(Stroke. 2000;31:2976.)
© 2000 American Heart Association, Inc.
Original Contributions |
Perimesencephalic Hemorrhage and CT Angiography
A Decision Analysis
From the Department of Neurology (Y.M.R., G.J.E.R., J. van G.); Julius Center for Patient Oriented Research (E.B.); and Department of Radiology (B.K.V.), University Medical Center Utrecht (Netherlands).
Correspondence to Y.M. Ruigrok, MD, Department of Neurology, University Medical Center Utrecht, PO Box 85500, 3500 GA Utrecht, Netherlands. E-mail ij.m.ruigrok{at}neuro.azu.nl
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Abstract |
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Background and Purpose—The method of choice for detecting or excluding a vertebrobasilar aneurysm still is a matter of debate in patients with a characteristically perimesencephalic pattern of subarachnoid hemorrhage (SAH) on CT. We used decision analysis to compare possible diagnostic strategies in these patients.
Methods—A decision analytic model was developed to evaluate the effect of 4 different diagnostic strategies following a perimesencephalic pattern of SAH on CT: 1, no further investigation; 2, digital subtraction angiography (DSA) by catheter; 3, CT angiography as initial modality, not followed by DSA if negative; and 4, CT angiography as initial modality, followed by DSA. We used a 4% prevalence of a vertebrobasilar aneurysm given a perimesencephalic pattern of hemorrhage, a 97% sensitivity and specificity of CT angiography, and a 99.5% sensitivity and 100% specificity of DSA. In a prospectively collected series, the complication rate from DSA in patients with a perimesencephalic pattern of hemorrhage was 2.6%. We calculated the expected utility of each of the 4 diagnostic options and used sensitivity analyses to examine the influence of the plausible ranges of the various estimates used.
Results—The expected utilities were 99.09 for CT angiography only, 98.96 for no further investigation, 98.22 for DSA, and 96.34 for CT angiography plus DSA. The results of the sensitivity analysis indicate that over a wide range of assumptions, CT angiography only is the most beneficial option. Only when the complication rate of catheter angiography is <0.2% is DSA the preferred strategy.
Conclusions—Our decision analysis shows that in patients with a perimesencephalic pattern of hemorrhage on CT, CT angiography only is the best diagnostic strategy. DSA can be omitted in patients with a perimesencephalic pattern of hemorrhage and a negative CT angiogram.
Key Words: angiography, computed tomographic • decision analysis • diagnosis • perimesencephalic hemorrhage
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Introduction |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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In patients with subarachnoid hemorrhage (SAH) and a characteristically perimesencephalic pattern of hemorrhage on CT, the likelihood of finding a vertebrobasilar aneurysm is approximately 4%.1 2 3 4 5 6 The remaining 96% have a nonaneurysmal cause of hemorrhage with a benign clinical course and an excellent outcome.5 6 7 8 9 The method of choice for detecting or excluding a vertebrobasilar aneurysm is still a matter of debate in patients with perimesencephalic pattern of hemorrhage on CT.1 10 Catheterization methods, now mostly digital subtraction angiography (DSA), are associated with a risk of persistent neurological deficit. The need to identify the aneurysm has to be weighed against the risk of complications from DSA in the remaining patients with no aneurysm and inherent good prognosis. An alternative imaging modality is CT angiography. CT angiography can accurately detect and exclude vertebrobasilar aneurysms.1 We assessed the risk of complication of catheter angiography in a large consecutive series of patients with perimesencephalic hemorrhage, using a decision analytic model11 to compare the diagnostic strategies of DSA and CT angiography and to determine the optimal strategy of diagnosis in patients with a perimesencephalic pattern of hemorrhage.
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Subjects and Methods |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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The Model
A decision analytic model was developed to evaluate the effect of 4 different diagnostic strategies: 1, no further investigation; 2, DSA by catheter; 3, CT angiography only: CT angiography as initial modality, not followed by DSA if negative; and 4, CT angiography plus DSA: CT angiography as initial modality, followed by DSA if negative. In cases of positive CT angiography, DSA was performed if deemed necessary by the neuroradiologist or neurosurgeon. To assign quantitative values to all factors used in the decision model, we combined relevant data from the literature and, in the absence of reliable information, expert opinions. A decision model with the branches representing the 4 different diagnostic strategies, followed by a sequence of actions and events with risks and rates was generated, resulting in various outcomes (Figure 1
). At the root of the
decision model is an adult patient with SAH and a perimesencephalic
pattern of hemorrhage on CT. The patient is in good clinical
condition, with a normal level of consciousness and no focal
neurological signs. The chance that a vertebrobasilar aneurysm
is present in patients with a perimesencephalic pattern of
hemorrhage approximates 4% (Table 1). This aneurysm may rerupture,
which may lead to death, morbidity, or recovery of the patient. DSA can
detect such an aneurysm but is also associated with a risk of
permanent neurological complications, which in a small proportion may
result in death. From a series of patients with perimesencephalic
hemorrhage undergoing DSA in the University Medical Center
Utrecht, we assessed this risk of permanent neurological
complication (see Available Data and Estimates). In case of an
aneurysm being demonstrated by CT angiography or DSA, operation
of the aneurysm is assumed to follow. Operation may be
successful or may result in perioperative complications
or death. In the decision model, 5 different end points are used:
uncomplicated, recovery, single and double disability, and death.
"Uncomplicated" means good health without a patent
aneurysm, since patients with a perimesencephalic
hemorrhage have an excellent outcome.5 6 7 8 9
"Recovery" means status after recovery after an episode of
aneurysmal SAH or status after a successfully operated
aneurysm. Most patients who recover from an aneurysmal
SAH still have a somewhat reduced quality of life, even if no
complications have occurred and the patient is
independent.12 "Disability-single" means that a single
episode of deterioration has occurred, such as a complication from DSA,
surgery, or a moderate recovery after an episode of aneurysmal
SAH, and "disability-double" means that 2 complications have
occurred, such as a complication from DSA, followed by rerupture or a
complication from surgery. All types of complication were considered
equally serious, irrespective of the underlying cause.
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) denotes the choice between the 4 strategies, the chance nodes
(
) represent the events that may follow this choice, and the
conventions (label) indicate a generally agreed action to follow an
event. A and B refer to structurally identical subtrees.
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The decision model was used to obtain a proportional distribution of the various outcomes. Furthermore, the expected utility of each of the 4 diagnostic options was calculated by multiplying the probability of each branch of the model by the utility of outcome attached to it and summing the values of all branches at the node. Sensitivity analysis was used to examine the influence of variation across the plausible ranges of the estimates. One-way sensitivity analysis denotes the effect of analyzing a single variable, whereas simultaneous changes in the values of 2 independent variables are assessed by 2-way sensitivity analysis.
Available Data and Estimates
Sensitivity and Specificity of CT Angiography
Estimates of the sensitivity and specificity of CT angiography
(Table 1
) were derived from a recent review
article.13 These test characteristics refer to the first
evaluation of the CT angiogram, resulting in a negative or a positive
finding. We assumed, according to the practice in our institution, that
a positive result (aneurysm identified) will lead to
reevaluation of the CT angiogram together with the neurosurgeon,
followed by an additional DSA in half the patients with a nonconclusive
positive CT angiogram.14 We considered the first
evaluation and the reevaluation as 2 successive tests with a 2x2 table
applicable to each test. For the calculation of the sensitivity and
specificity of the reevaluation of the positive outcome, we combined
the two 2x2 tables, using the test characteristics of the first
evaluation (97% sensitivity and specificity), the 4% chance of an
aneurysm given a perimesencephalic pattern of bleeding, and a
reported positive predictive value of 99% (74/75) of CT
angiography.15
Sensitivity and Specificity of DSA
Data on the test characteristics of DSA are scarce. Sensitivity
and specificity of DSA were therefore estimated at 99.5% and 100%,
respectively. These estimates are probably too high, but we chose these
high rates to indicate that the test characteristics of DSA are more
favorable than those of CT angiography. When DSA is preceded by
negative or nonconclusive positive CT angiography, sensitivity and
specificity of DSA are presumably lower.
Complications of CT Angiography and DSA
For CT angiography 130 to 145 mL of contrast is used, while for
4-vessel angiography there is an average usage of 130 to 210 mL. Thus,
the amounts of contrast for CT angiography and DSA are comparable. The
risk of a severe adverse or allergic reaction requiring treatment from
nonionic contrast material is small and similar for CT angiography and
DSA.16 Patients with a perimesencephalic pattern of
bleeding will have to undergo 4-vessel angiography, that is, both
vertebral arteries need to be visualized. For this specific procedure,
we could not find a complication rate in the literature. An estimate of
the risk of permanent neurological complications was therefore derived
from all patients with perimesencephalic hemorrhage who
underwent 4-vessel angiography in the University Medical Center
Utrecht during 1983–1998. In our series of 77 patients we
found 2 patients (2.6%; 95% CI, 0.3% to 9.6%) with a permanent
neurological deficit: 1 patient with dysphasia and 1 patient with
hemianopia. We found 192 patients with a perimesencephalic
hemorrhage reported in the
literature.2 3 6 8 17 18 19 20 21 22 Of these patients, 4 had a
transient ischemic deterioration after angiography and none had
permanent neurological complications (0%; 95% CI, 0% to 1.9%). The
average risk of permanent neurological complications from DSA in
patients with perimesencephalic hemorrhage in the literature
combined with our own series of patients is 0.74% (95% CI, 0.09% to
2.7%). We used this figure as the lower limit for the risk of
complications of DSA. In our own series of patients with
perimesencephalic hemorrhage who underwent 4-vessel
angiography, no patient died from DSA. We assumed that most cerebral
infarctions due to 4-vessel angiography occur in the posterior fossa,
and therefore we estimated the risk of death from infarction after
4-vessel DSA by using the risk of death from cerebellar infarction
(5%),23 which can be considered an upper limit of this
particular outcome in cerebellar infarction. The risk of death from DSA
would then be 2.6% times 5% or 0.13%.
Aneurysm Prevalence
The prevalence of a vertebrobasilar aneurysm given a
perimesencephalic pattern of bleeding was derived from 6 studies in
which the prevalence of vertebrobasilar aneurysms in patients
with perimesencephalic patterns of hemorrhage was
reported.1 2 3 4 5 6 When these studies are combined, the overall
chance of finding a vertebrobasilar aneurysm is 4.0% (95% CI,
1.0% to 10.0%).
Aneurysm Rerupture
For the risk of a rebleed of the aneurysm, we used
aggregated data from the guidelines of the American Heart
Association.24 Because the category of patients considered
in the decision model is in general in good clinical condition (despite
a possible first rupture of a vertebrobasilar aneurysm), we
assumed the outcome of a rebleed of the aneurysm to be equal to
the outcome after a first rupture.25 26 Overall, the case
fatality rate of an aneurysmal rebleed is
80%,27 28 but many patients who rebleed have a poor
clinical condition from the outset and accordingly a small chance for
complete recovery. We used 80% as the upper limit for the case
fatality rate after rebleeding.27 28
Aneurysm Surgery
Surgical mortality and morbidity data associated with the
clipping of a vertebrobasilar aneurysm have been reported in
several series.29 30 31 32 33 We used the results of these series,
in which patients were graded according to the Hunt and Hess
scale,34 and pooled the case fatality and morbidity
outcome of the patients in Hunt and Hess grades 0, 1, and
2.31 32 33 We assumed that clipping the aneurysm
prevents further SAH.
Utilities
A subjective factor is the evaluation of the quality of life or
utilities of the 5 different outcomes. We assigned a utility of 0% to
the outcome death. Because a perimesencephalic hemorrhage does
not reduce quality of life,9 we assigned a utility of
100% to the outcome uncomplicated when no aneurysm is
present. A recent study indicates that most patients who recover
without handicap from an aneurysmal SAH still have a somewhat
reduced quality of life.12 We therefore assigned a utility
of 90% to the outcome disability with a patent aneurysm, after
complete recovery from a rerupture of the aneurysm or with a
successfully operated aneurysm (recovery). A permanent
disability from a single complication (disability-single) was valued at
65%, irrespective of the cause of the complication, and permanent
disability from 2 successive complications (disability-double), eg,
angiographic complication followed by morbidity from a surgical
complication, was valued at 50%. Thus, we considered a first
complication to have more impact on quality of life than a second
successive complication.
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Results |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Standard Analysis
Of the 4 different diagnostic options, the best strategy is CT angiography only, with an overall expected utility of 99.09 (Table 2
). The option of no further
investigation has a somewhat lower expected utility of 98.96, while the
option of DSA implies a decrease of expected utility to 98.22. The
option of CT angiography plus DSA has the lowest expected utility
(96.34). The smallest proportion of patients who have an uncomplicated
outcome and the largest proportion of death, disability-single,
disability-double, and recovery occur in the latter strategy. The CT
angiography only strategy gives the lowest risk of death, while no
further investigation yields a marginally greater proportion of
patients in good health and, understandably, the smallest proportion of
patients becoming disabled by complications.
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One-Way Sensitivity Analysis
The results of the sensitivity analyses indicate that over
a wide range of assumptions, CT angiography only is the optimal
approach of diagnosis in patients with perimesencephalic pattern of
hemorrhage (Table 3). When the
sensitivity of CT angiography is varied over its range, CT angiography
only remains the preferred diagnostic option. Only at a
very low sensitivity (<42%) is CT angiography only no longer the
preferred option. In that case, the strategy of no further
investigation becomes optimal. The threshold specificity of CT
angiography is 93%; below that threshold, the strategy of no further
investigation again has the highest utility. At a very low prevalence
of a vertebrobasilar aneurysm with a perimesencephalic pattern
of hemorrhage (<1.8%), it would be preferable to opt for no
further investigation. When the probability of the risk of permanent
neurological complication from DSA is varied over its full range, the
option of CT angiography only remains superior. Only at very low
probability of complications from DSA (<0.22%) does DSA become more
beneficial than CT angiography only. The utility assigned to becoming
disabled from a complication of DSA or operation also has impact on the
utility of CT angiography only. A utility of <49.6% would make no
further investigation the most beneficial strategy compared with CT
angiography only. The option of CT angiography plus DSA is under no
circumstances the preferred diagnostic strategy.
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Two-Way Sensitivity Analysis
Two-way sensitivity analysis demonstrates that the
specificity of CT angiography above which CT angiography only is the
preferred diagnostic strategy varies according to the
utility of disability from a single complication (disability-single)
(Figure 2A). If the specificity of CT
angiography is low, CT angiography only is the favored option only if
the utility of disability-single is high. In contrast, the sensitivity
of CT angiography may become quite low if the utility of
disability-single remains reasonably high (Figure 2A). A 2-way
sensitivity analysis shows that if specificity of CT
angiography falls below approximately 96%, the utility of recovery has
to remain high for CT angiography only to remain superior over no
further angiography (Figure 2B).
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Two-way sensitivity analysis also demonstrates that if the
prevalence of a vertebrobasilar aneurysm given a
perimesencephalic pattern of hemorrhage is low, CT angiography
only is more beneficial than the option of no further investigation
only if the specificity of CT angiography is high (Figure 2C).
To a lesser extent, the same applies to a 2-way sensitivity
analysis on the prevalence of vertebrobasilar aneurysms
and the sensitivity of CT angiography (Figure 2C). Finally, a
2-way sensitivity analysis on the specificity of CT angiography
and risk of complications from DSA shows that if the probability of
complications from DSA is >0.22%, specificity of CT angiography has
to be high for CT angiography only to remain the favored strategy over
the option of no further investigation (Figure 2D). However,
this analysis also shows that if the probability of
complications from DSA falls to <0.22% and specificity of CT
angiography falls to <96%, the DSA strategy would be the favored
strategy.
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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In this study we found that CT angiography only is the most beneficial approach in patients with SAH and a characteristically perimesencephalic pattern of hemorrhage on CT. DSA can be omitted in patients with a perimesencephalic pattern of hemorrhage and a negative CT angiogram.
The various outcomes of the different diagnostic strategies of a decision analysis are obtained by multiplying the risk and rates of a sequence of actions and events with the utilities assigned to the various outcomes. The difference between the expected utilities of CT angiography only and the other 3 diagnostic options in our decision analysis is small. However, the sensitivity analysis shows that variation across the plausible ranges of the estimates hardly alters the conclusion of our analysis. The preference for CT angiography only is not sensitive to small alterations in key probabilities.
Additionally, 2-way sensitivity analysis did not reveal specific scenarios within plausible ranges that might alter the conclusion but made it clear that the test characteristics of CT angiography and the specificity in particular should remain optimal. A systematic review reported an overall sensitivity for CT angiography ranging from 76% to 98% and specificity ranging from 85% to 100%.13 A recent study showed that CT angiography can accurately exclude and detect vertebrobasilar aneurysms, with a sensitivity and a specificity of 100%.1 The 97% sensitivity and specificity of CT angiography that we assumed are therefore plausible. We found that only at a sensitivity <42% and a specificity <93% is CT angiography only no longer the preferred option. Under these circumstances, the strategy of no further investigation has the best expected outcome. This indicates that limited specificity of CT angiography is no valid reason to favor the strategy of CT angiography plus DSA.
Since DSA is considered the gold standard for diagnosing cerebral aneurysms as the cause of SAH, we chose to use high estimates for the test characteristics of DSA. Sensitivity of 99.5% (ie, DSA fails to detect only 1 of 200 aneurysms present) and specificity of 100% of DSA are probably too optimistic. Combined data of studies showed that in patients with SAH and an initially negative DSA, 22 aneurysms were revealed in 145 repeated angiograms.35 When DSA is preceded by mostly negative CT angiography, sensitivity of DSA will be <99.5% because in that case the relatively large aneurysms will have been eliminated. Our assumptions of 90% sensitivity and specificity for DSA when preceded by CT angiography are probably still an overestimation.
From our own series of patients with perimesencephalic pattern of hemorrhage who underwent bilateral vertebral angiography, we derived a 2.6% risk of permanent neurological complication from DSA. In a review of 3 large series concerning the neurological complications associated with DSA, the complication rate for patients with SAH was 0.25%.36 A likely explanation for the higher complication rate in our series is that most patients in our series had to undergo 4-vessel angiography, including both vertebral arteries. In only approximately 30% is the contralateral posterior inferior cerebellar artery sufficiently visualized after injection in the contralateral vertebral artery. In the series included in the review, bilateral vertebral injections were not reported; in an unspecified proportion of patients bilateral carotid and left vertebral artery injections were performed, and in an unknown proportion only 1 or 2 carotid arteries were selectively injected.36
In our sensitivity analysis we found that only when the complication rate of catheter angiography is <0.22% is DSA more beneficial than CT angiography only. Such a low risk of complications will be difficult to reach in patients with a perimesencephalic pattern of hemorrhage given the need for 4-vessel angiography and the 0.25% risk in series where a proportion of patients underwent only carotid angiography.
Currently, in many centers vertebrobasilar aneurysms are treated by the endovascular coiling technique.37 38 This treatment probably results in a lower case fatality and morbidity than conventional surgical clipping.39 Such a lower complication rate will not influence the diagnostic strategies of DSA, CT angiography only, and CT angiography plus DSA since surgery occurs in all 3 strategies.
Velthuis et al1 proposed earlier that CT angiography is an adequate screening examination for vertebrobasilar aneurysms in patients with perimesencephalic pattern of hemorrhage and that DSA can be withheld in patients with this type of hemorrhage and negative CT angiography. Since vertebrobasilar aneurysms may arise from unusual locations, such as the distal posterior cerebral artery or vertebrobasilar artery junction, CT angiograms of patients presenting with a perimesencephalic pattern of hemorrhage should be meticulously assessed, including axial source images, to attain the accuracy assumed in our model.20
In conclusion, our decision analysis shows that in patients with a perimesencephalic pattern of hemorrhage on CT, CT angiography only is the best diagnostic strategy. DSA can be omitted in patients with a perimesencephalic pattern of hemorrhage, and negative CT angiography and should be performed only if uncertainty exists about the presence or location of a vertebrobasilar aneurysm on the CT angiogram.
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Acknowledgments |
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This study was supported in part by an established clinical investigator grant from the Netherlands Heart Foundation to Dr Rinkel.
Received May 16, 2000; revision received August 23, 2000; accepted August 23, 2000.
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