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6.1 · Abdominal Aorta, Visceral andRenal Arteries
D2
orthogonal
D1
axial
D1 > D2
425
. Fig. 6.31 Sources of variation in measuring the maximum abdomi-
nal aortic aneurysm (AAA) diameter in a patient with an elongated aorta
and anterolateral deviation of its course. A maximum anteroposterior
(AP) diameter of 62.6mm (D1) is measured in the transverse abdominal
view (right image), while the maximum orthogonal diameter measured
perpendicular to the long axis of the aorta is 45.5mm (left image). At
the site of the AP diameter measurement in the transverse view, the
orthogonal diameter is 39.7mm (D3). The AP diameter is represented by
the white line, the orthogonal diameter by the yellow line. The AP diameter measured in the right image corresponds to the CT-based diameter
measurement in the axial plane (i.e., in the plane used for measuring
AAA size when CT is performed without multiplanar reconstruction)
6
. Fig. 6.30 Pitfall in measuring abdominal aortic aneurysm (AAA)
diameter. Patients with an aortic aneurysm often have an elongated aorta
with an outward curve to the left. When transverse images are obtained
with the transducer in the normal abdominal position, this can lead to
overestimation of the diameter because the aorta is being measured in
an elliptical plane (D1). Overestimation of aneurysm size by measurement
in the wrong scan plane can also lead to overestimation of the rupture
risk. The correct diameter of the aneurysm is measured by rotating the
transducer clockwise until a round image of the aorta comes into view
(D2). With the transducer in this position, the true transverse diameter is
measured orthogonally (perpendicular to the vessel axis)
ultrasound, this error can be avoided by rotating the transducer from the transverse abdominal position until it is perpendicular to the long aortic axis (conrmed when the oval
shape of the aorta becomes more rounded) (
. Figs.6.28, 6.29,
and 6.30). When the elongated aorta deviates anteriorly, the
diameter is best measured in the sagittal plane (. Fig.6.31).
Without this standardized approach, it is not possible to
take accurate and reproducible serial measurements of aortic
diameter. is must be taken into account when interpreting
discrepant results obtained with the same modality or with
dierent modalities.
Studies show good intraobserver and interobserver
agreement for sonographic measurement of the orthogonal
AAA diameter, which is a prerequisite for obtaining meaningful results in serial measurements. Such a standardized
approach is necessary to capture true size increases over
time and avoid errors resulting from poor methodology (Sun
2006; AbuRahma 2006; Collins etal. 2007; Stavropoulos and
Charagundla 2007).
Once again, adequate aortic diameter measurement
requires clockwise rotation of the transducer from the position showing the largest aortic diameter to the view allowing
diameter measurement perpendicular to the long aortic axis
(change from elliptical to rounded shape of the aortic crosssection) (
. Fig.6.30).
In summary, the following procedure is recommended
for the sonographic evaluation of the aorta and reliable AAA
diameter measurement:
5 Identify the aorta in the transverse plane and image its
course from the suprarenal segment to the bifurcation
5 Identify the renal artery origins and aortic bifurcation to
determine AAA extent in relation to these structures
5 Evaluate the entire aorta for possible elongation: may
require transverse, oblique, or even longitudinal trans-
ducer positions
5 Identify the widest (axial) aortic diameter
5 From this position, rotate the transducer for measure-
ment of AAA diameter perpendicular to the vascular axis
(rounded rather than elliptical shape of the aortic cross-sec-
tional area; may require a longitudinal view in some cases)
5 Use the leading-edge method to measure AAA diameter
5 Document ndings and measurements
New techniques such as 3D ultrasound and ultrasound/
CT image fusion have the potential to improve the accuracy
of aneurysm size determination in the future, especially in
serial examinations of patients with AAA (Bredahl et al.
2013; Pster 2014).
426
Chapter 6 · Visceral andRetroperitoneal Vessels
6.1.6.3.4 Comparison ofUltrasound
andComputed Tomography
No consistent picture emerges from studies comparing ultrasound and CT (Singh et al. 2004); discrepancies are oen
attributable to the study design (Beales etal. 2011). Investiga-
conditions. In view of the problems discussed here, there
appears to be an urgent need to standardize measurements
and ensure that we measure AAA diameter accurately and
reproducibly in serial examinations. A consensus should
specify how, where, and when to measure AAA diameter.
tors oen fail to describe details of the ultrasound technique
used to determine abdominal aortic aneurysm (AAA) size
(e.g., transducer position, plane in which diameter is measured). In a study reviewing the methodology of maximum
AAA diameter measurement (Long etal. 2012), only 40% of
the studies included (n= 23) specied the plane of acquisition and 30% the caliper positions, and only 10% of the
6
studies used the leading-edge method. Long etal. dened a
quality score for the description of methodology in the studies reviewed and found a mean quality score of 2.5 (of a total
of 4). Surprisingly, they found an even lower mean quality
score of 1.6 for the description of methodology in guidelines
for screening programs. Most of the guidelines they reviewed
did not specify the axis of measurement or caliper positions
(outer or inner diameter) (Long et al. 2012; Lederle et al.
1995), and these issues are rarely discussed (Moll etal. 2011).
Overall, the review of Long et al. conrms that a range of
dierent methods are in use for measuring AAA diameter.
Studies comparing ultrasound and CT show good
agreement of the two modalities (correlation coecient of
0.91) (Manning etal. 2009) with the majority of investigators concluding that ultrasound underestimates maximum
aneurysm diameter compared with CT (mostly measured
in AP plane) (Jaakkola et al. 1996, Sprouse et al. 2003,
Manning etal. 2009, Long et al. 2012). Conversely, other
authors point out that axial CT scans, without orthogonal
reformation, oen measure the diameter in oblique slices of
the AAA, which tend to overestimate aneurysm diameter
when there is relevant elongation of the aorta. is is clearly
apparent from two studies performed by Sprouse etal. (2003
and 2004). In the earlier study, CT yielded larger diameters
than ultrasound in 95% of cases. Specically, AAA diameters by CT were 5.69±0.89cm versus 4.74±0.91 cm by
ultrasound (and the dierence was signicant, p<0.05). In
the later study, Sprouse etal. (2004) found good agreement
between ultrasound and CT diameter measurements with
a mean dierence of only 0.8mm when CT measurements
were taken in reformatted slices allowing true orthogonal
measurement. Comparison of axial and orthogonal AAA
6.1.6.3.5 Abdominal Aortic Aneurysm
Screening: Rupture Risk
Accurate and reproducible (orthogonal) measurement of
aortic diameter is essential for preventing both excessive
diagnostic testing (stressful for patients) and excessive treatment (surgical risk, complications, and postoperative morbidity) in screening and surveillance programs (. Figs.6.36
and 6.37). Abdominal aortic aneurysm (AAA) is a non-
malignant condition and it is therefore even more important not to put patients at risk through poor measurement
methodology and operating on aneurysms that would never
rupture during their lifetime. In addition, the low risk of
rupture of <3–5%/year for AAA <5.5cm must be weighed
against the surgical risk and perioperative morbidity.
Patients undergoing endovascular aneurysm repair (EVAR)
also face several risks (endoleaks in up to 10% of cases,
risk of stent gra limb occlusion of up to 5%) and require
regular follow-up examinations with radiation and contrast
medium exposure.
Clinically, AAA rupture is suggested by ank and back
pain (occasionally abdominal pain), a palpable pulsating
tumor, and shock. Gray-scale imaging depicts a hypoechoic
structure of variable extent and comprising inhomogeneous
or layered portions around the aorta in the retroperitoneum
(
. Fig. 6.75b (Atlas)). In patients with a contained aneu-
ryms rupture, color duplex ultrasound demonstrates paravascular ow signals at the site of the leak. Leakage must be
dierentiated from other hypoechoic periaortic structures
such as retroperitoneal brosis, horseshoe kidneys, or lymphoma, which may occur in conjunction with an aneurysm
(see 7 Sect. 6.1.6.3.8; . Figs.6.38, 6.39, and 6.40; . Figs.6.85,
6.86,
and 6.87 (Atlas);). An examiner performing ultrasonography in emergency patients must pay special attention
to such accompanying conditions as they have important
implications.
If there is
may appear uid-lled. Fistula connections to the vena cava
can be demonstrated by color duplex.
perforation into the duodenum, the intestine
diameter measurements by CT revealed signicantly larger
mean diameters when measurements were taken in axial
slices compared with orthogonal slices (58 mm versus
54.7mm, p<0.05). e overestimation of axially measured
diameters increased with aortic angulation. ese results
clearly illustrate that selection of the correct slice for AAA
diameter measurement aects ultrasound (. Figs.6.29 and
6.30) and CT alike. Awareness of this pitfall is important
both in clinical routine and in the setting of clinical studies
(Long etal. 2012).
CT is generally considered the gold standard for measuring AAA diameter because it is not examiner-dependent and
less susceptible to errors resulting from poor examination
6.1.6.3.6 Aortic Dissection
Aortic dissection is only amenable to percutaneous ultrasound diagnosis if the intimal ap extends into the abdominal
aorta. In the abdominal aorta, sonography is a valid method
for assessing the extent of dissection, and spectral Doppler
evaluation is helpful in identifying extension into arteries
arising from the aorta or intermittent obstruction of blood
ow at the origin of these arteries by the intimal ap moving
synchronously with the heart (see . Fig.6.88 (Atlas)).
In a dissecting aneurysm, splitting of the arterial wall
with tearing of the intima is suggested on gray-scale ultrasonography by the presence of a ap in the vessel lumen;
2
ab
6.1 · Abdominal Aorta, Visceral andRenal Arteries
this ap can be identied by its hyperechoic reection and
typical undulating motion. Dissection is conrmed in the
color mode by dierent ow velocities and directions in the
true and false lumens (. Fig. 6.33). e power mode and
contrast-enhanced ultrasound (CEUS) will help demonstrate
slow ow in the false lumen and dierentiate it from partial
thrombosis. e color-coded ow directions contribute to
the identication of the entry and re-entry sites. Knowledge
of the relationships of the origins of the visceral and renal
arteries to the true and false lumens determines the therapeutic management. As the dissected ap may extend into
the groin, the iliac arteries must be included in the examination (see . Figs.6.88, 6.89, and 6.90 (Atlas)).
Spectral Doppler imaging at the sites of aortic branch ori-
gins for identifying extension of the dissection into renal or
visceral arteries
as well as intermittent occlusion or stenosis
of a branch artery by the intimal ap (dynamic blood ow
reduction) is important for the therapeutic approach. If there
is extension into an aortic branch, the Doppler waveform will
depict ow in the true and false lumens and may also contain
signals produced by oscillation of the intimal ap. If there is
narrowing or intermittent occlusion of a branch origin by the
intimal ap, spectral Doppler will reveal signs of stenosis or
systolic deceleration (decreased systolic velocity or even zero
ow) (
. Fig.6.88 (Atlas)). Dissection with intermittent ow
obstruction can lead to chronic ischemia and patients are at
risk of acute ischemic events. Dynamic ow obstruction is
dicult to detect with a morphologic imaging modality (CT,
angiography) when the lumen is lled with contrast medium.
Conversely, with isolated dissection of the abdominal
aorta, which is rare (Knabe etal. 2001), the proximal origin
is typically not detectable by transcutaneous sonography
(except with the transducer directed retrosternally from a
jugular position). In these cases, transesophageal echocardiography (Link 1999), computed tomography, or magnetic
resonance imaging is required for diagnosis. e diagnostic
accuracies in aortic dissection are 70% for ultrasound (Nienaber etal. 1993), 98% for transesophageal echocardiography
(Sommer etal. 1996), and 100% for MRI (Silverman 2000)
and CT.
6.1.6.3.7 Follow-Up After Open Surgical
andEndovascular Aneurysm Repair
Diagnostic Algorithm
z
Follow-up (see . Fig.6.32) aer open surgical repair of an
abdominal aortic aneurysm (AAA) or patch angioplasty of
aortic stenosis must ensure early identication of complications such as suture aneurysm, anastomotic stenosis, recurrent stenosis, or abscess.
Hypoechoic structures around a prosthesis, particularly
at the sites of anastomosis, can be checked for the presence
of ow using color duplex ultrasound to dierentiate suture
aneurysm from postoperative hematoma and abscess. Suture
aneurysms are pseudoaneurysms and hence are characterized by to-and-fro ow (steam engine sound) in the Doppler
waveform from the site of wall perforation (see . Fig.6.92
(Atlas)). An abscess suspected on clinical grounds can be
427
4
1
3
. Fig. 6.32a, b Complications of interventional and open surgi-
cal repair of abdominal aortic aneurysm (AAA). a Following surgical
Y-prosthesis implantation: 1 suture aneurysm (typically at the upper
anastomosis or, if the prosthesis extends into the femoral artery, at
the lower anastomosis); 2 occlusion of an iliac limb; 3 anastomotic
stenosis (distal anastomosis). b Types of endoleaks after endovascular
aneurysm repair (EVAR): 1 type I endoleak, at the proximal or distal
attachment site; 2 type II endoleak, from patent lumbar arteries;
3 type III endoleak, separation of modular components; 4 type IV
endoleak, device failure (porosity)
2
3
1
conrmed by ultrasound-guided ne-needle aspiration
biopsy.
Aer open surgical aneurysm repair, sonographic followup has sucient validity to identify typical complications
such as suture aneurysm (
. Fig.6.34), anastomotic stenosis,
and iliac limb occlusion (in patients with a Y-stent gra).
e following complications of open surgical and endovascular AAA repair have therapeutic implications and
require special attention in sonographic follow-up
:
5 Aer open surgical repair:
5 Recurrent aneurysm– suture aneurysm
5 Anastomotic stenosis/iliac limb occlusion
5 Abscess/infection
5 Aer endovascular aneruysm repair (EVAR):
5 Endoleaks (types I, II, III)
5 Further sac growth
5 Stent gra migration/fracture (domain of conven-
tional X-ray)
5 Iliac limb occlusion
5 rombotic deposits as a source of embolism or
cause of luminal narrowing
Aer EVAR, patients should undergo imaging surveillance at 6-month intervals. AAA shrinkage indicates adequacy of the repair and rules out an endoleak (Giannoni
etal. 1998; ompson etal. 1998). Conversely, even a small
further increase in aortic diameter (B-mode) points to a
therapeutically relevant endoleak (with increasing pressure
6
428
Chapter 6 · Visceral andRetroperitoneal Vessels
6
. Fig. 6.33 Aortic dissection of longer duration with sclerotic thickening of the dissection membrane (same patient as in . Fig.6.27). In this
patient, gray-scale imaging already shows the oating membrane (indicated by “d” in the color ow images) in the lumen and rules out intermittent obstruction of blood ow into arterial branches at their origins from the aorta. The waveforms shown along with the color ow images were
obtained in the true lumen (wl) and false lumen () (center and right, respectively). The bright artifact apparent in both waveforms in early systole
is due to oscillation of the dissection membrane. The membrane is also apparent in the corresponding CTA scan
. Fig. 6.34 Suture aneurysm
after open surgical stent graft
repair for abdominal aortic
aneurysm (AAA). The arrow in the
color ow images (transverse orientation on the left, longitudinal
orientation on the right) indicates
the site of leakage. The CT scan
was obtained for stent graft sizing prior to interventional closure
of the leak
in the aneurysm sac) and should prompt a careful search for
the site of leakage using color duplex ultrasound (CDUS).
If no endoleak is detected, the search should proceed using
contrast-enhanced ultrasound (CEUS) or computed tomography angiography (CTA).
Serial ultrasound follow-up should be supplemented by
an annual plain X-ray examination of the abdomen to rule
out stent fracture, which can be identied sonographically
only if an endoleak is presdent (type IV).
In summary, the following algorithm is proposed for the
follow-up of patients aer EVAR (in line with the general
policy of stepwise diagnostic workup advocated throughout
this book):
1. B-mode ultrasound (follow-up at 6-month intervals):
5 Development of AAA diameter over time
5 Diameter decreases → continue routine follow-up
5 Diameter remains constant or increases → search
for endoleak, successively using CDUS, CEUS, and
CTA (as required)
CDUS (PRF, gain): indicated if B-mode measurement shows
2.
constant or increasing sac diameter (orthogonal plane)
5 Type of endoleak
5 Types I and III: treatment
5 Type II (treatment required?):
5 Low-ow → follow-up (possibly at shorter intervals
of 3months)
5 High-ow → reintervention
3. CEUS: indicated if CDUS fails to identify an endoleak
despite increasing AAA diameter
5 Same diagnostic accuracy as CTA
5 Superior in detecting small low-ow endoleaks (late
retrograde blood ow into aneurysm sac via patent
lumbar artery)
4. CTA (gold standard): indicated to search for suspected
endoleak (B-mode ndings) not detected by CDUS or
CEUS
e basic idea of this stepwise approach is that the next
test following in the recommended sequence of diagnostic
6.1 · Abdominal Aorta, Visceral andRenal Arteries
429
6
procedures should only be performed if it is expected to provide therapeutically relevant information.
In addition, a systematic procedure is recommended to
ensure reliable identication of endoleaks and other complications aer EVAR (. Fig.6.32):
5 Gray-scale examination in transverse orientation to
evaluate the upper stent end and its relationship to the
renal artery origins.
5 Gray-scale measurement of the largest orthogonal diam-
eter of the residual aneurysm sac (see . Figs.6.77a and
6.82 (both Atlas)).
5 Transverse CDUS (low pulse repetition frequency) of the
aneurysm site and the stented segment from the renal
artery origins to the bifurcation, focusing on the origins
of the lumbar arteries and the inferior mesenteric artery
(. Figs.6.78 and 6.80 (both Atlas)).
5 Longitudinal CDUS evaluation of the stent ends with
spectral Doppler measurement to conrm patency, dem-
onstrate stenosis, and identify type I endoleaks using an
acute Doppler angle at the anchoring sites (
(Atlas)).
5 If CDUS reveals ow in the aneurysm sac, this must
be conrmed by spectral Doppler interrogation. is
is especially important in the early postinterventional
phase before complete thrombosis of the aneurysm has
occurred and movement of the stent can mimic ow
signals (pseudoendoleak). Such pseudoendoleaks are
dierentiated from true endoleaks by the demonstration
of to-and-fro ow in the spectral Doppler waveform
(especially with the sample volume at the site of leakage,
e.g., patent lumbar artery entering the aneurysm sac).
is ow pattern is characteristic of endoleaks, which
resemble pseudoaneurysms in terms of hemodynamics
(see . Fig.6.80 (Atlas)). Mirror artifacts can be ruled out
by insonation from dierent directions, supplemented
by waveform information.
5 Patients with type II endoleaks not requiring reinter-
vention (patent lateral branches, lumbar arteries, inferior
mesenteric artery) can be managed by shortening the
follow-up interval (see
(failure of xation) and type III endoleaks are reliably
detected by ultrasound.
Whether the ultrasound examination allows adequate evaluation aer AAA repair strongly depends on the individual
acoustic window. Published data on the reliability of ultrasound are inconsistent, especially with regard to the identication of type II endoleaks (Ashoke etal. 2005; Sanford
etal. 2006). Some authors showed CDUS to be sucient to
rule out endoleaks with reported sensitivities of 77–96% and
specicities of 90–94% (D’Audiret 2001; Golzarian et al.
2002; Sato etal. 1998; Sun 2006; AbuRahma 2006; Collins
etal. 2007; Stavropoulos and Charagundla 2007); however,
the patient populations investigated were small. e diculty in detecting an endoleak is that it requires not only a
good acoustic window and adequate machine settings (low
. Fig.6.32). Higher-ow type I
. Fig.6.79
pulse repetition frequency) but also great care in setting the
Doppler angle correction cursor relative to the leak jet so as
not to miss a type II endoleak. Moreover, motion and mirror
artifacts in the excluded aneurysm sac can mimic ow in the
color duplex examination, which must be dierentiated from
an endoleak by spectral Doppler interrogation (for technical
details and optimization of settings see
Therapeutic Relevance of CDUS-derived
z
Hemodynamic Information
Despite its inherent methodological limitations, color duplex
ultrasound allows reliable evaluation for endoleaks aer
EVAR. Doppler waveforms contribute therapeutically relevant supplementary hemodynamic information not provided
by CEUS or CTA (Schäberle etal. 2014).
e diagnostic questions to be answered by the
sonographic examination of patients with a suspected
endoleak can be summarized as follows:
5 Is an endoleak present?
5 If yes, which type (type I, II, III, or IV or a combined
endoleak)?
5 If a type II endoleak is present, is it fed by the inferior
mesenteric artery or by a patent lumbar artery?
5 How should the endoleak be managed?
5 Follow-up only
5 If treatment is required, how urgent is the reinter-
vention?
Ȥ elective
Ȥ urgent
Ȥ emergency intervention.
kCombined Endoleaks
Type I endoleaks develop in the early postinterventional
period and tend to occur in conjunction with other endoleaks, commonly type II.A second endoleak can relieve the
intrasac pressure buildup that would otherwise result from
blood entering the sac through a type I endoelak. CDUS provides information on blood ow velocity and other ow characteristics at the entry point, which is relevant for estimating
the acute risk of rupture associated with a type I endoleak.
Like a pseudoaneurysm, a type I endoleak is characterized
by to-and-fro ow with blood entering the sac during systole and leaving it during diastole. A monophasic waveform
showing ow into the aneurysm sac but little or no backward
ow indicates a high acute rupture risk or that the blood
leaves the sac through a second, paradoxical endoleak, which
may be termed an exoleak. Such a constellation is suggested
by the demonstration of untypical orthograde ow in the
lumbar artery or the inferior mesenteric artery draining the
aneurysm through the endoleak (see
(both Atlas)). A Doppler waveform from the inferior mesenteric artery or origin of a patent lumbar artery provides
the necessary hemodynamic information (ow character and
direction) to fully capture the ow situation. is information is essential for estimating the risk of rupture and to plan
an individual reintervention strategy.
7 Sect. 6.1.2.1.2).
. Figs. 6.78 and 6.79
430
Chapter 6 · Visceral andRetroperitoneal Vessels
6
. Fig. 6.35a, b Low-ow type II endoleak. a Flow in the former aneurysm sac fed by a patent right-sided lumbar artery (arrow) displayed in
red (ow toward transducer) along with blue-coded ow in the stent graft (both iliac limbs). The waveform shows to-and-fro ow of very low
frequency at the entry site, consistent with slow ow in the thin-caliber lumbar arteries and hence low ow volumes entering the aneurysm
sac. These hemodynamic features suggest that there is no risk of rupture and that the endoleak is likely to close spontaneously. In addition, the
anteroposterior aneurysm diameter has decreased from 5.7 to 5.1cm. With this constellation of ndings, no immediate reintervention is necessary. Instead, duplex ultrasound follow-up at 3-month intervals is indicated. b Angiogram with selective probing of the lumbar artery conrms a
low-ow endoleak and blood ow in a small portion of the aneurysm sac. An endoleak with these features can be managed by watchful waiting.
In this patient, coils were placed in the same angiography session
kHigh-ow and Low-ow Type II Endoleaks
e Doppler waveform from the endoleak jet provides
relevant information on endoleak hemodynamics (see
. Figs.6.77, 6.78, 6.79, 6.80, and 6.81 (all Atlas)). A low-ow
endoleak fed by a patent lumbar artery can be managed
by watchful waiting as long as the aneurysm sac does not
expand (see . Figs.6.81 and 6.82 (both Atlas). Because these
type II endoleaks tend to close spontaneously, the risk of rupture is low (spontaneous thrombosis in up to 50% of type II
endoleaks according to Carter etal. (2000)). However, validated criteria for the identication of low-ow endoleaks are
not available for any imaging modality (Liewald etal. 2001;
Parry etal. 2002; White etal. 2000). Time-intensity curves
derived from CEUS allow quantitative analysis of endoleak
ow dynamics. Again, validated data on the therapeutic relevance are not available. Methodologically, at least time-topeak curves are required, while the sum of intensities alone
is not sucient.
hemodynamic parameters derived from Doppler
Two
waveforms
obtained in the endoleak may be helpful in predicting the risk of rupture. On the one hand, the waveform
shape provides information on resistance to blood ow.
When a single endoleak is present, to-and-fro ow should
predominate (due to the variation in pressure through the
cardiac cycle, resulting in systolic ow into the aneurysm sac
and diastolic ow back into the feeding artery). Consistent
with this assumption, a higher spontaneous thrombosis rate
was reported for endoleaks with bidirectional ow compared
with endoleaks showing predominantly systolic inow (similar to the ow prole of peripheral arteries) and little diastolic
backward ow (Carter etal. 2000; Parent etal. 2002). Surprisingly, a more recent study identied bidirectional Doppler
ow to be associated with a higher rate of sac growth (Beeman etal. 2010). is observation is counterintuitive because
one would normally expect further aneurysm growth when
inow through an endoleak is higher than outow (i.e., the
waveform is monophasic), unless the blood leaves the sac via
another route– an exoleak (see
. Fig.6.79 (Atlas)). An aneu-
rysm with blood entering the sac through one endoleak and
leaving it through another is less likely to close spontaneously
than a sac with bidirectional ow through a single endoleak.
Correct placement of the sample volume for spectral Doppler interrogation is essential to capture blood ow directions at the endoleak site (patent lumbar artery or inferior
mesenteric artery) (see . Figs.6.36 and 6.82 (Atlas)). Else-
where in a perfused residual aneurysm sac, eddy ow with
circulatory movement of blood (like in a pseudoaneurysm)
may give rise to a monophasic waveform and misinterpretation of endoleak hemodynamics.
In addition, spectral Doppler can be used to measure
ow velocity at the blood entry site (patent lumbar artery,
inferior mesenteric artery) and thus estimate the ow volume. A high systolic velocity suggests a large endoleak volume or highly dynamic ow situation (
. Figs.6.35, 6.36, 6.81
(Atlas), and 6.82 (Atlas)). A study investigating intrasac ow
velocities proposed a Doppler cuto >80 cm/s to identify
endoleaks not expected to seal spontaneously (Arko 2003).
In the author’s experience, this cuto is rather high and a
cuto on the order of 50–40cm/s appears to better identify
endoleaks requiring repair (. Fig.6.35b). However, Beeman
et al. (2010) conclude that ow velocity in the aneurysm
sac is not a relevant predictor of sac growth. Again, it is
important to ensure that measurement is performed at the
site of entry of a patent feeder into the aneurysm sac and
with adequate Doppler angle correction (. Fig.6.36a). With
a meticulous technique, the time-averaged velocity (intensity-weighted) during systolic inow and diastolic outow
should be identical.
6.1 · Abdominal Aorta, Visceral andRenal Arteries
431
6
. Fig. 6.36a–j Sonographic endoleak characterization. a Endoleak in the upper portion of a stent graft following endovascular aneurysm
repair (EVAR) for abdominal aortic aneurysm (AAA). There is blue-coded ow in the former aneurysm sac adjacent to red-coded ow in the stent
graft (S). To determine whether a type I or type II endoleak is present, a Doppler waveform is obtained from the origin of the inferior mesenteric
artery (AMI), which shows high-frequency bidirectional ow with ow into the aneurysm sac during systole (S) and a PSV of 100cm. These ndings are consistent with a high-ow endoleak. b To-and-fro ow with a PSV of 105cm/s is conrmed along the course of the inferior mesenteric
artery (AMI; systolic ow (S) toward the excluded aneurysm (toward transducer) and diastolic ow (D) away from transducer). While the waveform
represents ow over time and thus captures its bidirectional nature, the color ow image selectively shows diastolic ow (blue-coded ow, away
from transducer) and thus suggests orthograde ow. c Hemodynamic evaluation at an arbitrary site in the aneurysm rather than at the blood
entry site is unsuitable for endoleak characterization. With the sample volume for spectral Doppler measurement placed away from the entry site
(as done here for illustration), the PSV is 49cm/s and ow is in one direction, which is usually due to circular ow in the sac. d Waveform from a
site adjacent to the Doppler sampling site in c: PSV of only 25cm/s but to-and-fro ow. e An additional endoleak is identied between the 2 iliac
limbs of the stent graft, through which blood enters the inferior portion of the aneurysm sac (PSV of 1m/s). Flow through this endoleak is unidirectional into the aneurysm sac with the blood taking a meandering course in the sac and leaving through the inferior mesenteric artery.
f In the contrast-enhanced ultrasound (CEUS) examination, the large endoleak (EL) from the inferior mesenteric artery can only be suspected.
g The second endoleak, fed by a patent lumbar artery between the iliac limbs, is visible in the same location as in the color ow image shown in
e. This endoleak must be dierentiated from the bright wall reection (WR). h This CEUS image was obtained more inferiorly and is shown here
to underline the importance of always interpreting contrast-enhanced images along with the corresponding unenhanced gray-scale images in
order not to mistake bright spots for endoleaks. When such spots are present without and with contrast enhancement (indicated by arrowheads),
they do not represent ow and hence do not suggest an endoleak. i The CTA examination in this patient demonstrates an endoleak with contrast
medium extravasation (arrow) in the upper portion of the stent graft without allowing clear identication of the source of the endoleak. j Contrast
medium extravasation into the aneurysm sac (arrow) is also seen more distally, and there appears to be a meandering communication between
the upper and lower stent portion. The CTA appearance does not allow clear identication of the number of endoleaks present in this patient
To-and-fro ow is not physiologic and only occurs in
endoleaks and pseudoaneurysms. A bidirectional waveform
thus dierentiates a true endoleak from mirror or pulsation
artifacts.
Another sonographic parameter that can help the examiner in identifying patients requiring reintervention aer
EVAR is the (anteroposterior) aneurysm diameter in the
time-motion mode. A pulsatile diameter variation of the
aneurysm sac indicates an endoleak that should be treated
(see . Fig.6.81 (Atlas)).
To the best of our knowledge, no published studies have
investigated the possible diagnostic role of pulsation-related
diameter variation of the residual aneurysm sac. In a small
pilot study of 18 patients with type II endoleaks aer EVAR
432
Chapter 6 · Visceral andRetroperitoneal Vessels
conducted by the author, all 6 high-ow endoleaks showed
a diameter variation of >2mm through the cardiac cycle in
the time-motion mode. Four of the 6 high-ow endoleaks led
to sac growth within 6months and were treated, while the
other two showed a diameter increase >4mm aer another
3 months. Nine low-ow endoleaks showed no relevant
pulsation (i.e., <2mm variation through the cardiac cycle)
and no sac growth over the next 6months (measurement
tolerance ±2mm). Four of these 9 endoleaks closed spontaneously. However, 3 low-ow endoleaks showed relevant
pulsation of 2–3mm. Pulsation of the residual aneurysm sac
is typically not observed when no endoleak is present.
e diagnostic and therapeutic relevance of sac pulsation
6
in the time-motion mode might depend on the type of stent
gra (structure of the prosthesis) used for EVAR.In this pilot
study, all patients were treated with Endurant (Medtronic) or
Zenith (Cook Medical) stent gras.
Atlas)). ese endoleaks, which may rupture, have higher
ow velocities at the site of leakage and are detected with
sensitivities and specicities of 95–100% (Karthikesalingam
etal. 2012). Overall, most published data suggest that CDUS
has adequate diagnostic accuracy for detection of type I and
III endoleaks and identication of therapeutically relevant
type II endoleaks aer EVAR.An occasional patient requires
supplementary CEUS or CTA to resolve inconclusive CDUS
ndings. While complications of CEUS are extremely rare, it
must be borne in mind that it is an invasive examination and
should only be performed by qualied examiners.
While a variety of diagnostic parameters exist, sac size
remains the most important criterion in deciding about the
management of patients with type II endoleaks after EVAR
(surveillance versus intervention). Shrinkage of the residual
aneurysm sac rules out a relevant endoleak, and the question regarding the best imaging modality becomes negligible.
Conversely, when the sac expands, this points to a relevant
kPreinterventional Identication of the Feeding Artery
When interventional closure of a type II endoleak is planned,
it is helpful to know whether a patent lumbar artery or the
inferior mesenteric artery is the culprit and whether it is a
right-sided or le-sided lumbar artery. e side is dicult to
identify using CEUS, and CTA at most provides some indirect clues. A Doppler waveform from the blood entry site with
demonstration of to-and-fro ow allows identication of the
side and also dierentiation between an inferior mesenteric
artery endoleak and a lumbar artery endoleak. A waveform
showing unidirectional rather than bidirectional ow suggests that a second endoleak functioning as an exoleak is
present and should be searched for (see . Fig.6.79 (Atlas)).
endoleak, which must be identied using the full armentarium of imaging modalities. Since aneurysm diameter
measurement is subject to some uncertainty, especially when
insonation conditions are poor, an unchanged orthogonal
diameter±0.5cm should prompt a CDUS evaluation to rule
out an endoleak. Patients with inconclusive CDUS ndings
should have a CEUS examination next. If the diagnosis still
remains unclear, CTA is indicated.
Multiphase CTA is considered the gold standard for fol-
low-up aer EVAR.However, caution is required regarding
the use of potentially nephrotoxic contrast agents in these
patients, who are typically elderly and have multiple comorbidities including renal insuciency. CDUS, which was initially used as an alternative to CTA in the follow-up of EVAR
Follow-Up of EVAR: CDUS Versus CEUS and CTA
z
While studies report adequate validity for color duplex
ultrasound (CDUS)
in identifying type II endoleaks that
require intervention, contrast-enhanced ultrasound (CEUS)
appears to be superior, especially in the detection of small
endoleaks and in identifying endoleaks in patients with poor
insonation conditions, and has even been reported to be
comparable to computed tomography angiography (CTA)
(Karthikesalingam etal. 2012). However, in all cases where
CDUS identies an endoleak that is conrmed by to-and-fro
ow in the Doppler waveform, CEUS or CTA is not necessary
before interventional endoleak closure (Carter et al. 2000;
Chaer etal. 2009). Misinterpretation of mirror or pulsation
artifacts in color ow imaging can be avoided by moving the
transducer around to view the suspected endoleak from a
dierent angle. Demonstration of to-and-fro ow conrms
an endoleak, ruling out mirror or pulsation artifacts. When
an endoleak has been identied by CTA or CEUS, CDUS can
contribute therapeutically relevant information (see above).
Spectral Doppler (possibly with echo enhancer) is also indispensable to identify steno-occlusive lesions at vessel origins
in patients with a branched stent gra.
Studies consistently conrm that, with adequate
insonation conditions, CDUS allows sucient identica-
type I and III endoleaks (. Figs.6.78 and 6.79 (both
tion of
(. Figs.6.35 and 6.36), shows discrepant results in terms of
sensitivity and specicity compared with CTA. However,
many investigators conclude CDUS follow-up to be sucient
or even equal to CTA, reporting sensitivities of 80–100% and
specicities of 74–100% (Beeman et al. 2009; Chaer et al.
2009; Schmieder et al. 2009; Mirza et al. 2010; Sato etal.
1998; Wolf etal. 2000; Zannetti etal. 2000; Parent etal. 2002;
McLaerty etal. 2002; ompson etal. 1998; Fletcher etal.
2000). A review of the literature reports a mean sensitivity
of 95% and mean specicity of 97% (McLaerty etal. 2002).
Some investigators also point out advantages of CDUS over
CTA such as the real-time evaluation of sac hemodynamics.
is improves the detection of small lumbar artery endoleaks
compared with CTA, which only displays the hemodynamic
situation at individual points in time (e.g., venous phase).
Other investigators reported inadequate diagnostic accuracy
of CDUS for endoleak detection aer EVAR (AbuRahma
2006; Schuster et al. 2009). A more recent meta-analysis
including 25 studies with a total of 3975 paired scans found
a pooled sensitivity of 0.74 and a pooled specicity of 0.96
for all types of endoleaks (predominantly type II endoleaks)
compared with CTA (Karthikesalingam etal. 2012).
Several studies conrm that the sonographic detection
and localization of endoleaks (especially of the more difcult to detect type II endoleaks) can be improved by the
6.1 · Abdominal Aorta, Visceral andRenal Arteries
433
. Fig. 6.37a–c Follow-up of a patient with a branched stent graft. a Ultrasound shows occlusion of the right iliac limb. The left iliac limb is pat-
ent but there is localized luminal narrowing (arrow) at its origin due to thrombus formation. b Thrombus formation (T) in the main stent graft
body extending to the iliac limb origins (S). c Stenosis of the superior mesenteric artery (A.MES.S) at the end of the branched graft segment. The
intrastenotic peak systolic velocity (PSV) is 350cm/s (see sample volume) with a prestenotic PSV of 125cm/s (not shown). The PSV ratio calculated
from these velocities is 3, consistent with 60–70% stenosis. (The main stent graft body in the aorta (A) is patent; the absence of color ow signals
is due to the obtuse angle of insonation and high PRF)
6
administration contrast microbubbles (Böhm et al. 2000;
Henao et al. 2006; McWilliams et al. 2002; Bendick et al.
2003; Heilberger etal. 1997; Clevert etal. 2008; Sarlon etal.
2009; Giannoni etal. 2007).
CEUS in Endoleak Detection
z
Following injection of the microbubble contrast agent (for
protocol details see 7 Sect. 6.1.2.1.2), the examiner begins by
searching for type I and III endoleaks at the stent gra ends
(where the microbubbles arrive rst). Type II endoleaks,
which are fed by patent lumbar arteries or the inferior mesenteric artery, enhance later due to a longer transit time of
the contrast microbubbles (and enhancement of these arteries may even persist into the venous phase). Following the
search for endoleaks (for 2–3min aer microbubble administration), the next 2–5min with persisting enhancement can
be exploited to search for steno-occlusive lesions of the renal
and mesenteric artery origins using color duplex utlrasound,
which is especially important in patients with branched stent
gras.
In patients with an initially inconclusive contrastenhanced scan, a second microbubble injection can be given
to then focus on sites with suspicious or inconclusive ndings aer the rst contrast bolus. If the results remain inconclusive, CTA should follow.
Published data consistently show CEUS to be comparable
to CTA in detecting endoleaks and even superior in characterizing them (Iezzi etal. 2010; Pster etal. 2009; Mirza
et al. 2009). A meta-analysis of 11 studies with 981 paired
scans comparing CEUS with CTA yielded a pooled sensitivity of 0.96 and a pooled specicity of 0.85 with follow-up and
angiography oen showing CEUS to be more accurate than
CTA (Karthikesalingam etal. 2012). A small type II endoleak
fed by retrograde ow in a patent lumbar artery enhances
relatively late (longer transit time of microbubbles through
long collateral pathways), and contrast medium extravasation may be missed, even during the venous phase of CT.e
dynamic real-time CEUS examination (. Fig.6.36) is more
exible and thus better able to detect such late-enhancing
endoleaks (Jung etal. 2008; Pster etal. 2009).
In a study investigating contrast harmonic imaging (CHI)
ultrasound (see
7 Sect. 1.1.5) in 50 patients with suspected
endoleaks following EVAR, CHI and CTA concordantly
detected endoleaks in 30 cases and found no endoleak in 20
cases. In one patient, a combined type I/II endoleak was misclassied as type II.In another patient, a type II endoleak was
initially only detected by CHI and later conrmed by followup CTA.us, CHI had 99% sensitivity, 93% specicity, 99%
negative predictive value, and 95% positive predictive value.
Time-intensity curve (TIC) analysis was used in this study to
evaluate perfusion of the aneurysm (Pster etal. 2009). Standardized signal analysis aer echo enhancer administration
can be used to compare enhancement in the stent gra and in
the aneurysm sac; the intensity of enhancement varies with the
amount of blood and can thus serve to quantify the endoleak,
identifying at-risk aneurysms that warrant treatment.
Other Complications After EVAR
z
Ultrasound is clearly inferior to radiological imaging modalities in the detection of stent fracture and stent migration.
Color duplex imaging will identify these complications only
if they cause an endoleak (. Fig.6.84 (Atlas)). is is why surveillance programs for patients aer EVAR should include an
annual plain X-ray examination of the site of the former AAA.
Further complications aer EVAR are occlusion of a stent
gra limb with peripheral ischemia (
. Fig.6.37a) and throm-
bus development in the main stent gra body, which may
be a source of peripheral embolism (. Fig.6.37b), especially
when the thrombus extends to the attachment site of a stent
gra limb. Patients with a complex stent gra are additionally at risk of organic ischemia due to stenosis (. Fig.6.37c)
or occlusion of the branched artery (renal artery, superior
mesenteric artery).
6.1.6.3.8 Aortitis: Retroperitoneal
Fibrosis– Inammatory Abdominal
Aortic Aneurysm
Inammation of the aorta is rare compared with atherosclerosis. Aortitis may occur with or without dilatation and is complicated by obstruction, rupture and dissection. Underlying
434
Chapter 6 · Visceral andRetroperitoneal Vessels
causes include endocarditis, local perivascular foci, and septicemia. e aorta is the most common site of bacterial infection. e dierentiation of bacterial and nonbacterial aortitis
Normal
Normal
VC
Ao
can be dicult, dilatation is possible, and patients are at risk
of aortic or aneurysm rupture (. Fig.6.91 (Atlas)). Develop-
Vertebra
ment of an eccentric or saccular aneurysm (mycotic aneurysm) is observed very early in the course of infection, and
Aortitis
infectious aortitis is rarely detected before an aneurysm has
Aortitis
formed (Narang and Rathlev 2007; Caspary 2016).
e aorta is involved in several large-artery vascular diseases including giant cell arteritis (. Fig6.40b) and Takayasu’s arteritis as well as Behçet’s disease and Cogan’s syndrome.
Ormond’s
Ormond’s
Infl. aneurysm
Infl. aneurysm
Aortic involvement is typically asyomptomatic or presents
6
with chest or back pain. Morphologic ultrasound ndings
include concentric wall thickening and sometimes dilatation
of the aorta. Magnetic resonance angiography (MRA) and
contrast-enhanced ultrasound (CEUS) may show increased
aortic wall perfusion as a sign of local inammation. e risk
of aneurysm rupture or dissection is higher in patients with
underlying vasculitis than in patients with atherosclerotic
aneurysm.
Especially in Behçet’s disease, dilatation is mostly eccentric, the increase in diameter can progress rapidly, and other
complications such as concomitant supercial phlebitis or
deep vein thrombosis may be present.
Occasionally, aortic inammation is found in association
with rheumatoid arthritis, systemic lupus erythematosus,
sarcoidosis or inammatory bowel diseases (Caspary 2016).
Isolated aortitis (possibly IgG4-related disease) is found
in chronic periaortitis, retroperitoneal brosis (Ormond’s
disease), and in inammatory aortic aneurysm. Inammatory aortic aneurysm (
. Fig. 6.39) may sometimes develop
from degenerative aortic aneurysm in the presence of perivascular inammation (Ketha et al. 2014) and aer stent
gra repair. In Ormond’s disease (idiopathic in 70–80% of
cases), inammation extends beyond the periaortic area
(. Fig6.40a) and spreads within the retroperitoneal tissue.
Aortic wall thickening can be dierentiated from perivascular, retroperitoneal conditions in the B-mode examination
by assessing the course of arterial branches arising from the
aorta. Retroperitoneal lymphomas are circumscribed round
lesions but may become conuent. Retroperitoneal brosis
. Fig. 6.38 Evaluation of the course of the proximal inferior mes-
enteric artery as it arises from the aorta for the dierentiation of
aortic wall thickening and retroperitoneal perivascular pathology
(see . Fig.6.85 (Atlas)). The topmost diagram illustrates the normal
anatomy of the aorta (Ao) and vena cava (VC). The diagram labeled
“Aortitis” illustrates the situation in giant cell arteritis: the inferior
mesenteric artery arises from the aorta and then courses outside the
hypoechoic, concentrically thickened wall of the aorta. In this condition, the mesenteric artery takes the shortest path possible through
the abnormal tissue (inammatory aortic wall). The diagram labeled
“In. aneurysm” illustrates the ndings in inammatory abdominal
aortic aneurysm (AAA). In this condition, the inferior mesenteric artery
also passes through the aneurysmatically dilated and thickened
abdominal wall, taking the shortest path possible, to then descend
toward the left lower abdomen outside the thickened structure. If atherosclerotic lesions are present, they can help in dierentiating inammatory wall thickening from thrombotic deposits in the aneurysm sac:
atherosclerotic plaques make the intima appear bright, thus allowing
dierentiation of thrombotic deposits extending into the lumen from
inammatory wall thickening on the other side of the intima. The
bottom diagram (labeled “Ormond’s”) illustrates the ndings in retroperitoneal brosis. The proximal segment of the inferior mesenteric
artery arising from the nonthickened aortic wall courses through the
hypoechoic abnormal tissue before emerging out of it and passing to
the left lower abdomen. In retroperitoneal brosis, the abnormal tissue
pushes a longer proximal segment of the inferior mesenteric artery
against the wall of the aorta. In patients with more advanced retroperitoneal brosis, which also encases the vena cava or even the ureter, the
diagnosis and dierentiation from other conditions are easier than in
early disease with brotic tissue surrounding only the aorta. Therefore,
the abnormal course of the proximal inferior mesenteric artery is the
decisive criterion for making the dierential diagnosis (Diagrams courtesy of K.Amendt)
is typically depicted as a more hypoechoic structure covering
the aorta from anteriorly and involving the vena cava. It tapers
o laterally and may also surround and compress the ureter.
Specically, the course of the inferior mesenteric artery
can help in dierentiating wall thickening of the aorta and
retroperitoneal brosis (
. Figs.6.38 and 6.40). In retroperi-
toneal brosis, the proximal inferior mesenteric artery is
pushed against the aorta and thus courses between the aortic
wall and the hypoechoic brosis for several centimeters before
piercing through the hypoechoic brotic cap (see . Fig.6.85
(Atlas)). In inammation of the aorta (e.g., giant cell arteritis), on the other hand, the inferior mesenteric artery pierces
the hypoechoic layer around the patent lumen of the aorta
directly at its origin to then descend into the le lower abdomen outside the hypoechoic thickening. Inammatory wall
thickening in aortitis and in inammatory aortic aneurysm is
circumferential and spares the vena cava (see
6.40). e exible selection of scanning planes in the ultra-
. Figs.6.39 and
sound examination facilitates determination of the relationships between the aorta, hypoechoic thickening, perivascular
structures, and other vessels, thereby contributing to the differential diagnosis.
ickening of the aortic wall due to vasculitis with aortic
dilatation or inammatory aortic aneurysm can be dierentiated from intraluminal thrombi by its relationship to the intimal layer. While this is relevant for diameter measurement,
dierentiation is only possible when atherosclerotic plaque is
present, which makes the intima appear brighter. e normal
intima is not visible sonographically (. Figs.6.38 and 6.39).