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Robert D. Brown Jr., David O. Wiebers, James C. Torner and W. Michael O'Fallon

✓ The purpose of this study was to determine the symptoms at presentation and the incidence of intracranial hemorrhage (ICrH) caused by intracranial vascular malformations (IVMs) in a defined population. The authors used the Mayo Clinic medical records linkage system to detect all cases of IVM among residents of Olmsted County, Minnesota, during the period 1965 through 1992. Forty-eight IVMs were detected over the 27-year period. Twenty-nine of the 48 patients were symptomatic at presentation. The most common presenting symptom was ICrH, which was present in 20 patients, 69% of all symptomatic cases. Sixty-five percent of arteriovenous malformations (AVMs) presented with ICrH. The most common subtype of ICrH was intracerebral hemorrhage, which was found in nine of 20 patients; the second most common subtype was subarachnoid hemorrhage. The peak occurrence of hemorrhage was during the fifth decade of life. The age- and gender-adjusted occurrence of a first ICrH from an IVM among residents of Olmsted County, Minnesota was 0.82 per 100,000 person years (95% confidence interval 0.46–1.19). There was no increase in the detection of IVM-related ICrH throughout the study period. The 30-day mortality rate following ICrH was 17.6% for patients with an AVM and 25% for all patients with IVMs. This study provides unique data on symptoms at presentation and the incidence of ICrH and hemorrhage subtypes from IVMs on a population basis.

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Wouter I. Schievink, Eelco F. M. Wijdicks, David G. Piepgras, Chu-Pin Chu, W. Michael O'Fallon and Jack P. Whisnant

✓ The first 48 hours after aneurysmal subarachnoid hemorrhage are critical in determining final outcome. However, most patients who die during this initial period are not included in hospital-based studies. We investigated the occurrence of subarachnoid hemorrhage in a population-based study to evaluate possible predictors of poor outcome. All patients diagnosed with aneurysmal subarachnoid hemorrhage between 1955 and 1984 were selected for analysis of mortality in the first 30 days using the medical record—linkage system employed for epidemiological studies in Rochester, Minnesota. One hundred and thirty-six patients were identified. The mean age of these 99 women and 37 men was 55 years. Rates for survival to 48 hours were 32% for the 19 patients with posterior circulation aneurysms, 77% for the 87 patients with anterior circulation aneurysms, and 70% for the 30 patients with a presumed aneurysm (p < 0.0001). Rates for survival to 30 days were 11%, 57%, and 53%, respectively, in these three patient groups (p < 0.0001). Clinical grade on admission to the hospital, the main variable predictive of death within 48 hours, was significantly worse in patients with posterior circulation aneurysms than in others (p < 0.0001).

The prognosis of ruptured posterior circulation aneurysms is poor. The high early mortality explains why posterior circulation aneurysms are uncommon in most clinical series of patients with subarachnoid hemorrhage. The management of incidentally discovered intact posterior circulation aneurysms may be influenced by these findings.

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Jack P. Whisnant, Sara E. Sacco, W. Michael O'Fallon, Nicolee C. Fode and Thoralf M. Sundt Jr.

✓ The objective of this study was to assess the effect of referral bias on survival in patients with subarachnoid hemorrhage (SAH). The characteristics of 49 patients with aneurysmal SAH from a single community were compared with those of 328 patients referred from outside the community, all treated in the same medical care setting. In addition, referral patients who received surgery were compared by differential survival analysis with those still awaiting surgery at Days 1 to 3, Days 4 to 10, and Days 11 to 15.

There was a dramatic difference in the 30-day survival rate between referral patients (83%) and community patients (59%), but most of the difference had occurred by the 2nd day after SAH. In the referral patients, the variables present at first medical attention that were found to have an independent effect on survival were clinical grade, presence of coma, number of days from SAH to referral, diastolic blood pressure, and patient age. There was a higher survival rate at 1 year for patients who were surgically treated compared with those awaiting surgery for each of the three time periods. Patients who underwent early surgical treatment had a 1-year survival rate almost identical to that of patients with late surgery.

Referral patients had a better early survival rate than did community patients because the referral group did not include patients who died and some who were in poor clinical condition before the opportunity for referral. The differential survival analysis described provides a new method for estimating survival for treated and untreated patients with SAH.

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Robert D. Brown Jr., David O. Wiebers, Glenn Forbes, W. Michael O'Fallon, David G. Piepgras, W. Richard Marsh and Robert J. Maciunas

✓ The authors conducted a long-term follow-up study of 168 patients to define the natural history of clinically unruptured intracranial arteriovenous malformations (AVM's). Charts of patients seen at the Mayo Clinic between 1974 and 1985 were reviewed. Follow-up information was obtained on 166 patients until death, surgery, or other intervention, or for at least 4 years after diagnosis (mean follow-up time 8.2 years). All available cerebral arteriograms and computerized tomography scans of the head were reviewed. Intracranial hemorrhage occurred in 31 patients (18%), due to AVM rupture in 29 and secondary to AVM or aneurysm rupture in two. The mean risk of hemorrhage was 2.2% per year, and the observed annual rates of hemorrhage increased over time. The risk of death from rupture was 29%, and 23% of survivors had significant long-term morbidity. The size of the AVM and the presence of treated or untreated hypertension were of no value in predicting rupture.

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David O. Wiebers, Jack P. Whisnant, Thoralf M. Sundt Jr. and W. Michael O'Fallon

✓ The authors report the results of a long-term follow-up study of 130 patients with 161 unruptured intracranial saccular aneurysms. Their findings suggest that unruptured saccular aneurysms less than 10 mm in diameter have a very low probability of subsequent rupture; The mean diameter of the aneurysms that subsequently ruptured was 21.3 mm, compared with a diameter of 7.5 mm for aneurysms defined after rupture at the same institution. Part of the explanation for this discrepancy may be that the size of the filling compartment of the aneurysm decreases after rupture. There is also evidence from the present study that intracranial saccular aneurysms develop with increasing age of the patient and stabilize over a relatively short period, if they do not initially rupture, and that the likelihood of subsequent rupture decreases considerably if the initial stabilized size is less than 10 mm in diameter. Consequently, the critical size for aneurysm rupture is likely to be smaller if rupture occurs at the time of or soon after aneurysm formation. There seems to be a substantial difference in potential for growth and rupture between previously ruptured and unruptured aneurysms.