To assess the efficacy of MR angiography (MRA) in detecting small asymptomatic cerebral aneurysms in clinical examination of the brain (CEB), we investigated the MRA data of 7,665 cases in our CEB between July 1990 and June 1993. A 1.5T system (Sigma Advantage; GE Medical Systems) was used in this study. Of the 7,665 cases, 410 aneurysms in 360 cases (4.7%) were found on MRA. These 360 cases included 152 males (3.8% of 3,956 male cases) and 208 females (5.6% of 3,709 female cases); females were slightly more prevalent than males. Aneurysms were diffusely distributed in all generations of adults, but more common in the fifties of both sexes than in other generations. Of 410 aneurysms, 209 (50.9%) originated from the IC-ophthalmic artery junction (IC-Oph), 85 (20.7%) from the IC-posterior communicating artery junction (ICPC), 57 (13.9%) from the middle cerebral artery (MCA), and 24 (5.9%) from the anterior communicating artery. IC-Oph aneurysms counted for half of all aneurysms. The size of aneurysms ranged from 1 mm to 14 mm. Two hundred and seventy-four aneurysms (66.8%) were less than 3 mm in diameter, 109 (26.6%) were 4-6 mm, 23 (5.6%) 7-9 mm, and 4 (0.9%) over 10 mm. Twenty-seven aneurysms 1 mm in diameter were the smallest found in our CEB and were distributed to IC-Oph in 17 cases, ICPC in 7, MCA in 2, and internal carotid artery bifurcation in 1. Conventional cerebral angiography was performed in 121 aneurysms in 107 cases, for whom we scheduled operation. One hundred and nine aneurysms in 96 cases (90.1%) were confirmed by angiography, while there were 12 false-positive (9.9%) and 6 false-negative cases. The presence of these false aneurysms was due to limited performance of the modern MRA system; insufficient spatial resolution or disappearance of small vessels. We conclude that it is necessary to read not only MRA, but axial source images of MRA carefully in order to detect aneurysms smaller than 3 mm and to decrease false cases as much as possible.
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