title: Mirror aneurysms: a reflection on natural history.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Neurology, Mayo Clinic, Rochester, Minnesota 55905, USA. imeissner@mayo.edu
authors.forename: Irene
authors.initials: I
authors.lastname: Meissner
authors.forename: James
authors.initials: J
authors.lastname: Torner
authors.forename: John
authors.initials: J
authors.lastname: Huston
authors.forename: Michele L
authors.initials: ML
authors.lastname: Rajput
authors.forename: David O
authors.initials: DO
authors.lastname: Wiebers
authors.forename: Lyell K
authors.initials: LK
authors.lastname: Jones
authors.forename: Robert D
authors.initials: RD
authors.lastname: Brown
mesh_terms: D017542:Aneurysm, Ruptured / Q000175:diagnosis / Q000235:genetics / Q000401:mortality; D002423:Cause of Death; D002533:Cerebral Angiography; D016009:Chi-Square Distribution; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D002532:Intracranial Aneurysm / Q000175:diagnosis* / Q000235:genetics / Q000401:mortality; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012737:Sex Factors; D013345:Subarachnoid Hemorrhage / Q000175:diagnosis* / Q000235:genetics / Q000401:mortality