Radiation diagnosis of abdominal aortic aneurysms

Four hundred and forty seven patients with aneurysms of the abdominal aorta (AAA), including 238 patients with aneurysmal rupture, were admitted to the Research Institute of Emergency Care in 1990 to 2000. The results of studies in 225 patients (ultrasonography in 197, computed tomography in 59, and angiography in 104), including 155 patients with aneurysmal rupture were analyzed. Computed tomography (CT) has proved to be the most accurate technique in the detection and estimation of the size of aneurysms, as well as in the identification of ruptures (83.9%) and inferior to angiography (AG) in the study of involvement of the branches of the abdominal aorta. Ultrasound study (US) ranks below CT in its accuracy (US detects ruptures in 67.8%); however, US surpasses CT and AS in screening, particularly valuable at an admission unit and an intensive care unit, which permits repeated studies. AG has turned out to be the most valid method in identifying the involvement of renal and iliac arteries in aneurysm and in detecting aortocaval anastomoses; yet it is inferior to US and CT (the former revealed rupture and dissection in 18.6% of cases) in solving other diagnostic tasks. Based on the analysis, the optimal sequence of studies in the patients is US, CT, and AG.     

Porohyperelastic finite element modeling of abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) is the gradual weakening and dilation of the infrarenal aorta. This disease is progressive, asymptomatic, and can eventually lead to rupture--a catastrophic event leading to massive internal bleeding and possibly death. The mechanical environment present in AAA is currently thought to be important in disease initiation, progression, and diagnosis. In this study, we utilize porohyperelastic (PHE) finite element models (FEMs) to investigate how such modeling can be used to better understand the local biomechanical environment in AAA. A 3D hypothetical AAA was constructed with a preferential anterior bulge assuming both the intraluminal thrombus (ILT) and the AAA wall act as porous materials. A parametric study was performed to investigate how physiologically meaningful variations in AAA wall and ILT hydraulic permeabilities affect luminal interstitial fluid velocities and wall stresses within an AAA. A corresponding hyperelastic (HE) simulation was also run in order to be able to compare stress values between PHE and HE simulations. The effect of AAA size on local interstitial fluid velocity was also investigated by simulating maximum diameters (5.5 cm, 4.5 cm, and 3.5 cm) at the baseline values of ILT and AAA wall permeability. Finally, a cyclic PHE simulation was utilized to study the variation in local fluid velocities as a result of a physiologic pulsatile blood pressure. While the ILT hydraulic permeability was found to have minimal affect on interstitial velocities, our simulations demonstrated a 28% increase and a 20% decrease in luminal interstitial fluid velocity as a result of a 1 standard deviation increase and decrease in AAA wall hydraulic permeability, respectively. Peak interstitial velocities in all simulations occurred on the luminal surface adjacent to the region of maximum diameter. These values increased with increasing AAA size. PHE simulations resulted in 19.4%, 40.1%, and 81.0% increases in peak maximum principal wall stresses in comparison to HE simulations for maximum diameters of 35 mm, 45 mm, and 55 mm, respectively. The pulsatile AAA PHE FEM demonstrated a complex interstitial fluid velocity field the direction of which alternated in to and out of the luminal layer of the ILT. The biomechanical environment within both the aneurysmal wall and the ILT is involved in AAA pathogenesis and rupture. Assuming these tissues to be porohyperelastic materials may provide additional insight into the complex solid and fluid forces acting on the cells responsible for aneurysmal remodeling and weakening.     

A methodology for in silico endovascular repair of abdominal aortic aneurysms

Endovascular aneurysm repair (EVAR) can involve some unfavorable complications such as endoleaks or stent-graft (SG) migration. Such complications, resulting from the complex mechanical interaction of vascular tissue, SG and blood flow or incompatibility of SG design and vessel geometry, are difficult to predict. Computational vascular mechanics models can be a predictive tool for the selection, sizing and placement process of SGs depending on the patient-specific vessel geometry and hence reduce the risk of potential complications after EVAR. In this contribution, we present a new in silico EVAR methodology to predict the final state of the deployed SG after intervention and evaluate the mechanical state of vessel and SG, such as contact forces and wall stresses. A novel method to account for residual strains and stresses in SGs, resulting from the precompression of stents during the assembly process of SGs, is presented. We suggest a parameter continuation approach to model various different sizes of SGs within one in silico EVAR simulation which can be a valuable tool when investigating the issue of SG oversizing. The applicability and robustness of the proposed methods are demonstrated on the example of a synthetic abdominal aortic aneurysm geometry.     

Mesenchymal stem cells for treatment of aortic aneurysms

An aortic aneurysm(AA) is a silent but life-threatening disease that involves rupture. It occurs mainly in aging and severe atherosclerotic damage of the aortic wall. Even though surgical intervention is effective to prevent rupture, surgery for the thoracic and thoraco-abdom-inal aorta is an invasive procedure with high mortality and morbidity. Therefore, an alternative strategy for treatment of AA is required. Recently, the molecular pathology of AA has been clarified. AA is caused by an imbalance between the synthesis and degradation of extracellular matrices in the aortic wall. Chronic inflam-mation enhances the degradation of matrices directly and indirectly, making control of the chronic inflamma-tion crucial for aneurysmal development. Meanwhile, mesenchymal stem cells(MSCs) are known to be ob-tained from an adult population and to differentiate into various types of cells. In addition, MSCs have not only the potential anti-inflammatory and immunosuppres-sive properties but also can be recruited into damagedtissue. MSCs have been widely used as a source for celltherapy to treat various diseases involving graft-versus-host disease, stroke, myocardial infarction, and chronicinflammatory disease such as Crohn's disease clinically.Therefore, administration of MSCs might be availableto treat AA using anti-inflammatory and immnosup-pressive properties. This review provides a summary ofseveral studies on "Cell Therapy for Aortic Aneurysm"including our recent data, and we also discuss the pos-sibility of this kind of treatment.     

Diagnosis and management of 528 abdominal aortic aneurysms.

Between 1960 and 1979 528 patients with abdominal aortic aneurysms presented to the university department of surgery. Of these, 222 (42%) were elective cases, 72 acute (14%), 174 had ruptured (33%), and four had had a spontaneous aortoduodenal fistula (1%). In all these patients resections were undertaken, but in another 56 patients (11%) the aneurysm was not resected. A review of these cases showed that 91% had symptoms at their first presentation; abdominal pain and backache being most common. The diagnosis could be established in 91% by the presence of pulsatile abdominal mass on clinical examination. The operative mortality for elective resection was 8%, for acute 19%, for ruptured cases 42%, and for spontaneous aortoduodenal fistula 50%. After successful resection the overall five-year survival was 65% by the life table method, and there was no significant difference between elective, acute, and ruptured cases. This five-year survival after resection compares favourably with the expected 76% survival of a similar normal population, and was considerably better than that for conservatively treated patients. As most cases have symptoms, and diagnosis may be established easily by routine physical examination in 91%, the prognosis for this condition could be considerably improved by increased awareness of its existence and early referral for treatment as an elective surgical procedure.     

Screening for abdominal aortic aneurysms: single centre randomised controlled trial

Objective To determine whether screening Danish men aged 65 or more for abdominal aortic aneurysms reduces mortality.Design Single centre randomised controlled trial.Setting All five hospitals in Viborg County, Denmark.Participants All 12 639 men born during 1921-33 and living in Viborg County. In 1994 we included men born 1921-9 (64-73 years). We also included men who became 65 during 1995-8.Interventions Men were randomised to the intervention group (screening by abdominal ultrasonography) or control group. Participants with an abdominal aortic aneurysm > 5 cm were referred for surgical evaluation, and those with smaller aneurysms were offered annual scans.Outcome measures Specific mortality due to abdominal aortic aneurysm, overall mortality, and number of planned and emergency operations for abdominal aortic aneurysms.Results 4860 of 6333 men were screened (attendance rate 76.6%). 191 (4.0% of those screened) had abdominal aortic aneurysms. The mean follow-up time was 52 months. The screened group underwent 75% (95% confidence interval 51% to 91%) fewer emergency operations than the control group. Deaths due to abdominal aortic aneurysms occurred in nine patients in the screened group and 27 in the control group. The number needed to screen to save one life was 352. Specific mortality was significantly reduced by 67% (29% to 84%). Mortality due to non-abdominal aortic aneurysms was non-significantly reduced by 8%. The benefits of screening may increase with time.Conclusion Mass screening for abdominal aortic aneurysms in Danish men aged 65 or more reduces mortality.     

Access sites to vascular system for endovascular abdominal aortic aneurysms repair

The authors describe their experience with access sites for endovascular abdominal aortic aneurysm repair in a group of 165 patients treated over a 10-year period.     

Web-site-based recruitment for research studies on abdominal aortic and intracranial aneurysms

Our current understanding on the pathogenesis of abdominal aortic and intracranial aneurysms is limited, but genetic and environmental factors as well as their interactions are likely to play important roles in the development and rupture of aneurysms. To identify genetic factors contributing to these diseases, we are carrying out genome-wide screening studies, which require a large number of patients and family members. Current methods of finding patients who qualify for genetic studies are, however, often costly and ineffective. To improve patient recruitment, a Web site was developed (cmmg.biosci.wayne.edu/ags). The site gives general information about our study, solicits participation into the study, and provides links to relevant medical and educational sites. During the time period of July, 1999, to December, 2000, the site received 5, 108 visits (13 visits/day). Approximately 20 research study applications are received each month. A total of 49% (57/117) of the individuals responding to the aortic aneurysm and 63% (84/134) responding to the intracranial aneurysm study report at least two affected blood relatives in the family and, therefore, qualify for our genetic studies. In conclusion, Web-based patient recruitment is successful and provides an improved success rate due to the fact that the responders are more motivated to participate in research studies.