Basilar artery fenestrations detected by MR angiography.

Basilar artery (BA) fenestrations are the most frequently observed fenestrations of the cerebral arteries. Our goal was to examine the magnetic resonance (MR) angiographic incidence, location, and characteristic configuration of BA fenestration. Between April 1996 and March 2000, 600 cranial MR angiographies were performed at our institution. The majority of the patients examined had or were suspected to have cerebrovascular disease. We retrospectively reviewed these 600 MR angiograms. A 1.5 Tesla scanner was used in all studies, and maximum intensity projection (MIP) images obtained using the three-dimensional time-of-flight (3D-TOF) technique were displayed stereoscopically. Ten BA fenestrations (1.7%) were detected on MR angiograms. In 87 cases from the early period, the vertebrobasilar (VB) junction was unfortunately not included in the imaging slices. Eight of the 10 fenestrations were located at the proximal BA: six of them were small with a slit-like shape, and two were relatively large with a convex-lens-like shape. A small fenestration was located at the distal BA, and the remaining one was a total duplication of the BA. We stress that knowledge and recognition of BA fenestration are useful and important in the interpretation of cranial MR angiography. Since saccular aneurysms are reported to arise frequently at BA fenestration, the VB junction should be included in the imaging slices of routine cranial MR angiography.