Patients With Small, Asymptomatic, Unruptured Intracranial Aneurysms and No History of Subarachnoid Hemorrhage Should Generally Be Treated Conservatively

t is well known that cerebral aneurysms are surprisingly prevalent in normal individuals and is estimated to be between 3.6% to 6.0% of the population. 1 The essential paradox appears to be the dichotomy between the epidemiological data and surgical experience.Wiebers' study 2 suggests that patients with unruptured cerebral aneurysms Ͻ7 mm in diameter have a benign natural history, but this contrasts with the experience of neurosurgeons, such as Weir, who are confronted by a substantial proportion of their patients with subarachnoid hemorrhage because of small ruptured aneurysms. 3 How could this paradox be explained?It seems to us that we still have a very incomplete picture of the prevalence, size, distribution, and natural history of unruptured aneurysms over longer time epochs.Furthermore, it is quite possible that aneurysms may form quickly, as suggested by Weir, and rupture early during their expansion phase, although still quite small in diameter.The duration of this growth period to rupture is uncertain.There does seem to be reasonable evidence that aneurysms of Յ7 mm, once detected (at an uncertain time after their development) have a fairly low rate of rupture over a 5-year period. 2 Both clinicians and their patients, however, are concerned about lifetime risk, and long-term data are still lacking.In assessing the risks and benefits of intervention in a patient who is found to have an unruptured aneurysm, the treatment decision is also influenced by the current evolution in therapeutic strategies.In ruptured cerebral aneurysms, endovascular coiling was shown to be superior to surgery in a single randomized controlled trial with a relatively short follow-up of 12 months. 4 It seems likely that these technologies will continue to improve, which will further alter the risk/benefit ratio of intervention in individual patients.