Abstract
We present a case of a large unruptured basilar tip aneurysm with concomitant hydrocephalus. Complete thrombosis of the aneurysm was observed after ventriculoperitoneal shunting. Analyzing preoperative and postoperative MRI and DSA images, we identified reduced intracranial pressure and widening of the aneurysm-artery inclination angle as possible factors influencing spontaneous thrombosis. To the best of our knowledge, this is the first report of aneurysm thrombosis occurring after CSF diversion.