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: Orthopaedics
[{'content': 'Chordoma can occur over all the following sites, except - \nSelect and explain. \nA. Rib, B. Clivus, C. Sacrum, D. Vertebral body', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Chordoma occurs only in vertebrae and clivus\xa0\nChordoma\n\nChordoma is a rare\xa0malignant tumour\xa0originating from the\xa0remnants of the primitive notochord.\nAs the vertebrae develop, notochord disappears and in adults, the normal remnant of notochord is nucleus pulpous of the intervertebral disc. In chordoma, this embryonic notochordal foci remains inside the vertebral body and forms tumours.\nIt occurs in adult males after 50 years.\nIt commonly occurs in the sacrococcygeal or in the sphere-occipital regions. The sacrum is the most common site: - Sacrum 50% clivus (35%), cervical thoracic/lumbar (15%).\nMost of them occur in vertebral bodies.', 'role': 'assistant'}]