC2002: 8719Uv, 8780-y, 8719Xx     

手术夹闭合并同侧胚胎型大脑后动脉的后交通动脉瘤预后因素分析

目的探讨手术夹闭存在胚胎型大脑后动脉的后交通动脉瘤(PCoAA)预后的影响因素。方法选择徐州医科大学附属医院神经外科2015年1月至2019年1月经显微手术夹闭合并胚胎型大脑后动脉的PCoAA患者80例,术后6个月采用改良Rankin量表评价患者预后,采用单因素分析和多因素Logistic回归分析影响患者预后的因素。结果性别、动脉瘤侧别、宽颈、动脉瘤大小、脑梗死史、手术时机、高血压史对手术预后影响不大;而年龄、Hunt-Hess分级、改良Fisher分级是影响手术预后的危险因素。结论年龄、术前Hunt-Hess分级以及改良Fisher分级是患者预后不良的独立影响因素;对于年龄不大、Hunt-Hess低分级、改良Fisher低分级这类患者,更早进行显微外科手术治疗,安全性更高,预后更好。     

A computational model based on fibrin accumulation for the prediction of stasis thrombosis following flow-diverting treatment in cerebral aneurysms

Flow diverters, the specially designed low porosity stents, have been used to redirect blood flow from entering aneurysm, which induces flow stasis in aneurysm and promote thrombosis for repairing aneurysm. However, it is not clear how thrombus develops following flow-diversion treatment. Our objective was to develop a computation model for the prediction of stasis-induced thrombosis following flow-diversion treatment in cerebral aneurysms. We proposed a hypothesis to initiate coagulation following flow-diversion treatment. An experimental model was used by ligating rat’s right common carotid artery (RCCA) to create flow-stasis environment. Thrombus formed in RCCA as a result of flow stasis. The fibrin distributions in different sections along the axial length of RCCA were measured. The fibrin distribution predicted by our computational model displayed a trend of increase from the proximal neck to the distal tip, consistent with the experimental results on rats. The model was applied on a saccular aneurysm treated with flow diverter to investigate thrombus development following flow diversion. Thrombus was predicted to form inside the sac, and the aneurysm was occluded with only a small remnant neck remained. Our model can serve as a tool to evaluate flow-diversion treatment outcome and optimize the design of flow diverters.     

Vortex Phenomena in Sidewall Aneurysm Hemodynamics: Experiment and Numerical Simulation

We carry out high-resolution laboratory experiments and numerical simulations to investigate the dynamics of unsteady vortex formation across the neck of an anatomic in vitro model of an intracranial aneurysm. A transparent acrylic replica of the aneurysm is manufactured and attached to a pulse duplicator system in the laboratory. Time-resolved three-dimensional three-component velocity measurements are obtained inside the aneurysm sac under physiologic pulsatile conditions. High-resolution numerical simulations are also carried out under conditions replicating as closely as possible those of the laboratory experiment. Comparison of the measured and computed flow fields shows very good agreement in terms of instantaneous velocity fields and three-dimensional coherent structures. Both experiments and numerical simulations show that a well-defined vortical structure is formed near the proximal neck at early systole. This vortical structure is advected by the flow across the aneurysm neck and impinges on the distal wall. The results underscore the complexity of aneurysm hemodynamics and point to the need for integrating high-resolution, time-resolved three-dimensional experimental and computational techniques. The current work emphasizes the importance of vortex formation phenomena at aneurysmal necks and reinforces the findings of previous computational work and recent clinical studies pointing to links between flow pulsatility and aneurysm growth and rupture.     

Effect of radioactivity on stent-graft incorporation after endovascular treatment of aneurysms: An animal study

Poor stent-graft (SG) incorporation into the vessel wall, following endovascular repair of abdominal aortic aneurysms (EVAR), can lead to endoleaks and SG migration. Low-dose radiation can prevent aneurysm recurrence after coil embolization, and has been associated with a "paradoxical" increase in neointima formation after stenting in a few studies. It was hypothesized that in situ beta radiation emitted from SG could improve its incorporation by preventing the persistence of circulating channels between the implant and the vessel wall and increasing neointima formation around the SG. Phosphorus 32 ((32)P, 200 or 400 kBq per SG (n = 6 each)) was ion implanted on the external surface of balloon-expandable SGs. Twelve radioactive and six non-radioactive SGs were deployed in iliac arteries of nine Mongrel dogs. Neointima formation inside the graft and the persistence of circulating flow through an artificial groove created during the endovascular procedure were assessed by follow-up imaging and by blinded, computerized histomorphometric analysis after animal sacrifice at 3 months. Occlusion occurred in four radioactive SGs. A lesser number of patent grooves was observed along high-activity SGs than along control SGs (1/3 versus 4/4). No difference in neointima formation was observed in radioactive and non-radioactive SGs. Alteration of external graft surface was observed after ion implantation. Ion implantation of (32)P on SGs does not seem to be a viable strategy to improve incorporation and prevent type-I endoleak after EVAR.     

Cold hibernated elastic memory foams for endovascular interventions

Cold hibernated elastic memory (CHEM) polyurethane-based foam is a new shape memory polymeric self-deployable structure.Standard cytotoxicity and mutagenicity tests were conducted on CHEM in vitro, to ensure biocompatibility before studying potential medical applications. In vivo, lateral wall aneurysms were constructed on both carotid arteries of eight dogs. Aneurysms were occluded per-operatively with CHEM blocks. In two dogs, CHEM embolization was compared with gelatin sponge fragment embolization. Internal maxillary arteries (Imax) were also occluded with CHEM using a 6F transcatheter technique. Angiography and pathology were used to study the evolution of aneurysms and Imax at 3 and 12 weeks. Imax embolized with CHEM foam remained occluded at 3 weeks. Most aneurysms embolized with CHEM showed a small residual crescent of opacification at initial angiography, but angiographic scores were significantly better at 3 weeks. Thick neointima formation over the CHEM at the neck of aneurysms was demonstrated at pathology. The foamy nature of CHEM favours the ingrowth of cells involved in neointima formation. New devices for endovascular interventions could be designed using CHEM's unique physical properties.     

Hemodynamics of small aneurysm pairs at the internal carotid artery

Cerebral aneurysms carry significant risks because rupture-related subarachnoid hemorrhage leads to serious and often fatal consequences. The rupture risk increases considerably for multiple aneurysms. Multiple aneurysms can grow from the same location of an artery, and the interaction between these aneurysms raises the rupture risk even higher. Four aneurysm pair cases at the internal carotid artery are investigated for their hemodynamic behaviors using patient-specific modeling. For each case, aneurysms are separated from the parent artery and three models are reconstructed, one with two aneurysms and the other two models with only one of the two aneurysms. Results show that the relative anatomic location of one aneurysm to the other may determine the hemodynamic environment of an aneurysm. The presence of a proximal aneurysm reduces the intra-aneurysmal flow into the distal aneurysm; the proximal aneurysm and larger aneurysm have a greater area under low wall shear stress. The average intra-aneurysmal inflow ratio ranges from 16% to 41%, and reduction of the inflow ratio by an aneurysm pair varies from 6% to 15%. The maximum wall shear stress increases for serial aneurysms, but decreases for parallel aneurysms. Interaction between parallel aneurysms is not significant; however, the proximal aneurysm in serial aneurysms may be subject to a greater rupture risk.     

Developing a new endograft for the treatment of juxtarenal aortic aneurysms: definition and experimentation

OBJECTIVES:To analyze angiotomographic parameters of juxtarenal aneurysms to assess the applicability of an endograft model to patients and to create in vitro and in vivo models to assess the new endograft.METHODS:A total of 49 patients with juxtarenal aneurysms were submitted to angiotomographic evaluation, and parameters such as the aortic diameter, the length of the neck, and the angulations of the celiac trunk, superior mesenteric artery and renal arteries; the distances between them; and anatomic variations were analyzed. Based on these parameters, an endograft model was developed and tested in a newly created in vitro model of juxtarenal aneurysm. An experimental model of juxtarenal aneurysm was then established in six pigs weighing 50–60 kg to assess the new endograft model.RESULTS:The angiotomographic parameters of juxtarenal aneurysm measured in this study were similar to those reported in the literature and allowed the development of an endograft based on the hourglass concept, which was applicable to 85.8% of the patients. The in vitro model of juxtarenal aneurysm evidenced good radiopacity and functionality and permitted adjustments in the new device and technical improvements in the procedures for treating these aneurysms. In addition, the porcine model of juxtarenal aneurysm was successfully created in all six animals using a bovine pericardial patch, and use of the new endograft in three pilot procedures evidenced its feasibility.CONCLUSIONS:The Hourglass endograft was rendered applicable to treatment of the majority of patients with juxtarenal aneurysms simply by changing its diameter. Moreover, the new in vitro and in vivo models were shown to be effective for assessing both the presented endograft and experiments assessing the endovascular treatment of juxtarenal aneurysms.