Surveillance After Endovascular Abdominal Aortic Aneurysm Repair

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  • REVIEW

    Surveillance After Endovascular Abdominal Aortic AneurysmRepair

    Donald M. L. Tse Charles R. Tapping

    Rafiuddin Patel Robert Morgan Mark J. Bratby

    Susan Anthony Raman Uberoi

    Received: 16 August 2013 / Accepted: 3 April 2014

    Springer Science+Business Media New York and the Cardiovascular and Interventional Radiological Society of Europe (CIRSE) 2014

    Abstract Surveillance after endovascular abdominal

    aortic aneurysm repair (EVAR) is widely considered

    mandatory. The purpose of surveillance is to detect

    asymptomatic complications, so that early secondary

    intervention can prevent late aneurysm rupture. CT angi-

    ography has been taken as the reference standard imaging

    test, but there is increasing interest in using other modali-

    ties to reduce the use of ionising radiation and iodinated

    contrast. As a result, there is wide heterogeneity in sur-

    veillance strategies used among EVAR centres. We

    reviewed the current evidence available on the outcomes of

    different imaging modalities and surveillance strategies

    following EVAR.

    Keywords Endovascular procedures Surveillance Abdominal aortic aneurysm Endoleak

    Introduction

    Endovascular abdominal aortic aneurysm repair (EVAR)

    has evolved over the past two decades into an established

    alternative to open surgical repair for patients with

    abdominal aortic aneurysms. The benefits of EVAR in

    terms of the reduction in perioperative mortality compared

    with open repair have been well documented in multiple

    trials and large registries [15]. The minimally invasive

    nature of EVAR enables its application in patients with

    significant comorbidities and high operative risk. However,

    as these trials and registries also have demonstrated, the

    short-term reduction in mortality from EVAR does not

    continue into the long term, due to a higher incidence of

    late complications and a linear rate of requirement for

    secondary interventions [69]. This has resulted in the

    consensus that surveillance following EVAR is mandatory.

    On the other hand, it has been noted that only 1.49 % of

    EVAR patients undergo reintervention solely because of

    surveillance-detected abnormalities, with the majority of

    reinterventions occurring in symptomatic patients with

    previously normal surveillance studies [1012]. This

    apparent discrepancy has led to much uncertainty and a

    wide heterogeneity regarding surveillance strategies

    employed by different centres [13]. The purpose of this

    review was to evaluate the rationale and evidence behind

    surveillance strategies post EVAR.

    Purpose of Surveillance Following EVAR

    The purpose of any surveillance strategy is to identify

    asymptomatic complications so that early treatment can

    result in better long-term outcomes and prevent late

    aneurysm rupture. For the prevention of aneurysm rupture

    following EVAR, the important features to detect include

    (a) enlargement of the aneurysm sac; (b) stent-graft struc-

    tural changes, including fracture; (c) stent-graft migration

    from its deployed position; (d) stenoses or occlusions in the

    endograft limbs or outflow iliac arteries; (e) endoleaks

    where there is blood flow external to the stent-graft inside

    the aneurysm sac. Type I and III endoleaks are particularly

    important to detect, because they invariably lead to sac

    D. M. L. Tse C. R. Tapping R. Patel M. J. Bratby S. Anthony R. Uberoi (&)Department of Radiology, Oxford University Hospitals,

    John Radcliffe Hospital, Oxford OX3 9DU, UK

    e-mail: raman.uberoi@ouh.nhs.uk

    R. Morgan

    Department of Radiology, St Georges Hospital,

    Blackshaw Road, London SW17 0QT, UK

    123

    Cardiovasc Intervent Radiol

    DOI 10.1007/s00270-014-0916-z

  • expansion and aneurysm rupture and require urgent treat-

    ment after detection. Although there is a general consensus

    that only type II endoleaks associated with sac expansion

    should be treated, it is still important to detect and observe

    these endoleaks [14]. Flow-limiting stenoses in the graft

    limbs or outflow arteries are important to detect even if

    they may be asymptomatic, as they may precipitate

    thrombosis and occlusion of the graft limb.

    EVAR Surveillance Using Computed Tomography

    Since the large, randomized, controlled trials and early

    registries, computed tomography angiography (CTA) has

    been taken as the reference standard imaging test for

    EVAR surveillance. The computed tomography (CT)

    scanning protocols used by centres vary widely [15, 16],

    but all include one or more of the following phases: non-

    contrast phase to help differentiate between contrast versus

    calcification in the arterial wall, thrombus, or graft mate-

    rial; arterial contrast phase to detect endoleaks; and venous

    or delayed phase at least 60 s after contrast injection to

    identify low-flow endoleaks that may not appear in the

    arterial phase [1719].

    One main issue of a surveillance strategy using CTA is

    the use of relatively high doses of ionising radiation, which

    can range from 15 to 31 mSv per study. This can lead to

    significant cumulative risks of solid organ cancer, espe-

    cially if EVAR is performed in younger patients and sur-

    veillance continues lifelong [2022]. The repeated use of

    iodinated contrast media for CTA also raises concerns

    regarding contrast nephrotoxicity, particularly in the

    elderly or patients with renal impairment. Image quality

    with CT is degraded by streak artifacts, which can be

    caused by metallic embolisation coils or high-density

    embolic agents, such as Onyx (Covidien, Irvine, CA). This

    poses a limitation for the detection of endoleaks on CTA

    for patients who have had embolisation treatment, as part

    of the primary EVAR procedure or for subsequent endo-

    leak. Furthermore, CTA is relatively expensive compared

    with modalities, such as ultrasound. Surveillance imaging

    and secondary procedures have been shown to increase the

    overall cost of EVAR by nearly 50 %, and this impacts on

    the cost effectiveness of EVAR as a treatment option [23].

    A number of studies have aimed at reducing the radi-

    ation dose of CTA by reducing the number of scan phases

    used. Iezzi et al. [24] compared: (1) arterial phase alone,

    (2) arterial and unenhanced phase, and (3) arterial and

    delayed phases, in the detection of endoleaks after EVAR.

    They found that in addition to the arterial phase, an un-

    enhanced phase can be performed at the first follow-up

    visit, which significantly increased the specificity (from 75

    to 97 %) and positive predictive value (from 55 to 93 %)

    for detecting endoleaks in their study population of 50

    patients, who had 14 endoleaks on CT 1 month post

    EVAR (2 type I, 14 type II, 1 type III). Although the

    addition of a delayed phase scan increased the detection of

    low-flow endoleaks, this did not reach statistical signifi-

    cance. Macari et al. [25] studied 110 CT examinations in

    85 patients and found that the 3 type I and 1 type III

    endoleaks were identified in both arterial and venous

    phases, but 3 of 28 type II endoleaks were only seen in the

    venous phase, and led the authors to conclude that the

    arterial phase can be omitted to reduce radiation dose.

    Bastos et al. [26] came to a similar conclusion in their

    study of 30 patients who underwent CTA and found that 3

    of 8 type II endoleaks were not visible in the arterial

    phase scans but were all visible in the venous phase (there

    were no type I or type III endoleaks in this series).

    However, the clinical significance of the endoleaks

    detected only in the venous phases in these studies was

    not known. In the study by Hong et al., in 144 patients

    with endoleaks, 8 of the endoleaks were detected in the

    delayed phase only but these all resolved spontaneously,

    suggesting that these low-flow endoleaks may not have

    clinical significance. The authors concluded that the

    delayed phase can be omitted from surveillance CT scans

    [27]. These studies are summarised in Table 1.

    Other researchers have investigated whether noncontrast

    CT scans can provide adequate information for surveil-

    lance after EVAR and obviate the need for contrast media.

    In the study by Bley et al. [28] of 70 patients, aortic volume

    analysis was performed on noncontrast images, and they

    found that in 10 type I or III endoleaks showed a mean

    10 % increase in aortic volume, whereas 37 type II en-

    doleaks showed a mean 5.4 % increase in aortic volume.

    The authors concluded that noncontrast CT with aortic

    volume analysis can be used for surveillance, and contrast-

    enhanced imaging only performed if there is an aortic

    volume increase of more than 2 %.

    Magnetic Resonance Imaging/Angiography

    Magnetic resonance imaging (MRI) and gadolinium-

    enhanced angiography provide an alternative imaging

    modality to CTA, with the obvious advantage being the

    avoidance of ionising radiation. Several different imaging

    protocols for MRI have been investigated. The majority of

    data on the use of magnetic resonance imaging/angiogra-

    phy (MRI/MRA) for surveillance post EVAR involves

    three-dimensional, gadolinium-enhanced dynamic and

    delayed MRA. More recently, time-resolved MRA has

    been used to provide