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: ENT
Delta-sign is seen in ? 
Select and explain. 
A. Petrositis, B. Acute mastoiditis, C. Sigmoid sinus thrombosis, D. Glomus tumor
C: Sigmoid sinus thrombosis
Answer: C: Sigmoid sinus thrombosis 
Explanation: Ans. is 'c' i.e., Sigmoid sinus thrombosis Contrast-enhanced CT scan can show sinus thrombosis by typical delta-sign. It is a triangular area with rim enhancement, and central low density area is seen in posterior cranial fossa on axial cuts. Delta-sign may also be seen on contrast enhanced M RI.