Aneurysmal pressure changes with nondetachable balloon placement and fluid infusion: rationale for liquid embolization

BACKGROUND AND PURPOSE:To improve the safety and efficacy of liquid embolization, we evaluated changes in pressures in experimental aneurysms. METHODS:We created three replicas of a lateral sidewall aneurysm and placed them in a physiologic flow circuit. A 3 x 10-mm nondetachable balloon was positioned in the parent vessel across the aneurysmal neck. Intra-aneurysmal pressures were measured at baseline and after balloon inflation. Fluid was infused into the sac via a 1.45F microcatheter during inflation, and maximal pressures were noted. Measurements were repeated eight times in each aneurysm. RESULTS: After balloon inflation, average intra-aneurysmal pressures increased: 12 mm Hg (13%, sigma(n - 1) = 0.46) for aneurysm 1 (baseline mean arterial pressure [MAP], 94 mm Hg), 15 mm Hg (58%, sigma(n - 1) = 0.88) for aneurysm 2 (baseline MAP, 26 mm Hg), and 15 mm Hg (58%, sigma(n - 1) = 0.92) for aneurysm 3 (baseline MAP, 26 mm Hg). During inflation and infusion, pressures increased slightly: 1.1 (0.94%, sigma(n - 1) = 0.64), 1.6 (3.9%, sigma(n - 1) = 1.1), and 1.9 (4.6%, sigma(n - 1) = 1.2) mm Hg for aneurysms 1, 2, and 3, respectively. Despite complete balloon occlusion of the distal aneurysmal neck, a channel between the proximal aneurysmal neck and the parent-vessel lumen persisted along the microcatheter. Fluid exited the sac via this channel, preventing a concomitant, significant increase in pressure during infusion. CONCLUSION: Intra-aneurysmal pressure modestly increased with inflation of a parent-vessel balloon across the neck. When liquid was infused into the sac during inflation, further increases were minimal.     

Physiologic and anatomic assessment of a canine carotid artery stenosis model utilizing phase contrast with vastly undersampled isotropic projection imaging

BACKGROUND AND PURPOSE: Noninvasive assessment of the hemodynamic significance of carotid stenosis is often performed with MR angiography and supplemented with carotid Doppler sonography. Phase contrast with vastly undersampled isotropic projection reconstruction (PC-VIPR), a novel MR imaging technique, accelerates phase-contrast MR flow imaging and provides both images of the vessels and measurements of blood-flow velocities. For this study, we determined the accuracy of PC-VIPR blood-flow velocity measurements to determine pressure gradients across an experimental carotid stenosis. MATERIALS AND METHODS: A focal stenosis was surgically created in each common carotid artery of 6 canines. Digital subtraction angiography (DSA) was performed, and the degree of stenosis was determined using the North American Symptomatic Carotid Endarterectomy Trial methodology. A microcatheter was positioned in the carotid artery proximal and distal to the stenosis, and pressures were measured in the vessel through the catheter. PC-VIPR was then performed on a 1.5T MR imaging scanner with parameters producing 0.8-mm isotropic voxel resolution. From the velocity measurements, pressure gradients were calculated from the Navier-Stokes relationship to compare with the pressures measured by a catheter. RESULTS: Carotid stenoses in the 50%-85% range were produced in the 12 arteries. Pressure gradients across the stenoses ranged from 6 to 26 mm Hg. The pressure gradient calculated from the PC-VIPR data correlated (r = 0.91, P < .0001) with the actual pressure measurements. CONCLUSION: With PC-VIPR, a novel MR imaging technique, the hemodynamic effect of a stenosis on flow and pressure can be evaluated.     

内漏对腹主动脉瘤腔内隔绝术后瘤腔内压力的影响

目的 探讨内漏状态下腹主动脉瘤(AAA)腔内隔绝术(EVE)后瘤腔内压力的变化。方法 通过建立犬AAA EVE后内漏模型，测定内漏存在前后瘤腔内压力的变化。结果 内漏状态下瘤腔内平均动脉压明显升高，而内漏封闭后压力显著下降，且曲线平直。结论 瘤腔内压力曲线可作为评估EVE后瘤壁所受负荷的变化，也可作为判断内漏存在的方法之一。     

支架孔率对脑动脉瘤血流动力学影响的三维数值模拟研究

目的 探讨不同支架网孔密度对支架植入后脑动脉瘤内血流动力学的影响.方法 建立宽颈的弯曲管侧壁型动脉瘤血流动力学三维数值模型,比较不同网孔密度支架植入前后,动脉瘤内血流动力学变化.结果动脉瘤远侧肇的速度峰值与壁面剪应力随着支架孔率下降而降低.瘤颈远侧壁及瘤顶部的压力场与支架孔率无明确的相关性.结论 数值模拟研究证实支架孔率是影响动脉瘤内血流动力学的关键因素,合适的支架孔率设计对动脉瘤血管重建治疗至关重要.     

Lingual artery bifurcation aneurysms for training and evaluation of neurovascular devices

We present a canine lingual artery bifurcation aneurysm and assess its value for training in endovascular techniques and testing new embolic agents. The experimental aneurysm described herein mirrors human bifurcation aneurysms, and with this model, we sought to reproduce endovascular technical difficulties. However, the lesions created in this canine model did not show angiographic or histologic evidence of aneurysmal recurrence. We conclude that this model may be useful for training in endovascular techniques, but because of the lack of sufficient aneurysmal recurrence, it is not suitable for evaluating new embolic agents.     

Natural history of the canine vein pouch aneurysm model

BACKGROUND AND PURPOSE: The canine vein pouch aneurysm model is widely used for testing and development of devices directed at the endovascular treatment of aneurysms. Our purpose was to determine the incidence of spontaneous thrombosis and rupture of these aneurysms. MATERIALS AND METHODS: A retrospective review of laboratory records of canine vein pouch aneurysms made during a 6-year period was performed. The aneurysm and parent artery dimensions as well as incidences of spontaneous thrombosis and rupture were noted. RESULTS: During the interval studied, 326 vein patch aneurysms were made in 310 canines. Of these, 102 were sidewall (lateral) and 224 were bifurcation aneurysms. Spontaneous occlusion occurred in 9 of the sidewall aneurysms and in only 1 of the bifurcation aneurysms. None of the aneurysms ruptured. CONCLUSION: Spontaneous occlusion of the sidewall canine vein patch aneurysm occurred less than 10% of the time; in the bifurcation aneurysms, it almost never occurred. These characteristics enhance the value of this model for use in testing of devices intended for the endovascular treatment of aneurysms.     

Endovascular neurointervention for cerebral aneurysm

Embolization would have an advantage in the treatment of cerebral aneurysms by eliminating the need for craniotomy. The recent protocol of endovascular treatment for cerebral aneurysm is classified into two main categories; is parent artery occlusion and intra-aneurysmal embolization. For aneurysms with a broad neck and large sac, it is recommended to consider proximal arterial occlusion if tolerance is confirmed by cerebral blood flow study at the time of balloon Matas' test. Parent artery occlusion is a classical technique, but still mandatory and effective clinically. In patients who have aneurysms with a has well-defined neck and who are not good candidates for craniotomy, intra-aneurysmal embolization would be recommended as an alternative means of treatment. Care should be taken to prevent problems and complications, including careful catheter and guidewire manipulation. Careful selection of cases and appropriate pre-, intra-, and post-procedure patient management is essential. Since the clinical application of Gugliemi's detachable coil (GDC) started, the potential of endovascular treatment for cerebral aneurysm has changed considerably. Preliminary results of embolization using GDC suggest that endovascular treatment would offer marked improvement in the management of patients harboring cerebral aneurysms.     

A case report of pericallosal aneurysm successfully treated with flow diverter stents

Pericallosal artery aneurysm (PAA) is a relatively uncommon type of intracranial aneurysm that tends to rupture more frequently and cause higher mortality rates than other types of cerebral aneurysms. Surgery to address PAA is difficult due to its deep-seated location, the size of the aneurysmal sac, and the limited surgical field. In recent years, with the development of percutaneous interventions, endovascular treatment has become the preferred, minimally invasive intervention method for the treatment of pericallosal aneurysms. In this article, we present a case of PAA that was successfully treated with flow diversion therapy in a 51-year-old male.     

A canine model for studying endoleak after endovascular aneurysm repair

PURPOSE: The aim of this study was to create an animal model of endoleak after stent-graft placement for abdominal aortic aneurysm (AAA) in which a large aneurysmal sac would be preserved for the testing of techniques for its percutaneous occlusion. MATERIALS AND METHODS: Infrarenal AAAs were created in nine dogs by anastomosis of an isolated segment of the inferior vena cava to the right side of the abdominal aorta in combination with a large anterior patch from the external jugular vein. One hour later, animals underwent percutaneous implantation of polytetrafluoroethylene-covered Z stent endografts with three 3-mm-diameter holes through the fabric. Aortograms were obtained before and after surgery, after endograft placement, and at the time of animal sacrifice at 1 week or 1, 2, 3, or 6 months. Pressures within the aorta and the aneurysm sac were recorded before animal sacrifice. Gross and histologic evaluations of the specimens were then carried out. RESULTS: Immediately after endograft placement, all nine animals had artificial type III endoleaks with angiographic filling of lumbar arteries and veins. One animal died of surgical complications within 2 days of surgery and is not included in our data analysis. One aneurysm ruptured at 1 week. At completion of the study, six endografts were patent and two were occluded. The aneurysm sac had enlarged by approximately 50% in seven animals. At follow-up, type I endoleak was present in three animals, type II endoleak was present in three, and the artificial type III endoleak was present in all six animals with patent endografts. The pressure differential between aorta and aneurysm sac was 36 mm Hg, with a mean aortic pressure of 87 mm Hg +/- 13.3 and a mean aneurysmal sac pressure of 51 mm Hg +/- 28.1. The aneurysmal sac exhibited early thrombus formation at 1 week, which progressed to complete thrombosis in 1-6 months. CONCLUSIONS: The model is technically feasible but would be useful in testing occlusive techniques for residual aneurysm sacs only in the acute phase after endograft placement. It would be not reliable for chronic evaluation because of rapidly progressive thrombosis in most aneurysm sacs and occasional complete thrombosis of the AAA and endograft.     

Outcome of emergency endovascular treatment of large internal iliac artery aneurysms with guidewires

Purpose

Guidewires have been reported as a useful occlusion material for large aneurysms of different locations with good short-term results. In this study we retrospectively evaluate long-term results of emergency embolization technique with guidewires in symptomatic internal iliac artery aneurysm (IIAA) impending rupture.

Patients and methods

In four patients presented with acute abdominal pain, multidetector computed tomography revealed unstable, 7-14 cm large, IIAAs. Two patients were treated with coil embolization of distal branches followed by occlusion of aneurysmal sac with guidewires. In two patients embolization of aneurysmal sac alone was performed.

Results

In three patients complete or near complete occlusion of the aneurysmal sac was achieved and abdominal pain ceased within hours. Two patients treated with embolization of distal iliac artery branches and aneurysmal sac developed claudication that lasted up to 1 year. Their aneurysms remained thrombosed and they were without symptoms until they died 31 and 56 months later of causes unrelated to IIAA. Two patients treated with embolization of the aneurysm alone were free of ischemic symptoms. Because of incomplete embolization of the sac in one patient open surgery treatment in a non-emergency setting was performed. Complete filling of aneurysmal sac was achieved in other patient but 2 years later his aneurysm re-opened and required open surgery treatment.

Conclusion

Embolization of aneurysmal sac of large IIAA with guidewires may be effective for immediate treatment of impending rupture. Long-term results were better when embolization of the aneurysmal sac was combined with embolization of distal IIA branches.     

Anatomically shaped internal carotid artery aneurysm in vitro model for flow analysis to evaluate stent effect

BACKGROUND AND PURPOSE: Stent implantation alone might not be sufficient to produce definitive treatment of cerebral aneurysms. Therefore, extended experimental work is needed to improve results. We show the feasibility of using an in vitro anatomically shaped elastic model for flow evaluation before and after stent implantation. METHODS: Based on human vascular casting, an anatomic elastic internal carotid artery model, including an aneurysm on the supraclinoid portion, was manufactured. The model was connected to a circulatory loop to simulate physiological flow. After visualization of the flow by using glass particles and laser sheet translumination, the digitally recorded data were transferred for computer analysis. Intra-saccular flow pattern changes and the vortex velocity reduction induced by the stent were investigated qualitatively and quantitatively. RESULTS: The distal neck of the aneurysm behaved as a flow divider. Therefore, it was directly exposed to the hemodynamic stress. Inside the sac, a well-defined vortex formed and progressed along the wall toward the proximal neck. After stent implantation this pattern changed significantly; the vortex appeared more dispersed and its residence time increased. The velocity reduction was 32%. Velocity peak was observed close to the distal neck in both cases. CONCLUSION: In vitro anatomic elastic models are feasible for flow evaluation with laser sheet translumination. In our model, stent implantation resulted in hemodynamic changes that might favor the exclusion of the aneurysm from the circulation and can prevent regrowth of the aneurysmal sac.     

Technical feasibility of embolizing aneurysms with glue (N-butyl 2-cyanoacrylate): experimental study in rabbits

BACKGROUND AND PURPOSE: Liquid embolic agents may have potential as a therapeutic option to reconstruct a defective vessel wall. We evaluated the feasibility of transarterial glue embolization in surgically constructed carotid artery aneurysms. METHODS: Reconstruction of arterial wall defects with use of glue casts was performed in 16 surgically constructed aneurysms of carotid arteries in rabbits. Via the transfemoral route, glue was injected without balloon protection through a microcatheter into the aneurysmal sac with (n = 8) and without (n = 8) a framework of coils. To identify safe and effective methods, four concentrations (28%, 33%, 40%, 50%) of glue-iodized oil mixtures were used in four aneurysms each. Immediate (n = 16) and 2-month follow-up (n = 10) postembolization angiograms were obtained to evaluate the residual aneurysmal sac and the carotid artery patency. RESULTS: Continuous column injection of glue was possible in all aneurysms, without fragmented migration of the injected glue cast. Catheter sticking or breakage did not occur during catheter retrieval. Glue embolization without a framework of coils (n = 8) resulted in complete obliteration of the aneurysmal sac in five aneurysms and incomplete obliteration with a small residual lumen in three. Two aneurysms resulted in carotid occlusion after catheter removal. A follow-up angiogram (n = 4) showed decreased residual lumen in two aneurysms, no change in the complete aneurysm occlusion in one, and carotid occlusion in one. Glue embolization with a coil framework (n = 8) resulted in complete obliteration of the aneurysmal sac in six aneurysms and incomplete obliteration with a small residual lumen in two. A small amount of spillage occurred in one owing to the improper position of the microcatheter caused by a difficult neck angle to the parent artery. Follow-up angiograms (n = 6) showed decreased residual lumen in one of two aneurysms and no change of the complete occlusion in five of six aneurysms. CONCLUSION: Effective glue embolization into the aneurysmal sac is technically feasible. Microcatheter position within the aneurysm, concentration of glue, and direction of the aneurysmal neck angle all must be considered. With a coil framework, glue injection was more complete, without deformity or spillage of the glue from the aneurysm.     

An Animal Model of Abdominal Aortic Aneurysm Created with Peritoneal Patch: Technique and Initial Results

The purpose of this study was to develop an abdominal aortic aneurysm model that more closely resembles the morphology of human aneurysms with potential for further growth of the sac. An infrarenal abdominal aortic aneurysm (AAA) model was created with a double-layered peritoneal patch in 27 domestic swine. The patch, measuring in average from 6 to 12 cm in length and from 2 to 3 cm in width, was sutured to the edge of an aortotomy. Pre- and postsurgical digital subtraction aortograms (DSA) were obtained to document the appearance and dimensions of the aneurysm. All animals were followed with DSA for up to 5 months. Laparoscopic examination enhanced by the use of laparoscopic ultrasound was also carried out in 2 animals to assess the aneurysm at 30 and 60 days following surgery. Histological examination was performed on 4 animals. All the animals that underwent the surgical creation of the AAA survived the surgical procedure. Postsurgical DSA demonstrated the presence of the AAA in all animals, defined as more than 50% increase in diameter. The aneurysmal mean diameter increased from the baseline of 10.27 ± 1.24 to 16.69 ± 2.29 mm immediately after surgery, to 27.6 ± 6.59 mm at 14 days, 32.45 ± 8.76 mm at 30 days (p < 0.01), and subsequently decreased to 25.98 ± 3.75 mm at 60 days. A total of 15 animals died of aneurysmal rupture that occurred more frequently in the long aneurysms (6 cm in length) than the short aneurysms (<6 cm in length) during the first 2 weeks after surgery (p < 0.05). No rupture occurred beyond 16 days after surgery. Four animals survived and underwent 60-day angiographic follow-up. Laparoscopic follow-up showed strong pulses, a reddish external appearance and undetectable suture lines on the aneurysmal wall. On pathology, the patches were well incorporated into the aortic wall, the luminal wall appeared almost completely endothelialized, and cellular and matrix proliferation were noted in the aneurysmal wall. A reproducible technique for the creation of an infrarenal AAA model was developed using a peritoneal patch in swine. The aneurysm model proved to have potential for further growth of the sac and a tendency to rupture. Because of the growth potential, this might be a better model than those with a noncompliant aneurysmal wall for the preclinical evaluation of stent-graft devices.     

Endovascular treatment of peripheral cerebellar artery aneurysms

BACKGROUND AND PURPOSE: Peripheral cerebellar artery aneurysms are rare and difficult to treat surgically. We report the angiographic results and the clinical outcomes for eight patients treated by embolization for peripheral cerebellar artery aneurysms. METHODS: Between 1994 and 2001, eight patients with peripheral cerebellar artery aneurysms were referred from the neurosurgery department for endovascular treatment. The patients consisted of four women and four men with a mean age of 43 years (range, 16-68 years). Seven patients presented with subarachnoid hemorrhage. In one patient, the aneurysm was incidental. In five cases, selective embolization of the aneurysmal sac was performed using GDCs. Two large peripheral cerebellar artery aneurysms and one small aneurysm with a wide neck were treated by parent vessel occlusion. Mean clinical and imaging follow-up duration was 18.5 months (range, 12-36 months). RESULTS: Endovascular treatment resulted in five complete occlusions, two neck remnants, and one residual aneurysmal flow. Clinical evaluation showed that good or excellent recovery was achieved by all patients. Imaging follow-up revealed seven complete occlusions and one residual aneurysmal flow. CONCLUSION: Our study showed that the endovascular approach to treat peripheral cerebellar artery aneurysms by selective embolization or parent vessel occlusion was feasible, safe, and effective. Imaging follow-up showed excellent anatomic results in accordance with clinical recovery.     

Wall shear stress on ruptured and unruptured intracranial aneurysms at the internal carotid artery

BACKGROUND AND PURPOSE: Hemodynamics is often recognized as one of the major factors in aneurysm rupture. Flow impingement, greater pressure, and abnormal wall shear stress are all indications for aneurysm rupture. Characterizing wall shear stress for intracranial aneurysms at similar anatomic locations may help in understanding its role.MATERIALS AND METHODS: Twenty-six intracranial aneurysms at the paraclinoid and superclinoid segments of the internal carotid artery from 25 patients between July 2006 and July 2007 were studied retrospectively. Among them, 8 aneurysms were ruptured and 18 were unruptured. Computational fluid dynamics was used to determine the wall shear distribution. Morphologic and hemodynamic variables was analyzed by using the Mann-Whitney rank sum test.RESULTS: Wall shear stress was qualitatively the same throughout the cardiac cycle; thus, only wall shear stress at the end of diastole was compared. Both ruptured and unruptured aneurysms have similar maximal wall shear stress (26 versus 23 N/m²), and mean wall shear stress is shown to be a function of the aneurysm area. Ruptured aneurysms also have a greater portion of aneurysm under low wall shear stress (27% versus 11% for unruptured aneurysms, P = .03).CONCLUSION: For intracranial aneurysms at the internal carotid artery, an area of low wall shear is associated with aneurysm rupture.

Hemodynamics is recognized as one of the many factors responsible for aneurysm rupture.¹ Many hemodynamic variables, including flow pattern and wall shear stress, are hypothesized to be the causes.^2,3 Intra-aneurysmal flow results in complex flow structure and different flow impinging sites, some at the ostium and some at the dome.^3,4 This complex flow yields a variable wall shear stress distribution on the aneurysm wall. Because wall shear stress regulates endothelial functions,^5,6 understanding of wall shear distribution on the aneurysm wall becomes very important.Recent development of numerical tools has enabled us to study hemodynamics in realistic patient aneurysm geometries.^3,7 Studies based on patient-specific aneurysm models are benefited greatly by advanced 3D angiography because 3D images capture detailed anatomic features that are often neglected in idealized geometry.^7-9 Fine anatomic details render a different flow structure, and these studies have improved our knowledge of the influence of aneurysm morphology on intra-aneurysmal flow.¹⁰ Studying aneurysms at similar anatomic locations allows us to focus on intra-aneurysmal flow, wall shear stress, and aneurysm behaviors. Therefore, we studied the wall shear stress distribution on 26 intracranial aneurysms at the paraclinoid and superclinoid segments of the internal carotid artery and examined the role of hemodynamic variables.     

Characterization of cerebral aneurysms for assessing risk of rupture by using patient-specific computational hemodynamics models

BACKGROUND AND PURPOSE: Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. This report describes a pilot clinical study of the association between intra-aneurysmal hemodynamic characteristics from computational fluid dynamic models and the rupture of cerebral aneurysms. METHODS: A total of 62 patient-specific models of cerebral aneurysms were constructed from 3D angiography images. Computational fluid dynamics simulations were performed under pulsatile flow conditions measured on a normal subject. The aneurysms were classified into different categories, depending on the complexity and stability of the flow pattern, the location and size of the flow impingement region, and the size of the inflow jet. The 62 models consisted of 25 ruptured and 34 unruptured aneurysms and 3 cases with unknown histories of hemorrhage. The hemodynamic features were analyzed for associations with history of rupture. RESULTS: A large variety of flow patterns was observed: 72% of ruptured aneurysms had complex or unstable flow patterns, 80% had small impingement regions, and 76% had small jet sizes. By contrast, unruptured aneurysms accounted for 73%, 82%, and 75% of aneurysms with simple stable flow patterns, large impingement regions, and large jet sizes, respectively. Aneurysms with small impingement sizes were 6.3 times more likely to have experienced rupture than those with large impingement sizes (P = .01). CONCLUSIONS: Image-based patient-specific numeric models can be constructed in an efficient manner that allows clinical studies of intra-aneurysmal hemodynamics. A simple flow characterization system was proposed, and interesting trends in the association between hemodynamic features and aneurysmal rupture were found. Simple stable patterns, large impingement regions, and jet sizes were more commonly seen with unruptured aneurysms. By contrast, ruptured aneurysms were more likely to have disturbed flow patterns, small impingement regions, and narrow jets.     

Delayed spontaneous rupture of a posterior inferior cerebellar artery aneurysm following treatment with flow diversion: a clinicopathologic study

In this report, we present the fatal spontaneous delayed rupture of a previously unruptured large PICA aneurysm following treatment with the PED. Pathology at postmortem examination has supported the theory that intra-aneurysmal thrombus may acutely destabilize the aneurysm wall. Aneurysms with an anatomic arrangement that promote continued flow into the neck may not be optimal candidates for the flow-diversion treatment strategy.     

In vitro study of haemodynamics in a giant saccular aneurysm model: influence of flow dynamics in the parent vessel and effects of coil embolisation

The purpose of this study was to investigate the influence of flow dynamics in the parent vessel and of intra-aneurysmal coil embolisation on flow pattern and pressure in an in vitro model of giant aneurysm. A pulsatile perfusion with a glycerol aqueous solution was installed in a silicone model of a lateral giant aneurysm. Flow visualisation and pressure measurements were performed while modifying the flow rate, the pulsatility and the pulse rate in the parent vessel, and after partial coil embolisation. Vortices were formed during systole at the downstream lip of the aneurysm and circulated around the aneurysm. The centre and dome of the aneurysm were areas of fluid stagnation. Flow rate and pulsatility were the main factors which varied the pattern of flow within the aneurysm. Partial coil embolisation induced major flow disturbances in the aneurysm, in particular fluid stagnation at the dome. Pressure measurements were similar in the aneurysm and in the parent vessel. It was concluded that the pulsatility of flow is as important as the flow rate when considering the haemodynamics in a giant aneurysm. In the clinical context, this could explain the efficacy of vertebral artery occlusion in thrombosing giant vertebrobasilar aneurysms. Studies with intra-aneurysmal coil embolisation showed early fluid stagnation at the dome. This could result in embolic migration during endovascular treatment. Partial coil embolisation may present early rebleeding; however, it may induce additional mural stresses resulting from new haemodynamic forces and compliance mismatch.     

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

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