The Thickness of the facial Nerve Sheath Consistently Varies by Region in Its Intra-Tympanic Course on Cadaveric Study.

In cases of cholesteatoma and keratosis obturans involving the vertical FN, the disease process can be separated from the FN sheath because of the sheath thickness in this region. Disease in the horizontal segment involves a thinner sheath and separating the disease process from the nerve is more difficult in this area.