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Late Disruption of Dacron Aortic Grafts
Late Disruption of Dacron Aortic Grafts Samuel E. Wilson, MD, Richard Krug, MD, Gregory Mueller, MD, and Latresia Wilson, MD, Long Beach, California
Aneurysmal degeneration, or complete disruption of Dacron grafts (as opposed to anastomotic complications such as pseudoaneurysms), are not expected by vascular surgeons. We have noted two such cases. A 65-year-old male who had an aortobifemoral, double-velour Dacron graft in 1980, presented in 1995 with a large, pulsatile mass in the right lower quadrant, caused by disruption of the mid-portion of the right limb of the Dacron graft. In a second case, a 68-year-old man had a Dacron aortobifemoral graft placed in 1968 which developed diffuse aneurysmal defects, noted clinically in 1987. Both patients had successful graft replacement. A review of the literature indicates that this complication, although unusual, has been noted periodically. Between 1970 and 1996, we identified 11 case reports of aortic Dacron graft rupture, including knitted Dacron (4), double velour (3), woven (1), knitted thin wall (1), and unspecified Dacron grafts (2). An inquiry to the FDA disclosed another 68 cases of Dacron graft failure in addition to those reported in the surgical literature. We present these cases to alert vascular surgeons of the possibility of Dacron graft degeneration, as late as 19 years after implantation. Diagnosis of the complication is readily apparent by clinical examination and imaging studies, which display an aneurysm of the graft remote from the anastomoses. (Ann Vasc Surg 1997;11:383-386.)
Largely through the pioneering work of DeBakey, Dacron (Polyethylene terephthalate) aortic grafts have been the standard prosthesis for aortic replacement since 1957.1 Dacron is utilized in approximately 95% of bypass grafts for arteries 1 cm or greater in diameter including aorto-femoral grafts and extra-anatomical grafts. When Dacron prosthetic grafts were first introduced, a simple knitted tubular graft was used. Over the ensuing years, improvements in graft characteristics led to a seamless, more tightly knitted structure as well as bifurcated grafts. A velour construction was initially From the Department of Surgery, UC Irvine College of Medicine and the Surgical Service, Long Beach Veterans Affairs Medical Center, Long Beach, CA. Presented at the Fifteenth Annual Meeting of the Southern California Vascular Surgical Society, Dana Point, CA, September 15–17, 1996. Correspondence to: S. E. Wilson, MD, Department of Surgery, UCI Medical Center, 101 The City Drive, Orange, CA 92868-3209, USA.
used for the internal surface of Dacron grafts in 1967.1 This modification allowed early fibrin deposition which was thought to decrease the risk of embolization while the porous graft structure afforded tissue incorporation. External velour grafts were introduced by Sauvage et al.2 and Cooley et al. described the double velour graft in 1978.3 For this report, we define primary failure as graft dilatation, aneurysm, or graft rupture caused by disintegration or separation of graft fibers which occurs without extrinsic etiologic factors such as graft infection or direct damage from puncture or external trauma. Focal defects may be caused by manufacturing defects or injury to the graft during insertion. Total graft disruption may be secondary to intrinsic weakness of graft structure. We report two cases of late Dacron graft failure occurring in aortobifemoral reconstructions.
CASE 1 A 65-year-old man underwent aortobifemoral bypass in 1980 for aortoiliac occlusion. A knitted Meadox-Cooley 383
384
Wilson et al.
Annals of Vascular Surgery
Fig. 1. Computed tomography of case report 1 shows aneurysm of right femoral graft limb with mural thrombus. Fig. 2. Arteriogram of aortobifemoral graft shows aneurysm proximal to femoral anastamosis (case report 1). Double Velour graft was placed without complications. The patient did well until March 1995 when he presented with a 2-week history of an enlarging right lower quadrant abdominal mass measuring 10 cm × 15 cm and pulsatile on palpation. A CAT scan was obtained revealing a 7 cm × 5 cm × 5 cm aneurysm of the graft with associated intramural clot consistent with a graft rupture (Fig. 1). The dilated segment was proximal to the femoral anastomosis with no obvious anastomotic involvement. Arteriogram showed a saccular dilation of the graft with contained ruptured and femoral vessels suitable for reconstruction (Fig. 2). Upon exploration the patient was noted to have a disruption of the mid portion of the right limb of the aortofemoral graft. The right femoral limb was replaced with a 1.0 cm diameter Dacron graft. The patient recovered without complications and at 2 years postoperative is asymptomatic without further dilatation of the graft. Hematoxylin and eosin stained specimens and depolarized microscopy showed separation of the graft fibers confirming primary graft failure.
CASE 2 A 68-year-old man underwent an aortobifemoral bypass in 1968 for aortoiliac occlusive disease. The type of Dacron graft was unspecified in the medical records. The patient had unlimited walking distance until 1987 when he presented with right leg ischemia. An arteriogram revealed occlusion of the right femoral limb of the graft. Surgical exploration of the right groin and retroperitoneal space showed multiple defects in the mid portion of the graft with surrounding hematoma. Exploration of the left groin exposed graft breakdown with a defect in the anterior portion of the left femoral graft limb. Abdominal exploration also revealed aneurysmal dilation of the body of the graft proximally. Because of the generalized deterioration, the entire graft was excised, and after recon-
struction with a new Dacron graft, the patient has done well at 4-year follow-up.
OTHER REPORTS OF DACRON GRAFT FAILURE Clinical data on 11 patients who had primary graft failure reported in the surgical literature between 1974 and 1989 are summarized in Table I.4–14 The average time to graft failure was 5.8 years in these patients. We have not identified reported cases since 1989. In addition to the cases of graft failure found in the literature, an inquiry to the FDA revealed 68 additional cases of Dacron grafts reported to have defects leading to graft failure. Twenty-one of these grafts were double velour Dacron implanted between 1977 and 1983, with an average time to failure of 7.4 years (range 4–18 years).
DISCUSSION The factors leading to Dacron graft removal include infection, anastomotic pseudoaneurysm formation, and occasionally thrombosis. The graft failure which occurred in the two patients we report appeared to be caused by a primary structural defect. A review of previous case reports of primary graft failure indicates that clinical presentation can vary greatly from graft dilatation, aneurysm formation, and thromboembolic limb ischemia to hemorrhage as in the case of a graft ureteral fistula.4–14 Success-
Vol. 11, No. 4, 1997
Late disruption of Dacron aortic grafts 385
Table I. Clinical data on 11 patients who developed primary Dacron graft failure
Reference
Operation
Interval to primary graft failure (years)
Type of graft
Defect
Outcome
Aortic tear Inguinal tear
4
Aortobifemoral
2
5
Iliofemoral
2
Knitted Dacron Unspecified
6
Aortobifemoral
3.5
Weavenit
Bifurcation tear
7
Aortic tube
Aortic rupture
8
Aortobifemoral
5
Bifurcation tear
Dead
9
Aortobifemoral
8
Knitted thinwall Knitted Dacron Weaveknit
Hematuria, dead Replaced, alive Replaced, alive Dead
Inguinal tear
10
Aortobifemoral
8
11
Aortoiliac/ femoral
6
Replaced, alive Hematuria, dead Replaced, alive
12
Aortobifemoral
5
13
Aorto right femoral
7
14
Aortobifemoral
7
10
ful treatment was marked by rapid diagnosis, early involvement of a vascular surgeon, and timely operation. Clagett et al. proposed a pathophysiology of graft failure based on analysis of gross appearance, and microbiologic and electron micrographic data of five cases.15 In four of five of the grafts the diameter had almost doubled in size compared to the recorded dimensions of the graft obtained at the initial operation. Scanning electron microscopic examination revealed that the interstices of the dilated grafts were greater than those in normal nondilated prosthesis. Using ultrasound evaluation, Nunn et al. discovered that Dacron grafts underwent a significant amount of dilation after graft placement.16 The average dilation of the 95 Dacron grafts studied was 17.6 percent, as measured by ultrasound comparison at 2 weeks postoperatively and compared to the diameter obtained 138 months postoperatively (average interval 33 months). Kim et al. postulated that grafts dilate in response to hydrostatic forces with most dilation occurring in the first 30 days
Tetoran woven Cooley double velour Cooley double velour Knitted double velour Unspecified
Aorti-ureter Right femoral aneurysm Inguinal tear
Replaced, alive
Right femoral aneurysm
Replaced, alive
Left femoral aneurysm
Replaced, alive
after graft placement.17 In a small number of patients these factors possibly result in enough stretching or weakening of the graft wall with resultant dilation to cause eventual graft rupture. Berger and Sauvage described Dacron failure due to actual breaking of the Dacron fiber or yarn.9 They postulated that graft failure was due to breakdown of individual Dacron fibers with eventual disintegration of the graft wall. Two types of broken fiber were identified. Fibers that had tapered or frayed ends were thought to have slowly deteriorated with chronic stretching leading to eventual breakage. The second type of damaged fibers were noted to have square ends, which suggested a sudden increase in stretch, causing the fibers to snap. Under chronic hydrostatic forces Dacron fibers may slowly stretch or ‘‘creep’’ until breaking. Localized areas of breakdown may be attributed to possible graft damage that has occurred during initial graft placement, perhaps due to traumatic instrumentation, or may stem from manufacturing defects. Multiple aneurysms have been reported in Dacron velour grafts.18
386
Wilson et al.
Given approximately 60,000 aortic reconstructions annually, the overall number of reported graft failures are small. An evaluation by Cooley et al. of 1040 of the Meadox-Cooley Double Velour knitted Dacron grafts showed that after a 4-year follow-up period, 911 of the grafts showed no evidence of dilation or aneurysmal changes.19 In conclusion, patients who have had Dacron grafts placed for aortoiliac reconstruction may present years later with primary graft failure. Diagnosis of graft failure may be suspected on clinical examination and confirmed by CT imaging studies. Arteriography helps plan replacement and reconstruction. Patients who present with this complication will require early surgical intervention to replace the graft. These two case reports of primary graft failure illustrate that graft breakdown may occur as late as 19 years after initial graft placement. REFERENCES 1. Hall CW, Liotta D, Chidoni JJ, DeBakey ME. Velour fabrics applied to medicine. J Biomed Mater Res 1967;1:179-196. 2. Sauvage LR, Berger K, Wood SJ, et al. An external velour surface for porous arterial prosthesis. Surgery 1971;70:940953. 3. Liebig C, Cooley DA. Vascular graft symposium. National Institutes of Health, 1976. Cooley DA, Wiskasch DC, Bennett JG, Trono R. Double velour knitted Dacron grafts for aorto-iliac vascular replacement. In Sawyer PN, Kaplett MJ, eds. Vascular Grafts, New York: Appleton-Century-Crofts, 1978, pp 197-207. 4. Cooke PA, Nobis RA, et al. Dacron aortic graft failure. Arch Surg 1974;103:101-103.
Annals of Vascular Surgery
5. Wren HB. False aneurysm of the femoral artery: a challenge in management. Ann Surg 1976;183:700. 6. Blumenberg RM, Gelfand ML. Failure of knitted Dacron as an arterial prosthesis. Surgery 1977;81:493-496. 7. Edwards WS. Arterial grafts of Teflon. In Sawyer PN, Kaplitt MJ, eds. Vascular Grafts. New York: Appleton-CenturyCrofts, 1978, pp 173-176. 8. Yashar JJ, Richman MH, Dyckman J, et al. Failure of Dacron prosthesis caused by structural defect. Surgery 1978;84:659663. 9. Berger K, Sauvage LR. Late fiber deterioration in Dacron arterial grafts. Ann Surg 1981;193:477-491. 10. Watanabe T, Kusaba A, Kuma H, et al. Failure of Dacron arterial prostheses caused by structural defects. J Cardiovasc Surg 1983;24:95-100. 11. Nucho RC, Gryborski WA. Aneurysms of a Double Velour aortic graft. Arch Surg 1984;119:1182-1184. 12. Trippestad A. Late rupture of knitted Dacron double velour arterial prostheses. ACTA Chir Scand 1985;151:191-195. 13. Ratto GB, Truini M, Succo A, et al. Multiple aneurysmal dilatations in a knitted Dacron velour graft. J Cardiovasc Surg 1985;26:589-591. 14. Friedman M, Zelikovski A, Mor C, et al. True aneurysm in a prosthetic aorto-femoral Dacron graft. J Cardiovasc Surg 1989;30:136-137. 15. Clagett GP, et al. Dilation of knitted Dacron aortic prostheses and anastomotic false aneurysm: Etiologic considerations. Surgery 1983;93:9-16. 16. Nunn DB, Freeman MH, et al. Postoperative alteration in size of Dacron aortic grafts. Ann Surg 1979;189:741-744. 17. Kim GE, Imparato AM, et al. Dilation of synthetic grafts and junctional aneurysms. Arch Surg 1979;114:1293-1296. 18. May J, Stephen M. Multiple aneurysms in Dacron velour grafts. Arch Surg 1978;113:320-321. 19. Cooley DA, Subram A, Houchin DP. Clinical experience in 1,040 patients with double-velour knitted Dacron vascular prosthesis: with particular reference to dilation and aneurysm formation. Tex Heart Inst J 1981;8:320-331.
Aneurysmal degeneration, or complete disruption of Dacron grafts (as opposed to anastomotic complications such as pseudoaneurysms), are not expected by vascular surgeons. We have noted two such cases. A 65-year-old male who had an aortobifemoral, double-velour Dacron graft in 1980, presented in 1995 with a large, pulsatile mass in the right lower quadrant, caused by disruption of the mid-portion of the right limb of the Dacron graft. In a second case, a 68-year-old man had a Dacron aortobifemoral graft placed in 1968 which developed diffuse aneurysmal defects, noted clinically in 1987. Both patients had successful graft replacement. A review of the literature indicates that this complication, although unusual, has been noted periodically. Between 1970 and 1996, we identified 11 case reports of aortic Dacron graft rupture, including knitted Dacron (4), double velour (3), woven (1), knitted thin wall (1), and unspecified Dacron grafts (2). An inquiry to the FDA disclosed another 68 cases of Dacron graft failure in addition to those reported in the surgical literature. We present these cases to alert vascular surgeons of the possibility of Dacron graft degeneration, as late as 19 years after implantation. Diagnosis of the complication is readily apparent by clinical examination and imaging studies, which display an aneurysm of the graft remote from the anastomoses. (Ann Vasc Surg 1997;11:383-386.)
Largely through the pioneering work of DeBakey, Dacron (Polyethylene terephthalate) aortic grafts have been the standard prosthesis for aortic replacement since 1957.1 Dacron is utilized in approximately 95% of bypass grafts for arteries 1 cm or greater in diameter including aorto-femoral grafts and extra-anatomical grafts. When Dacron prosthetic grafts were first introduced, a simple knitted tubular graft was used. Over the ensuing years, improvements in graft characteristics led to a seamless, more tightly knitted structure as well as bifurcated grafts. A velour construction was initially From the Department of Surgery, UC Irvine College of Medicine and the Surgical Service, Long Beach Veterans Affairs Medical Center, Long Beach, CA. Presented at the Fifteenth Annual Meeting of the Southern California Vascular Surgical Society, Dana Point, CA, September 15–17, 1996. Correspondence to: S. E. Wilson, MD, Department of Surgery, UCI Medical Center, 101 The City Drive, Orange, CA 92868-3209, USA.
used for the internal surface of Dacron grafts in 1967.1 This modification allowed early fibrin deposition which was thought to decrease the risk of embolization while the porous graft structure afforded tissue incorporation. External velour grafts were introduced by Sauvage et al.2 and Cooley et al. described the double velour graft in 1978.3 For this report, we define primary failure as graft dilatation, aneurysm, or graft rupture caused by disintegration or separation of graft fibers which occurs without extrinsic etiologic factors such as graft infection or direct damage from puncture or external trauma. Focal defects may be caused by manufacturing defects or injury to the graft during insertion. Total graft disruption may be secondary to intrinsic weakness of graft structure. We report two cases of late Dacron graft failure occurring in aortobifemoral reconstructions.
CASE 1 A 65-year-old man underwent aortobifemoral bypass in 1980 for aortoiliac occlusion. A knitted Meadox-Cooley 383
384
Wilson et al.
Annals of Vascular Surgery
Fig. 1. Computed tomography of case report 1 shows aneurysm of right femoral graft limb with mural thrombus. Fig. 2. Arteriogram of aortobifemoral graft shows aneurysm proximal to femoral anastamosis (case report 1). Double Velour graft was placed without complications. The patient did well until March 1995 when he presented with a 2-week history of an enlarging right lower quadrant abdominal mass measuring 10 cm × 15 cm and pulsatile on palpation. A CAT scan was obtained revealing a 7 cm × 5 cm × 5 cm aneurysm of the graft with associated intramural clot consistent with a graft rupture (Fig. 1). The dilated segment was proximal to the femoral anastomosis with no obvious anastomotic involvement. Arteriogram showed a saccular dilation of the graft with contained ruptured and femoral vessels suitable for reconstruction (Fig. 2). Upon exploration the patient was noted to have a disruption of the mid portion of the right limb of the aortofemoral graft. The right femoral limb was replaced with a 1.0 cm diameter Dacron graft. The patient recovered without complications and at 2 years postoperative is asymptomatic without further dilatation of the graft. Hematoxylin and eosin stained specimens and depolarized microscopy showed separation of the graft fibers confirming primary graft failure.
CASE 2 A 68-year-old man underwent an aortobifemoral bypass in 1968 for aortoiliac occlusive disease. The type of Dacron graft was unspecified in the medical records. The patient had unlimited walking distance until 1987 when he presented with right leg ischemia. An arteriogram revealed occlusion of the right femoral limb of the graft. Surgical exploration of the right groin and retroperitoneal space showed multiple defects in the mid portion of the graft with surrounding hematoma. Exploration of the left groin exposed graft breakdown with a defect in the anterior portion of the left femoral graft limb. Abdominal exploration also revealed aneurysmal dilation of the body of the graft proximally. Because of the generalized deterioration, the entire graft was excised, and after recon-
struction with a new Dacron graft, the patient has done well at 4-year follow-up.
OTHER REPORTS OF DACRON GRAFT FAILURE Clinical data on 11 patients who had primary graft failure reported in the surgical literature between 1974 and 1989 are summarized in Table I.4–14 The average time to graft failure was 5.8 years in these patients. We have not identified reported cases since 1989. In addition to the cases of graft failure found in the literature, an inquiry to the FDA revealed 68 additional cases of Dacron grafts reported to have defects leading to graft failure. Twenty-one of these grafts were double velour Dacron implanted between 1977 and 1983, with an average time to failure of 7.4 years (range 4–18 years).
DISCUSSION The factors leading to Dacron graft removal include infection, anastomotic pseudoaneurysm formation, and occasionally thrombosis. The graft failure which occurred in the two patients we report appeared to be caused by a primary structural defect. A review of previous case reports of primary graft failure indicates that clinical presentation can vary greatly from graft dilatation, aneurysm formation, and thromboembolic limb ischemia to hemorrhage as in the case of a graft ureteral fistula.4–14 Success-
Vol. 11, No. 4, 1997
Late disruption of Dacron aortic grafts 385
Table I. Clinical data on 11 patients who developed primary Dacron graft failure
Reference
Operation
Interval to primary graft failure (years)
Type of graft
Defect
Outcome
Aortic tear Inguinal tear
4
Aortobifemoral
2
5
Iliofemoral
2
Knitted Dacron Unspecified
6
Aortobifemoral
3.5
Weavenit
Bifurcation tear
7
Aortic tube
Aortic rupture
8
Aortobifemoral
5
Bifurcation tear
Dead
9
Aortobifemoral
8
Knitted thinwall Knitted Dacron Weaveknit
Hematuria, dead Replaced, alive Replaced, alive Dead
Inguinal tear
10
Aortobifemoral
8
11
Aortoiliac/ femoral
6
Replaced, alive Hematuria, dead Replaced, alive
12
Aortobifemoral
5
13
Aorto right femoral
7
14
Aortobifemoral
7
10
ful treatment was marked by rapid diagnosis, early involvement of a vascular surgeon, and timely operation. Clagett et al. proposed a pathophysiology of graft failure based on analysis of gross appearance, and microbiologic and electron micrographic data of five cases.15 In four of five of the grafts the diameter had almost doubled in size compared to the recorded dimensions of the graft obtained at the initial operation. Scanning electron microscopic examination revealed that the interstices of the dilated grafts were greater than those in normal nondilated prosthesis. Using ultrasound evaluation, Nunn et al. discovered that Dacron grafts underwent a significant amount of dilation after graft placement.16 The average dilation of the 95 Dacron grafts studied was 17.6 percent, as measured by ultrasound comparison at 2 weeks postoperatively and compared to the diameter obtained 138 months postoperatively (average interval 33 months). Kim et al. postulated that grafts dilate in response to hydrostatic forces with most dilation occurring in the first 30 days
Tetoran woven Cooley double velour Cooley double velour Knitted double velour Unspecified
Aorti-ureter Right femoral aneurysm Inguinal tear
Replaced, alive
Right femoral aneurysm
Replaced, alive
Left femoral aneurysm
Replaced, alive
after graft placement.17 In a small number of patients these factors possibly result in enough stretching or weakening of the graft wall with resultant dilation to cause eventual graft rupture. Berger and Sauvage described Dacron failure due to actual breaking of the Dacron fiber or yarn.9 They postulated that graft failure was due to breakdown of individual Dacron fibers with eventual disintegration of the graft wall. Two types of broken fiber were identified. Fibers that had tapered or frayed ends were thought to have slowly deteriorated with chronic stretching leading to eventual breakage. The second type of damaged fibers were noted to have square ends, which suggested a sudden increase in stretch, causing the fibers to snap. Under chronic hydrostatic forces Dacron fibers may slowly stretch or ‘‘creep’’ until breaking. Localized areas of breakdown may be attributed to possible graft damage that has occurred during initial graft placement, perhaps due to traumatic instrumentation, or may stem from manufacturing defects. Multiple aneurysms have been reported in Dacron velour grafts.18
386
Wilson et al.
Given approximately 60,000 aortic reconstructions annually, the overall number of reported graft failures are small. An evaluation by Cooley et al. of 1040 of the Meadox-Cooley Double Velour knitted Dacron grafts showed that after a 4-year follow-up period, 911 of the grafts showed no evidence of dilation or aneurysmal changes.19 In conclusion, patients who have had Dacron grafts placed for aortoiliac reconstruction may present years later with primary graft failure. Diagnosis of graft failure may be suspected on clinical examination and confirmed by CT imaging studies. Arteriography helps plan replacement and reconstruction. Patients who present with this complication will require early surgical intervention to replace the graft. These two case reports of primary graft failure illustrate that graft breakdown may occur as late as 19 years after initial graft placement. REFERENCES 1. Hall CW, Liotta D, Chidoni JJ, DeBakey ME. Velour fabrics applied to medicine. J Biomed Mater Res 1967;1:179-196. 2. Sauvage LR, Berger K, Wood SJ, et al. An external velour surface for porous arterial prosthesis. Surgery 1971;70:940953. 3. Liebig C, Cooley DA. Vascular graft symposium. National Institutes of Health, 1976. Cooley DA, Wiskasch DC, Bennett JG, Trono R. Double velour knitted Dacron grafts for aorto-iliac vascular replacement. In Sawyer PN, Kaplett MJ, eds. Vascular Grafts, New York: Appleton-Century-Crofts, 1978, pp 197-207. 4. Cooke PA, Nobis RA, et al. Dacron aortic graft failure. Arch Surg 1974;103:101-103.
Annals of Vascular Surgery
5. Wren HB. False aneurysm of the femoral artery: a challenge in management. Ann Surg 1976;183:700. 6. Blumenberg RM, Gelfand ML. Failure of knitted Dacron as an arterial prosthesis. Surgery 1977;81:493-496. 7. Edwards WS. Arterial grafts of Teflon. In Sawyer PN, Kaplitt MJ, eds. Vascular Grafts. New York: Appleton-CenturyCrofts, 1978, pp 173-176. 8. Yashar JJ, Richman MH, Dyckman J, et al. Failure of Dacron prosthesis caused by structural defect. Surgery 1978;84:659663. 9. Berger K, Sauvage LR. Late fiber deterioration in Dacron arterial grafts. Ann Surg 1981;193:477-491. 10. Watanabe T, Kusaba A, Kuma H, et al. Failure of Dacron arterial prostheses caused by structural defects. J Cardiovasc Surg 1983;24:95-100. 11. Nucho RC, Gryborski WA. Aneurysms of a Double Velour aortic graft. Arch Surg 1984;119:1182-1184. 12. Trippestad A. Late rupture of knitted Dacron double velour arterial prostheses. ACTA Chir Scand 1985;151:191-195. 13. Ratto GB, Truini M, Succo A, et al. Multiple aneurysmal dilatations in a knitted Dacron velour graft. J Cardiovasc Surg 1985;26:589-591. 14. Friedman M, Zelikovski A, Mor C, et al. True aneurysm in a prosthetic aorto-femoral Dacron graft. J Cardiovasc Surg 1989;30:136-137. 15. Clagett GP, et al. Dilation of knitted Dacron aortic prostheses and anastomotic false aneurysm: Etiologic considerations. Surgery 1983;93:9-16. 16. Nunn DB, Freeman MH, et al. Postoperative alteration in size of Dacron aortic grafts. Ann Surg 1979;189:741-744. 17. Kim GE, Imparato AM, et al. Dilation of synthetic grafts and junctional aneurysms. Arch Surg 1979;114:1293-1296. 18. May J, Stephen M. Multiple aneurysms in Dacron velour grafts. Arch Surg 1978;113:320-321. 19. Cooley DA, Subram A, Houchin DP. Clinical experience in 1,040 patients with double-velour knitted Dacron vascular prosthesis: with particular reference to dilation and aneurysm formation. Tex Heart Inst J 1981;8:320-331.