title: Surgical pitfalls encountered with the semi-implantable middle ear transducer ossicular stimulator (MET-Otologics).
abstract: OBJECTIVE
  To determine whether surgical pitfalls can be anticipated through a preoperative CT-Scan in case of middle ear implantation with a semi-implantable middle ear ossicular stimulator from Otologics (SIMOS). A second outcome measure was to assess the auditory gain obtained in the series.
  
  
  METHODS
  A retrospective analysis of 19 consecutive surgical procedure for a SIMOS implantations was achieved. Preoperative Ct-Scans were analyzed and several measurements of the mastoid were taken out from axial transverse views, ie. the distance between the incus and the cortical mastoid bone [d(i-c)], the distance between the sigmoid sinus and the incus [d(i-ss)], the distance between the sigmoid sinus and the cortical bone of the mastoid [d(c'-ss)]. On coronal images, the dura of the middle fossa was described as procident if it was lower than the head of malleus and/or body incus. Auditory gain was calculated on pure tone and speech audiometry with bisyllabic words.
  
  
  RESULTS
  All cases were successfully implanted. d(i-c) was on average at 33.1 +/- 2.6 mm in cases easy to implant. One case of contracted mastoid was difficult and led to the impaction of the sigmoid sinus. In this case the distance d(i-c) was shorter at 25 mm than the average minus 2 standard deviations of the others (27.9 mm). Also d(ss-c') was lower at 7 mm than the average minus 2 standard deviations of the others (7.6 mm). Two other cases led to difficult surgical procedures because of a low middle fossa dura. This too low middle fossa dura could be identified on preoperative coronal CT-scans in these two cases. Audiometric gains were remarkable, with an average of 39 +/- 16 dB. In case of severe sensorineural hearing loss the average gain was higher at 46 +/- 9 dB. Two revision-procedures were required, one for a device failure, the second because of skin alteration due to systemic inflammatory disease requiring corticosteroids. Mean follow-up was 50 +/- 22 months.
  
  
  CONCLUSIONS
  The SIMOS is a powerful middle ear implant that can undoubtedly give a huge audiometric gain. The implantation procedure requires a precise microsurgical operation that can be hampered by anatomical conditions of the petrous bone. A thorough examination of preoperative CT-scan is highly recommended in order to obtain measurements of the mastoid in axial views, and the analysis of the position of the middle fossa dura in coronal views.
authors.affiliation: CHU Gabriel Montpied, Universitary Hospital of Clermont-Ferrand, Department of Otolaryngology Head Neck Surgery, 30 place Henri Dunant, 63000 Clermont-Ferrand, France.
authors.forename: C
authors.initials: C
authors.lastname: Louvrier
authors.forename: A
authors.initials: A
authors.lastname: Montalban
authors.forename: B
authors.initials: B
authors.lastname: Lietin
authors.forename: J
authors.initials: J
authors.lastname: Gabrillargues
authors.forename: L
authors.initials: L
authors.lastname: Gilain
authors.forename: T
authors.initials: T
authors.lastname: Mom
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001301:Audiometry, Pure-Tone; D001302:Audiometry, Speech; D003051:Cochlea; D019929:Cochlear Implantation; D003054:Cochlear Implants; D004432:Ear, Middle; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007188:Incus; D008297:Male; D008307:Malleus; D008875:Middle Aged; D011300:Preoperative Care; D012189:Retrospective Studies; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D014159:Transducers; D016896:Treatment Outcome