Microanatomic Study Of Petrous Part Of Temporal Bone And Internal Auditory Canal By Middle Fossa Approach

Objective Observe and measure the bone structures of middle cranial fossa and petrous part of temporal bone. To supply anatomic basis for preserving facial nerve and cochlear nerve in the removal of acoustic neurinoma by middle fossa approach.Method Ten adult cadaveric heads fixed with formalin were used, red pigment were injected into the internal artery. Fixing these specimen on the operating table with headrest. A seven centimetres length skin incision is made in front of ear and perpendicular to the zygomatic root. A two multiply three bone-window is made while use the zygomatic root as the center. Use the bite-bone pincers made the bone-window parallel the zygomatic root. Lift the cerebral dura mater to exposure greater superficial petrosal nerve, facial hiatus and arcuate eminence. Use fisch's method to exposure internal auditory canal. To whet the outside bone at the back of arcuate eminence till to find the blue line which the surperior semicircular canal is below it. Then made a 60° angle to inside by take the surperior semicircular canal as the center, and whet the bone to the dirction of inside and bottom, until exposure the crest wall of internal auditory canal. Find Bill's crest , recognize facial nerve and vestibular nerve, whet the bone of the crest wall and open the cerebral dura mater at the outside. Observe anatomic structures of petrous part of temporal bone and internal auditory canal by microscope. After the operation take away the brain, reserve the cerebral dura mater and petrous part of temporal bone, exposure the cochlea, vestibule, geniculate ganglion etc, and measure the datas.Results Surperior semicircular canal mostly under the front of arcuate eminence, their distance is between 0~3.26mm. The angle between internal auditory canal and surperior semicircular canal is about 59.10±1.70°. The length of internal auditory is 9.85±0.91mm, and the thickness from inside to outside of back wall of internal auditory is 7.82-3.86mm.Conclusion Middle fossa approach can expose far-laternal end of internal auditory canal enough. And it is valid method to remove little acoustic neurinoma and preserve facial nerve and cochlear nerve on the foundation of defined the anatomy in petrous part of temporal bone.