This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Surgery
[{'content': "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? \nSelect and explain. \nA. An arachnoid cyst, B. A cystic astrocytoma, C. Rathke's cleft cyst, D. Glioblastoma multiforme", 'role': 'user'}, {'content': "Answer: B \nExplanation: 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.", 'role': 'assistant'}]