This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
Most difficult site to remove cholesteatoma, i.e. sinus tympani is related with: 
Select and explain. 
A. Tympanic segment of facial nerve, B. Mastoid segment of facial nerve, C. Epitympanum, D. Hypotympanum
B: Mastoid segment of facial nerve
Answer: B: Mastoid segment of facial nerve 
Explanation: (b) Mastoid segment of facial nerve(Ref. Cummings, 6th ed., 2193)The sinus tympani area is the hidden area of the middle ear and is the most common site of residual cholesteatoma. It lies medial to the bulge of the vertical part of fallopian canal, i.e. mastoid segment of facial nerve. It being a hidden area, it is the most difficult site to remove cholesteatoma.It can be visualised through the posterior tympanotomy approach.