Mirror aneurysms: a reflection on natural history

Clinical article

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Object

Investigators conducting the International Study of Unruptured Intracranial Aneurysms, sponsored by the National Institutes of Health, sought to evaluate predictors of future hemorrhage in patients who had unruptured mirror aneurysms. These paired aneurysms in bilateral arterial positions mirror each other; their natural history is unknown.

Methods

Centers in the US, Canada, and Europe enrolled patients for prospective assessment of unruptured intracranial aneurysms. Central radiological review confirmed the presence or absence of mirror aneurysms in patients without a history of prior subarachnoid hemorrhage (SAH) (Group 1). Outcome at 1 and 5 years and aneurysm characteristics are compared.

Results

Of 3120 patients with aneurysms treated in 61 centers, 376 (12%) had mirror aneurysms, which are more common in women than men (82% [n = 308] vs 73% [n = 1992], respectively; p <0.001) and in patients with a family history of aneurysm or SAH (p <0.001).

Compared with patients with nonmirror saccular aneurysms, a greater percentage of patients with mirror aneurysms had larger (>10 mm) aneurysms (mean maximum diameter 11.7 vs 10.4 mm, respectively; p <0.001). The most common distribution for mirror aneurysms was the middle cerebral artery (34% [126 patients]) followed by noncavernous internal carotid artery (32% [121]), posterior communicating artery (16% [60]), cavernous internal carotid artery (13% [48]), anterior cerebral artery/anterior communicating artery (3% [13]), and vertebrobasilar circulation (2% [8]). When these patients were compared with patients without mirror aneurysms, no statistically significant differences were found in age (mean age 54 years in both groups), blood pressure, smoking history, or cardiac disease. Aneurysm rupture rates were similar (3.0% for patients with mirror aneurysms vs 2.8% for those without).

Conclusions

Overall, patients with mirror aneurysms were more likely to be women, to report a family history of aneurysmal SAH, and to have larger aneurysms. The presence of a mirror aneurysm was not an independent predictor of future SAHs.

Abbreviations used in this paper:ISUIA = International Study of Unruptured Intracranial Aneurysms; SAH = subarachnoid hemorrhage; TICS = Telephone Interview for Cognitive Status.

Article Information

Address correspondence to: Irene Meissner, M.D., Department of Neurology, Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905. email: imeissner@mayo.edu.

Please include this information when citing this paper: published online March 9, 2012; DOI: 10.3171/2012.1.JNS112120.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Comparison of sizes of mirror aneurysms (MA) versus nonmirror aneurysms (non-MA). Frequencies of aneurysms within size categories (maximum diameter) are compared between mirror and nonmirror aneurysms.

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    Comparison of locations of mirror aneurysms versus nonmirror aneurysms. AC = anterior cerebral artery; Acom = anterior communicating artery; Cav = cavernous internal carotid artery; IC = internal carotid artery; Pcom = posterior communicating artery; VBP = vertebrobasilar circulation.

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    Comparison of behavioral risk factors and comorbid conditions in patients with mirror aneurysms versus nonmirror aneurysms. OCs = oral contraceptive medications.

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    Survival curves of patients with mirror aneurysms versus patients with nonmirror aneurysms. Poor outcome is defined as a TICS score of less than 27 or a Rankin score of 3 to 5; the denominator for outcome is based on number of patients with known status at the end of the follow-up period.

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