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: Radiology
[{'content': 'Delta sign on CT is seen in? \nSelect and explain. \nA. Gradenigo syndrome, B. Subdural hematoma, C. Extradural hematoma, D. Sagittal sinus thrombosis', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., Sagittal sinus thrombosis* The delta sign (or empty delta sign) is CT sign of dural venous sinus thrombosis of the superior sagittal sinus, where contrast outlines a triangular filling defect.", 'role': 'assistant'}]