Incidence and histologic characteristics of blebs in patients with abdominal aortic aneurysms

Scannographic Study of Risk Factors of Abdominal Aortic Aneurysm Rupture

BACKGROUND

Current decision about when to operate abdominal aortic aneurysms (AAAs) is based only on the maximum aneurysm diameter (MAD). However, small aneurysms still rupture and we can observe very large AAA without any symptom. A simple morphologic analysis could be a tool to assess the risk of rupture. The main objective of this study was to assess the relevance of ratios between MAD and healthy aorta on computed tomography (CT) as a risk factor of AAA rupture. The secondary objective was to evaluate CT signs as risk factors of AAA rupture.

METHODS

Retrospective observational bicentric study comparing CT scans of a ruptured AAA group and a control group treated electively was conducted. Appariement 1:1 based on MAD was applied. Ratios between healthy aorta diameters at several levels, celiac trunk (CTR), superior mesenteric artery (SMA), highest renal artery (RA), and the MAD were calculated. The presence of blebs, crescent signs, ruptures of calcifications of the aneurysm sack, and draped aorta were notified.

RESULTS

From 2010 to 2016, 38 ruptured AAA and 38 controls were included. Ratios were superior in the rupture group, respectively: MAD/CTR [2.77 (±0.5) versus 2.58 (±0.4) P < 0.095], MAD/SMA [2.92 (±0.7) versus 2.74 (±0.5) P < 0.194], and MAD/RA [3.02 (±0.70) versus 2.76 (±0.5) P < 0.054] but not significatively. Receiver operating characteristic curve analysis demonstrated optimal threshold to detect rupture at 2.8 for the ratio MAD/CTR (area under the curve (AUC) 0.593, sensitivity 47.4%, specificity 78.9%), at 3.3 for the ratio MAD/SMA (AUC 0.564, sensitivity 31.6%, specificity 92.1%), and at 3.3 for the ratio MAD/RA (AUC 0.591, sensitivity 31.6%, specificity 94.7%). Bivariate analysis for rupture risk factor showed significance for the three ratios (MAD/CTR > 2.8 [OR = 11 (1.42; 85.20) P < 0.0217], MAD/SMA > 3.3 [OR = 10 (1.28; 78.12) P < 0.0281], and MAD/RA >3.3 [OR = 11.00 (1.42; 85.20) P < 0.0217]). One scannographic sign was more present in the rupture group: crescent sign 36.8% versus 5.3%, P = 0.0007, as well in bivariate analysis [OR = 7 (1.59; 30.80) P < 0.0326].

CONCLUSIONS

In our experience, specific ratios when they exceed calculated threshold, seem to be more prone to rupture. We could consider that these measures, easy to apply in clinical practice, would be complementary keys for rupture risk individual assessment.

Imaging Modalities for Aortic Endografting

One of the most fundamental and influential differences between conventional surgery and endovascular grafting for aortic aneurysm is the central role of imaging in every aspect of management. This review summarizes five imaging techniques for aortic endografting: intravascular ultrasound, contrast angiography, conventional computed tomography (CT), spiral CT with image processing, and magnetic resonance angiography (MRA).

External ultrasound and intravascular ultrasound have important relevance to endovascular aortic surgery. Artifacts of arteriography include magnification, thrombus effect, foreshortening of tortuosity, loss of luminal detail, parallax error, and projection errors. Conventional CT scans have artifacts and difficulties also. Diameter measurement by CT suffers from methodology errors and observer variability. If conventional CT and angiography are used for endovascular aortic graft planning, both should be obtained since neither alone provides sufficient data.

The use of spiral CT scanning and computerized image processing has clearly aided the preoperative definition of aneurysm morphology both in terms of dimensional accuracy and by adding diagnostic information. MRA is capable of producing three-dimensional images, axial sections, and longitudinal projections in any plane. It can detect blood flow without contrast medium, but gadolinium enhances MRA by avoiding the “signal dropout” artifact.

Technology exists to provide new forms of imaging for endovascular surgery that combines three-dimensional models with on-line image data in a process called “data fusion.” This may offer improved ease and accuracy for conducting endovascular procedures in the future.

Elastin and collagen fibre microstructure of the human aorta in ageing and disease: a review

Aortic disease is a significant cause of death in developed countries. The most common forms of aortic disease are aneurysm, dissection, atherosclerotic occlusion and ageing-induced stiffening. The microstructure of the aortic tissue has been studied with great interest, because alteration of the quantity and/or architecture of the connective fibres (elastin and collagen) within the aortic wall, which directly imparts elasticity and strength, can lead to the mechanical and functional changes associated with these conditions. This review article summarizes the state of the art with respect to characterization of connective fibre microstructure in the wall of the human aorta in ageing and disease, with emphasis on the ascending thoracic aorta and abdominal aorta where the most common forms of aortic disease tend to occur.

Biomechanical determinants of abdominal aortic aneurysm rupture

Rupture of abdominal aortic aneurysm (AAA) represents a significant clinical event, having a mortality rate of 90% and being currently ranked as the 13th leading cause of death in the US. The ability to reliably evaluate the susceptibility of a particular AAA to rupture on a case-specific basis could vastly improve the clinical management of these patients. Because AAA rupture represents a mechanical failure of the degenerated aortic wall, biomechanical considerations are important to understand this process and to improve our predictions of its occurrence. Presented here is an overview of research to date related to the biomechanics of AAA rupture. This includes a summary of results related to ex vivo and in vivo mechanical testing, noninvasive AAA wall stress estimations, and potential mechanisms of AAA wall weakening. We conclude with a demonstration of a biomechanics-based approach to predicting AAA rupture on a patient-specific basis, which may ultimately prove to be superior to the widely and currently used maximum diameter criterion.

Regional distribution of wall thickness and failure properties of human abdominal aortic aneurysm

The regional distribution of wall thickness and failure properties in human abdominal aortic aneurysm (AAA) was explored. Three unruptured and one ruptured AAA were harvested as a whole during necropsy. Thickness was measured at about every 1.5 cm(2) wall surface area for an average of 100 measurement sites per AAA. Multiple longitudinally oriented rectangular specimen strips were cut at various locations from each AAA for a total of 48 strips. The strips were subjected to uniaxial extension until failure. Wall thickness varied regionally and between AAA from as low as 0.23 mm at a rupture site to 4.26 mm at a calcified site (median=1.48 mm). Wall thickness was slightly lower in the posterior and right regions. The failure tension (ultimate) of specimen strips varied regionally and between AAA from 5.5 N/cm close to a blister site in the ruptured AAA to 42.3N/cm at the undilated neck of a 4 cm diameter unruptured AAA (median=14.8 N/cm). Failure stress (ultimate) varied from 33.6 to 235.1N/cm(2) (median=126.6N/cm(2)). There was no perceptible pattern in failure properties along the circumference. Failure tension of specimen strips at or close to blisters was mostly low. The rupture site in the ruptured aneurysm had the lowest recorded wall thickness of 0.23 mm with only slightly higher readings within a 1cm radius. The failure tension of the specimen strip close to the rupture site was low (11.1 N/cm) compared to its neighborhood in the ruptured aneurysm.

Contribution of PET scanning to the evaluation of abdominal aortic aneurysm

The size of abdominal aortic aneurysms (AAA) is the most usual predictor of the risk for rupture. Because chronic metalloproteinases production and activation by inflammatory cells causes degradation of elastin and collagen in the aneurysmal wall, the detection of an increased metabolic process preceding fissuration and rupture could be a more sensitive predictor of rupture risk. We investigated the metabolic activity of the aneurysmal wall by whole-body positron emission tomography (PET) in 26 patients with a documented AAA (mean diameter 63 mm, extremes 45 mm and 78 mm). A positive (18)F-fluorodeoxyglucose ((18)F-FDG) uptake at the level of the AAA was observed in 38% of the cases (10 of 26 patients). Nine of these 10 patients required emergent or urgent aneurysmectomy for ruptured (n = 1), leaking (n = 1), rapidly expanding (n = 2), or painful (n = 5) aneurysms; the negative (18)F-FDG uptake patients had a more benign course. This preliminary study suggests a possible correlation between (18)F-FDG uptake by the aneurysm wall and the triggering of processes leading to rupture. The (18)F-FDG uptake in the aneurysm wall may correspond to the accumulation of inflammatory cells responsible for the production and activation of degrading enzymes. PET scan seems useful in high-risk patients. Positive PET imaging in these cases would help us to decide to proceed with surgery, despite factors favoring a surveillance strategy.

Guidelines for the treatment of abdominal aortic aneurysms. Report of a subcommittee of the Joint Council of the American Association for Vascular Surgery and Society for Vascular Surgery

Decision-making in regard to elective repair of abdominal aortic aneurysms (AAA) requires careful assessment of factors that influence rupture risk, operative mortality, and life expectancy. Individualized consideration of these factors in each patient is essential, and the role of patient preference is of increasing importance. It is not possible or appropriate to recommend a single threshold diameter for intervention which can be generalized to all patients. Based upon the best available current evidence, 5.5 cm is the best threshold for repair in an "average" patient. However, subsets of younger, good-risk patients or aneurysms at higher rupture risk may be identified in whom repair at smaller sizes is justified. Conversely, delay in repair until larger diameter may be best for older, higher-risk patients, especially if endovascular repair is not possible. Intervention at diameter <5.5 cm appears indicated in women with AAA. If a patient has suitable anatomy, endovascular repair may be considered, and it is most advantageous for older, higher-risk patients or patients with a hostile abdomen or other technical factors that may complicate standard open repair. With endovascular repair, perioperative morbidity and recovery time are clearly reduced; however, there is a higher reintervention rate, increased surveillance burden, and a small but ongoing risk of AAA rupture. There is no justification at present for different indications for endovascular repair, such as earlier treatment of smaller AAA. Until long-term outcome of endoluminal repair is better defined and results of randomized trials available, the choice between endovascular and open repair will continue to rely heavily on patient preference.

Accuracy of three-dimensional simulation in the sizing of aortic endoluminal devices

The purpose of this study is to examine the accuracy of a 3D simulation generated by inclusion of various intensity-selected portions of spiral CT data into a proprietary software program (Preview, Medical Media Systems, MMS) in preoperative and postoperative assessment of the anatomical features of abdominal aortic aneurysm (AAA). The accuracy of this software was measured against two other modalities-intravascular ultrasound (IVUS) and axial CT scan-using the IVUS as the reference. Eighty-five patients were included; 43 underwent AAA endovascular exclusion with Talent devices, and 42 with Aneurx devices. Measurement of proximal neck diameter was performed using IVUS, Preview software, and axial CT scan with manual calipers. Measurement of the AAA maximum diameter was performed using Preview software and axial CT scan; 253 measurements in the 85 patients were included. These measurements were compared by means of both linear regression and Bland-Altman agreement analysis. Our results showed that the 95% confidence interval between the Preview software and mean IVUS measurement of proximal AAA neck (3.1 and 2.5) is narrow enough for the software to be used in sizing AAA. This would be especially important for having the properly sized devices available preoperatively. The Preview software tended to be more accurate than CT scans although it was not statistically significant.

Proteolysis of the abdominal aortic aneurysm wall and the association with rupture

PURPOSE

to investigate proteolysis of the abdominal aortic aneurysm (AAA) wall and the association with rupture.

METHODS

levels of matrix metalloproteinases (MMP-2 and MMP-9) and tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-2) were measured in the walls of medium-sized (5-7 cm in diameter) ruptured AAA (rAAA) (n =30) and large (> or = 7 cm in diameter) asymptomatic AAA (aAAA) (n=30).

RESULTS

MMP-2 levels (median, range) were significantly higher in the walls of large aAAA (165 ng/g AAA tissue, 50-840) than from medium-sized rAAA (110 ng/g AAA tissue, 47-547, p=0.007). MMP-9 levels were significantly higher in the walls of medium-sized rAAA (107 ng/g AAA tissue, 19-582) than from large aAAA (55 ng/g AAA tissue, 11-278, p=0.012). TIMP-1 and TIMP-2 levels were equivalent. There was a positive correlation between MMP-2 and the diameter of aAAA (r=0.54, p=0.002), but a negative correlation with MMP-9 (r= -0.44, p=0.017). No significant correlations were found between aAAA diameter and TIMP-1 or TIMP-2.

CONCLUSION

AAA rupture is associated with higher levels of MMP-9. There is no association with TIMP-1 or TIMP-2 levels. MMP-2 levels are positively, whereas MMP-9 levels are negatively, correlated with aAAA size. MMP-9 may play a role in the progression towards rupture, whereas MMP-2 may play a role in expansion.

Abdominal aortic aneurysm wall mechanics and their relation to risk of rupture

PURPOSE

to see whether aneurysmal aortic wall mechanics can be used as a predictor of abdominal aortic aneurysm (AAA) rupture.

METHOD

among 285 individuals, followed conservatively for AAA and monitored for aneurysm growth and wall mechanics on at least one occasion at our institution between January 1991 and January 1998, eleven subsequently ruptured. Wall mechanics were estimated as stiffness (beta). This was calculated from diameter and pulsatile diameter change, determined non-invasively by an ultrasonic echo-tracking system and blood pressure obtained by the auscultatory method. The results were compared with those of 121 individuals electively operated on for AAA.

RESULTS

no difference in aortic stiffness was found between those that subsequently ruptured (beta=35, median) compared to those non-ruptured (beta=38, median) AAAs (p=0.855). There was no difference in diameter in ruptured (58.8 mm) compared with non-ruptured (54.1 mm) AAAs (p=0.129). All ruptured AAAs showed an expansion of diameter over time.

CONCLUSION

this study shows no difference in aneurysmal aortic wall mechanics in those AAAs that subsequently ruptured compared with electively operated AAAs. The results indicate that it is not possible to use aneurysmal aortic wall stiffness as a predictor of rupture.

Saccular outpouchings of an ascending aortic aneurysm: transesophageal echocardiographic appearance

The differential diagnosis of cavities in the ascending aorta includes pseudoaneurysms, intimal flaps, and abscesses. We describe the transesophageal echocardiographic and pathologic appearance of a fusiform ascending aortic aneurysm that contained atypical outpouchings that were initially confused with an intimal flap. Awareness of this unreported abnormality and its echocardiographic features will avoid the misdiagnosis of more serious aortic pathology such as acute aortic dissection or infective endocarditis.

Imaging modalities for aortic endografting

One of the most fundamental and influential differences between conventional surgery and endovascular grafting for aortic aneurysm is the central role of imaging in every aspect of management. This review summarizes five imaging techniques for aortic endografting: intravascular ultrasound, contrast angiography, conventional computed tomography (CT), spiral CT with image processing, and magnetic resonance angiography (MRA). External ultrasound and intravascular ultrasound have important relevance to endovascular aortic surgery. Artifacts of arteriography include magnification, thrombus effect, fore-shortening of tortuosity, loss of luminal detail, parallax error, and projection errors. Conventional CT scans have artifacts and difficulties also. Diameter measurement by CT suffers from methodology errors and observer variability. If conventional CT and angiography are used for endovascular aortic graft planning, both should be obtained since neither alone provides sufficient data. The use of spiral CT scanning and computerized image processing has clearly aided the preoperative definition of aneurysm morphology both in terms of dimensional accuracy and by adding diagnostic information. MRA is capable of producing three-dimensional images, axial sections, and longitudinal projections in any plane. It can detect blood flow without contrast medium, but gadolinium enhances MRA by avoiding the "signal dropout" artifact. Technology exists to provide new forms of imaging for endovascular surgery that combines three-dimensional models with on-line image data in a process called "data fusion." This may offer improved ease and accuracy for conducting endovascular procedures in the future.