Virtual arterial endoscopy as a diagnostic aid in a patient with basilar artery fenestration and thromboembolic pontine infarct.

Focal signal intensity loss of the basilar artery on MR angiograms obtained in a 69-year-old man was considered to be caused by an embolus, and thrombolytic therapy was initiated. On the follow-up MR angiograms, the same oval signal intensity loss of the basilar artery was observed. On the basis of a virtual endoscopic look into the basilar artery, the diagnosis of a rare vascular anomaly--a fenestration of the basilar artery--was confirmed and the presence of a thrombus at the site of the signal intensity loss was excluded.