MRI locates a posterior fossa aneurysm in the fourth ventricle.

We report a rare case of a ruptured aneurysm of the choroidal branch of the left posterior inferior cerebellar artery (PICA) located in the fourth ventricle. Digital subtraction angiography revealed this PICA aneurysm but the exact location remained unknown. The unique location in the fourth ventricle was subsequently shown by magnetic resonance imaging (MRI). The patient died and the final diagnosis was confirmed by autopsy. To our knowledge, this is one of the few reported cases of a PICA aneurysm in the fourth ventricle and the only one which was confirmed by the combination of MRI and autopsy.