This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Intracranial Space Occupying Lesion, Subject name: Medicine
[{'content': 'Thumb sign on CT head is seen in? \nSelect and explain. \nA. Chordoma, B. Metastasis, C. Glioblastoma multiforme, D. Astrocytoma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Thumb sign on CT head is seen in Chordoma. Sella Chordoma Presents with bony clivus erosion and local invasion. Calcification also occurs On FNAC- mucinous material obtained', 'role': 'assistant'}]