Initial experience in evaluating the prevalence of unruptured intracranial aneurysms detected on 3-tesla MRI.

Background: Given the very poor outcome of ruptured intracranial aneurysms, detection and treatment of unruptured intracranial aneurysms by a less invasive examination have become important. For this purpose, 3-tesla (3T) magnetic resonance imaging (MRI) is the most suitable candidate, owing to its high signal/noise ratio and frequency resolution. However, few reports have investigated the prevalence of intracranial aneurysms with high-tesla MRI. Here, we evaluated the prevalence of intracranial aneurysms and the effectiveness of a 3T MRI system in their detection.

Methods: During a 1-year period, a total of 3,414 consecutive patients undergoing MR angiography with 3T MRI for the first time were enrolled. Diagnosis of intracranial aneurysm was made by two neuroradiologically trained medical doctors under complete blinding to patient information. When intracranial aneurysm was suspected, volume-rendering images were created for more accurate diagnosis.

Results: Surprisingly, 317 unruptured intracranial aneurysms were identified in 286 of 3,414 cases (8.4%); 151 unruptured aneurysms (47.6%) occurred in the internal carotid artery, 85 (26.8%) in the middle cerebral artery, 54 (17.0%) in the anterior cerebral artery, and 27 (8.5%) in the posterior circulation. Of these, 152/317 (47.9%) were <3 mm, 104 (32.8%) ranged from 3 to 5 mm, 5 (11.0%) from 5 to 7 mm, and 26 (8.2%) were >7 mm. No significant difference in size was seen among the four locations.

Conclusions: For the first time, this study assessed the detection rate of intracranial aneurysms using 3T MRI. Results showed a higher detection rate than previously documented. The reason for this higher rate is likely the improved ability of this modality to detect unruptured aneurysms in the internal carotid artery and those <3 mm.