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 64-year-old woman complains of gait imbalance, headache and deterioration of mental status over the past several months. Her vision is normal. A CT scan reveals hydrocephalus, but the lumbar puncture pressure is unexpectedly low. What does she have? \nSelect and explain. \nA. Meningitis, B. Normal-pressure hydrocephalus, C. Sigmoid sinus thrombosis, D. Echinococcus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Normal-pressure hydrocephalus is a condition seen in the elderly in which there is symmetrical enlargement of the entire ventricular system. When patients with this condition are studied by lumbar puncture, it is found that despite ventriculomegaly, the ICP is abnormally low. This syndrome presents with a characteristic triad of symptoms - dementia, ataxia, and urinary incontinence.', 'role': 'assistant'}]