title: Implanting straight into cochlea risks the facial nerve: a Cartesian coordinate study.
abstract: OBJECTIVE
  To describe the straight-into-cochlea line that affords the best access for an electrode array to enter via the round window, and how this line relates to the facial nerve, the incus, and mastoid size. The straight-into-cochlea line is important to minimize the cochlear trauma and maximize the likelihood of placement into the scala tympani.
  
  
  METHODS
  High-resolution CT scans were obtained for ten craniums with the extremes of large (N = 5) and small (N = 5) mastoid pneumatization; the specimens were from a series of 41 ear normal craniums. Using FIJI, a publicly available software program, the straight-into-cochlea insertion line was determined by defining the x-y-z coordinates of the middle of the round window and a point 6.0 mm into the cochlea on its centrifugal wall. Then, from the extended straight-into-cochlea insertion line, we determined the shortest perpendicular distance to the middle of the fallopian canal, and from that "fallopian point" to the apex of the posterior process of the incus.
  
  
  RESULTS
  We found good repeatability of measurements. We found the extended straight-into-cochlea insertion lines routinely close to or in the midst of the fallopian canal (50 % ≤ 1.0 mm). We found the lines 4.7-7.8 mm from the apex of the posterior process of the incus. Line positions relative to "fallopian point" and incus showed no relation to mastoid pneumatization. For the distance "fallopian point" to incus, bilateral symmetry was suggested.
  
  
  CONCLUSIONS
  Using landmarks registered in an x-y-z coordinate system, straight-into-cochlea insertion via the round window puts the facial nerve at risk.
authors.affiliation: Department of Otolaryngology, Head and Neck Surgery, Emory University School of Medicine, 2015 Uppergate Drive NE, Atlanta, GA, 30329, USA.
authors.forename: Anita S
authors.initials: AS
authors.lastname: Deshpande
authors.affiliation: Department of Otolaryngology, Head and Neck Surgery, Emory University School of Medicine, 2015 Uppergate Drive NE, Atlanta, GA, 30329, USA. ntodd@emory.edu.
authors.forename: N
authors.initials: N
authors.lastname: Wendell Todd
mesh_terms: D000328:Adult; D019929:Cochlear Implantation / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods*; D003054:Cochlear Implants / Q000009:adverse effects*; D003198:Computer Simulation; D020220:Facial Nerve Injuries / Q000517:prevention & control*; D006801:Humans; D007188:Incus / Q000033:anatomy & histology; D008416:Mastoid / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000294:innervation; D011183:Postoperative Complications / Q000517:prevention & control*; D012307:Risk Factors; D012405:Round Window, Ear / Q000033:anatomy & histology / Q000294:innervation*; D014057:Tomography, X-Ray Computed
keywords: Cochlear implant; Electrode; Facial nerve; Mastoid pneumatization; Proximity bias; Round window