[Location of tympanic segment and mastoid segment of facial nerve and prevention of prosopoplegia in operations].

OBJECTIVE: To study the location of facial nerve and prevent facial nerve injury in middle ear surgery according to dissection of temporal bone and experience of middle ear surgery. METHOD: Thirty sides of temporal bones were exposed tympanic and mastoid segment of facial nerve with facial nerve decompression. The course of facial nerve was located by the markers of middle ear. RESULT: Tympanic segment of facial nerve passed between horizontal semicircular canal and stapes,then superior and anterior to the cochleariform process. Mastoid segment of facial nerve located in posterior wall of tympanic cavity. The mastoid segment of facial nerve travelled below the level of horizontal semicircular canal and annulus membrane tympani, and the extension line of its posterior margin and posterior-one-third of horizontal semicircular canal intersected to form an included angle (117.04 +/- 2.42) degrees. External genu of facial nerve located anterior and inferior to the horizontal semicircular canal. The shortest distance was (1.97 +/- 0.53) mm between middle point of horizontal semicircular canal and facial nerve, (1.03 +/- 0.29) mm between incus short process and facial nerve, (0.93 +/- 0.25) mm between cochleariform process and facial nerve, (1.18 +/- 0.42) mm between head of stapes and facial nerve, (3.08 +/- 0.28) mm between tympani sulcus and facial nerve at the vestibule window level, and (2.13 +/- 0.34) mm between tympani sulcus and facial nerve at round window level, respectively. CONCLUSION: Horizontal semicircular canal carina, incus short process, stapes, annulus membrane tympani and cochleariform process are ideal landmarks of tympanic and mastoid segment of facial nerve, which are helpful in middle ear surgery.