This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Otosclerosis, Subject name: ENT
Carhart's notch is seen in- 
Select and explain. 
A. Meneire's disease, B. Otosclerois, C. Acousticneuroma, D. Glomus tumour
B: Otosclerois
Answer: B: Otosclerois 
Explanation: Ans. is 'b' i.e., Otosclerois Pure tone audiometry in otosclerosiso Shows loss of air conduction, more for lower frequencies with characteristic rising patterno Bone conduction is normal. However in some cases, there is a dip in bone conduction curve which is maximum at 2000 Hz (2 KHz) and is called the Carhart's notcho Dip in bone conduction in otosclerosis (Carhart's notch) - 2000 Hzo Dip in noise induced hearing loss (Acoustic dip) - 4000 Hz