The risk of intracranial saccular aneurysm enlargement determined by serial MR Angiography

106 Background and Purpose: To determine the frequency of unruptured intracranial aneurysm enlargement using serial MR angiography, and to determine if there are factors predicting change in aneurysm size. Methods: We retrospectively reviewed MR angiography studies performed between January 1991 and December 1999. Fifty-seven patients had 62 unruptured, untreated saccular aneurysms. The ratio of females to males was 2.6: 1. An average of 3 measurements of the maximal dimension as measured on source images was defined as the aneurysm size. Both the mean and median aneurysm diameter was 5 mm (range 2–15 mm). An aneurysm was defined to have enlarged if it increased in size by more than 1 mm when the size of the aneurysm was less than 5 mm and more than 2 mm when the aneurysm was equal to or larger than 5 mm. The mean and median time between studies was 50 months and 47 months respectively, with a range of 17–90 months. Results: No aneurysm ruptured during the period of follow-up. Four (7%) of the aneurysms increased in size with the median time to aneurysm growth of 40 months (range 23–66 months). None of the aneurysms less than 9 mm diameter increased in size. Four of the 9 aneurysms (44%) 9 mm or larger increased in size. Factors which predicted aneurysm growth includes size (p = 0.002), and multiple lobes or daughter sacs (p = 0.02). Aneurysm location did not predict an increased risk of enlargement. Conclusions: Patients with medium or large size aneurysms and multiple lobes or daughter sacs may be at increased risk for aneurysm growth and should be considered for follow up imaging if left untreated.