High levels of 18F-FDG uptake in aortic aneurysm wall are associated with high wall stress

Can Biomarkers and PET Imaging Predict Abdominal Aortic Aneurysm Growth Rate?

Background: Abdominal aortic aneurysm (AAA) is a life-threatening condition due to the risk of aneurysm growth and rupture. Biomarkers linked to AAA pathogenesis are attractive candidates for AAA diagnosis and prognosis. The aim of this study was to assess circulating biomarkers levels relationship with PET imaging positivity and their predictive value in AAA growth rate. Methods: A total of 164 patients with AAA had whole body [18F]FDG PET/CT examination and blood drawn for biomarkers analysis at inclusion. Of these, 121 patients had at least one follow-up imaging assessment for AAA progression. Median (quartiles) imaging follow-up period was 32.8 months (15.2-69.6 months). Results: At baseline, PET was visually positive in 28 (17%) patients. Among PET+ patients, female proportion was higher compared to PET-patients (respectively, n = 6, 21.4% vs. n = 11, 8.1%, p = 0.046). Biomarkers of inflammation (CRP, CCL18), of proteolytic activity (MMP9), of extracellular matrix, and calcification regulation (OPN, OPG) were all significantly increased in PET+ patients (p < 0.05). During follow-up, rapid AAA growth (increase in size ≥ 1 cm per year) was observed in 36 (29.8%) patients and several biomarkers (CRP, MMP9, OPN, and OPG) were increased in those patients compared to patients without rapid growth (p < 0.05). Conclusions: Although PET positivity at baseline was not associated with rapid growth, CRP levels showed a significant association.

Significant thrombus in saccular aneurysm in a patient with polycythemia: a case report

BACKGROUND

Morphologically, the risk of aortic aneurysm rupture is mainly evaluated based on its type (e.g., fusiform or saccular) and diameter. Based on the finite element analysis, peak wall stress has been identified as a more sensitive and specific predictor of rupture in recent years. Moreover, in finite analysis, the neck of aneurysm is the highest peak wall stress and is associated with the rupture point.

CASE PRESENTATION

A saccular aortic aneurysm (84 mm) was incidentally detected during preoperative examination for chronic empyema in a 74-year-old male patient with a history of polycythemia. Aortic arch graft replacement using an open stent was performed.

CONCLUSIONS

Morphologically, this case was associated with a very high risk of rupture; nevertheless, it did not rupture. In this case, a mural thrombus (likely formed due to polycythemia) covered the neck of aneurysm that is experiencing the highest peak wall stress and is associated with the rupture point. The mural thrombus decreased peak wall stress and could reduce the risk of rupture even for huge saccular aneurysms. Furthermore, the mural thrombus was fully occupied in aneurysms, such as during coil embolization. Thus, polycythemia could decrease the risk of rupture of huge saccular aneurysms.

A preliminary study of relationship among the degree of internal carotid artery stenosis, wall shear stress on MR angiography and 18F-FDG uptake on PET/CT

BACKGROUND

This preliminary study was undertaken to evaluate relationship among the degree of internal carotid artery (ICA) stenosis, wall shear stress (WSS) by computational fluid dynamics (CFD) on magnetic resonance angiography (MRA) and 18F-FDG uptake of ICA on PET/CT.

METHODS

A total of 40 carotid arteries in 20 patients with carotid atherosclerotic disease were examined with MRA and 18F-FDG PET/CT. Atherosclerotic risk factors were assessed in all patients. Degree of ICA stenosis was calculated according to NASCET method. CFD analysis was performed and maximum WSS (WSSmax) was measured. 18F-FDG uptake in ICA was quantified using maximum target-to-blood pool ratio (TBRmax).

RESULTS

Atherosclerotic risk factors did not affect imaging findings. There were significant correlations between WSSmax and degree of ICA stenosis (ρ = .81, P < .001), WSSmax and TBRmax (ρ = .64, P < .001), and TBRmax and degree of ICA stenosis (ρ = .50, P = .001).

CONCLUSIONS

These preliminary results indicate that there may be significant correlations among the degree of ICA stenosis, WSSmax and TBRmax in patients with carotid artery stenosis.

A stable aneurysm sac after endovascular aneurysm repair as a predictor for mortality, an in-depth analysis

OBJECTIVES

The aim of this study was to compare the long-term survival in patients with a stable aneurysmal sac and those with aneurysmal sac regression after endovascular aneurysm repair (EVAR) and to identify independent risk factors for aneurysmal sac regression and mortality after EVAR.

METHODS

We reviewed all patients who underwent EVAR between 2005 and 2018 with a computed tomography angiography available at 1-year follow-up. Aneurysm sac regression was defined as a diameter decrease of more than 10%. We used a multivariable regression to identify independent risk factors for sac regression. Kaplan-Meier analysis and Cox regression were done to test differences in 5-year mortality between a stable sac and sac regression.

RESULTS

The inclusion criteria were met by 325 patients, 185 in the sac regression group and 140 in the stable sac group. Multivariable logistic regression analysis showed that treatment for a ruptured aneurysm was an independent risk factor for aneurysmal sac regression (hazard ratio [HR], 0.26; 95% confidence interval [CI], 0.07-0.96). Age (HR, 1.05; 95% CI, 1.01-1.09), ischemic heart disease (HR, 1.94; 95% CI, 1.13-3.31), neck thrombus (HR, 2.72; 95% CI, 1.07-6.95), and a type II endoleak (HR, 19.21; 95% CI, 7.32-50.40) were independent risk factors for a stable aneurysm sac diameter. Multivariable Cox regression showed a significantly increased risk of mortality for patients with a stable aneurysm sac after EVAR (odds ratio, 2.25; 95% CI, 1.36-3.72). There was no significant difference in cause of death between the two groups.

CONCLUSION

A stable aneurysm sac after EVAR is associated with increased mortality. Age, ischemic heart disease, neck thrombus, and a type II endoleak are independent risk factors for a stable sac. However, a well-founded explanation for this finding is still lacking. Future research should be focussed on aggressive treatment of type II endoleaks and inflammatory processes as potential pathophysiological mechanisms.

Prospect of positron emission tomography for abdominal aortic aneurysm risk stratification

Abdominal aortic aneurysm (AAA) disease is characterized by an asymptomatic, permanent, focal dilatation of the abdominal aorta progressing towards rupture, which confers significant mortality. Patient management and surgical decisions rely on aortic diameter measurements via abdominal ultrasound surveillance. However, AAA rupture can occur at small diameters or may never occur at large diameters, implying that anatomical size is not necessarily a sufficient indicator. Molecular imaging may help identify high-risk patients through AAA evaluation independent of aneurysm size, and there is the question of the potential role of positron emission tomography (PET) and emerging role of novel radiotracers for AAA. Therefore, this review summarizes PET studies conducted in the last 10 years and discusses the usefulness of PET radiotracers for AAA risk stratification. The most frequently reported radiotracer was [18F]fluorodeoxyglucose, indicating inflammatory activity and reflecting the biomechanical properties of AAA. Emerging radiotracers include [18F]-labeled sodium fluoride, a calcification marker, [64Cu]DOTA-ECL1i, an indicator of chemokine receptor type 2 expression, and [18F]fluorothymidine, a marker of cell proliferation. For novel radiotracers, preliminary trials in patients are warranted before their widespread clinical implementation. AAA rupture risk is challenging to evaluate; therefore, clinicians may benefit from PET-based risk assessment to guide patient management and surgical decisions.

Intraluminal thrombus: Innocent bystander or factor in abdominal aortic aneurysm pathogenesis?

BACKGROUND

Abdominal aortic aneurysms (AAAs) represent a complex multifactorial hemodynamic, thrombotic, and inflammatory process that can ultimately result in aortic rupture and death. Despite improved screening and surgical management of AAAs, the mortality rates have remained high after rupture, and little progress has occurred in the development of nonoperative treatments. Intraluminal thrombus (ILT) is present in most AAAs and might be involved in AAA pathogenesis. The present review examined the latest clinical and experimental evidence for possible involvement of the ILT in AAA growth and rupture.

METHODS

A literature review was performed after a search of the PubMed database from 2012 to June 2020 using the terms "abdominal aortic aneurysm" and "intraluminal thrombus."

RESULTS

The structure, composition, and hemodynamics of ILT formation and propagation were reviewed in relation to the hemostatic and proteolytic factors favoring ILT deposition. The potential effects of the ILT on AAA wall degeneration and rupture, including a review of the current controversies regarding the position, thickness, and composition of ILT, are presented. Although initially potentially protective against increased wall stress, increasing evidence has shown that an increased volume and greater age of the ILT have direct detrimental effects on aortic wall integrity, which might predispose to an increased rupture risk.

CONCLUSIONS

ILT does not appear to be an innocent bystander in AAA pathophysiology. However, its exact role remains elusive and controversial. Despite computational evidence of a possible protective role of the ILT in reducing wall stress, increasing evidence has shown that the ILT promotes AAA wall degeneration in humans and in animal models. Further research, with large animal models and with more chronic ILT is crucial for a better understanding of the role of the ILT in AAAs and for the potential development of targeted therapies to slow or halt AAA progression.

Imaging Predictive Factors of Abdominal Aortic Aneurysm Growth

Background: Variable imaging methods may add important information about abdominal aortic aneurysm (AAA) progression. The aim of this study is to assess available literature data regarding the predictive imaging factors of AAA growth. Methods: This systematic review was conducted using the PRISMA guidelines. A review of the literature was conducted, using PubMed, EMBASE and CENTRAL databases. The quality of the studies was assessed using the Newcastle-Ottawa Scale. Primary outcomes were defined as AAA growth rate and factors associated to sac expansion. Results: The analysis included 23 studies. All patients (2244; mean age; 69.8 years, males; 85%) underwent imaging with different modalities; the initial evaluation was followed by one or more studies to assess aortic expansion. AAA initial diameter was reported in 13 studies (range 19.9–50.9 mm). Mean follow-up was 34.5 months. AAA diameter at the end was ranging between 20.3 and 55 mm. The initial diameter and intraluminal thrombus were characterized as prognostic factors associated to aneurysm expansion. A negative association between atherosclerosis and AAA expansion was documented. Conclusions: Aneurysm diameter is the most studied factor to be associated with expansion and the main indication for intervention. Appropriate diagnostic modalities may account for different anatomical characteristics and identify aneurysms with rapid growth and higher rupture risk. Future perspectives, including computed mathematical models that will assess wall stress and elasticity and further flow characteristics, may offer valuable alternatives in AAA growth prediction.

Global Sensitivity Analysis for Patient-Specific Aortic Simulations: The Role of Geometry, Boundary Condition and Large Eddy Simulation Modeling Parameters

Numerical simulations for computational hemodynamics in clinical settings require a combination of many ingredients, mathematical models, solvers and patient-specific data. The sensitivity of the solutions to these factors may be critical, particularly when we have a partial or noisy knowledge of data. Uncertainty quantification is crucial to assess the reliability of the results. We present here an extensive sensitivity analysis in aortic flow simulations, to quantify the dependence of clinically relevant quantities to the patient-specific geometry and the inflow boundary conditions. Geometry and inflow conditions are generally believed to have a major impact on numerical simulations. We resort to a global sensitivity analysis, (i.e., not restricted to a linearization around a working point), based on polynomial chaos expansion (PCE) and the associated Sobol' indices. We regard the geometry and the inflow conditions as the realization of a parametric stochastic process. To construct a physically consistent stochastic process for the geometry, we use a set of longitudinal-in-time images of a patient with an abdominal aortic aneurysm (AAA) to parametrize geometrical variations. Aortic flow is highly disturbed during systole. This leads to high computational costs, even amplified in a sensitivity analysis -when many simulations are needed. To mitigate this, we consider here a large Eddy simulation (LES) model. Our model depends in particular on a user-defined parameter called filter radius. We borrowed the tools of the global sensitivity analysis to assess the sensitivity of the solution to this parameter too. The targeted quantities of interest (QoI) include: the total kinetic energy (TKE), the time-average wall shear stress (TAWSS), and the oscillatory shear index (OSI). The results show that these indexes are mostly sensitive to the geometry. Also, we find that the sensitivity may be different during different instants of the heartbeat and in different regions of the domain of interest. This analysis helps to assess the reliability of in silico tools for clinical applications.

Greater aortic inflammation and calcification in abdominal aortic aneurysmal disease than atherosclerosis: a prospective matched cohort study

Objective

Using combined positron emission tomography and CT (PET-CT), we measured aortic inflammation and calcification in patients with abdominal aortic aneurysms (AAA), and compared them with matched controls with atherosclerosis.

Methods

We prospectively recruited 63 patients (mean age 76.1±6.8 years) with asymptomatic aneurysm disease (mean size 4.33±0.73 cm) and 19 age-and-sex-matched patients with confirmed atherosclerosis but no aneurysm. Inflammation and calcification were assessed using combined 18F-FDG PET-CT and quantified using tissue-to-background ratios (TBRs) and Agatston scores.

Results

In patients with AAA, 18F-FDG uptake was higher within the aneurysm than in other regions of the aorta (mean TBRmax2.23±0.46 vs 2.12±0.46, p=0.02). Compared with atherosclerotic control subjects, both aneurysmal and non-aneurysmal aortae showed higher 18F-FDG accumulation (total aorta mean TBRmax2.16±0.51 vs 1.70±0.22, p=0.001; AAA mean TBRmax2.23±0.45 vs 1.68±0.21, p<0.0001). Aneurysms containing intraluminal thrombus demonstrated lower 18F-FDG uptake within their walls than those without (mean TBRmax2.14±0.43 vs 2.43±0.45, p=0.018), with thrombus itself showing low tracer uptake (mean TBRmax thrombus 1.30±0.48 vs aneurysm wall 2.23±0.46, p<0.0001). Calcification in the aneurysmal segment was higher than both non-aneurysmal segments in patients with aneurysm (Agatston 4918 (2901-8008) vs 1017 (139-2226), p<0.0001) and equivalent regions in control patients (442 (304-920) vs 166 (80-374) Agatston units per cm, p=0.0042).

Conclusions

The entire aorta is more inflamed in patients with aneurysm than in those with atherosclerosis, perhaps suggesting a generalised inflammatory aortopathy in patients with aneurysm. Calcification was prominent within the aneurysmal sac, with the remainder of the aorta being relatively spared. The presence of intraluminal thrombus, itself metabolically relatively inert, was associated with lower levels of inflammation in the adjacent aneurysmal wall.

Endovascular Aneurysm Sealing is Associated with Higher Medium-Term Survival than Traditional EVAR

BACKGROUND

Endovascular aneurysm repair (EVAR) is the dominant treatment modality for abdominal aortic aneurysm (AAA). Periprocedural risks are low, and cardiovascular events are the principle determinants of long-term survival. Recently, the concept of endovascular aneurysm sealing (EVAS) has been introduced into clinical investigation. In previous cohort studies, EVAS has been associated with a lower all-cause mortality than expected despite device issues. We used a propensity weighted approach to investigate whether EVAS was associated with lower all-cause mortality after aneurysm repair.

METHODS

We compared 333 patients in the Nellix United States Investigational Device Exemption trial to 15,431 controls from the Vascular Quality Initiative between 2014 and 2016 after applying the exclusion criteria from the investigational device exemption (hemodialysis, creatinine > 2.0 mg/dL, or rupture). We calculated propensity scores and applied inverse probability weighting to compare risk adjusted medium-term survival using Kaplan-Meier and Cox regression.

RESULTS

After weighting, patients treated with the Nellix EVAS system experienced higher 3-year survival than controls from the Vascular Quality Initiative (93% vs. 88%, respectively). This corresponded to a 41% lower risk of mortality for EVAS compared with EVAR (HR 0.59 [0.38-0.92], P = 0.02). Subgroup analysis demonstrated that the association between EVAS and higher survival was strongest in the subgroup of patients with aneurysms over 5.5 cm (P for interaction < 0.001). In this subgroup, EVAS patients experienced half the rate of mortality as those patients treated with EVAR, with 3-year survival of 92% compared with 86% (HR 0.5 [0.3-0.9], P = 0.02).

CONCLUSIONS

In this select group of patients, EVAS was associated with higher medium-term survival than traditional EVAR. Although issues with the device have recently surfaced, this exploratory analysis shows that the concept of sac sealing may hold promise. Further study is needed to confirm this finding and determine whether EVAS is associated with lower rates of cardiovascular events.

Abdominal aortic aneurysms

An abdominal aortic aneurysm (AAA) is a localized dilatation of the infrarenal aorta. AAA is a multifactorial disease, and genetic and environmental factors play a part; smoking, male sex and a positive family history are the most important risk factors, and AAA is most common in men >65 years of age. AAA results from changes in the aortic wall structure, including thinning of the media and adventitia due to the loss of vascular smooth muscle cells and degradation of the extracellular matrix. If the mechanical stress of the blood pressure acting on the wall exceeds the wall strength, the AAA ruptures, causing life-threatening intra-abdominal haemorrhage - the mortality for patients with ruptured AAA is 65-85%. Although AAAs of any size can rupture, the risk of rupture increases with diameter. Intact AAAs are typically asymptomatic, and in settings where screening programmes with ultrasonography are not implemented, most cases are diagnosed incidentally. Modern functional imaging techniques (PET, CT and MRI) may help to assess rupture risk. Elective repair of AAA with open surgery or endovascular aortic repair (EVAR) should be considered to prevent AAA rupture, although the morbidity and mortality associated with both techniques remain non-negligible.

Role of PET/CT in the Evaluation of Aortic Disease

Positron emission tomography (PET) /computed tomography (CT) has been established as a standard imaging modality in the evaluation of malignancy. Although PET/CT has played a major role in the management of oncology patients, its clinical use has also increased for various disorders other than malignancy. Growing evidence shows that PET/CT images have many advantages in aortic disease as well. This review article addresses the potential role of PET/CT in diseases involving the aorta, emphasizing its usefulness with regard to acute thoracic aortic syndromes, aortic aneurysm, atherosclerotic lesions, aortitis and aortic tumors.

Relationship between inflammation and progression of an abdominal aortic aneurysm in a rabbit model based on 18F-FDG PET/CT imaging

OBJECTIVE

To explore the relationship between abdominal aortic aneurysm development and inflammation in the rabbit through the establishment of a rabbit infrarenal abdominal aortic aneurysm model and the use of 18F-FDG PET/CT imaging.

METHODS

Twenty male New Zealand rabbits were administered an elastase intracavity perfusion to induce an infrarenal abdominal aortic aneurysm model. Prior to surgery, the rabbits underwent abdominal aorta ultrasonic testing and blood collection from the ear veins. Of the original 20 rabbits, 10 rabbits were euthanized two weeks after the operation following ultrasonic testing, PET/CT scanning and blood collection, and their arterial tissue samples were prepared for pathological and immunohistochemical staining. The remaining 10 rabbits were euthanized four weeks after the operation following ultrasonic testing, PET/CT scanning and blood collection, and the arterial tissue samples were prepared for pathological and immunohistochemical staining.

RESULTS

Compared with the preoperative measurement, the maximum growth rate of the aneurysm diameter is 89.21 ± 0.02% (the absolute increase in diameter is 2.040 ± 0.376 mm) two weeks after the operation. Compared with the two-week postoperative value, the maximum growth rate of the aneurysm diameter is 15.8 ± 0.01% (the absolute increase in diameter is 0.684 ± 0.115 mm) four weeks after the operation. Compared with the preoperative values, the blood MMP-2 and MMP-9 levels significantly increase two weeks after surgery, P < 0.05. Compared with the two-week postoperative values, the blood MMP-2 and MMP-9 levels significantly decrease after four weeks post-surgery, P < 0.05. At two weeks after the operation, the SUVmax and the TBR of the 18F-FDG PET/CT of the AAA wall are 0.90 ± 0.03 and 1.19 ± 0.09, respectively. At four weeks after the operation, the SUVmax and the TBR of the 18F-FDG PET/CT of the AAA wall are 0.35 ± 0.05 and 1.15 ± 0.12, respectively. Compared with two weeks after the operation, the SUVmax significantly decreases at four weeks after the operation, P < 0.05. Compared with two weeks after the operation, there is no significant difference in the TBR at four weeks after the operation, P > 0.05. Immunohistochemical staining shows that the CD68-positive cell rate at four weeks after the operation significantly decreases ( P < 0.05) compared with the CD68-positive cell rate at two weeks after the operation.

CONCLUSION

In the early stages of abdominal aortic aneurysm development, the inflammatory response of the arterial wall is significant, the local metabolic activity is strengthened, the SUVmax value of 18F-FDG is high, and the abdominal aortic aneurysm diameter experiences rapid growth. In the later stages of abdominal aortic aneurysm development, the diameter continues to increase; however, there are decreases in the wall inflammatory response, the local metabolic activity, and the SUVmax value of 18F-FDG. Thus, inflammation plays an important role in the early development of abdominal aortic aneurysm.

Molecular targets in aortic aneurysm for establishing novel management paradigms

Aortic aneurysm (AA) is a lethal disease and presents a large challenge for surgeons in the clinic. Although surgical management remains the major choice of AA, operative mortality remains high. With advances in understanding of the mechanisms of AAs, molecular targets, such as matrix metalloproteinases (MMPs), D-dimer, and inflammation markers, including C-reactive protein, interleukins and phagocytes, are important in the pathology of development of AA. These markers may become important for improving the diagnostic quality and provide more therapeutic choices for treatment of AA. Although these new markers require long-term trials before they can be translated into the clinic, they can still be helpful in determining new directions. The main aim of this review is to discuss the current findings of molecular targets in progression of AA and discuss the potential application of these new targets for managing this disease.

Exploring the Biological and Mechanical Properties of Abdominal Aortic Aneurysms Using USPIO MRI and Peak Tissue Stress: A Combined Clinical and Finite Element Study

Inflammation detected through the uptake of ultrasmall superparamagnetic particles of iron oxide (USPIO) on magnetic resonance imaging (MRI) and finite element (FE) modelling of tissue stress both hold potential in the assessment of abdominal aortic aneurysm (AAA) rupture risk. This study aimed to examine the spatial relationship between these two biomarkers. Patients (n = 50) > 40 years with AAA maximum diameters > = 40 mm underwent USPIO-enhanced MRI and computed tomography angiogram (CTA). USPIO uptake was compared with wall stress predictions from CTA-based patient-specific FE models of each aneurysm. Elevated stress was commonly observed in areas vulnerable to rupture (e.g. posterior wall and shoulder). Only 16% of aneurysms exhibited co-localisation of elevated stress and mural USPIO enhancement. Globally, no correlation was observed between stress and other measures of USPIO uptake (i.e. mean or peak). It is suggested that cellular inflammation and stress may represent different but complimentary aspects of AAA disease progression.

High Structural Stress and Presence of Intraluminal Thrombus Predict Abdominal Aortic Aneurysm 18F-FDG Uptake: Insights From Biomechanics

Supplemental Digital Content is available in the text.

Background—

Abdominal aortic aneurysm (AAA) wall inflammation and mechanical structural stress may influence AAA expansion and lead to rupture. We hypothesized a positive correlation between structural stress and fluorine-18-labeled 2-deoxy-2-fluoro-d-glucose (¹⁸F-FDG) positron emission tomography–defined inflammation. We also explored the influence of computed tomography–derived aneurysm morphology and composition, including intraluminal thrombus, on both variables.

Methods and Results—

Twenty-one patients (19 males) with AAAs below surgical threshold (AAA size was 4.10±0.54 cm) underwent ¹⁸F-FDG positron emission tomography and contrast-enhanced computed tomography imaging. Structural stresses were calculated using finite element analysis. The relationship between maximum aneurysm ¹⁸F-FDG standardized uptake value within aortic wall and wall structural stress, patient clinical characteristics, aneurysm morphology, and compositions was explored using a hierarchical linear mixed-effects model. On univariate analysis, local aneurysm diameter, thrombus burden, extent of calcification, and structural stress were all associated with ¹⁸F-FDG uptake (P<0.05). AAA structural stress correlated with ¹⁸F-FDG maximum standardized uptake value (slope estimate, 0.552; P<0.0001). Multivariate linear mixed-effects analysis revealed an important interaction between structural stress and intraluminal thrombus in relation to maximum standardized uptake value (fixed effect coefficient, 1.68 [SE, 0.10]; P<0.0001). Compared with other factors, structural stress was the best predictor of inflammation (receiver-operating characteristic curve area under the curve =0.59), with higher accuracy seen in regions with high thrombus burden (area under the curve =0.80). Regions with both high thrombus burden and high structural stress had higher ¹⁸F-FDG maximum standardized uptake value compared with regions with high thrombus burdens but low stress (median [interquartile range], 1.93 [1.60–2.14] versus 1.14 [0.90–1.53]; P<0.0001).

Conclusions—

Increased aortic wall inflammation, demonstrated by ¹⁸F-FDG positron emission tomography, was observed in AAA regions with thick intraluminal thrombus subjected to high mechanical stress, suggesting a potential mechanistic link underlying aneurysm inflammation.

Multifocal Intrahepatic Artery Aneurysm with FDG-avid Thrombosis Simulating Metastasis: Report of a Rare Case

Hepatic artery aneurysm (HAA), although rare, represents a serious diagnostic and therapeutic challenge due to high rupture rate and associated mortality. Early detection and accurate diagnosis are essential for successful management. Here, we present an extremely rare case of multi-focal intrahepatic HAA with confined intrahepatic rupture and hypermetabolic activity at PET imaging, simulating metastasis of melanoma. A retrospective review found only two other HAA at our institution between 2000 and 2015, both of which involved the extrahepatic artery. This report highlights the importance of clinical, radiological, and pathological correlation in the management of this rare condition.

Increased Expression of Lamin A/C Correlate with Regions of High Wall Stress in Abdominal Aortic Aneurysms

BACKGROUND

Since aortic diameter is the most -significant risk factor for rupture, we sought to identify stress-dependent changes in gene expression to illuminate novel molecular processes in aneurysm rupture.

MATERIALS AND METHODS

We constructed finite element maps of abdominal computerized tomography scans (CTs) of seven abdominal aortic aneurysm (AAA) patients to map wall stress. Paired biopsies from high- and low-stress areas were collected at surgery using vascular landmarks as coordinates. Differential gene expression was evaluated by Illumina Array analysis, using the whole genome DNA-mediated, annealing, selection, extension, and ligation (DASL) gene chip (n = 3 paired samples).

RESULTS

The sole significant candidate from this analysis, Lamin A/C, was validated at the protein level, using western blotting. Lamin A/C expression in the inferior mesenteric vein (IMV) of AAA patients was compared to a control group and in aortic smooth muscle cells in culture in response to physiological pulsatile stretch. -Areas of high wall stress (n = 7) correlate to those -regions which have the thinnest walls [778 µm (585-1120 µm)] in comparison to areas of lowest wall stress [1620 µm (962-2919 µm)]. Induced expression of Lamin A/C -correlated with areas of high wall stress from AAAs but was not significantly induced in the IMV from AAA patients compared to controls (n = 16). Stress-induced expression of Lamin A/C was mimicked by exposing aortic smooth muscle cells to prolonged pulsatile stretch.

CONCLUSION

Lamin A/C protein is specifically increased in areas of high wall stress in AAA from patients, but is not increased on other vascular beds of aneurysm patients, suggesting that its elevation may be a compensatory response to the pathobiology leading to aneurysms.

Identification of early vascular calcification with (18)F-sodium fluoride: potential clinical application

Vascular calcification plays a prominent role in cardiovascular disease. Once considered to be a passive consequence of aging, this pathological process is now accepted to be dynamic and tightly regulated, its onset triggered by inflammation and necrosis and its progression bearing key similarities to osteogenesis. A major potential advance in our ability to understand the natural history and clinical implications of vascular calcification is the detection of its early and dynamic stages through the use of the positron-emitting radiotracer, (18)F-sodium fluoride. Alongside anatomical information gained from computed tomography, hybrid positron emission and computed tomography (PET/CT) imaging with (18)F-sodium fluoride has, for the first time, enabled the non-invasive detection of microcalcification within the aortic valve, great vessels, and vulnerable coronary plaque. This has raised promise that exploring this process may allow improved risk prediction, better application of current therapies and ultimately the development of novel treatments to target this widespread pathology.

Positron Emission Tomography and Magnetic Resonance Imaging of Cellular Inflammation in Patients with Abdominal Aortic Aneurysms

Objectives

Inflammation is critical in the pathogenesis of abdominal aortic aneurysm (AAA) disease. Combined ¹⁸F-fludeoxyglucose (¹⁸F-FDG) positron emission tomography with computed tomography (PET-CT) and ultrasmall superparamagnetic particles of iron oxide (USPIO)-enhanced magnetic resonance imaging (MRI) are non-invasive methods of assessing tissue inflammation. The aim of this study was to compare these techniques in patients with AAA.

Materials and methods

Fifteen patients with asymptomatic AAA with diameter 46 ± 7 mm underwent PET-CT with ¹⁸F-FDG, and T2*-weighted MRI before and 24 hours after administration of USPIO. The PET-CT and MRI data were then co-registered. Standardised uptake values (SUVs) were calculated to measure ¹⁸F-FDG activity, and USPIO uptake was determined using the change in R2*. Comparisons between the techniques were made using a quadrant analysis and a voxel-by-voxel evaluation.

Results

When all areas of the aneurysm were evaluated, there was a modest correlation between the SUV on PET-CT and the change in R2* on USPIO-enhanced MRI (n = 70,345 voxels; r = .30; p < .0001). Although regions of increased ¹⁸F-FDG and USPIO uptake co-localised on occasion, this was infrequent (kappa statistic 0.074; 95% CI 0.026–0.122). ¹⁸F-FDG activity was commonly focused in the shoulder region whereas USPIO uptake was more apparent in the main body of the aneurysm. Maximum SUV was lower in patients with mural USPIO uptake.

Conclusions

Both ¹⁸F-FDG PET-CT and USPIO-MRI uptake identify vascular inflammation associated with AAA. Although they demonstrate a modest correlation, there are distinct differences in the pattern and distribution of uptake, suggesting a differential detection of macrophage glycolytic and phagocytic activity respectively.

(18)F-FDG PET scanning of abdominal aortic aneurysms and correlation with molecular characteristics: a systematic review

Purpose

The purpose of this study is to give an overview of studies investigating the role of fludeoxyglucose F18 (¹⁸F-FDG) positron emission tomography (PET) scanning in patients with aortic aneurysms with a focus on molecular characteristics of the aneurysm wall.

Methods

MEDLINE, EMBASE, and the Cochrane database were searched for relevant articles. After inclusion and exclusion, we selected 18 relevant articles reporting on ¹⁸F-FDG PET scanning of aortic aneurysms.

Results

The sample size of studies is limited, and there are no standardized imaging protocols and quantification methods. ¹⁸F-FDG PET scanning was shown to display molecular characteristics of the aortic wall. Different studies showed contradictory findings of aortic ¹⁸F-FDG uptake in aneurysm patients compared to controls.

Conclusions

Non-invasively determining molecular characteristics of aortic wall weakening might lead to better rupture and growth prediction. This might influence the decision of the surgeon between conservative and surgical treatment of aneurysms. To date, there is conflicted evidence regarding the use of ¹⁸F-FDG PET scanning to predict aneurysm rupture and growth. The role of ¹⁸F-FDG PET scanning in rupture risk prediction needs to be further investigated, and standardized imaging protocols and quantification methods need to be implemented.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-015-0153-8) contains supplementary material, which is available to authorized users.

Gene expression study in positron emission tomography-positive abdominal aortic aneurysms identifies CCL18 as a potential biomarker for rupture risk

Rupture of abdominal aortic aneurysm (AAA) is a cause of significant mortality and morbidity in aging populations. Uptake of 18-fluorodeoxyglucose (FDG) detected by positron emission tomography (PET) is observed in the wall of 12% of AAA (A+), with most of them being symptomatic. We previously showed that the metabolically active areas displayed adventitial inflammation, medial degeneration and molecular alterations prefacing wall rupture. The aim of this study was to identify new factors predictive of rupture. Transcriptomic analyses were performed in the media and adventitia layers from three types of samples: AAA with-out FDG uptake (A0) and with FDG uptake (A+), both at the positive spot (A+(Pos)) and at a paired distant negative site (A+(Neg)) of the same aneurysm. Follow-up studies included reverse-transcriptase-polymerase chain reaction (RT-PCR), immunohistochemical staining and enzyme-linked immunosorbent assay (ELISA). A large number of genes, including matrix metalloproteinases, collagens and cytokines as well as genes involved in osteochondral development, were differentially expressed in the A+(Pos) compared with A+(Neg). Moreover, a series of genes (notably CCL18) was differentially expressed both in the A+(Neg) and A+(Pos) compared with the A0. A significant increase of CCL18 was also found at the protein level in the aortic wall and in peripheral blood of A+ patients compared with A0. In conclusion, new factors, including CCL18, involved in the progression of AAA and, potentially, in their rupture were identified by a genome-wide analysis of PET-positive and -negative human aortic tissue samples. Further work is needed to study their role in AAA destabilization and weakening.

Assessing the potential risk of rupture of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) involve complex interplays between inflammatory and biomechanical factors that can be elucidated with anatomical and functional imaging. Although AAA size has been well-established in the literature to correlate with risk of rupture (and subsequent need for vascular intervention), there are other less-well-known characteristics about AAAs that also contribute to higher risk of rupture. This review focuses on biomechanical, radiological, and epidemiological characteristics of AAAs that are associated with higher rupture risk. For clinicians, knowing and considering a wide variety of risk factors in addition to AAA size is important to initiate early and proper intervention for AAA repair. Although there is no official quantitative risk score of AAA rupture risk that takes other non-size-related variables into account, if clinicians are aware of these other parameters, it is hoped that intervention can be appropriately performed for higher-risk AAAs that have not met the size-threshold for elective repair.

Functional and molecular imaging techniques in aortic aneurysm disease

PURPOSE OF REVIEW

Functional and molecular aortic imaging has shown great promise for evaluation of aortic disease, and may soon augment conventional assessment of aortic dimensions for the clinical management of patients.

RECENT FINDINGS

A range of imaging techniques is available for evaluation of patients with aortic disease. Magnetic resonance blood flow imaging can identify atherosclerosis prone aortic regions and may be useful for predicting aneurysm growth. Computational modeling can demonstrate significant differences in wall stress between abdominal aortic aneurysms of similar size and may better predict rupture than diameter alone. Metabolic imaging with fluorodeoxyglucose-PET [(FDG)-PET] can identify focal aortic wall inflammation that may portend rapid progression of disease. Molecular imaging with probes that target collagen and elastin can directly exhibit changes in the vessel wall associated with disease.

SUMMARY

The complexity of aortic disease is more fully revealed with new functional imaging techniques than with conventional anatomic analysis alone. This may better inform surveillance imaging regimens, medical management and decisions regarding early intervention for aortic disease.

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 (18)F-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.

THE IMPACT OF THE NUMBER OF TEARS IN PATIENT-SPECIFIC STANFORD TYPE B AORTIC DISSECTING ANEURYSM: CFD SIMULATION

It is believed that the progression of Stanford type B aortic dissection is closely associated with vascular geometry and hemodynamic parameters. The hemodynamic differences owing to the presence of greater than two tears have not been explored. The focus of the present study is to investigate the impact of an additional re-entry tear on the flow, pressure and wall shear stress distribution in the dissected aorta. A 3D aorta model with one entry and one re-entry tear was generated from computed tomography (CT) angiographic images of a patient with Stanford Type B aortic dissection. To investigate the hemodynamic effect of more than two tear locations, an additional circular re-entry tear was added 24 mm above the original re-entry tear. Our simulation results showed that the presence of an additional re-entry tear provided an extra return path for blood back to the true lumen during systole, and an extra outflow path into the false lumen during diastole. The presence of this additional path led to a decrease in the false lumen pressure, particularly at the distal region. Meanwhile, the presence of this additional tear causes no significant difference on the time average wall shear stress (TAWSS) distribution except at regions adjacent to re-entry tear 2. Moderate and concentrated TAWSS was observed at the bottom region of this additional tear which may lead to further extension of the tear distally.

Family members of patients with abdominal aortic aneurysms are at increased risk for aneurysms: analysis of 618 probands and their families from the Liège AAA Family Study

BACKGROUND

The objectives were to answer the following questions with the help of a well-characterized population in Liège, Belgium: 1) what percentage of patients with abdominal aortic aneurysm (AAA) have a positive family history for AAA? 2) what is the prevalence of AAAs among relatives of patients with AAA? and 3) do familial and sporadic AAA cases differ in clinical characteristics?

METHODS

Patients with unrelated AAA diagnosed at the Cardiovascular Surgery Department, University Hospital of Liège, Belgium, between 1999 and 2012 were invited to the study. A detailed family history was obtained in interviews and recorded using Progeny software. We divided the 618 patients into 2 study groups: group I, 296 patients with AAA (268; 91% men) were followed up with computerized tomography combined with positron emission tomography; and group II, 322 patients with AAA (295; 92% men) whose families were invited to ultrasonographic screening.

RESULTS

In the initial interview, 62 (10%) of the 618 patients with AAA reported a positive family history for AAA. Ultrasonographic screening identified 24 new AAAs among 186 relatives (≥50 years) of 144 families yielding a prevalence of 13%. The highest prevalence (25%) was found among brothers. By combining the number of AAAs found by ultrasonographic screening with those diagnosed previously the observed lifetime prevalence of AAA was estimated to be 32% in brothers. The familial AAA cases were more likely to have a ruptured AAA than the sporadic cases (8% vs. 2.4%; P < 0.0001).

CONCLUSIONS

The findings confirm previously found high prevalence of AAA among brothers, support genetic contribution to AAA pathogenesis, and provide rationale for targeted screening of relatives of patients with AAA.

Multifactorial relationship between 18F-fluoro-deoxy-glucose positron emission tomography signaling and biomechanical properties in unruptured aortic aneurysms

BACKGROUND

The relationship between biomechanical properties and biological activities in aortic aneurysms was investigated with finite element simulations and 18F-fluoro-deoxy-glucose (18F-FDG) positron emission tomography.

METHODS AND RESULTS

The study included 53 patients (45 men) with aortic aneurysms, 47 infrarenal (abdominal aortic) and 6 thoracic (thoracic aortic), who had ≥1 18F-FDG positron emission tomography/computed tomography. During a 30-month period, more clinical events occurred in patients with increased 18F-FDG uptake on their last examination than in those without (5 of 18 [28%] versus 2 of 35 [6%]; P=0.03). Wall stress and stress/strength index computed by finite element simulations and 18F-FDG uptake were evaluated in a total of 68 examinations. Twenty-five (38%) examinations demonstrated ≥1 aneurysm wall area of increased 18F-FDG uptake. The mean number of these areas per examination was 1.6 (18 of 11) in thoracic aortic aneurysms versus 0.25 (14 of 57) in abdominal aortic aneurysms, whereas the mean number of increased uptake areas colocalizing with highest wall stress and stress/strength index areas was 0.55 (6 of 11) and 0.02 (1 of 57), respectively. Quantitatively, 18F-FDG positron emission tomographic uptake correlated positively with both wall stress and stress/strength index (P<0.05). 18F-FDG uptake was particularly high in subjects with personal history of angina pectoris and familial aneurysm.

CONCLUSIONS

Increased 18F-FDG positron emission tomographic uptake in aortic aneurysms is strongly related to aneurysm location, wall stress as derived by finite element simulations, and patient risk factors such as acquired and inherited susceptibilities.

Fluid dynamics of coarctation of the aorta and effect of bicuspid aortic valve

Up to 80% of patients with coarctation of the aorta (COA) have a bicuspid aortic valve (BAV). Patients with COA and BAV have elevated risks of aortic complications despite successful surgical repair. The development of such complications involves the interplay between the mechanical forces applied on the artery and the biological processes occurring at the cellular level. The focus of this study is on hemodynamic modifications induced in the aorta in the presence of a COA and a BAV. For this purpose, numerical investigations and magnetic resonance imaging measurements were conducted with different configurations: (1) normal: normal aorta and normal aortic valve; (2) isolated COA: aorta with COA (75% reduction by area) and normal aortic valve; (3) complex COA: aorta with the same severity of COA (75% reduction by area) and BAV. The results show that the coexistence of COA and BAV significantly alters blood flow in the aorta with a significant increase in the maximal velocity, secondary flow, pressure loss, time-averaged wall shear stress and oscillatory shear index downstream of the COA. These findings can contribute to a better understanding of why patients with complex COA have adverse outcome even following a successful surgery.

Three-dimensional sensitivity assessment of thoracic aortic aneurysm wall stress: a probabilistic finite-element study

OBJECTIVES

In clinical practice, maximum diameter is used as a criterion to estimate aneurysm-rupture risk; however, it is only a general indicator and its value becomes difficult to estimate in the thoracic segment. Improved understanding of aortic aneurysm complexity and biomechanics is needed to achieve advancements in surgical repair techniques. The objective of this study was to determine the maximum wall stress by using imaging-derived data and a specific probabilistic design integrated into finite element (FE) analysis.

METHODS

Computed tomography images of thoracic aortic aneurysms from our database were analysed and the main morphological features were identified by means of a specific automatic routine. Morphological data were used to develop an idealized finite element library of thoracic aortic arch models. Sensitivity analyses were performed by using the geometrical parameters as input variables for a statistical wall stress assessment. Numerical results were compared with those obtained from deterministic analysis on patient-specific three-dimensional reconstructions.

RESULTS

The results showed that in small aneurysms, wall stress values similar to those of large aneurysms can be obtained if a significant eccentricity is achieved. In small aneurysms, the peak stress is primarily affected by the eccentricity of the bulge [correlation coefficient (CC) = 0.86], while for diameters in the range of 50-60 mm, the CC is 0.43 for the eccentricity and 0.72 for the maximum diameter.

CONCLUSIONS

The stress distribution in small aneurysms may contribute to the pathogenesis of aortic rupture and dissections. Our method can provide a novel and efficient procedure for generating computational models to estimate the wall stress in a comparative multivariate manner.

New Insights Into Aortic Diseases: A Report From the Third International Meeting on Aortic Diseases (IMAD3)

The current state of research and treatment on aortic diseases was discussed in the "3rd International Meeting on Aortic Diseases" (IMAD3) held on October 4-6, 2012, in Liège, Belgium. The 3-day meeting covered a wide range of topics related to thoracic aortic aneurysms and dissections, abdominal aortic aneurysms, and valvular diseases. It brought together clinicians and basic scientists and provided an excellent opportunity to discuss future collaborative research projects for genetic, genomics, and biomarker studies, as well as clinical trials. Although great progress has been made in the past few years, there are still a large number of unsolved questions about aortic diseases. Obtaining answers to the key questions will require innovative, interdisciplinary approaches that integrate information from epidemiological, genetic, molecular biology, and bioengineering studies on humans and animal models. It is more evident than ever that multicenter collaborations are needed to accomplish these goals.

Molecular imaging in atherosclerosis: FDG PET

18F-FDG PET is a new noninvasive tool for inflammation functional imaging. Low spatial resolution is now compensated by coregistration with CT or MRI. New mechanistic insights have emerged from animal and histology to explain the obtained signals by hypoxia, macrophage infiltration, and differentiation. Mixed results have been found in biomarkers studies. Interesting data have come recently linking plaque anatomy and function in carotids and in aortic aneurysms as well as inflammation and events. In coronary arteries, plaque assessment is still hampered by myocardium uptake but developments are being made. 18-FDG PET has been able to monitor inflammation before and after several therapies in animals and humans but to date the lack of standardization and the absence of prospective event-driven studies prevent this promising technique to be used in clinical practice.

Standardization of outcome measures in clinical trials of pharmacological treatment for abdominal aortic aneurysm

An abdominal aortic aneurysm (AAA) is a common aortic wall disease with an increased prevalence in the elderly population (4-8% for those aged >65 years). Many AAAs are slow growing and remain insidious. Current standard of care for patients with small AAAs (<49 mm) is surveillance, with interventional therapy (open surgical repair or endovascular aneurysm repair) recommended for large (>50-55 mm), rapidly growing (>10 mm/year) or symptomatic AAAs. Although open surgical repair or endovascular aneurysm repair are effective, significant short- and long-term postoperative morbidity and mortality occurs. Currently, there is no pharmacological treatment specific for AAA; the need for the development of targeted pharmacological therapies based on clinically relevant and feasible outcomes acceptable to the medical community, regulatory agencies and third-party payers is high. A consensus on such end points will be critical to accelerating the development of pharmacological agents to prevent formation, arrest the expansion and reduce the rupture risk of AAA.

ACR Appropriateness Criteria® pulsatile abdominal mass, suspected abdominal aortic aneurysm

Clinical palpation of a pulsating abdominal mass alerts the clinician to the presence of a possible abdominal aortic aneurysm (AAA). Generally an arterial aneurysm is defined as a localized arterial dilatation ≥50% greater than the normal diameter. Imaging studies are important in diagnosing the cause of a pulsatile abdominal mass and, if an AAA is found, in determining its size and involvement of abdominal branches. Ultrasound (US) is the initial imaging modality of choice when a pulsatile abdominal mass is present. Noncontrast computed tomography (CT) may be substituted in patients for whom US is not suitable. When aneurysms have reached the size threshold for intervention or are clinically symptomatic, contrast-enhanced multidetector CT angiography (CTA) is the best diagnostic and preintervention planning study, accurately delineating the location, size, and extent of aneurysm and the involvement of branch vessels. Magnetic resonance angiography (MRA) may be substituted if CT cannot be performed. Catheter arteriography has some utility in patients with significant contraindications to both CTA and MRA. The American College of Radiology Appropriateness Criteria(®) are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances where evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

Correlation of biomechanics to tissue reaction in aortic aneurysms assessed by finite elements and [18F]-fluorodeoxyglucose-PET/CT

Mechanobiological interactions are essential for the adaption of the cardiovascular system to altered environmental and internal conditions, but are poorly understood with regard to abdominal aortic aneurysm (AAA) pathogenesis, growth and rupture. In the present study, we therefore calculated mechanical AAA quantities using nonlinear finite element methods and correlated these to [18F]-fluorodeoxyglucose (FDG)-metabolic activity in the AAA wall detected by positron emission tomography/computed tomography (PET/CT). The interplay between mechanics and FDG-metabolic activity was analyzed in terms of maximum values and the three-dimensional spatial relationship, respectively. Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) data sets of n = 18 AAA patients were studied. Maximum FDG-uptake (SUV max ) in the AAA wall varied from 1.32 to 4.60 (average SUV max 3.31 ± 0.87). Maximum wall stresses and strains ranged from 10.0 to 64.0 N∕cm(2) (38.2 ± 13.8  N∕cm(2)) and from 0.190 to 0.260 (0.222 ± 0.023), respectively. SUV max was significantly correlated to maximum wall stress and strain (SUV max to stress: r = 0.71, p = 0.0005; SUV max to strain: r = 0.66, p = 0.0013). To evaluate the three-dimensional spatial interaction between FDG-uptake and acting wall stress, element-wise correlations were performed. In all but 2 AAAs, positive element-wise correlation of FDG-uptake to wall stress was obtained, with the Pearson's correlation coefficient ranging from -0.168 to 0.738 ( 0.372 ± 0.263). The results indicate that mechanical stresses are correlated quantitatively and spatially to FDG-uptake in the AAA wall. It is hypothesized that unphysiologically increased loading in the AAA wall triggers biological tissue reaction, such as inflammation or regenerative processes, causing elevated FDG-metabolic activity. These findings strongly support experimental hypotheses of mechanotransduction mechanisms in vivo.

Aneurysm sac shrinkage after endovascular treatment of the aorta: Beyond sac pressure and endoleaks

The isolation of the aneurysm sac from systemic pressure and its consequent shrinkage are considered criteria of success after endovascular repair (EVAR). However, the process of shrinkage does not solely depend on the intrasac pressure, the predictive role of which remains ambiguous. This brief review summarizes the additional pathophysiological mechanisms that regulate the biomechanical properties of the aneurysm wall and may interfere with the process of aneurysm sac shrinkage.