Contrast enhanced ultrasound in the surveillance of abdominal aortic aneurysm repair

  • Shelly Finch

    Student thesis: Doctoral Thesis


    This study aimed to evaluate the clinical effectiveness of Contrast Enhanced Ultrasound (CEUS) in detecting the presence of endoleaks after Endovascular Aortic Aneurysm Repair (EVAR) and in comparing the diagnostic accuracy with other imaging modalities. Observing Type II endoleak behaviour allowed the practitioner to determine the endoleak origin, communication with branch vessels and categorise endoleak behaviour based on underlying haemodynamics as a tool for interventional decision making.
    One hundred and seven patients, all post-EVAR, underwent surveillance utilising CEUS, Colour Doppler Ultrasound (CDU) and Computed Tomography Angiography (CTA). Each modality assessed for the presence of an endoleak. The existence of contrast within the stent graft established patency, and contrast within the residual aneurysm sac indicated an endoleak presence. Endoleaks were classified by type, origin, and size with quantitative comparison made between each modality.
    There is a statistically significant increased rate of endoleak detection, especially for low amplitude, slow flowing endoleaks using CEUS compared to CDU and CTA. Two-tailed P value was calculated with McNemar’s Test and continuity correction at<.0001. CDU identified thirty-six endoleaks, CTA identified thirty-nine endoleaks and CEUS identified sixty-three endoleaks. Statistical analysis has also highlighted that CDU in comparison to CTA in the detection of Endoleaks is not statistically significant. These two imaging modalities were considered to be equivalent. Type II endoleaks were subcategorised based on the vessel origin, behaviour, channel connection, and spectral Doppler characterisation. CEUS enhanced the spectral Doppler signal to enable identification of low flow endoleaks and vessel origins. Apart from the Type II subcategories A and B already identified, two further Type II subcategories, namely C and D occurred. The differing characteristics of these new subcategories were classified based on the haemodynamic effect and the physical characteristics of the endoleak.
    In this study, CEUS has proven to be an extremely effective imaging modality in the detection, visualisation, and classification of endoleaks in comparison to CDU and CTA. CEUS is a sensitive adjunct to unenhanced ultrasound and is an extremely useful imaging modality in patients where CTA is contraindicated. CEUS is an accurate and minimally invasive way to interrogate these endografts and has in this study, demonstrated statistically significant improvements in the detection of endoleaks. CEUS has enabled additional sub-categorisations of Type II endoleaks based on their flow dynamics. The additional sub-categorisations of Type II B (i) and (ii), C and D has shown initial benefit in determining an ‘at risk’ Type II endoleak. Type IIC endoleaks seem to be associated with an increasing aortic sac size. This suggested that EVARs that have Type IIC endoleaks may be at risk of rupture due to continued pressurisation of the residual aneurysmal sac and should be considered an indication for secondary intervention.
    An enhanced understanding of Type II endoleaks will aid in future interventional and implementation strategies, which will ultimately lead to EVAR success. If the advances in ultrasound imaging technology, with the use of contrast agents, continue to demonstrate its dominance, CEUS will become a routine part of EVAR surveillance.
    Date of Award2021
    Original languageEnglish
    SupervisorRob Davidson (Supervisor), Rod Mcgregor (Supervisor) & Karen Pollard (Supervisor)

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