Microanatomical study of the area in which the facial nerve being easy to damage in mastoid surgery

Objective To study the microanatomy of the area in which the facial nerve being easy to damage in mastoid surgery, in order to provide microanatomical datas for the clinical works. Methods In 20 adult wet skull specimens (40 temporal bones), the segments of facial nerve and their adjacent structures in the area in which the facial nerve being easy to damage were observed according to operation of mastoid surgery. Results The length of the horizontal segment was (8.85 ± 1.01) mm (7.10-11.25 nun), the diameter was (1.88 ± 0.65) mm (1.55-1.90 mm); The angle opening towards anterior direction between horizontal segment and vertical segment was (115.50 ± 6.89°) (109.5°-128.6°); The vertical distance from the cochlearform process to this segment was (1.89 ± 0.58) mm (0.90-3.05 mm); The vertical distance from the midpoint of the base of stapes to this segment was (1.92 ± 0.52) mm (1.44-2.56 mm); The vertical distance from the head of the stapes to this segment was (2.30 ± 0.85) mm (1.97-3.11 mm); The angle towards posterior direction between horizontal segment of facial nerve and tympanic tegmen was (28.5°± 3.66°) (25.8°-31.5°); The diameter of the pyramidal segment of facial nerve was (1.89 ± 0.65) mm (1.56-1.88 mm); The distance between the su mmit of pyramidal segment of facial nerve and the apex of shor limb of incus was (2.55 ± 0.21) mm (2.10-2.90 mm); The distance from the su mmit to the eminence of the lateral semicircular canal was (2.86 ± 0.31) mm (2.23-3.56 mm); The diameter of the proximal part of vertical segment of facial nerve was (2.13 ± 0.13) mm (1.90-2.40 mm); The angle towards superior direction between verical segment of facial nerve and chorda tympani nerve was (38.60 ± 1.99°) (28.5°-52.5°); The vertical distance from the top of the pyramidal eminence to the vertical segment of the facial nerve was (2.05 ± 0.65) mm (1.85-2.36 mm). Conclusions The eminence of the lateral semicircular canal, short limb of incus, cochlearform process, tympanic tegmen, stapes, pyramidal eminence, chorda tympani nerve in the area are important landmarks to be located in mastoid surgery. The anatomic relations in this area are complicated and compact. Anatomical knowledge is very important to the surgery of this area. Key words: Facial nerve;  Mastoid; Microanatomy