title: Intracranial aneurysm enlargement on serial magnetic resonance angiography: frequency and risk factors.
abstract: OBJECTIVE
  Size of an unruptured intracranial aneurysm (UIA) may be an important risk factor for rupture. Accordingly, serial noninvasive imaging is commonly used to assess untreated UIA for enlargement. Few data exist regarding the frequency and predictors of enlargement. We obtained this information from a group of patients followed with serial MR angiography (MRA).
  
  
  METHODS
  We retrospectively identified 165 patients with 191 UIA followed with serial MRA. Fusiform aneurysms, UIA <2 mm, and UIA that were surgically or endovascularly treated before the first MRA were excluded. MRA was performed using 1.5-T and 3-T MRI. Maximal diameter was determined on MRA source images. Multivariate regression analysis was used to determine independent risk factors for growth.
  
  
  RESULTS
  Twenty aneurysms (10%) grew over a median follow-up period of 47 months. Frequency of enlargement was 6.9%, 25%, and 83% for aneurysms <8 mm, 8 to 12 mm, and >or=13 mm, respectively (P<0.001 for trend). Of the variables we evaluated, original aneurysm diameter (OR, 1.28 per mm; 95% CI, 1.07 to 1.58) was the only independent predictor of enlargement. Aneurysms >or=8 mm in diameter were at highest risk for enlargement (OR, 7.25; 95% CI, 1.96 to 27.1). There was a trend toward increased risk of enlargement in patients with multiple aneurysms (OR, 2.50; 95% CI, 0.86 to 7.53).
  
  
  CONCLUSIONS
  Over a median follow-up period of 47 months, 10% of UIA enlarged. Larger aneurysms had a significantly increased risk of enlargement. The likelihood of enlargement was highest in aneurysms with diameters >or=8 mm. However, a clinically significant proportion of small aneurysms grow, and this growth can be detected by serial MRA.
authors.affiliation: Departments of Neurology, Mayo Clinic, Rochester, Minn 55905, USA.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Burns
authors.forename: John
authors.initials: J
authors.lastname: Huston
authors.forename: Kennith F
authors.initials: KF
authors.lastname: Layton
authors.forename: David G
authors.initials: DG
authors.lastname: Piepgras
authors.forename: Robert D
authors.initials: RD
authors.lastname: Brown
mesh_terms: D000368:Aged; D017542:Aneurysm, Ruptured / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D002532:Intracranial Aneurysm / Q000453:epidemiology* / Q000473:pathology*; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D015588:Observer Variation; D012189:Retrospective Studies; D012307:Risk Factors