History: The patient was a 53 year-old man who presented with a 3 week old history of headache associated with walking and vision changes. Imaging studies demonstrated prominent dilation of lateral ventricles and a cyst in the third ventricle. On MRI scan, the cyst is 13 x 9 x 9 mm and is located at the roof of the third ventricle. It has an enhancing mural nodule. The cyst was removed and generated the specimen here.

What is your diagnosis?  Discussion