This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous topics, Subject name: ENT
Halo sign is positive and handkerchief test is negative in: 
Select and explain. 
A. CSF Rhinorrhoea, B. Deted nasal septum, C. Nasal Myiasis, D. Choanal atresia
A: CSF Rhinorrhoea
Answer: A: CSF Rhinorrhoea 
Explanation: To distinguish CSF rhinorrhoea from simple rhinorrhoea of rhinitis the following tests can be done: 1)Handkerchief test:Mucus stiffens the handkerchief but CSF does not. 2)Halo sign/Target sign: This test is useful when CSF rhinorrhoea is associated with epistaxis (in the immediate period after trauma). A drop is put on Whatman's filter paper. The blood in the drop produces a central circle and if CSF is present in the drop it produces a halo around the blood circle.