Postoperative Color Flow Duplex Scanning in Aortic Endografting

Accuracy of contrast-enhanced ultrasound in diagnosing extracranial carotid occlusion: A meta-analysis

AIM

This study aimed to assess the accuracy of contrast-enhanced ultrasound (CEUS) in detecting extracranial carotid artery occlusion.

MATERIALS AND METHODS

A systematic literature search was conducted in the Cochrane, PubMed, and EMBASE databases. Prospective or retrospective studies that reported sensitivity and specificity of CEUS for the diagnosis of carotid artery occlusion were selected. Eight studies (354 arteries) were included in the meta-analysis. A bivariate random-effect model was used to estimate overall sensitivity and specificity. The results were also summarized by developing a summary receiver operating characteristic (SROC) curve.

RESULTS

The overall sensitivity, specificity, positive, and negative likelihood ratios were 0.99 (95% CI: 0.83-1.00), 0.97 (95% CI: 0.90-0.99), 30.0 (95% CI: 9.8-91.4), and 0.01 (95% CI: 0.00-0.21), respectively; the odds ratio for diagnosis was 4,796 (95% CI: 119-192,584).

CONCLUSION

The diagnostic test accuracy suggests that CEUS is a reliable tool for diagnosis of extracranial carotid artery occlusion.

Can we replace computed tomography angiography by contrast-enhanced ultrasound in the surveillance of patients submitted to aortoiliac aneurysm repair?

OBJECTIVES

This study was designed for evaluation of CEUS (contrast-enhanced ultrasound) for the detection of endoleaks after EVAR (endovascular aortic aneurysms repair) as an alternative to CTA (computed tomography angiography), the gold standard in post-EVAR surveillance.

METHODS

Post-EVAR surveillance of patients who underwent CEUS and CTA was retrospectively analyzed to compare the accuracy of CEUS compared to CTA. For that, the following parameters were analyzed: the largest aneurysm diameter, type of endoleaks, and the time elapsed after EVAR using both surveillance tests.

RESULTS

The study involved 110 pairs of exams in patients with infrarenal aortoiliac or isolated iliac artery aneurysm, covering predominantly a male population (89%). The time elapsed after EVAR using CEUS or CTA exams were statistically similar, ranging from one to 58 months (mean 12.2) and one to 65 months (mean 9.7), respectively (p = 0.124). CEUS sensitivity was 75.5%, specificity 96.7%, false positives were 24.5%, and false negatives were 3.3%. The accuracy between the two exams was 87.3%. A secondary analysis, comparing CTA with CEUS as a reference standard, revealed CEUS sensitivity of 24.5%, higher than CTA for detecting endoleaks, with a concordance rate of true positive results of 75.5%. Among the endoleaks detected solely by CEUS (12 cases), one case was type Ia and eleven were type II, while those detected only by CTA (2 cases), one was type Ia and one type II. Additionally, a type II endoleak associated with type Ib, identified by CEUS, was seen as type II for CTA only. There was no difference between the pre-EVAR and the post-EVAR diameters of aortoiliac aneurysm (p = 0.058), both for CEUS and CTA. Computed tomography angiography, on the other hand, showed significant aneurysm diameter reduction compared to CEUS for isolated iliac artery aneurysms (p < 0.001).

CONCLUSION

Contrast-enhanced ultrasound was more effective than CTA in identifying and characterizing endoleaks in patients undergoing EVAR, especially type II endoleaks. The advantages include efficacy and, particularly, safety, and must be considered in EVAR surveillance protocols so that its use becomes widespread. We understand that CEUS, as a surveillance exam, considerably reduces risks to patients compared to CTA.

A Narrative Review on Contrast-Enhanced Ultrasound in Aortic Endograft Endoleak Surveillance

Endovascular repair of abdominal aortic aneurysms have been performed successfully since 1991. However, 20% to 50% of these patients may develop an endoleak or continued aneurysmal sac expansion or perfusion despite stent graft coverage. Current recommendations suggest lifelong surveillance with computed tomographic angiography (CTA) at least 1 month after intervention and yearly after that. In select patients with a stable aneurysm sac on computed tomography performed 1 year after treatment, future screening could be performed with ultrasonography. However, color Doppler ultrasound can fail to detect as many as 31% of endoleaks. Contrast-enhanced ultrasound (CEUS) provides an alternative approach to excluded aneurysm sac follow-up imaging. The Society for Vascular Surgery notes a need for further research on the role of CEUS in endovascular aortic repair surveillance. The European Federation of Societies for Ultrasound in Medicine and Biology suggests that early results are promising. Meta-analyses report pooled sensitivities and specificities of CEUS compared with CTA for the detection of endoleak between 89% and 98% and 86% and 88%, respectively. Owing to the dynamic flow information it provides, CEUS may actually be more sensitive than CTA at detection and characterization in select circumstances. Challenges with adoption, patient selection, and operator dependency remain, but current and future research suggests a role for CEUS in endoleak surveillance.

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.

Computed Tomography Versus Color Duplex Ultrasound for Surveillance of Abdominal Aortic Stent-Grafts

PURPOSE

To compare the ability of computed tomography (CT) and color duplex ultrasound (CDUS) to detect endoleak and accurately measure aortic aneurysm diameters after endovascular repair.

METHODS

Between February 2000 and October 2004, 178 consecutive patients (156 men; mean age 74 years, range 49-89) were treated with aortic stent-grafts (86 Ancure, 55 AneuRx, and 37 Excluder). The follow-up protocol included serial CT and CDUS at 1 month and every 6 months thereafter. Sensitivity, specificity, positive predictive value, negative predictive value, and Kappa statistics (kappa) were calculated using CT as the gold standard; Bland-Altman analysis was used to determine the 95% limits of agreement. Paired and unpaired t tests and correlation coefficients were used to compare the methods.

RESULTS

Follow-up ranged from 1 to 53 months (mean 16), during which 367 paired CT and CDUS studies were acquired. The mean diameter of the AAA sac after repair was 5.15 cm by CT versus 4.99 cm by CDUS (p=0.07); 93% of paired studies were somewhat similar (<or=5 mm). Mean pre to postoperative AAA size changes throughout follow-up were -0.60 mm for CT versus -0.58 mm for CDUS (p=0.78). Thirty-four (19%) endoleaks were detected (26 early and 8 late). Versus CT, the sensitivity, specificity, positive predictive value, and negative predictive value of CDUS for detecting endoleaks were 68%, 99%, 85%, and 97%, respectively (kappa=0.73). CDUS was more accurate in detecting type I endoleak than type II (88% versus 50%, p=0.046).

CONCLUSIONS

Although CDUS has good correlation to CT in measuring the size of AAAs, it has a lower sensitivity in detecting endoleak, particularly type II. Therefore, CT scans should remain the primary imaging modality for the diagnosis of endoleak.

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

PURPOSE

To synthesize the available evidence regarding the diagnostic accuracy of color duplex ultrasonography (CDU) versus the accepted gold-standard of contrast-enhanced computed tomography (CT) for the detection and classification of endoleaks after aortic endografting.

METHODS

A systematic search of the literature was conducted using electronic bibliographical databases and other means to gather articles published between 1991 and 2004. Articles were scrutinized against inclusion/exclusion criteria that broadly followed the QUADAS quality assessment guidelines. The results of diagnostic CDU were expressed for each study as a 2x2 contingency table, and summary statistics (sensitivity/specificity with 95% confidence intervals [CI]) were calculated. Pooled and random effects meta-analyses were performed.

RESULTS

Eight published studies and 2 unpublished studies from Charing Cross and St. George's Hospitals (711 patients, 1355 paired scans performed > or = 1 month after endografting) were eligible for inclusion. From meta-analyses, the pooled sensitivity of CDU (versus CT as the gold standard) was 69% (95% CI 52% to 87%) and the specificity of CDU was 91% (95% CI 87% to 95%). These parameters did not appear to vary over time when a smaller dataset of 117 patients with 239 paired scans was used to compare CT and CDU specifically at 3, 12, and 24 months after endografting. Endoleak classification data, which was derived from only 5 small studies, indicated that CDU appeared to have better diagnostic accuracy in detecting type I or type III endoleaks compared with type II endoleaks; however, the data were insufficient for statistical analysis.

CONCLUSIONS

CDU currently does not have sufficient diagnostic accuracy for the detection of all endoleaks in routine clinical practice. The diagnostic accuracy of CDU may improve if type II endoleaks are ignored.

Aortic diameter is an insensitive measurement of early aneurysm expansion after endografting

PURPOSE

To determine the sensitivity of various methods of diameter measurement to detect abdominal aortic aneurysm (AAA) size change following endovascular grafting.

METHODS

Sixty-eight patients (59 men; mean age 68 years, range 47-84) with 3-dimensional reconstruction of 196 computed tomography (CT) studies (68 preoperative, 128 follow-up) were studied. Implanted devices included 50 bifurcated and 18 straight stent-grafts. All diameter measurements were obtained from reformatted CT slices perpendicular to the center of blood flow. Three diameter measurements were made for each study: (1) transverse (TR), (2) anteroposterior (AP), and (3) maximum diameter in any orientation (Dmax). Volume measurements were calculated from the lowest main renal artery to the aortic bifurcation. Changes in diameter and volume were determined by subtracting follow-up measurements from preop measurements. Diameter and volume changes >5 mm and 10%, respectively, were considered significant.

RESULTS

AAA volume significantly increased in 20 (15%) studies, decreased in 84 (66%), and remained unchanged in 24 (19%). Agreement between methods of diameter measurement (TR, AP, Dmax) and volume change were 35%, 15%, and 25% for volume increase >10%, respectively, and 70%, 88%, and 74%, respectively, for volume decrease >10%. The orientation of maximum diameter varied in individual serial exams in 19 (28%) patients. Three of 12 patients with a study showing volume increase failed to demonstrate endoleak.

CONCLUSIONS

Diameter measurements were not sensitive in detecting enlarging AAA after endografting. Volume measurement determined by 3D reconstruction is the preferred method for early diagnosis of patients with enlarging AAA that may indicate increased risk of rupture after aortic endografting.

Midterm outcomes of thoracic aortic stent-grafts: complications and imaging techniques

PURPOSE

To evaluate the midterm outcomes of thoracic aortic stent-grafting and the performance of computed tomographic angiography (CTA), radiography, and magnetic resonance angiography (MRA) in endograft surveillance.

METHODS

Forty-seven patients with traumatic thoracic aortic ruptures (n=16), aneurysms (n=14), false aneurysms (n=3), penetrating ulcers (n=3), and dissections (n=11) treated with stent-grafts were monitored in follow-up using chest radiography and CTA in all patients and MRA in 23 patients. Two perpendicular maximal aortic diameters, the sum of these diameters, and the elliptical cross-sectional area were determined and compared to baseline for the entire group and in subgroup analyses according to lesion type. CTA, MRA, and radiography were compared for their ability to detect endoleak, monitor stent-graft configuration, and measure aortic diameters.

RESULTS

The mortality rate was 8.5%. Severe complications were observed in 14.8% (6% neurological complications); 12 (25.5%) patients had primary endoleaks. Over a mean 11-month follow-up (range 0.25-46 months), the aortic diameters decreased for all patients without endoleak (p<0.001). In the diameter/area subgroup analyses, only the traumatic rupture cohort demonstrated significant decreases in all 4 measurements. CTA and MRA measurements correlated well, but chest radiography was superior to both for visualizing stent-graft shape. In terms of endoleak detection, MRA missed only 1 (12.5%) endoleak (type II) seen on CTA; there were no false positive results with MRA.

CONCLUSIONS

Morbidity and mortality observed after thoracic stent-grafting are acceptable. Radiography is better for monitoring stent-graft conformation, while CTA provides the best overall morphological information. The performance of MRA in endoleak detection is encouraging.

Contrast-enhanced ultrasound imaging for aortic stent-graft surveillance

PURPOSE

To compare unenhanced and enhanced ultrasound imaging to computed tomographic angiography (CTA) or magnetic resonance angiography (MRA) for surveillance of aortic endografts.

METHODS

Thirty consecutive patients (29 men; mean age 69 years, range 50-82) who underwent endovascular aortic aneurysm repair agreed to participate in a follow-up program. Patients underwent CTA (26/30) or MRA (4/30), plain abdominal radiography, and unenhanced and enhanced ultrasound examinations at 3, 12, and 24 months to evaluate aneurysm diameter, endoleaks, and graft patency. The accuracy of ultrasound was compared with CTA or MRA as the reference standards.

RESULTS

Twenty-six patients reached the 24-month assessment (mean follow-up 30 months, range 6-60). All endoleaks detected by CTA or MRA were confirmed by enhanced ultrasound; the aneurysm diameter in these patients remained unchanged or increased. In patients without endoleaks on any imaging method, the sac diameter remained unchanged or decreased. Endoleaks disclosed by enhanced ultrasound alone, all type II, numbered 16 at 3 months, 6 at 12 months, and 3 at 24 months. In this group, the aneurysm diameter remained unchanged or increased. Enhanced ultrasound yielded 100% sensitivity in detecting endoleaks, but compared with CTA and MRA, all endoleaks detected by enhanced ultrasound alone were false positives (mean specificity 65%). Nevertheless, because changes in the postoperative aneurysm diameter were similar in patients with endoleaks detectable on CTA/MRA and on enhanced ultrasound ("true positives") and in those with endoleaks detectable only on enhanced ultrasound ("false positives"), some endoleaks were possibly "true positive" results.

CONCLUSIONS

Enhanced ultrasound is a useful method in the long-term surveillance of endovascular aortic aneurysm repairs, possibly in association with CTA or MRA. Enhanced ultrasound also seems able to identify endoleaks missed by other imaging techniques, but this conclusion awaits further investigation.

Thromboembolic complications after endovascular aortic aneurysm repair

PURPOSE

To evaluate the frequency and significance of thromboembolic complications following endovascular treatment of aortic aneurysms.

METHODS

One hundred seventy-four patients (153 men; mean 71.4 years, range 26-90) underwent endovascular repair of aneurysms of the thoracic (n = 38) or abdominal (n = 136) aorta using a variety of endografts. All patients were examined preprocedurally using 3-phase helical computed tomography (CT) to determine appropriate endograft size. To exclude the occurrence of infarction in parenchymal organs, the first postprocedural CT scan was compared with preoperative findings. Newly recognized perfusion deficits were taken as evidence of procedure-related infarction.

RESULTS

Infarctions were detected in 16 (9.2%) patients: 13 in the kidneys, 2 in the spleen, with 1 in the mesentery; only the mesenteric infarction was clinically symptomatic. Both splenic infarctions were associated with deployment of stent-grafts in the thoracic aorta (5.3% of the 38 patients), while the mesenteric and 13 renal infarctions were seen in patients with infrarenal abdominal aortic aneurysms (0.7% and 9.6%, respectively, of 136 patients). One patient experienced complete thromboembolic occlusion of a renal artery, which was partially recanalized with intraoperative lysis.

CONCLUSIONS

Thromboembolic complications of endovascular aortic aneurysm repairs are not uncommon, and although usually asymptomatic, these sequelae have the potential to be life threatening. Perfusion abnormalities may respond to immediate lytic therapy with complete dissolution of the thrombus in certain isolated cases.

Does complete aneurysm exclusion ensure long-term success after endovascular repair?

PURPOSE

To examine whether complete aneurysm exclusion is a reliable marker for successful long-term endovascular abdominal aortic aneurysm (AAA) repair.

METHODS

The medical records, computed tomographic (CT) scans, and duplex examinations of all the patients who underwent endovascular AAA repair at a single institution and had at least 12 months of follow-up were reviewed. Sixty-seven patients (58 men; mean age 74 years, range 57-87) were identified. Complete aneurysm exclusion was defined by the absence of an endoleak at any time before an adverse event. The primary endpoint included all major adverse events that occurred during the postoperative period, including aneurysm expansion, acute symptoms referable to the AAA, late secondary procedures, ruptures, and deaths from ruptures and all other causes.

RESULTS

There were 44 adverse events (8 expanding aneurysms, 4 acute symptoms, 17 secondary procedures, and 15 deaths from other causes) in 28 (42%) patients. Among 36 (54%) patients who had initial complete aneurysm exclusion (no endoleak), 12 (33%) experienced adverse events, compared with 16 (52%) events in 31 patients who had endoleak (chi2 = 1.59, p = 0.21).

CONCLUSIONS

There was no statistically significant difference in adverse events based on the presence or absence of endoleak. Complete aneurysm exclusion as defined by absence of an endoleak does not indicate an event-free postoperative course. A better marker of clinical success of endovascular AAA repair is needed.

Embolization of type II endoleaks fed by the inferior mesenteric artery: using the superior mesenteric artery approach

PURPOSE

To evaluate the use of a superior mesenteric artery (SMA) approach to embolize type II endoleaks arising from the inferior mesenteric artery (IMA).

TECHNIQUE

When reperfusion of the aneurysmal sac via the SMA occurs through the IMA, as shown by computed tomography (CT) and angiography, the IMA origin can be accessed via the marginal artery or the anastomosis of Riolan. The SMA is catheterized with a 5-F catheter, and a coaxial catheter is advanced to the leak to deliver 2- to 8-mm-diameter minicoils to embolize the IMA origin and entire aneurysmal sac. Embolization usually requires from 1 to 2 hours to complete. In our experience with this technique in 11 cases, complications have not occurred, and there has been only one very small residual leak that sealed the next day. Over a 24.5-month follow-up (range 12-39), the endoleaks have remained sealed according to serial color duplex scans.

CONCLUSIONS

Successful percutaneous treatment of type II endoleak due to IMA inflow can be accomplished using an SMA access via the Riolan anastomosis or marginal artery. The procedure appears to be safe and has no adverse effects.

The need for clinical trials of endovascular abdominal aortic aneurysm stent-graft repair: The EUROSTAR Project. EUROpean collaborators on Stent-graft Techniques for abdominal aortic Aneurysm Repair

EUROSTAR (EUROpean collaborators on Stent-graft Techniques for abdominal aortic Aneurysm Repair) was established for the purpose of combining and studying data on endovascular abdominal aortic aneurysm (AAA) repair, EUROSTAR is independent of any commercial interest and has as its ultimate goal an independent, scientifically reliable assessment of endovascular AAA grafting. A standardized case record form is used for data collection and transmission, and the database is maintained in a central registry office. A comprehensive set of clinical, imaging, technical, and laboratory data obtained at initial admission and follow-up are recorded; these data are analyzed periodically and reports generated on the collated experience. As a first priority, an observational study without controls was initiated in July 1996 to address the issues of procedural safety, device durability, and long-term effect upon the aneurysms. Several ancillary studies have been initiated, including a "Retrieval and Analysis Study" for the evaluation of explanted devices. While a randomized study does not seem feasible at present, this may be organized at the appropriate time when the devices and techniques become more standardized.