A case of aneurysm of the jugular and mediastinal veins — radioisotopic blood pool study of venous aneurysm

Venous aneurysm not associated with other cardiovascular disease or trauma is a rare condition. A case is presented of bilateral jugular and mediastinal venous aneurysm, which was detected and depicted to a full extent by means of a blood-pool study with ^99mTc-fibrinogen, undertaken because of concurrent thrombocytopenia. The aneurysm was confirmed by subsequent X-ray angiography and surgery. In radioisotopic blood pool study venous aneurysm, unlike arterialor aortic aneurysm, may be filled to the equilibrium state later than the appearance of the cardiac pool.     

18F-FDG PET-CT uptake is a feature of both normal diameter and aneurysmal aortic wall and is not related to aneurysm size

Purpose

Aortic metabolic activity is suggested to correlate with presence and progression of aneurysmal disease, but has been inadequately studied. This study investigates the 2-[¹⁸F] fluoro-2-deoxy-D-glucose (¹⁸F-FDG) uptake in a population of infra-renal abdominal aortic aneurysms (AAA), compared to a matched non-aneurysmal control group.

Methods

The Positron Emission Tomography – Computed Tomography (PET/CT) database was searched for infra-renal AAA. Exclusion criteria were prior repair, vasculitis, and saccular/mycotic thoracic or thoraco-abdominal aneurysms. Matching of 159 non-aneurysmal (<3 cm diameter) controls from the same population was assessed. Infra-renal aortic wall FDG uptake was assessed using visual analysis; maximum standardized uptake value (SUV_max) and target to background mediastinal blood pool ratio (TBR) were documented. Predictors of FDG uptake (age, sex, aortic diameter, hypertension, statin use, and diabetes) were assessed using univariate analysis. Follow-up questionnaires were sent to referring clinicians.

Results

Aneurysms (n?=?151) and controls (n?=?159) were matched (p?>?0.05) for age, sex, diabetes, hypertension, smoking status, statin use, and indication for PET/CT. Median aneurysm diameter was 5.0 cm (range 3.2–10.4). On visual analysis there was no significant difference in the overall numbers with increased visual uptake 24 % (36/151) in the aneurysm group vs. 19 % (30/159) in the controls, p?=?ns. SUV_max was slightly lower in the aneurysm group vs. controls (mean (2 SD) 1.75(0.79) vs. 1.84(0.58), p?=?0.02). However there was no difference in TBR between the AAA group and controls (mean (2 SD) 1.03 (0.46) vs. 1.05(0.31), p?=?0.36). During a median 18 (interquartile range 8–35) months’ follow-up 20 were repaired and four were confirmed ruptured.

Conclusions

The level of metabolic activity as assessed by ¹⁸F-FDG PET/CT in infra-renal AAA does not correlate with aortic size and does not differ between aneurysms and matched controls.     

CT after Endovascular Repair of Abdominal Aortic Aneurysms: Diagnostic Accuracy of Diameter Measurements for the Detection of Aneurysm Sac Enlargement

Purpose

To evaluate the diagnostic accuracy of diameter measurements for the detection of aneurysm volume increase during follow-up after endovascular aortic repair (EVAR) of abdominal aortic aneurysms (AAAs).

What is the relationship between <Superscript>18</Superscript>F-FDG aortic aneurysm uptake on PET/CT and future growth rate?

Purpose  

In this study we investigate the relationship between ¹⁸F-fluorodeoxyglucose (FDG) metabolism and future aneurysm expansion measured by serial duplex ultrasound. Current screening programmes are increasing the identification of patients with abdominal aortic aneurysm (AAA). The management of these patients remains challenging and methods of risk stratification are sought.     

Emergence of molecular imaging of aortic aneurysm: Implications for risk stratification and management

Imaging cellular and molecular processes associated with aneurysm expansion, dissection, and rupture can potentially transform the management of patients with thoracic and abdominal aortic aneurysm. Here, we review recent advances in molecular imaging of aortic aneurysm, focusing on imaging modalities with the greatest potential for clinical translation and application, PET, SPECT, and MRI. Inflammation (e.g., with ¹⁸F-FDG, nanoparticles) and matrix remodeling (e.g., with matrix metalloproteinase-targeted tracers) are highlighted as promising targets for molecular imaging of aneurysm. Potential alternative or complementary approaches to molecular imaging for aneurysm risk stratification are briefly discussed.     

Prevalence of Intracranial Aneurysms in Patients with Aortic Aneurysms

BACKGROUND AND PURPOSE:Previous studies have suggested an association between aortic aneurysms and intracranial aneurysms with a higher prevalence of intracranial aneurysms in patients with aortic aneurysms. The aims of the present study were to evaluate the incidence of intracranial aneurysms in a large cohort of patients with aortic aneurysms and to identify potential risk factors for intracranial aneurysms in this population.MATERIALS AND METHODS:We included all patients with aortic aneurysms (either abdominal and/or thoracic) who had available cerebral arterial imaging and were seen at our institution during a 15-year period. We identified patients with intracranial aneurysms. Patient demographics, comorbidities, and aortic aneurysm and intracranial aneurysm sizes and locations were analyzed. Univariate analysis was performed with a χ² test for categoric variables and a Student t test or ANOVA for continuous variables.RESULTS:A total of 1081 patients with aortic aneurysms were included. Of them, 440 (40.7%) had abdominal aortic aneurysms, 446 (41.3%) had thoracic aortic aneurysms, and 195 (18.0%) had both abdominal aortic and thoracic aortic aneurysms. The overall prevalence of associated intracranial aneurysms in patients with aortic aneurysms was 11.8% (128/1081), with 12.7% (56/440), 10.8% (48/446), and 12.3% (24/195), respectively, in patients with abdominal aortic aneurysms, thoracic aortic aneurysms, and both thoracic aortic aneurysms and abdominal aortic aneurysms. Female patients had a higher risk of associated intracranial aneurysms (OR = 2.08; 95% CI, 1.49–3.03; P = .0002). There was a slight association between abdominal aortic aneurysm size and the prevalence of intracranial aneurysms (OR = 1.02; 95% CI, 1.01–1.03; P = .045). There was no significant association between the locations of the aortic and intracranial aneurysms (P = .93).CONCLUSIONS:The prevalence of intracranial aneurysms is high in patients with aortic aneurysms. Further studies examining the role and cost-effectiveness of intracranial aneurysm screening in patients are warranted.

The overall prevalence of unruptured intracranial aneurysms (IAs) in the general population is estimated as 3.2%.¹ The overall prevalence of aortic aneurysms (AAs), with both thoracic (TAAs) and abdominal (AAAs) aortic aneurysms, is estimated at around 1%–2% in the general population with up to 10% prevalence in older age groups.² Previous studies have identified a link between intracranial aneurysms and aortic diseases such as coarctation of the aorta or a bicuspid aortic valve.^3–6 A few studies have reported an association between abdominal aortic aneurysms and thoracic aortic aneurysms and IAs, with a higher prevalence of IA in patients with aortic aneurysms.^6–14 However, contrary to other pathologies such as autosomal dominant polycystic kidney disease (ADPKD), which is associated with IA in 12.4% of cases, no systematic screening for IA is proposed for patients with AA.¹⁵ The aims of the present study were to evaluate the prevalence of IA in a large cohort of patients with AA and to identify potential risk factors for IA in this population.     

Development of a New Intravascular Low-Profile Device for Exclusion of Aortic Aneurysm: An Experimental Pilot Study

Purpose: To present a new intravascular device for the treatment of aorto-iliac aneurysms. Methods: This new device was tested in five dogs with abdominal aortic aneurysm created experimentally by overdilation of a balloon-expandable stent with a 16 or 18 mm wide PTA balloon catheter. The design of the device is based on a self-expanding aortic stent which consists of two stretchable circular frames filled with a textile Dacron mesh membrane that is suspended horizontally into the infrarenal abdominal aorta proximally to the aneurysm. The frames are part of a preshaped double helical structure that is introduced longitudinally through a catheter in a parallel fashion and forming the desired shape at the vessel site to be occluded. Two iliac stent-grafts are introduced in a low-profile status through the membrane sealing the aneurysm sac and holding the stent-grafts in place. After stent-graft expansion, a new bifurcation located more proximally than the natural one is created. The follow-up of the dogs was performed clinically and angiographically, and specimens were evaluated histomorphologically. Results: The membrane device can be introduced through a 9 Fr vascular sheath. Technical success was achieved in four of five dogs. Nine of ten stent-grafts could be fixed securely within the membrane, thus preventing dislocation. Aneurysms were excluded immediately, and blood flow to the external iliac arteries was restored by the stent-grafts. At 6–9 months follow-up of technically successful implanted devices, there were no endoleaks, no migration, no stenoses at contact sites between the implant material and vascular wall, and no stenosis or occlusion of the stent-grafts. At microscopic evaluation, the interspace between the membranes was filled with thrombotic material, thus ensuring exclusion of the aneurysm. Conclusion: This new device was found to be flexible, low profile and useful in excluding abdominal aortic aneurysm in the experimental setting.     

Oversizing in transcatheter aortic valve replacement,a commonly used term but a poorly understood one: Dependency on definition and geometrical measurements

BackgroundIn transcatheter aortic valve replacement, prosthesis oversizing is essential to prevent paravalvular regurgitation. However, the estimated extent of oversizing strongly depends on the measurement used for annular sizing.PurposeThe aim was to investigate the influence of geometrical parameters for calculation of relative oversizing in transcatheter aortic valve replacement, reported as percentage in relation to the native annulus size, to standardize reporting.MethodsElectrocardiogram-gated cardiac dual-source CT data of 130 consecutive patients with severe aortic stenosis (mean age, 81 ± 8 years; 56 men; mean aortic valve area, 0.67 ± 0.18 cm²) were included. Aortic annulus dimensions were quantified by means of planimetry that yielded area and perimeter at the level of the basal attachment points of the aortic cusps during systole. Area- and perimeter-derived diameters were calculated as D_A = 2 × √(A/π) and D_P = P/π. Hypothetical prosthesis sizing was based on D_A (23-mm prosthesis for 19–22 mm; 26-mm prosthesis for 22–25 mm; 29-mm prosthesis for 25–28 mm). Relative oversizing for hypothetical prosthesis selection was calculated as percentage in relation to the native annulus size.ResultsMean annulus area was 492.12 ± 94.9 mm² and mean perimeter was 80.1 ± 7.6 mm. D_P was significantly larger than D_A (25.5 ± 2.4 mm vs 24.9 ± 2.4 mm; P < .001). Mean maximum diameter was 28.1 ± 3.0 mm and mean minimal diameter was 22.8 ± 2.4 mm. Calculated eccentricity index [EI = 1 − minimal diameter/maximum diameter)] was 0.19 ± 0.06. Difference between D_P and D_A correlated significantly with EI (r = 0.67; P < .001). Relative oversizing was 10.2% ± 3.8% and 21.6% ± 8.4% by D_A and area, and 7.8% ± 3.9% by both D_P and perimeter.ConclusionFor planimetric assessment of aortic annulus dimensions with CT, the percentage oversizing calculated strongly depends on the geometrical variable used for quantifying annular dimensions. Standardized nomenclature seems warranted for comparison of future studies.     

Tuberculous Aneurysm of the Abdominal Aorta: Endovascular Repair Using Stent Grafts in Two Cases

Tuberculous aneurysm of the aorta is exceedingly rare. To date, the standard therapy for mycotic aneurysm of the abdominal aorta has been surgery involving in-situ graft placement or extra-anatomic bypass surgery followed by effective anti-tuberculous medication. Only recently has the use of a stent graft in the treatment of tuberculous aortic aneurysm been described in the literature. We report two cases in which a tuberculous aneurysm of the abdominal aorta was successfully repaired using endovascular stent grafts. One case involved is a 42-year-old woman with a large suprarenal abdominal aortic aneurysm and a right psoas abscess, and the other, a 41-year-old man in whom an abdominal aortic aneurysm ruptured during surgical drainage of a psoas abscess.     

Ten Years of Experience with the GORE EXCLUDER? Stent-Graft for the Treatment of Aortic and Iliac Aneurysms: Outcomes from a Single Center Study

Purpose

This study was designed to assess the long-term outcome of selected patients with aortic, aortoiliac, and isolated common iliac aneurysms treated with the GORE EXCLUDER^? stent-graft.

Methods

Between December 1998 and June 2010, 121 nonconsecutive patients underwent insertion of a GORE EXCLUDER^? stent-graft to treat an aortic (n?=?80; 66%), aortoiliac (n?=?25; 21%), or isolated common iliac (n?=?16; 13%) aneurysm. Procedural and follow-up data were collected prospectively. Primary endpoints are overall survival, intervention-free survival, and freedom from aneurysm rupture. Secondary endpoints are device- and procedure-related complications, including all types of endoleaks or endotension, and reintervention.

Results

The mean follow-up is 4.98?years (standard deviation, 3.18; median follow-up, 4.05?years). The estimated percentage overall survival (with 95% confidence interval) after respectively 5 and 10?years of follow-up is 74.5% (65.8; 81.3) and 57.8% (47.7; 66.7). The estimated intervention-free survival after respectively 5 and 10?years is 90% (84.3; 96.1) and 77.7% (67; 88.4). There was no aneurysm rupture during follow-up. Early postoperative complications occurred in 16 patients (13%); none were fatal. Late reinterventions were performed in 18?patients (15%). Finally, throughout the follow-up period, endoleaks were identified: type I (n?=?4; 3%); type II (n?=?39; 32%); type?III (n?=?0; 0%); endotension was seen in 11 patients (9%).

Conclusions

Aneurysm exclusion with use of the GORE EXCLUDER^? stent-graft is durable through a mean follow-up of nearly 5?years. There was no postprocedural aneurysm rupture. Complications occurred throughout the follow-up period, requiring continued clinical and radiological surveillance.     

Quantifying Intracranial Aneurysm Wall Permeability for Risk Assessment Using Dynamic Contrast-Enhanced MRI: A Pilot Study

BACKGROUND AND PURPOSE:Pathological changes in the intracranial aneurysm wall may lead to increases in its permeability; however the clinical significance of such changes has not been explored. The purpose of this pilot study was to quantify intracranial aneurysm wall permeability (K^trans, V_L) to contrast agent as a measure of aneurysm rupture risk and compare these parameters against other established measures of rupture risk. We hypothesized K^trans would be associated with intracranial aneurysm rupture risk as defined by various anatomic, imaging, and clinical risk factors.MATERIALS AND METHODS:Twenty-seven unruptured intracranial aneurysms in 23 patients were imaged with dynamic contrast-enhanced MR imaging, and wall permeability parameters (K^trans, V_L) were measured in regions adjacent to the aneurysm wall and along the paired control MCA by 2 blinded observers. K^trans and V_L were evaluated as markers of rupture risk by comparing them against established clinical (symptomatic lesions) and anatomic (size, location, morphology, multiplicity) risk metrics.RESULTS:Interobserver agreement was strong as shown in regression analysis (R² > 0.84) and intraclass correlation (intraclass correlation coefficient >0.92), indicating that the K^trans can be reliably assessed clinically. All intracranial aneurysms had a pronounced increase in wall permeability compared with the paired healthy MCA (P < .001). Regression analysis demonstrated a significant trend toward an increased K^trans with increasing aneurysm size (P < .001). Logistic regression showed that K^trans also predicted risk in anatomic (P = .02) and combined anatomic/clinical (P = .03) groups independent of size.CONCLUSIONS:We report the first evidence of dynamic contrast-enhanced MR imaging–modeled contrast permeability in intracranial aneurysms. We found that contrast agent permeability across the aneurysm wall correlated significantly with both aneurysm size and size-independent anatomic risk factors. In addition, K^trans was a significant and size-independent predictor of morphologically and clinically defined high-risk aneurysms.

Intracranial aneurysms (IAs) affect 2%–6% of the population, with nearly 30,000 Americans having an aneurysm rupture each year.¹ Aneurysmal subarachnoid hemorrhage has an approximate 50% mortality, with survivors incurring a tremendous personal and financial burden due to permanent disabilities. Despite the potential devastating effects of IAs, the universal treatment of unruptured IAs still remains controversial. The largest prospective study to date on unruptured IAs, the International Study of Unruptured Intracranial Aneurysms (ISUIA), indicated lower rupture rates than previously suspected.² However, multiple subsequent reports challenged these findings,^3,4 thus further complicating management decisions. The exact pathogenesis and pathoevolution of IAs is largely unknown, with only a fraction of IAs progressing to rupture annually (<2%), suggesting potential differences in the pathobiology of ruptured-versus-unruptured IAs. Aneurysm risk stratification has been attempted by identifying specific characteristics of ruptured IAs, including size, location, and morphologic factors (eg, irregular contour⁵ and daughter sacs⁶), but also clinical factors, such as symptomatic lesions, hypertension, smoking, alcohol/drug abuse, and genetic predispositions to aneurysm formation/rupture. However, without absolute risk-stratification parameters for unruptured IAs, patients and physicians encounter difficult management decisions regarding the risk-benefit analysis for treatment. Aneurysm size measured by CTA, MRA, or DSA is the primary imaging marker of rupture risk and is used for clinical decisions to either treat with coil embolization/microsurgical clipping or offer conservative management with routine imaging follow-up evaluations and clinical risk-factor control.The pathobiology of IAs and alterations in the aneurysm wall have been shown to involve a multitude of histopathologic changes, such as disruption of the internal elastic lamina, smooth-muscle cell migration, and myointimal hyperplasia leading to irregular surfaces with variable thickness. In fact, direct inspection of the IA wall during surgery has demonstrated heterogeneous features, such as thin translucent regions,⁷ but these are not resolved with noninvasive imaging. Noninvasive CT or MR imaging of the morphologic phenotype of the aneurysm wall may be useful in assessing IA stability. It is plausible, given the aforementioned changes in IA wall histology, specifically apoptosis of endothelial cells, loss of collagen, and remodeling of the extracellular matrix, that contrast agents could extravasate or permeate these compromised areas into the surrounding CSF. This may be interpreted as a macroscopic manifestation of microscopic tracer permeability, which occurs through the capillary bed into tissue. The contrast agent permeability rate (K^trans) could then provide a surrogate measure of vessel wall integrity and focal degradation resulting from environmental factors such as hemodynamic stresses, typically assessed with advanced MR imaging acquisitions⁸ and postprocessing algorithms.⁹The purpose of this work was to determine the feasibility of quantifying aneurysm wall permeability by using widely available dynamic contrast-enhanced (DCE)–MR imaging. Our goal was to develop an adjunctive imaging metric to complement existing anatomic and developing flow-based imaging markers of aneurysm risk (size, location, morphology, computational/4D flow dynamics). We report the results of a prospective pilot study comparing aneurysm wall permeability by using DCE–MR imaging with anatomic and clinical metrics that predispose IAs to rupture. We hypothesized that increased IA wall permeability may be associated with IA size, location, morphology, and multiplicity and clinically defined high-risk or symptomatic lesions.     

The burden of hard atherosclerotic plaques does not promote endoleak development after endovascular aortic aneurysm repair: a risk stratification

Purpose  

To objectify the influence of the atherosclerotic burden in the proximal landing zone on the development of endoleaks after endovascular abdominal aortic aneurysm repair (EVAR) or thoracic endovascular aneurysm repair (TEVAR) using objective aortic calcium scoring (ACS).     

Prevalence of Intracranial Aneurysms in Patients with Aortic Dissection

BACKGROUND AND PURPOSE:There is an uncertainty about the association between intracranial aneurysms and aortic dissection. We aimed to determine the prevalence of intracranial aneurysms in patients with aortic dissection and evaluate the independent risk factors for the presence of intracranial aneurysms in these patients.MATERIALS AND METHODS:Seventy-one patients with a confirmed aortic dissection who underwent additional brain imaging were enrolled as the aortic dissection group, and 2118 healthy individuals with brain imaging, as controls. Demographic data were obtained from their medical records, including age, sex, comorbidities, and arch vessel involvement of aortic dissection. Two readers reviewed all brain images independently regarding the presence, morphology, size, and location of intracranial aneurysms. Baseline characteristics were compared between the aortic dissection group and controls by propensity score matching, and logistic regression analysis was performed for independent risk factors for the presence of intracranial aneurysms.RESULTS:The prevalence of intracranial aneurysms was 12.96% in the aortic dissection group and 1.85% in controls (P = .022). The mean diameter of intracranial aneurysms was significantly larger in the aortic dissection group (5.79 ± 3.26 mm in aortic dissection versus 3.04 ± 1.57 mm in controls; P = .008), and intracranial aneurysms of >7 mm were also more common in the aortic dissection group (28.6% in aortic dissection versus 5.3% in controls, P = .003). On multivariate analysis, arch vessel involvement of aortic dissection was an independent risk factor for the presence of intracranial aneurysms (odds ratio, 6.246; 95% confidence interval, 1.472–26.50; P = .013).CONCLUSIONS:Patients with aortic dissection have a high prevalence of intracranial aneurysms, and selective screening for brain vessels could be considered in these patients with arch vessel involvement. A further prospective study is needed to demonstrate a substantial prevalence of intracranial aneurysms.

Intracranial aneurysms (IAs) are found in approximately 3% of the general population,¹ and IA rupture with subarachnoid hemorrhage is a life-threatening event with substantial morbidity and mortality.^2,3 With the advancement of the imaging modalities, early diagnosis of IA is relevant, especially in at-risk patients with selected conditions associated with an increased occurrence of IAs.⁴IAs and aortic diseases are different disease entities but have a similar pathophysiologic mechanism, which may be caused by excessive hemodynamic stress to the vessel wall or genetic factors for vascular fragility. The guidelines for unruptured IAs⁴ have suggested that there is an increased the risk of aneurysm formation in some aortic pathologies such as bicuspid aortic valve and coarctation of the aorta. Recently, some authors^5–7 have published the link between IA and aortic aneurysm, which showed an IA incidence of 9%–11% in patients with aortic aneurysms. However, there are a limited number of genetic or experimental studies^8–10 and case reports^11–13 for the association between IA and aortic dissection (AD).Therefore, we aimed to demonstrate the prevalence of IA in patients with AD and investigate independent risk factors for the presence of IA in these patients.     

Aortic volume as an indicator of disease progression in patients with untreated infrarenal abdominal aneurysm

Objective

The maximal diameter of an abdominal aortic aneurysm (AAA) and the change in diameter over time reflect rupture risk and are used for surgical planning. However, evidence has emerged that aneurysm volume may be a better indicator of AAA remodeling. The purpose of this study was to assess the relationship between the volume and maximal diameter of the abdominal aorta in patients with untreated infrarenal AAA.

Materials and methods

This was a retrospective study of 100 patients with infrarenal AAA who were followed for more than 6 months. We examined 2 sets of computed tomography images for each patient, acquired ≥6 months apart. The maximal diameter and volume of the infrarenal abdominal aorta were determined by semiautomated segmentation software.

Results

At baseline, mean maximal infrarenal diameter was 5.1 ± 1.0 cm and mean aortic volume was 139 ± 72 mL. There was good correlation between the maximal diameter and aortic volume at baseline (r² = 0.55; P < 0.001). The mean change in maximal diameter between studies was 0.2 ± 0.3 cm and the mean volume change was 19 ± 19 mL. However, the correlation between diameter change and volume change was modest (r² = 0.34; P = 0.001). Most patients (n = 64) had no measurable change in maximal diameter between studies (≤2 mm), but the change in volume was found to vary widely (−2 to 69 mL).

Conclusion

In patients with untreated infrarenal AAA, a change in aortic volume can occur in the absence of a significant change in maximal diameter. Additional work is needed to examine the relationship between change in AAA volume and outcomes in this patient group.     

Breathhold time‐resolved three‐directional MR velocity mapping of aortic flow in patients after aortic valve‐sparing surgery

Purpose

To evaluate the utility of breathhold time‐resolved three‐directional MR velocity mapping for quantifying the restoration of normal flow patterns in patients after aortic valve‐sparing surgery.

Materials and Methods

Breathhold time‐resolved three‐directional MR velocity mapping was performed on 13 patients with aortic valve‐sparing surgery. Ten healthy volunteers and 12 patients with ascending aortic aneurysm underwent the same MR examination for comparison. Aortic laminar flow, turbulent flow, and the presence of vortical flow in the sinuses of Valsalva were semiquantitatively assessed and statistically compared between the three groups of subjects.

Results

The average score of laminar flow in the ascending aorta for patients with surgery was not significantly different from that of volunteers (P = 0.210), but was significantly greater than that of patients with aneurysm (P < 0.01). The average score of turbulent flow in patients with surgery was significantly smaller than that of patients with aneurysm (P < 0.01). The presence of systolic vortical flow in the sinuses of Valsalva for patients with surgery was not significantly different from that of healthy volunteers (P = 0.405) and patients with aneurysm (P = 0.238).

Conclusion

Breathhold time‐resolved three‐directional MR velocity mapping allows for quantifying flow patterns in the aortic root and ascending aorta. Normal laminar flow in the ascending aorta and vortical flow in the sinuses of Valsalva can be restored in patients after aortic valve‐sparing surgery. J. Magn. Reson. Imaging 2009;29:569–575. © 2009 Wiley‐Liss, Inc.     

Intracranial Aneurysmal Pulsatility as a New Individual Criterion for Rupture Risk Evaluation: Biomechanical and Numeric Approach (IRRAs Project)

BACKGROUND AND PURPOSE:The present study follows an experimental work based on the characterization of the biomechanical behavior of the aneurysmal wall and a numerical study where a significant difference in term of volume variation between ruptured and unruptured aneurysm was observed in a specific case. Our study was designed to highlight by means of numeric simulations the correlation between aneurysm sac pulsatility and the risk of rupture through the mechanical properties of the wall.MATERIALS AND METHODS:In accordance with previous work suggesting a correlation between the risk of rupture and the material properties of cerebral aneurysms, 12 fluid-structure interaction computations were performed on 12 “patient-specific” cases, corresponding to typical shapes and locations of cerebral aneurysms. The variations of the aneurysmal volume during the cardiac cycle (ΔV) are compared by using wall material characteristics of either degraded or nondegraded tissues.RESULTS:Aneurysms were located on 6 different arteries: middle cerebral artery (4), anterior cerebral artery (3), internal carotid artery (1), vertebral artery (1), ophthalmic artery (1), and basilar artery (1). Aneurysms presented different shapes (uniform or multilobulated) and diastolic volumes (from 18 to 392 mm³). The pulsatility (ΔV/V) was significantly larger for a soft aneurysmal material (average of 26%) than for a stiff material (average of 4%). The difference between ΔV, for each condition, was statistically significant: P = .005.CONCLUSIONS:The difference in aneurysmal pulsatility as highlighted in this work might be a relevant patient-specific predictor of aneurysm risk of rupture.

Intracranial aneurysms kill about 15,000 people in Europe each year. Most are young, between 40 and 60 years old. New medical imaging techniques are now able to clearly depict intracranial aneurysm, but no systematic screening of this disease exists at the moment. The main reason is that 2%–6% of the general population lives with an aneurysm,¹ but only 0.5% of these will rupture. Screening for intracranial aneurysm is not justified unless it is capable of detecting vulnerable aneurysms. Subarachnoid hemorrhage is the consequence of aneurysm rupture and approximately 12% of patients with SAH die before receiving medical attention, 40% of patients will die within the first month, and 30% will present with a severe permanent disability. Nevertheless, with brain imaging being more frequently and widely used, a growing number of intracranial aneurysms are being diagnosed, introducing the question of which aneurysms harbor a sufficiently high risk of rupture to merit a prophylactic repair. This question remains unsolved at the moment and the therapeutic decision for an unruptured aneurysm is still a challenging point discussed by the neurosurgeon/neurointerventionist based on sparse epidemiologic clinical data that cannot represent the specific individual risk of the patient.Recent publications have addressed this issue and have demonstrated that, among other variables affecting the natural history of aneurysms, size and location represent independent predictors of both risk of rupture and surgical/endovascular repair outcomes.^2,3 Other parameters, such as irregular aneurysm shape and the presence of blebs are recognized as markers of weak wall structure and high risk of rupture. Rapid aneurysm growth is also likely a risk factor for rupture.⁴From a mechanical point of view, the rupture of an aneurysm occurs when wall tension exceeds the strength of the wall tissue. Because these quantities cannot be assessed via conventional medical imaging, a natural approach is to compute the wall tension and set a rupture threshold.Few studies consider the coupled fluid-structure interaction (FSI) problem, where the flow equations for blood are solved together with the structural equations for the tissue.⁵ The problem is the lack of data on mechanical properties of cerebral arteries and aneurysms; most of the studies based on an FSI^6–10 framework do not use experimental mechanical behavior of the aneurysm wall as input. A few exceptions exist for abdominal aorta aneurysms^11,12 but not for intracranial aneurysms until recently when, in a study by Costalat et al,¹³ the aneurysm wall properties were characterized and a classification of aneurysm wall behavior was carried out. One of the main conclusions of this work was that the clinical status of the aneurysm (unruptured, preruptured, and ruptured) was strongly correlated with the mechanical behavior of the aneurysm wall and, hence, a classification was proposed (stiff, intermediate, and soft).This was followed with FSI computations by Sanchez et al,¹⁴ who demonstrated for 1 specific aneurysm that the different mechanical properties of the aneurysm wall (stiff or soft) are responsible for significantly different variations in aneurysm volume over the cardiac cycle (pulsatility). A parametric study was also achieved in this work and demonstrated that uncertainties did not change the main conclusion.The further application of these results to the in vivo setting and in particular to cerebral aneurysms arising from the circle of Willis is an additional important step.The aim of this work was to investigate and verify the correlation between wall biomechanical properties (stiff and soft) and aneurysmal volume variation during the cardiac cycle for a variety of aneurysms that differ in shape and location in the circle of Willis.This study was conceived and carried out as part of the Individual Risk of Rupture Assessment consortium, which is a research project dedicated to the evaluation of patient-specific risk of rupture of cerebral aneurysms. The consortium brings together neurosurgeons, neuroradiologists, and researchers in biomechanical engineering in a common translational research project.     

Age related changes of human aortic distensibility: evaluation with ECG-gated CT

Aortic distensibility is a parameter to grade vascular diseases and age-related effects because it is related to the elastic properties of the vessel wall. In this study vascular cross-sectional area changes have been determined using ECG-gated CT to analyse the age dependency of aortic distensibility. Distensibility measurements of the aorta were performed in 31 subjects (28 to 85 years). Time-resolved images were acquired either with a 4- or 16-detector row CT system using a modified CT angiography protocol. Cross-sectional area changes of the aorta were calculated by semiautomatic segmentation, and distensibility values were obtained using additional systemic blood pressure measurements. The aorta could be segmented successfully in all subjects. A decrease of aortic distensibility with age was found (r=0.50). Below (above) the renal arteries, the annual decrease was Δ D _infrarenal =(−2.1±0.7)·10⁻⁷ Pa⁻¹a⁻¹, (D _suprarenal Δ=(−3.5±1.1)·10⁻⁷ Pa⁻¹a⁻¹). Differences between the ages, the youngest third and oldest third studied, were found to be significant (P _suprarenal =0.003; P _infrarenal =0.025). An age-dependent decrease of aortic wall elasticity can be determined in a modified routine CT angiography study.     

Assessment of macrophage infiltration in a Murine model of abdominal aortic aneurysm

Purpose

To evaluate the use of an ultrasmall superparamagnetic iron oxide (USPIO) contrast agent as a marker for the detection of macrophage in a preclinical abdominal aortic aneurysm animal (AAA) model.

Materials and Methods

Osmotic pumps were implanted subcutaneously in apoE^?/? mice for continuous infusion of Angiotensin II (Ang‐II). Weekly bright‐blood gradient echo scans were performed on the suprarenal abdominal aorta to evaluate aneurysm development. Once an AAA was detected, animals were administered 1000 μmol/kg of the USPIO contrast agent ferumoxtran‐10 (Combidex®) followed by in vivo scanning 24 h post‐USPIO administration. After in vivo imaging, aortas were harvested for ex vivo imaging, histology, iron quantification, and gene expression analysis.

Results

Reduced signal intensity was evident in the post‐USPIO transverse images of the abdominal aorta. The areas of reduced signal were primarily along the aneurysm shoulder and outer perianeurysm areas and corresponded to regions of macrophage infiltration and colocalized USPIO determination by means of histological staining. The absolute iron content measured significantly correlated to the area of signal reduction in the ex vivo images (r = 0.9; P < 0.01). In the AAA tissue, the macrophage‐driven cytokine gene expression was up‐regulated along with a matrix metalloproteinase known to mediate extracellular matrix breakdown in this disease model.

Conclusion

These results demonstrate the feasibility of using an USPIO contrast agent as a surrogate for detecting the acute inflammatory process involved in the development of abdominal aneurysms. J. Magn. Reson. Imaging 2009;30:455–460. Published by Wiley‐Liss, Inc.

     

Enhanced Aneurysmal Flow Diversion Using a Dynamic Push-Pull Technique: An Experimental and Modeling Study

BACKGROUND AND PURPOSE:Neurovascular flow diverters are flexible, braided stent-meshes for intracranial aneurysm treatment. We applied the dynamic push-pull technique to manipulate the flow-diverter mesh density at the aneurysm orifice to maximize flow diversion. This study investigated the hemodynamic impact of the dynamic push-pull technique on patient-specific aneurysms by using the developed high-fidelity virtual-stenting computational modeling technique combined with computational fluid dynamics.MATERIALS AND METHODS:We deployed 2 Pipeline Embolization Devices into 2 identical sidewall anterior cerebral artery aneurysm phantoms by using the dynamic push-pull technique with different delivery-wire advancements. We then numerically simulated these deployment processes and validated the simulated mesh geometry. Computational fluid dynamics analysis was performed to evaluate detailed hemodynamic changes by deployed flow diverters in the sidewall aneurysm and a fusiform basilar trunk aneurysm (deployments implemented previously). Images of manipulated flow diverter mesh from sample clinical cases were also evaluated.RESULTS:The flow diverters deployed in silico accurately replicated in vitro geometries. Increased delivery wire advancement (21 versus 11 mm) by using a dynamic push-pull technique produced a higher mesh compaction at the aneurysm orifice (50% metal coverage versus 36%), which led to more effective aneurysmal inflow reduction (62% versus 50% in the sidewall aneurysm; 57% versus 36% in the fusiform aneurysm). The dynamic push-pull technique also caused relatively lower metal coverage along the parent vessel due to elongation of the flow diverter. High and low mesh compactions were also achieved for 2 real patients by using the dynamic push-pull technique.CONCLUSIONS:The described dynamic push-pull technique increases metal coverage of pure braided flow diverters over the aneurysm orifice, thereby enhancing the intended flow diversion, while reducing metal coverage along the parent vessel to prevent flow reduction in nearby perforators.

Used for intracranial aneurysm treatment, a neurovascular flow diverter (FD) is a braided stent-mesh device highly flexible in stretch and compression. A bench top study showed that an FD can form varied mesh densities through longitudinal compression,¹ consistent with our recent findings.² Meanwhile, there are concerns with using FDs in perforator-rich territories due to the likely occlusion of small vessel ostia. While increased mesh density at the aneurysm orifice may help aneurysmal flow reduction, it would be beneficial for the mesh density to be reducible in perforator-rich regions to preserve the perforators and branch vessels.We used the dynamic push-pull technique (DPPT) to effectively control the local FD mesh density. The concept of dynamic push-pull was originally introduced to keep the laser-cut stent at vessel centerline during its deployment.³ It was later extensively used in FD deployment to achieve complete opening and good wall apposition at highly curved locations.^4,5 Here, we further extended the technique, targeting flow control with the following objectives: 1) to adjust for the distal foreshortening of the FD, 2) to optimize the mesh density across the aneurysm neck to increase flow diversion, and 3) to decrease the mesh density to avoid occlusion of perforator ostia and branch vessels. The deployment technique involves individually varying the push and pull of the microcatheter and the delivery wire to control the FD mesh density and the positioning.To examine the DPPT in detail, we used in vitro testing and numerical modeling. Due to the limited resolution of current clinical angiography, it is still difficult to visualize and characterize the real-time FD deployment in patients. However, simulations of FD deployment and aneurysmal hemodynamics allow us to visualize, verify, and better understand the DPPT operation, which represents a significant advancement in intracranial aneurysm intervention.We have recently developed a finite-element-analysis workflow,⁶ referred to as the high-fidelity virtual stent-placement method. A follow-up study validated it through FD deployment in a fusiform phantom,² where DPPT was used on 2 FDs in 2 identical fusiform (basilar artery) aneurysm phantoms for differential mesh densities. We did not verify the posttreatment hemodynamic changes and did not investigate sidewall aneurysm morphology. In the current study, we further applied DPPT for the sidewall anterior cerebral artery aneurysm both experimentally and numerically. Computational fluid dynamics analyses were then performed in all 4 flow-diversion scenarios, including the sidewall and the previously deployed fusiform morphologies to evaluate the hemodynamic impact of DDPT on intra-aneurysmal flow.     

Preliminary results of the luna aneurysm embolization system in a rabbit model: a new intrasaccular aneurysm occlusion device

BACKGROUND AND PURPOSE:Recent advances in endovascular devices have been aimed at providing high density, mesh-like metallic materials across the aneurysm neck, in place of coil technology. Therefore our aim was to report the in vivo preclinical performance of a self-expanding intrasaccular embolization device.MATERIALS AND METHODS:Elastase-induced aneurysms were created in 12 rabbits. Each aneurysm was embolized with a Luna AES. DSA was performed preimplantation; 5, 10, and 30 minutes postimplantation; and at 1 month in 12 rabbits and at 3 months in 8 rabbits. Early postimplantation intra-aneurysmal flow was graded as unchanged, moderately diminished, or completely absent. One- and 3-month DSAs were graded by using a 3-point scale (complete, near-complete, or incomplete occlusion). Aneurysms were harvested for gross and microscopic histologic evaluation at 1 month (n = 4) and at 3 months (n = 8). Tissues within the aneurysm dome and across the aneurysm neck were assessed by using HE staining.RESULTS:Ten (83%) of 12 aneurysms demonstrated complete cessation of flow within 30 minutes of device implantation. At 1-month follow-up, 10 (83%) of 12 aneurysms were completely occluded. At 3 months, 7 of 8 (88%) aneurysms remained completely occluded. One-month gross examination in 4 rabbits demonstrated that membranous tissue completely covered the device in 3 subjects (75%). Microscopic examination showed that 3 aneurysms had loose connective tissue filling the aneurysm cavity. Three-month gross and microscopic examinations demonstrated membranous tissue completely covering the device, loose connective tissue filling the aneurysm cavity, and neointima formation crossing the aneurysm neck in 8 of 8 (100.0%) subjects.CONCLUSIONS:The Luna AES achieved high rates of complete angiographic occlusion and showed promising histologic findings in the rabbit aneurysm model.

The goals of endovascular procedures for the treatment of cerebral aneurysms are to exclude the aneurysm sac from the cerebral arterial circulation and preserve parent vessel patency. There are 2 main categories of endovascular aneurysm treatment, intrasaccular and endoluminal procedures.The safety and efficacy of intrasaccular detachable coil embolization is well documented^1–3 but has limitations. Even with evolving procedural techniques and technology, the rate of aneurysmal total occlusion remains suboptimal.^4,5 The prevalence of coil compaction, which results in posttreatment recanalization and recurrence, is frequent.^4,6,7Conceptually, endoluminal flow diverters direct blood flow away from the aneurysm cavity primarily by placing a stent-like device across the aneurysm neck. However, flow diverters have had limited clinical utility, though they have shown excellent occlusion rates, even in large and giant aneurysms.^8–12 These devices may remain problematic in ruptured aneurysms, not only because they require concomitant use of dual antiplatelet therapy but also because immediate aneurysm occlusion usually does not occur. Furthermore, there are drawbacks when placing these devices in bifurcation aneurysms due to the inherent design limitations.In the present study, we describe the in vivo performance of a new type of embolization device. This new device, the Luna AES (NFocus Neuromedical, Palo Alto, California) is a self-expanding ovoid braided implant that when placed into an aneurysm cavity, provides an attenuated mesh of metal across the neck. The purpose of this study was to evaluate the safety, performance, and efficacy of the Luna AES in the rabbit elastase-induced aneurysm model.