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
Delta sign on CT is seen in? 
Select and explain. 
A. Gradenigo syndrome, B. Subdural hematoma, C. Extradural hematoma, D. Sagittal sinus thrombosis
D: Sagittal sinus thrombosis
Answer: D: Sagittal sinus thrombosis 
Explanation: 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.