ABSTRACT
<p><b>BACKGROUND</b>Fenestration of the proximal anterior cerebral artery (ACA) A1 segment is a rare anatomic variation. The purpose of the this study was to report the incidence of fenestration in the proximal segment of the anterior cerebral artery and to delineate its configurations on cranial MR angiography.</p><p><b>METHODS</b>Magnetic resonance angiography (MRA) was performed in 762 patients using 1.5 T imagers during the period July 2007 through September 2008. All images were obtained by the three-dimensional time-of-flight (3D TOF) technique. Volume rendering (VR) images in the horizontal rotation view were displayed stereoscopically. The presence of fenestration in the proximal segment of the anterior cerebral artery was identified and evaluated retrospectively by MRA.</p><p><b>RESULTS</b>Six patients (four men and two women, 15 to 63 years of age, median age 50 years) had proximal ACA fenestration. The appearance rate of ACA fenestration was 0.8% (6/762). All 6 fenestrations were located at the A1 segment: three of them were with a slit-like shape and three were with a convex-lens-like shape, 5 of the right A1 segment, 1 of the left A1 segment.</p><p><b>CONCLUSION</b>Recognizing ACA fenestration is important to interpret cranial MR angiographys and helpful to make a plan for neurosurgical procedures or neurological intervention.</p>