Considering CTA as the gold standard, DUS was
found to have a sensitivity and specificity of 75%
and 100%, respectively for endoleak detection in the
current study. For detecting type 1 endoleak, DUS
demonstrated a sensitivity and specificity of 100% and
100%, respectively and it had a sensitivity of 50% and
specificity of 100% for type 2 endoleak detection.
Persistent type 1 and 3 endoleaks may cause an
increase in the pressure in the aneurysm sac, leading
to enlargement of the aneurysm; therefore, rupture
and death may occur. Type 2 endoleak occurs as a
result of retrograde flow from patent side branches
to the aneurysm sac and is considered as a low
pressure endoleak.[15] Therefore, after repair with
EVAR, follow-up should be done at 1, 6, and 12
months and annually thereafter up to five years
according to risk status of endoleaks.[16] The CTA
is the gold-standard imaging method with a short
examination duration, minimal patient dependence,
and three-dimensional reformat image advantages.
However, it requires ionizing radiation and potentially
nephrotoxic and allergic contrast agents.[17] Doppler
US is a potentially alternative imaging modality to
CTA. It has advantages such as not having ionizing
radiation, not requiring the use of nephrotoxic and
allergic contrast agents, being relatively inexpensive,
non-invasive, and reproducible. However, it is a user-dependent method and has technical limitations
in cases with obesity and meteorism.[18]
Studies comparing CTA and DUS in the diagnosis
of post-repair endoleak with EVAR demonstrated the
sensitivity of DUS to be between 25 and 100%.[16] The
effectiveness of DUS varies according to the device,
user experience, and endoleak types detected in the
study groups. In our study, CTA was superior to DUS
in the detection of type 2 endoleaks. On the other
hand, no superiority was demonstrated in the detection
of type 1 endoleaks. Overall, specificity of DUS
to detect all subtypes of endoleaks was found to be
100%, sensitivity for type 1A and type 1B were 100%,
sensitivity for type 2 was 50% in the current study.
A previous study showed that DUS had a sensitivity
and specificity of 74% and 94%, respectively in which
they concluded that DUS could detect type 1 and 3
endoleak after EVAR.[19] In our study, the sensitivity
was relatively low and the specificity was higher,
considering the high level of the devices we used,
indicating that it is needed to gain experience in
detecting type 2 endoleaks.
The effectiveness of DUS varies according to the
endoleak types detected in the study groups with
different results. A study showed a sensitivity and
specificity of 100% for endoleak detection with DUS,
while DUS was concluded to even be superior to
CTA in endoleak detection.[20] On the other hand,
AbuRahma et al.[17] reported that DUS is more
sensitive in detecting type 1 endoleaks than type 2
endoleaks (88% and 50%, respectively) and that DUS had a low sensitivity, particularly in detecting type 2
endoleaks and should not be used alone. However, they
also mentioned that most of the type 2 endoleaks
regressed spontaneously and the intervention decisions
of these patients should be determined according to the
aneurysm diameter increase. In our study, the presence
of type 2 endoleak, which could not be detected
in DUS in two cases, was revealed by CTA. No
progression or spontaneous thrombosis was detected
in these patients, and after the endoleak detection,
DUS follow-up was appropriate and performing CTA
did not have any additional contribution. Doppler US
can be used in follow-up owing to its high sensitivity
and NPV compared to CTA; however, more aggressive
invasive diagnostic methods can be applied when
endoleak is suspected. Furthermore, low sensitivity of
DUS for detecting type 2 endoleaks is acceptable, since
undetected endoleaks are clinically insignificant.[21]
The increase in the aneurysm diameter is critical
for intervention decision in cases with type 2 endoleak.
Doppler US is a method that can be used in aneurysm
diameter follow-up. Raman et al.[22] reported that CTA
and DUS showed a high correlation for aneurysm
diameter follow-up. Besides, it has been proposed
that, although DUS is a method that can be used in
the diagnosis of endoleak thanks to its high sensitivity
and specificity, it gives very different results with CTA
in the follow-up of aneurysm diameter.[23] Ultrasound
may underestimate aortic size compared to CTA with
the inner-to-inner measurement method.[24] In our
study, anteroposterior and transverse diameters were
measured at the widest level of the aneurysm which
showed a correlation between the two measurements.
However, the aneurysm diameter was measured smaller
with DUS than with CTA. This difference should be
kept in mind while using DUS for aneurysm diameter
monitoring. In the current study, CTA measurements
were made on reformat images, taking into account the
tortuosity of the aorta, in the transverse plane, at its
widest point, and from outer to outer.
AbuRahma et al.[17] reported that, apart from the
known limitations of DUS, it was not exactly known
how the stent graft could affect the sound conduction
as a factor that might cause errors in the detection of
endoleaks. The decrease in the transmission of sound
waves by the stent may cause the sensitivity of DUS
to decrease in endoleak detection. In our study, color
artifacts behind the graft during DUS examination
were also problematic. Similar to mirror artifact behind
the stent, pulsating artifacts such as color coding of the flow in the stent may occur. To distinguish it from true
endoleak, it was examined from different angles. The
location of the true endoleak remains constant, while
the artifacts change their location and are always seen
behind the stent, enabling the distinction between
endoleak and artifact.
In their study, Berdejo et al.[25] reported that DUS
might be an effective technique for the postoperative
evaluation of patients treated with endovascular
grafts and might be the main diagnostic method in
the post-intervention follow-up in the near future.
According to their own experience, false negative
results depended on suboptimal examinations or the
examination technique. They also emphasized that it
was necessary to know the underlying pathology and
the details of the procedure performed in each patient.
Bargellini et al.[26] compared the results of CTA and
DUS in 196 patients after EVAR and showed that
DUS was a method that could be used alone after the
first-year follow-up after repair with EVAR, bearing
in mind the low diagnostic value in aneurysm diameter
measurements, and CTA should be used in cases with
persistent diameter increase. In our study, CTA and
DUS results were correlated, suggesting that DUS
is an alternative method to CTA in the diagnosis of
endoleak. Unlike the previous study, the current study
demonstrates that DUS can be a method that can be
used in the aneurysm diameter follow-up.
Through the evaluation of the hemodynamics of the
artery with pulse wave DUS, waveforms or measuring
current velocities for type 2 endoleak persistency can
be detected.[27] Therefore, it can be speculated that
DUS, with the help of hemodynamic parameters, can
contribute to the determination of the prognosis and
prevention of more serious complications. In our study,
the possibility of thrombosis was not evaluated by
comparing intra-endoleak flow velocity measurements
or evaluating waveforms. The presence of arterial
flow in the aneurysm was investigated and after the
endoleak was detected, the vascular structure that
could be the source was determined.
Several studies have also been conducted on the
use of contrast media in post-repair ultrasonographic
examination with EVAR. While there are studies
that argue that contrast-enhanced US is not a reliable
method in the follow-up after repair with EVAR,
there are also studies suggesting that it can detect
endoleaks even that CTA cannot detect.[28] In the
current study, unfortunately, we were unable to use contrast agents during DUS and could not compare
the further results.
The main limitations of the present study include
its single-center, retrospective design with a relatively
small sample size. In addition, follow-up period was
short and optimal time point for follow-up could not
be achieved, and pulse wave measurements were not
available.
In conclusion, DUS is potentially an alternative
imaging modality to CTA, although it has low
sensitivity for detecting type 2 endoleaks during
post-repair follow-up after EVAR. It has many
advantages over CTA during routine follow-up. It may
be appropriate to evaluate with CTA when an increase
in the aneurysm diameter, graft migration or rupture
is suspected. It is important to strictly adhere to the
DUS examination protocol and evaluation criteria to
minimize false-positive or false-negative results. As
the number of cases and experience increase, it may be
possible to use DUS as an alternative to CTA in the
routine follow-up of all patients.
Declaration of conflicting interests
The authors declared no conflicts of interest with respect
to the authorship and/or publication of this article.
Funding
The authors received no financial support for the research
and/or authorship of this article.