Study suggests treating intracranial aneurysms larger than 5 mm



SAN DIEGO – Analyses of a single-center cohort of nearly 3,400 patients with unruptured aneurysms who underwent either treatment or observation suggest that aneurysms larger than 5 mm should be treated.

"Treatment, of course, has complications, and some patients deteriorate clinically. However, we find that unruptured aneurysm treatment-related complications leave no effect on function, as measured by modified Rankin Scale scores. On the other hand, once an aneurysm ruptures, there is a high incidence of death and disability. Based on that, we conclude unruptured aneurysms larger than 5 mm should be treated," Dr. Yuichi Murayama said at the annual meeting of the American Society of Neuroradiology.

In the cohort of 3,395 patients with unruptured intracranial aneurysms (UIAs), 28% were treated while the remaining 72% were managed conservatively and underwent biannual 3D computed tomography angiography (CTA). They were referred to Jikei University in Tokyo between January 2003 and December 2012.

Most UIAs were measured using 3D CTA because magnetic resonance angiography (MRA) was thought to be less accurate and more invasive. Patients were recommended for treatment (with either endovascular coiling or microsurgical clipping) if the aneurysm was larger than 5 mm and considered safely treatable, multiple aneurysms were present and one had previously ruptured, or there was a family history of subarachnoid hemorrhage. Endovascularly treated patients underwent MRA follow-up at 3, 6, and 12 months after treatment and then subsequently underwent annual MRA and magnetic resonance imaging (MRI) studies. Surgically treated patients had angiography at 12 months after treatment and then 3D CTA.

Almost 1,700 patients with UIAs who were not treated were followed over the 10-year period with CTA. Overall, 49 (2.9%) aneurysms ruptured, yielding an annual rupture rate of 0.8%/year. The average size of aneurysms in the treatment group was 7.8 mm, compared with 4.4 mm in the observation group. The frequency of treatment increased with size: 10% of small aneurysms (up to 4.9 mm in diameter), 50% of medium aneurysms (5.0-9.9 mm), and almost 100% of large (10.0-24.9 mm) and giant aneurysms (greater than 25 mm), reported Dr. Murayama, director of the center of endovascular surgery at Jikei University.

Rupture rates were 0.35%/year for small aneurysms, 2.2%/year for medium, 10.75%/year for large, and 50%/year for giant. Although the risk of rupture of small aneurysms is low, 17 small aneurysms ruptured within the observation period. Furthermore, Dr. Murayama said that while most ruptures occurred within the first 2 years of discovery, even apparently stable aneurysms might rupture after 2 years. The most common sites for aneurysm rupture were the anterior cerebral, middle cerebral, vertebral, and posterior communicating arteries.

About 200 additional patients were followed with MRA rather than CTA, Dr. Murayama said after the meeting. Ongoing analyses of the rupture rates in these patients may change the rupture rates for various aneurysm sizes, he said.

Dr. Murayama compared the results from his institution to the findings of another Japanese cohort in the UCAS study, which included 5,700 patients with almost 6,700 aneurysms enrolled from 283 medical centers (N. Engl. J. Med. 2012;366:2474-82). The annual risk of rupture for small aneurysms was 0.36%, very similar to that found by the Jikei group (0.35%). Similarly, the annual risk for 7- to 10-mm aneurysms was 1.7%, which was very similar to that found by the Jikei group (1.5%).

There was a more substantial difference between the two studies in the annual risk of rupture for aneurysms measuring 5-7 mm (0.5% in the UCAS cohort vs. 2.3% in the Jikei cohort). "For this size, the decision to treat is difficult because the risk of rupture is relatively low but treatment risk also exists. That is why, in our database, 50% of patients with 5- to 7-mm-sized aneurysms went to observation," Dr. Murayama said.

Using 3D CTA, Dr. Murayama addressed the question whether UIAs grow. In the Jikei cohort, 10% of aneurysms grew in size (defined as a change of 1 mm or more between the baseline measurement and follow-up). "If you see a change in morphology, treat without delay," he said.

Dr. Murayama reported no relevant financial relationships.

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