Analysis of Expansion Patterns in 4-4.9 cm Abdominal Aortic Aneurysms

Investigation of commonly used aortic aneurysm growth rate metrics: Comparing their suitability for clinical and research applications

An aneurysm is a pathological widening of a blood vessel. Aneurysms of the aorta are often asymptomatic until they rupture, killing approximately 10,000 Americans per year. Fortunately, rupture can be prevented through early detection and surgical repair. However, surgical risk outweighs rupture risk for small aortic aneurysms, necessitating a policy of surveillance. Understanding the growth rate of aneurysms is essential for determining appropriate surveillance windows. Further, identifying risk factors for fast growth can help identify potential interventions. However, studies in the literature have applied many different methods for defining the growth rate of abdominal aortic aneurysms. It is unclear which of these methods is most accurate and clinically meaningful, and whether these heterogeneous methodologies may have contributed to the varied results reported in the literature. To help future researchers best plan their studies and to help clinicians interpret existing studies, we compared five different models of aneurysmal growth rate. We examined their noise tolerance, temporal bias, predictive accuracy, and statistical power to detect risk factors. We found that hierarchical mixed effects models were more noise tolerant than traditional, unpooled models. We also found that linear models were sensitive to temporal bias, assigning lower growth rates to aneurysms that were detected earlier in their course. Our exponential mixed model was noise-tolerant, resistant to temporal bias, and detected the greatest number of clinical risk factors. We conclude that exponential mixed models may be optimal for large studies. Because our results suggest that choice of method can materially impact a study's findings, we recommend that future studies clearly state the method used and demonstrate its appropriateness.

The prognostic impact of vascular calcification on abdominal aortic aneurysm progression

OBJECTIVE

The maximal aortic diameter is currently the only clinically applied predictor of abdominal aortic aneurysm (AAA) progression. It is known that risk of rupture is associated with aneurysm size, hence accurate monitoring of AAA expansion is crucial. Aneurysmal vessel wall calcification and its implication on AAA expansion are insufficiently explored. We evaluated the vascular calcification using longitudinal computed tomography angiographies (CTA) of AAA patients and its association with AAA growth.

METHODS

We conducted a retrospective study of 102 AAA patients with a total number of 389 abdominal CTAs at six-month intervals, treated and followed-up at the Division of Vascular Surgery, Department of General Surgery, Medical University of Vienna. Digitally stored CTAs were reviewed for vascular calcification (volume and score) of the infrarenal aorta and common iliac arteries as well as for morphometric AAA analysis. In the prognostic setting, slow versus fast AAA progression was defined as < 2 or ≥ 2 mm increase in AAA diameter over six months. In addition, to analyze the association of vascular calcification and AAA growth rate with longitudinal monitoring data, a specifically tailored log-linear mixed model was employed.

RESULTS

An inverse relation of increased abdominal vessel wall calcification and short-term AAA progression was detected. Compared to fast progressing AAA, the median calcification volume of the infrarenal aorta (1225.3 vs 519.8 mm³, P = 0.003), the median total calcification volume (2014.1 vs 1434.9 mm³, P = 0.008) and the median abdominal total customized Agatston calcium (cAC) score (1663.5 vs 718.4, P = 0.003) were significantly increased in slow progressing AAA. Importantly, a log-linear mixed model efficiently predicted AAA expansion based on current diameter and abdominal total cAC score (P = 0.042).

CONCLUSION

We assessed the prognostic value of CTA-measured vascular calcification for AAA progression. Increased vascular calcification stabilizes the aortic aneurysmal wall and likely protects against progressive AAA expansion, resulting in a significant decrease of aneurysm growth over time. As a consequence, this may have implications for rupture risk, mortality, morbidity, and cost.

Defining a master curve of abdominal aortic aneurysm growth and its potential utility of clinical management

OBJECTIVE

The maximum diameter measurement of an abdominal aortic aneurysm (AAA), which depends on orthogonal and axial cross-sections or maximally inscribed spheres within the AAA, plays a significant role in the clinical decision making process. This study aims to build a total of 21 morphological parameters from longitudinal CT scans and analyze their correlations. Furthermore, this work explores the existence of a "master curve" of AAA growth, and tests which parameters serve to enhance its predictability for clinical use.

METHODS

106 CT scan images from 25 Korean AAA patients were retrospectively obtained. We subsequently computed morphological parameters, growth rates, and pair-wise correlations, and attempted to enhance the predictability of the growth for high-risk aneurysms using non-linear curve fitting and least-square minimization.

RESULTS

An exponential AAA growth model was fitted to the maximum spherical diameter, as the best representative of the growth among all parameters (r-square: 0.94) and correctly predicted to 15 of 16 validation scans based on a 95% confidence interval. AAA volume expansion rates were highly correlated (r=0.75) with thrombus accumulation rates.

CONCLUSIONS

The exponential growth model using spherical diameter provides useful information about progression of aneurysm size and enables AAA growth rate extrapolation during a given surveillance period.

Outcomes of Small Incidental Abdominal Aortic Aneurysms in Octogenarian and Nonagenarian Patients in Northern Spain

OBJECTIVE

Greater population life expectancy and consistent improvement in diagnostic techniques have increased the diagnosis of abdominal aortic aneurysms (AAAs) in the elderly population. The aim was to study the natural history of small (< 55 mm) incidental AAAs in octogenarian and nonagenarian patients to assess the need for follow up and/or invasive treatment.

METHODS

This was a retrospective analysis of a prospective registry. Patients ≥ 80 years old at the time of diagnosis of a < 55 mm AAA in 1988-2018 were selected. Clinical and anatomical characteristics were registered. Patients were divided in three groups: 30 - 39 mm, 40 - 49 mm, and 50 - 54 mm AAA. The outcome variables were aorto-iliac rupture, AAA reaching a surgical threshold (≥ 55 mm), and death. A descriptive statistical analysis was performed and life tables, Kaplan-Meier curves, and uni- and multivariable Cox regression were used.

RESULTS

Three hundred and ten patients were included, 256 (82.6%) men, with mean index age of 84.5 years (standard deviation [SD] 3.5), and median follow up of 37.9 months (interquartile range [IQR] 18.2 - 65.4). Eighteen (5.8%) AAAs ruptured; four of these patients were operated on and only one survived. Sixty-two (20%) AAA reached a surgical size; eight were repaired electively, with 0% early mortality. The survival rates were 81%, 70%, and 38% at one, two, and five years. The rupture rates were 1%, 2%, and 6% and the AAAs reaching surgical threshold were 1%, 4%, and 19% for the same time periods. AAA size < 40 mm was an independent protective factor from rupture (0.13; 95% confidence interval [CI] 0.03 - 0.48), reaching surgical threshold (0.08; 95% CI 0.04 - 0.16) and death (0.63; 95% CI 0.42 - 0.95).

CONCLUSION

The risk of late rupture of small incidental AAA diagnosed in octogenarian and nonagenarian patients is very small, especially when the AAA is < 40 mm in diameter. In contrast, global mortality is high. Conservative management seems sensible, with strict selection of the patients who would benefit from follow up and eventual repair.

Evaluating Growth Patterns of Abdominal Aortic Aneurysm Diameter With Serial Computed Tomography Surveillance

Importance

Small abdominal aortic aneurysms (AAAs) are common in the elderly population. Their growth rates and patterns, which drive clinical surveillance, are widely disputed.

Objective

To assess the growth patterns and rates of AAAs as documented on serial computed tomography (CT) scans.

Design, Setting, and Participants

Cohort study and secondary analysis of the Non-Invasive Treatment of Abdominal Aortic Aneurysm Clinical Trial (N-TA3CT), a randomized, double-blind placebo-controlled clinical trial conducted from 2013 to 2018, with CT imaging every 6 months for 2 years. The trial was a multicenter, observational secondary analysis, not related to treatment hypotheses of data collected in the N-TA3CT. Participants included 254 patients with baseline AAA diameter between 3.5 and 5.0 cm.

Exposures

Patients received serial CT scan measurements, analyzed for maximum transverse diameter, at 6-month intervals.

Main Outcomes and Measures

The primary study outcome was AAA annual growth rate. Secondary analyses included characterizing AAA growth patterns, assessing likelihood of AAA diameter to exceed sex-specific intervention thresholds over 2 years.

Results

A total of 254 patients, 35 women with baseline AAA diameter 3.5 to 4.5 cm and 219 men with baseline diameter 3.5 to 5.0 cm, were included. Yearly growth rates of AAA diameters were a median of 0.17 cm/y (interquartile range [IQR], 0.16) and a mean (SD), 0.19 (0.14) cm/y. Ten percent of AAAs displayed minimal to no growth (<0.05 cm/y), 62% displayed low growth (0.05-0.25 cm/y), and 28% displayed high growth (>0.25 cm/y). Baseline AAA diameter accounted for 5.4% of variance of growth rate (P < .001; R2, 0.054). Most AAAs displayed linear growth (70%); large variations in interval growth rates occurred infrequently (3% staccato growth and 4% exponential growth); and some patients' growth patterns were not clearly classifiable (23% indeterminate). No patients with a maximum transverse diameter less than 4.25 cm exceeded sex-specific repair thresholds at 2 years (men, 0 of 92; 95% CI, 0.00-0.055; women, 0 of 25 ; 95% CI, 0.00-0.247). Twenty-six percent of patients with a maximum transverse diameter of at least 4.25 cm exceeded sex-specific repair thresholds at 2 years (n = 12 of 83 men with diameter ranging from 4.25 to <4.75 cm; 95% CI, 0.091-0.264; n = 21 of 44 men with diameter ranging from 4.75-5.0 cm; 95% CI, 0.362-0.669; n = 3 of 10 women with diameter ≥4.25 cm; 95% CI, 0.093-0.726).

Conclusions and Relevance

Most small AAAs showed linear growth; large intrapatient variations in interval growth rates were infrequently observed over 2 years. Linear growth modeling of AAAs in individual patients suggests smaller AAAs (<4.25 cm) can be followed up with a CT scan in at least 2 years with little chance of exceeding interventional thresholds.

Trial Registration

ClinicalTrials.gov Identifier: NCT01756833.

Multidimensional Analysis of Descending Aortic Growth After Acute Type A Aortic Dissection

BACKGROUND

After repair of acute type A aortic dissection, typical geometric variables of conventional aortic surveillance focus on maximum diameter and its rate of growth, potentially missing important geometric changes elsewhere. We determined additional information provided by a semiautomated, 3-dimensional (3D), nonlinear growth model of the descending thoracic aorta after repair of type A aortic dissection.

METHODS

Computed tomographic angiography data were retrospectively collected after hemiarch repair of type A aortic dissection. The descending aorta was systematically reconstructed to generate a 3D model made up of individual segments. The baseline and follow-up diameters were measured semiautomatically for each segment, and the nonlinear interval growth was determined.

RESULTS

The fastest growing segment expanded at a rate of 3.8 mm/y (interquartile range, 2.2 to 5.4 mm/y) vs 0.6 mm/y (interquartile range, -0.3 to 1.7 mm/y) when measured at the original site of maximum diameter (P < .01). The maximum baseline diameter was a poor predictor of location with fastest growth (r = 0.10, P > .1). Using the society recommended growth limits, a greater proportion of patients would be considered "at risk" when assessed by our method vs conventional surveillance measures.

CONCLUSIONS

Our model identifies areas of rapid aortic growth after repair of type A dissection that would likely be missed using current surveillance techniques. The increased precision, resolution, and reproducibility provided by our technique may improve on limitations of current surveillance techniques, provide novel geometric data on aortic remodeling, and contribute to the pursuit of a comprehensive patient-specific approach to aortic risk stratification.

A comparison of hemodynamic metrics and intraluminal thrombus burden in a common iliac artery aneurysm

Aneurysms of the common iliac artery (CIAA) are typically found in association with an abdominal aortic aneurysm (AAA). Isolated CIAAs, in the absence of an AAA, are uncommon. Similar to AAAs, CIAA may develop intraluminal thrombus (ILT). As isolated CIAAs have a contralateral common iliac artery for comparison, they provide an opportunity to study the hemodynamic mechanisms behind ILT formation. In this study, we compared a large isolated CIAA and the contralateral iliac artery using computational fluid dynamics to determine if hemodynamic metrics correlate with the location of ILT. We performed a comprehensive computational fluid dynamics study and investigated the residence time of platelets and monocytes, velocity fields, time-averaged wall shear stress, oscillatory shear index, and endothelial cell activation potential. We then correlated these data to ILT burden determined with computed tomography. We found that high cell residence times, low time-averaged wall shear stress, high oscillatory shear index, and high endothelial cell activation potential all correlate with regions of ILT development. Our results show agreement with previous hypotheses of thrombus formation in AAA and provide insights into the computational hemodynamics of iliac artery aneurysms.

Surrogate Markers of Abdominal Aortic Aneurysm Progression

The natural course of many abdominal aortic aneurysms (AAA) is to gradually expand and eventually rupture and monitoring the disease progression is essential to their management. In this publication, we review surrogate markers of AAA progression. AAA diameter remains the most widely used and important marker of AAA growth. Standardized reporting of reproducible methods of measuring AAA diameter is essential. Newer imaging assessments, such as volume measurements, biomechanical analyses, and functional and molecular imaging, as well as circulating biomarkers, have potential to add important information about AAA progression. Currently, however, there is insufficient evidence to recommend their routine use in clinical practice.

Evidence of Cyclic Changes in the Metabolism of Abdominal Aortic Aneurysms During Growth Phases: ¹⁸F-FDG PET Sequential Observational Study

The rates of growth of medically treated abdominal aortic aneurysms (AAA) are difficult to determine, and relationships with parietal inflammation and with metabolic parameters from (18)F-FDG PET remain unclear. This (18)F-FDG PET sequential observational study was aimed at analyzing the metabolic changes accompanying the growth phases of medically treated AAA.

METHODS

Thirty-nine patients (37 men; age [mean ± SD], 71 ± 12 y) exhibiting small and medically treated AAA (maximal diameter, 46 ± 3 mm) underwent (18)F-FDG PET and CT angiography at baseline and 9 mo later. Clinical and imaging parameter correlates of the 9-mo increase in maximal diameter were investigated; these included (18)F-FDG maximal standardized uptake values (SUVmax) averaged for slices encompassing the AAA volume.

RESULTS

Of the 39 patients, 9 (23%) had a significant (≥2.5 mm) increase in maximal diameter at 9 mo, whereas the remaining 30 did not. The patients with an increase in maximal diameter at 9 mo exhibited lower SUVmax within the AAA at baseline than patients who did not have such an increase (1.80 ± 0.45 vs. 2.21 ± 0.52; P = 0.04); they also displayed a trend toward greater changes in SUVmax at 9 mo (difference between 9 mo and baseline: +0.40 ± 0.85 vs. -0.06 ± 0.57; P = 0.07). Similar levels were ultimately reached in both groups at 9 mo (2.20 ± 0.83 and 2.15 ± 0.66). SUVmax was a significant, yet modest, baseline predictor of the absolute change in maximal diameter during follow-up (P = 0.049).

CONCLUSION

The enhancement in the maximal diameter of small AAA was preceded by a stage with a low level of (18)F-FDG uptake, but this low level of uptake was no longer documented after the growth phases, suggesting a pattern of cyclic metabolic changes.

Multidimensional growth measurements of abdominal aortic aneurysms

BACKGROUND

Monitoring the expansion of abdominal aortic aneurysms (AAAs) is critical to avoid aneurysm rupture in surveillance programs, for instance. However, measuring the change of the maximum diameter over time can only provide limited information about AAA expansion. Specifically, regions of fast diameter growth may be missed, axial growth cannot be quantified, and shape changes of potential interest for decisions related to endovascular aneurysm repair cannot be captured.

METHODS

This study used multiple centerline-based diameter measurements between the renal arteries and the aortic bifurcation to quantify AAA growth in 51 patients from computed tomography angiography (CTA) data. Criteria for inclusion were at least 1 year of patient follow-up and the availability of at least two sufficiently high-resolution CTA scans that allowed an accurate three-dimensional reconstruction. Consequently, 124 CTA scans were systematically analyzed by using A4clinics diagnostic software (VASCOPS GmbH, Graz, Austria), and aneurysm growth was monitored at 100 cross-sections perpendicular to the centerline.

RESULTS

Monitoring diameter development over the entire aneurysm revealed the sites of the fastest diameter growth, quantified the axial growth, and showed the evolution of the neck morphology over time. Monitoring the development of an aneurysm's maximum diameter or its volume over time can assess the mean diameter growth (r = 0.69, r = 0.77) but not the maximum diameter growth (r = 0.43, r = 0.34). The diameter growth measured at the site of maximum expansion was ~16%/y, almost four times larger than the mean diameter expansion of 4.4%/y. The sites at which the maximum diameter growth was recorded did not coincide with the position of the maximum baseline diameter (ρ = 0 .12; P = .31). The overall aneurysm sac length increased from 84 to 89 mm during the follow-up (P < .001), which relates to the median longitudinal growth of 3.5%/y. The neck length shortened, on average, by 6.2% per year and was accompanied by a slight increase in neck angulation.

CONCLUSIONS

Neither maximum diameter nor volume measurements over time are able to measure the fastest diameter growth of the aneurysm sac. Consequently, expansion-related wall weakening might be inappropriately reflected by this type of surveillance data. In contrast, localized spots of fast diameter growth can be detected through multiple centerline-based diameter measurements over the entire aneurysm sac. This information might further reinforce the quality of aneurysm surveillance programs.

Unraveling biomarkers of abdominal aortic aneurisms by iTRAQ analysis of depleted plasma

Abdominal aortic aneurysm (AAA) is a significant health problem in Western countries. The diameter of AAA is a surrogate marker of its growth rate that reflects the magnitude of the degenerative process in the vascular wall, although most AAAs show discontinuous growth patterns and alternate periods of stability and nongrowth with periods of acute expansion and occasionally ruptures. Thus, the identification of biomarkers of AAA in plasma could aid in the diagnosis, prognosis, and therapy of AAA progression. However, owing to the complex composition of plasma, depletion methods must be applied before the analytical approaches for detecting low-abundant plasma protein components. In the present work, we describe a proteomic study on MARS 14-depleted plasma based on mass spectrometry (MS) which combines peptide labelling (isobaric tagging for relative and absolute quantification, iTRAQ) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). This quantitative approach revealed altered levels of several proteins related to the complement system in AAA patients.

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.

Diagnosis and monitoring of abdominal aortic aneurysm: current status and future prospects

Abdominal aortic aneurysm (AAA) remains an important cause of morbidity and mortality in elderly men, and prevalence is predicted to increase in parallel with a global aging population. AAA is commonly asymptomatic, and in the absence of routine screening, diagnosis is usually incidental when imaging to assess unrelated medical complaints. In the absence of approved diagnostic and prognostic markers, AAAs are monitored conservatively via medical imaging until aortic diameter approaches 50-55 mm and surgical repair is performed. There is currently significant interest in identifying molecular markers of diagnostic and prognostic value for AAA. Here we outline the current guidelines for AAA management and discuss modern scientific techniques currently employed to identify improved diagnostic and prognostic markers.

Systematic review and meta-analysis of growth rates of small abdominal aortic aneurysms

BACKGROUND

Small abdominal aortic aneurysms are usually asymptomatic and managed safely in ultrasound surveillance programmes until they grow to a diameter threshold where intervention is considered. The aim of this study was to synthesize systematically the published data on growth rates for small aneurysms to investigate the evidence basis for surveillance intervals.

METHODS

This was a systematic review of the literature published before January 2010, which identified 61 potentially eligible reports. Detailed review yielded 15 studies providing growth rates for aneurysms 3·0-5·5 cm in diameter (14 in millimetres per year, 1 as percentage change per year). These studies included 7630 people (predominantly men) enrolled during 1976-2005.

RESULTS

The pooled mean growth rate was 2·32 (95 per cent confidence interval 1·95 to 2·70) mm/year but there was very high heterogeneity between studies; the growth rate ranged from - 0·33 to + 3·95 mm/year. Six studies reported growth rates by 5-mm diameter bands, which showed the trend for growth rate to increase with aneurysm diameter. Simple methods to determine growth rate were associated with higher estimates. Meta-regression analysis showed that a 10-mm increase in aneurysm diameter was associated with a mean(s.e.m.) 1·62(0·20) mm/year increase in growth rate. Neither mean age nor percentage of women in each study had a significant effect. On average, a 3·5-cm aneurysm would take 6·2 years to reach 5·5 cm, whereas a 4·5-cm aneurysm would take only 2·3 years.

CONCLUSION

There was considerable variation in the reported growth rates of small aneurysms beyond that explained by aneurysm diameter. Fuller evidence on which to base surveillance intervals for patients in screening programmes requires a meta-analysis based on individual patient data.

A relation between near-wall particle-hemodynamics and onset of thrombus formation in abdominal aortic aneurysms

A novel computational particle-hemodynamics analysis of key criteria for the onset of an intraluminal thrombus (ILT) in a patient-specific abdominal aortic aneurysm (AAA) is presented. The focus is on enhanced platelet and white blood cell residence times as well as their elevated surface-shear loads in near-wall regions of the AAA sac. The generalized results support the hypothesis that a patient's AAA geometry and associated particle-hemodynamics have the potential to entrap activated blood particles, which will play a role in the onset of ILT. Although the ILT history of only a single patient was considered, the modeling and simulation methodology provided allow for the development of an efficient computational tool to predict the onset of ILT formation in complex patient-specific cases.

Thrombus volume is associated with cardiovascular events and aneurysm growth in patients who have abdominal aortic aneurysms

BACKGROUND

Patients with abdominal aortic aneurysms (AAA) are predisposed to cardiovascular events and often experience continual expansion of their aneurysm. Cardiovascular events and expansion rates are positively correlated with aneurysm size. AAA is usually associated with intraluminal thrombus, which has previously been implicated in AAA pathogenesis. This study prospectively assessed the association of infrarenal abdominal aortic thrombus volume with cardiovascular events and AAA growth.

METHODS

Ninety-eight patients with AAAs underwent computed tomography angiography (CTA). The volume of infrarenal aorta thrombus was measured by a previously validated technique. Patients were monitored prospectively for a median of 3 years (interquartile range [IQR], 2.0-3.6 years), and cardiovascular events (nonfatal stroke, nonfatal myocardial infarction, coronary revascularization, amputation, and cardiovascular death) were recorded. Of the original patients, 39 underwent repeat CTA a median of 1.5 years (IQR, 1.1-3.3 years) after entry to the study. Kaplan-Meier and Cox proportional analysis were used to examine the association of aortic thrombus with cardiovascular events and average weighted AAA growth.

RESULTS

There were 28 cardiovascular events during follow-up. The incidence of cardiovascular events was 23.4% and 49.2% for patients with small (smaller than the median) and large (median or larger) volumes of aortic thrombus, respectively, at 4 years (P = .040). AAA thrombus volume of median or larger was associated with increased cardiovascular events (relative risk [RR] 2.8, 95% confidence interval [CI], 1.01-5.24) independent of other risk factors, including initial AAA diameter, but was only of borderline significance when patients were censored at the time of AAA repair (RR, 2.35; 95% CI, 0.98-5.63). In the subset of patients with CTA follow-up, the median annual increase in AAA volume was 5.1 cm³ (IQR, 0.8-10.3 cm³). Annual AAA volume increase was positively correlated with initial AAA diameter (r = 0.44, P = .006) and thrombus volume (r = 0.50, P = .001). Median or larger aortic thrombus volume was associated with rapid AAA volume increase (≥ 5 cm/y), independent of initial aortic diameter (RR, 15.0; 95% CI, 1.9-115.7; P = .009).

CONCLUSION

In this small cohort, infrarenal aortic thrombus volume was associated with the incidence of cardiovascular events and AAA progression. These results need to be confirmed and mechanisms underlying the associations clarified in large further studies.

Lower respiratory tract infection and rapid expansion of an abdominal aortic aneurysm: a case report

INTRODUCTION

The rate of abdominal aortic aneurysm expansion is related to multiple factors. There is some evidence that inflammation can accelerate aneurysm expansion. However, the association between pulmonary sepsis and rapid abdominal aortic aneurysm expansion is rarely reported.

CASE PRESENTATION

Here we present a case of a rapidly expanding abdominal aortic aneurysm in a 68-year-old Caucasian man with a concomitant lower respiratory tract infection and systemic sepsis requiring intensive monitoring and urgent endovascular intervention. Our patient had an uncomplicated post-operative recovery and a follow-up computed tomography scan at one month demonstrated no evidence of an endoleak.

CONCLUSION

This case highlights the potential association between pulmonary sepsis and rapid abdominal aortic aneurysm expansion. In such cases, a policy of frequent monitoring should be adopted to identify those patients requiring definitive management.

Rupture rates of small abdominal aortic aneurysms: a systematic review of the literature

BACKGROUND

Small aneurysms of the abdominal aorta (3.0-5.5 cm in diameter) often are managed by regular surveillance, rather than surgery, because the risk of surgery is considered to outweigh the risk of aneurysm rupture. The risk of small aneurysm rupture is considered to be low. The purpose of this review is to summarise the reported estimates of small aneurysm rupture rates.

METHODS AND FINDINGS

We conducted a systematic review of the literature published before 2010 and identified 54 potentially eligible reports. Detailed review of these studies showed that both ascertainment of rupture, patient follow-up and causes of death were poorly reported: diagnostic criteria for rupture were never reported. There were only 14 studies from which rupture rates (as ruptures per 100 person-years) were available. These 14 published studies included 9779 patients (89% male) over the time period 1976-2006 but only 7 of these studies provided rupture rates specifically for the diameter range 3.0-5.5 cm, which ranged from 0 to 1.61 ruptures per 100 person-years.

CONCLUSIONS

Rupture rates of small abdominal aortic aneurysms would appear to be low, but most studies have been poorly reported and did not have clear ascertainment and diagnostic criteria for aneurysm rupture.

Increased metabolic activity in abdominal aortic aneurysm detected by 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT)

OBJECTIVES

Abdominal aortic aneurysms (AAAs) are associated with an inflammatory cell infiltrate and enzymatic degradation of the vessel wall. The aim of this study was to detect increased metabolic activity in the wall of the AAA with 18F-fluorodeoxyglucose ((18)F-FDG), mediated by glucose transporter protein (GLUTs), using a dedicated hybrid PET/64-detector CT. DESIGN, METHOD AND MATERIALS: 14 patients (All male, mean age 73.6 years, range 61-82) with AAA under surveillance underwent PET/CT scanning with 175 MBq of intravenous (18)F-FDG. The maximum aneurysm diameter and calcification score were determined on the attenuation correction CT. A volume of interest was placed on the aneurysm sac and the maximum Standardised Uptake Value (SUV(max)) measured.

RESULTS

The mean aneurysm diameter was 5.4 cm (SD+/-0.8). Two aneurysms had the CT characteristics of inflammatory aneurysms. Twelve aneurysms showed increased FDG uptake (SUV(max)>2.5). There was no significant difference in FDG uptake between heavily calcified aneurysms and non-heavily calcified aneurysms (t-test). There was a significant increase in the FDG uptake in the two inflammatory aneurysms compared to the other twelve aneurysms (t-test; P=0.04).

CONCLUSION

The findings in this study offer in vivo evidence that the AAA wall shows increased glucose metabolism, mediated by the GLUTs: this increased metabolic activity as detected by PET/CT may be present in most AAAs.