This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
[{'content': 'Delta-sign is seen in \nSelect and explain. \nA. Petrositis, B. Acute mastoiditis, C. Sigmoid sinus thrombosis, D. Glomus tumor', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Delta-sign is seen in sigmoid sinus thrombosis. Contrast-enhanced CT scan can show sinus thrombosis by typical delta sign. It is a triangular area with rim enhancement, and the central low-density area is seen in a posterior cranial fossa on axial cuts. "Delta sign" may also be seen on contrast-enhanced MRI. (Ref: Textbook of diseases of ENT, PL Dhingra, 7th edition, pg no. 92,93)', 'role': 'assistant'}]