This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'Bony clival erosion with inta-cranial calcification is seen in - \nSelect and explain. \nA. Sella chordoma, B. Craniopharyngioma, C. Medulloblastoma, D. Papilloma of the choroids plexus', 'role': 'user'}, {'content': "Answer: A \nExplanation: Chordomas\n\nChordomas are rare, slow growing, locally aggressive neoplasms of bone that arise from embryonic remnants of the notochord.\nThese tumors typically occur in the axial skeleton and are most common in the sphenooccipital region of the skull base and in the sacral regions.\nIn adults, 50 percent of chordomas involve the sacrococcygeal region, 35 percent occur at the base of the skull, and 15 percent are found elsewhere in the vertebral column,\xa0\nCraniocervical chordomas most often involve the dorsum sella, clivus, and nasopharynx.\nThey are associated with bone erosion.\nPurely intrasellar chordoma without bony erosions are very' uncommon.\nChordoma of the clivus causes erosion of the clivus and extend in the direction of the nasopharynx as well as posteriorly.", 'role': 'assistant'}]