Anterior cerebral artery variations detected by MR angiography

Introduction: From anatomical and angiographic studies, it is well known that there are several variations of the anterior cerebral artery (ACA). However, ACA variations have rarely been studied by magnetic resonance (MR) angiography. The purpose of this study was to investigate not only the type, location, configuration, and incidence of ACA variations, but also coexisting arterial pathology such as aneurysms detected by cranial MR angiography. Methods: We retrospectively reviewed cranial MR angiography images of 891 patients at our institution. All images were obtained with one of two 1.5-T scanners using the three-dimensional time-of-flight technique. Maximum intensity projection (MIP) images in the horizontal rotation view were displayed stereoscopically. We reviewed these horizontal MIP images, inferosuperior MIP images, and source images, and identified variations of the ACA. Results: We found 50 instances (5.6%) of unilateral A1 segment aplasia, 27 (3.0%) of three A2 segments, 18 (2.0%) of an unpaired A2 segment, and 11 (1.2%) fenestrations of the A1 and/or A2 segment. Seven anterior communicating artery (ACoA) aneurysms and one ACA territory embolic infarction were found among the 50 patients with unilateral A1 segment aplasia. One ACoA aneurysm and one pericallosal infarction were found in the 27 patients with three A2 segments. Two distal ACA aneurysms were detected among the 18 patients with an unpaired A2 segment. No associated aneurysm was seen at the fenestrations. Conclusion: Although the clinical significance of ACA variations is usually minor, an associated aneurysm is found relatively frequently. Thus, recognizing ACA variations during the interpretation of cranial MR angiograms is important.