Intracranial aneurysms: from vessel wall pathology to therapeutic approach

Subarachnoid hemorrhage then thrombosis of posterior inferior cerebellar artery dissection: is early surgical exploration warranted?

The natural history of spontaneous cerebral artery dissection and thrombosis remains uncertain. Concurrent subarachnoid hemorrhage further complicates the therapeutic approach. Thus the best strategy for managing patients with acute vessel thrombosis in the setting of subarachnoid hemorrhage is unclear. Here we present a case of spontaneous posterior inferior cerebellar artery dissection presenting with subarachnoid hemorrhage and acute thrombosis. Although the patient was initially managed conservatively, angiographic follow-up demonstrated recanalization of the diseased vessel, necessitating definitive treatment. Thus we propose that angiographic follow-up is necessary in the management of patients with subarachnoid hemorrhage in association with apparent vessel thrombosis.

Subarachnoid hemorrhage then thrombosis of posterior inferior cerebellar artery dissection: is early surgical exploration warranted?

The natural history of spontaneous cerebral artery dissection and thrombosis remains uncertain. Concurrent subarachnoid hemorrhage further complicates the therapeutic approach. Thus the best strategy for managing patients with acute vessel thrombosis in the setting of subarachnoid hemorrhage is unclear. Here we present a case of spontaneous posterior inferior cerebellar artery dissection presenting with subarachnoid hemorrhage and acute thrombosis. Although the patient was initially managed conservatively, angiographic follow-up demonstrated recanalization of the diseased vessel, necessitating definitive treatment. Thus we propose that angiographic follow-up is necessary in the management of patients with subarachnoid hemorrhage in association with apparent vessel thrombosis.

Narrowing the Expertise Gap for Predicting Intracranial Aneurysm Hemodynamics: Impact of Solver Numerics versus Mesh and Time-Step Resolution

BACKGROUND AND PURPOSE

Recent high-resolution computational fluid dynamics studies have uncovered the presence of laminar flow instabilities and possible transitional or turbulent flow in some intracranial aneurysms. The purpose of this study was to elucidate requirements for computational fluid dynamics to detect these complex flows, and, in particular, to discriminate the impact of solver numerics versus mesh and time-step resolution.

MATERIALS AND METHODS

We focused on 3 MCA aneurysms, exemplifying highly unstable, mildly unstable, or stable flow phenotypes, respectively. For each, the number of mesh elements was varied by 320× and the number of time-steps by 25×. Computational fluid dynamics simulations were performed by using an optimized second-order, minimally dissipative solver, and a more typical first-order, stabilized solver.

RESULTS

With the optimized solver and settings, qualitative differences in flow and wall shear stress patterns were negligible for models down to ∼800,000 tetrahedra and ∼5000 time-steps per cardiac cycle and could be solved within clinically acceptable timeframes. At the same model resolutions, however, the stabilized solver had poorer accuracy and completely suppressed flow instabilities for the 2 unstable flow cases. These findings were verified by using the popular commercial computational fluid dynamics solver, Fluent.

CONCLUSIONS

Solver numerics must be considered at least as important as mesh and time-step resolution in determining the quality of aneurysm computational fluid dynamics simulations. Proper computational fluid dynamics verification studies, and not just superficial grid refinements, are therefore required to avoid overlooking potentially clinically and biologically relevant flow features.

MR imaging of myeloperoxidase activity in a model of the inflamed aneurysm wall

BACKGROUND AND PURPOSE

Although myeloperoxidase activity in vivo can be visualized by using noninvasive imaging, successful clinical translation requires further optimization of the imaging approach. We report a motion-sensitized driven-equilibrium MR imaging approach for the detection of a myeloperoxidase activity-specific gadolinium-containing imaging agent in experimental aneurysm models, which compensates for irregular blood flow, enabling vascular wall imaging in the aneurysm.

MATERIALS AND METHODS

A phantom was built from rotational angiography of a rabbit elastase aneurysm model and was connected to a cardiac pulse duplicator mimicking rabbit-specific flow conditions. A T1-weighted turbo spin-echo-based motion-sensitized driven-equilibrium pulse sequence was optimized in vitro, including the addition of fat suppression and the selection of the velocity-encoding gradient parameter. The optimized sequence was applied in vivo to rabbit aneurysm models with and without inflammation in the aneurysmal wall. Under each condition, the aneurysms were imaged before and after intravenous administration of the imaging agent. The signal-to-noise ratio of each MR imaging section through the aneurysm was calculated.

RESULTS

The motion-sensitized driven-equilibrium sequence was optimized to reduce flow signal, enabling detection of the myeloperoxidase imaging agent in the phantom. The optimized imaging protocol in the rabbit model of saccular aneurysms revealed a significant increase in the change of SNR from pre- to post-contrast MR imaging in the inflamed aneurysms compared with naïve aneurysms and the adjacent carotid artery (P < .0001).

CONCLUSIONS

A diagnostic MR imaging protocol was optimized for molecular imaging of a myeloperoxidase-specific molecular imaging agent in an animal model of inflamed brain aneurysms.

A comparative review of the hemodynamics and pathogenesis of cerebral and abdominal aortic aneurysms: lessons to learn from each other

OBJECTIVE

Cerebral aneurysms (CAs) and abdominal aortic aneurysms (AAAs) are degenerative vascular pathologies that manifest as abnormal dilations of the arterial wall. They arise with different morphologies in different types of blood vessels under different hemodynamic conditions. Although treated as different pathologies, we examine common pathways in their hemodynamic pathogenesis in order to elucidate mechanisms of formation.

MATERIALS AND METHODS

A systematic review of the literature was performed. Current concepts on pathogenesis and hemodynamics were collected and compared.

RESULTS

CAs arise as saccular dilations on the cerebral arteries of the circle of Willis under high blood flow, high wall shear stress (WSS), and high wall shear stress gradient (WSSG) conditions. AAAs arise as fusiform dilations on the infrarenal aorta under low blood flow, low, oscillating WSS, and high WSSG conditions. While at opposite ends of the WSS spectrum, they share high WSSG, a critical factor in arterial remodeling. This alone may not be enough to initiate aneurysm formation, but may ignite a cascade of downstream events that leads to aneurysm development. Despite differences in morphology and the structure, CAs and AAAs share many histopathological and biomechanical characteristics. Endothelial cell damage, loss of elastin, and smooth muscle cell loss are universal findings in CAs and AAAs. Increased matrix metalloproteinases and other proteinases, reactive oxygen species, and inflammation also contribute to the pathogenesis of both aneurysms.

CONCLUSION

Our review revealed similar pathways in seemingly different pathologies. We also highlight the need for cross-disciplinary studies to aid in finding similarities between pathologies.

Genome-wide microRNA changes in human intracranial aneurysms

Background

Intracranial aneurysms are pathological dilatations of the cerebral artery, while rupture of intracranial aneurysms causes life-threatening subarachnoid hemorrhage. The molecular mechanisms of pathogenesis of intracranial aneurysms are poorly understood. MicroRNAs have fundamental roles in modulating vascular biology and disease. In the present study, we carried out a genome-wide characterization on expressions of microRNAs, and performed integrative analyses in conjunction with changes of the transcriptome in human intracranial aneurysms.

Methods

Genome-wide microRNA screening was performed in 6 intracranial aneurysmal samples and 6 normal superficial temporal arteries. Each case and control pair was individually matched with gender, age (±5 years), and high blood pressure history. Microarray analysis was performed using Agilent Human miRNA arrays.

Results

As compared to normal arteries, we identified 157 microRNAs that were differentially expressed in the aneurysmal tissue (P < 0.05 and fold change ≥ 2), including 72 upregulated and 85 downregulated. The changed microRNAs included endothelium-enriched microRNAs such as members of the let-7 family, miR-17, miR-23b, miR-126, hsa-miR-24-1 and miR-222, and vascular smooth muscle-enriched miRNAs such as miR-143 and miR-145. Moreover, miR-1, miR-10a, miR-125b, and miR-26a, which were implicated in modulating vascular smooth muscle cell functions such as proliferation, apoptosis and shift of phenotype, were also changed. In contrast, microRNAs involved in monocyte and macrophage functions, such as miR-155, miR-146a, miR-223, and miR-124a, were not significantly changed. Bioinformatic analysis revealed that the changed microRNAs were associated with several biological processes related to aneurysm formation, including inflammation, dysregulation of extracellular matrix, smooth muscle cell proliferation, programmed cell death, and response to oxidative stress. Interestingly, we found that a subset of the potential microRNA target genes belonged to the protein translation machinery, including various eukaryotic translation initiation factors and ribosomal proteins, and this finding was highly correlated with our previous transcriptome data showing that multiple genes of the ribosomal proteins and translation initiation and elongation factors were significantly downregulated in human intracranial aneurysms.

Conclusions

Our results support that dysregulated microRNAs may have a pathogenic role in intracranial aneurysms. Disruption of the protein translation process may have a pathogenic role in the development of intracranial aneurysms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-014-0188-x) contains supplementary material, which is available to authorized users.

Evolution of management strategies for cavernous carotid aneurysms: a review

OBJECTIVE

Cavernous carotid aneurysms are considered benign lesions with indolent natural history. Apart from idiopathic aneurysms, traumatic, iatrogenic, and mycotic aneurysms are common in the cavernous segment of the carotid artery. With rapid advances in endovascular therapy, management of cavernous carotid aneurysms has evolved. Our aim was to review the management options available for cavernous carotid aneurysms.

METHODS

The English literature was searched for various studies describing the management of cavernous carotid aneurysms and the evolution of various treatments was studied.

RESULTS

Numerous treatment options are available such as conservative management, Hunterian ligation, surgical clipping, and endovascular therapy. The introduction of flow-diverting stents has revolutionized the management of these lesions. The evolution of various treatment strategies are described.

CONCLUSIONS

A thorough knowledge of all the options is paramount to individualize therapy. We discuss the indications of treatment, various management options for cavernous carotid aneurysms and their outcomes.

Endovascular biopsy: evaluating the feasibility of harvesting endothelial cells using detachable coils

The absence of safe and reliable methods to harvest vascular tissue in situ limits the discovery of the underlying genetic and pathophysiological mechanisms of many vascular disorders such as aneurysms. We investigated the feasibility and comparable efficacy of endothelial cell collection using a spectrum of endovascular coils. Nine detachable coils ranging in k coefficient (0.15-0.24), diameter (4.0 mm-16.0 mm), and length (8.0 cm-47.0 cm) were tested in pigs. All coils were deployed and retrieved within the iliac artery of pigs (three coils/pig). Collected coils were evaluated under light microscopy. The total and endothelial cells collected by each coil were quantified. The nucleated cells were identified by Wright-Giemsa and DAPI stains. Endothelial and smooth muscle cells were identified by CD31 and α-smooth muscle actin antibody staining. Coils were deployed and retrieved without technical difficulty. Light microscopy demonstrated sheets of cellular material concentrated within the coil winds. All coils collected cellular material while five of nine (55.6%) coils retrieved endothelial cells. Coils collected mean endothelial cell counts of 89.0±101.6. Regression analysis demonstrated a positive correlation between increasing coil diameter and endothelial cell counts (R(2)=0.52, p = 0.029). Conventional detachable coils can be used to harvest endothelial cells. The number of endothelial cells collected by a coil positively correlated with its diameter. Given the widespread use of coils and their well-described safety profile their potential as an endovascular biopsy device would expand the availability of tissue for cellular and molecular analysis.

Mind the gap: impact of computational fluid dynamics solution strategy on prediction of intracranial aneurysm hemodynamics and rupture status indicators

BACKGROUND AND PURPOSE

Computational fluid dynamics has become a popular tool for studying intracranial aneurysm hemodynamics, demonstrating success for retrospectively discriminating rupture status; however, recent highly refined simulations suggest potential deficiencies in solution strategies normally used in the aneurysm computational fluid dynamics literature. The purpose of the present study was to determine the impact of this gap.

MATERIALS AND METHODS

Pulsatile flow in 12 realistic MCA aneurysms was simulated by using both high-resolution and normal-resolution strategies. Velocity fields were compared at selected instants via domain-averaged error. We also compared wall shear stress fields and various reduced hemodynamic indices: cycle-averaged mean and maximum wall shear stress, oscillatory shear index, low shear area, viscous dissipation ratio, and kinetic energy ratio.

RESULTS

Instantaneous differences in flow and wall shear stress patterns were appreciable, especially for bifurcation aneurysms. Linear regressions revealed strong correlations (R(2) > 0.9) between high-resolution and normal-resolution solutions for all indices except kinetic energy ratio (R(2) = 0.25) and oscillatory shear index (R(2) = 0.23); however, for most indices, the slopes were significantly <1, reflecting a pronounced underestimation by the normal-resolution simulations. Some high-resolution simulations were highly unstable, with fluctuating wall shear stresses reflected by the poor oscillatory shear index correlation.

CONCLUSIONS

Typical computational fluid dynamics solution strategies may ultimately be adequate for augmenting rupture risk assessment on the basis of certain highly reduced indices; however, they cannot be relied on for predicting the magnitude and character of the complex biomechanical stimuli to which the aneurysm wall may be exposed. This impact of the computational fluid dynamics solution strategy is likely greater than that for other modeling assumptions or uncertainties.

MicroRNA/mRNA profiling and regulatory network of intracranial aneurysm

Background

Intracranial aneurysm (IA) is one of the most lethal forms of cerebrovascular diseases characterized by endothelial dysfunction, vascular smooth muscle cell phenotypic modulation, inflammation and consequently loss of vessel cells and extracellular matrix degradation. Besides environmental factors, genetics seem to be a very important factor in the genesis of this disease. Previous mRNA expression studies revealed a large number of differentially expressed genes between IA and control tissue. However, microRNAs (miRNA), small non-coding RNAs which are post-transcriptional regulators of gene expression, have been barely studied. Studying miRNAs could provide a hypothetical mechanism underlying rupture of IA.

Methods

A microarray study was carried out to determine difference in microRNAs and mRNA between patients’ IA tissues and controls. Quantitative RT-PCR assay compared the expression level between two groups (14 IA domes vs. 14 controls) were used for validation. Validated miRNAs were analyzed using Ingenuity Pathway Analysis (IPA) to identify the networks and pathways.

Results

18 miRNAs were confirmed by qPCR to be robustly down-regulated in 14 ruptured IA patients including hsa-mir-133b, hsa-mir-133a, hsa-mir-1, hsa-mir-143-3p, hsa-mir-145-3p, hsa-mir-145-5p, hsa-mir-455-5p, hsa-mir-143-5p, hsa-mir-23b-3p etc., of which 11 miRNAs are clusters: hsa-mir-1/has-mir-133a, hsa-mir-143/hsa-mir-145, hsa-mir-23b/hsa-mir-24-1, and hsa-mir-29b-2/hsa-mir-29c. 12 predicted functions were generated using IPA which showed significant associations with migration of phagocytes, proliferation of mononuclear leukocytes, cell movement of mononuclear leukocytes, cell movement of smooth muscle cells etc.

Conclusion

These data support common disease mechanisms that may be under miRNA control and provide exciting directions for further investigations aimed at elucidating the miRNA mechanisms and targets that may yield new therapies for IA.

An experimental investigation of the hemodynamic variations due to aplastic vessels within three-dimensional phantom models of the circle of Willis

A complete circle of Willis (CoW) is found in approximately 30-50% of the population. Anatomical variations, such as absent or surgically clamped vessels, can result in undesirable flow patterns. These can affect the brain's ability to maintain cerebral perfusion and the formation of cerebral aneurysms. An experimental test system was developed to simulate cerebral physiological conditions through three flexible 3D patient-specific models of complete and incomplete CoW geometries. Flow visualizations were performed with isobaric dyes and the mapped dye streamlines were tracked throughout the models. Three to seven flow impact locations were observed for all configurations, corresponding to known sites for aneurysmal formation. Uni and bi-directional cross-flows occurred along the communicating arteries. The greatest shunting of flow occurred for a missing pre-communicating anterior (A1) and posterior (P1) cerebral arteries. The anterior cerebral arteries had the greatest reduction (15-37%) in efferent flow rates for missing either a unilateral A1 or bilateral P1 segments. The bi-directional cross-flows, with multiple afferent flow mixing, observed along the communicating arteries may explain the propensity of aneurysm formation at these sites. Reductions in efferent flow rates due to aplastic vessel configurations may affect normal brain function.

Pregnancy causes diminished myogenic tone and outward hypotrophic remodeling of the cerebral vein of Galen

Pregnancy increases the risk of several complications associated with the cerebral veins, including thrombosis and hemorrhage. In contrast to the cerebral arteries and arterioles, few studies have focused on the effect of pregnancy on the cerebral venous side. Here, we investigated for the first time the effect of pregnancy on the function and structure of the cerebral vein of Galen in rats. Our major finding was that cerebral veins from late-pregnant (LP, n=11) rats had larger lumen diameters and thinner walls than veins from nonpregnant (NP, n=13) rats, indicating that pregnancy caused outward hypotrophic remodeling of the vein of Galen. Moreover, veins from NP animals had a small amount of myogenic tone at 10 mm Hg (3.9±1.0%) that was diminished in veins during pregnancy (0.8±0.3%; P<0.01). However, endothelium-dependent and -independent vasodilation of the veins was unchanged during pregnancy. Using immunohistochemistry, we show that the vein of Galen receives perivascular innervation, and that serotonergic innervation of cerebral veins is significantly higher in veins from LP animals. Outward hypotrophic remodeling and diminished tone of cerebral veins during pregnancy may contribute to the development of venous pathology through elevated wall tension and wall stress, and possibly by promoting venous blood stasis.

Endothelial progenitor cells contribute to neointima formation in rabbit elastase-induced aneurysm after flow diverter treatment

AIMS

Endothelial progenitor cells (EPCs) are involved in vascular repair and homeostasis after vascular injuries. In this study, we aimed to explore whether bone marrow (BM)-derived EPCs contribute to neointima formation and reendothelialization in rabbit elastase-induced aneurysm after flow diverter treatment.

METHODS

Elastase-induced aneurysms were created in New Zealand male rabbits. Three weeks after model creation, flow diverter was implanted to cover the induced aneurysm neck. Autologous EPCs were isolated from bone marrow, expanded ex vivo, double labeled with Hoechst 33,342 and CFSE(carboxyfluorescein diacetate succinimidyl ester), and transplanted transvenously into the rabbits. The rabbits were assigned into three groups. The first group received autologous transfusion of double-labeled EPCs from the first day after stent implantation, and the second group received transfusion from the fifteenth day. The autologous transfusion was given at a 3-day interval and continued for 2 weeks. Fluorescence-labeled cells were tracked under fluorescence microscope at the aneurysm neck and parent artery in the two groups. The third group was established as control group without EPCs transplantation. Scanning electron microscope was used to investigate the reendothelialization rate between the former two groups and the control group.

RESULTS

In the first group, double-positive EPCs were found in 3/5 rabbits and mainly located in the subendothelial space and around the stent struts. In the second group, double-positive EPCs were found in 2/5 rabbits and mainly located on the surface of neointima. More endothelial-like cells were observed on the neointima of aneurysm neck and stented parent artery in the groups with EPCs transplantation than control group without EPCs transplantation, but the difference on the number of these cells did not reach statistical significance.

CONCLUSIONS

BM-derived EPCs participate in neointima formation and reendothelialization in elastase-induced aneurysm after flow diverter treatment. The EPCs may differentiate into different cell types according to the stages of neointima formation in vivo.

Incidental Intracranial Aneurysm in a Dog Detected by 16-Multidetector Row Computed Tomography Angiography

This paper describes a small intracranial aneurysm incidentally found in a 24-month-old Nova Scotia Duck Tolling Retriever evaluated for a recent history of lethargy, fever, and cervical pain. The clinicopathological analysis revealed leukocytosis, and increased haptoglobin and C-reactive protein consistent with severe flogistic process. Nonenhanced computed tomography of the brain and cervical spine showed a diffuse encephalopathy and moderate cervical syringohydromyelia. Computed tomography angiography series of the brain showed a small saccular dilation at the joining point of the two rostral cerebral arteries consistent with a small aneurysm. Cerebrospinal fluid examination led to the final diagnosis of aseptic meningitis. The dog was discharge with a long-term corticosteroid therapy for the meningitis. At two-month follow-up evaluation, the cerebrospinal fluid examination was normal and the computed tomography of the brain showed no abnormalities except for the stable aneurysm. To our knowledge, this is the first description of a spontaneous cerebral aneurysm in dogs and serves to broaden the spectrum of cerebrovascular diseases in this species.

Pipeline embolization device in aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The PED is an FDS designed for the treatment of intracranial aneurysms. Data regarding the use of this device in acute or subacute aSAH is limited to a few case reports or small series. We aimed to demonstrate the feasibility of using an FDS, the PED, for the treatment of ruptured intracranial aneurysms with challenging morphologies.

MATERIALS AND METHODS

We conducted a retrospective review of all known patients treated with the PED for aSAH at 4 institutions between June 2008 and January 2012. Pertinent clinical and radiologic information was submitted by individual centers for central collation. The decision to treat with the PED was made on a case-by-case basis by a multidisciplinary team under compassionate use.

RESULTS

Twenty patients (15 women; median age, 54.5 years; IQR, 8.0 years) were found. There were 8 blister, 8 dissecting or dysplastic, 2 saccular, and 2 giant aneurysms. Median time to treatment was 4 days (range, 1-90 days; IQR, 12.75 days) from rupture. Three patients had previous failed treatment. Procedure-related symptomatic morbidity and mortality were 15%, with 1 (5%) procedure-related death. Two patients died relative to medical complications, and 1 patient was lost to follow-up. Sixteen patients were available for follow-up, 81% had a GOS of 5, and 13% had a GOS of 4 attributed to a poorer initial clinical presentation. One patient died of urosepsis at 4 months. Occlusion rates were 75% and 94% at 6 months and 12 months, respectively. There were 3 delayed complications (1 silent perforator infarct, 2 moderate asymptomatic in-stent stenoses). No symptomatic delayed complications or rehemorrhages occurred.

CONCLUSIONS

The FDS may be a feasible treatment option in the acute or subacute setting of selected ruptured aneurysms, especially blister aneurysms. Ruptured giant aneurysms remain challenging for both surgical and endovascular techniques; at this stage, FDSs should be used with caution in this aneurysm subtype.