Natural course of unruptured cerebral aneurysms varies according to the size, location, and shape


A study from Japan, published in late June in the New England Journal of Medicine, provides information on the natural history of unruptured cerebral aneurysms from over 6,600 aneurysms.

The UCAS Japan Investigators carried out the study and highlighted that the natural history of unruptured cerebral aneurysms has not been clearly defined. In general, there are many factors that influence the management of patients with unruptured intracranial aneurysms including the site, size, and group specific risks of the natural history balanced against the risk of treatment. In a 2003 article in Stroke, Peter A Rasmussen and Marc R Mayberg, from the Department of Neurosurgery, Cleveland Clinic Foundation, Cleveland, USA, wrote “the optimal management of patients with unruptured cerebral aneurysms remains controversial and requires a precise assessment of the risks for various treatment strategies and accurate knowledge of the natural history of the disease process.” Since it is clear that not all aneurysms are destined to rupture, any data on the factors that influence the natural course of unruptured cerebral aneurysms is important.

The UCAS Japan Investigators enrolled patients with recently identified, unruptured cerebral aneurysms in Japan from January 2001 until April 2004. The cohort included 5720 patients (mean age, 62.5 years; 68% women) who had saccular aneurysms that were 3mm or more in the largest dimension and who initially presented with no more than a slight disability. “Information on the rupture of aneurysms, deaths, and the results of periodic follow-up examinations were recorded,” the authors wrote.

There has been a rise in the detection of unruptured intracranial aneurysms due to an increased use of brain imaging.

The investigators of the Japanese study have written in the NEJM study that of the 6697 aneurysms studied, 91% were discovered incidentally. In terms of aneurysm location, 36% were in the middle cerebral arteries and 34% in the internal carotid arteries. The mean size of the aneurysms was 5.7±3.6mm.

Findings from the study:

  • During a follow-up period that included 11,660 aneurysm-years, ruptures were documented in 111 patients, with an annual rate of rupture of 0.95%
  • The risk of rupture increased with increasing size of the aneurysm
  • As compared with aneurysms in the middle cerebral arteries, those in the posterior and anterior communicating arteries were more likely to rupture
  • Aneurysms with an irregular protrusion of the wall of the aneurysm were also more likely to rupture