Stent-assisted coil embolization and computational fluid dynamics simulations of bilateral vertebral artery dissecting aneurysms presenting with subarachnoid hemorrhage: case report

A case of bilateral vertebral artery dissection treated by bilateral surgical occlusion and low-flow bypass

Background

Bilateral vertebral artery dissection aneurysm (VADA) is a rare condition that leads to severe stroke. However, the surgical strategy for its treatment is controversial because the pathology is very complicated and varies in each case. Here, we report a case of bilateral VADA that was successfully treated with staged bilateral VADA occlusion and low-flow bypass.

Case Description

A Japanese man in his 40s presented with bilateral VADA with subarachnoid hemorrhage. He had only mild headaches without any other neurological deficits. Subsequently, the ruptured left VADA was surgically trapped. However, on postoperative day 11, the contralateral VADA enlarged. The right VADA was then proximally clipped via a lateral suboccipital approach. Furthermore, a superficial temporal artery-superior cerebellar artery bypass was performed through a subtemporal approach in advance to preserve cerebral flow in the posterior circulation. The bilateral VADA was obliterated, and the patient had an uneventful postoperative course during the 1-year and 6-month follow-up period.

Conclusion

Bilateral VADA can be successfully treated with staged bilateral VADA obstruction and low-flow bypass. In this case, as the posterior communicating arteries were the fetal type and the precommunicating segments of the posterior cerebral arteries (P1) were hypoplastic, a low-flow bypass was used to supply the basilar and cerebellar arteries, except the posterior cerebral and posterior inferior cerebellar arteries. Furthermore, low-flow bypass is a less invasive option than high-flow bypass.

A Case of Bilateral Vertebral Artery Dissecting Aneurysm Treated With Multimodality Therapy Under Superficial Temporal Artery Assistance-Posterior Cerebral Artery Bypass

A ruptured bilateral vertebral artery dissecting aneurysm (BVDA) is a challenging vascular disorder. Trapping surgery with bypass assistance could be a potential treatment; however, there is a risk of ischemic complications. Recently, endovascular treatment has been reported, but its long-term outcomes remain uncertain. The patient was a 57-year-old male who presented with subarachnoid hemorrhage. Digital subtraction angiography showed a dilated dominant left vertebral artery (VA) and a narrowed right VA, suggesting a BVDA. First, we performed a right superficial temporal artery-superior cerebellar artery (STA-SCA) insurance bypass. We then performed proximal clipping of the left vertebral VA. The pulsation of the STA-SCA bypass disappeared on day 6. Three-dimensional computed tomography angiography (3DCTA) showed the emergence of a fusiform aneurysm and proximal stenosis of the contralateral VA. On day 31, we performed a superficial temporal artery-posterior cerebral artery (STA-PCA) insurance bypass. Stent-assisted coil embolization was planned for two days after the STA-PCA bypass. However, preoperative angiography showed progression of right proximal VA stenosis, and stenting appeared impossible. There was no change in somatosensory evoked potential (SEP), and angiography showed sufficient retrograde blood flow to the posterior circulation during the right VA balloon occlusion test (BOT). Therefore, internal trapping of the right VA was performed. Postoperative angiography showed perfect patency of the left STA-PCA bypass and retrograde blood flow to the posterior circulation. There was no additional neurological deficit after endovascular treatment. Multimodality therapy could be a potential treatment for bilateral VA dissection.

Computational fluid dynamics (CFD) analysis in a ruptured vertebral artery dissecting aneurysm implanted by Pipeline when recurrent after LVIS-assisted coiling treatment: Case report and review of the literatures

BACKGROUNDS

Hemodynamics plays an important role in the natural history of the process of rupture and recurrence of intracranial aneurysms. This study aimed to investigate the role of hemodynamics for recurrence in a vertebral artery dissecting aneurysm (VADA).

METHODS

A patient with a ruptured VADA firstly treated by low-profile visualized intraluminal support (LVIS)-assisted coiling, and was implanted with a Pipeline Embolization Device (PED) after aneurysm recurrence. Finite element analysis and computational fluid dynamics simulations were conducted in 6 serial imaging procedures, and the calculated hemodynamics was correlated with aneurysm recurrence.

RESULTS

Wall shear stress (WSS) was not effectively suppressed, resulting in aneurysm recurrence with initial entry tear to occur above the protuberance after 7 months of LVIS stent-assisted coiling. With the implantation of PED, WSS, inflow stream and velocity at the aneurysm neck significantly decreased. During the 3-month follow-up after PED deployment, there was significant shrinkage of the sac and the blood flow in the sac was reduced considerably. The 27-month follow-up after PED deployment indicated the aneurysm was stable.

CONCLUSIONS

The present case study suggests that insufficient suppression of high WSS and high inflow velocity at the neck of the parent artery, especially near the posterior inferior cerebellar artery, might be associated with aneurysm recurrence.

Reconstructive embolization for contralateral vertebral artery dissecting aneurysm that developed after internal trapping of ruptured vertebral artery dissection: A case report and literature review

Background:

It is not well-known that contralateral vertebral artery dissecting aneurysms (VADA) may be newly revealed after parental artery occlusion for unilateral VADA. However, the optimal treatment strategies and perioperative management have not been established. In this report, we present the case of a patient who required reconstructive embolization in the subacute stage for contralateral VADA developed after endovascular internal trapping of the ruptured VADA.

Case Description:

A 61-year-old man developed subsequent disturbance of consciousness. Head CT showed a diffuse and symmetrical SAH. 3DCT revealed a fusiform aneurysm of the left intracranial vertebral artery with bleb formation. We performed emergency endovascular parent artery occlusion of the left vertebral artery. A digital subtraction angiography on postoperative day 16 showed continued occlusion of the left VA, and a fusiform aneurysm was noted at the right VA. We performed reconstructive embolization and the patient eventually recovered with minimal persistent symptoms.

Conclusion:

Since the outcomes of contralateral VAD complicated by infarction or hemorrhage are poor, and most cases develop within 7–14 days after endovascular internal trapping for unilateral VAD, performing bilateral radiographic reinspection within this time frame is recommended for early detection and preventive treatment of possible contralateral VADs.

Case Report: De novo Vertebral Artery Dissection After Intravascular Stenting of the Contralateral Unruptured Vertebral Artery Aneurysm

Spontaneous vertebral artery dissecting aneurysm has been increasingly attributed as a major cause of focal neurological deficits due to vertebrobasilar artery ischemia or subarachnoid hemorrhage (SAH). Although the development of spontaneous vertebral artery dissecting aneurysm (VADA) is rare, de novo VADA after treatment of contralateral vertebral artery (VA) is more less frequently observed. There are only a few reports related to de novo VADA after treatment of the contralateral VA in the medical literature. The mechanisms responsible for de novo dissection after treatment of unilateral VADA are still not clearly understood. In this manuscript, we report an unusual case of a patient with a de novo VADA after placement of a pipeline embolization device (PED) stent on the contralateral VA along with a thorough review of the literature. A 42-years old male patient was referred to the hospital with sudden onset of dizziness, nausea, and vomiting. Initial digital subtraction angiography (DSA) images demonstrated a VADA in the fourth segment of the left VA without the involvement of the posterior inferior cerebellar artery (PICA). There were no significant abnormalities found in the right vertebral artery. He underwent an endovascular pipeline embolization to treat the dissecting aneurysm (DA). Surprisingly, follow-up DSA imaging 14 months after the initial treatment showed a segmental dilatation and narrowing of the right VA, which suggested a de novo VADA on the right side that had occurred postoperatively. This was followed by a tent-assisted coil embolization therapy for occluding this de novo VADA. This patient showed an uneventful postoperative course with no neurological abnormalities. In addition to hemodynamic stress changes, the unique clinicopathological features of dissecting aneurysms may contribute significantly to the pathogenesis of de novo VA dissection. Given that VA in VADA patients may be vulnerable on both sides, it is important to consider the risk of de novo dissection after initial aneurysm treatment. The bilateral vertebral artery has to be carefully observed when treating any VADA patient to prevent any complications.

Computational fluid dynamics as a risk assessment tool for aneurysm rupture

OBJECTIVE

The authors reviewed the clinical role of computational fluid dynamics (CFD) in assessing the risk of intracranial aneurysm rupture.

METHODS

A literature review was performed to identify reports on CFD assessment of aneurysms using PubMed. The usefulness of various hemodynamic parameters, such as wall shear stress (WSS) and the Oscillatory Shear Index (OSI), and their role in aneurysm rupture risk analysis, were analyzed.

RESULTS

The authors identified a total of 258 published articles evaluating rupture risk, growth, and endovascular device assessment. Of these 258 articles, 113 matching for CFD and hemodynamic parameters that contribute to the risk of rupture (such as WSS and OSI) were identified. However, due to a lack of standardized methodology, controversy remains on each parameter's role.

CONCLUSIONS

Although controversy continues to exist on which risk factors contribute to predict aneurysm rupture, CFD can provide additional parameters to assess this rupture risk. This technology can contribute to clinical decision-making or evaluation of efficacy for endovascular methods and devices.

Endovascular treatment of bilateral intracranial vertebral artery aneurysms: an algorithm based on a 10-year neurointerventional experience

BACKGROUND

The management of bilateral intracranial vertebral artery dissecting aneurysms (IVADAs) is controversial, and requires the development of endovascular treatment modalities and principles. We aim to investigate the endovascular treatment strategy and outcomes of bilateral IVADAs.

METHODS

We identified all bilateral IVADAs at a high-volume neurointerventional centre over a 10-year period (from January 2009 to December 2018). Radiographic and clinical data were recorded, and a treatment algorithm was derived.

RESULTS

Twenty-seven patients with bilateral IVADAs (54 IVADAs in total, 51 unruptured, 3 ruptured) were diagnosed. Four patients (14.8%) received single-stage endovascular treatment, 12 patients (44.4%) with staged endovascular treatment and 11 patients (40.8%) with unilateral endovascular treatment of bilateral IVADAs. Thirty-six IVADAs (85.7%) have complete obliteration at the follow-up angiography. Two of three ruptured IVADAs with stent-assisted coiling recanalised, and had further recoiling. Three patients (11.1%) have intraprocedural or postprocedural complications (two in single-stage and one in staged). Twenty-five patients (92.6%) had a favourable clinical outcome, and two patients (7.4%, all in single-stage) showed an unfavourable clinical outcome at follow-up. For the patients with unilateral reconstructive endovascular treatment, the contralateral untreated IVADAs were stable and had no growth or ruptured during follow-up period. None of all IVADAs had rebleeding during the clinical follow-up.

CONCLUSIONS

Endovascular treatment can be performed in bilateral IVADAs with high technical success, high complete obliteration rates and acceptable morbidity/mortality. Contralateral IVADAs had low rates of aneurysm growth and haemorrhage when treated in a staged/delayed fashion.

A case of unilateral vertebral artery dissection progressing in a short time period to bilateral vertebral artery dissection

Background

Vertebral artery dissection (VAD) is an important cause of stroke in young and middle- aged people. Bilateral occurrence of VAD is generally considered rare, but the number of reports of bilateral VAD has been increasing in recent years. In this paper, we report a case of de novo VAD on the contralateral side presenting with subarachnoid hemorrhage in the acute stage of cerebral infarction due to unilateral VAD.

Case Description

A 52-year-old man developed sudden-onset left occipital headache, dizziness, dysphagia, and right-sided hemiparesthesia and was admitted to our hospital. Head magnetic resonance imaging on admission showed a left lateral medullary infarction due to the left VAD. At this point, the right vertebral artery was normal. However, on day 9 after onset, he suddenly presented with subarachnoid hemorrhage due to the right VAD. Emergency endovascular treatment was performed for the dissecting aneurysm of the right vertebral artery. The patient's condition improved gradually after the procedure, and he was discharged with a modified Rankin Scale score of 1.

Conclusion

Bilateral occurrence of VAD may be more common than previously believed. Even in cases of unilateral VAD, we need to pay attention to the occurrence of de novo VAD on the contralateral side.

One-stage Stent-assisted Coil Embolization for Rupture-side-unknown Bilateral Vertebral Artery Dissecting Aneurysms in an Acute Stage: A Case Report

Bilateral vertebral artery dissecting aneurysms (VADAs) with subarachnoid hemorrhage (SAH) are rare and their management is still challenging. In this report, we successfully performed one-stage stent-assisted coil embolization (SAC) for bilateral VADAs with SAH in an acute stage, because the ruptured side could not be diagnosed. A 47-year-old woman presented with a sudden onset of headache without laterality, and left-side dominant SAH with bilateral VADAs was noted on computed tomography (CT) scans. The size of aneurysmal dome and neck was similar between the two VADAs, and a bleb was observed only on the right VADA. In computational fluid dynamics (CFD) simulations, findings of wall shear stress (WSS), normalized WSS, and WSS gradient suggested that the left VADA was ruptured, while the oscillatory shear index and aneurysm formation indicator suggested the opposite-side one to be ruptured. Thus, we could not determine which VADA was ruptured by clinical data and CFD analyses. Therefore, we performed simultaneous treatment for the bilateral VADAs by using SAC technique 8 h after the onset under dual antiplatelet and anticoagulation therapies. There was no evidence of rebleeding and stent thrombosis. Stent thrombosis was monitored by duplex color-coded ultrasonography after the intervention. She was discharged without neurological deficits, and 6-month follow-up cerebral angiography demonstrated no recanalization of VADAs. This is the first report showing bilateral VADAs with SAH treated by one-stage SAC within 24 h of SAH, and the potential risks are discussed.

Critical role of angiographic acquisition modality and reconstruction on morphometric and haemodynamic analysis of intracranial aneurysms

Background

Subtracted 3-D rotational angiography (3DRA) and cone-beam computed tomography angiography (CBCT-A) are often used in assessing cerebral aneurysm shape and haemodynamic profile. We sought to evaluate the effect of imaging modality, reconstruction parameters, and kernel selection on patient-derived aneurysm morphology and computational fluid dynamic (CFD) analysis to assess its potential contribution to inter-study variability.

Methods

Four patients (five aneurysms) underwent concurrent 3DRA followed by high-resolution CBCT-A. Six models were reconstructed per aneurysm: 3DRA reconstructed with 0.28 and 0.14 mm voxel sizes (large and small volume of interest (VOI) respectively), and two kernel types (normal/smooth). CBCT-A was reconstructed over small VOI using normal/sharp kernel. Maximal dome dimension, neck diameter and dome/neck ratio were evaluated in 3D. Wall shear stress (WSS) magnitude was evaluated on the entire aneurysm dome and in the 5% dome areas covered by lowest (LWSS) and highest (HWSS) WSS. Parameters were evaluated with pairwise t-test analysis.

Results

Smaller VOI reconstructions resulted in smaller Dmax (P value=0.03) and Dmax/neck (P value=0.006) and in larger LWSS (P value=0.03). Use of sharp kernel led to narrower neck (P value=0.04) and higher Dmax/neck values (P value=0.02). CBCT-A resulted in statistically different aneurysm shape (up to 24% difference) and haemodynamics (up to 97% difference) compared with 3DRA.

Conclusion

The choice of catheter 3D angiographic modality and reconstruction kernel has a critical impact on derived aneurysm morphological and haemodynamic analysis. The resultant variability can confound and obscure underlying differences within patient populations and between studies performed at different centres using divergent techniques, compromising the accuracy of quantitative aneurysm analysis.

Treatment Strategies of Subarachnoid Hemorrhage from Bilateral Vertebral Artery Dissection: A Case Report and Literature Review Focusing on the Availability of Stent Placement

BACKGROUND

Bilateral vertebral artery dissection (VAD) may result in subarachnoid hemorrhage (SAH). However, a variety of factors contribute to the difficulties with treating SAH. We report a case of bilateral VAD with SAH, as well as a literature review.

CASE DESCRIPTION

A 32-year-old woman developed headache. Computed tomography demonstrated diffuse SAH, and 3-dimensional computed tomography indicated bilateral VAD. Her left vertebral artery was severely stenosed, and the basilar artery retrogradely flowed via the posterior communicating artery. Her bilateral VAD was trapped with the use of staged craniotomy. The postoperative course was uneventful for 13 days; however, severe neurologic deterioration remained in the area of the cerebral infarction, due to vasospasm of the internal carotid artery. This is the first report of hemorrhagic bilateral VAD treated with bilateral trapping and aggressive spasm treatment in the acute phase. However, the treatment was not successful.

CONCLUSIONS

Because of the increasing use of stent therapy, there has been a shift toward this treatment choice. For cases in which stents cannot be used, treatment methods based on prestenting protocols are helpful. A literature review indicated that conservative treatment for 2 weeks, in which vasospasm and rebleeding are controlled, may be considered compared with acute-stage stent treatment. Following our literature review, in situations in which stents cannot be used, only the ruptured side should be trapped with strict blood pressure control and detailed radiological images should be observed for 2 weeks. In conclusion, patient selection is essential to subject the patient to open surgery in such cases.

De novo vertebral artery dissecting aneurysm after internal trapping of the contralateral vertebral artery

We present the case of a de novo vertebral artery dissecting aneurysm (VADA) after endovascular trapping of a ruptured VADA on the contralateral side. The first ruptured VADA involved the posterior inferior cerebellar artery, which was successfully treated by endovascular internal trapping using a stent. A follow-up study at 3 months revealed a de novo VADA on the contralateral side. The second VADA was successfully embolized using coils while normal arterial flow in the vertebral artery was preserved using a stent. Increased hemodynamic stress may cause the development of a de novo VADA on the contralateral side.

Successful Retreatment of Recurrent Intracranial Vertebral Artery Dissecting Aneurysms After Stent-Assisted Coil Embolization: A Self-Controlled Hemodynamic Analysis

BACKGROUND

Intracranial vertebral artery dissecting aneurysms (VADAs) tend to recur despite successful stent-assisted coil embolization (SACE). Hemodynamics is useful in evaluating aneurysmal formation, growth, and rupture. Our aim was to evaluate the hemodynamic patterns of the recurrence of VADA.

METHODS

Between September 2009 and November 2013, all consecutive patients with recurrent VADAs after SACE in our institutions were enrolled. Recurrence was defined as recanalization and/or regrowth. We assessed the hemodynamic alterations in wall shear stress (WSS) and velocity after the initial SACE and subsequently after retreatment of the aneurysms that recurred.

RESULTS

Five patients were included. After the initial treatment, 3 patients showed recanalization and 2 showed regrowth. In the 2 patients with regrowth, the 2 original aneurysms maintained complete occlusion; however, de novo aneurysm regrowth was confirmed near the previous site. Compared with 3 recanalized aneurysms, the completely occluded aneurysms showed high mean reductions in velocity and WSS after initial treatment (velocity, 77.6% vs. 57.7%; WSS, 74.2% vs. 52.4%); however, WSS remained high at the region near the previous lesion where the new aneurysm originated. After the second retreatment, there was no recurrence in any patient. Compared with the 3 aneurysms that recanalized, the 4 aneurysms that maintained complete occlusion showed higher reductions in velocity (62.9%) and WSS (71.1%).

CONCLUSIONS

Our series indicated that hemodynamics might have an important role in recurrence of VADAs. After endovascular treatment, sufficient hemodynamic reduction in aneurysm dome, orifice, and parent vessel may be one of the key factors for preventing recurrence in VADAs.

Radical treatment for bilateral vertebral artery dissecting aneurysms by reconstruction of the vertebral artery

OBJECTIVE

Bilateral vertebral artery dissecting aneurysms (VADAs) have a poor prognosis because progressive enlargement of the aneurysms compresses the brainstem or causes subarachnoid hemorrhage. The trapping of 1 vertebral artery (VA) places increased hemodynamic stress on the contralateral VA and may lead to enlargement and rupture. Therefore, management strategies are controversial. This study describes a radical treatment for bilateral VADAs using bypass surgery.

METHODS

Seven patients with bilateral VADAs were included. Three patients were treated by trapping of 1 VA via coiling or clipping at another hospital; the previously treated VA in 1 patient and the contralateral untreated VA in 2 patients subsequently enlarged. The other 4 patients presented without previous intervention and progressive enlargement of the aneurysms.

RESULTS

The post–coil embolization patients underwent V3–posterior cerebral artery (PCA) bypass and trapping. The other 4 patients underwent VA reconstruction via V3–V4 or V4–V4 bypass, with contralateral trapping on a separate day in 3 patients and observation in 1 patient. Perioperative complications included 1 case of cerebrospinal fluid leakage for which the patient required an additional operation, 1 case of dysphagia and facial palsy due to sigmoid sinus thrombosis, and 1 case of dysphagia. The long-term outcomes of these patients were favorable.

CONCLUSIONS

Patients with bilateral VADAs require treatment on both sides. If VA trapping is performed first, the treatment options for the other side are limited to V3-PCA bypass and trapping. This procedure is effective; however, it is also invasive and technically difficult. In cases of bilateral VADAs in which it is feasible to reconstruct 1 side, the best approach is to begin by reconstructing the VA that appears technically easiest, followed by trapping of the contralateral VADA. This strategy allows enough time to suture vessels because contralateral reverse flow is maintained.

Stent-assisted coil embolisation for bilateral vertebral artery dissecting aneurysms presenting with subarachnoid haemorrhage

Bilateral dissecting aneurysms presenting with subarachnoid haemorrhage are rare. The treatment strategy for bilateral vertebral artery dissecting aneurysms is controversial because the contralateral vertebral artery is already dissected and can easily undergo enlargement or bleed after non-reconstructive treatment procedures such as trapping or proximal occlusion. Here, we report a case of bilateral vertebral artery dissecting aneurysm presenting with subarachnoid haemorrhage that was treated with stent-assisted coiling for the ruptured side. A 42-year-old man was admitted to our hospital with sudden headache (WFNS grade 1). Computed tomography showed a high-density region in the basal cistern and posterior fossa with more haemorrhage on the right side (Fisher group 3). Three-dimensional computed tomography and three-dimensional rotational angiography demonstrated a bilateral round protrusion on the vertebral arteries with a diameter of 5 mm just distal to the posterior inferior cerebellar artery. Stent-assisted coiling was performed for the ruptured right side and conservative therapy was selected for the contralateral side. The ruptured side was well embolised, and the contralateral side was stable over the 12-month follow-up period after treatment. The treatment strategy for bilateral vertebral artery dissecting aneurysms presenting with subarachnoid haemorrhage is different from that for unilateral vertebral artery dissecting aneurysms. Non-reconstructive treatment procedures such as trapping may cause contralateral enlargement or rupture; therefore, reconstructive treatment may be appropriate for the ruptured side.

Therapeutic Progress in Treating Vertebral Dissecting Aneurysms Involving the Posterior Inferior Cerebellar Artery

Among the variations of vertebral artery dissecting aneurysms (VDAs), VDAs involving the posterior inferior cerebellar artery (PICA), especially ruptured and high-risk unruptured aneurysms, are the most difficult to treat. Because the PICA is an important structure, serious symptoms may occur after its occlusion. Retained PICAs are prone to re-bleeding because VDAs are difficult to completely occlude. There is therefore confusion regarding the appropriate treatment for VDAs involving the PICA. Here, we used the PubMed database to review recent research concerning VDAs that involve the PICA, and we found that treatments for VDAs involving the PICA include (i) endovascular treatment involving the reconstruction of blood vessels and blood flow, (ii) occluding the aneurysm using an internal coil trapping or an assisted bypass, (iii) inducing reversed blood flow by occluding the proximal VDA or forming an assisted bypass, or (iv) the reconstruction of blood flow via a craniotomy. Although the above methods effectively treat VDAs involving the PICA, each method is associated with both a high degree of risk and specific advantages and disadvantages. The core problem when treating VDAs involving the PICA is to retain the PICA while occluding the aneurysm. Therefore, the method is generally selected on a case-by-case basis according to the characteristics of the aneurysm. In this study, we summarize the various current methods that are used to treat VDAs involving the PICA and provide schematic diagrams as our conclusion. Because there is no special field of research concerning VDAs involving the PICA, these cases are hidden within many multiple-cases studies. Therefore, this study does not review all relevant documents and may have some limitations. Thus, we have focused on the mainstream treatments for VDAs that involve the PICA.

Flow-diverting stents allow efficient treatment of unruptured, intradural dissecting aneurysms of the vertebral artery: An explanatory approach using in vivo flow analysis

OBJECT

Our study aimed to evaluate the efficiency of flow-diverting stents (FDS) in treating unruptured, intradural dissecting aneurysms of the vertebral artery (VADAs). Additionally, the effect of FDS on the aneurysmal flow pattern was investigated by performing in vivo flow analysis using parametric color coding (PCC).

METHODS

We evaluated 11 patients with unruptured, intradural VADAs, treated with FDS. Pre- and postinterventional DSA-series were postprocessed by PCC, and time-density curves were calculated. The parameters aneurysmal inflow-velocity, outflow-velocity and relative time-to-peak (rTTP) were calculated. Pre- and postinterventional values were compared and correlated with the occlusion rate after six months.

RESULTS

Follow-up DSA detected 10 aneurysms occluded, meaning an occlusion rate of 91%. No procedure-related morbidity and mortality was found. Flow analyses revealed a significant reduction of aneurysmal inflow- velocity and prolongation of rTTP after FDS deployment. Concerning aneurysm occlusion, the postinterventional outflow-velocity turned out to be a marginally statistically significant predictor. A definite threshold value (-0.7 density change/s) could be determined for the outflow-velocity that allows prediction of complete aneurysm occlusion with high sensitivity and specificity (100%).

CONCLUSIONS

Using FDS can be considered an efficient and safe therapy option in treating unruptured, intradural VADA. From in vivo flow analyses the postinterventional aneurysmal outflow-velocity turned out to be a potential predictor for later complete aneurysm occlusion. Here, it might be possible to determine a threshold value that allows prediction of aneurysm occlusion with high specificity and sensitivity. As fast, applicable and easy-to-handle tool, PCC could be used for procedural monitoring and might contribute to further treatment optimization.

The Computational Fluid Dynamics Rupture Challenge 2013—Phase I: prediction of rupture status in intracranial aneurysms

BACKGROUND AND PURPOSE

Rupture risk assessment for intracranial aneurysms remains challenging, and risk factors, including wall shear stress, are discussed controversially. The primary purpose of the presented challenge was to determine how consistently aneurysm rupture status and rupture site could be identified on the basis of computational fluid dynamics.

MATERIALS AND METHODS

Two geometrically similar MCA aneurysms were selected, 1 ruptured, 1 unruptured. Participating computational fluid dynamics groups were blinded as to which case was ruptured. Participants were provided with digitally segmented lumen geometries and, for this phase of the challenge, were free to choose their own flow rates, blood rheologies, and so forth. Participants were asked to report which case had ruptured and the likely site of rupture. In parallel, lumen geometries were provided to a group of neurosurgeons for their predictions of rupture status and site.

RESULTS

Of 26 participating computational fluid dynamics groups, 21 (81%) correctly identified the ruptured case. Although the known rupture site was associated with low and oscillatory wall shear stress, most groups identified other sites, some of which also experienced low and oscillatory shear. Of the 43 participating neurosurgeons, 39 (91%) identified the ruptured case. None correctly identified the rupture site.

CONCLUSIONS

Geometric or hemodynamic considerations favor identification of rupture status; however, retrospective identification of the rupture site remains a challenge for both engineers and clinicians. A more precise understanding of the hemodynamic factors involved in aneurysm wall pathology is likely required for computational fluid dynamics to add value to current clinical decision-making regarding rupture risk.

Flow visualization of recurrent aneurysms after coil embolization by 3D phase-contrast MRI

BACKGROUND

Flow patterns in cerebral aneurysms are clinically important. Information on inflow patterns into aneurysms is especially helpful in preventing a recurrence after coil embolization. Computational fluid dynamics (CFD) simulations of patient-specific cerebral aneurysms are feasible and provide information on flow patterns. However, flow visualization by CFD simulations is challenging for recurrent aneurysms after coil embolization because coils make it difficult to obtain precise geometry of the recurrent aneurysms. In this study, we assessed the feasibility of flow visualization of recurrent aneurysms using 3D phase-contrast magnetic resonance imaging (PC-MRI).

METHOD

Time-of-flight magnetic resonance angiography and 3D PC-MRI were performed in eight cases of recurrent aneurysms after coil embolization. We attempted to visualize flow inside the aneurysms using data of 3D PC-MRI and evaluated the visualization. Additionally, CFD simulations were performed in a single case.

RESULTS

Inflow into aneurysms was visualized in all eight cases (100%). Flow patterns inside aneurysms were visualized in six cases (75%), and these were associated with a large size of recurrent aneurysms (mean size, 10.3 mm for visualized cases vs. 4.8 mm for unvisualized cases; p = 0.046, Mann-Whitney test). Flow patterns were similar between PC-MRI and CFD simulations. PC-MRI was faster and easier for observing inflow patterns than CFD simulations.

CONCLUSIONS

This is the first study to demonstrate that flow visualization of recurrent aneurysms by 3D PC-MRI is feasible. This technique may be more practical and easier than CFD simulations, and may provide clinically helpful information.

Proximal stenosis may induce initiation of cerebral aneurysms by increasing wall shear stress and wall shear stress gradient

Hemodynamic parameters, such as wall shear stress (WSS), WSS gradient (WSSG), aneurysm formation indicator (AFI), or gradient oscillatory number (GON), have been proposed to be linked to initiation of cerebral aneurysms. However, how such conditions occur in humans is unclear. We encountered a rare and interesting case to address this issue. A patient had a newly formed aneurysm with proximal stenosis, which was confirmed by serial imagings. We made two pre-aneurysm models: one with stenosis and the other without stenosis. We performed computational fluid dynamics simulations for these models. Owing to jet flow caused by the stenosis, the maximum WSS and WSSG on the aneurysm initiation site were approximately doubled and tripled, respectively. However, the oscillatory shear index (OSI), AFI, and GON did not change substantially by the stenosis. Computer simulations using artificial vascular models with different degrees of proximal stenosis at different distances demonstrated that oscillatory shear index, AFI, and GON did not change substantially by the stenosis. These results showed that proximal stenosis caused high WSS and high WSSG at the aneurysm initiation site, possibly leading to aneurysm initiation. Proximal stenosis may be a potential factor to induce initiation of one class of cerebral aneurysms by increasing WSS and WSSG.

Hemodynamic effects of stent struts versus straightening of vessels in stent-assisted coil embolization for sidewall cerebral aneurysms

Background

Recent clinical studies have shown that recanalization rates are lower in stent-assisted coil embolization than in coiling alone in the treatment of cerebral aneurysms.

Objective

This study aimed to assess and compare the hemodynamic effect of stent struts and straightening of vessels by stent placement on reducing flow velocity in sidewall aneurysms, with the goal of reducing recanalization rates.

Methods

We evaluated 16 sidewall aneurysms treated with Enterprise stents. We performed computational fluid dynamics simulations using patient-specific geometries before and after treatment, with or without stent struts.

Results

Stent placement straightened vessels by a mean (±standard deviation) of 12.9°±13.1° 6 months after treatment. Placement of stent struts in the initial vessel geometries reduced flow velocity in aneurysms by 23.1%±6.3%. Straightening of vessels without stent struts reduced flow velocity by 9.6%±12.6%. Stent struts had significantly stronger effects on reducing flow velocity than straightening (P = 0.004, Wilcoxon test). Deviation of the effects was larger by straightening than by stent struts (P = 0.01, F-test). The combination of stent struts and straightening reduced flow velocity by 32.6%±12.2%. There was a trend that larger inflow angles produced a larger reduction in flow velocity by straightening of vessels (P = 0.16).

Conclusion

In sidewall aneurysms, stent struts have stronger effects (approximately 2 times) on reduction in flow velocity than straightening of vessels. Hemodynamic effects by straightening vary in each case and can be predicted by inflow angles of pre-operative vessel geometry. These results may be useful to design a treatment strategy for reducing recanalization rates.

Changes in wall shear stress magnitude after aneurysm rupture

Computational fluid dynamics (CFD) studies on cerebral aneurysms have attempted to identify surrogate hemodynamic parameters to predict rupture risk. We present a case of bilateral mirror image aneurysms, one of which ruptured soon after imaging. Wall shear stress values of the ruptured aneurysm changed by 20-30% after rupture because of change in the aneurysm shape. Findings from our case suggest that CFD studies comparing unruptured and ruptured aneurysms may not yield valid estimation on aneurysm rupture risk because of changes in aneurysm shape after rupture. Changes in aneurysm shape after rupture should be considered in CFD research.

Hemodynamics of 8 different configurations of stenting for bifurcation aneurysms

BACKGROUND AND PURPOSE

SACE is performed for complex aneurysms. There are several configurations of stent placement for bifurcation aneurysms. We investigated hemodynamics among 8 different configurations of stent placement, which may relate to the recanalization rate.

MATERIALS AND METHODS

We created a silicone block model of a patient-specific asymmetric bifurcation aneurysm. Enterprise closed-cell stents were deployed in the model as various configurations. 3D images of these stents were obtained by micro-CT. We performed CFD simulations for a no-stent model and 8 stent models: a single stent from a proximal vessel to a right or left distal vessel, a horizontal stent, a kissing-Y stent with a uniformly narrowed structure, a nonoverlapping-Y stent, a virtual-Y stent with no narrowed structure (fusion of 2 single stents), and 2 different crossing-Y stents with a focally narrowed structure. Hemodynamic parameters were evaluated.

RESULTS

Cycle-averaged velocity and WSS in the aneurysm were reduced because of stent placement in the following order: single stent (19% reduction in cycle-averaged velocity) < nonoverlapping-Y stent (29%) < virtual-Y stent (32%) < horizontal stent (39%) < kissing-Y stent (48%) < crossing-Y stent (54%). Kissing- and crossing-Y stents redirected impingement flow into the distal vessels because of lowered porosity of stents due to narrowed structures.

CONCLUSIONS

Among 8 different configurations of stent placement, kissing- and crossing-Y stents showed the strongest reduction in flow velocity in the aneurysm because of lowered porosity of stents and redirection of impingement flow. This may be a desirable reconstruction of flow hemodynamics and may decrease recanalization rates in SACE.