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Prevalence of Unsuspected Abdominal Aortic Aneurysms in Male Veterans
Prevalence of Unsuspected Abdominal Aortic Aneurysms in Male Veterans Richard J. Fowl, MD, John Blebea, MD, Anthony Stallion, MD, Jeffrey T. Marsch, MD, Joanne G. Marsch, RN, RVT, Mary Love, RN, RVT, Robert B. Patterson, MD, and Richard F. Kempczinski, MD, Cincinnati, Ohio
Abdominal aortic aneurysms (AAA) are potentially lethal arterial lesions that are best managed by elective surgical repair. However, asymptomatic AAAs may go undetected on routine physical examination or patients with such lesions may not consult a physician. To determine the prevalence of asymptomatic AAAs in a high-risk population, we retrospectively reviewed all abdominal CT scans on veterans >50 years of age that had been ordered for indications other than aneurysmal disease during a recent 10-month period. Of the 111 patients studied, 15 (13.5%) had suprarenal and/or infrarenal AAAs (one patient had both). Patients with AAAs were significantly older (p = 0.0001) and were heavier tobacco users (p = 0.003). For patients >60 years of age with peripheral vascular occlusive disease and a history of tobacco use, there was a 29.2% prevalence for AAA compared with 0% in those without any of these risk factors ~ = 0.04). There was a very definite trend suggesting that patients with peripheral vascular disease (p = 0.06) were more likely to have an AAA. Because of the high prevalence of AAAs found in this population we then conducted a prospective study over a 24-month period during which patients >60 years of age with known peripheral vascular disease and a history of smoking who presented to the vascular laboratory for evaluation of problems not related to AAA were asked to undergo an abdominal CT scan. Fifty-six volunteers agreed to participate in the study. Seven patients had AAAs and one patient had an isolated iliac aneurysm, for a 14.3% overall prevalence of aneurysms. There was no difference in the incidence of risk factors-in those patients with aneurysms and those without aneurysms. This represents one of the highest incidences for AAA thus far reported. If immediate repair is not performed, such patients must be followed closely for the development of symptoms or enlargement of their AAA. (Ann Vasc Surg 1993;7:117-121 .)
Since rupture of an abdominal aortic a n e u r y s m (AAA) is associated with an unacceptably high operative mortality, identification and repair prior to rupture are essential and result in prolonged survival of patients with such lesions. ~An abdomiThis study reflects the views of the authors and does not necessarily represent the view of the Department of Veterans Affairs or the United States Government. From the Department of Surgery, Division of VascularSurgery, and Department of Radiology, University of Cincinnati Medical Center and Cincinnati Veterans Affairs Medical Center, Cincinnati, Ohio. Reprint requests: Richard J. Fowl, MD, Department of Surgery, University of Cincinnati Medical Center, 231 Bethesda Ave. ML 558, Cincinnati, OH 45267.
nal CT scan is one of the most accurate m e t h o d s for detecting the size and extent of AAAs. 2 Since CT scans are also performed for the diagnostic w o r k u p of a variety of intra-abdominaI conditions, we w o n d e r e d h o w often unsuspected AAAs w o u l d be detected during the evaluation of patients with nonvascular abdominal conditions. After analyzing this retrospective data w e observed an alarming incidence of unrecognized AAAs in a specific subgroup of this population, and w e then conducted a prospective study to determine if the incidence of AAAs was indeed this high. This study reports the prevalence of AAAs in t w o subgroups of veterans. One was a retrospective analysis of patients with multiple atherosclerotic 117
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T a b l e I. Prevalence of atherosclerotic risk factors
Age (mean) White race* Hypertension Cardiac disease Chronic obstructive pulmonary disease Diabetes Vascular disease Smoking history Pack-years smoked
Retrospective survey AAA No AAA (n = 15) p value (n = 96) 72.5 yr 0.0001 64.7 yr 64 (66.7%) 13 (86.7%) 0.10 6 (40.0%) 0.98 35 (36.5%) 5 (33.3%) 0.28 22 (22.9%) 19 ( 19.8% ) 6(40.0% ) 0.08 5 (33.3%) 0.17 18 (18.8%) 7(46.7% ) 0.06 22 (22.9%) 79 (82.3%) 14 (93.3%) 0.25 63.5 yr 0.003 36.1 yr
Prospective survey No AAA AAA (n = 48) (n = 8) p value 69.0 yr 38 (79.2%) 26 (54.2%) 23 (47.9%) 7(14.6%) 17 (35.4%) 48 (100%) 48(100%) 55.9 yr
67.4 yr 7(87.5% ) 4 (50.0%) 1 (12.5%) 1(12.5%) 2 (25.0%) 8(100%) 8(100%) 68.8 yr
0.47 0.95 0.87 0.14 0.70 0.86 --0.25
*All other patients were black.
risk factors on w h o m a b d o m i n a l CT scans have b e e n p e r f o r m e d for indications exclusive of AAA. The o t h e r was a prospective analysis of patients with k n o w n peripheral vascular disease a n d a history of smoking o n w h o m CT scans w e r e perf o r m e d to screen for a s y m p t o m a t i c AAAs. MATERIAL
AND
METHODS
During the period July 1988 to M a y 1989, 110 male patients a n d o n e female patient >50 years of age u n d e r w e n t a b d o m i n a l CT scanning for indications o t h e r t h a n for evaluation of AAA at the Cincinnati Veterans Affairs Medical Center. CT scans that visualized t h e entire abdominal aorta w e r e accepted for inclusion in t h e retrospective a r m of this study. In addition to the indications for the scan, appropriate d e m o g r a p h i c i n f o r m a t i o n and risk factors for atherosclerotic vascular disease w e r e r e c o r d e d for each patient. All CT scans w e r e i n t e r p r e t e d by a staff radiologist and w e r e spedfically screened for AAA (suprarenal or infrarenal), iliac, renal, or visceral aneurysms, and n o n a n e u rysmal atheroscleroticvascular disease. AAAs w e r e defined as a n y segmental aortic dilatation at least 1.5 times t h e size of the normal, proximal, contiguous aorta. 3 Because o u r retrospective analysis revealed a n alarming rate of AAAs in a specific subgroup of patients, w e t h e n c o n d u c t e d a prospective screening study. All patients seen in the vascular laboratory f r o m J a n u a r y 1990 t h r o u g h D e c e m b e r 1991 w e r e offered an a b d o m i n a l CT scan if t h e y h a d all of t h e following risk factors: (1) age 60 years or older, (2) d o c u m e n t e d peripheral arterial o c d u sive disease, a n d (3) history of smoking. Patients
w h o h a d u n d e r g o n e prosthetic graft replacement of t h e aorta and those with previously docum e n t e d small AAAs that w e r e being followed were excluded. Fifty-six patients v o l u n t e e r e d for this study. D e m o g r a p h i c a n d atherosclerotic risk factors w e r e also recorded for this group of patients. Statistical analysis was p e r f o r m e d using Fisher's exact test for comparing risk factors b e t w e e n patients w i t h a n d w i t h o u t aneurysms. Unpaired Student's t test was used to c o m p a r e ages and the n u m b e r of pack-years of cigarette use. RESULTS In the retrospective survey, 15 ( 13.5 %) of the 111 patients h a d an u n s u s p e c t e d AAA o n CT scan. One patient h a d a n isolated 6.0 c m suprarenal AAA and a n o t h e r patient h a d b o t h a 6.0 cm suprarenal AAA and a 4.0 cm infrarenal AAA. The remaining 13 patients h a d a n e u r y s m s confined to the infrarenal aorta ranging in size f r o m 3.0 to 7.0 cm (mean 4.4 cm with n i n e a n e u r y s m s >4.0 cm) in diameter. The only risk factors that differed significantly w e r e age a n d t h e n u m b e r of pack-years of cigarette use (Table I). All 15 veterans with AAAs were >60 years of age ( 15 / 19, 16.5 %), w h e r e a s n o n e of t h e veterans <60 years old had a n e u r y s m s (p = 0.04). Additionally, patients o v e r age 60 years with peripheral vascular disease and a history of tobacco use h a d a 2 9 . 2 % p r e v a l e n c e for AAA compared w i t h 0 % in those w i t h o u t a n y of these risk factors (p = 0.04). Hypertension, cardiac disease, diabetes, history of smoking, a n d race w e r e n o t significant risk factors for t h e presence of aneurysms. However, t h e r e was a strong t r e n d toward increased p r e v a l e n c e of AAAs in veterans with
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Prevalence of unsuspected AAAs in male veterans
Table II. Indications for abdominal CT scan in patients studied retrospectively Indications
No AAA (n = 96)
AAA (n = 15)
Abdominal mass/malignancy Infection/abscess Benign genitourinary lesions Benign pancreas/liver disease Miscellaneous*
59 8 3 7 19
9 3 0 0 3
*These indications included evaluation of abdominal pain, nonspedfic disease, ventral hernia, pelvic bone lesions, etc.
peripheral vascular occlusive disease (p = 0.06). Table II lists the indications for the CT scan in the group of patients studied retrospectively. The majority of patients were e x a m i n e d to evaluate or follow-up intra-abdominal malignancies or infections. In the group studied prospectively, 8 (14.3%) of the 56 patients had an intra-abdominal aneurysm. Seven patients had an AAA, and the eighth patient had a c o m m o n iliac aneurysm. Five AAAs were 4.0 cm in diameter and the other two were 3.5 cm (mean 3.86 cm). The c o m m o n iliac a n e u r y s m was 3.5 cm in diameter. There were no significant differences in the incidence of atherosclerotic risk factors between those with aneurysms and those without aneurysms (Table I).
DISCUSSION The reported prevalence of AAAs in a given population has varied widely in the literature. Factors affecting this prevalence include age, sex, ethnic background, medical risk factors present, and the diagnostic modality used to evaluate the population (autopsy vs. clinical examination vs. radiographic imaging). In a 30-year population-based study from Rochester, Minnesota, the overall incidence of AAAs in this predominantly white population was 21.8 per 100,000 patient-years. However, the incidence for m e n was 32.1 compared with 13.4 per 100,000 patient-years for w o m e n . The overall incidence increased 4-fold b e t w e e n the first and third decades of the study period. In both sexes the incidence increased markedly with age. 4 In a study of persons over 55 years of age, based on both autopsy and clinical data from Perth, Australia, between 1971 and 1981, there was an AAA incidence of 117.2 per 100,000 persons in
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m e n and 33.9 per 100,000 persons for w o m e n . During this time there was a 57% increase in m e n a n d a 94% increase in w o m e n . There was a 5-fold increased incidence in m e n over 75 years old compared with m e n 55 to 64 years of age. There was also a nearly 4-fold increase in w o m e n of similar age groups2 J o h n s o n et al. 6 reviewed 1665 autopsies and 545 CT scans from a racially m i x e d North Carolina population over 50 years of age. On autopsy, t h e y f o u n d that white males h a d a significantly greater incidence of AAAs (4.0%) t h a n white females (0.9%) and blacks of either sex (1.5% to 1.8%). On CT scan a significant increase in AAAs was also f o u n d for white males (5.4%) as compared to white females ( 1.9% ) and blacks ( 1.0% ). Although AAAs were more c o m m o n in white males t h a n in blacks in our population, the small n u m b e r of blacks in our population precluded d o c u m e n t i n g a statistically significant difference. A review of 4000 autopsies performed at the Houston Veterans Administration Hospital between 1949 and 1960 revealed an AAA incidence of 6% in male patients over age 50 years. Two thirds of the patients had evidence of hypertension. 7 Another autopsy study from Great Britain revealed a 3% incidence of AAAs a m o n g 1544 p o s t m o r t e m examinations performed on patients over 50 years of age. Nearly three fourths of these patients also had evidence of hypertension. 8 Four recent studies have used abdominal ultrasound as a screening modality for AAAs. Scott et al. 9 reviewed the abdominal ultrasonograms of 753 patients 65 to 80 years of age in a general practice population in Great Britain and f o u n d an incidence of AAAs (>3.5 cm) of 2.7 %. In a study of 120 patients (90 m e n and 30 w o m e n ) from a general cardiology practice, there was a 5 % overall incidence of AAAs (>4 cm).~° In m e n the incidence of AAAs (>4 cm) was 6.7% but was 27.8% if aortas >3 cm were included. M e n w h o both smoked and were hypertensive had a statistically significant increase in aortic diameter compared to m e n without those risk factors. In a n o t h e r study, 100 patients with k n o w n symptomatic vascular disease had a 20% incidence of aortic a n e u r y s m or ectasia in males compared to a 2 % incidence in a control population w i t h o u t vascular disease, n Twomey et al) 2 screened 84 male hypertensive patients and found nine (10.7%) with AAAs. It is important to note that populations w i t h risk factors for AAAs, such as those cited above and our study, have been s h o w n to have a m u c h higher incidence of aneu-
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rysms t h a n f o u n d in screening studies performed in the general population. The two most important determinants of w h e n to proceed with elective repair of AAAs are the size of the a n e u r y s m and the overall health of the patient. The m i n i m u m size required before recomm e n d i n g elective repair of an AAA is controversial, but m a n y surgeons accept a diameter of 4 cm. This is based on the autopsy study by Darling et al) 3 in w h i c h 9.5% of AAAs with a diameter of 4 cm or less had ruptured. These authors reco m m e n d e d surgical repair of all AAAs (4 cm or greater) if the predicted operative mortality rate for elective repair was <2%. However, a recent study from Rochester, Minnesota, failed to identify any ruptures in AAAs that were <5 cm in diameter. In this same study, the 5-year rupture risk for 5 to 7 cm AAAs was 26% and for >7 cm AAAs was 38%. Consequently, these authors reco m m e n d e d elective repair of all aneurysms >5 cm but favored selective m a n a g e m e n t for smaller ane u r y s m s ) 4 If 4 cm is accepted as the m i n i m u m size for elective repair, I1 of our 15 patients (73%) with unsuspected AAAs in the retrospective group a n d five of seven (71%) patients studied prospectively might have been considered for elective repair. If 5 cm is chosen as the m i n i m u m size requirement, only six patients (40%) from our retrospective study and n o n e from the group studied prospectively w o u l d have been operative candidates. Identification of small AAAs is important because they can be expected to grow at an average rate of 0.4 cm/yr. ~5In fact, a n o t h e r veteran population study reported an average growth rate of nearly 0.8 c m / y r (range 0 to 6 c m ) ) 6 Thus most 3 cm AAAs m a y be expected to become 5 cm within 5 years, at which point elective repair w o u l d generally be considered. Therefore all patients with small aneurysms w h o do not undergo elective repair require a n n u a l ultrasound or CT scan examination. However, in developing screening programs for AAAs, a n o t h e r important factor is expense. Alt h o u g h we did not specifically evaluate cost w h e n we performed our prospective study, we were able to determine the cost of CT scans retrospectively using data from the University of Cincinnati Hospital. In 1992 an abdominal CT scan cost $570 for technical and professional fees. Therefore the total cost for the patients in the prospective study would have been 56 x $570 = $31,920. Since eight patients with AAAs were detected, the cost for identifying an a n e u r y s m was $31,920/8 = $3990 per patient. An abdominal ultrasound costs only $244
and would have been m u c h less expensive to use for general screening of AAAs ($1708 per aneurysm detected). Although both these screening tests are expensive, w h e n one considers the potential cost of hospitalization for a ruptured a n e u r y s m ($20,000 to $500,000 in our previous experience), such screening seems cost effective. Several risk factors appear to predispose patients to AAAs. Two studies have demonstrated a clear relationship b e t w e e n AAA and increasing age. 4,5 Furthermore, white males are at increased risk as compared to females and blacks. 4-6 Alt h o u g h our study failed to show that hypertension was an important risk factor, three other studies have suggested an association with AAA. 7,~°A2Finally, our study as well as others has demonstrated an association b e t w e e n tobacco use and occlusive peripheral vascular disease with a n e u r y s m format i o n ) °,n
CONCLUSION The m a r k e d l y higher prevalence of AAAs in our population (13.5% to 14.3%) as compared to other similar studies m a y be attributable to the high incidence of multiple risk factors present in our patients. However, t h e y were not dissimilar to those seen by most vascular surgeons. All patients over age 60 years with k n o w n peripheral vascular occlusive disease and a history of tobacco use should be evaluated for AAAs by ultrasonography or CT scan. This is especially important in patients w h o are obese since physical examination often will fail to detect AAAs. The risk/benefit ratio in these high-risk patients clearly favors such an aggressive diagnostic approach.
REFERENCES 1. Szilagyi DE, Smith RF, DeRusso FJ, et al. Contribution of abdominal aortic aneurysmectomy to prolongation of life. Ann Surg 1966;164:678-699. 2. GomesMN, Chouke PL Pre-operative evaluation of abdomihal aortic aneurysms: Ultrasound or computed tomography? J Cardiovascular Surg 1987;28:159-166. 3. Cronenwett JL, Murphy TF, Zelenock GB, et al. Actuarial analysis of variables associated with rupture of small abdominal aortic aneurysms. Surgery 1985;98:472-483. 4. Bickerstaff LK, Hollier LH, Van Peenen HJ, et al. Abdominal aortic aneurysms: The changing natural history. J Vase Stlrg 1984;1:6-12. 5. Castleden WM, Mercer JC, The Members of the West Australian Vascular Service. Abdominal aortic aneurysms in Western Australia: Descriptive epidemiology and patterns of rupture. Br J Surg 1985;72:109-112. 6. Johnson GJ Jr, Avery A, McDougal G, et al. Aneurysms of the abdominal aorta: Inddence in blacks and whites in North Carolina. Arch Surg t 985; 120:1138-1140.
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7. Halpert B, Willms RK. Aneurysms of the aorta: An analysis of 249 necropsies. Arch Pathol 1962;74:163-168. 8. Turk KAD. The post-mortem incidence of abdominal aortic aneurysm. Proc R Soc Med 1965;58:869-870. 9. Scott RAP, Ashton H, Sutton GLJ. Ultrasound screening of a general practice population for aortic aneurysm. Br J Surg 1986;73:318. 10. Thurmond AS, Semler ILl. Abdominal aortic aneurysm: Incidence in a population at risk. J Cardiovasc Surg 1986;27: 457-460. 11. Allardice JT, Allwright GJ, Wafila JMC, et al. High prevalence of abdominal aortic aneurysm in men with peripheral vascular disease: Screening by ultrasonography. Br J Surg 1988;75: 240-242.
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12. Twomey A, Twomey EM, Wflkins RA, et al. Unrecognized aneurysmal disease in male hypertensive patients. Br J Surg 1984;71:307-308. 13. Darling RC, Messina CR, Brewster DC, et al. Autopsy study of unoperated abdominal aortic aneurysms. Circulation 1977; 56 (SuppI 2):161-164. 14. Nevitt MP, Ballard DJ, Hallett, JW Jr. Prognosis of abdominal aortic aneurysms: A population based study. N Engl J Med 1989;321:1009-1014. 15. Bernstein EF, Chan EL. Abdominal aortic aneurysm in highrisk patients. Outcome of selective management based on size and expansion rate. Ann Surg 1984;200:255-263. 16. Littooy FN, Steffan G, Greisler HP, et al. Use of sequential B-mode ultrasonography to manage abdominal aortic aneurysms. Arch Surg 1989;124:419-421.
Abdominal aortic aneurysms (AAA) are potentially lethal arterial lesions that are best managed by elective surgical repair. However, asymptomatic AAAs may go undetected on routine physical examination or patients with such lesions may not consult a physician. To determine the prevalence of asymptomatic AAAs in a high-risk population, we retrospectively reviewed all abdominal CT scans on veterans >50 years of age that had been ordered for indications other than aneurysmal disease during a recent 10-month period. Of the 111 patients studied, 15 (13.5%) had suprarenal and/or infrarenal AAAs (one patient had both). Patients with AAAs were significantly older (p = 0.0001) and were heavier tobacco users (p = 0.003). For patients >60 years of age with peripheral vascular occlusive disease and a history of tobacco use, there was a 29.2% prevalence for AAA compared with 0% in those without any of these risk factors ~ = 0.04). There was a very definite trend suggesting that patients with peripheral vascular disease (p = 0.06) were more likely to have an AAA. Because of the high prevalence of AAAs found in this population we then conducted a prospective study over a 24-month period during which patients >60 years of age with known peripheral vascular disease and a history of smoking who presented to the vascular laboratory for evaluation of problems not related to AAA were asked to undergo an abdominal CT scan. Fifty-six volunteers agreed to participate in the study. Seven patients had AAAs and one patient had an isolated iliac aneurysm, for a 14.3% overall prevalence of aneurysms. There was no difference in the incidence of risk factors-in those patients with aneurysms and those without aneurysms. This represents one of the highest incidences for AAA thus far reported. If immediate repair is not performed, such patients must be followed closely for the development of symptoms or enlargement of their AAA. (Ann Vasc Surg 1993;7:117-121 .)
Since rupture of an abdominal aortic a n e u r y s m (AAA) is associated with an unacceptably high operative mortality, identification and repair prior to rupture are essential and result in prolonged survival of patients with such lesions. ~An abdomiThis study reflects the views of the authors and does not necessarily represent the view of the Department of Veterans Affairs or the United States Government. From the Department of Surgery, Division of VascularSurgery, and Department of Radiology, University of Cincinnati Medical Center and Cincinnati Veterans Affairs Medical Center, Cincinnati, Ohio. Reprint requests: Richard J. Fowl, MD, Department of Surgery, University of Cincinnati Medical Center, 231 Bethesda Ave. ML 558, Cincinnati, OH 45267.
nal CT scan is one of the most accurate m e t h o d s for detecting the size and extent of AAAs. 2 Since CT scans are also performed for the diagnostic w o r k u p of a variety of intra-abdominaI conditions, we w o n d e r e d h o w often unsuspected AAAs w o u l d be detected during the evaluation of patients with nonvascular abdominal conditions. After analyzing this retrospective data w e observed an alarming incidence of unrecognized AAAs in a specific subgroup of this population, and w e then conducted a prospective study to determine if the incidence of AAAs was indeed this high. This study reports the prevalence of AAAs in t w o subgroups of veterans. One was a retrospective analysis of patients with multiple atherosclerotic 117
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T a b l e I. Prevalence of atherosclerotic risk factors
Age (mean) White race* Hypertension Cardiac disease Chronic obstructive pulmonary disease Diabetes Vascular disease Smoking history Pack-years smoked
Retrospective survey AAA No AAA (n = 15) p value (n = 96) 72.5 yr 0.0001 64.7 yr 64 (66.7%) 13 (86.7%) 0.10 6 (40.0%) 0.98 35 (36.5%) 5 (33.3%) 0.28 22 (22.9%) 19 ( 19.8% ) 6(40.0% ) 0.08 5 (33.3%) 0.17 18 (18.8%) 7(46.7% ) 0.06 22 (22.9%) 79 (82.3%) 14 (93.3%) 0.25 63.5 yr 0.003 36.1 yr
Prospective survey No AAA AAA (n = 48) (n = 8) p value 69.0 yr 38 (79.2%) 26 (54.2%) 23 (47.9%) 7(14.6%) 17 (35.4%) 48 (100%) 48(100%) 55.9 yr
67.4 yr 7(87.5% ) 4 (50.0%) 1 (12.5%) 1(12.5%) 2 (25.0%) 8(100%) 8(100%) 68.8 yr
0.47 0.95 0.87 0.14 0.70 0.86 --0.25
*All other patients were black.
risk factors on w h o m a b d o m i n a l CT scans have b e e n p e r f o r m e d for indications exclusive of AAA. The o t h e r was a prospective analysis of patients with k n o w n peripheral vascular disease a n d a history of smoking o n w h o m CT scans w e r e perf o r m e d to screen for a s y m p t o m a t i c AAAs. MATERIAL
AND
METHODS
During the period July 1988 to M a y 1989, 110 male patients a n d o n e female patient >50 years of age u n d e r w e n t a b d o m i n a l CT scanning for indications o t h e r t h a n for evaluation of AAA at the Cincinnati Veterans Affairs Medical Center. CT scans that visualized t h e entire abdominal aorta w e r e accepted for inclusion in t h e retrospective a r m of this study. In addition to the indications for the scan, appropriate d e m o g r a p h i c i n f o r m a t i o n and risk factors for atherosclerotic vascular disease w e r e r e c o r d e d for each patient. All CT scans w e r e i n t e r p r e t e d by a staff radiologist and w e r e spedfically screened for AAA (suprarenal or infrarenal), iliac, renal, or visceral aneurysms, and n o n a n e u rysmal atheroscleroticvascular disease. AAAs w e r e defined as a n y segmental aortic dilatation at least 1.5 times t h e size of the normal, proximal, contiguous aorta. 3 Because o u r retrospective analysis revealed a n alarming rate of AAAs in a specific subgroup of patients, w e t h e n c o n d u c t e d a prospective screening study. All patients seen in the vascular laboratory f r o m J a n u a r y 1990 t h r o u g h D e c e m b e r 1991 w e r e offered an a b d o m i n a l CT scan if t h e y h a d all of t h e following risk factors: (1) age 60 years or older, (2) d o c u m e n t e d peripheral arterial o c d u sive disease, a n d (3) history of smoking. Patients
w h o h a d u n d e r g o n e prosthetic graft replacement of t h e aorta and those with previously docum e n t e d small AAAs that w e r e being followed were excluded. Fifty-six patients v o l u n t e e r e d for this study. D e m o g r a p h i c a n d atherosclerotic risk factors w e r e also recorded for this group of patients. Statistical analysis was p e r f o r m e d using Fisher's exact test for comparing risk factors b e t w e e n patients w i t h a n d w i t h o u t aneurysms. Unpaired Student's t test was used to c o m p a r e ages and the n u m b e r of pack-years of cigarette use. RESULTS In the retrospective survey, 15 ( 13.5 %) of the 111 patients h a d an u n s u s p e c t e d AAA o n CT scan. One patient h a d a n isolated 6.0 c m suprarenal AAA and a n o t h e r patient h a d b o t h a 6.0 cm suprarenal AAA and a 4.0 cm infrarenal AAA. The remaining 13 patients h a d a n e u r y s m s confined to the infrarenal aorta ranging in size f r o m 3.0 to 7.0 cm (mean 4.4 cm with n i n e a n e u r y s m s >4.0 cm) in diameter. The only risk factors that differed significantly w e r e age a n d t h e n u m b e r of pack-years of cigarette use (Table I). All 15 veterans with AAAs were >60 years of age ( 15 / 19, 16.5 %), w h e r e a s n o n e of t h e veterans <60 years old had a n e u r y s m s (p = 0.04). Additionally, patients o v e r age 60 years with peripheral vascular disease and a history of tobacco use h a d a 2 9 . 2 % p r e v a l e n c e for AAA compared w i t h 0 % in those w i t h o u t a n y of these risk factors (p = 0.04). Hypertension, cardiac disease, diabetes, history of smoking, a n d race w e r e n o t significant risk factors for t h e presence of aneurysms. However, t h e r e was a strong t r e n d toward increased p r e v a l e n c e of AAAs in veterans with
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Prevalence of unsuspected AAAs in male veterans
Table II. Indications for abdominal CT scan in patients studied retrospectively Indications
No AAA (n = 96)
AAA (n = 15)
Abdominal mass/malignancy Infection/abscess Benign genitourinary lesions Benign pancreas/liver disease Miscellaneous*
59 8 3 7 19
9 3 0 0 3
*These indications included evaluation of abdominal pain, nonspedfic disease, ventral hernia, pelvic bone lesions, etc.
peripheral vascular occlusive disease (p = 0.06). Table II lists the indications for the CT scan in the group of patients studied retrospectively. The majority of patients were e x a m i n e d to evaluate or follow-up intra-abdominal malignancies or infections. In the group studied prospectively, 8 (14.3%) of the 56 patients had an intra-abdominal aneurysm. Seven patients had an AAA, and the eighth patient had a c o m m o n iliac aneurysm. Five AAAs were 4.0 cm in diameter and the other two were 3.5 cm (mean 3.86 cm). The c o m m o n iliac a n e u r y s m was 3.5 cm in diameter. There were no significant differences in the incidence of atherosclerotic risk factors between those with aneurysms and those without aneurysms (Table I).
DISCUSSION The reported prevalence of AAAs in a given population has varied widely in the literature. Factors affecting this prevalence include age, sex, ethnic background, medical risk factors present, and the diagnostic modality used to evaluate the population (autopsy vs. clinical examination vs. radiographic imaging). In a 30-year population-based study from Rochester, Minnesota, the overall incidence of AAAs in this predominantly white population was 21.8 per 100,000 patient-years. However, the incidence for m e n was 32.1 compared with 13.4 per 100,000 patient-years for w o m e n . The overall incidence increased 4-fold b e t w e e n the first and third decades of the study period. In both sexes the incidence increased markedly with age. 4 In a study of persons over 55 years of age, based on both autopsy and clinical data from Perth, Australia, between 1971 and 1981, there was an AAA incidence of 117.2 per 100,000 persons in
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m e n and 33.9 per 100,000 persons for w o m e n . During this time there was a 57% increase in m e n a n d a 94% increase in w o m e n . There was a 5-fold increased incidence in m e n over 75 years old compared with m e n 55 to 64 years of age. There was also a nearly 4-fold increase in w o m e n of similar age groups2 J o h n s o n et al. 6 reviewed 1665 autopsies and 545 CT scans from a racially m i x e d North Carolina population over 50 years of age. On autopsy, t h e y f o u n d that white males h a d a significantly greater incidence of AAAs (4.0%) t h a n white females (0.9%) and blacks of either sex (1.5% to 1.8%). On CT scan a significant increase in AAAs was also f o u n d for white males (5.4%) as compared to white females ( 1.9% ) and blacks ( 1.0% ). Although AAAs were more c o m m o n in white males t h a n in blacks in our population, the small n u m b e r of blacks in our population precluded d o c u m e n t i n g a statistically significant difference. A review of 4000 autopsies performed at the Houston Veterans Administration Hospital between 1949 and 1960 revealed an AAA incidence of 6% in male patients over age 50 years. Two thirds of the patients had evidence of hypertension. 7 Another autopsy study from Great Britain revealed a 3% incidence of AAAs a m o n g 1544 p o s t m o r t e m examinations performed on patients over 50 years of age. Nearly three fourths of these patients also had evidence of hypertension. 8 Four recent studies have used abdominal ultrasound as a screening modality for AAAs. Scott et al. 9 reviewed the abdominal ultrasonograms of 753 patients 65 to 80 years of age in a general practice population in Great Britain and f o u n d an incidence of AAAs (>3.5 cm) of 2.7 %. In a study of 120 patients (90 m e n and 30 w o m e n ) from a general cardiology practice, there was a 5 % overall incidence of AAAs (>4 cm).~° In m e n the incidence of AAAs (>4 cm) was 6.7% but was 27.8% if aortas >3 cm were included. M e n w h o both smoked and were hypertensive had a statistically significant increase in aortic diameter compared to m e n without those risk factors. In a n o t h e r study, 100 patients with k n o w n symptomatic vascular disease had a 20% incidence of aortic a n e u r y s m or ectasia in males compared to a 2 % incidence in a control population w i t h o u t vascular disease, n Twomey et al) 2 screened 84 male hypertensive patients and found nine (10.7%) with AAAs. It is important to note that populations w i t h risk factors for AAAs, such as those cited above and our study, have been s h o w n to have a m u c h higher incidence of aneu-
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rysms t h a n f o u n d in screening studies performed in the general population. The two most important determinants of w h e n to proceed with elective repair of AAAs are the size of the a n e u r y s m and the overall health of the patient. The m i n i m u m size required before recomm e n d i n g elective repair of an AAA is controversial, but m a n y surgeons accept a diameter of 4 cm. This is based on the autopsy study by Darling et al) 3 in w h i c h 9.5% of AAAs with a diameter of 4 cm or less had ruptured. These authors reco m m e n d e d surgical repair of all AAAs (4 cm or greater) if the predicted operative mortality rate for elective repair was <2%. However, a recent study from Rochester, Minnesota, failed to identify any ruptures in AAAs that were <5 cm in diameter. In this same study, the 5-year rupture risk for 5 to 7 cm AAAs was 26% and for >7 cm AAAs was 38%. Consequently, these authors reco m m e n d e d elective repair of all aneurysms >5 cm but favored selective m a n a g e m e n t for smaller ane u r y s m s ) 4 If 4 cm is accepted as the m i n i m u m size for elective repair, I1 of our 15 patients (73%) with unsuspected AAAs in the retrospective group a n d five of seven (71%) patients studied prospectively might have been considered for elective repair. If 5 cm is chosen as the m i n i m u m size requirement, only six patients (40%) from our retrospective study and n o n e from the group studied prospectively w o u l d have been operative candidates. Identification of small AAAs is important because they can be expected to grow at an average rate of 0.4 cm/yr. ~5In fact, a n o t h e r veteran population study reported an average growth rate of nearly 0.8 c m / y r (range 0 to 6 c m ) ) 6 Thus most 3 cm AAAs m a y be expected to become 5 cm within 5 years, at which point elective repair w o u l d generally be considered. Therefore all patients with small aneurysms w h o do not undergo elective repair require a n n u a l ultrasound or CT scan examination. However, in developing screening programs for AAAs, a n o t h e r important factor is expense. Alt h o u g h we did not specifically evaluate cost w h e n we performed our prospective study, we were able to determine the cost of CT scans retrospectively using data from the University of Cincinnati Hospital. In 1992 an abdominal CT scan cost $570 for technical and professional fees. Therefore the total cost for the patients in the prospective study would have been 56 x $570 = $31,920. Since eight patients with AAAs were detected, the cost for identifying an a n e u r y s m was $31,920/8 = $3990 per patient. An abdominal ultrasound costs only $244
and would have been m u c h less expensive to use for general screening of AAAs ($1708 per aneurysm detected). Although both these screening tests are expensive, w h e n one considers the potential cost of hospitalization for a ruptured a n e u r y s m ($20,000 to $500,000 in our previous experience), such screening seems cost effective. Several risk factors appear to predispose patients to AAAs. Two studies have demonstrated a clear relationship b e t w e e n AAA and increasing age. 4,5 Furthermore, white males are at increased risk as compared to females and blacks. 4-6 Alt h o u g h our study failed to show that hypertension was an important risk factor, three other studies have suggested an association with AAA. 7,~°A2Finally, our study as well as others has demonstrated an association b e t w e e n tobacco use and occlusive peripheral vascular disease with a n e u r y s m format i o n ) °,n
CONCLUSION The m a r k e d l y higher prevalence of AAAs in our population (13.5% to 14.3%) as compared to other similar studies m a y be attributable to the high incidence of multiple risk factors present in our patients. However, t h e y were not dissimilar to those seen by most vascular surgeons. All patients over age 60 years with k n o w n peripheral vascular occlusive disease and a history of tobacco use should be evaluated for AAAs by ultrasonography or CT scan. This is especially important in patients w h o are obese since physical examination often will fail to detect AAAs. The risk/benefit ratio in these high-risk patients clearly favors such an aggressive diagnostic approach.
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7. Halpert B, Willms RK. Aneurysms of the aorta: An analysis of 249 necropsies. Arch Pathol 1962;74:163-168. 8. Turk KAD. The post-mortem incidence of abdominal aortic aneurysm. Proc R Soc Med 1965;58:869-870. 9. Scott RAP, Ashton H, Sutton GLJ. Ultrasound screening of a general practice population for aortic aneurysm. Br J Surg 1986;73:318. 10. Thurmond AS, Semler ILl. Abdominal aortic aneurysm: Incidence in a population at risk. J Cardiovasc Surg 1986;27: 457-460. 11. Allardice JT, Allwright GJ, Wafila JMC, et al. High prevalence of abdominal aortic aneurysm in men with peripheral vascular disease: Screening by ultrasonography. Br J Surg 1988;75: 240-242.
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12. Twomey A, Twomey EM, Wflkins RA, et al. Unrecognized aneurysmal disease in male hypertensive patients. Br J Surg 1984;71:307-308. 13. Darling RC, Messina CR, Brewster DC, et al. Autopsy study of unoperated abdominal aortic aneurysms. Circulation 1977; 56 (SuppI 2):161-164. 14. Nevitt MP, Ballard DJ, Hallett, JW Jr. Prognosis of abdominal aortic aneurysms: A population based study. N Engl J Med 1989;321:1009-1014. 15. Bernstein EF, Chan EL. Abdominal aortic aneurysm in highrisk patients. Outcome of selective management based on size and expansion rate. Ann Surg 1984;200:255-263. 16. Littooy FN, Steffan G, Greisler HP, et al. Use of sequential B-mode ultrasonography to manage abdominal aortic aneurysms. Arch Surg 1989;124:419-421.