Patients With Small, Asymptomatic, Unruptured Intracranial Aneurysms and No History of Subarachnoid Hemorrhage Should Be Treated Conservatively
Section Editors: Geoffrey A. Donnan MD, FRACP Stephen M. Davis MD, FRACP
It 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’ study2 suggests that patients with unruptured cerebral aneurysms <7 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 ≤7 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.
For these reasons, we still believe that there is an enormous amount of work to do in terms of understanding the genesis, factors influencing rupture rates, and lifetime risk before we can be too rigorous about treatment algorithms for unruptured aneurysms. Fortunately, both protagonists are of our view that the decision about surgery needs to be individualized with numerous factors coming into play, including the general health of the patient, the patient’s age, the risks of the interventional treatment and, of course, the patient’s own wishes. Given the immediate risk of an intervention designed to modify outcome, the risk-tolerance of individual patients becomes an issue.5 Clearly, size isn’t everything!
- Received May 11, 2004.
- Accepted November 17, 2004.
Wiebers DO, Whisnant JP, Huston J 3rd, Meissner I, Brown RD Jr, Piepgras DG, Forbes GS, Thielen K, Nichols D, O’Fallon WM, Peacock J, Jaeger L, Kassell NF, Kongable-Beckman GL, Torner JC; International Study of Unruptured Intracranial Aneurysms Investigators. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet. 2003; 362: 103–110.
Molyneux A, Kerr R, Stratton I, Sandercock P, Clarke M, Shrimpton J, Holman R; International Subarachnoid Aneurysm Trial (ISAT) Collaborative Group. International Subarachnoid Aneurysm Trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised trial. Lancet. 2002; 360: 1267–1274.
Sarasin FP, Bounameaux H, Bogousslavsky J. Asymptomatic severe carotid stenosis: immediate surgery or watchful waiting? A decision analysis. Neurology. 1995; 45: 2147–2153.