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
Mastoid reservoir phenomenon is positive in: 
Select and explain. 
A. CSOM, B. Petrositis, C. Coalescent otitis media, D. Coalescent mastoiditis
D: Coalescent mastoiditis
Answer: D: Coalescent mastoiditis 
Explanation: Mastoid reservoir phenomenon is the latent infection in the mastoid resulting from inadequate treatment of ASOM. (Also called as masked /latent mastoiditis). It is a slow process of destruction of mastoid air cells without acute features.