Applied Anatomic Study On The Cochlea And Ossicular Chain

Background Ossicular chain is located in tympanic cavity, composing by malleus, incus and stapes. Many reasons contribute to the destruction of ossicular chain, resulting in conduction deafness. Reconstruction of ossicular chain is the effective method to heal the conduction deafness. The dates about reconstruction of ossicular chain are abundant,therapeutic effect is stable,but the rate of exodus and ineffective are the matter. Dates about ossicular chain are centered in the stapes, others are seldom. Dates on the anatomy of ossicular chain are important to the achievement ratio of operation,decrease the rate of exodus,resulting in the elevation of audibility threshold.Cochlea getting its name because of the shape to resemble volute, is a projecting in an anterior direction of from the vestibule. Cochlea is composed of modiolus and cochear spiral canal. Osseous spiral lamina around modiolus,divide the cochear spiral canal into scala vestibule, scala tympani, and cochlear duct. The scala vestibule and scala tympani communicate with each other through helicotrema. Cochlear duct occupying the middle part of the cochlear canal between the scala vestibule and the scala tympani, is a spiral blind tube fixed firmly to the internal and external walls of the cochlear canal of the bony labyrinth. The spinal organ, the receptor of auditory stimuli, is situated on the basilar membrane of the cochlear duct. Artificial cochlea is a auditory prosthesis to stimulate the cochlear function used to cure the extremely heavily neurosensory deafness,containing two parts,language treater and implant button. The key technique is drilling hole to implant the electrode into SV or ST.The procedures are follows:1. Rubbing a bony bed above acoustic duct to place the voice receiver and stimulator.2. The classic mastoid process approach: contouring the circumscription, enter tympanic cavity through facial recess, wearing out the bone before anterior magin of cochlear window to expose the ST and insert the electrode into ST or insert the electrode through secondary tympanic membrane.3. Middle cranial fossa approach: opening a window on temporal squama, draft the brain, dissociate the cerebral dura mater, expose the undersurface of middle cranial fossa. Rubbing the surface bone of basal turn,insert the electrode into cochlea.Objective To provide anatomic data for reconstruction of auditory ossicular chain and cochlear implantation via tympanic cavity and the middle cranial fossa,and find the method of locating the cochleostomy site(CS).Methods Micranatomical study was carried out on 30 sides of human temporal bones to measure the location of umbo in tympanic membrane,the distance between handle of malleus and head of stapes,the diameter of handle of malleus and so on. Observing and measuring bony spiral lamina below promontory,including its location,course and adjacent structures. Observing and measuring the depth from the crista petrosa to the superior portion of the basal turn (SPBT) and distances from the facial,greater petrosal nerves and the round window.Results1. The distance between handle of malleus and stapes head was (2.38±0.19)mm (2.00~2.70mm), the point selecting for measuring were outer margin of handle of malleus and head of stapes.2. The cross section form of inferior one-third of the handle of malleus was triangle, the anteroposterior diameter of handle of malleus was (0.79±0.12)mm, the exterior and interior diameter was (0.58±0.10)mm at the crook point; angle of line of handle of malleus laid (83.24±8.33)°(66~98°) posteroinferior to zygomatic arch.3. The long axis of prosthesis form (27.60±1.75)°(24.6~30.2°) angle with the perpendicular of stapes.4. The dependablity between the malleus-stapes distance and transverse diameter of tympanic cavity,the location of umbo in tympanic membrane,the diameter of manubrium mallei,angle of line of manubrium mallei and arch of zygoma are not statistically significant.5. The basal turn spiral lamina below promontory can be divided into three segments: the hook segment of (1.52±0.16) mm,the anteroinferior round window segment of (3.83±0.37)mm and the forwarding segment of (2.70±0.36) mm by two hinge points of which one was located at anterior of the junction of superior margin and anterior border of RW,the other was located at anteroinferior of the round window.6. The plane of anteroinferior round window segment of BSL lay(51.00±5.97)°anteroinferior to horizontal segment of the facial nerve and comparative permanently meet posterior margin of stapes head; Made posterior margin of stapes head as a fixation point and draw a line on promontory lay (51.00±5.97)°anteroinferior to horizontal segment of the facial nerve, then this line can be thought as the projection of anteroinferior round window segment of BSL on promontory.7. The depth from the petrosal crest to SPBT of the cochlea was (8.58±2.28)mm. Distances from the cochleostomy site to the fundus of internal acoustic meatus(IAM),to the greater superficial petrosal nerve(GSPN),to the labyrinthine portion of the facial nerve(FN),and to the superior semicircular canal(SSC) was (1.47±0.30)mm, (3.88±0.52)mm, (2.80±0.26)mm, (9.46±1.01)mm respectively.8. The length of scala tympani from the cochleostomy site to the round window was (12.03±1.26)mm.9. The bend portion of internal carotid artery (ICA) located medial and inferior to the basal turn of the cochlea. The bony interval between the cochlea and the ICA canal was (1.54±0.47)mm,the depth from SPBT to the ICA was (6.67±2.07)mm.Conclusion1. The distance between handle of malleus and stapes,the diameter of handle of malleus are important to the design of prosthesis.2. The long axis of prosthesis form less than a 30°angle with the perpendicular of stapes,the strength contributed to inner ear is about eighty-nine percent of virgin power,the strength contributed to transversal is forty-six percent.3. The basal turn spiral lamina below promontory can be divided into three segments (the hook segment, the anteroinferior round window segment and the forwarding segment) by two hinge points.4. The projection of anteroinferior round window segment of BSL and the features exhibited in its course provide reference for locating the basal turn scala tympani and offer firm anatomical basis for minimal invasive intervention during cochlear implantation.5. Greater petrosal nerve was identification of cochleostomy, the labyrinthine portion of the facial nerve was the important anatomic structure should be protected.