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Bifurcated devices are used in approximately 90% of

cases (Vallabhaneni and Harris 2001; EVAR Trial

Participants 2005a; Prinssen et al. 2004). These are of two

varieties, modular grafts which comprise two or three

separate components that are carefully assembled in vivo

and single-piece bifurcated grafts. Modular devices tend to

be more versatile and offer the potential to treat more

aneurysms than single-piece systems.

The aorto-uni-iliac (AUI) device is a graduated tube

stent-graft which is deployed from above the aneurysm

into one iliac artery only. The contralateral iliac artery is

then occluded with an endovascular occlusion device in

order to prevent retrograde blood into the aneurysm sac.

A femoro-femoral crossover graft is required to maintain

blood ﬂow to the opposite limb. Use of this device is

recorded in approximately 10% of cases (Vallabhaneni and

Harris 2001; EVAR Trial Participants 2005a; Prinssen

et al. 2004) and provides a solution in the presence of a

poor iliac landing zone or previous occlusion of an iliac

artery.

For stent manufacture, nitinol has superior superelastic

properties and shape memory capabilities and is generally

preferred to stainless steel. Radiographically, nitinol stents

are less radio-opaque than their stainless steel equivalents

but nitinol stents are associated with signiﬁcantly lower

MRI artefacts. This is important as some centres may wish

to consider MRI as a follow-up imaging modality since it

avoids the radiation and iodinated contrast risks associated

with repeated CT examinations. The Zenith AAA

Endovascular Graft (Cook Inc, Bloominghton, IN) was

originally manufactured using stainless steel and at times

has been heavily criticised for its lack of MR compati-

bility. Of note, the Zenith Low Proﬁle AAA Endovascular

Graft now has a nitinol skeleton. Small radio-opaque gold

or platinum markers are also placed on the stent-graft to

improve visibility and aid orientation during deployment.

There is great debate regarding the added value of bare

suprarenal ﬁxation on aortic stent-grafts. Many proponents

argue that it provides additional protection from proximal

migration whilst its opponents claim that it can induce

problems in angulated necks and when crossing renal

artery ostia. A recent observational study compared infra

and suprarenal ﬁxation in 89 patients with short aortic

necks. Study ﬁndings concluded that there were no

differences in proximal migration or early and late type I

endoleaks between the two conﬁgurations of device

(Hager et al. 2011).

Migration of an aortic stent-graft is a serious durability

issue. Stent-grafts rely on the radial force of the stents in

order to provide ﬁxation and resist movement. Many

devices now have the proximal barbs (Fig. 1) which

embed into the aortic wall and provide further protection

against migration. It is universally accepted that the

Fig. 1 AP abdominal radiograph of patient with a bifurcated Endu-

rant (Medtronic) stent-graft (a). Magniﬁed lateral projection (b), the

Endurant has proximally mounted barbs which help maintain ﬁxation

following deployment

134 A. England et al.

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addition of barbs does provide extra protection from

migration. This was conﬁrmed when it was demonstrated

that the inclusion of barbs increased the pull-out forces

needed to displace an implanted stent-graft by a factor of

ten when compared to radial forces alone (Malina et al.

1998). The fabric of the endograft is typically either

woven polyster (Dacron) or PTFE (polytetraﬂuoroethyl-

ene). The principle difference between the two is that

PTFE is more porous than woven polyester.

4 Planning the Procedure

Endovascular management of an AAA requires careful

preprocedural planning. Traditional workstation evaluations

using thick-section CT data were often time consuming and

morphological measurements of complex anatomy could be

unreliable. Recently there have been improvements in the

resolution of CT data and advances in 3D post-processing.

Fig. 2 3D-reconstruction of an

infrarenal AAA based on CT

angiography data. The central

luminal line (CLL) is used to

measure distances along the

length of a vessel. Reformatted

CT images perpendicular to the

CLL can be used to conﬁrm the

start/end location of length

measurements and provide

diameters for stent-graft sizing

Endovascular Abdominal Aortic Aneurysm Repair 135

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Workstations now provide excellent opportunities for

visualising the full axis of the aorta and its branches in three

dimensions. Displaying aortic anatomy as a series of virtual

3D models has allowed the execution of the EVAR proce-

dure to become a simpler, more predictable, faster, and

safer exercise.

Modern 3D workstations can post-process thin-section

CT data quickly, recognising the dataset as an aortic CT

examination and optimising the 3D display accordingly.

Using a workstation allows the adequacy of the access

vessels, the diameter, length and quality of the proximal

aortic neck and the suitability of the distal landing zones

to be assessed. In order to facilitate this, it must be pos-

sible to display the CT data as multiplanar reformatted

images (MPRs), maximum intensity projections (MIPs),

volume-rendered (VR) and surface-shaded images. Soft-

ware must also allow evaluation of anatomical structures

in any anatomical plane, with rapid image rendering

between projections. The evaluation of vascular CT anat-

omy has been limited by vessel tortuosity and overlap

from bony structures. Automatic bone removal is now a

widely available function and provides ‘true’ 3D angio-

gram style images.

Changes in vessel calibre, length measurements and

relationships to surrounding structures can be evaluated

using a 3D image constructed along the central channel of

the vessel. This post-processing option is termed a central

luminal or ﬂow line (CLL/CFL) and can be generated either

automatically or by semiautomated means. CLLs provide an

easy to create and reproducible reference line for obtaining

accurate measurements along the length of a vessel (Fig. 2).

Corresponding oblique reformatted images can be generated

from the CLL perpendicular to the long-axis of the vessel.

Oblique reformatted images are extremely useful for the

careful sizing of graft components at the seal zones. More

advanced systems can now undertake device-speciﬁc mea-

surements with full automation, further quantitative mea-

surements of vessel angulation, calciﬁcation and mural

thrombus can also be provided. Whatever system is used the

clinician must visually inspect and verify all images and

measurements before deciding on a procedural plan,

ordering components or embarking on implantation.

The sealing stents of the endograft are oversized by

approximately 15–20% to the external diameter of the aorta

and iliac landing zones although there are manufacturer

speciﬁc guidelines and some manufacturers recommend

using the internal aortic diameter for endograft planning.

One of the aims is to cover the entire aorto-iliac segment

from below the renal arteries to the common iliac artery

bifurcation. Vessel length measurements are therefore very

important and endografts are planned to be of adequate

length whilst allowing sufﬁcient overlap of the modular

components.

Occasionally a small lower pole accessory renal artery

may be sacriﬁced if there is only a short segment of aortic

neck below this and a longer segment above the accessory

vessel but below the main renal arteries. The decision to

sacriﬁce a renal artery depends on the amount of renal

cortex supplied by this branch and the patient’s existing

renal function. Current evidence suggests that the inten-

tional coverage of accessory renal arteries will not be

associated with any additional clinical signs or symptoms,

even in patients with mild or moderate renal impairment

(Karmacharya et al. 2006).

If the common iliac artery is aneurysmal then a decision

is made on whether to extend the stent-graft limb into the

external iliac artery. If this is the case then it may be

necessary to embolise the internal iliac artery using coils or

a vascular plug to prevent backﬁlling of the aneurysm sac.

As previously stated iliac branch devices can also be

considered and are an option for preserving blood ﬂow into

the internal iliac artery (Karthikesalingam et al. 2010).

Whichever strategy is employed, every effort is made to

preserve at least one internal iliac artery. Bilateral internal

iliac artery occlusion is associated with a risk of pelvic

ischaemia and neurological sequelae (Bratby et al. 2008;

Rayt et al. 2008).

CLLs are used to evaluate aortic anatomy at multiple

stages during the EVAR planning process. In most situa-

tions the CLL will closely follow the central channel of the

vessel. A CLL may deviate considerably in the presence of

very large or saccular aneurysms, especially those without

thrombus. Deviation can also exist in the presence of poor

arterial contrast enhancement, extreme vessel calciﬁcation

and abrupt vessel angulations. An incorrect CLL can lead to

over or underestimation of vessel lengths and provide

inaccurate oblique reformats for diameter measurements.

It is essential that clinicians validate and adjust where

necessary CLL images before ﬁnalising a management

strategy. It is also important to consider how the path of the

CLL will relate to the path of the guidewire and endograft

delivery system during deployment. In many cases there

may be a difference between the two and this could add

complexity to a procedure or affect technical outcomes.

When embarking on an endovascular programme it is

also essential that each department has a sufﬁcient inventory

of stock to cover all procedural eventualities. With the

expensive nature of some items such as stent-graft com-

ponents, one option is to hold a consignment stock in which

payment is made upon use. For cases which require the

implantation of a complex endograft the preprocedural

planning time can be substantial. The available engineering

options for a complex device can also change over time and

clinicians need to keep abreast of any such changes in order

to provide the optimum treatment option for the patient. To

address these issues some stent-graft manufacturers provide

136 A. England et al.

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the option of using a dedicated graft planning centre. This

can provide a valuable resource for a busy clinician and

reduce the time needed for patient selection and graft

planning whilst allowing all available manufacturing

options to be considered.

5 Technique

In the UK, EVAR is typically performed by an endovas-

cular team that includes a vascular surgeon and an inter-

ventional radiologist, whereas arrangements vary in other

countries around the world. Procedures are generally per-

formed in either an endovascular suite, which should pro-

vide theatre-grade sterility, or an operating theatre using a

high-powered mobile image intensiﬁer and a carbon-ﬁbre

table. Neither situation is totally optimal as facilities for

open surgery must be available and may rarely be required

if arterial rupture occurs upon attempted device delivery or

if there is a need for conversion to open surgery. The

incidence of primary conversion to open surgical repair is,

however, now very low (1–2%) (Schermerhorn et al. 2008).

Some centres have a ﬁxed high-quality angiography unit

mounted in the operating theatre (Fig. 3). This ‘hybrid’

theatre combines the advantages of the angiography suite

with that of the operating theatre (Sikkink et al. 2008). With

the increasing number and complexity of endovascular

procedures, regulatory bodies such as the UK based Medi-

cines and Healthcare products Regulatory Agency (MHRA),

now recommend that EVAR is conducted using high-quality

ﬁxed imaging equipment (MHRA 2010). This should also be

in a room with a full operating theatre speciﬁcation and

anaesthetic and recovery facilities available.

Procedures may be performed under local, regional or

general anaesthesia. Surgical exposure and control of the

common femoral arteries is the most common means of

delivering the device. Totally percutaneous EVAR is now

possible and closure is usually achieved using a percuta-

neous suturing device. High technical success can be

achieved but careful preoperative imaging of the common

femoral arteries and precise positioning of the arterial

access sites is required. Many clinicians still have reserva-

tions about a totally percutaneous procedure especially

when using devices up to 24 F. There is the option of an

intermediate procedure of a fascial closure/mini cut-down

(Harrison et al. 2011a). Fascial closure can reduce the

possibility of serious wound complications and delayed

discharge and has the additional advantage of not requiring

an expensive endovascular closure device.

Intravenous heparinisation is necessary and in view of the

variable procedure lengths repeat doses may be necessary.

Ideally theactivated clottingtime (ACT)should bemonitored

throughout the procedure and adjusted accordingly.

For modular devices the main component (main body) is

inserted transfemorally over a stiff guidewire. This is

deployed so thatthe fabricatthe proximalmargin of thestent-

graft is close to but does not cover the most caudal renal

artery. Before the device is released, angiography is per-

formed to determine the level of the renal arteries and the X-

ray tube is angled craniocaudally, if required, to avoid

Fig. 3 Hybrid operating theatre (picture courtesy of Mr S. Rao Vallabhaneni, Royal Liverpool and Broadgreen University Hospital NHS Trust,

Liverpool, UK)

Endovascular Abdominal Aortic Aneurysm Repair 137

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foreshortening of the aortic neck, which may occur with

anterior angulation just below the renal arteries. Oblique

angulation, typically left anterior oblique (LAO), is used to

proﬁle the ostium of the lowest renal artery, which is posi-

tioned in the centre of the image to avoid parallax errors.

Estimations of the anglesnecessaryto successfully proﬁle the

renal arteries can be obtained using the preoperative CT data

and should be part of preprocedural planning. For this reason

it is important to have access to PACS images within the

endovascular suite. Access to 3D reconstructions can aid

mental registration of the most caudal renal artery against an

appropriate vertebral body marker. This is useful as the

delivery system can be moved to the correct level and be

ready for deployment prior to the administration of iodinated

contrast medium. Once deployment has started, a check

angiogram can be undertaken to conﬁrm the deployment

position, with this being a purely positioning angiogram the

contrast volume can be reduced. Such techniques can help

reduce the volume of iodinated contrast mediumrequiredand

decrease the risk of any adverse renal events.

Typically iodinated contrast is used for angiography,

however, where available, carbon dioxide has proven to be

a viable alternative, providing protection for the kidneys

from contrast-induced-nephrotoxicity (CIN) (Chao et al.

2007). Intravascular ultrasound (IVUS) is used in a few

centres to help with the ﬁnal decisions regarding stent-graft

sizing and for identiﬁcation of the aortic anatomy at

deployment (Hoshina et al. 2010). Currently, the cost of

procuring the necessary equipment and single-use nature of

IVUS probes limit its availability to only a few centres.

Once the main body is released there is the need to

extend on both sides into the common iliac arteries. This is

straightforward on the side of the main component as there

is already a guidewire through the device and it is a simple

manoeuver to overlap a limb extension from the bifurcation

of the main body into the lower common iliac artery on the

ipsilateral side. Implanting the contralateral limb is more

difﬁcult as this requires cannulation of the short leg or

‘stump’ of the main body prior to introduction of the

contralateral limb. This can be challenging in large aneu-

rysms when the 12 mm diameter opening of the short leg

must be cannulated within a large space of several centi-

metres. If there is no mural thrombus and a large aneurysm

then this can pose further challenges to cannulation. For

difﬁcult cases contralateral limb cannulation can be facili-

tated by using a contralateral snare to capture an ipsilateral

guidewire or by using a guidewire inserted from the bra-

chial artery. Whatever technique is used to cannulate the

short limb of the main body it is important to verify correct

intraluminal positioning within the stent-graft. This can be

achieved by rotating a pig tail catheter within the device

main body, using real-time ﬂuoroscopy whilst obliquely

rotating the image intensiﬁer or inﬂating a moulding

balloon within the contralateral limb gate.

Once the device is assembled in vivo then completion

angiography is performed to exclude the presence of an

endoleak andensure that thevisceral andiliac arteries remain

patent. Every effort ismade to treat endovascularly any graft-

related endoleak. There is evidence to suggest that an

unresolved proximal type Iendoleak may increase ratherthan

decrease theriskof ruptureof ananeurysm (Harriset al.2000;

Wyss et al. 2010). Type IIor sidebranch endoleaks are seen in

10–20% ofcompletion angiograms (Farieset al. 2003;Sheehan

et al. 2006; Jones et al. 2007) and no further intervention is

necessary at this stage.

6 Stent-Graft Complications

and Surveillance

Stent-graft complications can occur early or late. Renal

impairment, graft-related endoleak, occlusion, migration,

infection, wound site complications, post-implantation

syndrome and distal embolisation may be encountered fol-

lowing stent-graft implantation.

A fall in estimated glomerular ﬁltration rate (eGFR) is

often seen after EVAR and usually reverts back to preop-

erative levels. Permanent damage to renal parenchyma may

result from deliberate or unintentional coverage of a renal

artery by the endograft fabric, toxic effects of the iodinated

contrast media and cholesterol emboli. The risk of acute

renal impairment is lower for EVAR patients than those

Fig. 4 Follow-up CT surveillance demonstrating an occluded left

iliac limb (arrow)

138 A. England et al.

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undergoing open surgical repair although renal function at

1 year is comparable (Greenberg et al. 2004).

Occlusion of a stent-graft is generally the result of poor

blood ﬂow due to either graft kinking or poor outﬂow

(Cochennec et al. 2007). Graft thrombectomy and adjunc-

tive stenting may be undertaken to correct any related

symptoms. If a limb is lost through occlusion then (Fig. 4),

for some patients, a femoro-femoral crossover graft may be

necessary.

Infection of an aortic stent-graft is rare and single-centre

case series estimate an incidence of 0.5–1.3% (Ducasse

et al. 2004; Sharif et al. 2007; Heyer et al. 2009). Infection

can be detected using CT or labelled leucocyte nuclear

medicine scanning. Gas bubbles within the aneurysm sac

are often seen on early post-operative CT and if there are no

other indicators then infection can usually be excluded. If

infection is present then treatment with appropriate antibi-

otic therapy is recommended and management should be

similar to that for an infected surgical graft.

Vascular access for EVAR is typically performed with

bilateral femoral cut-down arteriotomies. Seriousgroin access

complications are rare but include haematoma, infection and

seroma. Occasionally a groin will need to be re-explored

to repair a false aneurysm or evacuate a haematoma.

Systemic Inﬂammatory Response Syndrome (SIRS) or

post-implantation syndrome generally includes fever, leuc-

ocytosis and raised inﬂammatory markers. SIRS occurs

within a few days of the EVAR procedure and is seen in

around 35% of patients (Arnaoutoglou et al. 2011). There is

debate around the myriad of symptoms which fall under the

remit of post-implantation syndrome which appear at worst

to prolong post-EVAR hospitalisation.

Very rarely patients who have undergone EVAR may

suffer embolisation of the lower limb from arterial debris

dislodged during the stent-graft implantation. Treatment is

generally difﬁcult so care must be taken when manipu-

lating the device within the aorta and cases where there is

severe mural thrombus in the aortic neck or distal aorta

should be avoided. If distal embolisation does occur then

treatment, either radiological or surgical will depend on

the level of underlying ischaemia.

Persistent blood ﬂow outside the stent-graft and within

the aneurysm sac is deﬁned by White et al. (1996)asan

endoleak. Endoleaks have been classiﬁed according to the

source of the perigraft ﬂow into four groups (White et al.

1997, 1998):

Type I Proximal (a) or distal (b) graft attachment site

leaks.

Type II Retrograde ﬂow into the aneurysm sac from

aortic side-branches such as the lumbar or

inferior mesenteric arteries.

Fig. 5 Intra-operative angiography of a patient with a deployed talent

(medtronic) stent-graft and a large proximal type I endoleak (arrow)

Fig. 6 Angiography of a patient with a distal type I endoleak (arrow)

resulting from incomplete apposition of the iliac limb against the

common iliac artery wall

Endovascular Abdominal Aortic Aneurysm Repair 139

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Fig. 7 A type II IMA endoleak detected by follow-up ultrasound

(a, b) and CT (c) surveillance. During follow-up the aneurysm had

continued to expand and a decision was made to embolise the endoleak

using coils. This secondary intervention was successful, subsequent CT

scanning showed no evidence of endoleak (e) and ultrasound conﬁrmed

the absence of any echopoor areas within the aneurysm sac (d)

140 A. England et al.

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Type III Caused by a defect in the graft either due to

fabric disruption or disconnection of the mod-

ular overlap.

Type IV Graft wall porosity.

The most serious endoleaks are type I (Figs. 5, 6) and III

which areassociatedwith aneurysmenlargement andrupture.

Secondary intervention to correct these endoleaks is almost

always necessary. Whilst rupture hasbeen reported with type

II endoleaks these are considered to have a more benign

course and a conservative approach to management is taken

unless there is evidence of continuing sac enlargement

(Fig. 7).

Stent-grafts are subjected to distraction forces in vivo due

to the relentless force of pulsatile blood ﬂow. These distrac-

tion forcesact longitudinally andchallenge the ﬁxation of the

graft and the overlap zones. The stent-graft resists these

forces due to its ﬁxation mechanisms which include radial

force of the sealing stent and the barbs which engage into the

aortic wall. The columnar strength of a device is also

important in resisting distraction. Distraction forces are

dependent on a patient’s blood pressure and the cross-

sectional area reduction between the proximal/aortic and

distal/iliac sealing stents (Sutalo et al. 2005). Failure of

ﬁxation will lead to migration or modular disconnection with

late type I or type IIIendoleak and risk of aortic rupture. Graft

limb distortion with subsequent thrombosis can also arise

secondary to device migration. The detection of migration

during post-operative surveillance is important as it may lead

to pre-emptive intervention to prevent graft failure.

Wireform fractures have been reported in most stent-

grafts. These fractures may lead to diminished stent strength

and loss of radial force which can result in migration.

Additionally the jagged ends of fractured metal may cause

tears in the fabric and subsequent endoleaks. These factures

are best demonstrated on plain abdominal radiographs

(Fig. 8). The use of serial plain radiographs during follow-

up is well established. Migration, metallic fractures and

conformational changes can all be detected using a com-

bination of AP and lateral abdominal radiographs (Fig. 9).

The diagnostic accuracy of this examination is improved

by adherence to speciﬁc plain radiography protocols

(Liverpool/Perth) (Murphy et al. 2003).

It is mandatory that all patients are entered into a

planned surveillance programme following repair. Device

failure with continued sac enlargement can signiﬁcantly

increase the risk of aneurysm rupture. Wyss et al. (2010)

reported on 27 ruptures following EVAR (EVAR trials 1

and 2) which equated to a 0.7% rupture rate per 100

person-years. Eighty-two percentage of ruptures occurred

greater than 30-days following implantation, the majority

of these (63%) were in patients with previously reported

complications or signs of failed EVAR. Of the patients

with post-EVAR rupture two-thirds died as a result.

Schlösser et al. (2009) reported on 270 ruptures identiﬁed

within a review of the literature and the mean time to

rupture was 24 months. 35 patients had no prior abnor-

malities found during follow-up and for the 101 patients

where sac diameter was known, 39 ruptures showed no

change and 26 showed evidence of aneurysm regression

(Schlösser et al. 2009). Wyss et al. further identiﬁed type I

and II (with sac enlargement) endoleaks, migration and

kinking as risk factors for rupture. With the possibility of

rupture in patients with and without prior abnormalities

and in expanding, stable and regressing AAAs, follow-up

surveillance cannot be omitted for any patient where

secondary intervention would be considered.

The EUROSTAR registry reported on outcomes of

2,846 patients who had EVAR between 1999 and 2004.

Reintervention rates at 1, 2, 3 and 4 years were 6, 9, 12

and 14% respectively (Hobo and Buth 2006) these rates

were similar for the UK EVAR trials where reintervention

rates of 8, 8, 11 and 16% respectively were reported

(Brown et al. 2010). Complication and reintervention rates

appear to be greatest during the ﬁrst 6 months following

deployment (particularly the ﬁrst 30 days post-implanta-

tion), with a lull from 6 to 24 months followed by an

increase. This late increase has also been demonstrated

with the EUROSTAR registry data (Hobo and Buth 2006).

Studies which have reported EVAR outcomes beyond

5 years have also reported complications and secondary

reinterventions in years 6, 7 and 8 (Coppi et al. 2008;

Brewster et al. 2006). Complications can therefore occur at

Fig. 8 Follow-up lateralabdominal radiograph (magniﬁed)illustrating

a fractured SMA stent (arrow) in a patient with a fenestrated stent-graft

Endovascular Abdominal Aortic Aneurysm Repair 141

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any time point and often necessitate the need for reinter-

vention. Based on the available evidence follow-up sur-

veillance must be recommended for life, the exception

would be patients with contraindications to secondary

intervention e.g. severe comorbidities.

Graft-related complications have been found more

frequently inolder patients and thosewith larger pre-operative

AAA diameters (Brown et al. 2010). Neck angulation and

calciﬁcation were also found to be predictive of graft-related

complications together with high levels of iliac artery throm-

bus and tortuosity (Wyss et al. 2011). Even based on these

reportswe arestill not ina position toexclude anypatient from

follow-up based on pre-operative or perioperative factors.

Current protocols for surveillance after EVAR are mostly

based on costly and time-consuming imaging procedures and

aim todetect adverse eventssuch as graft migration, endoleaks

or aneurysm sac enlargement. These imaging procedures are

either associated with serial radiation exposure or may be

potentially harmful due to the use of iodine- or gadolinium-

based contrast agents. CT angiography is considered by many

as thegoldstandard forimagingsurveillancefollowingEVAR.

Multidetector CT allows for the easy acquisition of multiple

phases andmany authors recommend triphasic CT comprising

unenhanced, arterial phase and delayed phase studies. Unen-

hanced CT images are sometimes helpful in differentiating

endoleaks from calciﬁcation although comparison with the

pre-operative imagesis normallysufﬁcient. Delayed-phaseCT

images may demonstrate endoleaks not seen on arterial phase

CT imaging. The routine use of tri-phasic CT is therefore

questionable. Iezzi etal. reported thatthe addition of a delayed

phase scan wasuseful in only1 outof 12ofendoleaks detected

by CT (IEZZI et al. 2006). In their study endoleaks were

detectedin 36%of patients meaning thatan additional delayed

phase scan would provide extra information in around 3% of

patients. It is likely that these patients would demonstrate

evidence of sac enlargement and that a delayed phase scan

could be factored into any subsequent CT examinations if

necessary. Similarly when considering the inclusion of a

non-enhanced scan, Iezzisuggested that thismay be helpfulin

differentiating an endoleak from calciﬁcation in only 20% of

abnormal arterial phase CT scans. For most patients under-

goingCT surveillancea single arterial phasestudy issufﬁcient.

A small numberof patients may need to be recalled for further

imaging if there is uncertainty regarding calciﬁcation or if

aneurysm enlargement is thought to require a search for a low

ﬂow endoleak.

There is concern regarding the cumulative radiation

exposure from serial CT examinations together with the risk

of acute and cumulative nephrotoxicity from iodinated

contrast media. With the additional economic and logistical

drawbacks of repeat CT scanning demand has arisen for an

alternative examination. A combination of duplex ultra-

sound (DUS) and plain abdominal radiography (AXR) is the

likely alternative.

Fig. 9 Follow-up lateral

abdominal radiographs

highlighting caudal migration of

a stent-graft. Caudal movement is

clearly evident when comparing

the position of the stent-graft

relative to the vertebral bodies on

the pre-discharge (a) and the

2-year (b) images

142 A. England et al.

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DUS is able to accurately determine aneurysm size,

identify and characterise endoleaks and study ﬂow haemo-

dynamics which may be indicative of adverse structural

issues such as kinking. For endoleak detection a recent

meta-analysis has reported sensitivities for DUS of between

64 and 86% (Mirza et al. 2010). The majority of endoleaks

that are missed by DUS are type II endoleaks that do not

require any intervention. The accuracy of ultrasound in the

detection of endoleaks can be further improved by the use

of contrast agents. Reports investigating the use of contrast-

enhanced ultrasound (CEUS) document sensitivity rates of

between 90 and 99% (Mirza et al. 2010). CEUS provides

temporal information about endoleaks as the time of arrival

of the microbubbles in the aorta may be compared to the

arrival time in the endoleak itself. If there is no temporal

separation then this indicates a graft-related endoleak.

Sidebranch endoleaks are typically seen a few seconds after

the microbubbles arrive in the aorta. With the need for non-

invasive more economical alternatives three studies have

sought to evaluate the efﬁcacy of solely DUS-based sur-

veillance (Collins et al. 2007; Chaer et al. 2009; Beeman

et al. 2009). Within these three series there have been no of

cases of aneurysm rupture associated with ultrasound-only

surveillance (Bakken and Illig 2010). CTA will still provide

a role when the diagnostic ability of DUS is limited by body

habitus or overlying bowel gas. CTA will also have a role in

evaluating a potential abnormality identiﬁed by ultrasound

such as aneurysm enlargement or endoleak. DUS can only

yield its full potential when observers have appropriate

training and experience and where good quality ultrasound

equipment is available.

DUS is restricted inits ability to identify device migration

and structural disintegration. Early identiﬁcation of these

complications may allow the opportunity for pre-emptive

intervention in order to prevent more serious complications.

With this in mind, the combination of DUS and plain radi-

ography has the potential to reveal all of the necessary

information sought by surveillance. Plain radiography is an

easily accessible imaging modality and is an essential tool

for documenting graft kinking, stent fracture and structural

disintegration of the stent-graft. When performed according

to a strict protocol it is able to detect migration and distin-

guish artefactual from actual migration.

Both clinicians and trial investigators now accept that the

most dangerous post-EVARsituations cannow beadequately

demonstrated by DUS. For cases where the ﬁrst post-opera-

tive CT scan is unremarkable surveillance protocols can be

safely modiﬁed to include annual DUS and AXR (Harrison

et al.2011b). This changein imaging cultureis spreading; for

example the US Society of Vascular Surgery now recom-

mends that post-EVAR surveillance should be undertaken at

1 and 12 months by contrast-enhanced CT, an additional CT

scan at 6 months if there is an abnormality on the 1 month

scan. Any subsequent annual surveillance imaging can be by

DUS if the aneurysm remains stable (Chaikof et al. 2009).

Magnetic resonance imaging (MRI) has a role in surveil-

lance when CTA or DUS fails to provide sufﬁcient informa-

tion to guide management. Contrast-enhanced MR

angiography (CE-MRA) can be used speciﬁcally to detect

endoleaks and provides an option for surveillance especially

in patients who have contra-indications to iodine-based

contrast media e.g. severe allergy (Shah and Stavropoulos

2009). High quality MR imaging depends on the metallic

composition of the endograft with nitinol-based stent-grafts

being good in this context (Alerci et al. 2009). However, for

grafts with stainless steel endoskeletons there will be signif-

icant susceptibility artefact. One of the most commonly used

devices (Cook Zenith) has recently switched to nitinol from

stainless steel in the low proﬁle device, which now provides

an opportunity forMR follow-up. Forendoleak detectionCE-

MRA is as sensitive as CTA and when using time-resolved

MRA (TR-MRA) there may be improved detection and

classiﬁcation of endoleaks (Cohen et al. 2008).

The advantages of EVAR in the short term are

compromised by the necessity for life-long surveillance and

alternative techniques for follow-up are under investigation.

One option is to perform pressure measurements directly

within the aneurysm sac. Non-invasive, telemetric pressure

sensing has been tested in vitro as well asin clinical trials and

is ableto identifysuccessful aneurysmexclusion afterEVAR.

The telemetric pressure sensors have shown a promising

efﬁcacy and accuracy when detecting type I and type III

endoleaks andcan helpto clarifythe clinicalrelevance oftype

II endoleaks (Springer et al. 2008). Despite a signiﬁcant

amount of interest in telemetric pressure sensing this method

of surveillance has not yet become part of routine clinical

practice.

There has also been speculation in the literature

regarding the role of biochemical markers for monitoring

post-EVAR success. Matrix metalloproteinases (MMP) are

enzymes which are capable of breaking down all compo-

nents of extracellular matrix. MMPs have been linked to

aneurysm formation and their levels are elevated in aortic

aneurysm tissue and plasma. Researchers hypothesised that

MMP levels should decrease when an AAA is excluded

either by open surgery or EVAR. A study by Lorelli et al.

in 2002 demonstrated that plasma MMP levels in patients

treated by EVAR fell in comparison to those treated by

EVAR with the presence of an endoleak (Lorelli et al.

2002). At the time it was suggested that biological MMP

enzymatic markers may have a role in the long-term

identiﬁcation of endoleaks. Since its introduction in 2002

there have only been a few reports within the literature

discussing its potential. Biochemical markers are not

currently included in any routine post-EVAR follow-up

strategy.

Endovascular Abdominal Aortic Aneurysm Repair 143

https://t.me/med1917

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