Is the aspect ratio a reliable index for predicting the rupture of a saccular aneurysm?

OBJECTIVE: The present retrospective study was undertaken to prove the reli ability of the aspect ratio (aneurysm depth to aneurysm neck width) for pre dicting an aneurysmal rupture. The aspect ratio is considered a better geom etric index than aneurysm size for determining the intra-aneurysmal blood f low. METHODS: We measured the aspect ratios and the sizes of aneurysms, as deter mined by examining angiographic films magnified 1.4 x, in 129 patients with ruptured aneurysms and in 72 patients with 78 unruptured aneurysms. After categorizing the aneurysms into four groups on the basis of their locations (aneurysms of the anterior communicating artery, middle cerebral artery, i nternal carotid artery-posterior communicating artery [ICA-PComA], and othe r aneurysms), a statistical analysis of ruptured and unruptured aneurysms w as performed. RESULTS: The mean aneurysm size was found to be statistically significant i n the aneurysms at the ICA-PComA and in locations excluding the anterior co mmunicating artery, the middle cerebral artery, and the ICA-PComA. However, the mean aspect ratio was statistically significant at all four locations. In patients with ruptured aneurysms, no ruptured aneurysms with an aspect ratio of less than 1.0 were found. The distribution of the ruptured group v ersus the unruptured group with an aspect ratio of less than 1.6 at each lo cation was 13 versus 79%, respectively, at the anterior communicating arter y, 11 versus 58% at the middle cerebral artery, 11% versus 85% at the ICA-P ComA, and 7 versus 81% at other locations. CONCLUSION: The aspect ratio between ruptured aneurysms and unruptured aneu rysms was found to be statistically significant, and almost 80% of the rupt ured aneurysms showed an aspect ratio of more than 1.6, whereas almost 90% of the unruptured aneurysms showed an aspect ratio of less than 1.6. This s tudy therefore suggests that the aspect ratio may be useful in predicting i mminent aneurysmal ruptures.