Applied Anatomy Related To Cochlear Implantation Through Facial Recess Approach

ObjectionTo investigate the related parameters of temporal bone structure in the surgery of cochlear implantation through facial recess approach.MaterialLearns from wet head specimen,20ears of10adult body examples soaked in formalin, among which, there are14ears of7feminine examples and6ears of3masculine examples. Measure tool:The imitated stapes measure instrument compasses with long needle, divided precision0.01mm vernier calipers, surgical microscope, electric drill and conventional surgical instrument of otology.Methods1.Experiment Process:Simulating the surgical procedure of cochlear implantation through facial recess approach, open facial recess between facial nerve and chorda tympanic nerve, expose incudostapedial joint, pyramidalis eminence, underneath stapes, round window niche, round window, facial nerve in the horizontal segment and spoon tuber. Locate scala tympani inlet and expose the second cochlea turn, finally, enter tympanic scale. Measure the indexs that are setted before experiment in the above processes.2. Main Observation Indexs:Distance between suprameatal spinean and short pocess of incus. Distance between crotch of chorda tympani nerve and stylomastoid foramen. Distance between short process of incus and crotch of chorda tympani nerve. Distance between maximal width of the facial recess and short process of incus and crotch of chorda tympani nerve, respectively. The maximal width of the facial recess. The width of the facial recess at level of stapes. The width of the facial recess at level of round window. Distance between pyramidalis eminence and anterior round window. Distance between stapes and underneath round window. Distance between short process of incus and round window niche. Distance between stapes and round window niche. Distance between facial nerve in the perpendicular paragraph and round window niche. Minimal distance between implanting electrode and vestibular window. Distance between cochleariform process and round window niche. Distance between cochlear inserting the electrode array and the second cochlear turn underneath stapes. Distance between cochlear inserting the electrode array and the second cochlear turn.3. Measure point choice:The measure point of suprameatal spine is the root of stapes, anvil short foot is the terminal part,foramen stylomastoideum is inside entrance of the stylomastoid foramen, round window niche is the down-edge and up-edge, facial nerve in the perpendicular paragraph is the front-edge, pyramidalis eminence is the root of stapes, the front-edge of round window membrane is the perpendicular line, the down-edge of round window membrane is the perpendicular line, the width of the facial recess is the shortest distance between facial nerve and chorda tympani nerve, cochleariform process is its down-edge, the up-edge of round window membrane is the down-edge of round window niche, the entrance of tympanic canal is the down-edge of the basilar membrane, oval window is its down-edge and the second turn is the down-edge of the basilar membrane. The distance between facial nerve in the perpendicular paragraph and round window niche is the shortest.4. Statistical Disposal:All data take the average of3times measure. Results are expressed by means x±s(min～max) mm.Results1. The vertical segment of the facial nerve is not in a straight line vertical downlink, but first outside the curvature of an arch, and then within the next stylomastoid hole and out of temporal bone, thus forming a curvature of the maximum position of the vertical segment of the facial nerve. The overall trend is the gradual shift of the anterior medial, lateral, and travel back and forth direction of the "C"-shaped bend. The maximal radian position of vertical segment of facial nerve is about6.28mm from short process of incus.2. One of horizontal segment of facial nerve bony canal agenesis; Two of the vertical segment of facial nerve forward and impact the exposure of the round niche. Two of the chorda tympani nerve come from foramen stylomastoideum; one of chorda tympani nerve variation. one of the round window niche variation.3. The position of suprameatal spine into short process of incus was12.44±1.58mm (8.35～14.46mm). Distance between crotch of chorda tympani nerve and stylomastoid foramen was2.67±1.50mm (0～5.22mm). Distance between short process of incus and crotch of chorda tympani nerve was15.22±2.67mm (10.35-20.24mm). The location of maximal width of the facial recess into short process of incus, crotch of chorda tympani nerve were6.28±1.27mm (14.23±8.88mm),9.81±2.16mm (5.55～13.76mm), respectively. The maximal width of the facial recess was2.73±0.64mm (1.61～4.01mm). The width of the facial recess at level of stapes and round window were2.48±0.68mm (1.42～3.70mm),2.24+0.61mm (1.28～3.33mm), respectively. Distance between pyramidalis eminence and anterior round window was2.22±0.70mm (1.46～4.16mm). Distance between stapes and underneath round window was2.16±0.48mm (1.24±2.88mm). Distance between short process of incus and round window niche was5.91±0.84mm(4.49～8.02mm). Distance between stapes and round window niche was2.11±0.58mm (1.31～3.79mm). Distance between facial nerve in the perpendicular paragraph and round window niche was6.70±0.61mm (5.02～7.78mm). Minimal distance between implanting electrode and vestibular window was2.12±0.56mm (1.24～3.43mm) Distance between cochleariform process and round window niche was3.79±0.56 mm (3.07～5.23mm). The position of cochlear inserting the electrode array into the second cochlear turn was2.25±0.43mm (1.35～2.93mm) underneath stapes. The location of cochlear inserting the electrode array into the second cochlear turn was2.28±0.62mm (1.54～4.09mm) inferior to pyramidalis eminence.ConclusionCutting the facial recess and locating of the inlet of the scala tympani is the key to the surgery of cochlear implantation through facial recess approach, related to the success of the operation or not. The trauma of facial nerve is one of quite serious illness complication of the cochlear implantation. This study suggests that the width of facial recess on the maximal curvature of the vertical segment of the facial nerve is the largest, the probability of facial nerve and chorda tympani nerve injury is the smallest when cutting facial recess, and this position is the started cutting and fully opening the facial recess position. Underneath stapes and pyramidalis eminence is relatively easy to find and relatively constant anatomical landmark. When the round window niche exposed bad or should not be exposed and cochlea turn ossification, we can refer to underneath stapes and pyramidalis eminence to locate the inlet of the scala tympani. These parameters provide a reference value to determine the position of cochlear inserting the electrode array into the scale tympani and be beneficial for opening facial recess firstly to avoid the traumatic of facial nerve and chorda tympani nerve when surgery.