Abdominal Aortic Aneurysm Morphology in Candidates for Endovascular Repair Evaluated with Spiral Computed Tomography and Digital Subtraction Angiography

Purpose:

To analyze the morphology of abdominal aortic aneurysms (AAAs) and to study the usefulness of spiral computed tomography (CT) versus digital subtraction angiography (DSA) in the evaluation of patients for endovascular repair.

Methods:

Of 133 AAA patients (120 men, mean age 67 years, range 52 to 84) evaluated preoperatively with CT imaging, 77 endograft candidates (68 men) were also assessed with intra-arterial DSA. Arterial parameters were measured on axial CT scans and angiographic films for comparison.

Results:

Mean maximum AAA diameter was 58 ± 11 mm (range 39 to 95). Aneurysmal neck diameter was consistently smaller on DSA than on CT (20.7 ± 3.6 mm versus 23.0 ± 3.5 mm, p < 0.0001). The distance from the most distal renal artery to the aortic bifurcation was longer on angiography than on CT (mean difference 10.0 mm, p < 0.0001). There was a positive correlation between the maximum AAA diameter and the AAA length (r = 0.49, p < 0.0001) and an inverse relationship between the neck length and the neck diameter (r = −0.36, p < 0.0001). No correlation was found between the maximum AAA diameter and maximum iliac diameter, angulation, or length.

Conclusions:

AAA anatomy varies widely and independently of the aneurysm size. Therefore, the maximum size of the aneurysm is a poor predictor of whether or not an aneurysm is suitable for endovascular repair. The discrepancy between angiographic and axial CT measurements suggests that neither alone is sufficient as a preoperative imaging technique when evaluating a patient for an endovascular graft procedure.

Diagnostic value of CT virtual intravascular endoscopy in aortic stent-grafting

PURPOSE

To investigate the diagnostic value of postprocessing techniques for 3-dimensional (3D) computed tomography (CT), with emphasis on CT virtual intravascular endoscopy (VIE), in patients with abdominal aortic aneurysms (AAA) treated with suprarenal stent-grafts.

METHODS

The preprocedural and postprocedural CT datasets from 47 AAA patients (40 men; mean age 75 years, range 61-87) undergoing aortic stent-grafting with suprarenal fixation were examined. The CT datasets were processed to create various 3D reconstructions: shaded surface display (SSD), maximum intensity projection (MIP), and VIE. Three independent radiologists assessed various diagnostic parameters for each 3D reconstruction method and compared them to axial CT images.

RESULTS

Scores for VIE reconstructions were inferior to axial CT images in the visualization of normal arterial branches, measurement of the aneurysm diameter and neck length, as well as assessment of vessel patency and presence of endoleaks. VIE was rated superior to axial CT and other 3D imaging methods in visualizing the configuration of stent struts relative to the aortic branch ostia and the number of stent wires crossing the ostia in >80% of cases.

CONCLUSIONS

VIE was not found to play a role in most preoperative situations compared to axial CT images. However, VIE provided additional postgrafting information on the 3D relationship of the suprarenal stent struts to the aortic branch ostia (in particular the renal and superior mesenteric arteries). VIE findings might aid clinicians in accurately assessing the effect of suprarenal stent-grafting on the renal arteries.

Endoluminal AAA repair using intravascular ultrasound for graft planning and deployment: a 2-year community-based experience

PURPOSE

To examine the effectiveness of intravascular ultrasound (IVUS) and digital subtraction angiography (DSA) for preoperative planning and intraoperative deployment of stent-grafts to treat abdominal aortic aneurysms.

METHODS

One hundred seventy patients (143 men; mean age 73.6+/-7.2 years, range 51-89) underwent successful DSA and IVUS to determine suitability for stent-graft repair. Patients subsequently received the AneuRx (n=157) or Ancure (n=13) device; intraprocedural IVUS was used to survey the proximal endograft for proper apposition to the aortic wall.

RESULTS

Reliable preoperative IVUS measurements were obtained in all patients. Plaque morphology was assessed in 140 (82.3%) aortic necks; in 36 (25.7%), preoperative IVUS showed high-grade atherosclerotic plaque in the nonaneurysmal abdominal aortic neck. The procedure was successful in 168 (98.8%) cases (1 [0.6%] acute conversion and 1 access failure). There were 2 (1.2%) periprocedural deaths related to bowel ischemia. Four (2.3%) patients developed graft occlusion/kinking and 2 (1.2%) developed renal failure requiring dialysis within 30 days. Multivariate logistic regression analysis revealed that female gender (p=0.0247), a short nonaneurysmal aortic neck (p=0.0185), and presence of high-grade atherosclerotic plaque (p=0.0185) correlated with major acute complications. Over a mean 10.4-month follow-up (range 1-25), 11 patients died of unrelated causes; there was no known AAA rupture or device failure. The Kaplan-Meier estimate of survival at 1 year was 91.0%+/-2.8%. Sixteen (9.4%) patients underwent 17 secondary procedures for endoleak or graft limb occlusion at a mean 5.4 months after stent-graft repair (freedom from secondary intervention at 1 year 86.5%+/-3.2%).

CONCLUSIONS

Our findings suggest that IVUS may identify patients at increased risk of major adverse complications following endovascular repair. The combination of IVUS and DSA for endoluminal stent-graft planning and placement provides excellent short- and mid-term patient outcomes.

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.

Stent-graft migration following endovascular repair of aneurysms with large proximal necks: anatomical risk factors and long-term sequelae

PURPOSE

To evaluate the outcome of aortic endografts deployed in large infrarenal necks and to identify any association of preoperative aneurysm characteristics and postoperative morphological changes with the incidence of neck dilatation and device migration in this patient subset.

METHODS

The records of 47 patients (41 men; mean age 74, range 55-84) with large aortic neck diameters treated with Talent stent-grafts from 1998 to 2001 were reviewed. Patients with anatomical criteria that precluded aneurysm exclusion with currently available devices were preferentially selected. Mean baseline aneurysm morphology included 27.6-mm (range 18-33.4) suprarenal and 28.1-mm (range 24-34) infrarenal neck diameters; the infrarenal neck length was 26 +/- 16 mm with angulation of 37 degrees +/- 18 degrees. Computed tomographic (CT) angiograms up to 3 years were analyzed using specialized interactive software; migration was defined as >1-cm change in the distance from the lower renal artery to the top of the device. Pre- and postoperative morphological characteristics of the aneurysm were compared between patients with and without migration.

RESULTS

Of the 45 patients successfully treated, 40 had complete CT data for analysis. During a mean 17-month follow-up, 7 (17.5%) of the 40 devices exhibited distal migration. Six patients required secondary procedures; 5 were in the migration cohort. No preoperative anatomical characteristic or degree of neck dilatation over time was predictive of stent-graft migration. Aneurysm sac regression was significant at 1 (-0.09 +/- 4.90 mm) and 2 (-1.48 +/- 2.56 mm) years in endografts without migration (p<0.001). Distal endograft migration >1 cm predicted the need for secondary interventions (p<0.001), with 83% sensitivity and 94% specificity.

CONCLUSIONS

Endovascular repair is successful in patients with large infrarenal necks and complex neck morphology. Changes in aneurysm remodeling over time were similar to reported observations in patients with more favorable neck criteria. Although no anatomical factor associated with migration could be identified from this analysis, distal displacement >1 cm correlated with the need for a secondary intervention.

Surgical conversion after endovascular grafting for abdominal aortic aneurysms

PURPOSE

To analyze the indications, results, and technical problems associated with conversion after endoluminal repair of abdominal aortic aneurysms (AAA) based on a 6-year experience in endovascular grafting.

METHODS

From August 1994 to May 2000, 520 patients with AAA were deemed candidates for endovascular therapy based on data from contrast-enhanced computed tomography and aortography. Any conversions were performed using an open operation modified according to the indication for conversion, elapsed time from the endoluminal repair, and type of endograft (tube, bifurcated, infra-/suprarenal fixation).

RESULTS

Conversion to open repair was required in 37 (7.1%) cases: 23 tube grafts and 14 bifurcated devices. Seventeen (3.2%) conversions occurred at the original operation and 20 (3.8%) were performed secondarily. Indications for primary conversion were mainly device defects (n = 5) or access problems (n = 5), while secondary conversion was primarily owing to type I endoleak (n = 16). The conversion rate was significantly higher in modular devices (5.9%) than unibody designs (1.4%) (p = 0.003). The rate of primary conversions diminished from 10.9% in 1994-1995 to 2.4% between 1996 and 2000, as did the overall mortality rate, from 8.3% in the first time period to 0% in the second for elective conversions, but emergency operations had 40% mortality.

CONCLUSIONS

Most AAAs require bifurcated devices for complete exclusion, and older model modular grafts have higher conversion rates. Primary conversion decreases as more experience in endoluminal grafting is acquired. Emergency open repair results in a high mortality rate.

CT artifacts of the proximal aortic neck: an important problem in endograft planning

PURPOSE

To describe the imaging error introduced by noncircular abdominal aortic aneurysm (AAA) necks in axial and reformatted computed tomographic (CT) images and discuss the potential implications for aortic endografting.

METHODS

The records of 120 endograft patients with preoperative CT axial scans and subsequent 3-dimensional (3D) computerized reconstructions were reviewed. Maximum and minimum infrarenal aortic neck diameters were measured from axial CT scans and 3D reformatted slices at the same point on the vessel. Diameter measurements were made at the largest point within the 10-mm segment of vessel below the lowest renal artery. Excluded were aneurysms with proximal neck minimum diameters >30 mm, neck lengths < 15 mm, or angulation > 75 degrees measured on the axial CT slice.

RESULTS

Measuring from reformatted CT slices, 86 (71.6%) cases had < or = 2-mm differences between maximal and minimal neck diameters, comprising the "round neck" group A. In 34 (28.4%) cases, the neck was not round: 26 (21.7%) had diameter differences between 2 and 4 mm (group B) and 8 (6.7%) had a > 4-mm difference (group C; range 4.1-8.1 mm). Although AAA diameter, neck length, and neck angle progressively increased as the difference between neck maximum and minimum diameters grew, i.e., greater eccentricity, these trends did not reach statistical significance. Mean infrarenal neck maximum diameter was significantly larger in group C (30.2 +/- 3.4 mm) compared to groups A (23.0 +/- 2.9 mm, p = 0.0002) and B (23.8 +/- 3.6 mm, p = 0.0003). Hence, 28.4% of AAAs had a noncircular aortic neck of varying degree, and 6.7% had an eccentricity factor that may have clinical significance.

CONCLUSIONS

This study confirms the importance of selecting an endoprosthesis sized 15% to 20% larger than the infrarenal aortic neck diameter. Three-dimensional reconstruction using reformatted CT slices perpendicular to the flow lumen is an important tool that offers enhanced accuracy of infrarenal aortic neck evaluation.

A simple technique to improve the accuracy of proximal AAA endograft deployment

PURPOSE

To report a technique for overcoming the positioning errors caused by angulation and rotation of the proximal aortic neck when anteroposterior fluoroscopic imaging is used during endograft deployment.

TECHNIQUE

Aortic neck angulation and rotation were measured preoperatively using spiral computed tomographic angiography in sagittal and axial projections. Before proximal graft deployment, the proximal end of the endograft was centered in the field of view, and the position of the C-arm was adjusted to the aortic neck angulation. Using this technique, optimal positioning of the endograft relative to the true position of the renal arteries can be achieved.

CONCLUSIONS

C-arm angulation and rotation is helpful in facilitating perfect positioning for an optimal seal between the endograft and the infrarenal aortic neck.

Can preoperative spiral CT scans alone determine the feasibility of endovascular AAA repair? A comparison to angiographic measurements

PURPOSE

To determine whether computed tomography (CT) alone can be used for excluding patients from endovascular repair for abdominal aortic aneurysms (AAA).

METHODS

Among 71 patients evaluated for endovascular AAA repair using spiral CT imaging and angiography, 31 were selected who had both studies performed within 6 months of each other using a graduated measuring catheter or guidewire. Measurements of aneurysm neck diameter, neck length, and infrarenal aortic length were made from the CT and angiographic images using handheld calipers with calibration markers as guides. Infrarenal aortic length and neck length were determined from CT images by multiplying the width of the cuts by the number of slices between the lowest renal artery and the aortic bifurcation or the top of the aneurysm, respectively.

RESULTS

CT neck diameter measurements differed significantly from the angiographic dimensions (6.3 +/- 5.1-mm mean difference, p < 0.001). In the majority of patients (25, 81%), CT neck diameters were larger (mean 7.3 +/- 3.8 mm). The mean difference in neck length measurements was 0.5 +/- 15.9 mm (p = NS). Twenty-two (71%) patients had aortic length measurements that were longer on the angiogram (mean 15.4 +/- 17.2 mm, p = NS). Five patients who would have been excluded as candidates based on overestimated CT neck diameter measurements subsequently underwent successful endovascular aneurysm repair.

CONCLUSIONS

Considerable discrepancies exist between preoperative neck diameter and infrarenal aortic length measurements obtained from CT scans and angiograms used to evaluate candidates for endovascular aortic aneurysm repair. CT alone may not be adequate for predicting the feasibility of endovascular AAA repair.

Endograft planning without preoperative arteriography: a clinical feasibility study

PURPOSE

To investigate an alternative method of preprocedural planning for aortic endografting based solely on spiral computed tomography (CT) with 3-dimensional (3D) reconstruction without preoperative arteriography.

METHODS

From August 1997 to April 1998, 25 consecutive patients with abdominal aortic aneurysms (AAA) were evaluated for endovascular repair by spiral CT scans (2-mm slice thickness) and computerized 3D model construction. No additional imaging for planning was performed. The aortoiliac dimensions, thrombus load, calcification, and vessel tortuosity were measured and evaluated from the 3D model of the aortoiliac segment. These data were used for selecting the patients; the configuration, diameter, and length of the endograft; and the attachment sites for deployment.

RESULTS

Primary procedural success was 92% (23/25). All endografts were deployed as planned, and there were no conversions to open repair. Six patients required adjunctive procedures for delivery system access or for iliac aneurysm exclusion, as predicted by the 3D model. Mean procedural time was 91 minutes (range 24 to 273). Two (8%) type II (side branch) endoleaks both sealed spontaneously within 1 month. No graft-related complications or death occurred, for a 30-day technical success rate of 100%.

CONCLUSIONS

This computerized 3D model provided accurate data for preoperative evaluation of the aortoiliac segment for endovascular AAA repair. Satisfactory technical outcomes for aortic endografts can be achieved without the use of preprocedural invasive imaging.

Abdominal aortic aneurysm morphology in candidates for endovascular repair evaluated with spiral computed tomography and digital subtraction angiography

PURPOSE

To analyze the morphology of abdominal aortic aneurysms (AAAs) and to study the usefulness of spiral computed tomography (CT) versus digital subtraction angiography (DSA) in the evaluation of patients for endovascular repair.

METHODS

Of 133 AAA patients (120 men, mean age 67 years, range 52 to 84) evaluated preoperatively with CT imaging, 77 endograft candidates (68 men) were also assessed with intra-arterial DSA. Arterial parameters were measured on axial CT scans and angiographic films for comparison.

RESULTS

Mean maximum AAA diameter was 58 +/- 11 mm (range 39 to 95). Aneurysmal neck diameter was consistently smaller on DSA than on CT (20.7 +/- 3.6 mm versus 23.0 +/ 3.5 mm, p < 0.0001). The distance from the most distal renal artery to the aortic bifurcation was longer on angiography than on CT (mean difference 10.0 mm, p < 0.0001). There was a positive correlation between the maximum AAA diameter and the AAA length (r = 0.49, p < 0.0001) and an inverse relationship between the neck length and the neck diameter (r = -0.36, p < 0.0001). No correlation was found between the maximum AAA diameter and maximum iliac diameter, angulation, or length.

CONCLUSIONS

AAA anatomy varies widely and independently of the aneurysm size. Therefore, the maximum size of the aneurysm is a poor predictor of whether or not an aneurysm is suitable for endovascular repair. The discrepancy between angiographic and axial CT measurements suggests that neither alone is sufficient as a preoperative imaging technique when evaluating a patient for an endovascular graft procedure.