Journal of Vascular Surgery
Volume 37, Issue 1 , Pages 86-90, January 2003

Endoluminal repair of abdominal aortic aneurysm prevents enlargement of the proximal neck: A 9-year life-table and 5-year longitudinal study☆☆☆★

Department of Surgery, University of Sydney; and the Department of Vascular Surgery, Royal Prince Alfred Hospital, NHMRC Trials Centre, University of Sydney. Sydney, Australia

Received 2 April 2002; accepted 17 June 2002.

Article Outline

Abstract 

Objective: Endoluminal repair of abdominal aortic aneurysm (AAA) is predicated on stability of the proximal neck of the aneurysm. Reports on morphologic changes in the proximal neck after endoluminal repair of AAA have thus far been limited in duration to 3 years or less. The aim of this study was to document changes in diameter of the proximal neck of AAA in a group of patients who had undergone endoluminal repair between 5 and 9 years previously. Methods: Between May 1992 and December 1996, 61 patients with AAA were treated with endoluminal repair by the senior author. The following patients were excluded from the study group: those requiring primary conversion to open repair at the original operation (n = 8), those with false aneurysm (n = 1), and those with dissection in the proximal neck (n = 1). Fifty-one patients (48 men and three women) with a mean age of 71 years remained in the study group. The endoprostheses used were modified Parodi (n = 4), Endovascular Technologies (n = 14), White-Yu (n = 10), Stentor/Vanguard (n = 21), and Bard 1996 prototype (n = 2). Morphologic changes in the proximal aortic neck were studied with contrast computed tomographic scan with the methodology recommended by the Ad Hoc Committee for Standardized Reporting Practices for Endovascular AAA Repair (revised version). The maximum transverse diameter of the proximal neck was measured 1 cm below the most inferior renal artery. A Kaplan-Meier analysis was performed showing the proportion of patients at risk with a demonstrated enlargement of the neck at each interval of time compared with the predischarge computed tomographic scan. A longitudinal study of morphologic changes in the proximal aortic neck was also undertaken in 28 patients with successful endoluminal repair who survived 5 years. Results: The Kaplan-Meier curve showed a probability of no dilatation of the proximal neck of 0.943 at 7 years after endoluminal AAA repair. Of 28 patients with 5 years of follow-up after discharge, only two had increases in the diameter of the proximal neck greater than 2 mm. The endograft in both patients had undergone migration before any proximal neck dilation. A paired t test showed that the overall average increase of 0.4 mm (standard error, 0.3 mm) in these 28 patients was not statistically significant (P = .23). Conclusion: A high probability (0.943 at 7 years) exists of no enlargement of the proximal neck of AAA after endoluminal repair. We hypothesize that endografts positioned correctly immediately below the renal arteries protect the proximal neck from dilatation in a manner that does not occur after open repair of AAA. (J Vasc Surg 2003;37:86-90.)

 

Endoluminal repair of abdominal aortic aneurysm (AAA) is predicated on stability of the proximal neck of the aneurysm. If endoluminal repair does not prevent the natural progression of aneurysmal degeneration into the proximal neck, much of the endeavor to repair aneurysms with this method will have been in vain. Dilatation of the proximal neck may lead to treatment failure by device migration or the occurrence of an endoleak with resulting aneurysm expansion. Reports on morphologic changes in the proximal neck after endoluminal repair of AAA have thus far been limited in duration to 3 years or less.1, 2, 3, 4, 5, 6, 7, 8, 9, 10 The aim of this study was to document changes in diameter of the proximal neck of AAA in a group of patients who had undergone endoluminal repair between 5 and 9 years previously.

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Patients and methods 

Between May 1992 and December 1996, 61 patients with AAA were treated with endoluminal repair by the senior author. The following patients were excluded from the study group: those requiring primary conversion to open repair at the original operation (n = 8), those with false aneurysm (n = 1), and those with dissection in the proximal neck of the aneurysm (n = 1). Fifty-one patients (48 men and three women) with a mean age of 71 years remained in the study group.

Imaging protocol 

All patients underwent contrast-enhanced computerized tomographic (CT) scan of the abdominal aorta and iliac arteries with 0.3-cm to 0.5-cm cuts being taken between the renal arteries and the iliac artery bifurcation. All patients had an aortogram with a calibrated pigtail catheter.

Endoluminal prostheses 

The endoprostheses used in the study were modified Parodi (n = 4), Endovascular Technologies (EVT) (n = 14) (Menlo Park, Calif), White-Yu (n = 10), Stentor/Vanguard (n = 21) (Boston Scientific, Natick, Mass), and Bard 1996 prototype (n = 2) (Haverhill, Mass). The Parodi and White-Yu prostheses were balloon expandable, and the EVT, Stentor/Vanguard, and Bard were self-expanding. The protocol for deployment of the EVT and Stentor/Vanguard prostheses included the use of a compliant balloon contained within the delivery catheter. The configuration of the prostheses was tubular (n = 16), aortouniiliac (n = 11), and bifurcated (n = 24).

Endovascular procedure 

All procedures were elective and were performed with general anesthesia in the operating room. A 24F introducing sheath was required for the modified Parodi, EVT, and White-Yu prostheses. The Stentor/Vanguard required a 21F delivery catheter, and the Bard an 18F delivery catheter.

Follow-up methodology for measurement of changes in neck dimension and analysis 

Follow-up examination with contrast CT scan was conducted before discharge and at 6 months and 12 months after operation and annually thereafter. Morphologic changes in the proximal aortic neck were studied with the methodology recommended by the Ad Hoc Committee for Standardized Reporting Practices for Endovascular AAA Repair (revised version).11 The maximum transverse diameter of the proximal neck was measured 1 cm below the most inferior renal artery. In all but one patient this CT scan cut contained the complete circumference of the body of the endoprosthesis. The outer perimeter of the aortic neck wall was used as the reference point for all measurements. If the aortic segment did not run perpendicular to the plane of measurement, the smaller diameter (minor axis of the elliptic cross section) was used as an appropriate approximate of the true diameter. All measurements were made by one investigator. The intraobserver variability of diameter measurement obtained from blinded CT scan images was 2 mm. Consequently, a change of 3 mm or greater was considered significant. Changes in maximum transverse diameter of the proximal neck were referenced to the measurement on the predischarge CT scan after endoluminal AAA repair. A Kaplan-Meier curve was constructed showing the proportion of patients at risk with a demonstrated enlargement of the neck at each interval of time compared with the predischarge CT scan. A longitudinal study of morphologic changes in the proximal aortic neck was also undertaken in 28 patients with successful endoluminal repair, all of whom survived 5 years.

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Results 

One perioperative death and 18 late deaths occurred in patients with successfully excluded aneurysms. Three secondary conversions to open repair were required for persistent endoleak (n = 1), endotension (n = 1), and rupture in a patient with a known type I endoleak (n = 1). Successful secondary endovascular intervention was undertaken in seven patients for type I endoleak (n = 5), type II endoleak (n = 1), and type III endoleak (n = 1).

Proximal neck changes 

Enlargement of the maximum transverse diameter of the proximal neck greater than 2 mm was observed in two patients at 3 and 5 years, respectively. In the first patient, the endograft (White-Yu balloon expandable aortouniiliac) had been deployed in a less than optimal position 1.5 cm below the most inferior renal artery. Further migration of 1.0 cm (total migration, 2.5 cm) occurred over the subsequent 3 years. No intervention was undertaken because the AAA had a long neck and no endoleak occurred. This resulted in a paradoxical situation where the uncovered portion of the proximal neck dilated and the excluded aneurysm sac diminished in size despite the migration (Fig 1).

  • View full-size image.
  • Fig. 1. 

    Diagram shows sequence of events in one of two similar patients in whom proximal neck enlarged after endoluminal AAA repair. On left, migration has left long proximal neck uncovered. Three years after operation (right), aneurysm sac has shrunk and uncovered segment of proximal neck has dilated. Covered segment of proximal neck remains unchanged.

A similar situation occurred in the second patient whose endograft (EVT self-expanding bifurcated), in the absence of any increase in diameter of the proximal neck, was noted to have migrated 1 cm between the 3-year and 4-year CT scans and a further 1 cm (total migration, 2 cm) between the 4-year and 5-year CT scans. Significant enlargement of the proximal neck was not observed until the 5-year CT scan.

Migration of the body of the prostheses occurred in three other patients in the absence of any enlargement in diameter of the proximal neck. Migration and the consequent endoleak were repaired promptly in all three patients with deployment of secondary tubular endoprostheses. No subsequent enlargement of the proximal neck was observed in these patients after secondary endoluminal AAA repair.

Kaplan-Meier study 

The Kaplan-Meier curve for proximal neck enlargement after endoluminal AAA repair showed a probability of no enlargement at 7 years of 0.943 (Fig 2), at which point 15 patients were at risk.

The Kaplan-Meier study included 23 patients who did not reach 5 years to qualify for inclusion in the longitudinal study because of death (n = 19) and secondary conversion to open repair (n = 3) and one patient who was censored after a major stroke after which it was considered that further CT scan follow-up was inappropriate. Enlargement of the maximum transverse diameter of the proximal neck greater than 2 mm was not observed in these 23 patients.

Longitudinal study 

Of 28 patients with 5 years of follow-up after discharge, only two had increases in the diameter of the neck greater than 2 mm. One had an increase of 5 mm, and the other 4 mm. A paired t test showed that the overall average increase of 0.4 mm in these 28 patients was not statistically significant (P = .23; Table).

Longitudinal study of changes in proximal neck after endoluminal AAA repair (n = 28)
Before discharge5 years
Mean diameter (mm)25.2525.64
Range (mm)22-3020-34
Mean increase (mm)0.4(standard error, 0.3)

P value, .23.

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Discussion 

The natural history of untreated AAA involves the aneurysm degenerative process spreading progressively from the sac to the proximal neck of the aneurysm. Information is also available concerning changes in morphology after open repair of AAA. Illig et al12 reported a CT scan study after open AAA repair in which one third of all patients had significant dilation of the proximal neck over time. They noted that this was more likely to happen if the original diameter of the neck was 28 mm or greater. In a CT scan study, Sonesson et al13 reported dilation of the proximal aortic neck of approximately 1.5 mm annually after open aneurysm surgery.

Controversy exists over dilation of the proximal neck of AAA after endoluminal repair. The authors1, 2 reported early dilation of the proximal neck after endoluminal repair. This was an increase in diameter relative to the preoperative CT scan measurements and attributed to deliberate oversizing of the prostheses. No subsequent increases in diameter of the proximal neck were noted out to 18 months of follow-up. Matsumura et al3 initially found a slight but not statistically significant increase in diameter of the proximal neck in a study of patients treated with endoluminal repair with EVT prostheses. In a subsequent publication from Matsumura and Chaikof,4 a significant and continued increase in diameter of the proximal neck was reported. Malina et al,5 Sonesson et al,6 and Resch et al,7 all from the one group in Malmo, reported an increase in the diameter of the proximal neck, and Resch et al7 noted that the increase in diameter occurred only in a subset of patients. Makaroun and Deaton8 reported 20% of proximal aortic necks increase in diameter 2 years after endoluminal AAA repair. Prinssen et al9 reported a progressive enlargement of the proximal aortic neck of 1 mm per year in a 3-year longitudinal study. Walker et al10 and Parodi (personal communication, 2001), however, have noted no increase in diameter of the proximal neck. The Revised Version of Standardized Reporting Practices for Endovascular AAA Repair has sensibly recommended that any changes in dimensions of the proximal neck be referenced to the first postoperative CT scan and not the preoperative CT scan, thus eliminating the changes from oversizing of prostheses.

In addition to the influence of oversizing, two other possible explanations exist for why the present data are at variance with those of six previous investigators. The first concerns the different locations that were measured in these studies. Matsumura and Chaikof4 measured the most cephalad image containing a complete hook set. The neck diameter was thus dependent on the site at which the endograft was deployed. The Malmo group in three reports measured the infrarenal aorta at different locations in each. These were the mid level of the graft anchoring stent,5 3 mm inferior to the lowermost renal artery,6 and the level of the most caudal renal artery.7 Makaroun and Deaton8 measured “the first CT slice that contained at least one half of the circumference of the proximal attachment system,” potentially allowing the measurement location to change with migration of the device. Prinssen et al9 measured the cross-sectional area as distinct from, and probably more accurate than, the diameter. The level selected was the most cephalad image in which all eight hooks of the attachment system were visible.

The second explanation for variance with previous investigators is that a conservative approach to case selection was used at the time when patients in this study were treated. No attempt was made to treat patients with a short, wide, or excessively angled proximal neck. The mean diameter of the proximal neck after endoluminal repair and before discharge in the longitudinal study was 25.25 mm. The mean diameter of the proximal neck before surgery was 10% less than this figure because of the influence of deliberately oversizing the endografts. Only five patients had proximal necks of larger diameter than 26 mm before discharge. The comparatively small mean neck diameter may be one explanation for the disparity between this study and other reports on changes in morphology of the proximal neck after endoluminal AAA repair. One may also speculate that patients with proximal necks of larger diameter than those in this study may not show the same stability in the proximal neck over time. If further studies14 confirm that small proximal necks are more stable than larger necks, this could be an important factor in case selection of younger patients where durability is an issue.

This study of changes in dimensions of the proximal neck of AAA after endoluminal repair provides a much longer period of follow-up than previous reports (Fig 3).

It was believed that both a longitudinal study and a Kaplan-Meier analysis were necessary to provide the maximum information from the data. A longitudinal study has the advantage of every patient reaching the endpoint of 5 years without the need to extrapolate the probable outcome in those who did not reach this point. On the other hand, those patients who failed to reach 5 years may be the very ones in whom dilatation of the proximal neck may have occurred. It is necessary therefore to account for all patients in the study group irrespective of their outcome.

The results of this study suggest that correctly positioned endografts prevent enlargement of the proximal neck, which is seen after open repair of the AAA. Our hypothesis is that placement of an endograft over the superior most 2 to 3 cm of the infrarenal aorta may protect this segment from the degenerative changes responsible for dilation after open AAA repair. In this study, endografts were noted to be less than 1 cm from the renal arteries when the diameter of the proximal neck was measured at this level before discharge in all patients except one. The endograft in this patient and one other underwent migration of 2.5 cm and 2.0 cm, respectfully, in the absence of any dilatation of the proximal neck. The migration did not result in endoleak and was left untreated in both patients for 2 to 3 years. During this time, the uncovered proximal necks of both patients dilated. Best surgical practice for open AAA repair recommends replacement of the entire infrarenal aorta with a graft. It should be noted however that 1.5 to 2 cm of aorta are required for the application of the clamp and placement of deep sutures in the proximal anastomosis in most patients.

The limitations of this study must be acknowledged. The quality of CT scans in the early years of this 9-year study were inferior to those currently available. Reconstructions perpendicular to the centerline of the aorta were not available. If the aortic segment did not run perpendicular to the plane of measurement, the smaller diameter (minor axis of the elliptic cross section) was taken as an appropriate approximate of the true neck diameter. The opportunity to use cross-sectional area of the proximal neck for the assessment of enlargement was not available.

The use of a single type of endoprostheses rather than several different varieties is generally regarded as a desirable feature because it eliminates one variable in the study. Conversely, however, it could be argued that the use of five types of endoprostheses in this study is advantageous in that it suggests that protection of the proximal neck against aneurysmal expansion is not dependent on either balloon-expandable or self-expanding mechanism or specific varieties of endoprostheses.

We conclude from this study that there is a high probability of no enlargement of the proximal neck of AAA for at least 5 years after endoluminal repair. We hypothesize that endografts positioned correctly immediately below the renal arteries protect the superior 2 cm of infrarenal aorta in a manner that does not occur after open repair of AAA. Further studies with large numbers and longer follow-up are required to confirm these findings.

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References 

  1. May J, White GH, Yu W, Waugh RC, Stephen MS, Harris JP. A prospective study of changes in morphology and dimensions of abdominal aortic aneurysm following endoluminal repair: a preliminary report. J Endovasc Surg. 1995;2:343–347
  2. May J, White G, Yu W, Waugh R, Stephen M, Harris J. A prospective study of anatomico-pathological changes in abdominal aneurysms following endoluminal repair: is the aneurysmal process reversed?. Eur J Vasc Endovasc Surg. 1996;12:11–17
  3. Matsumura JS, Pearce WH, McCarthy WJ, Yao JS. Reduction in aortic aneurysm size: early results after endovascular graft placement. EVT Investigators. J Vasc Surg. 1997;25:113–123
  4. Matsumura JS, Chaikof EL. Continued neck expansion of aortic necks after endovascular repair of abdominal aortic aneurysms. J Vasc Surg. 1998;28:422–430
  5. Malina M, Ivancev K, Chuter TAM, Lindh M, Lanne T, Lindblad B, et al.  Changing aneurysmal morphology after endovascular grafting: relation to leakage or persistent perfusion. J Endovasc Surg. 1997;4:23–30
  6. Sonesson B, Malina M, Ivancev K, Lindh M, Lindblad B, Brunkwall J. Dilatation of the infrarenal aneurysm neck after endovascular exclusion of abdominal aortic aneurysm. J Endovasc Surg. 1998;5:195–200
  7. Resch T, Ivancev K, Brunkwall J, Nirhov N, Malina M, Lindblad B. Mid-term changes in aortic aneurysm morphology after endovascular repair. J Endovasc Surg. 2000;7:279–285
  8. Makaroun MS, Deaton DH. Is proximal aortic neck dilatation after endovascular aneurysm exclusion a cause for concern?. J Vasc Surg. 2001;33:S39–S45
  9. Prinssen M, Wever JJ, Mali WPTM, Eikelboom BC, Blankensteijn JD. Concerns for the durability of the proximal abdominal aortic aneurysm endograft fixation from a 2-year and 3-year longitudinal computed tomography angiography study. J Vasc Surg. 2001;33:S64–S69
  10. Walker SR, Macierewicz J, Elmarasy NM, Gregson RH, Whitaker SC, Hopkinson BR. A prospective study to assess changes in proximal aortic neck dimensions after endovascular repair of abdominal aortic aneurysm. J Vasc Surg. 1999;29:625–630
  11. Chaikof EL, Blankensteijn JD, Harris PL, White GH, Zarins CK, Bernhard VM, et al.  Reporting standards for endovascular aortic aneurysm repair. J Vasc Surg. 2002;35:1048–1060
  12. Illig KA, Green RM, Ouriel K, Riggs P, Bartos S, DeWeese JA. Fate of the proximal aortic cuff: implications for endovascular aneurysm repair. J Vasc Surg. 1997;26:492–501
  13. Sonesson B, Resch T, Lanne T, Ivancev K. The fate of the infrarenal aortic neck after open aneurysm surgery. J Vasc Surg. 1998;28:889–894
  14. Cao P, Verzini F, Zannetti S, De Rango P, Parlani G, Lupattelli L, et al.  Device migration after endoluminal abdominal aortic aneurysm repair: analysis of 113 cases with a minimum follow up period of 2 years. J Vasc Surg. 2002;35:229–235

☆ Competition of interest: Dr May has been paid consulting fees by Boston Scientific, Medtronic. Dr White has been paid a consulting fee by Baxter.

☆☆ Reprint requests: James May, Department of Surgery, University of Sydney DO6, New South Wales 2006, Australia (e-mail: vascsurg@med.usyd.edu.au).

★ 0741-5214/2003/$30.00 + 0

PII: S0741-5214(02)75250-6

doi:10.1067/mva.2003.109

Journal of Vascular Surgery
Volume 37, Issue 1 , Pages 86-90, January 2003

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