Interventional Cardiology
Figure 4: Type II Endoleak AB
inexpensive and does not carry radiation risk or nephrotoxicity). Measurement of the aortic diameter can be reliably performed with CDUS, although it has been noted that US can result in underestimation of the maximum diameter compared with CTA.33 However, CDUS performs poorly in the detection of endoleak,34,35 and according to two systematic review studies pooled sensitivity and specificity rates were 66–69% and 91–93%, respectively36,37
(see
Figure 4). A specific advantage of CDUS is the detection of the direction of flow, which is important in the classification and management of endoleaks.
A: Computed tomography angiography during endovascular aortic aneurysm repair (EVAR) follow-up depicts contrast enhancement of the aortic sac; B: Colour Doppler ultrasound depicts intrasac flow.
Figure 5: Type II Endoleak
reported excellent results on the sensitivity of CEUS with detection of endoleak even in cases where the other modalities (CECT) had failed, the results of other investigators are not so encouraging. McWilliams et al.39
and relatively high false-positive rate of CEUS using CECT as the gold standard comparison technique. AbuRahma et al.35
Recently, many investigators have concentrated on the role of contrast-enhanced US (CEUS) in the surveillance of patients after EVAR and the detection of endoleaks. US contrast agents consist of gas bubbles that are intensely echogenic and have an excellent safety profile. Evident signs of an endoleak are presence of contrast enhancement within the aneurysm sac with or without identification of the origin or the inflow and outflow collateral vessels. Time of delay between injection and sac enhancement, as well as the morphology of the enhancement (diffuse or concentrated on a pseudocavity within the thrombosed sac), may have a potential role in the origin of the endoleak. The use of recently developed agents and tissue harmonic imaging has improved the sensitivity of CEUS. Although Napoli et al.25 Benedick et al.38
and reported a 50% sensitivity found the
overall sensitivity of CEUS for detection of endoleaks to be 68%. The detection of type II endoleaks was significantly lower (sensitivity 50% for type II versus 88% for type I).
Recently, Chaer et al.40 published an interesting approach in the domain
Time-resolved magnetic resonance angiography (MRA) image of the same patient depicts the type II endoleak.
associated aneurysm sac enlargement does not seem to be associated with an overall increased risk of rupture and therefore necessitate no treatment.28–30
can degrade images and make detection of endoleaks difficult.
In most centres, follow-up protocols include MDCTA control at months one, three, six and 12, and yearly thereafter. Total effective dose with the above protocols is around 145–204mSv over a five-year period. For a total dose of 204mSv, the risk of cancer for a patient 70 and 50 years of age is 0.60 and 1.03, respectively (one in 170 and one in 100 patients, respectively).16
Thus, the radiation dose of MDCTA is indeed a topic of concern when long-term surveillance is necessary.
In terms of CTA’s ability to detect the structural changes of the endograft, this is achievable with the currently available MDCT, although subtle non-displaced fractures cannot be identified.31,32
Unenhanced Colour Doppler and Enhanced Ultrasound Colour Doppler ultrasonography (CDUS) has successfully been used in population screening for abdominal aortic aneurysm, and would be ideal for EVAR follow-up (it is non-invasive, widely available and
86
of EVAR surveillance and the role of ultrasonography. The authors evaluated the safety of colour duplex US scanning on a specific category of patients after EVAR, specifically those with stable or shrinking aneurysm, and concluded that US-only surveillance post-EVAR was safe in this population and could be initiated early after treatment.
Streak artefacts from embolisation coils
Generally, US imaging has specific benefits and limitations. On the one hand, the technique is convenient and safe (no radiation exposure) and inexpensive, and US agents cause no allergy or nephrotoxicity (unlike radio-opaque contrast agents). On the other hand, it is operator- and patient-dependent (obesity and bowel gas can interfere with US scanning and patient collaboration is always required), and provides no information on endograft integrity and aneurysm morphological changes (kinking).25
Furthermore, while CE
imaging can be performed for analysis of one previously defined area of the aneurysmal sac, if no evidence of the site of the endoleak is present, selection of the field to image can be problematic.25
Magnetic Resonance Angiography
MRA is used as a follow-up method after EVAR, most commonly in patients with impaired renal function or a known allergy to iodinated contrast media. It has been proved that MRI can be safely used with non-ferromagnetic stent-grafts in terms of stent deflection and heating.41
Nitinol-based stents are MR-compatible with no major artefacts that could cause image deterioration.
EUROPEAN CARDIOLOGY
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