CT-angiography of abdominal aortic aneurysms after transfemoral endovascular aneurysm management

Beyond Diameter: Enhancing Abdominal Aortic Aneurysm Surveillance with Volumetric Assessments after Endovascular Aneurysm Repair (EVAR)

This study aimed to investigate the relationship between maximum transverse diameter (MTD) and volume measurements in patients who underwent reoperations after endovascular aneurysm repair (EVAR), and their association with the occurrence of endoleaks. The study included 51 patients who underwent EVAR and subsequent re-operations caused by endoleaks type I-III. In some number of events, multiple re-operations were needed. MTD was measured using the Horos software, and segmentations of the AAA were performed using 3D Slicer. This study first evaluated post-operative computed tomography angiography (CTA) to measure MTD and volume. Then, similar measurements were made in the control scan for re-operation qualification. Negative remodeling (increase in MTD and/or volume) was observed in 40 cases using MTD, and 48 cases using volume measurements. The volume measurement showed lower missed negatives than MTD, indicating its effectiveness in screening for negative remodeling (p < 0.001). Combining both methods identified 51 negative remodeling cases and 8 positive changes, with a higher sensitivity compared to MTD alone. The volume of the sac did not predict specific endoleak types. Decreases in MTD were observed in smaller sacs, with smaller volume changes. Volume measurement is a valuable screening tool, and combining MTD and volume enhances sensitivity. However, sac volume does not predict endoleak type.

Critical Ischemia

Conventional aortic surgery carries a significant mortality and morbidity. Transfemoral endoluminal aortic management (TEAM) offers a minimally invasive alternative. This article reports seven cases of TEAM for aortoiliac disease and abdominal aortic aneurysms with a patency rate of 100% at 24 months. Our data suggests that primary stenting can achieve excellent physiologic results and restoration of blood flow in selected patients with aortoiliac disease. Long-term study and follow-up is essential to determine the place of TEAM in the field of vascular surgery.

Imaging Modalities for Aortic Endografting

One of the most fundamental and influential differences between conventional surgery and endovascular grafting for aortic aneurysm is the central role of imaging in every aspect of management. This review summarizes five imaging techniques for aortic endografting: intravascular ultrasound, contrast angiography, conventional computed tomography (CT), spiral CT with image processing, and magnetic resonance angiography (MRA).

External ultrasound and intravascular ultrasound have important relevance to endovascular aortic surgery. Artifacts of arteriography include magnification, thrombus effect, foreshortening of tortuosity, loss of luminal detail, parallax error, and projection errors. Conventional CT scans have artifacts and difficulties also. Diameter measurement by CT suffers from methodology errors and observer variability. If conventional CT and angiography are used for endovascular aortic graft planning, both should be obtained since neither alone provides sufficient data.

The use of spiral CT scanning and computerized image processing has clearly aided the preoperative definition of aneurysm morphology both in terms of dimensional accuracy and by adding diagnostic information. MRA is capable of producing three-dimensional images, axial sections, and longitudinal projections in any plane. It can detect blood flow without contrast medium, but gadolinium enhances MRA by avoiding the “signal dropout” artifact.

Technology exists to provide new forms of imaging for endovascular surgery that combines three-dimensional models with on-line image data in a process called “data fusion.” This may offer improved ease and accuracy for conducting endovascular procedures in the future.

Postoperative Color Flow Duplex Scanning in Aortic Endografting

Purpose:

To report the feasibility and sensitivity of duplex sonography compared to computed tomography (CT) for aortic endograft follow-up surveillance.

Methods:

In a 26-month period, 113 aortic aneurysm patients received 79 tube and 34 bifurcated stent-grafts. Follow-up used contrast-enhanced CT scanning and duplex sonography with an intravenous ultrasound contrast agent (Levovist).

Results:

Eleven patients (9.7%) were converted to open repair; 1 died from hemorrhagic shock secondary to retroperitoneal hematoma. The mean follow-up time was 7.2 months (range 1 to 24), during which 5 patients died of unrelated causes. Sixteen primary (within 30 days) and 5 secondary endoleaks were detected by duplex after tube graft implantation. Among 5 endoleaks due to retrograde side-branch perfusion, 3 were detected only with contrast-enhanced duplex scanning. Iliac artery occlusion was also documented using duplex; however, 2 stent fractures could not be seen with ultrasound. Ten primary endoleaks were detected in bifurcated stent-graft patients. One endoleak originating from the distal iliac limb anchoring site was missed by duplex owing to bowel gas. Graft limb thrombosis was clearly identified by lack of a flow signal on duplex.

Conclusions:

Duplex sonography could be a valuable, reliable, and economical surveillance tool for endovascular aortic reconstructions. The adjunctive use of an intravenous ultrasound contrast agent increased the sensitivity for detecting endoleak to a level comparable to contrast-enhanced CT scanning. However, stent fractures may not be seen on ultrasound, and bowel gas can interfere with obtaining an adequate image.

Duplex Ultrasound versus Computed Tomography for the Postoperative Follow-Up of Endovascular Abdominal Aortic Aneurysm Repair. Where Do We Stand Now?

In the last decade, endovascular aneurysm repair (EVAR) has rapidly developed to be the preferred method for infrarenal abdominal aortic aneurysm repair in patients with suitable anatomy. EVAR offers the advantage of lower perioperative mortality and morbidity but carries the cost of device-related complications such as endoleak, graft migration, graft thrombosis, and structural graft failure. These complications mandate a lifelong surveillance of EVAR patients and their endografts. The purpose of this study is to review and evaluate the safety of color-duplex ultrasound (CDU) as compared with computed tomography (CT), based on the current literature, for post-EVAR surveillance. The post-EVAR follow-up modalities, CDU versus CT, are evaluated questioning three parameters: (1) accuracy of aneurysm size, (2) detection and classification of endoleaks, and (3) detection of stent-graft deformation. Studies comparing CDU with CT scan for investigation of post-EVAR complications have produced mixed results. Further and long-term research is needed to evaluate the efficacy of CDU versus CT, before CDU can be recommended as the primary imaging modality for EVAR surveillance, in place of CT for stable aneurysms.

Endovascular abdominal aortic aneurysm repair: surveillance of endoleak using maximum transverse diameter of aorta on non-enhanced CT

BACKGROUND

Repeat volumetric analysis of abdominal aortic aneurysm (AAA) after endovascular AAA repair (EVAR) is time-consuming and requires advanced processing, dedicated equipment, and skilled operators.

PURPOSE

To clarify the validity of measuring the maximal short-axis diameter (Dmax) of AAA in follow-up non-enhanced axial CT as a means of detecting substantial endoleaks after EVAR.

MATERIAL AND METHODS

CT images were retrospectively reviewed in 47 patients (7 women, 40 men; mean age, 76.2 years) who had no endoleak on initial contrast-enhanced CT after EVAR. Regular follow-up CT studies were performed every 6 months. At each CT study, the Dmax on the CT axial image was measured and compared with that on the last CT (115 data-sets). Contrast-enhanced CT was regarded as the standard of reference to decide the presence or absence of endoleaks. The appearance of endoleak was defined as the end point of this study.

RESULTS

Endoleaks were detected in 17 patients during the follow-up period. Mean Dmax changes for 6 months were significant between positive and negative endoleak cases (1.8 ± 1.9 vs. -1.1 ± 3.0 mm, P < 0.0001). When the Dmax change ≤ 0 mm for 6 months was used as the threshold for negative endoleak, the sensitivity, specificity, positive predictive value, and negative predictive value were 74.5, 82.4, 96.1, and 35.9%, respectively. When Dmax change ≤-1 mm was used as the threshold, the sensitivity, specificity, PPV, and NPV were 38.8, 100, 100, and 22.1%, respectively.

CONCLUSION

Contrast-enhanced CT is not required for the evaluation of endoleaks when the Dmax decreases by at least 1 mm over 6 months after EVAR.

A multidetector tomography protocol for follow-up of endovascular aortic aneurysm repair

OBJECTIVE

The purpose of this study was to improve the use of 64-channel multidetector computed tomography using lower doses of ionizing radiation during follow-up procedures in a series of patients with endovascular aortic aneurysm repair.

METHODS

Thirty patients receiving 5 to 29 months of follow-up after endovascular aortic aneurysm repair were analyzed using a 64-channel multidetector computed tomography device by an exam that included pre-and postcontrast with both arterial and venous phases. Leak presence and type were classified based on the exam phase.

RESULTS

Endoleaks were identified in 8/30 of cases; the endoleaks in 3/8 of these cases were not visible in the arterial phases of the exams.

CONCLUSION

The authors conclude that multidetector computed tomography with pre-contrast and venous phases should be a part of the ongoing follow-up of patients undergoing endovascular aortic aneurysm repair. The arterial phase can be excluded when the aneurism is stable or regresses. These findings permit a lower radiation dose without jeopardizing the correct diagnosis of an endoleak.

Endovascular Repair of Abdominal Aortic Aneurysms: Analysis of Aneurysm Volumetric Changes at Mid-Term Follow-Up

PURPOSE

To evaluate the volumetric changes in abdominal aortic aneurysms (AAA) after endovascular AAA repair (EVAR) in 24 months of follow-up.

METHODS

We evaluated the volume modifications in 63 consecutive patients after EVAR. All patients underwent strict duplex ultrasound and computed tomography angiography (CTA) follow-up; when complications were suspected, digital subtraction angiography was also performed. CTA datasets at 1, 6, 12, and 24 months were post-processed through semiautomatic segmentation, to isolate the aneurysmal sac and calculate its volume. Maximum transverse diameters (Dmax) were also obtained in the true axial plane, Presence and type of endoleak (EL) were recorded. A statistical analysis was performed to assess the degree of volume change, correlation with diameter modifications, and significance of the volume increase with respect to ELs.

RESULTS

Mean reconstruction time was 7 min. Mean volume reduction rates were 6.5%, 8%, and 9.6% at 6, 12, and 24 months follow-up, respectively. Mean Dmax reduction rates were 4.2%, 6.7%, and 12%; correlation with volumes was poor (r = 0.73-0.81). ELs were found in 19 patients and were more frequent (p = 0.04) in patients with higher preprocedural Dmax, The accuracies of volume changes in predicting ELs ranged between 74.6% and 84.1% and were higher than those of Dmax modifications. The strongest independent predictor of EL was a volume change at 6 months < or = 0.3% (p = 0.005), although 6 of 19 (32%) patients with EL showed no significant AAA enlargement, whereas in 6 of 44 (14%) patients without EL the aneurysm enlarged.

CONCLUSION

The lack of volume decrease in the aneurysm of at least 0.3% at 6 months follow-up indicates the need for closer surveillance, and has a higher predictive accuracy for an endoleak than Dmax.

New post-imaging software provides fast and accurate volume data from CTA surveillance after endovascular aneurysm repair

PURPOSE

To quantify intra- and interobserver variabilities when measuring total aneurysm volume after endovascular aneurysm repair using the Vitrea 2 System and to compare it in terms of accuracy and processing time with the gold standard methods using the Easy Vision workstation.

METHODS

Total aneurysm volumes from 30 postendograft CTA datasets were randomly selected from a database consisting of approximately 400 CTA datasets recorded in 89 patients. The intra- and interobserver variabilities were measured on the Vitrea workstation by 2 investigators. The intermodality variability was calculated for the same measurements using the Easy Vision workstation. The differences of each pair of measurements were plotted against their mean, and the repeatability coefficient (RC) was calculated. The mean differences were also expressed as a percentage of the first measurements.

RESULTS

The intraobserver mean difference was 1.6 mL (1.4%) with an RC of 10.8 mL (10.1%) and the interobserver mean difference was -1.4 mL (-1.4%) with an RC of 11.7 mL (10.2%). The intermodality mean difference was 1.8 mL (2.0%) with an RC of 15.8 mL (11.1%). The Vitrea workstation required a median of 8 minutes (interquartile range 7-10) for 1 observer and 6 minutes (interquartile range 5-8) for the other to perform a complete volume segmentation of each patient dataset compared to an estimated average of 30 minutes using the Easy Vision workstation.

CONCLUSIONS

The Vitrea workstation provides fast and accurate volume data from spiral CTA follow-up of endovascular aneurysm repair. This software may enhance the acceptability of volume surveillance in daily practice.

Interactive segmentation of abdominal aortic aneurysms in CTA images

A model-based approach to interactive segmentation of abdominal aortic aneurysms from CTA data is presented. After manual delineation of the aneurysm sac in the first slice, the method automatically detects the contour in subsequent slices, using the result from the previous slice as a reference. If an obtained contour is not sufficiently accurate, the user can intervene and provide an additional manual reference contour. The method is inspired by the active shape model (ASM) segmentation scheme (), in which a statistical shape model, derived from corresponding landmark points in manually labeled training images, is fitted to the image in an iterative manner. In our method, a shape model of the contours in two adjacent image slices is progressively fitted to the entire volume. The contour obtained in one slice thus constrains the possible shapes in the next slice. The optimal fit is determined on the basis of multi-resolution gray level models constructed from gray value patches sampled around each landmark. We propose to use the similarity of adjacent image slices for this gray level model, and compare these to single-slice features that are more generally used with ASM. The performance of various image features is evaluated in leave-one-out experiments on 23 data sets. Features that use the similarity of adjacent image slices outperform measures based on single-slice features in all cases. The average number of slices in our datasets is 51, while on average eight manual initializations are required, which decreases operator segmentation time by a factor of 6.

Volume regression of abdominal aortic aneurysms and its relation to successful endoluminal exclusion

OBJECTIVES

Evaluating the success of endoluminal repair of abdominal aortic aneurysms (AAAs) is frequently based on diameter measurements and determining the presence of endoleaks. The use of three-dimensional volumetric data and observation of morphologic changes in the aneurysm and device have been proposed to be more appropriate for postdeployment surveillance. The purpose of this study was to analyze the long-term volumetric and morphologic data of 161 patients who underwent endovascular AAA exclusion and to assess the utility of volume measurements for determining successful AAA repair.

METHODS

Patients with spiral computed tomography scans obtained preoperatively, within the first postoperative month, at 6 months, and annually thereafter, were included in this analysis. Computerized interactive three-dimensional reconstruction of each AAA scan was performed. Total aneurysm sac volume was measured at each time interval (mean preoperative volume 169.0 +/- 78.5 mL), and the significance of volume changes was determined by mixed linear modeling, a form of repeated measures analysis, to account for longitudinal data clustered at the individual level. Sixty-two patients (38%) developed endoleaks at some time during follow-up-15 type I leaks, 45 type II leaks, and 2 type III leaks. The patients with type I and type III leaks were treated with cuffs, and the type II leaks were treated either with observation, side-branch embolization, or required open conversion.

RESULTS

Aneurysm sac volume increased slightly at 1-month follow-up (+3.3%), and then decreased steadily to -12.9% at 5 years (P <.0001). This effect remained unchanged after controlling for the three device types used in our study population. Patients who did not exhibit an endoleak (n = 99) showed a significant decrease in aneurysm volume across the entire follow-up duration when compared with those who did exhibit an endoleak (n = 62) (P <.0001). The presence of a 10% or greater decrease in volume at 6 months demonstrated a sensitivity of 64%, a specificity of 95%, a positive predictive value of 95%, a negative predictive value of 62%, and an accuracy of 75% for predicting primary clinical success defined by successful deployment of the device; freedom from aneurysm- or procedure-related death; freedom from endoleak, rupture, migration, or device malfunction; or conversion to open repair.

CONCLUSIONS

Volumetric analysis may be used to predict successful endoluminal exclusion of AAAs. Volume regression appears to be device-independent and should be expected in most clinically successful cases. The presence of volume increases in the first 6 months is suspicious for an endoleak that is pressurizing the aneurysm sac and heralds the need for closer evaluation and possible intervention. A volume decrease of 10% or greater at 6 months and continuing regression over time is associated with successful endovascular repair.

Thoracic aortic stent graft: comparison of contrast-enhanced MR angiography and CT angiography in the follow-up: initial results

The objective of this study was to compare contrast-enhanced magnetic resonance angiography (CE MRA) and multislice computed tomographic angiography (MS CTA) in the follow-up of thoracic stent-graft placement. The CE MRA and MS CTA were performed following nitinol stent-graft treatment due to thoracic aneurysm ( n=4), intramural bleeding ( n=2) and type-B aortic dissection ( n=5). Corresponding evaluation of arterial-phase imaging characteristics focused on the stent-graft morphology and leakage assessment. Stent-graft and aneurysm extensions were comparable between both techniques. Complete exclusion (aneurysm, n=4; dissection, n=2) was assessed with high confidence with CE MRA and MS CTA. Incomplete exclusion (intramural bleeding, n=2; dissection, n=3) was assigned to lower confidence scores on CE MRA compared with MS CTA. On CE MRA the stent-graft lumen demonstrated an inhomogeneous signal, the stent struts could not be assessed. The CE MRA can be used as alternative non-invasive imaging for follow-up of nitinol stent grafts. Arterial-phase leak assessment can be less evident in CE MRA compared with MS CTA studies; therefore, the use of late-phase imaging seems to be necessary. The diagnostic gap of stent-graft fracture evaluation using MRA may be filled with plain radiographs.

Endovascular treatment of thoracic aortic pathology: feasibility and mid-term results

OBJECTIVE

to report our experience with 21 consecutive patients treated with a thoracic stent-graft.

DESIGN

retrospective analysis.

MATERIALS AND METHODS

Between October 1998 and February 2002, 21 patients (12 male), mean age 55.6 years (range 19-86 years), were treated for aorticortic pathology localized to the descending aorta (18 patients), the aortic arch (2 patients) and the ascending aorta (1 patient) and comprising true aneurysms (8 patients), false aneurysms (6 patients), traumatic rupture (4 patients), mycotic aneurysms (2 patients), and ruptured aneurysm (1 patient). Plain chest X-rays and computed tomography was performed at 3, 6 and 12 months postoperatively and then annually.

RESULTS

the median (range) operation time was 85min (50-305min), hospital stay 6 days (3-63 days) and follow-up 24 months (5-44 months). Complications occurred in 5 patients and comprised intraoperative migration (1), type I endoleak (1), type II endoleak (1), ischemic myelopathy (1), pneumonia (2), suture granuloma (1) and common femoral artery dissection (1).

CONCLUSIONS

stent-grafting can be successfully employed to treat a wide range of thoracic aortic pathologies with a mortality, morbidity and resource utilization that is considerably less than that associated with conventional surgery. However, long term follow-up on safety and efficacy is needed.

Detection of endoleaks after endovascular repair of abdominal aortic aneurysm: value of unenhanced and delayed helical CT acquisitions

PURPOSE

To assess unenhanced and delayed phase computed tomographic (CT) images combined with arterial phase images for detecting endoleaks after endovascular treatment for abdominal aortic aneurysm (AAA).

MATERIALS AND METHODS

CT scans were retrospectively evaluated for the presence of endoleaks after endovascular treatment of AAAs in 33 patients with endoleak (positive group) and 40 patients without evidence of endoleak or aneurysm enlargement (negative group). All patients underwent unenhanced and biphasic contrast material-enhanced CT. The CT scans were reviewed in the following combinations: (a) arterial phase and unenhanced scans (uniphasic/unenhanced set), (b) arterial and delayed phase scans only (biphasic set), and (c) arterial and delayed phase scans with unenhanced scans (complete set). Each set was reviewed by two radiologists blinded to the diagnosis of endoleak. Findings were recorded as positive, negative, or indeterminate for endoleak.

RESULTS

Within the positive group, endoleaks were diagnosed with the uniphasic/unenhanced, biphasic, and complete image sets in 30 (91%), 32 (97%), and 33 (100%) patients, respectively. With the uniphasic/unenhanced set, three (9%) endoleaks (seen only on delayed phase images) were missed. With the biphasic set, one (3%) endoleak was interpreted as indeterminate. Within the negative group, uniphasic/unenhanced, biphasic, and complete image sets were negative for endoleaks in 100%, 80%, and 100% of patients, respectively. With the biphasic set, results were indeterminate in 20% of cases.

CONCLUSION

A delayed CT acquisition enables detection of additional endoleaks, while an unenhanced acquisition helps eliminate indeterminate results. Thus, both acquisitions contribute to accurate diagnosis of endoleaks when combined with an arterial phase acquisition.

Localization and segmentation of aortic endografts using marker detection

A method for localization and segmentation of bifurcated aortic endografts in computed tomographic angiography (CTA) images is presented. The graft position is determined by detecting radiopaque markers sewn on the outside of the graft. The user indicates the first and the last marker, whereupon the remaining markers are automatically detected. This is achieved by first detecting marker-like structures through second-order scaled derivative analysis, which is combined with prior knowledge of graft shape and marker configuration. The identified marker centers approximate the graft sides and, derived from these, the central axis. The graft boundary is determined by maximizing the local gradient in the radial direction along a deformable contour passing through both sides. Three segmentation methods were tested. The first performs graft contour detection in the initial CT-slices, the second in slices that were reformatted to be orthogonal to the approximated graft axis, and the third uses the segmentation from the second method to find a more reliable approximation of the axis and subsequently performs contour detection. The methods have been applied to ten CTA images and the results were compared to manual marker indication by one observer and region growing aided segmentation by three observers. Out of a total of 266 markers, 262 were detected. Adequate approximations of the graft sides were obtained in all cases. The best segmentation results were obtained using a second iteration orthogonal to the axis determined from the first segmentation, yielding an average relative volume of overlap with the expert segmentations of 92%, while the interexpert reproducibility is 95%. The averaged difference in volume measured by the automated method and by the experts equals the difference among the experts: 3.5%.

IVUS guidance of thoracic and complex abdominal aortic aneurysm stent-graft repairs using an intracardiac echocardiography probe: preliminary report

PURPOSE

To report our learning experience using an intracardiac echocardiography (ICE) probe to guide endovascular aortic procedures.

METHODS

Between November 1999 and July 2001, 17 patients (12 men; mean age 73.1+/-2.3 years) underwent endovascular repair of 9 thoracic, 6 complex abdominal, and 2 thoracoabdominal aortic aneurysms. The most suitable dimensions and configuration of the stent-graft were based on preoperative computed tomographic (CTA) or magnetic resonance (MRA) angiography. Intraoperative intravascular ultrasound (IVUS) imaging was obtained using a 9-F, 9-MHz ICE probe, 110 cm in length, inserted through a 10-F, 55 degrees precurved long polyethylene sheath.

RESULTS

The endografts were deployed as planned by CTA or MRA. Before stent-graft deployment, interrogation with the ICE probe visualized the aortic arch and descending thoracoabdominal aorta without position-related artefacts and identified the sites of stent-graft fixation. After stent-graft deployment, visualization with the ICE probe detected the need for additional procedures in 8 patients, including 2 incompletely expanded thoracic grafts, which were treated with adjunctive balloon angioplasty. In 1 patient, ICE probe interrogation determined that the lesion was inappropriate for endovascular exclusion.

CONCLUSIONS

ICE probe interrogation provides accurate information on the anatomy of thoracic and abdominal aortic aneurysms and allows rapid identification of attachment sites and stent-graft characteristics. It might be considered as a valid imaging modality for monitoring all phases of endovascular procedures.

Endovascular AAA repair: classification of aneurysm sac volumetric change using spiral computed tomographic angiography

PURPOSE

To classify and analyze the volumetric changes seen on spiral computed tomographic angiography (CTA) following endovascular abdominal aortic aneurysm (AAA) repair.

METHODS

Fifty patients (46 men; mean age 71 years, range 51-83) with >1 year of imaging follow-up were retrospectively selected. The volume of the aneurysm sac was calculated on standard CT workstations to obtain plots of volume changes over time. For the purpose of this study, a 10% change in sac volume was considered significant.

RESULTS

Over a mean 32-month follow-up, 256 CTA scans were performed; initial mean sac volume was 259 mL and initial mean AAA diameter was 6.5 cm. Six distinct patterns of volume change were recognized: group Ia (28 patients, 56%): progressive reduction in aneurysm sac volume; group Ib (3 patients, 6%): transient initial increase then same as Ia; group II (4 patients, 8%): no significant change; group IIIa (5 patients, 10%): late increase in volume; group IIIb (8 patients, 16%): progressive increase in volume; and group IV (2 patients, 4%): late reduction in volume after secondary intervention. Group III changes were associated with endoleak types I and III (p<0.0001).

CONCLUSIONS

This classification system of spiral CTA volumetric changes features 6 patterns with recognized clinical significance and predictive value for endoleaks. Group I is the ideal outcome when the aneurysm sac shrinks and often completely disappears, while group III is associated with types I and type III endoleak and should prompt further investigation. Long-term volumetric analysis of all patients is advised.

Prediction of aortoiliac stent-graft length: comparison of measurement methods

PURPOSE

To determine the accuracy of helical computed tomography (CT), projectional angiography derived from CT angiography, and intravascular ultrasonographic withdrawal (IUW) length measurements for predicting appropriate aortoiliac stent-graft length.

MATERIALS AND METHODS

Helical CT data from 33 patients were analyzed before and after endovascular repair of abdominal aortic aneurysm (Aneuryx graft, n = 31; Excluder graft, n = 2). The aortoiliac length of the median luminal centerline (MLC) and the shortest path (SP) that remained at least one common iliac arterial radius away from the vessel wall were calculated. Conventional angiographic measurements were simulated from CT data as the length of the three-dimensional MLC projected onto four standard viewing planes. These predeployment lengths and IUW length, available in 24 patients, were compared with the aortoiliac arterial length after stent-graft deployment.

RESULTS

The mean error values of SP, MLC, the maximum projected MLC, and IUW were -2.1 mm +/- 4.6 (SD) (P =.013), 9.8 mm +/- 6.8 (P <.001), -5.2 mm +/- 7.8 (P <.001), and -14.1 mm +/- 9.3 (P <.001), respectively. The preprocedural prediction of the postprocedural aortoiliac length with the SP was significantly more accurate than that with the MLC (P <.001), maximum projected MLC (P <.001), and IUW (P <.001).

CONCLUSION

The shortest aortoiliac path length maintaining at least one radius distance from the vessel wall most accurately enabled stent-graft length prediction for 31 AneuRx and two Excluder stent-grafts.

Serial CT volume measurements after endovascular aortic aneurysm repair

PURPOSE

To evaluate the efficacy of transluminal stent-graft placement in aortic aneurysms using postoperative enhanced spiral computed tomographic (CT) volumetric measurements of the aneurysm sac, the intra-aneurysmal vascular channel (IAVC), the thrombus, and the stent-graft.

METHODS

Among 53 patients (45 men; mean age 74 years, range 59-85) who underwent elective endovascular aortic aneurysm repair, 37 patients with 27 abdominal and 10 thoracic aortic aneurysms completed at least a 6-month follow-up that included computerized CT volumetric analysis prior to discharge and at 3, 6, 12, 24, and 36 months. A variety of bifurcated (n = 23) and tube (n = 14) stent-grafts were observed for signs of endoleak and aneurysm enlargement.

RESULTS

Mean follow-up was 16 months (range 6-48). Total aneurysm volumes and thrombus volumes decreased, whereas IAVC and stent-graft volumes increased over time. Between the postoperative and 12-month imaging studies, reductions in total aneurysm (p 0.011) and thrombus (p < 0.001) volumes were significant. No statistically significant difference in volume changes for the aneurysm sac (p = 0.555) or the thrombus (p = 0.920) was found when comparing the 24 patients without primary leak to the 12 with primary type-II leak. In all 5 cases with secondary leak, the volume of the aneurysm sac increased after initial shrinkage.

CONCLUSIONS

Postoperative CT volumetric analysis is an effective tool for evaluating the outcome of endovascular aortic aneurysm repair. Thrombus volume measurements are more accurate than total aneurysm volumes. In patients in whom contrast agents are contraindicated, volume measurements can also be obtained without the use of contrast.

Prospective evaluation of magnetic resonance imaging after endovascular treatment of infrarenal aortic aneurysms

OBJECTIVES

to evaluate the sensitivity and specificity of magnetic resonance imaging (MRI) in the detection of type II endoleaks during follow-up after endovascular treatment of intra-renal aortic aneurysms.

DESIGN

prospective study.

MATERIAL AND METHODS

between March 1996 and November 1999, 31 patients with infra-renal aortic aneurysms who underwent stentgraft implantation were followed with helical CT and MRI, including magnetic resonance angiography (MRA), at 1 and 6 months after the procedure. Arteriography was performed between 6 and 12 months after intervention. The parameters studied included the change in the maximum anteroposterior and transverse diameters, the nature of the signal on T1 and T2 weighted sequences (homogeneous vs heterogeneous), the presence or absence of Gadolinium uptake on MRI or of contrast uptake on helical CT (early and late phases) in the sac of the aneurysm. On MRA, stentgraft patency and endoleak detection were studied.

RESULTS

arteriography demonstrated an endoleak in 19 patients (18 type II, and 1 type I endoleak). MRI at 6 months detected 18/19 endoleaks on T1 weighted sequences after injection of Gadoliniumj; there were 2 false positives. MRA sequences confirmed stentgraft patency in all patients, but did not diagnose type II endoleaks. Helical CT (late phase) at 6 months detected 10/19 endoleaks; there was 1 false positive. The sensitivity of MRI after injection of Gadolinium and of helical CT for the detection of type II endoleaks were 94% and 50% (p=0.003) respectively. The mean maximal anteroposterior and transverse diameters were similar on MRI and on helical CT at 1 month and at 6 months.

CONCLUSION

MRI after injection of Gadolinium is more sensitive than helical CT in the detection of type II endoleaks after stentgraft implantation. Its more widespread use may permit earlier intervention in such patients.

Accuracy of plastic replica of aortic aneurysm using 3D-CT data for transluminal stent-grafting: experimental and clinical evaluation

PURPOSE

To plan stent-grafting for aortic aneurysms with complicated morphology, we prepared life-sized aortic replicas by laser stereolithography using helical 3D--CT data. The accuracy of the replica was evaluated by measurement of vessel phantoms and clinical 3D--CT data.

METHOD

An imaginary aortic wall was created from helical CT images of the aorta, and a hollow plastic replica was produced by laser stereolithography. The accuracy of the replica was evaluated in five abdominal aortic aneurysms by experimental phantom studies and measurements of the replicas.

RESULTS

The mean difference in measurements between 3D--CT images and model vessels and between 3D--CT images and aortic replicas was 0.2 mm each. Therefore, the difference in measurements between real aortic aneurysms and the replicas was at most 0.4 mm.

CONCLUSION

The accuracy of the replica is satisfactory, making it useful for preoperative evaluation and simulation for stent-grafting.

Risk factors for rupture of abdominal aortic aneurysm based on three-dimensional study

PURPOSE

Factors influencing the development or rupture of abdominal aortic aneurysms (AAAs) have not yet been confirmed. This study delineated the risk factors for rupture of AAAs as evaluated by means of a combination of three-dimensional (3D) reconstruction and clinical data analysis.

METHODS

The study population comprised Japanese patients in whom an atherosclerotic AAA had been diagnosed between January 1980 and December 1997. We obtained 3D-based data by means of computer-aided 3D reconstruction from computed tomography studies of AAAs. The data included the tortuosity of the aneurysm, maximum transverse diameter, length of the aneurysm, aneurysmal volume, aneurysmal surface area, largest aneurysmal cross-sectional area, ratio of transverse aneurysmal diameter to the length of the aneurysm (T/L), and amount of mural thrombus. Clinical data were collected from patient files. All data were assessed by means of multivariate analysis for their predictive value for expansion or rupture of AAA.

RESULTS

The most efficient predictor of annual expansion rate of maximum transverse diameter (EX-D) was a combination of largest aneurysmal cross-sectional area, tobacco use, and tortuosity. The most efficient predictor of annual expansion rate of aneurysmal volume (EX-V) was a combination of aneurysmal volume and blood urea nitrogen level. The most efficient predictors of aneurysmal rupture was a combination of EX-D, diastolic blood pressure, and T/L.

CONCLUSION

Three-dimensional-based data on aneurysmal morphology, including T/L, largest aneurysmal crosssectional area, and aneurysmal volume, had strong predictive value for expansion and rupture of AAAs.

Comparison of color duplex ultrasound and computed tomography scan for surveillance after aortic endografting

Endovascular repair of abdominal aortic aneurysms (AAA) requires regular surveillance for early detection of endograft failure. CT scanning is the gold standard surveillance procedure. The purpose of this study was to assess the reliability of color duplex ultrasound (CDU) in comparison to CT scanning for detection of endoleaks and changes in aneurysmal diameter. From November 1996 to September 1999, a total of 41 patients treated by aortic endografting underwent regular surveillance with both CT scanning and CDU. There were 39 men and 2 women with a mean age of 71 years (range, 50-83). Endovascular treatment involved deployment of a straight aorto-aortic stent in 6 cases, bifurcated stent in 33, and aorta-to-unilateral iliac artery stent in 2. Stent deployment failed in one case; the procedure was conversion to open surgery. Primary or secondary endoleaks were detected in 17 patients (42%). Our findings indicated that CDU is less reliable than the CT scan for detection of endoleaks, but that reliability of CDU for surveillance of aneurysmal diameter is fair.

Diagnosis and treatment of type II endoleak after stent placement for exclusion of an abdominal aortic aneurysm

After endovascular treatment of AAA, regular clinical and radiologic surveillance is necessary for early diagnosis and treatment of mid-term and long-term complications. The purpose of this report was to evaluate the efficacy of magnetic resonance imaging (MRI) in screening for type II endoleaks and assessing the results of treatment by embolization. From March 1996 to November 1999, 64 patients with uncomplicated infrarenal abdominal aortic aneurysm (AAA) were treated by endovascular exclusion with a covered aortic stent. Radiological surveillance included plain abdominal roentgenogram (PAR), CT scan, and pelvioabdominal MRI at 1 month, 3 months, 6 months, and every 6 months thereafter. Arteriography was performed routinely after 1 year or sooner if an endoleak was suspected. Based on the results of this study, MRI seems to be more sensitive than CT scanning for detection of type II endoleaks. The negative predictive value of MRI is also better. In this series, all endoleaks were treated by embolization. In most cases, the maximum transverse diameter and maximum anteroposterior diameter decreased after embolization. Further follow-up will be necessary to confirm these findings.

Diameter changes in isolated iliac artery aneurysms 1 to 6 years after endovascular graft repair

OBJECTIVE

Precise diameter changes in iliac artery aneurysms (IAAs) after endovascular graft (EVG) repair are yet to be determined. This report describes the midterm size changes in isolated IAAs 13 to 72 months after treatment with an EVG.

METHODS

From January 1993 to April 1999, 31 patients with 35 true isolated IAAs (32 common iliac and 3 hypogastric) had these lesions treated with EVGs and coil embolization of the hypogastric artery or its branches. The EVG used in this study consisted of a balloon-expandable stent attached to a polytetrafluoroethylene graft. Contrast-enhanced spiral computed tomographic scans were performed at 3- to 6-month intervals to follow the aneurysms for change in diameter and endoleaks.

RESULTS

Thirty patients had a decrease in the size of their iliac aneurysms with EVG repair. All EVGs remained patent. All patients, except for one, were followed up for 13 to 72 months (mean, 31 months). The pretreatment aneurysm size ranged from 2.5 to 11.0 cm in diameter (mean, 4.6 +/- 1.62 cm). After EVG treatment, the aneurysms ranged from 2.0 to 8.0 cm in diameter (mean, 3.8 +/- 1.36 cm). The change in aneurysm diameter ranged from 0.5 to 3.1 cm (mean, 1.1 +/- 0.62 cm) with an average change of -0.516 +/- 0.01 cm/y for the first year. Five patients died of their intercurrent medical conditions during the follow-up period. One of the patients had a new endoleak and an increase in common iliac aneurysm size 18 months after EVG treatment, despite an early contrast-enhanced computed tomographic scan that showed no endoleak. This patient's aneurysm ruptured, and a standard open surgical repair was successfully performed. Another patient had a decrease in hypogastric aneurysm size after EVG treatment and no radiographic evidence of an endoleak, but eventually the aneurysm ruptured. He was successfully treated with a standard open surgical repair.

CONCLUSIONS

EVGs can be an effective treatment for isolated IAAs. Properly treated with EVGs, IAAs decrease in size. The enlargement of an IAA, even if no endoleak can be detected, appears to be an ominous sign suggestive of an impending rupture. IAAs that enlarge should be closely evaluated for an endoleak. If an endoleak is detected, it should be eliminated if possible. If an endoleak cannot be found, open surgical repair should be considered.

Inter- and intraobserver variability of CT measurements obtained after endovascular repair of abdominal aortic aneurysms

OBJECTIVE

Important decisions are made on the basis of CT angiographic measurements of aneurysm size obtained after endovascular abdominal aortic aneurysm repair; however, little is known about the variability of these measurements. We evaluated the variability of CT angiographic measurements of aneurysm size obtained after endovascular abdominal aortic aneurysm repair.

MATERIALS AND METHODS

Thirty CT angiographic data sets were randomly chosen from 91 sets, including preoperative, postoperative, and follow-up CT images. All images were obtained according to a standardized acquisition protocol. On a workstation, three parameters were measured: maximum aneurysm diameter, maximum aneurysm cross-sectional area, and aneurysm volume. All data sets were measured twice by two investigators in a random order. The difference of each pair of measurements was plotted against the mean value. The mean difference and its standard deviation were calculated with a repeatability coefficient.

RESULTS

The intraobserver repeatability coefficient for observer 1 was 3.8 mm for diameter, 201.7 mm(2) for cross-sectional area, and 5.6 mL for volume. For observer 2, these figures were 3.0 mm, 219.0 mm(2), and 8.1 mL, respectively. The interobserver repeatability coefficients were 3.9 mm, 236.2 mm(2), and 10.3 mL.

CONCLUSION

Determination of the repeatability coefficient of aneurysm size measurements obtained after endovascular abdominal aortic aneurysm repair provides a good description of precision.

Midterm changes in aortic aneurysm morphology after endovascular repair

PURPOSE

To study midterm changes in aortic aneurysm morphology after endovascular aneurysm repair.

METHODS

Of 94 patients with abdominal aortic aneurysms (AAAs) treated with endografts between November 1993 and August 1998, 84 were available for follow-up. Patients were evaluated preoperatively by spiral computed tomography (CT) and aortography; in follow-up, spiral CT scanning was performed at 1, 3, and 6 months and semiannually thereafter. Measurements of the aneurysm neck diameter, maximum aneurysm diameter, and the distance from the lowermost renal artery to the aortic bifurcation were made preoperatively and in follow-up.

RESULTS

Mean follow-up was 17.5 +/- 1.1 months; 56 (67%) patients were followed for 1 year and 28 (33%) for > or = 2 years. There was a median 2-mm increase (interquartile range [IQR] 0 to 3) in neck diameter at 18 months. However, a > or = 3-mm increase was seen in 18 (46%) of 39 patients examined at 18 months (median 4 mm, IQR 3 to 4, p = 0.0001). The maximum AAA diameter decreased by 9 mm (IQR 4 to 16, p = 0.0003) at 24 months, but after 18 months, no further interval decrease was seen. Aneurysms with a persistent endoleak showed either increasing or unchanged AAA diameters. There was no change in the renal artery to bifurcation distance.

CONCLUSIONS

The infrarenal aortic neck appears to dilate after AAA endografting, but only in a subset of patients. Shrinkage of aneurysms after successful stent-grafting seems to stop after 18 months, implying that the only indication of late failure in the absence of endoleak might be aneurysm enlargement. Graft-related endoleaks are often associated with an increase in aneurysm diameter.

Maximal aneurysm diameter follow-up is inadequate after endovascular abdominal aortic aneurysm repair

BACKGROUND

follow-up after endovascular abdominal aortic aneurysm repair (EAR) generally consists of serial diameter measurements. A size change after EAR, however, is the consequence of alterations of the excluded aneurysm sac volume.

OBJECTIVE

to assess the agreement between diameter measurements and volume measurements after endovascular aneurysm repair.

PATIENTS AND METHODS

from 53 consecutive patients scheduled for EAR, follow-up of at least 6 months was available in 35 patients. CTA was performed on all patients at discharge, at 6 months and yearly thereafter. The resulting 113 datasets were processed on a workstation in a blinded and random order. Maximal aneurysm diameter (DMAX) was measured along the central lumen line. Total aneurysm volume was measured by manual segmentation. All measurements of an individual patient were compared with each other, resulting in 149 comparisons. The significance of individual size changes was classified based on the 95% confidence limits of the intra-observer variability, using difference-of-means analysis. DMAX changes were compared to volume changes.

RESULTS

in 37% of the comparisons, discordance was found between DMAX and volume measurements. A decrease in aneurysm size was missed using DMAX in 14% of cases and an increase in 19% of cases.

CONCLUSION

aneurysm size changes after EAR are not noticed using maximal diameter measurements in over one-third of cases.

The value of intraoperative intravascular ultrasound for determining stent graft size (excluding abdominal aortic aneurysm) with a modular system

Since the introduction of endovascular stent grafts at our institution we have used intraoperative intravascular ultrasound (IVUS) to definitively determine stent graft size. In this study, expected stent graft size, based on preoperative helical CT scan measurements, was compared with the actual final size, based on intraoperative IVUS measurements. Between December 1996 and January 1998, 54 patients were treated with an AneuRxTM bifurcated stent graft. Preoperatively all patients underwent angiography and helical CT scanning. Expected stent graft size was determined according to these measurements. The final stent graft size was based on IVUS measurements acquired during the procedure. Differences in expected and final size were compared and follow-up endoleaks were also noted. Differences in diameter measurements between CT and IVUS were compared using the paired Student's t-test. Differences in expected and chosen stent graft length were compared using the McNemar's test for paired proportions of binomial outcomes. Our results showed that helical CT scanning overestimates diameter and underestimates length. This underestimation of length is explained by the tortuosity of the aorta and iliac arteries while using axial slices of the CT scan. The last-minute corrections based on the intraoperative IVUS measurements did not result in a high incidence of endoleaks at fixation zones. In our opinion, the possibility of making final corrections in the choice of diameter or length of the stent graft is the additional value of intraoperative IVUS.

Dilatation of the proximal neck of infrarenal aortic aneurysms after endovascular AAA repair

OBJECTIVES

to assess size changes of the proximal aortic neck after endograft placement.

METHODS

since 1994, 54 consecutive patients have undergone abdominal aortic aneurysm (AAA) repair with the Endovascular Technologies (EVT) endograft. The study group comprised the 33 patients who had completed at least six months of the prospective follow-up protocol. The pre-, postoperative and follow-up helical computed tomography (CT) angiograms (CTAs) were processed on a workstation. The proximal neck dimensions were measured perpendicular to the central lumen line of the aortic neck. The cross-sectional area was measured at the proximal attachment system and at 1 cm proximal to the renal arteries.

RESULTS

while the dimensions of suprarenal aorta did not change, a significant dilatation of the proximal neck was found. The median increase was 10.3% at 6 months and 15.5% at 12 months. No correlation could be found between the amount of dilatation and pre- or postoperative neck-size, graft diameter and amount of graft-oversizing.

CONCLUSION

the infrarenal aortic neck demonstrates continued dilatation during follow-up after endograft placement.

Length measurements of the aorta after endovascular abdominal aortic aneurysm repair

BACKGROUND

successful endovascular repair of abdominal aortic aneurysms (AAA) generally leads to a decrease in aneurysm size. Theoretically, this may lead to foreshortening of the excluded segment. If so, vertically rigid endografts may dislocate over time and cover renal or hypogastric arteries.

AIM

to assess length changes of the infrarenal aorta after endovascular AAA exclusion.

PATIENTS AND METHODS

forty-four consecutive patients were scheduled for the EndoVascular Technologies endograft, a vertically non-rigid prosthesis which would potentially accommodate longitudinal changes. Twenty-four patients had completed at least 6 months of follow-up. In 18/24 patients a decrease in size was established by aneurysm volume measurements at 6 months' follow-up. Helical computer tomography (CT) angiograms were processed on a workstation. Aortic lengths were measured along the central lumen line from the lower renal artery orifice to the native aortic bifurcation. The computer tomography angiogram (CTA) reconstruction thickness of 2 mm yields at least a 4-mm error for each length measurement.

RESULTS

in the shrinking aneurysm group, the median length change was 0 mm (range -9 mm to +4 mm) at 6 months' follow-up (n =18) and also 0 mm (range -7 mm to +4 mm) at 12 months' follow-up ( n =10). In 16/18 patients, length changes remained within the measurement error range of 4 mm.

CONCLUSION

in this group of shrinking aneurysms after endovascular AAA repair, foreshortening of the excluded aortic segment appears not to be a clinically significant problem.

Mid-term fixation stability of the EndoVascular Technologies endograft. EVT Investigators

AIM OF THE STUDY

to determine the positional stability of the EndoVascular Technologies (EVT) endograft after endovascular aneurysm repair during morphologic changes of the abdominal aorta during follow-up.

PATIENTS AND METHODS

all patients treated worldwide with an EVT endograft with an adequate postoperative and at least 12 months postoperative CT scan were included (n=125). Endograft migration was investigated by recording the position of the endograft attachment systems relative to the renal arteries and the aortic or iliac bifurcations. The vertical body axis served as a scale to quantify migration. Aortic cross-sectional areas were measured in the suprarenal aorta and in the proximal and distal aneurysm necks. Length changes of the infrarenal aorta during follow-up were measured, comparing the distance between the left renal artery and the aortic bifurcation.

RESULTS

the median follow-up was 24 months (range 12-48 months). Graft migration was identified in 4 out of 125 patients (3%). Significant infrarenal aortic dilation was observed at the proximal and distal aneurysm neck during follow-up. However, aortic neck dilation was not associated with endograft migration. The length of the infrarenal aorta did not change significantly after endovascular repair.

CONCLUSION

fixation by stents containing hooks of the EVT design appear to be effective in preventing migration of endografts with an unsupported trunk for up to four years. A stable position was maintained in spite of changes in cross-sectional areas of the aneurysm neck.

New imaging techniques in endovascular surgery

Imaging requirements for endovascular surgery are quite different from imaging requirements for open surgical procedures. As with the entire field of endovascular surgery, imaging techniques and recommendations are changing rapidly. Preoperative imaging is crucial--once deployed, an endograft cannot be retrieved without conversion to open surgical repair. As with any surgical procedure, patient selection and preoperative planning are at least as important as technical skills and at least as difficult to learn. Nonetheless, good imaging technology is no substitute for good judgement. Endovascular procedures are also unique because intraoperative and postoperative imaging are also keys to the success of the procedure. Postoperative imaging techniques are evolving more slowly as long-term data are gathered but seem to be vitally important.

Early clinical results and studies of aortic aneurysm morphology after endovascular repair

Endovascular repair is a feasible treatment alternative with favorable short-term results compared with standard operations. Nonrandomized, multicenter trials already in progress should help to define the role of endovascular grafting in the treatment of patients who are otherwise candidates for conventional repair. Long-term follow-up studies will test the durability of the procedure, including clinical repercussions of late endoleaks and migration related to slow alterations in aortic morphology, such as neck dilation and aortic shortening. More research is needed into long-term aortic morphologic changes; further insights into these changes may allow subclinical prediction of clinical events and permit intervention before a catastrophic failure. How great an advantage this procedure has over observation in high-risk patients for whom no open surgical alternative is available is also unknown because the overall mortality of this patient cohort may mitigate any treatment benefits. In today's cost-conscious world, the viability of this new technology may be dependent on balancing the short-term benefits of this procedure against its associated requirements for monitoring and subsequent reinterventions.