(Stroke. 1999;30:1621-1627.)
© 1999 American Heart Association, Inc.
Original Contributions |
Cost-Effectiveness Analysis of Screening for Asymptomatic, Unruptured Intracranial Aneurysms
A Mathematical Model
From the Department of Neurosurgery, Koshigaya Hospital, Dokkyo University School of Medicine, Saitama, and Department of Neurosurgery, Dokkyo University School of Medicine, Tochigi, Japan.
Correspondence to Dr Yuhei Yoshimoto, Department of Neurosurgery, Koshigaya Hospital, Dokkyo University School of Medicine, 2-1-50 Minami-Koshigaya, Koshigaya, Saitama 343-8555, Japan.
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Abstract |
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Background and Purpose—Subarachnoid hemorrhage (SAH) due to aneurysmal rupture is a major cause of cerebrovascular disease–related death. This problem could be eliminated by diagnosis and successful treatment of aneurysms before rupture. Recent developments in high-resolution imaging technology have made screening for unruptured aneurysms possible in the general population. Such screening has become widespread in Japan ("No Dokku," or brain checkup). As a result, unruptured aneurysms are being identified with increasing frequency. However, the economic implications of treatment decisions for unruptured aneurysms have not been analyzed. Therefore, we performed such an analysis.
Methods—We used a Markov model to evaluate the cost-effectiveness of screening for asymptomatic, unruptured intracranial aneurysms. The model involved a set of variables describing discrete health states. Each state was assigned a quality of life score and an associated medical cost. A comparison of the expected outcomes was then made between 2 hypothetical cohorts, one receiving screening and the other no screening. A sensitivity analysis was performed by altering the input values within clinically reasonable ranges to reflect uncertainty in the baseline analysis and then assessing the effects on outcomes.
Results—Combining the incremental cost and effectiveness data revealed a cost per quality-adjusted life-year of $7760 for an annual rate of subarachnoid hemorrhage due to unruptured aneurysms (rupture rate) of 0.02; this cost was $39 450 for a rupture rate of 0.01. There was no benefit (negative quality-adjusted life-year benefit) for a rupture rate of 0.005, the rupture rate found in a recently published international cooperative study. The risks of surgery for unruptured aneurysms and the discounting ratio used to assess the impact of timing of costs and benefits on future outcomes also had significant effects on the results. Other variables had little impact on cost-effectiveness.
Conclusions—The cost-effectiveness of screening for an unruptured aneurysm is highly sensitive to the annual rate of subarachnoid hemorrhage due to unruptured aneurysms. The low annual rupture rate seen in the recent large international cooperative study implies that screening asymptomatic populations to identify and treat unruptured aneurysms would not be cost cost-effective.
Key Words: aneurysm • cost-benefit analysis • quality of life • subarachnoid hemorrhage
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Introduction |
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Subarachnoid hemorrhage (SAH) due to aneurysmal rupture is a major cause of cerebrovascular disease–related death1 . The solution to this problem could be to diagnose and treat aneurysms before rupture. Several investigators have tried to devise methods of estimating the risk posed by incidentally discovered aneurysms to guide decisions regarding the need for surgery.2 3 4 Until the early 1980s, asymptomatic, unruptured aneurysms came to clinical attention only when they were found in SAH patients with multiple aneurysms5 6 7 8 9 10 or during investigations for other diseases.11
Magnetic resonance angiography12 and 3-dimensional CT angiography have been increasingly used to detect unruptured aneurysms among the general population of Japan ("No Dokku," or brain checkup).13 As a result, unruptured aneurysms are being identified at an ever-increasing rate.14 Screening followed by surgical repair of unruptured aneurysms has been introduced to reduce the number of patients developing SAH, and many neurosurgeons have reported reasonably good results in several series of patients.9 10 13 15 16 17 18 19 20 These authors all advocate surgical treatment, but do their results indicate that all asymptomatic, unruptured aneurysms should be repaired? If so, should wide-scale screening be implemented for asymptomatic populations? Although a large-scale, hospital-based, multicenter study was recently published,21 no population-based analysis has been performed.
Society and governments alike are increasingly aware of the economic implications of certain treatment decisions, and treatments that are not cost-effective will increasingly be rejected by public funding and private insurance reimbursement systems. Does the cost of screening for asymptomatic, unruptured intracranial aneurysms outweigh the potential cost posed by risk of a future SAH? To address these questions, we used a mathematical model to predict whether a screening program designed to identify individuals with asymptomatic aneurysms would be a cost-effective strategy for SAH prevention.
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Methods |
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Markov Model
We used a Markov model to analyze the expected outcomes of 2 alternative strategies, screening and no screening (Figure 1
).22 23 Such mathematical
modeling techniques allow complex problems to be analyzed in an
idealized manner. Although some simplification is inevitable,
modeling offers the advantage of permitting quantitative exploration of
the problem. The present model was defined by a set number of
discrete health states (well, well without aneurysm, disabled
without aneurysm, and dead). Each state was assigned a quality
of life score and an associated medical cost. Transitions between
states were assumed to occur at the midpoints of the each yearly cycle.
The analysis was continued until all individuals in the
hypothetical cohort died of their aneurysms or other
causes.
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We made several simplifying assumptions. Our baseline case considered screening in a cohort of 50-year-old asymptomatic individuals. In our model, surgery was the only treatment available and was assumed to remove permanently the risk of SAH due to aneurysmal rupture. Although endovascular techniques are being developed for the treatment of intracranial aneurysms, their role has yet to be established in long-term follow-up studies; therefore, they were not considered in this study.
Screening Group
Screened individuals could be shown to have no unruptured
intracranial aneurysms (well without aneurysm) or to
have an aneurysm at the beginning of the first cycle. All of
the latter group were assumed to undergo aneurysm surgery. They
might then die perioperatively (dead), survive with
neurological deficits and a repaired aneurysm (disabled without
aneurysm), or survive with normal neurological function and a
repaired aneurysm (well without aneurysm). In
succeeding years, survivors were assumed to live at the postoperative
level of functioning until they died of causes other than
aneurysmal SAH. We also assumed that the aneurysm would
never rupture after surgery and that each patient would have the same
death rate as the general population.
No-Screening Group
Subjects who did not undergo screening would live without
knowing whether they had an intracranial aneurysm. They might
die of causes other than aneurysmal SAH or develop SAH. We
assumed that all unruptured aneurysms would rupture at a
constant rate over time and that all patients who developed
aneurysmal SAH and were admitted to hospital would undergo
surgical repair of the aneurysm. They might then die, survive
with a neurological deficit and a repaired aneurysm (disabled
without aneurysm), or survive without a neurological deficit
and a repaired aneurysm (well without aneurysm). It was
also assumed that patients with a repaired aneurysm would not
develop SAH in the future and would have the same death rate as the
general population.
Annual Death Rate of the General Population
The hazard function p(x), namely, the annual death
rate of the general population at age x, is known to
approximate well to an exponential function.24 25 We
plotted yearly death rates for each age group included in the model
using Japanese life statistics data from 1990.26 By
regression analysis, the following approximation of
p(x) was obtained2 :
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Baseline Analyses
Probabilities
Incidence of Unruptured Aneurysms
In previous autopsy27 28 29 30 31 32 and angiographic
series,11 13 29 33 34 35 there has been a wide range in the
incidence of unruptured aneurysms in the general population
(0.5% to 7.9%). For our baseline analyses, we chose an
incidence of unruptured aneurysm of 3.0% in 50-year-old
subjects.
Annual Rate of SAH Due to Unruptured Aneurysms
Many attempts have been made to clarify the natural history of
unruptured aneurysms.3 5 7 21 29 36 37 38 39 40 41 42 Juvela et
al37 followed up 142 patients with 181 aneurysms
for an average of 13.9 years (total of 1994 patient-years) and found a
yearly rupture rate of 1.4%. This rupture rate was stable over the
first, second, and third decades of follow up. Yasui et
al41 reported results for 234 patients with unruptured
intracranial aneurysms, with a mean follow-up period of 75
months, showing an average annual rupture rate of 2.3%.
However, lower annual rupture rates of unruptured intracranial aneurysms were found in a recently reported international cooperative study21 : The overall rupture rate for the 1449 patients in this retrospective cohort (12 023 patient-years of follow-up) was 0.5% per year. Because of the range of the above, we chose 3 different annual rupture rates, 0.02, 0.01, and 0.005, for our baseline analyses.
Mortality and Morbidity Due to Aneurysmal SAH
The authors of the International Cooperative Study on Timing of
Aneurysm Surgery reported that in their 3521 hospitalized
patients, the mortality rate was 26% and the morbidity rate was 16%;
58% of the patients recovered fully.43 44 However, more
recent articles have reported far higher mortality rates for SAH (52%
to 67%).21 37 40 41 45 Thus, we assumed that the
mortality rate of SAH would be 50% and that half of the 50% who
survived would have some disability and that the remainder would fully
recover.
Risks of Surgery for Unruptured Aneurysms
A review and meta-analysis of 28 separate articles
reporting the results of elective surgery for unruptured
asymptomatic aneurysms in 733 patients found a
morbidity rate of 4.1% (95% confidence interval, 2.8% to 5.8%) and
a mortality rate of 1% (95% confidence interval, 0.4% to
2.0%).46 These data may have been influenced by differing
sources of patient referral or selection and/or by publication
bias47 (ie, the tendency for excellent surgical results to
be published more often than average or poor results). A recent
prospective international study reported a much higher rate (combined
mortality and morbidity, 13.1% to 15.7%).21 Morbidity in
that study included cognitive impairment as well as physical
disability. We assumed the surgery-related mortality and morbidity
rates to be 10% in the baseline analysis. We also assumed
that, among those who had surgical complications, 20% died and the
rest (80%) survived and had some disability.
Costs
Each health state in the Markov model is associated with one of
the following cost considerations: (1) examination costs of
screening, (2) hospital costs of surgery for unruptured
aneurysms, (3) hospital costs of surgery for ruptured
aneurysms and acute care for SAH, and (4) rehabilitation and
nursing home costs in subsequent years of survival. We selected
magnetic resonance angiography as the screening method because of its
noninvasiveness and reliability,12 and we set the
screening cost at $200 (we are aware of much higher costs in other
countries). Thirty percent of SAH patients were assumed to die before
admission (prehospital death, zero cost). Accurate data on treatment
costs were not available for our baseline analysis; we
estimated the cost of a surgical admission for SAH, including acute
care, to be $20 000 and that for unruptured aneurysm to be
$15 000; these amounts are based on the scale of reimbursement used by
the Japanese health insurance system. We estimated the average cost of
long-term care for disabled patients after surgery or SAH to be
$10 000 per year. Our evaluation included only direct medical costs;
indirect costs, such as loss of earnings through inability to work,
were omitted.
Quality-Adjusted LifeYears
We expressed the outcome of each treatment strategy in terms of
the expected number of quality-adjusted life-years (QALYs) gained. To
establish the expected number of QALYs, we identified a "QALY
weight" score, ranging between 0.00 and 1.00, for each health state
in the model. Lifetime QALYs then equaled the sum of the number of
years spent in each health state, multiplied by the QALY weight
associated with that state.
Death
By convention, death is assigned a value of zero.
Postoperative or Post-SAH Recovery Period
On the basis of clinical experience, we assigned all patients
who underwent surgery for an unruptured aneurysm a
postoperative recovery period of 1 month. Three months were assigned
for those who underwent surgery after SAH due to a ruptured
aneurysm. For the postoperative recovery period, we assumed a
quality of life score equal to 60% of the full value.
Postoperative or Post-SAH Deficits
Several methods of measuring the quality of life after stroke
have been devised.48 49 Previous work in decision
analysis has also estimated the value of living with a
neurological deficit as 0.50 to 0.75. Thus, we assumed a value of 0.70
for survival with a postoperative or post-SAH neurological
deficit.50
Well Without Aneurysm
Normal function without an aneurysm or with a repaired
aneurysm was assigned a value of 1.00.
Well Without Screening
Normal function without knowing whether an unruptured
aneurysm was present was also assigned a value of 1.00.
Discounting
Benefits and costs are more significant if they occur earlier.
To account for this phenomenon, current values for both benefits and
costs were calculated by discounting the original values at the rate of
3% per year.
Cost-Effectiveness Ratios
We calculated the expected benefits and costs associated with
screening. A treatment strategy that yielded the greatest
quality-adjusted survival for the least expensive intervention would
obviously become the treatment of choice. However, for a strategy that
yielded greater quality-adjusted survival but was more expensive,
additional analysis would be necessary to determine whether the
longer survival justified the extra costs. This was calculated
using the incremental cost-effectiveness ratio:
Cost-effectiveness=(Cost A-Cost
B)/(Effectiveness A-Effectiveness B),
where A and B are 2 different treatment
options.
Sensitivity Analysis
The sensitivity analysis was performed by altering the
input values for individual variables within a clinically
reasonable range to assess the effects of uncertainties in the
assumptions made in the baseline analyses. The ranges of
variables tested included (1) incidence of unruptured
aneurysm (0.01 to 0.10), (2) mortality due to SAH (0.40 to
0.60), (3) overall mortality and morbidity due to surgery for an
unruptured aneurysm (0.05 to 0.15), (4) cost of surgery for an
unruptured aneurysm ($10 000 to $20 000), (5) cost of surgery
for a ruptured aneurysm plus acute care costs ($10 000 to
$30 000), (6) cost of long-term care for a disability ($5000 to
$15 000 per year), (7) examination costs of screening (magnetic
resonance angiography) ($100 to $300), (8) QALY value for postoperative
or post-SAH recovery period (0.50 to 0.70), (9) QALY value for living
with neurological deficits (0.60 to 0.80), (10) QALY value for living
without the knowledge of whether an unruptured aneurysm is
present (without having screening) (0.999 or 0.998), (11)
subject age (40 to 60 years), and (12) discount rate (0.05).
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Results |
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Baseline Analysis
Screening for asymptomatic aneurysms yielded an additional 0.0690 and 0.0210 QALYs in the first and second analyses, respectively (annual rupture rates of 0.02 and 0.01), for 50-year-old subjects. In the third analysis (annual rupture rate of 0.005), however, the screening strategy proved to be less effective than no screening (ie, there were negative QALY benefits). In all analyses, screening was more expensive than no screening: The average cost per person for individuals who underwent screening was $1121 regardless of the annual rate of SAH from unruptured aneurysms, whereas costs for subjects who did not undergo screening were $583, $293, and $147 in the first, second, and third analyses, respectively. Costs for the unscreened group reflected the weighted average of zero cost plus the discounted costs for patients who developed SAH at some point, followed by death, hospitalization (acute care, including surgery), and/or nursing care.
Combining the incremental cost and effectiveness data in the baseline
analyses revealed a cost per QALY of $7760 and $39 450 in the
first and second analyses, respectively, which corresponded to
the additional cost for the gain in QALYs between the screening and
no-screening strategies. In the third analysis, a cost per QALY
was undefined because of a negative QALY benefit. Figure 2 shows the effects of annual rate of SAH
from unruptured aneurysms on the cost per QALY generated by
screening, indicating the marked impact of this variable.
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Sensitivity Analysis
The sensitivity analyses for other selected model
variables are shown in the Table. Overall mortality and morbidity
of surgery for unruptured aneurysms had significant effects on
the results in all analyses. The relationship between the risks
of surgery for unruptured aneurysms and the cost-effectiveness
ratio is demonstrated in Figure 3A. As
the overall mortality and morbidity rose from 0.05 to 0.15, the cost
per QALY rose from $3360 to $13 810 in the first analysis,
from $17 290 to $138 200 in the second analysis, and from
$73 160 to undefined in the third analysis, indicating a
significant impact of this parameter in the second and
third analyses. Cost-effectiveness ratios are undefined when
screening is less effective and more expensive than no screening.
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The effects of the incidence of unruptured aneurysms on the
cost-effectiveness relationship are shown in Figure 3B
. In the
first and second analyses, the costs per QALY were relatively
stable for this variable, varying from $5989 to $13 380 and
$33 410 to $57 640, respectively. In the third analysis,
screening was less effective and more expensive than no screening,
regardless of the incidence of unruptured aneurysms.
Age and the discounting ratio also have some influence on the cost per QALY: Older subjects and a high discount ratio (0.05) are less favored for screening. It is to be noted that input QALY scores of 0.999 and 0.998 for being well without screening significantly lowered the cost per QALY even in the third analysis (rupture rate=0.005). Other variables, including mortality of SAH and all aspects of the cost and QALY scores, had relatively little impact on the cost per QALY in all analyses.
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Discussion |
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Although the exact limits for cost-effectiveness are controversial, interventions that cost less than $50 000 to $100 000 per QALY are generally considered acceptable.51 For example, screening for hypertension costs $8370 to $44 400 per QALY,52 screening for cervical cancer every 3 years costs $15 500 per QALY,53 and screening of perimenopausal women for osteoporosis costs $11 700 to $22 100 per QALY.54 Installation of driver's side air bags results in net health benefits at an incremental cost of $24 000 per QALY.55 In contrast, although the Asymptomatic Carotid Atherosclerosis Study showed that carotid endarterectomy was beneficial for symptom-free patients with carotid stenosis of 60% or more,56 Lee et al57 reported that a program to identify candidates for endarterectomy by screening asymptomatic populations for carotid stenosis would cost $120 000 per QALY.
In the baseline calculations of our study, screening for unruptured aneurysms produced an incremental cost-effectiveness ratio of $7760 and $39 450 per QALY in the first and second analyses (annual rupture rate of 0.02 and 0.01, respectively), both of which are comparable to those of other widely practiced prophylactic interventions. There was no benefit from screening in our analysis for an annual rupture rate of 0.005.
In sensitivity analyses, we examined other factors that might
make screening more or less cost-effective. The risk of surgery for
unruptured aneurysms was a significant factor: At the 0.005
annual rupture rate, only extremely low surgical mortality and
morbidity would justify screening (Figure 3A). Age had
significant effects on the results, as did discount rate. At higher
discount rates, screening techniques with early costs and risks
(screening and aneurysmal surgery) and delayed benefits
(increased quality-adjusted survival and decreased long-term care cost)
are less favored. Conversely, screening would be preferable at a lower
discount rate.
In contrast, the cost-effectiveness ratio was relatively robust when most other parameters, such as mortality due to SAH, costs of screening and surgery, and QALY scores in each health state, were considered.
The cost-effectiveness of screening was sensitive to the incidence of
unruptured aneurysms to some extent (see our second
analysis). The effects, however, seem to be limited, because
application of higher values resulted in a higher cost as well as a
greater QALY gain. This is relevant, because some populations are known
to have a greater-than-normal tendency to develop intracranial
aneurysms and SAH, eg, patients with polycystic kidney
disease58 and familial aneurysm.59 60
Our results do not support elective screening in such populations. We
recognized that some of these high-risk individuals have an excessive
fear of future SAH, even if they have no clinical symptoms. If such
patients have even a slight devaluation of their quality of life (cf
Table, QALY score of well without screening: 0.999 or 0.998),
the cost-effectiveness analysis of screening is markedly
affected, regardless of whether the potentially higher incidence of an
unruptured aneurysm is considered. Screening of such patients
might be recommended, because this may ameliorate their psychological
distress about the possible future occurrence of SAH. We advocate that
the decision of whether to undergo screening should be left to
individuals and do not propose the use of public resources for this
purpose. Rupture of an aneurysm is a long-term risk over many
years, but screening and surgery generate an immediate risk. Some
patients may prefer to avoid surgery, even at the cost of a later
excess in risk; others may not.4
It must be recognized that the assumptions necessary for the construction of a mathematical model place limitations on the reliability of the conclusions. Thus, we assumed that all patients with unruptured aneurysms would undergo surgery and at the same level of risk. It may be reasonable to repair only aneurysms larger than 10 mm in diameter, because the recently published international study21 suggested that surgical intervention is not likely to improve the natural history of patients with aneurysms smaller than 10 mm. Satisfactory data on the risk of surgery by size of aneurysm would be of value but are not available.
Also, we assumed that SAH did not develop after screening showed no aneurysms or after an aneurysm was obliterated by surgery. This assumption may be false. Because aneurysms are rarely seen in younger subjects,32 it is obvious that they are not congenital but mostly develop during middle age. Therefore, after screening or successful surgery, some de novo aneurysms could grow, enlarge, and eventually rupture. However, to date, no data on the rate of de novo formation of aneurysms have been published. We postulate that the effect of de novo aneurysm formation on our results would be relatively small, because they would develop at the same rate in both the screening and no-screening populations.
Finally, the cost aspect of our study was restricted to direct medical costs.
Conclusion
Our study indicated that the cost-effectiveness of screening for
unruptured aneurysms was highly sensitive to assumptions about
the annual rate of SAH from an unruptured aneurysm. Screening
asymptomatic populations to avoid future SAH might be
cost-effective in a population with a high rupture rate (0.01 to 0.02
per year). In contrast, such screening is neither cost-effective nor
beneficial if the rupture rate is 0.005 per year (as recently
reported21 ). Under such circumstances, only extremely low
rates of surgical mortality and morbidity would make screening
justifiable.
Received February 23, 1999; revision received May 24, 1999; accepted May 24, 1999.
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References |
|---|
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
-
Ingall TJ, Whisnant JP, Wiebers DO, O'Fallon WM.
Has there been a decline in subarachnoid hemorrhage
mortality? Stroke. 1989;20:718–724.
[Abstract/Free Full Text] - Chang HS, Kirino T. Quantification of operative benefit for unruptured cerebral aneurysms: a theoretical approach. J Neurosurg. 1995;83:413–420.[Medline] [Order article via Infotrieve]
- Dell S. Asymptomatic cerebral aneurysm: assessment of its risk of rupture. Neurosurgery. 1982;10:162–166.[Medline] [Order article via Infotrieve]
-
Van Crevel H, Habbema JD, Braakman R. Decision
analysis of the management of incidental intracranial saccular
aneurysms. Neurology. 1986;36:1335–1339.
[Abstract/Free Full Text] - Heiskanen O. Risks of bleeding from unruptured aneurysms in cases with multiple intracranial aneurysms. J Neurosurg. 1981;55:524–526.[Medline] [Order article via Infotrieve]
- Mizoi K, Suzuki J, Yoshimoto T. Surgical treatment of multiple aneurysms: review of experience with 372 cases. Acta Neurochir. 1989;96:8–14.[Medline] [Order article via Infotrieve]
- Mount LA, Brisman R. Treatment of multiple intracranial aneurysms. J Neurosurg. 1971;35:728–730.[Medline] [Order article via Infotrieve]
- Moyes PD. Surgical treatment of multiple aneurysms and of incidentally discovered unruptured aneurysms. J Neurosurg. 1971;35:291–295.
- Salazar JL. Surgical treatment of asymptomatic and incidental intracranial aneurysms. J Neurosurg. 1980;53:20–21.[Medline] [Order article via Infotrieve]
- Solomon RA, Fink ME, Pile-Spellman J. Surgical management of unruptured intracranial aneurysms. J Neurosurg. 1994;80:440–446.[Medline] [Order article via Infotrieve]
- Pia HW, Obrador S, Martin JG. Association of brain tumors and arterial intracranial aneurysms. Acta Neurochir. 1972;27:189–204.[Medline] [Order article via Infotrieve]
- Grandin CB, Mathurin P, Duprez T, Stroobandt G, Hammer F, Goffette P, Cosnard G. Diagnosis of intracranial aneurysms: accuracy of MR angiography at 0.5 T. Am J Neuroradiol. 1998;19:245–252.[Abstract]
- Nakagawa T, Hashi K. The incidence and treatment of asymptomatic, unruptured cerebral aneurysms. J Neurosurg. 1994;80:217–223.[Medline] [Order article via Infotrieve]
-
Yamashita K, Kashiwagi S, Kato S, Takasago T, Ito H.
Cerebral aneurysms in the elderly in Yamaguchi, Japan:
analysis of the Yamaguchi data bank of cerebral
aneurysms from 1985 to 1995. Stroke. 1997;28:1926–1931.
[Abstract/Free Full Text] - Eskesen V, Rosenorn J, Schmidt K, Espersen JO, Haase J, Harmsen A, Hein O, Knudsen V, Marcussen E, Midoholm S, Rasmussen P, Ronde F, Voldby B, Hansem L. Clinical features and outcome in 48 patients with unruptured intracranial saccular aneurysms: a prospective consecutive study. Br J Neurosurg. 1987;1:47–52.[Medline] [Order article via Infotrieve]
- Heiskanen O, Poranen A. Surgery of incidental intracranial aneurysms. Surg Neurol. 1987;28:432–436.[Medline] [Order article via Infotrieve]
- Piepgras DG. Management of incidental intracranial aneurysms. Clin Neurosurg. 1989;35:511–518.[Medline] [Order article via Infotrieve]
- Rice BJ, Peerless SJ, Drake CG. Surgical treatment of unruptured aneurysms of the posterior circulation. J Neurosurg. 1990;73:165–173.[Medline] [Order article via Infotrieve]
- Samson DS, Hodosh RM, Clark WK. Surgical management of unruptured asymptomatic aneurysms. J Neurosurg. 1977;46:731–734.[Medline] [Order article via Infotrieve]
- Wirth FP. Surgical treatment of incidental intracranial aneurysms. Clin Neurosurg. 1986;33:125–135.[Medline] [Order article via Infotrieve]
-
International Study of Unruptured Intracranial
Aneurysms Investigators. Unruptured intracranial
aneurysms: risk of rupture and risks of surgical intervention.
N Engl J Med. 1998;339:1725–1733.
[Abstract/Free Full Text] - Gold MR, Siegel JE, Russel LB, Weinstein MC. Cost-Effectiveness in Health and Medicine. New York, NY: Oxford University Press; 1996.
- Sonnenberg FA, Beck JR. Markov models in medical decision making: a practical guide. Med Decis Making. 1993;13:322–338.
- Beck JR, Kassirer JP, Pauker SG. A convenient approximation of life expectancy (The "DEALE"), I: validation of the method. Am J Med. 1982;73:883–888.[Medline] [Order article via Infotrieve]
- Beck JR, Kassirer JP, Pauker SG. A convenient approximation of life expectancy (The "DEALE"), II: use in medical decision-making. Am J Med. 1982;73:889–897.[Medline] [Order article via Infotrieve]
- Ministry of Health and Welfare. Vital Statistics of Japan [in Japanese]. Tokyo, Japan: Statistics and Information Department, Minister's Secretariat; 1992.
- Housepian EM, Pool JL. A systemic analysis in intracranial aneurysms from the autopsy file of the Presbyterian Hospital. J Neuropathol Exp Neurol. 1958;17:409–423.[Medline] [Order article via Infotrieve]
- Inagawa T, Hirano A. Autopsy study of unruptured incidental intracranial aneurysms. Surg Neurol. 1990;34:361–365.[Medline] [Order article via Infotrieve]
-
Rinkel GJE, Djibuti M, Algra A, van Gijn J. Prevalence
and risk of ruptured of intracranial aneurysms: a systematic
review. Stroke. 1998;29:251–256.
[Abstract/Free Full Text] - Rosenorn J, Eskesen V, Schmidt K. Unruptured intracranial aneurysms: an assessment of the annual risk of rupture based on epidemiological and clinical data. Br J Neurosurg. 1988;2:369–378.[Medline] [Order article via Infotrieve]
- Sehkar LN, Heros RC. Origin, growth, and rupture of saccular aneurysms: a review. Neurosurgery. 1981;8:248–260.[Medline] [Order article via Infotrieve]
- Stehbens WE. Aneurysms and anatomical variations of cerebral arteries. Arch Pathol. 1963;75:45–64.[Medline] [Order article via Infotrieve]
- Atkinton JLD, Sundt TM, Houser OW, Whisnant JP. Angiographic frequency of anterior circulation intracranial aneurysms. J Neurosurg. 1989;70:551–555.[Medline] [Order article via Infotrieve]
- du Boulay GH. Some observations on the natural history of intracranial aneurysms. Br J Radiol. 1965;38:721–757.[Medline] [Order article via Infotrieve]
- Iwata K, Misu N, Terada K, Kawai S, Momose M, Nakagawa H. Screening for unruptured asymptomatic intracranial aneurysms in patients undergoing coronary angiography. J Neurosurg. 1991;75:52–55.[Medline] [Order article via Infotrieve]
- Jane JA, Winn HR, Richardson AE. The natural history of intracranial aneurysms: rebleeding rates during the acute and long term period and implication for surgical management. Clin Neurosurg. 1977;24:176–184.[Medline] [Order article via Infotrieve]
- Juvela S, Porras M, Heiskanen O. Natural history of unruptured intracranial aneurysms: a long-term follow-up study. J Neurosurg. 1993;79:174–182.[Medline] [Order article via Infotrieve]
- Wiebers DO, Whisnant JP, O'Fallon WM. The natural history of unruptured intracranial aneurysms. N Engl J Med. 1981;304:696–698.[Abstract]
- Wiebers DO, Whisnant JP, Sundt TM, O'Fallon WM. The significance of unruptured intracranial aneurysms. J Neurosurg. 1987;66:23–29.[Medline] [Order article via Infotrieve]
- Winn HR, Richardson AE, Jane JA. The long-term prognosis in untreated cerebral aneurysms, I: the incidence of late hemorrhage in cerebral aneurysms: 10-year evaluation of 364 patients. Ann Neurol. 1977;1:358–370.[Medline] [Order article via Infotrieve]
- Yasui N, Suzuki A, Nishimura H, Suzuki K, Abe T. Long-term follow-up study of unruptured intracranial aneurysms. Neurosurgery. 1997;40:1155–1160.[Medline] [Order article via Infotrieve]
- Zacks DJ, Russel DB, Miller MB. Fortuitously discovered intracranial aneurysms. Arch Neurol. 1980;37:39–41.[Abstract]
- Kassel NF, Torner JC, Jane JA, Haley EC, Adams HP, Kongable GL. The International Cooperative Study on the Timing of Aneurysm Surgery, part 1: Overall management results. J Neurosurg. 1990;73:18–36.[Medline] [Order article via Infotrieve]
- Kassel NF, Torner JC, Jane JA, Haley EC, Adams HP. The International Cooperative Study on the Timing of Aneurysm Surgery, part 2: surgical results. J Neurosurg. 1990;73:37–47.[Medline] [Order article via Infotrieve]
- Whisnant JP, Phillips LH, Sundt TM. Aneurysmal subarachnoid hemorrhage: timing of surgery and mortality. Mayo Clin Proc. 1982;57:471–475.[Medline] [Order article via Infotrieve]
- King JT, Berlin JA, Flamm ES. Morbidity and mortality from elective surgery for asymptomatic, unruptured, intracranial aneurysms: a meta-analysis. J Neurosurg. 1994;81:837–842.[Medline] [Order article via Infotrieve]
- Easterbrook PJ, Berlin JA, Gopalan R, Matthews DR. Publication bias in clinical research. Lancet. 1991;337:867–872.[Medline] [Order article via Infotrieve]
-
Ahlsio B, Britton M, Murray V, Theorell T. Disablement
and quality of life after stroke. Stroke. 1984;15:886–890.
[Abstract/Free Full Text] -
de Haan R, Aaronsom N, Limburg M, Hewer RL, van Crevel
H. Measuring quality of life in stroke. Stroke. 1993;24:320–327.
[Abstract/Free Full Text] - King JT, Glick HA, Mason TJ, Flamm ES. Elective surgery for asymptomatic, unruptured, intracranial aneurysms: cost-effectiveness analysis. J Neurosurg. 1995;83:403–412.[Medline] [Order article via Infotrieve]
- Laupacis A, Feeny D, Detsky AS, Tugwell PX. How attractive does a new technology have to be to warrant adoption and utilization? Tentative guidelines for using clinical and economic evaluation. Can Med Assoc J. 1992;146:473–481.[Abstract]
- Littenberg B, Garber AM, Sox HC. Screening for hypertension. Ann Intern Med. 1990;112:192–202.
- Eddy DM. Screening for cervical cancer. Ann Intern Med. 1990;113:214–226.
- Tosteson ANA, Rosenthal DI, Melton LJM, Weinstein MC. Cost-effectiveness of screening perimenopausal white women for osteoporosis: bone densitometry and hormone replacement therapy. Ann Intern Med. 1990;113:594–603.
- Graham JD, Thompson KM, Goldie SJ, Segui-Gomez M, Weinstein MC. The cost-effectiveness of air bags by seating position. JAMA. 1997;278:1418–1425.[Abstract]
- Executive Committee for the Asymptomatic Carotid Atherosclerosis Study. Endarterectomy for asymptomatic carotid artery stenosis. JAMA. 1995;273:1421–1428.[Abstract]
-
Lee TT, Solomon NA, Heidenreich PA, Oehlert J, Garber
AM. Cost-effectiveness of screening for carotid stenosis in
asymptomatic persons. Ann Intern Med. 1997;126:337–346.
[Abstract/Free Full Text] - Chapman AB, Rubinstein D, Hughes R, Stears JC, Earnest MP, Johnson AM, Gabow PA, Kaehny WD. Intracranial aneurysms in autosomal dominant polycystic kidney disease. N Engl J Med. 1992;327:916–920.[Abstract]
- Ronkainen A, Hernesniemi J, Puranen M, Niemitukia L, Vanninen R, Ryynanen M, Kuivaniemi H, Tromp G. Familial intracranial aneurysms. Lancet. 1997;349:380–384.[Medline] [Order article via Infotrieve]
- Wakai S. Familial intracranial aneurysms. Lancet. 1997;349:1478–1479.[Medline] [Order article via Infotrieve]
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