Role of volume in small abdominal aortic aneurysm surveillance

OBJECTIVE

Current management of small abdominal aortic aneurysms (AAAs) primarily involves serial imaging surveillance of maximum transverse diameter (MTD) to estimate rupture risk. Other measurements, such as volume and tortuosity, are less well-studied and may help characterize and predict AAA progression. This study evaluated predictors of AAA volume growth and discusses the role of volume in clinical practice.

METHODS

Subjects from the Non-invasive Treatment of Abdominal Aortic Aneurysm Clinical Trial (baseline AAA MTD, 3.5-5.0 cm) with ≥2 computed tomography scans were included in this study (n = 250). Computed tomography scans were conducted approximately every 6 months over 2 years. MTD, volume, and tortuosity were used to model growth. Univariable and multivariable backwards elimination least squares regressions assessed associations with volume growth.

RESULTS

Baseline MTD accounted for 43% of baseline volume variance (P < .0001). Mean volume growth rate was 10.4 cm³/year (standard deviation, 8.8 cm³/year) (mean volume change +10.4%). Baseline volume accounted for 30% of volume growth variance; MTD accounted for 13% of volume growth variance. More tortuous aneurysms at baseline had significantly larger volume growth rates (difference, 32.8 cm³/year; P < .0001). Univariable analysis identified angiotensin II receptor blocker use (difference, -3.4 cm³/year; P = .02) and history of diabetes mellitus (difference, -2.8 cm³/year; P = .04) to be associated with lower rates of volume growth. Baseline volume, tortuosity index, current tobacco use, and absence of diabetes mellitus remained significantly associated with volume growth in multivariable analysis. AAAs that reached the MTD threshold for repair had a wide range of volumes: 102 cm³ to 142 cm³ in female patients (n = 5) and 105 cm³ to 229 cm³ in male patients (n = 20).

CONCLUSIONS

Baseline AAA volume and MTD were found to be moderately correlated. On average, AAA volume grows about 10% annually. Baseline volume, tortuosity, MTD, current tobacco use, angiotensin II receptor blocker use, and history of diabetes mellitus were predictive of volume growth over time.

How Precise Are Preinterventional Measurements Using Centerline Analysis Applications? Objective Ground Truth Evaluation Reveals Software-Specific Centerline Characteristics

PURPOSE

To evaluate different centerline analysis applications using objective ground truth from realistic aortic aneurysm phantoms with precisely defined geometry and centerlines to overcome the lack of unknown true dimensions in previously published in vivo validation studies.

METHODS

Three aortic phantoms were created using computer-aided design (CAD) software and a 3-dimensional (3D) printer. Computed tomography angiograms (CTAs) of phantoms and 3 patients were analyzed with 3 clinically approved and 1 research software application. The 3D centerline coordinates, intraluminal diameters, and lengths were validated against CAD ground truth using a dedicated evaluation software platform.

RESULTS

The 3D centerline position mean error ranged from 0.7±0.8 to 2.9±2.5 mm between tested applications. All applications calculated centerlines significantly different from ground truth. Diameter mean errors varied from 0.5±1.2 to 1.1±1.0 mm among 3 applications, but exceeded 8.0±11.0 mm with one application due to an unsteady distortion of luminal dimensions along the centerline. All tested commercially available software tools systematically underestimated centerline total lengths by -4.6±0.9 mm to -10.4±4.3 mm (maximum error -14.6 mm). Applications with the highest 3D centerline accuracy yielded the most precise diameter and length measurements.

CONCLUSION

One clinically approved application did not provide reproducible centerline-based analysis results, while another approved application showed length errors that might influence stent-graft choice and procedure success. The variety and specific characteristics of endovascular aneurysm repair planning software tools require scientific evaluation and user awareness.

Serial CT Volume and Thrombus Length Measurements after Endovascular Repair of Stanford Type B Aortic Dissection

Purpose:

To evaluate the outcome of stent-graft placement in Stanford type B aortic dissection using contrast-enhanced spiral computed tomographic (CT) measurements of true and false lumen volumes and thrombus length.

Methods:

Among 18 consecutive patients (13 men; mean age 60 years, range 44–79) who underwent endovascular repair of Stanford type B dissection, 12 completed at least a 12-month follow-up, which included CT measurements of true and false lumen volumes and thrombus lengths prior to discharge and at 6 and 12 months postimplantation. Volumes were assessed in 3 different aortic segments (A1, A2, A3) extending from the proximal attachment site of the prosthesis to the aortic bifurcation. In addition, thrombus length was measured to evaluate the influence of clot formation on outcome of the false lumen volume.

Results:

Mean follow-up was 27 months (range 12–60). Within 12 months, mean true lumen volumes showed statistically significant increases in the A1 (p<0.001) and A2 (p=0.003) segments; false lumen volumes showed a significant decrease in the A1 segment (p=0.002) but an insignificant increase in the A2 segment. No substantial volume changes were observed in the A3 segment. Extension of clot formation in the false lumen varied among patients and over time. Length of stent-grafts, percentage of stented dissection length, or visceral arteries originating from the false lumen did not significantly influence thrombus development, nor did these parameters or thrombus formation distal to the prosthesis have a relationship to false lumen volumes.

Conclusions:

Volumetric analysis after endovascular repair of Stanford type B dissection shows optimal technical outcome in the stented segment, whereas the false lumen in the segment immediately adjacent to the stent-graft seems to be a vulnerable area. Extension of clot formation beyond the endograft seems to be no reliable predictor of outcome.

Endotension is Influenced by Aneurysm Volume: Experimental Findings

Purpose:

To investigate in an in vitro model whether and to what extent pressure is influenced by aneurysm size.

Methods:

Latex aneurysms of 3 different volumes (24, 30, and 81 mL) were inserted into an in vitro circulation model. The systemic mean pressure (SPmean) was varied from 50 to 120 mmHg. The aneurysms were excluded using a woven polyethylene graft. Aneurysm sac mean pressure (ASPmean) was measured.

Results:

In the in vitro model, endovascular aneurysm repair created a closed chamber without endoleak but showed a relevant aneurysm sac pressure. At an SPmean of 80 mmHg, the ASPmean was 42.0 ± 0.6 mmHg in the 24-mL aneurysm, 40.5 ± 0.5 mmHg in the 30-mL model, and 19.3 ± 0.5 mmHg in the 81-mL aneurysm (p < 0.05). The ASPmean rose with increasing SPmean and was inversely dependent on the aneurysm volume.

Conclusions:

This in vitro model demonstrated that the sac mean pressure correlated to the systemic pressure and that a greater aneurysm volume reduced aneurysm sac pressure. These data highlight the need for further studies regarding endotension.

Non-Axisymmetrical (Life-Like) Abdominal Aortic Aneurysm Models: A Do-It-Yourself Approach

Purpose:

To construct life-like non-axisymmetrical abdominal aortic aneurysm models from latex.

Technique:

A computed tomographic 3-dimensional reconstruction of an actual abdominal aortic aneurysm was cast in plastic to provide a core for a “chemical metal” mould. The mould was then coated with nonadhesive prevulcanized dipping latex and cured to provide an idealized hollow reconstruction of the aneurysm.

Conclusions:

Chemical metal can be manipulated quite easily to make a mould of any required size or surface character, which then allows the manufacture of a well-matched latex model for biophysical studies of non-axisymmetrical abdominal aortic 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.

Another late complication after endovascular aneurysm repair: aneurysmal degeneration at the iliac artery landing site

The purpose of this article is to describe a hitherto underreported late complication of infrarenal endovascular aneurysm repair (EVAR), namely type Ib endoleakage resulting from aneurysmal degeneration at the iliac artery landing site. In a prospectively recorded audit, between 1994 and 2007, 297 patients underwent EVAR. All cases that developed iliac artery aneurysm (IAA) were studied. Ten cases of IAA in seven patients (2.4% of the cohort) developed 5 to 9 years after EVAR. Eight of the 10 involved the lower landing site of the stent graft. Landing site diameter before EVAR was 12 mm (range 10-15 mm). Three IAAs presented as emergencies with rapidly expanding sacs and impending rupture. All cases underwent further endovascular intervention with no < 30-day mortality. Iliac artery landing site aneurysm formation after EVAR occurs uncommonly after 5 or more years. It should be regarded as an indication for intervention prior to type Ib endoleakage development. The need for lifelong surveillance is highlighted.

Assessing the effectiveness of endografts: Clinical and experimental perspectives

The increasing use of endografts to treat abdominal aortic aneurysms has prompted the need for improved postoperative imaging and surveillance. Although patients benefit from decreased morbidity with endovascular repair compared with open abdominal aortic aneurysm repair, the long-term outcome of stent repair has yet to be fully determined. The persistence of endoleaks highlights the need for close follow-up, particularly because this may lead to aneurysm rupture, even after endograft repair. The current mainstay of assessing the healing of endografts is obtaining serial helical computed tomography angiography (CTA) to identify endoleaks, graft migration, thrombosis, and structural failure. CTA is not completely effective at identifying endoleaks and predicting aneurysm rupture, however. Other modalities have been studied to improve on current imaging methods, including three-dimensional CTA with volumetric analysis, contrast-enhanced duplex ultrasound imaging, cine magnetic resonance angiography, and explant analysis. In vitro and large-animal models of abdominal aortic aneurysm have also been developed to study the pathophysiology and treatment response of aneurysm exclusion. Thus, clinical and experimental models of endograft healing are attempting to define the optimal method of postoperative surveillance of endovascular repair.

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.

Aortic aneurysm volume calculation: effect of operator experience

BACKGROUND

We have successfully applied sequential volumetric analysis of abdominal aortic aneurysms to exclude endoleak in patients who have an aortic endostent. This study compared the effect of variable operator experience on volumetric calculation accuracy.

METHODS

Four operators with different experience levels calculated abdominal aneurysm volumes in 10 patients at two different times (>/= 1 week apart). The four reviewers were ranked as having a high level of experience (one full-time laboratory worker specializing in three dimensions with 3 years of experience), a moderate level of experience (one part-time laboratory worker specializing in three dimensions/computed tomographic technician with 1 year of part-time experience), and a low level of experience (two individuals taught volumetric measurements for the purposes of this study: a fellow in abdominal imaging and a computed tomographic technician). All volumes were calculated with a GE Advantage 4.0 workstation (General Electric, Waukesha, WI, USA).

RESULTS

Mean aneurysm volume and volume difference between two measurements were calculated for four operators. The average (standard deviation) percent volume differences were 1.2% (0.2%) for the experienced reader, 3.2% (0.3%) for the moderately experienced reader, and 6.0% (1.0%) and 5.8% (1.1%) for the two readers with light experience. Differences between averages were statistically significant (p < 0.005).

CONCLUSION

We have defined a percent margin of error for aortic aneurysm volume measurement and have shown a direct correlate to level of experience. Diagnosis of endoleak based on aneurysm volume enlargement on serial scans needs to account for the level of operator experience.

Preliminary Results

PURPOSE

To assess aortic wall compliance as a portent of rupture risk in patients with abdominal aortic aneurysms.

METHODS

In this pilot study, 38 patients (32 men; median age 78 years, range 63-95) underwent an ultrasound scan: 20 pre-repair and 24 post-repair (18 endovascular [EVR] and 6 open). Six patients from the pre-repair group were included in a post repair study after EVR. Cine loop images were analyzed offsite using wall tracking software, which measured aortic diameter changes during cardiac cycles. Brachial blood pressure was measured, and elastic modulus (Ep) and stiffness (beta) were calculated. Preop Ep and beta were determined at the neck, inflection points (IP), and mid sac levels. Postop Ep and beta were calculated in mid sac only for technical reasons.

RESULTS

Preoperative Ep and beta were significantly higher at IP compared with neck (median Ep 24.22 versus 12.95 N/cm(2), p<0.003; median beta 16.27 versus 8.65, p<0.003). At the mid sac, Ep and beta were also significantly higher compared with neck: Ep 26.41 versus 12.95 N/cm(2), p=0.001; beta 17.94 versus 8.65, p=0.001. The values for IP and mid sac were Ep 24.22 versus 26.41 N/cm(2), p=0.64; beta 16.27 versus 17.94, p=0.64. In the postop cases (n=24), Ep and beta in successful endovascular repair (n=12) were significantly higher than in open repair, respectively: median Ep 34.31 versus 12.33 N/cm(2), p<0.001; median beta 23.18 versus 8.24, p<0.001. Patients with endoleaks or endotension (n=6) had significantly elevated Ep and beta compared with those without endoleaks (n=12): median Ep 79.79 versus 34.31 N/ cm(2), p=0.002; median beta 51.52 versus 23.18, p<0.002. Six patients scanned before and after EVR showed a decrease of Ep and beta in 3, no change in 1, and an increase in 2. An increase greater than 2 fold was noted in a patient with a gross type II endoleak.

CONCLUSIONS

This pilot study shows that estimates of aortic wall compliance agree well with known values for wall stress distribution. EVR leaves patients with greater wall stiffness than those undergoing open repair, a situation accentuated by endoleaks. Wall compliance and stiffness measurement promises to be useful for the evaluation of success of endovascular repair.

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.

Changes in Abdominal Aortic Aneurysm Size after Endovascular Repair with Zenith, AneuRx, and Custom-made Stent-Grafts

The aim of this study was to determine the maximal aneurysm diameter (MAD), the total aneurysm volume (TAV), the intra-aneurysm vascular channel (IAVC), and total thrombus volume (TTV) and compare changes in those parameters during a 12-month time period. In addition, these parameters for three different endovascular grafts were compared. A retrospective review of 42 patients who had undergone endovascular aneurysm repair (EVAR) between July 1999 and March 2001, and without evidence of an endoleak or migration, was performed. The minimum follow-up in this group was 12 months. The three grafts deployed were Dacron-stainless steel bifurcated grafts with suprarenal fixation [Zenith; Cook, Inc. ( n = 14)], Dacron stainless steel aorto uni-iliac grafts with suprarenal fixation [custom-made ( n = 10)], and externally supported Dacron nitinol bifurcated grafts [AneuRx; Medtronic, Inc. ( n = 18)]. Volumetric measurements were obtained from CT images performed preoperatively, at 1 month and 12 months thereafter, using a 3-D Magicview 1000 workstation (Siemens, Inc.). Regardless of the type of endograft, a significant Change in MAD and TAV ( P = 0.008), IAVC ( P = 0.031), and TTV ( P = 0.001) was observed over the 12-month postoperative period. Both maximum diameter and total aneurysm volume appear to reflect accurately successful aneurysm exclusion. We conclude that both two-dimensional, maximal aneurysm diameter and three-dimensional, total aneurysm volume accurately reflect changes in morphology after endovascular aneurysm repair.

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.

Endotension is Influenced by Wall Compliance in a Latex Aneurysm Model

OBJECTIVES

Even though endovascular aneurysm repair (EVAR) creates a closed chamber except for patent branches, the intra-sac pressure is never zero. This study was designed to investigate whether, and to what extent, aneurysm wall compliance influences intra-sac pressure.

DESIGN

In vitro experimental study.

METHODS

Aneurysm models with six and 12 latex layers were produced, resulting in elastic and stiff circumferential compliance (3.5 +/- 0.5 and 0.9 +/- 0.3%/100 mmHg, respectively). The models with an 18 mm internal neck and maximum aneurysm diameter of 60 mm were inserted into an in vitro circulation system. The systemic mean pressure (SPmean) was varied from 50 to 120 mmHg. After the aneurysm was excluded with a knitted polyethylene graft, aneurysm sac mean pressure (ASPmean) and aneurysm sac pulse pressure (ASPpulse) were measured. Data are presented as mean +/- SD. Statistics were performed using repeated measurements of variance; p<0.05 was considered significant.

RESULTS

In the model EVAR created a closed chamber without endoleak, but with an aneurysm sac pressure related to wall compliance. In the elastic aneurysm model with six latex coats the aneurysm sac mean pressure (ASPmean) and the aneurysm sac pulse pressure (ASPpulse) at all systemic pressures were significantly lower than they were in the stiffer model with 12 latex coats (p<0.05). At a SPmean of 90 mmHg, the ASPmean was 21.0 +/- 0.9 mmHg (six latex coats) and 26.0 +/- 0.2 mmHg (12 latex coats) (p<0.05), the ASPpulse was 5.7 +/- 0.2 mmHg (six latex coats) and 8.8 +/- 0.3 mmHg (12 latex coats) (p<0.05).

CONCLUSIONS

This in vitro model demonstrated that the aneurysm sac mean pressure (ASPmean) and the aneurysm sac pulse pressure (ASPpulse) were significantly influenced by the compliance of the aneurysm wall. These data highlight the need for further studies regarding endotension.

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.

Secondary intervention following endovascular repair of abdominal aortic aneurysm: A single centre experience

AIMS

We aim from a review of our early and late experience of secondary intervention for technical failures, to examine and describe the impact of endovascular and open interventions.

METHODS

108 Abdominal Aortic Aneurysms (AAAs) repaired endoluminally between 1995-2001 were analysed. In our early experience, during 1995/96 home made pre-expanded polytetrafluoroethylene grafts fixed with Palmaz stents were used (n = 26). In our later experience, 1997/2001 Talent (n = 70) or Zenith endografts (n = 12) were used. All cases underwent spiral CT at 5 days and 6 monthly intervals post-op. Angiography was performed when further intervention was intended. All technical failures requiring intervention or not were studied.

RESULTS

There were 28 (26%) technical failures identified of which 14 of 26 (54%) occurred in our early experience, and 14 of 86 (16%) occurred in our later experience (p < 0.05). Eleven in all required open conversion at the time of endovascular repair. Our study cohort were the remaining 17 cases requiring secondary intervention, seven were from our early experience and 10 from our later experience. There were 12 endoleaks, including two as a result of graft migration, two graft occlusions, two graft distortions and one graft infection. Overall 10 (66%) technical failures were treated by endoluminal repair and seven (34%) by open methods. However, in our later experience significantly more endoluminal techniques (80%) were used (p < 0.05).

CONCLUSIONS

Technical failure rates were significantly higher in our earlier experience. Open repair, which was a feature of our early experience, has been avoided over the final 3 years. Instead, endoluminal techniques were used without further morbidity or mortality. Aneurysm rupture has not so far been experienced in this experience.

Noninvasive evaluation of the effectiveness of endovascular AAA exclusion

PURPOSE

To evaluate the relationship between aneurysm sac pressure and endograft wall motion in vitro and in vivo and to compare this to sac volume changes after endovascular aneurysm repair.

METHODS

In a flow model of an aneurysm with a stent-graft in situ, sac pressure was incrementally increased by adding volume to an otherwise excluded sac; sac pressure waves were registered. Clinically, 43 patients who had unsupported endografts were monitored for stent-graft wall motion using electrocardiographically-guided M-mode ultrasonography. At 3 predetermined points in the cardiac cycle, 2 independent observers measured the maximal endograft diameter. Graft wall motion was then compared to changes in aneurysm thrombus volume (shrinking, static, growth) based on serial spiral computed tomographic angiography measurements.

RESULTS

In the in vitro model, as the sac was incrementally pressurized, the initially static pressure waveform changed to a more dynamic waveform identical to that of the systemic pressure. Additionally, graft wall motion was noted visually when the pressure exceeded 40 mm; it became increasingly vigorous at higher pressures. The 0.13-cm wall motion in the growth group (n=5) was significantly larger than the 0.04 cm in the static group (n=19; p=0.012) and the 0.03 cm in the shrinking group (n=19; p=0.002). No significant difference was found between the static and the shrinking groups (p=0.209).

CONCLUSIONS

Increases in sac pressure are reflected as increased wall motion in unsupported endografts. Clinically, increased endograft wall motion can be demonstrated by M-mode ultrasound; in growing aneurysms, the significant change in wall motion may suggest increased sac pressures as the etiology of the aneurysm growth.

Two-dimensional versus three-dimensional CT scan for aortic measurement

PURPOSE

To examine if 3-dimensional (3D) reconstructions of computed tomographic (CT) data, by imaging perpendicular to blood flow, can improve aortic diameter measurement accuracy over axial (2D) CT.

METHODS

Two independent, blinded observers used electronic calipers to measure the minor axis and the line perpendicular to it on 40 2.5-mm 2D CT scans from 31 patients. A circular electronic tool was used to estimate diameters on 3D reconstructions from the same 40 scans. Measurements of the aortic neck were obtained 5 mm below the renal arteries and the widest slice of the aneurysm was used to measure sac diameter. Only the minor axis was measured at the iliac arteries immediately above the left (LI) and right (RI) iliac bifurcations. Datasets were compared with an intraclass correlation coefficient (ICC), Bland and Altman variation assessments, and absolute differences.

RESULTS

ICC between 2D and 3D scans demonstrated high correlation with 2D minor axis measurements (neck=0.9282, sac=0.8956, RI=0.8755, LI=0.7381). 3D to 2D major axis correlation was lower (neck=0.6388, sac=0.8995). Variation between 3D and 2D minor axis measurements was low (0.51-mm average variation from the mean for the minor axis and 1.30-mm variation for the major axis). Average absolute difference between 3D and 2D diameters was 1.01 mm (minor axis) versus 2.61 mm (major axis). Interobserver correlation was highest for sac measurements both in 2D minor axis (ICC=0.8990) and 3D (ICC=0.9518).

CONCLUSIONS

Minor axis measurements on axial CT scan can substitute for diameters obtained from 3D reconstructions in most clinical situations.

Controversies in the management of type II "branch" endoleaks following endovascular abdominal aortic aneurysm repair

Successful endovascular aortic aneurysm repair (EVAR) is often defined as complete exclusion of blood flow within the aneurysm sac. Perigraft flow, also known as endoleak, is the most common complication following EVAR. Attachment site related endoleaks (type I) are generally considered to warrant some form of intervention due to the belief that they represent a risk for future rupture. Management of type II endoleaks, also known as branch or collateral endoleaks, is more controversial. Some advocate a policy of watchful-waiting whereas others treat all type II endoleaks as soon as they are discovered. The following review explores the controversies pertaining to the management, diagnosis and surveillance imaging, and treatment of type II endoleaks.

Does fresh clot shrink faster than preexistent mural thrombus after endovascular AAA repair?

PURPOSE

To correlate the amount of preexistent thrombus in abdominal aortic aneurysms (AAA) to sac shrinkage after endovascular repair.

METHODS

From January 1993 through April 2000, 76 patients underwent endovascular AAA repair and were examined at 12 months to identify aneurysms that had decreased in size by > or = 10%. Volume measurements were performed using a standardized spiral computed tomographic angiography (CTA) protocol with 3-dimensional postprocessing. Volume measurements were unavailable or incomplete in 16 patients, and another 16 did not have sac shrinkage > or = 10%, leaving 44 patients in the study group. The percentage of preexistent mural thrombus in shrinking sacs (OldThr%) was calculated by dividing the preoperative thrombus volume by the postoperative nonluminal thrombus volume. The 12-month volume change, expressed as a percentage of the postoperative thrombus volume and as an absolute value, was correlated with OldThr% using the Pearson product moment test.

RESULTS

The median proportional shrinkage at 12 months was 56% (range 15%-89%) and the absolute nonluminal thrombus volume shrinkage was 49 mL (range 6-186). The median OldThr% was 53% (range 6%-94%). The correlation coefficients of OldThr% were 0.130 (p=0.40) with the proportional shrinkage in thrombus volume and 0.235 (p=0.13) with the absolute volume change.

CONCLUSIONS

The rate of shrinkage of successfully excluded aneurysm sacs after endovascular repair is independent of the preoperative mural thrombus volume in the aneurysm. Other factors are responsible for the large variation in shrinkage.

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.

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.

Differing morphological changes following endovascular AAA repair using balloon-expandable or self-expanding endografts

PURPOSE

To determine whether changes in aneurysm morphology after endovascular abdominal aortic aneurysm (AAA) repair differ according to the type of endograft (self-expanding versus balloon-expandable).

METHODS

Among 88 patients with AAA treated with either homemade polytetrafluoroethylene (PTFE) aortomonoiliac endografts or Talent stent-grafts, 30 patients (24 males; mean age 73 years, range 55-93) were selected for this study based on a >2-year follow-up and freedom from endoleak or conversion. Of these, 12 had PTFE endografts and 18 Talent devices. All patients had spiral computed tomographic angiography with 3-dimensional reconstruction at 5 days posttreatment and 6-month intervals thereafter. Neck dimensions (length and diameters at 3 levels) were measured, along with volumes and maximal diameters of the sac and lengths of the aneurysm and endograft. Intra- and interobserver errors were <5% for linear and volume measurements.

RESULTS

Both groups had an initial 20-mL increase in median volume (p = 0.02) followed, only in Talent patients, by marked shrinkage at 6 months (-87.4 mL; p = 0.09). PTFE patients had no further changes in sac volume. Maximal sac diameters reflected volumes, but only after day 5. PTFE patients had an immediate increase (p = 0.03) in aneurysm neck diameters, which then remained stable. Talent patients had continuing increases in diameter to 6 months (p < 0.05), with no change thereafter. Length changes were not significant in either group. PTFE patients had an increase in median aneurysm length at day 5 (+3.2 mm, p = 0.04) and again at 1.5 years (+6.4 mm, p = 0.03). Endograft length slowly increased (+18.7 mm) over 1.5 years (p = 0.02). Talent patients had no length changes in the device or aneurysm.

CONCLUSIONS

Aneurysm morphology appeared to alter according to the type of endograft deployed. With PTFE endografts, aneurysm volume does not change, whereas impressive sac shrinkage occurs in conjunction with the Talent system. Aneurysm/graft lengths increase with unsupported stent-grafts. Neck diameter increases immediately with balloon-expandable endografts and then remains constant. In the self-expanding models, neck diameter increases at 6 months but not thereafter.

Abdominal aortic aneurysm rupture following endoluminal graft deployment: report of a predictable event

PURPOSE

To describe the predictability of an abdominal aortic aneurysm (AAA) rupture secondary to a type II endoleak following stent-graft exclusion.

METHODS AND RESULTS

An 81-year-old man with an enlarging AAA underwent endovascular repair using an AneuRx aortic stent-graft, but a type II endoleak fed by an accessory renal artery was detected at postprocedural computed tomography (CT). Surveillance CT scans at 6 and 16 months showed an increase in the aneurysm diameter and endoleak volume, but the patient refused advised treatment to close the leak. He suffered a fatal aneurysm rupture 24 months after endografting. Retrospective analysis of CT data documented progressive aneurysm enlargement that correctly predicted the rupture.

CONCLUSIONS

Type II endoleaks can lead to aneurysm rupture. Three-dimensional (3D) spiral CT angiography offers an opportunity to track endoleak volume and the effect of exposure to systemic pressure on the aneurysm sac.

A prospective study of changes in aneurysm and graft length after endovascular exclusion of AAA using balloon and self-expanding endograft systems

PURPOSE

Longitudinal shrinkage of aneurysms post-endovascular repair, employing unvalidated measurement techniques has been held to account for endograft disruption. In this study we record changes in aneurysm length, diameter and volume using the gold standard of calibrated spiral CT angiography (SCTA).

METHOD

From 179 patients with AAA scanned by SCTA, 68 were selected for endografting. Twenty-seven had PTFE home-made prostheses while 41 patients had Talent endografts. SCTA was performed on the fifth postoperative day and 6-monthly intervals thereafter. The distance between the lowest renal artery and the aortic bifurcation (VBL - vertical body length) and the luminal centre line length (LCL) were measured. Maximal sac diameters and volumes were recorded using 3DCT reconstruction.

RESULTS

Significant increase was noted in VBL (3.2) mm for PTFE-treated patients accompanied by an increase in sac volume at day 5 (12.5 ml). No changes in LCL or maximal diameters were evident. At 1.5 years further lengthening of both VBL (6.4 mm) and LCL (9.3 mm) was unaccompanied by sac diameter/volume changes. Talent patients - no changes in VBL or LCL were evident. Volumes and maximal AP and transverse diameters showed marked shrinkage: AP -11. 2 mm; transverse -2.6 mm; volumes by -35.5 ml at 6 months.

CONCLUSION

With PTFE increase in VBL but not graft length, without concurrent changes in maximal diameters at day 5, is commensurate with increase in sac volume; after 1.5 years graft lengthening overtakes aortic lengthening. In Talent patients VBL/graft length remained unchanged. There is no evidence for longitudinal aneurysmal contracture. Volumes and maximal diameters for the Talent endograft but not for PTFE show shrinkage.