Adaptive Remodeling in the Elastase-induced Rabbit Aneurysms

BACKGROUND

Rupture of brain aneurysms is associated with high fatality and morbidity rates. Through remodeling of the collagen matrix, many aneurysms can remain unruptured for decades, despite an enlarging and evolving geometry.

OBJECTIVE

Our objective was to explore this adaptive remodeling for the first time in an elastase induced aneurysm model in rabbits.

METHODS

Saccular aneurysms were created in 22 New Zealand white rabbits and remodeling was assessed in tissue harvested 2, 4, 8 and 12 weeks after creation.

RESULTS

The intramural principal stress ratio doubled after aneurysm creation due to increased longitudinal loads, triggering a remodeling response. A distinct wall layer with multi-directional collagen fibers developed between the media and adventitia as early as 2 weeks, and in all cases by 4 weeks with an average thickness of 50.6 ± 14.3 μm. Collagen fibers in this layer were multi-directional (AI = 0.56 ± 0.15) with low tortuosity (1.08 ± 0.02) compared with adjacent circumferentially aligned medial fibers (AI = 0.78 ± 0.12) and highly tortuous adventitial fibers (1.22 ± 0.03). A second phase of remodeling replaced circumferentially aligned fibers in the inner media with longitudinal fibers. A structurally motivated constitutive model with both remodeling modes was introduced along with methodology for determining material parameters from mechanical testing and multiphoton imaging.

CONCLUSIONS

A new mechanism was identified by which aneurysm walls can rapidly adapt to changes in load, ensuring the structural integrity of the aneurysm until a slower process of medial reorganization occurs. The rabbit model can be used to evaluate therapies to increase aneurysm wall stability.

Characteristics of Cerebral Aneurysms in Japan

The characteristics of cerebral aneurysms in Japan differ from other countries in the higher incidence of unruptured cerebral aneurysm detected by brain check-up screening, higher rupture rate of unruptured cerebral aneurysm, higher incidence of subarachnoid hemorrhage, and superior outcome after subarachnoid hemorrhage based on meta-analysis. Head shape, genetic features, environmental factors, demographics, and medical system in Japan are also different from other countries. Unruptured cerebral aneurysms are 2.8 times more likely to rupture in Japanese than western aneurysms, resulting in the highest incidence of subarachnoid hemorrhage in the world. The exact and specific mechanisms of de novo, growth, and rupture of cerebral aneurysms have not been elucidated. Investigations will contribute to the understanding of cerebral aneurysms and subarachnoid hemorrhage worldwide. Some features of cerebral aneurysm in Japan are discussed for possible research guidance in the elucidation of the predominance of subarachnoid hemorrhage in Japan.

Morphological parameters and anatomical locations associated with rupture status of small intracranial aneurysms

Characterization of the rupture risk factors for small intracranial aneurysms (SIAs, ≤5 mm) is clinically valuable. The present study aims to identify image-based morphological parameters and anatomical locations associated with the rupture status of SIAs. Two hundred and sixty-three patients with single SIAs (128 ruptured, 135 unruptured) were included, and six morphological parameters, including size, aspect ratio (AR), size ratio (SR), height–width ratio (H/W), flow angle (FA) and aneurysm width–parent artery diameter ratio, and the aneurysm locations were evaluated using three-dimensional geometry, and were used to identify a correlation with aneurysm rupture. Statistically significant differences were observed between ruptured and unruptured groups for AR, SR, H/W, FA, and aneurysm locations, from univariate analyses. Logistic regression analysis further revealed that AR (p = 0.034), SR (p = 0.004), H/W (p = 0.003), and FA (p < 0.001) had the strongest independent correlation with ruptured SIAs after adjustment for age, gender and other clinical risk factors. A future study on a larger SIA cohort need to establish to what extent the AR, SR, H/W and FA increase the risk of rupture in patients with unruptured SIAs in terms of absolute risks.

Size and location correlations with higher rupture risk of intracranial aneurysms

AIM

The purpose of this study was to investigate the impact of size and location of the intracranial aneurysm on rupture probability.

MATERIAL AND METHODS

265 patients with diagnosis of intracranial aneurysms were admitted to the department from January 2012 to December 2013. The characteristic of aneurysm, such as median size, location, single and multiple aneurysms and presentation were retrospectively reviewed using cerebral angiography reports.

RESULTS

There were 265 patients admitted with the diagnosis of intracranial aneurysms, 193 with single and 72 with multiple aneurysms. Among them there were 197 women (74,3%) and 68 men (25,7%). The total number of aneurysms harbored by the patients with multiple aneurysms were 184. Among all patients 96 had ruptured aneurysm, most of them located at the AComA and the minority of ruptured aneurysms were located at the ICA and MCA, In most cases the size of ruptured aneurysm was smaller than 10 mm.

CONCLUSION

The location of an aneurysm is an important factor allowing to predict the rupture probability and to plan proper treatment. The size of the aneurysm is also very useful predictor especially correlated with the location but the impact on rupture probability still needs further examination.

Evaluation of Endovascular Embolization of Cerebral Aneurysms by Hydrogel Coils

BACKGROUND

Hydrogel coils were created to improve the chances of an effective endovascular treatment of cerebral aneurysms. Achieving a high packing density of coils in the lumen of aneurysms can decrease the risk of recurrence. The aim of the present study is to report our initial experience on the effectiveness and safety of endovascular treatment of intracranial aneurysms with the use hydrogel coils.

MATERIAL/METHODS

Sixty patients (age: 28-72 years) (45 women, 15 men) were treated. In 18 patients (30%), subarachnoid hemorrhage was present. Digital subtraction angiography (DSA) of cerebral vessels with rotational scanning was performed. Image analysis was performed by the Philips Integris 3D RA device,which is a specialized workstation (Three-Dimensional Rotational Angiography). 3D reconstructions of cerebral arteries were created based on the data. Sixty-six cerebral aneurysms were embolized with hydrogel coils, which expand in contact with blood. reaching the maximum diameter in about 20 minutes. In 29 aneurysms (43.9%), the effect of the procedure was confirmed on a follow-up DSA after 8.0±4.1 months from the initial treatment.

RESULTS

A complete embolization was performed in 55 aneurysms (83.3%), and partial embolization in 11 aneurysms (16.7%). In 6 aneurysms (9.1%), re-embolization was necessary and it resulted in a complete embolization of 5 aneurysms. On a follow-up DSA, complete embolization was present in 25 aneurysms (86.2%), and partial embolization in 4 aneurysms (13.8%), respectively.

CONCLUSIONS

Endovascular embolization with hydrogel coils is an effective and safe treatment method for cerebral aneurysms, although it carries the risk of some complications.

Bifurcation Location Is Significantly Associated with Rupture of Small Intracranial Aneurysms (<5 mm)

BACKGROUND AND OBJECTIVE

Patients with small (<5 mm) unruptured intracranial aneurysms (UIAs) are at risk of subarachnoid hemorrhage, but risk assessment of these patients remains controversial in daily clinical practice. We aimed to identify the risk factors of aneurysmal rupture in these patients.

METHODS

We retrospectively analyzed consecutive patients with small UIAs who were admitted to our center between February 2009 and December 2014. The enrolled patients were divided into ruptured and unruptured groups. The risk factors for aneurysmal rupture were determined using multivariate logistic regression analysis.

RESULTS

A total of 548 patients with 618 small intracranial aneurysms (267 ruptured and 351 unruptured) were included. Univariate analysis showed that rupture of small aneurysms was related to sex, age, smoking, hypertension, aspect ratio, size ratio, irregular shape, aneurysm width, height, and neck diameter, and location at bifurcation or posterior circulation. Multivariate logistic regression showed that rupture was associated with bifurcation location (odds ratio [OR], 5.409; 95% confidence interval [CI], 3.656-8.001; P < 0.001), size ratio (OR, 3.092; 95% CI, 2.002-4.774; P < 0.001), location (OR, 2.624; 95% CI, 1.428-4.824; P = 0.002), hypertension (OR, 1.698; 95% CI, 1.1140-2.527; P = 0.009), and age at diagnosis of UIA (OR, 1.826; 95% CI, 1.225-2.723; P = 0.003).

CONCLUSIONS

This study showed that 70.4% of small ruptured intracranial aneurysms (<5 mm) were located at parent artery bifurcations and that bifurcation location was a significant independent factor for the risk of rupture of small UIAs (<5 mm). Prophylactic treatment should be recommended for small UIAs in this location.

Larger size ratio associated with the rupture of very small (≤3 mm) anterior communicating artery aneurysms

Background

Anterior communicating artery (AcoA) aneurysms have a high rupture risk, and ruptured AcoA aneurysms tend to be smaller than other intracranial aneurysms. We aimed to determine the incidence and morphologic predictors of aneurysm rupture of very small AcoA aneurysms.

Methods

We conducted a retrospective analysis of 519 consecutive patients with single AcoA aneurysms between December 2007 and February 2015 in our hospital. Aneurysm morphologies were re-measured using CT angiography images. Very small aneurysms were defined as those with a maximum size ≤3 mm, and small aneurysms were defined as those with a maximum size ≤5 mm. Multivariate regression analyses were used to determine the association between aneurysm morphology and aneurysm rupture status.

Results

Of the 474 ruptured AcoA aneurysms, 134 (28.3%) aneurysms were very small and 278 (58.6%) aneurysms were small. In the univariate analysis for very small aneurysms, larger aneurysm size (p=0.037), larger size ratio (p=0.002), higher aneurysm height (p=0.038), smaller vessel size (p=0.012), and dominant A1 segment configuration (p=0.011) were associated with aneurysm rupture. Multivariate analysis revealed that a larger size ratio was independently associated with the rupture status of the very small aneurysms (OR 3.69, 95% CI 1.5 to 9.0; p=0.004), and larger aneurysm size, larger size ratio, and dominant A1 segment configuration were associated with the rupture of small aneurysms.

Conclusions

About one-third of ruptured AcoA aneurysms were very small. A larger size ratio, rather than other aneurysm morphologies, was independently associated with the rupture of very small AcoA aneurysms.

Controversies in the anesthetic management of intraoperative rupture of intracranial aneurysm

Despite great advancements in the management of aneurysmal subarachnoid hemorrhage (SAH), outcomes following SAH rupture have remained relatively unchanged. In addition, little data exists to guide the anesthetic management of intraoperative aneurysm rupture (IAR), though intraoperative management may have a significant effect on overall neurological outcomes. This review highlights the various controversies related to different anesthetic management related to aneurysm rupture. The first controversy relates to management of preexisting factors that affect risk of IAR. The second controversy relates to diagnostic techniques, particularly neurophysiological monitoring. The third controversy pertains to hemodynamic goals. The neuroprotective effects of various factors, including hypothermia, various anesthetic/pharmacologic agents, and burst suppression, remain poorly understood and have yet to be further elucidated. Different management strategies for IAR during aneurysmal clipping versus coiling also need further attention.

The expression of SPARC in human intracranial aneurysms and its relationship with MMP-2/-9

Objective

SPARC is a key determinant of invasion and metastasis in some tumors, such as gliomas, melanomas and prostate tumors. SPARC can change the composition and structure of the matrix and promote angiogenesis; these effects are closely related to clinical stage and the prognosis of tumors such as meningiomas. However, little is known about the expression of SPARC in intracranial aneurysms. The goal of this study was to establish the role of SPARC in human intracranial aneurysms.

Methods

Thirty-one intracranial aneurysms were immunohistochemically stained for SPARC, MMP-2 and MMP-9. As controls, normal Circle of Willis arteries were similarly immunostained. All specimens were retrieved during autopsies and were embedded in paraffin. To evaluate the expression levels of SPARC, MMP-2 and MMP-9, western blotting was also performed in three available intracranial aneurysm specimens. The limited availability of fresh intracranial aneurysm tissue was the result of the majority of patients choosing endovascular embolization.

Results

The results showed that SPARC, MMP-2 and MMP-9 were strongly expressed in intracranial aneurysm tissues; however, these proteins were expressed minimally or not at all in normal Circle of Willis arteries. The western blot results showed that the expression levels of SPARC, MMP-2 and MMP-9 were significantly up-regulated in intracranial aneurysms relative to the expression levels in the normal Circle of Willis arteries. Data analysis showed that SPARC was significantly correlated with MMP-2 and MMP-9, also with age and risk factors but not with the Hunt-Hess grade or with sex.

Conclusion

The results indicate that SPARC is widely expressed in human intracranial aneurysms, and its expression correlates with MMP-2 and MMP-9 expression, age and risk factors but not with the Hunt-Hess grade. The results of this study suggest that SPARC has a pathogenic role in the alteration of the extracellular matrix of intracranial arteries during aneurysm formation.

The natural history and treatment options for unruptured intracranial aneurysms

Recent advances in angiographic technique have raised our awareness of the presence of unruptured intracranial aneurysms (UIAs). However, the appropriate management for these lesions remains controversial. To optimize patient outcomes, the physician must weigh aneurysmal rupture risk associated with observation against the complication risks associated with intervention. In the case that treatment is chosen, the two available options are surgical clipping and endovascular coiling. Our paper summarizes the current body of literature in regards to the natural history of UIAs, the evolution of the lesion if it progresses uninterrupted, as well as the safety and efficacy of both treatment options. The risks and benefits of treatment and conservative management need to be evaluated on an individual basis and are greatly effected by both patient-specific and aneurysm-specific factors, which are presented in this paper. Ultimately, this body of data has led to multiple sets of treatment guidelines, which we have summated and presented in this paper.

The role of the renin—angiotensin system in the pathogenesis of intracranial aneurysms

Introduction: Recent work has begun to elucidate the pathogenesis of intracranial aneurysms (IA) and has shown that many genes are involved in the risk for this condition. There has also been increasing research interest in the renin—angiotensin system (RAS) in the brain and its involvement in a range of cardiovascular and neurological disorders. The possibility that the RAS is implicated in the pathogenesis of IA merits further investigation. The aim of this article is to review the literature on the pathogenesis of IA and the pathophysiological significance of the brain RAS, and to identify directions for research into their association.

Methods and results : A survey of the literature in these fields shows that although factors contributing to systemic hypertension predispose to IA, a large number of genes involved in endothelial cell adhesion, smooth muscle activity, extracellular matrix dynamics and the inflammatory and immune responses are also implicated. The brain RAS has a significant role in regulating blood pressure and in maintaining cerebrovascular autoregulation, but angiotensin II receptors are also involved in the maintenance of endothelial cell and vascular smooth muscle function and in the inflammatory response in the brain.

Conclusions: There is strong, albeit largely circumstantial, evidence in the literature for a relationship between the brain RAS and the formation of IA. Research on the association between polymorphisms in RAS-related genes and the incidence of unruptured and ruptured IA is indicated.