| Objective: To study the microsurgical anatomy of facial nerve from cerebellopontine angle segment to stylomastoid foramen and its surroundings in detail, so as to provide anatomic parameters for clinical surgical procedures of facial nerve. Methods: We operated on ten adult cadaver heads(20 sides)fixed in 10% formalin by mimicking the approach combined transmastoid and middle cranial fossa under surgical microscope,exposed the facial nerve from cerebellopontine angle segment to stylomastoid foramen, the different segment and anatomic landmarks of facial nerve and its surroundings were observed and measured. Results: The facial nerve from the point left brainstem to stylomastoid foramen were divided into five segments named cerebellopontine angle segment,internal acoustic meatus segment,labyrinthine segment,tympanum segment and mastoid segment. The cerebellonpontine angle segment and internal acoustic meatus segment paralleled the vestibulocochlear nerve. The labyrinthine segment is the thinest and shortest, With the diameter of 1.47±0.08(mm) and the length of 2.64±0.37(mm), and is closely related with cochlear and supperior semicircular canal.The length and diameter of tympanum segment is 10.75±0.98(mm), 1.94±0.15(mm).The mastoid segment, 14.31±1.71(mm) long, 2.37±0.18(mm)wide,leaves the cranium from stylomastoid foramen.The important and perpetual anatomic landmarks looking for facial nerve in the course of operation are horizontal semicircular canal,digastric ridge,facial recess,cochleariform process,tarin foramen, arcuate eminence and foramen spinosum. Conclusion: The important and perpetual anatomic landmarks looking for facial nerve in the course of operation are horizontal semicircular canal,digastric ridge,facial recess,cochleariform process,tarin foramen, arcuate eminence and foramen spinosum.Learning the anatomic landmarks and characteristics of the facial nerve by heart would help to look for and protect the nerve in the course of operation.
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