Surveillance After Endovascular Abdominal Aortic Aneurysm Repair

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 [1–5]. 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 [6–9]. This has resulted in the

consensus that surveillance following EVAR is mandatory.

On the other hand, it has been noted that only 1.4–9 % 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 [10–12]. 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: [email protected]

R. Morgan

Department of Radiology, St George’s 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 [17–19].

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 [20–22]. 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 information on the direction of flow

of contrast medium post EVAR [29–31]. Both extracellular

and blood-pool contrast agents have been used successfully

D. M. L. Tse et al.: Surveillance After EVAR

123

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5]

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123

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[30]


123

to image endoleaks, with blood pool agents suggested to

improve the detection of slow flow endoleaks [29, 30, 32].

MRI is limited by cost and availability and is contra-

indicated in patients with pacemakers or claustrophobic

patients. The extensive susceptibility artefacts seen with

stainless steel also mean that MRI has a very limited role in

the imaging of patients with grafts containing stainless

steel (e.g., Zenith Flex device; Cook, Bloomington, IN), as

opposed to nitinol-based grafts, which produce less arte-

fact. Moreover, as stainless steel embolization coils also

produce MR artefact, MRI is not a good modality for the

follow-up of patients who have undergone coil emboliza-

tion of the internal iliac artery before EVAR. Patients with

chronic kidney disease (CKD) stage 4 or 5 (GFR\30 mL/

min) are at high risk of developing nephrogenic systemic

fibrosis (NSF) after gadolinium administration, and there-

fore the use of gadolinium-based contrast agents in these

patients is contraindicated, whereas its use should be with

caution in patients with CKD stage 3 (GFR 30–59 mL/min)

who are at lower risk of developing NSF [33].

MRA has been shown to be comparable to CT for the

measurement of the aortic diameter and thus the sac size

[34]. For the detection of endoleaks, MRI has been eval-

uated against CTA in several studies, 11 of which were

included in a recent systematic review, totalling 369

patients and 562 pairs of MRI and CTA examinations [30,

34–44]. These studies are summarised in Table 2. Overall,

MRI detected 132 additional endoleaks compared with

CTA, including 86 type II (187 for MRI vs. 101 for CTA)

and 26 indeterminate (39 for MRI vs. 13 for CTA) en-

doleaks. MRA missed 2 of 15 type I endoleaks detected on

CTA. In one of these cases, a type Ib endoleak was masked

by vessel wall calcification and the platinum markers of a

distal limb, whereas in the other case, consensus reading of

CTA and MRA between two readers concluded no type I

endoleak [37, 38]. Twelve additional cases of type III en-

doleaks were detected on MRI. In 1 case, the additional

type III endoleak was classified as type II on subsequent

catheter angiography [36]; among the other 11 cases

reported by Pitton et al. [37], only 1 resulted in secondary

treatment, and it was unclear why the other cases were not

treated, as currently all type III endoleaks require treat-

ment. Similarly, because information on aneurysm growth

was not available, it is not clear how many of the additional

type II endoleaks were clinically significant.

There is difficulty in assessing device integrity with

MRI, which limits its use as a sole modality for surveil-

lance, and to date no published studies have evaluated the

clinical outcomes of an MRI-based surveillance protocol.

However, the added sensitivity for endoleaks from MRI

means that it can be a useful complementary test, partic-

ularly in cases where endoleak is suspected due to aneu-

rysm growth, but not demonstrable on CTA.

Duplex Ultrasound and Contrast-Enhanced Ultrasound

There is considerable interest in the use of duplex ultrasound

(DUS) and contrast-enhanced ultrasound (CEUS) as alterna-

tives to CTA. There are obvious benefits of ultrasound, which

uses no ionising radiation and no nephrotoxic contrast agents,

and allows dynamic examination of the areas of interest. DUS

allows an assessment of the direction and velocity of flow, is

widely available, and is less expensive than CTA. Regarding

CEUS, after the intravenous injection of contrast microbub-

bles, the appearance of the contrast medium can be followed in

real-time as it appears within the graft and any endoleak can be

visualised as contrast outside the graft in the aneurysm sac.

This provides a dynamic assessment of the endoleak, which

enables the radiologist to identify the site of origin of the

endoleak and therefore define the endoleak type. Because the

contrast microbubbles can persist in the blood pool for some

time, the ultrasound assessment can extend into the delayed

phase continuously. The disadvantages of using ultrasound

include operator dependence and the variability in image

quality depending on patient body habitus. The use of contrast

agents also adds to the cost of the examination, although

CEUS is reported to still be cheaper than CTA [45].

In a meta-analysis by Karthikesalingam et al., including 25

studies comparing DUS, CEUS against CT for EVAR sur-

veillance, the pooled sensitivities for all endoleaks were 0.74

for DUS and 0.96 for CEUS and pooled specificities were 0.94

for DUS and 0.85 for CEUS. However, when comparing

ultrasound against CTA for only types I and III endoleaks,

features that alone would be sufficient to necessitate reinter-

vention, the pooled sensitivities were 0.83 for DUS and 0.99

for CEUS, and pooled specificities were 1.00 for both DUS

and CEUS [46]. The results suggest that the added benefit of

CEUS over DUS would be in diagnosing type II endoleaks,

which unless there is sac enlargement, do not require rein-

tervention. Meanwhile, there is good correlation between US

and CT for the measurement of aneurysm sac size, and

although US may consistently underestimate sac diameter

compared with CT, for individual patients it is the change in

sac size that is most relevant [47–50]. Therefore, aneurysm sac

enlargement could be detected by DUS alone and direct fur-

ther investigation with CEUS or CTA. Meanwhile, asymp-

tomatic type II endoleaks without sac enlargement may be

missed by DUS. However, type II endoleaks generally do not

require intervention. Studies evaluating surveillance strate-

gies using DUS and/or CEUS are summarised in Table 3 and

discussed below.

Plain Radiography

The main role of plain radiographs is to assess the structural

integrity and detect limb kinks or endograft migration. Plain


123

Ta

ble

3S

tud

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eval

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surv

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stra

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Inte

rven

tio

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nic

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llin

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[59]

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07

16

0D

US

at1

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nth

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lyn

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yp

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end

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,

1o

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firm

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end

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rela

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dea

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pe

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6o

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CT

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Ty

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(wit

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om

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(25

%)

wit

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(10

%)

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6an

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llan

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123

radiography has no role in the assessment of aneurysm sac size

and endoleak detection. Plain radiographs, when taken using

consistent centring protocols, such as the Liverpool/Perth

protocol, allow reliable detection of kinks and migration of the

stent graft down to within 2 mm, at a fraction of the dose of CT

[32, 51–53]. However, plain radiographs cannot be used as a

sole surveillance modality and must be combined with a

modality, such as US, which can detect endoleaks and sac size

enlargement.

The complementary role of the abdominal radiograph

(AXR) was reported by Harrison et al., which used annual

AXR and DUS as the primary surveillance studies, with CTA

performed only when there are significant findings on AXR or

DUS, or if views of the aneurysm were unsatisfactory on DUS

[54]. In 194 patients undergoing a median of 36 months of

follow-up, AXR showed migration in 16 cases. Fifteen of the

patients were investigated by CTA and migration was con-

firmed in 10 patients, giving a positive predictive value (PPV)

for AXR of 67 %. This protocol of AXR and DUS for follow-

up reduced the use of CTA by 83, and 65 % of patients did not

require any CTA at 4 years [54]. In another study, Dias et al.

showed in 279 patients undergoing annual CT following

EVAR that only 26 (9.3 %) of the patients benefited from CT

surveillance and required reinterventions based on asymp-

tomatic findings. Of these 26 patients, only 1 patient, who had

partial coverage of the superior mesenteric artery and mal-

perfusion, would not have been detected by AXR and simple

diameter measurements using US [11]. These findings led to

their conclusion that CT is not required for the follow-up of the

majority of patients but should be used as a problem solver

when DUS or AXR suggest a problem.

Digital Subtraction Angiography

Digital subtraction angiography (DSA) has a no role in the

routine surveillance of patients following EVAR, given its

invasive nature and availability of other highly sensitive

imaging tests. However, DSA allows demonstration of contrast

flow direction and therefore is more helpful than CTA for the

classification of endoleaks in selected patients, where there is a

question regarding the type of endoleak type on CTA. There-

fore, the current role of DSA is as a problem solver to (a) define

the type of endoleak where there is uncertainty on noninvasive

imaging, and (b) as a final imaging modality to detect and treat

an endoleak when there is an enlarging aneurysm sac and no

visible endoleak on noninvasive imaging, including CEUS.

Aneurysm Sac Pressure Measurement

As an alternative to using imaging techniques, measure-

ment of the aneurysm sac pressure provides physiological

information about the repaired aneurysm [55]. Direct

pressure measurement by percutaneous sac puncture has

been reported by Dias et al. [56] in the follow-up of 37

patients, which showed that high sac pressure was associ-

ated with sac expansion, whereas low sac pressure was

associated with shrinkage. Successful endoleak embolisa-

tion in four patients resulted in pressure reduction. Non-

invasive pressure measurement involves the use of wireless

sensors, which can be implanted into the aneurysm sac at

the time of EVAR. Okhi et al. [57] showed in a multicentre

trial of 76 patients the safety profile of a wireless pressure

sensor, and demonstrated a sensitivity of 0.94 and speci-

ficity of 0.80 for the detection of type I or III endoleaks.

Ellozy et al. [58] showed in 21 patients who underwent

EVAR with an implantable remote pressure sensor that the

sac pressure was significantly lower in patients who have

aneurysm sac shrinkage compared with those with no

aneurysm shrinkage. However, despite early promising

results pressure measurements for EVAR surveillance its

use has not become widespread. Limitations including the

lack of information on graft structural integrity or graft

migration, and the lack of long-term follow-up data.

Can We Move Away From CT to US Plus AXR

for Surveillance?

Several groups have reported on the use of DUS alone for

surveillance and reserving CTA for only patients with

abnormal or inadequate US. These data are summarised in

Table 3. Collins et al. reported a 5-year retrospective

review of 160 patients who underwent DUS surveillance,

with CTA performed in the event of aneurysm sac

enlargement or endoleak on DUS. Forty-one endoleaks

were identified out of 359 DUS exams in these patients; in

35 cases investigated on subsequent CTA, 14 were con-

firmed. In three cases CTA demonstrated endoleaks that

were not detected on DUS, and in all three cases DUS

demonstrated sac enlargement; however, none of these

three endoleaks required additional intervention [59].

Chaer et al. [60] initially moved to a surveillance protocol

of using DUS alone from as early as 1 year post-EVAR, for

patients with a collapsed aneurysm sac. Subsequently they

expanded the use of DUS alone for surveillance in patients

with any sac shrinkage by C5 mm or stable size over

2 years. In their cohort of 184 patients with an average

DUS-only follow-up of 24 months, 3 endoleaks were

detected, including 2 type I endoleaks, which required limb

extensions, and 1 type II endoleak, which did not require

treatment. There were no adverse events, ruptures, device

failures, or limb occlusions observed as a consequence of

the DUS alone protocol [60]. Beeman et al. [48] converted

from a combined CTA and DUS surveillance protocol to


123

Ta

ble

4S

tud

ies

eval

uat

ing

EV

AR

surv

eill

ance

stra

teg

ies

wit

hre

du

ced

scan

nin

gin

terv

als

or

usi

ng

risk

stra

tifi

cati

on

Au

tho

rsY

ear

pu

bli

shed

NS

urv

eill

ance

stra

teg

yF

oll

ow

-up

du

rati

on

Ab

no

rmal

itie

so

nsu

rvei

llan

ceIn

terv

enti

on

sC

lin

ical

ou

tco

mes

Go

etal

.[6

4]

20

08

13

0If

no

rmal

CT

Aat

1m

on

th,

CT

Aat

6

and

12

mo

nth

s

All

[1

yea

rA

t6

mo

nth

s,2

typ

eII

end

ole

aks

En

do

leak

sat

6m

on

th:

no

inte

rven

tio

nre

qu

ired

1g

raft

thro

mb

osi

s

(no

rmal

surv

eill

ance

)A

t1

2m

on

ths,

1n

ewty

pe

Ien

do

leak

,2

new

typ

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end

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aks,

1p

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sten

tty

pe

IIen

do

leak

Ty

pe

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do

leak

at1

2m

on

ths

trea

ted

20

6If

no

rmal

CT

Aat

1m

on

th,

CT

Aat

12

mo

nth

so

nly

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[1

yea

r7

typ

eII

end

ole

aks

2ty

pe

IIen

do

leak

str

eate

d1

lim

b

thro

mb

osi

sat

9m

on

ths

Oth

ers

ob

serv

ed

Waa

sdo

rpet

al.

[63

]2

00

82

91

CT

Ap

red

isch

arg

e,at

3,

12

mo

nth

s,

ann

ual

lyaf

ter

n/a

Pre

dis

char

ge

CT

A:

1g

raft

thro

mb

osi

s,9

3en

do

leak

s

(8ty

pe

I;8

4ty

pe

II;

1ty

pe

III)

4in

terv

enti

on

sb

efo

re3

mo

nth

s

(2ty

pe

I,1

typ

eII

,1

typ

eII

I

end

ole

aks)

No

rup

ture

in

firs

t6

mo

nth

s

3m

on

thC

TA

:3

gra

ftth

rom

bo

ses,

1st

ent

mig

rati

on

,

43

end

ole

aks

(3ty

pe

I,4

0ty

pe

II)

5in

terv

enti

on

sd

uri

ng

3-1

2m

on

ths

(2ty

pe

I,3

typ

e

IIen

do

leak

s)

4th

rom

bo

sed

gra

fts

req

uir

ing

surg

ery

Pat

elet

al.

[74]

20

10

34

5C

TA

at1

,6

,

12

mo

nth

s,an

nu

ally

afte

r

5y

ears

12

3p

atie

nts

wit

hen

do

leak

—9

5%

are

typ

eII

end

ole

aks

56

inte

rven

tio

ns

for

end

ole

ak

(18

typ

eI,

37

typ

eII

,1

end

ote

nsi

on

)

No

rup

ture

s

3in

terv

enti

on

sfo

rm

igra

tio

n3

mig

rati

on

s

13

inte

rven

tio

ns

for

lim

b/a

rter

y

sten

osi

s/th

rom

bo

sis

Go

nca

lves

etal

.[7

3]

20

13

69

CT

Ap

red

isch

arg

e,at

6

and

12

mo

nth

s,

ann

ual

lyaf

ter

4.1

±2

yea

rsA

tp

red

isch

arg

eC

TA

,6

9h

igh

risk

(sea

l\1

0m

m

and

/or

end

ole

ak)—

38

end

ole

aks,

15

sac

enla

rgem

ent

du

rin

gfo

llo

w-u

p

31

inte

rven

tio

ns

in2

6h

igh

risk

pat

ien

ts(3

8%

)

No

rup

ture

s

2sa

cg

row

thd

uri

ng

foll

ow

-up

in6

2lo

w-r

isk

pat

ien

ts

4in

terv

enti

on

sin

4lo

w-r

isk

pat

ien

ts(6

%)

4co

nv

ersi

on

sto

op

enre

pai

r

So

rted

by

yea

ro

fp

ub

lica

tio

n


123

using DUS only, with additional imaging only if a problem

was detected. In 117 patients who underwent the DUS only

surveillance for average of 1.6 years, 29 patients (25 %)

had an endoleak detected, although only 3 required sec-

ondary intervention. There were no adverse events, such as

rupture, graft migration, or limb occlusion, observed as a

consequence of this change of strategy [48]. It was sug-

gested that using DUS alone led to cost savings of $1,595

per patient per year in their cohort [48].

To date, there have been no studies evaluating surveil-

lance protocols using CEUS alone or in combination with

AXR to replace CTA surveillance. In a recent study of 539

patients by Millen et al., the surveillance protocol consisted

of the following: CTA at 1 month, followed by annual

AXR and DUS, with further CTA only if AXR or DUS

showed abnormality or inconclusive results; CEUS was

used when there were discordant or nondiagnostic findings

(including the identification of endoleak type, and signifi-

cant sac expansion without identifiable endoleak) [45]. Of

27 patients who had an endoleak of indeterminate type,

CEUS demonstrated 4 to be type I (all confirmed at sec-

ondary intervention); 21 endoleaks were demonstrated to

be type II (5 of the 21 cases went on to secondary inter-

vention and were confirmed as type II); in 2 cases CEUS

excluded an endoleak but in 1 of these 2 patients, a type II

endoleak was found on subsequent follow-up. Four patients

in this study had sac enlargement with no endoleak dem-

onstrated on DUS or CTA. CEUS demonstrated one type II

endoleak confirmed at secondary treatment; in the other

three patients no endoleak was detected, although in one

patient a small type II endoleak was shown on subsequent

follow-up (Table 4). The authors suggested that CEUS can

be used to complement EVAR surveillance when other

imaging modalities are nondiagnostic.

Timing and Duration of Surveillance

Most complications and secondary interventions, including

ruptures, occur within the first 2-3 years following EVAR

[61, 62]. As a result, most surveillance protocols involve

early surveillance at most if not all of the following time

points: at discharge, 1, 3, 6, 12 months, with subsequent

annual follow-up after [61, 62].

Several studies have investigated the value of surveil-

lance at certain time points; these are summarised in

Table 4. In the study by Waasdorp et al., CT was per-

formed postprocedure and at 3 months. It was found that in

287 of 291 patients, the postprocedural CT performed

before discharge did not influence the treatment policy in

the first 3 months after EVAR and led the authors to

conclude that the predischarge postprocedural CT scan can

be omitted after an uneventful EVAR procedure [63].

However, in their cohort, four patients required early sec-

ondary interventions based on predischarge CTA findings,

including two type I and one type III endoleaks, which

required extension or interposition cuffs, and coiling of a

type II endoleak [63].

The utility of the surveillance CT at 6 months was

challenged in the study by Go et al. [64], which demon-

strated that in 130 patients with a normal CTA at 1 month,

no clinically significant findings warranting intervention

were identified at 6 months, with only two type II en-

doleaks without sac enlargement. Incidentally only 1 of the

130 patients had an abnormal CTA at 1 year that required

intervention. The omission of the surveillance at 6 months

for low-risk patients also was reported in the 5-year follow-

up study in the US Zenith multicentre trial, which included

739 patients [65]. Indeed, surveillance at 6 months was not

a requirement for the recent ENGAGE registry of the En-

durant stent graft (Medtronic, Santa Rosa, CA) [66].

While reducing the frequency and type of early sur-

veillance studies has been studied in some detail, there is

relatively little data or enthusiasm regarding the cessation

of long-term imaging surveillance post EVAR. The paucity

of very long-term (10?) years follow-up data for EVAR,

especially for the newer generation of stent grafts, and the

knowledge that at least up to 8 years there is still a linear

rate for reinterventions means that for most patients the

safest option would still be to continue surveillance [62].

However, Nordon et al. [62] have proposed that patients

who complete 3 years of surveillance without detection of

endoleak or sac enlargement can be discharged from fol-

low-up. Indeed, in a recently published survey of surveil-

lance practice in the U.K., most centres would continue

surveillance indefinitely annually, with some reducing the

frequency to biannually but seemingly without much evi-

dence-base [15].

Risk Stratification for Surveillance

In the large, clinical trials and registries of EVAR, the

follow-up protocols are mostly uniform throughout. How-

ever, in routine clinical practice, the spectrum of patients

being treated is much wider and clearly a ‘‘one size fits all’’

surveillance strategy would likely result in over-investi-

gation of low-risk patients and reduce the cost-effective-

ness of an EVAR programme. It is known that hostile neck

anatomy represents an independent risk factor for early and

late complications after EVAR [67–71]. In an evaluation of

the Endurant stent graft (Medtronic) comparing patients

treated according to device-specific instructions for use

(IFU) against off-label use with unfavourable proximal

neck anatomy, there was a significant increase in type I

endoleak at 1 year in the off-label use group [72]. An


123

association between larger aneurysm size and an increased

rupture risk after EVAR also has been seen in several trials

[61]. These known risk factors suggest that it is possible to

risk stratify patients for the risk of complications and target

more intensive surveillance regimes to the high-risk

patients only.

The use of an initial surveillance imaging test to risk

stratify patients also has been explored; the aim is to

stratify patients into those at a high risk of complications

and therefore justifying a more intensive protocol closer to

the traditional CT-based surveillance schedule, and those at

a low risk of complications where less frequent surveil-

lance and the use of DUS should be considered. These

studies are summarised in Table 4.

The use of the initial predischarge CTA to stratify

patients into high- or low-risk groups was investigated by

Goncalves et al. in a cohort of 131 patients with 4.1 years

follow-up. Patients were categorised as high risk if on the

predischarge CTA there was a proximal or distal seal

length of\10 mm, or if there was an endoleak; otherwise,

they were categorised as low risk [73]. Of 62 low-risk

patients, only 3 patients required secondary interventions,

whereas 23 of 69 high-risk patients required secondary

interventions. Freedom from aneurysm-related adverse

events at 5 years was 98 % for the low-risk group and

52 % for the high-risk group [73]. These results led the

authors to conclude that surveillance in low-risk patients

can be substantially reduced. The findings from this paper

Fig. 1 Proposed EVAR

surveillance pathway


123

are echoed by Patel and Carpenter who showed in their

cohort of 345 patients that the initial postoperative CT was

negative for endoleak in 247 patients, and only 9 of 247

received subsequent secondary procedures, giving a nega-

tive predictive value for freedom from secondary inter-

vention of 96.4 %; the authors suggested that with DUS

surveillance after initial CT to detect sac size expansion,

the negative predictive value of follow-up can be improved

to 97.6 % [74].

In the European Society for Vascular Surgery (ESVS)

2010 guidelines for the management of abdominal aortic

aneurysms, following EVAR, the 1-month CTA and AXR

should be used to dichotomise patients into those with and

without endoleak. Patients without an endoleak should

undergo one further CTA at 12 months and DUS ? AXR

thereafter. Patients with a type II endoleak should undergo

CTA at 6 and 12 months and annual CT and AXR thereafter

[14].

Conclusions

There is a need to improve current surveillance strategies to

reduce radiation dose, cost, and maintain quality of life for

patients with a minimal risk of secondary complications

particularly aneurysm-related rupture. Just as EVAR stent

graft technology continues to evolve, strategies for sur-

veillance after EVAR also are undergoing continuous

refinement and will be expected to do so for the foreseeable

future as more data accrues.

We propose a surveillance strategy based on the above

evidence (Fig. 1). Risk stratification is implemented

throughout the strategy to reduce the use of CTA, and thus

ionising radiation and iodinated contrast. DUS in combi-

nation with AXR replaces CTA for low-risk patients, based

on the findings of previous studies summarised in Table 3,

which have demonstrated the sensitivity DUS and AXR for

type I and III endoleaks, or sac enlargement, which can

then trigger further investigation with CTA. The very high

sensitivity demonstrated in meta-analyses of CEUS and

MRA compared with CTA means that CEUS or MRA may

be used as a replacement for CTA in selected patients [30,

46]. Risk stratification occurs at multiple points:

(a) immediately postprocedure where a larger aneurysm or

unfavourable anatomy places the patient in higher risk of

complications, as described by Torsello et al. [72]; (b) after

predischarge CTA in high-risk patients, based on findings

by Goncalves et al. and Carpenter et al. [73, 74]; (c) after

1 year, at which point patients are stratified into low and

high risk with potential for transition between the two

groups based on subsequent follow-up findings, as sup-

ported by the studies investigating DUS, and the ESVS

2010 guidelines [14]. In terms of timing of surveillance

studies, predischarge imaging allows the detection of type I

and III endoleaks, which require immediate treatment, and

risk stratification for subsequent follow-up; surveillance

study at 6 months is eliminated based on lack of utility as

demonstrated by Go et al. [64]; the discharge of low-risk

patients from lifelong surveillance, while not widely

practised, has been suggested in this strategy.

Finally, it is evident that the precise surveillance strat-

egy employed by each unit is likely to vary due to differ-

ences in the choice of stent-graft, local expertise and

experience, financial constraints, and availability of DUS

and CEUS services until compelling data are available that

will mandate a universal approach to surveillance after

EVAR.

Conflict of interest Donald M.L. Tse, Charles R. Tapping, Raf-

iuddin Patel, Robert Morgan, Mark J. Bratby, Susan Anthony, Raman

Uberoi have no conflict of interest.

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Surveillance After Endovascular Abdominal Aortic Aneurysm Repair