The Natural History of Unruptured Intracranial Aneurysms

J Mocco, M.D.; Ricardo J. Komotar, M.D.; Sean D. Lavine, M.D.; Philip M. Meyers, M.D.; E. Sander Connolly, M.D.; Robert A. Solomon, M.D.


Neurosurg Focus. 2004;17(5) 

In This Article

Abstract and Introduction

Since the publication of preliminary results from the International Study of Unruptured Intracranial Aneurysms in 1998 there has been a great deal of debate concerning the natural history of these lesions and their attendant risk of aneurysmal subarachnoid hemorrhage. Therefore, the authors reviewed a selected number of crucial studies concerning this topic to determine the best evidence-based estimate of a rupture rate for these lesions. Based on this analysis, the yearly risk of bleeding for an unruptured intracranial aneurysm is estimated to be approximately 1% for aneurysms 7 to 10 mm in diameter. This risk of rupture increases with aneurysm size and it likewise diminishes as the size of the lesion decreases. This general rule serves as a reasonable interpretation of the results reported in the current body of literature.

Over the past 5 years there has been a great deal of contention regarding the appropriate management of unruptured intracranial aneurysms. The kindling for this heated debate was the publication of preliminary results from the ISUIA[1] in the New England Journal of Medicine in December of 1998. Much of the discussion has centered on the natural history of unruptured aneurysms and the attendant risk of aneurysmal SAH. The ISUIA investigators made claims regarding the risk of aneurysmal SAH from small (< 10 mm) aneurysms that were drastically lower (by a factor of 10–20) than what had been generally accepted previously. The result has been an enormous volume of impassioned editorials, balanced discussion, and new attempts at evidence-based assessment.