Color Duplex Ultrasonography Is Insensitive for the Detection of Endoleak After Aortic Endografting: A Systematic Review

Type II endoleaks: when is intervention indicated and what is the index of suspicion for types I or III?

One of the principal reasons for failure of endovascular aneurysm repair (EVAR) is the occurrence of endoleaks, which regardless of size or type can transmit systemic pressure to the aneurysm sac. There is little debate that type I endoleaks (poor proximal or distal sealing) are associated with continued risk of aneurysm rupture and require treatment. Similarly, with type III endoleak, there is agreement that the defect in the device needs to be addressed; however, what to do with type II endoleaks and their effect on long-term outcome are not so clear. Aneurysm sac change is a primary parameter for determining the presence of an endoleak and assessing its impact. While diameter measurement has been the most commonly used method for determining sac changes, volume measurement has now been proven superior for monitoring structural changes in the 3-dimensional sac. Determining the source of an endoleak and the direction of flow are necessary for proper classification; however, while computed tomographic angiography has high sensitivity and specificity for detecting endoleaks, it is limited in its ability to show the direction of flow. Contrast-enhanced duplex ultrasound, on the other hand, is better able to quantify flow and characterize endoleaks. Flow is evidence of pressure, and increasing intrasac pressure increases wall tension, thus inducing progressive aneurysm expansion until rupture. Hence, determining intrasac pressure is becoming a vital component of endoleak assessment. All endoleaks can create systemic pressure inside the aneurysm sac, and there are a variety of intrasac pressure transducers being evaluated to assess this effect. A clinical pathway for patients with suspected type II endoleaks is based on a combination of imaging and pressure measurements. Imaging alone requires at least two interval examinations to determine the trend, while pressure measurements give immediate reassurance or an indication to intervene. Although still under development, pressure measurement is destined for general use and will provide a scientific basis for the management of type II endoleaks.

“Unpredictable” Late Rupture of an Abdominal Aortic Aneurysm After Bifurcated Ancure Endograft Repair

The goal of endovascular repair of an abdominal aortic aneurysm is to exclude the aneurysm from systemic arterial pressure, thereby preventing rupture. However, the long-term durability of endovascular repair continues to be in question, as aneurysm rupture after endovascular repair continues to be reported. We report the case of an 89-year-old patient who underwent endovascular repair of a 7.1-cm abdominal aortic aneurysm with an Ancure endograft 5 years earlier. Despite close follow-up and a shrinking aneurysm sac on annual contrast-enhanced computed tomography, he presented with aneurysm rupture and a new proximal type I endoleak. The endoleak and rupture were successfully repaired with endovascular placement of a main body extension.

Ultrasound surveillance of endovascular aneurysm repair: a safe modality versus computed tomography

Routine ultrasound surveillance is adequate and safe for monitoring endovascular aneurysm repairs (EVARs). A retrospective chart review including 160 endograft patients was performed from August 2000 to September 2005. All ultrasound examinations (n = 359) were performed by a board-certified vascular surgery group's accredited laboratory. Registered vascular technologists utilized the same equipment consisting of Siemens Antares high-definition ultrasonography with tissue harmonics and color flow Doppler. An identical protocol was followed by each technologist: scan body and both limbs of the endograft and distal iliac vessels, measure anterior-posterior aneurysm sac size, and detect intrasac pulsatility and color flow. Statistical analysis utilized Pearson's correlation coefficient and the paired t-test. Forty-one endoleaks were discovered out of the 359 exams (11.4%). There were type I (7, 17%), type II (26, 63%), and combined type I with type II (8, 20%) endoleaks. Correlation with computed tomography (CT) was obtained in 35 of these cases. CT discovered three endoleaks that were not seen with ultrasound. However, these particular ultrasound exams were inadequate due to additional factors (bowel gas, body habitus, hernia), which prompted CT investigation and, hence, endoleak discovery. Of the 41 endoleaks found on ultrasound, only 14 were seen on CT. Specifically, 26 type II endoleaks were seen with ultrasound versus only nine during CT. Additional factors addressed included comparison between ultrasound and CT of residual aneurysm sac measurements and conditions limiting ultrasound examination. Although criticized in the past, color flow ultrasonography is a safe and effective modality for surveillance of aortic endografts. Utilizing ultrasound to analyze abdominal aortic aneurysm (AAA) sac dimensions and endoleak detection is statistically sound for screening AAA status post-EVAR.

Aneurysm Sac pressure measurement with minimally invasive implantable pressure sensors: an alternative to current surveillance regimes after EVAR?

Current protocols for surveillance after endovascular repair (EVAR) of abdominal aortic aneurysms are mostly based on costly and time-consuming imaging procedures and aim to detect adverse events such as graft migration, endoleaks or aneurysm sac enlargement. These imaging procedures are either associated with radiation exposure to the patients or may be harmful to the patient due to the use of iodine- or gadolinium-containing contrast agents. Furthermore the advantages of EVAR in the short term might be negated by the necessity for endograft surveillance over years. Thus, alternative modalities for follow-up are being investigated. One of these technologies provides pressure information directly from the aneurysm sac. This noninvasive, telemetric pressure sensing was tested in vitro as well as in first clinical trials and was able to identify successful aneurysm exclusion after EVAR. The telemetric pressure sensors showed a promising efficacy and accuracy in detecting type I and type III endoleaks and will help to clarify the clinical relevance of type II endoleaks. This article provides an overview of the in vitro sensors investigated as well as the first clinical trials and the sensors' potential to change the current endograft surveillance regimes.

Imaging Techniques for Detection and Management of Endoleaks after Endovascular Aortic Aneurysm Repair1

Endovascular aortic aneurysm repair (EVAR) is evolving into a viable alternative to open surgical repair for many patients with abdominal and thoracic aortic aneurysms. Endoleak development is a complication of EVAR and represents one of the limitations of this procedure. Endoleaks represent blood flow outside the stent-graft lumen but within the aneurysm sac. Lifelong imaging surveillance of patients after EVAR is critical to detect endoleaks for the patient's benefit and to determine the long-term performance of the stent-graft. Although computed tomographic angiography is the most commonly used examination for imaging surveillance, magnetic resonance angiography, ultrasonography, and digital subtraction angiography all have a role in endoleak detection and management. This review will focus on imaging techniques used for endoleak detection and the role imaging surveillance plays in the overall care of the post-EVAR patient.

Detection of Endoleaks after Endovascular Aneurysm Repair with Use of Technetium-99m Sulfur Colloid and 99m Tc-labeled Red Blood Cell Scans

PURPOSE

This study was performed to determine whether endoleaks could be detected after endovascular aneurysm repair (EVAR) with use of technetium-99m sulfur colloid and (99m)Tc-labeled red blood cell (RBC) nuclear medicine scans.

MATERIALS AND METHODS

There were 13 patients enrolled in this study: nine with endoleaks seen on computed tomographic (CT) angiography and four with no endoleak on CT angiography. All patients underwent regularly scheduled surveillance CT angiography examination after EVAR to evaluate for endoleak. Endoleak detection was then attempted in each patient with two nuclear medicine scans: a (99m)Tc sulfur colloid scan and a (99m)Tc-labeled RBC scan. Flow images (5 seconds per frame) were obtained for 1 minute after intravenous administration of 555 MBq (15 mCi) (99m)Tc sulfur colloid. Sequential dynamic images were then obtained every minute for 30 minutes. Next, a (99m)Tc-labeled RBC study was performed after the intravenous administration of 370-1,073 MBq (10-29 mCi) in vitro labeled (99m)Tc RBCs. Flow images were obtained, followed by sequential dynamic images obtained every minute for 30 minutes. Single photon emission CT images of the abdomen were then acquired. The nuclear medicine scans were evaluated for the presence or absence of endoleak independent of the CT angiography findings.

RESULTS

Of the nine patients with endoleaks on CT angiography, seven (78%) had them detected by nuclear medicine examinations. Two of the nine endoleaks seen on CT angiography (22%) were not seen on either scintigraphic examination. All patients with no endoleak on CT angiography had their nuclear medicine scans correctly interpreted as showing no endoleak present (n = 4; 100%). No complications occurred as a result of the nuclear medicine scans.

CONCLUSIONS

Endoleaks can be detected with (99m)Tc sulfur colloid and (99m)Tc-labeled RBC nuclear medicine scans. This initial work suggests that the sensitivities of these scintigraphic scanning methods for endoleak detection are lower than that of CT angiography.

Duplex Ultrasound Scanning is Reliable in the Detection of Endoleak Following Endovascular Aneurysm Repair

OBJECTIVE

To investigate the value of duplex ultrasound scanning (DUSS) in the routine follow up of patients following EVAR.

METHODS

Imaging was reviewed for 310 consecutive patients undergoing EVAR at a single centre. Concurrent ultrasound and CT scans were defined as having occurred within 6 months of each other. There were 244 paired concurrent DUSS and CT scans which were used for further analysis. These modalities were compared with respect to sensitivity, specificity, positive and negative predictive values and level of agreement (by Kappa statistics) using CT as the 'gold standard'.

RESULTS

DUSS failed to detect a number of endoleaks which were seen on CT and the sensitivity of this test was therefore poor (67%). However, the specificity of DUSS compared more favourably with a value of 91%. Positive predictive values ranged from 33-100% but negative predictive values were more reliable with values of 91-100% at all time points post operatively. There were no type I leaks, or endoleaks requiring intervention which were missed on DUSS. Overall, there was a 'fair' level of agreement between the two imaging modalities using Kappa statistics.

CONCLUSION

Although DUSS is not as sensitive as CT scanning in the detection of endoleak, no leaks requiring intervention were missed on DUSS in this study. DUSS is much cheaper than CT and avoids high doses of radiation. DUSS therefore remains a valuable method of follow up after EVAR and can reduce the need for repeated CT scans.

Fate of Endoleaks Detected by CT Angiography and Missed by Color Duplex Ultrasound in Endovascular Grafts for Abdominal Aortic Aneurysms

PURPOSE

To analyze the clinical implications of endoleaks documented by computed tomographic angiography (CTA) and missed by color duplex ultrasound (CDU).

METHODS

During a recent 5-year period, 232 patients underwent endovascular aortic reconstruction (EVAR) and were followed according to a protocol that included CTA and CDU at 1 month and every 6 months thereafter. CTA was the gold standard for determining the presence of endoleaks. The size of the AAA sac at the latest postoperative follow-up was compared to the preoperative size and correlated to the type of endoleak and clinical outcome. This study analyzed only patients with endoleak documented by CTA and CDU and specifically analyzed the outcome of patients with false negative CDU studies for endoleaks.

RESULTS

Thirty-nine endoleaks were documented in 35 (15%) of 232 patients using CTA. Four patients had both early and late endoleaks. The mean follow-up was 25 months (range 1-64). CDU was more helpful in detecting type I endoleaks than type II endoleaks (89% versus 58%, p<0.05). There were 18 (46%) type I endoleaks (12 early, 6 late) detected by CTA; 16 (89%) of these were detected by CDU (2 late endoleaks missed). Nineteen (49%) type II endoleaks (16 early, 3 late) were diagnosed using CTA, 11 (58%) of which were detected by CDU (6 early and 2 late missed). Of the 2 (5%) early type IV endoleaks found on CTA, 1 (50%) was missed by CDU. Overall, CDU failed to identify endoleak in 11 (28%) of 39 endoleaks [2 late type I, 8 type II (6 early, 2 late), and 1 early type IV]. Consequences to treatment occurred in 2 (20%): 1 type I endoleak required treatment and 1 type II endoleak would have missed treatment.

CONCLUSION

CDU has a lower sensitivity in detecting endoleak, particularly type II; therefore, EVAR surveillance should not be based solely on CDU. Although a significant number of type II endoleaks resolved spontaneously, intervention can be offered for type II endoleaks if associated with an increasing sac size.

Comparison of Contrast-Enhanced Ultrasound and Computed Tomography in Classifying Endoleaks After Endovascular Treatment of Abdominal Aorta Aneurysms: Preliminary Experience

The purpose of the study was to assess the effectiveness of contrast-enhanced ultrasonography (CEUS) in endoleak classification after endovascular treatment of an abdominal aortic aneurysm compared to computed tomography angiography (CTA). From May 2001 to April 2003, 10 patients with endoleaks already detected by CTA underwent CEUS with Sonovue to confirm the CTA classification or to reclassify the endoleak. In three conflicting cases, the patients were also studied with conventional angiography. CEUS confirmed the CTA classification in seven cases (type II endoleaks). Two CTA type III endoleaks were classified as type II using CEUS and one CTA type II endoleak was classified as type I by CEUS. Regarding the cases with discordant classification, conventional angiography confirmed the ultrasound classification. Additionally, CEUS documented the origin of type II endoleaks in all cases. After CEUS reclassification of endoleaks, a significant change in patient management occurred in three cases. CEUS allows a better attribution of the origin of the endoleak, as it shows the flow in real time. CEUS is more specific than CTA in endoleak classification and gives more accurate information in therapeutic planning.

Future of Endograft Surveillance

Frequent and sustained surveillance continues to be mandated for all patients who undergo endovascular repair of the aneurysmal aorta in order to minimize the small but attendant risk of aneurysm rupture. The primary motivation for surveillance includes evaluation of residual aneurysm sac size and presence of endoleak, as well as potential adverse device specific events, such as endograft migration, module disconnection, or component fatigue and failure. The current standard of care and future surveillance modalities after endovascular repair of both abdominal aortic and thoracic aortic aneurysms will be reviewed.

Diagnostic Value of Color Duplex Ultrasonography in the Follow-up of Endovascular Repair of Abdominal Aortic Aneurysma

PURPOSE

To systematically review the findings of diagnostic value of color duplex ultrasound (US) in the follow-up of endovascular repair of abdominal aortic aneurysms (AAAs).

MATERIALS AND METHODS

A search of PubMed and Medline databases for English-language literature was performed to find studies published between 1991 and 2005. Studies comparing the diagnostic accuracy of color duplex US with that of computed tomographic (CT) angiography were included, and analysis was performed of the detection of endoleaks and measurement of aneurysm diameter.

RESULTS

Twenty-one studies (39 separate comparisons) met the criteria and were included for analysis. Pooled estimates of sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of color duplex US compared with CT angiography (with 95% CIs) were 66% (52%-81%), 93% (89%-97%), 76% (65%-87%), 90% (86%-95%), and 91% (86%-97%), respectively, for unenhanced color duplex US; and 81% (52%-100%), 82% (68%-97%), 58% (26%-90%), 95% (87%-100%), and 98% (91%-100%), respectively, for enhanced color duplex US. The sensitivity in the detection of endoleak was significantly improved with contrast material-enhanced color duplex US compared with unenhanced color duplex US (P < .05); however, no significant difference was found regarding the specificity, PPV, NPV, and accuracy between unenhanced and enhanced color duplex US (P > .05). Color duplex US was insensitive in measurement of aneurysm diameter compared with CT angiography in most situations.

CONCLUSIONS

Color duplex US is not as accurate as CT angiography and cannot replace CT angiography in the follow-up of endovascular aortic repair of AAAs. However, the use of contrast material-enhanced color duplex US resulted in improvement of diagnostic accuracy in the detection of endoleak and warrants further study.