This patient was referred for MRI investigation of a suspected intracranial cystic mass, after initially presenting with bizarre behavior. MRI demonstrates a large simple intraventricular cyst compressing the left hippocampus, which may be the cause of the patient's symptomatology.

The origin of these cysts is uncertain and can arise from a number of structures. Some are arachnoid cysts whereas others ependymal cysts, neuroepithelial cysts or very large choroid plexus cysts. Distinguishing between them on imaging is impossible.