[A distal posterior inferior cerebellar artery aneurysm in the fourth ventricle: a case report].

: The authors reported a case of a fourth ventricle aneurysm originating from the choroidal branch of the posterior inferior cerebellar artery (PICA). A 65-year-old woman became comatose following the acute onset of a severe headache and vomiting. She was moribund on admission, showing decerebrate posture. CT scan revealed a massive hematoma in the fourth ventricle up to the lateral ventricle. Extension of blood to the cisterna magna through the cerebellar vermis was also noted. Angiography demonstrated an aneurysm distally located on the right PICA across the midline. The aneurysm lodged in the choroid plexus which was exclusively fed by the right PICA was excised without difficulty through suboccipital craniectomy. Postoperative course was uneventful. She regained her full consciousness by two days after the operation, and was discharged with a minimal truncal ataxia. To our knowledge, this is the first report of a ruptured aneurysm developing in the choroid plexus of the fourth ventricle. Hemodynamic stress is speculated to be a causative factor of such a lesion.