The relation between aneurysm size and outcome in patients with subarachnoid hemorrhage
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Abstract
Article abstract The balance of risks of treatment for unruptured aneurysms might change if the prognosis after rupture depends on the size of the aneurysm. In a prospective series of patients with subarachnoid hemorrhage in whom aneurysmal size was measured by CT angiography performed on admission, poor outcome occurred more often in patients with large (≥10 mm) aneurysms (63%) than in patients with small (<10 mm) aneurysms (41%; RR = 1.5; 95% CI 1.0 to 2.2). The relative risk remained essentially the same after adjustment for age, gender, location of the aneurysm, and amount of cisternal blood.
After subarachnoid hemorrhage (SAH), half the patients die and 10 to 20% remain dependent on help.1 Neurologists and neurosurgeons therefore often advise preventive treatment for unruptured aneurysms, depending on the age of the patient, the perceived surgical risk, and the size of the unruptured aneurysm.2 Large aneurysms have a higher risk of rupture,3 but also a higher risk for complications of treatment.4 The decision on preventive operation might change if outcome is also influenced by the size of the aneurysm.
Until recently, the size of aneurysms could be determined only by means of conventional angiography, but this technique has important limitations for studying the relation between aneurysm size and outcome. It is usually not performed in patients who are in poor clinical condition and therefore not candidates for surgery. Also, the magnification factor of angiograms varies, and it is not routinely recorded. From July 1995 on, we have performed CT angiography (CTA) immediately after admission CT scan in all patients with SAH. This technique provides accurate data on aneurysm size,5 and enables us to study the relation between size and outcome.
Material and methods.
From July 1995 to March 1997, 138 patients with SAH were admitted to the Utrecht University Hospital. The diagnosis of SAH was based on demonstration of extravasated blood on CT or, if CT was negative, by xanthochromia in the CSF. Seventeen patients were excluded: 10 were moribund on admission, and contrast injection was withheld, and in 7 patients no aneurysm was found.
The size of the ruptured aneurysm was measured on CTA by indicating on the workstation the outer borders of the aneurysm on the screen. The computer calculated the distance in millimeters. We defined aneurysms as large if the diameter was at least 10 mm. The radiologist measured the size of aneurysm during the clinical assessment of the CTA, and was thus unaware of the final outcome of the patient.
We used the World Federation of Neurologic Surgeons (WFNS) scale to assess the clinical condition on admission.6 In the analysis we dichotomized between good (WFNS 1–3) and poor condition on admission. The amount of cirsternal blood was assessed by means of the grading scale described by Hijdra et al.7 The total amount of blood on this semiquantative scale ranges from 0 to 30. In the analysis this variable was dichotomized at the median. We classified the operation as difficult if procedures such as temporary occlusion of a parent artery or a bypass procedure had to be undertaken. We defined secondary ischemia as a gradual decrease in level of consciousness, appearance of focal signs, or both, for which other causes had been excluded. A rehemorrhage was defined as a sudden decrease in consciousness and an increased amount of blood on CT, compared with the previous scan. We assessed outcome at 3 months by means of the Glasgow Outcome Scale and dichotomized into poor (death, persistent vegetative state, or dependency) and good outcome (independent or good recovery).
In the comparison of outcome for patients with large and small aneurysms, we used relative risks (RR) and corresponding 95% CI. We used stratified analyses and logistic regression analyses to calculate adjusted RR and corresponding 95% CI.
Results.
The sizes of the ruptured aneurysms in the 121 patients ranged from 1.5 to 24 mm. The 27 patients with large aneurysms more often had a poor clinical condition on admission (RR = 1.96; 95% CI 0.98 to 3.9) and tended to have smaller amounts of extravasated blood on admission CT (table 1).
Characteristics on admission in patients with large (≥10 mm) and small (<10 mm) aneurysms at time of rupture
Patients with large aneurysms tended to be operated on less frequently (table 2), to have more rehemorrhages and fewer episodes of ischemia, and to die more often from the effect of the initial bleeding and secondary ischemia.
Clinical course and outcome in patients with large (≥10 mm) and small (<10 mm) aneurysms at time of rupture of the aneurysm
Seventeen (63%) of the 27 patients with a large aneurysm had a poor outcome, compared with 39 (41%) of the 94 patients with a small aneurysm (RR = 1.5; 95% CI 1.0 to 2.2). In stratified analyses (table 3), the worse outcome in the group with the large aneurysms was not markedly influenced by age, gender, location of the aneurysm, or amount of cisternal blood. Logistics regression analyses with these baseline characteristics did not change the OR by more than 0.15.
Stratified analyses
Discussion.
Patients with large aneurysms have a greater chance of poor outcome after SAH than patients with small aneurysms. Patients with large aneurysms more often have a poor clinical condition on admission but the risk of clinical and surgical complications is essentially the same as in patients with small aneurysms. These data suggest that the worse outcome in patients with large aneurysms is mainly caused by a greater initial impact of the hemorrhage. The lesser amount of cisternal blood in patients with large aneurysms seems not to substantiate this suggestion, but the amount of blood is a less powerful predictor for poor outcome than the clinical condition.8 We did not use the clinical condition on admission as adjustment factor because it is a factor in the causative pathway to poor outcome, in which situation adjustment is incorrect.
A limitation of our study is that 10 patients were moribund on admission and CTA was therefore not performed. Exclusion of these patients may have introduced a selection bias, but even if these 10 patients all would have had small aneurysms and a poor outcome, the outcome in the entire series would still be worse for patients with large aneurysms (RR = 1.34; 95% CI 0.94 to 1.90). We found one other study on aneurysm size and outcome; in that study no relation was found.9 Two factors may have introduced a bias toward patients with good outcome in that study. First, the study was performed in a tertiary care center; secondly, aneurysm size was assessed on conventional angiograms, and thus not in patients who are not candidates for operation because of a poor condition. Yet, in that study, patients with large aneurysms had a longer period of unconsciousness after the hemorrhage and patients with small aneurysms had a greater chance of complete recovery. The data of this previous study are therefore in agreement with our data.
In our series, patients with large aneurysms were less frequently operated. This implies that the poor outcome in these patients might partly be explained by an increase in frequency of rehemorrhage, but this was not the case (see table 2). The larger proportion of patients with large aneurysms who have not been operated can be explained by the worse clinical condition from the outset, and is therefore a consequence and not so much a causal factor for the poor outcome.
Acknowledgments
Acknowledgment
The authors thank Prof. J. van Gijn for critical review of this manuscript.
- Received September 13, 1999.
- Accepted in final form March 22, 2000.
References
- ↵Hop JW, Rinkel GJE, Algra A, van Gijn J. Case fatality rates and functional outcome after subarachnoid hemorrhage: a systematic review. Stroke 1997;28:660–664.
- ↵van Crevel H, Habbema JDF, Braakman R. Decision analysis of the management of incidental intracranial aneurysms. Neurology 1986;36:1335–1339.
- ↵Rinkel GJE, Djibuti M, Algra A, van Gijn J. Prevalence and risk of rupture of intracranial aneurysms. Stroke 1998;29:251–256.
- ↵Raaymakers TWM, Rinkel GJE, Limburg M, Algra A. Mortality and morbidity from surgery of unruptured aneurysms: a systematic review. Stroke 1998;29:1531–1535.
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- ↵Hijdra A, Brouwers PJAM, Vermeulen M, van Gijn J. Grading amount of blood on computed tomograms after subarachnoid hemorrhage. Stroke 1990;21:1156–1161.
- ↵Hop JW, Rinkel GJE, Algra A, van Gijn J. Initial loss of consciousness and risk of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage. Stroke 1999;30:2268–2271.
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