A 15-year-old boy complains of right-sided weakness and gait impairment. A CT scan shows a large, non-enhancing cyst in the posterior cranial fossa, with an enhancing tumor nodule in the left cerebellum. What is the most likely diagnosis?

Cystic astrocytoma's are neoplasms of the CNS. They usually consist of a large, non-enhancing cyst on the wall of which is an enhancing tumor nodule. They are most commonly found within the substance of the cerebellar hemispheres of children and young adults. A Rathke's cleft cyst is a remnant of the embryologic Rathke's pouch. These are found within the sella turcica.