Annual rupture risk of growing unruptured cerebral aneurysms detected by magnetic resonance angiography

Clinical article

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In this paper, the authors' goals were to clarify the characteristics of growing unruptured cerebral aneurysms detected by serial MR angiography and to establish the recommended follow-up interval.


A total of 1002 patients with 1325 unruptured cerebral aneurysms were retrospectively identified. These patients had undergone follow-up evaluation at least twice. Aneurysm growth was defined as an increase in maximum aneurysm diameter by 1.5 times or the appearance of a bleb.


Aneurysm growth was observed in 18 patients during the period of this study (1.8%/person-year). The annual rupture risk after growth was 18.5%/person-year. The proportion of females among patients with growing aneurysms was significantly larger than those without growing aneurysms (p = 0.0281). The aneurysm wall was reddish, thin, and fragile on intraoperative findings. Frequent follow-up examination is recommended to detect aneurysm growth before rupture.


Despite the relatively short period, the annual rupture risk of growing unruptured cerebral aneurysms detected by MR angiography was not as low as previously reported. Surgical or endovascular treatment can be considered if aneurysm growth is detected during the follow-up period.

Abbreviations used in this paper:ACoA = anterior communicating artery; ICA = internal carotid artery; MCA = middle cerebral artery; MRA = magnetic resonance angiography; SAH = subarachnoid hemorrhage.

Article Information

Address correspondence to: Takashi Inoue, M.D., Department of Neurosurgery, Kohnan Hospital, 4-20-1 Nagamachiminami, Taihaku-ku, Sendai, Miyagi 982-8523, Japan. email:

Please include this information when citing this paper: published online April 27, 2012; DOI: 10.3171/2012.4.JNS112225.

© AANS, except where prohibited by US copyright law.



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    Case 11. Magnetic resonance angiograms. A: A 5.0-mm-diameter right ICA aneurysm is seen on admission. B and C: Slight growth of the aneurysm is seen 3 (B) and 9 (C) months later. D: Fifteen months later, the aneurysm diameter was 8.0 mm, which was defined as a growing aneurysm.

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    Case 14. Magnetic resonance angiograms showing a small right MCA aneurysm on admission (upper), and obvious growth of the aneurysm 6 months later (lower, arrow).

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    Case 7. A and B: Magnetic resonance angiograms showing a 1.6-mm-diameter ACoA aneurysm on admission (A). The aneurysm had grown to 3.8 mm in diameter 9 months later (B). C and D: Intraoperative photographs showing the thin and reddish aneurysm wall (arrow) and bleeding due to rupture (arrowhead) (C) and clipping of the aneurysm (D).


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