title: Cochlear duct length-one size fits all?
abstract: OBJECTIVE
  Recent studies demonstrated the utility of high-resolution computed tomography (HRCT) scans in measuring basal cochlear length and cochlear insertion depths. These studies showed significant variations in the anatomy of the cochlea amongst humans. The aim of our study was to investigate for gender and racial variations in the basal turn length of the human cochlea in an Asian population.
  
  
  METHODS
  HRCT temporal bone data from year 1997 till 2012 of patients with normally developed cochleae who reported with otologic disease was obtained. Reconstruction of the full basal turn was performed for both ears. The largest distance from the midpoint of the round window, through the midmodiolar axis, to the lateral wall was measured (distance A). Length of the lateral wall of the cochlea to the first turn (360°) was calculated and statistically analyzed.
  
  
  RESULTS
  HRCT temporal bone data from 161 patients was initially obtained. Four patients were subsequently excluded from the study as they were of various other racial groups. Study group therefore comprised of 157 patients (314 cochleae). Mean distance A was statistically different between the two sides of the ear (right 9.09mm; left 9.06mm; p=0.0069). Significant gender and racial differences were also found. Mean distance A was 9.17mm in males and 8.97mm in females (p=0.0016). The racial groups were Chinese (39%), Malay (38%) and Indian (22%). Between racial groups, mean distance A was 9.11mm (Chinese), 9.11mm (Malays) and 8.99mm (Indians). The mean basal turn lengths ranged from 19.71mm to 25.09mm. With gender factored in, significant variation in mean basal turn lengths was found across all three racial groups (p=0.04).
  
  
  CONCLUSIONS
  The view of the basal turn of the cochlea from HRCT is simple to obtain and reproducible. This study found significant differences in basal cochlear length amongst male and female Asian patients, as well as amongst various racial groups. This has implications for cochlear electrode insertion as well as electrode array design.
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, Changi General Hospital, Singapore.
authors.forename: J F
authors.initials: JF
authors.lastname: Thong
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, Changi General Hospital, Singapore. Electronic address: yongming@singnet.com.sg.
authors.forename: D
authors.initials: D
authors.lastname: Low
authors.affiliation: Department of Radiology, Changi General Hospital, Singapore.
authors.forename: A
authors.initials: A
authors.lastname: Tham
authors.affiliation: Department of Radiology, Changi General Hospital, Singapore.
authors.forename: C
authors.initials: C
authors.lastname: Liew
authors.affiliation: Department of Radiology, Changi General Hospital, Singapore.
authors.forename: T Y
authors.initials: TY
authors.lastname: Tan
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, Changi General Hospital, Singapore.
authors.forename: H W
authors.initials: HW
authors.lastname: Yuen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002681:China; D003051:Cochlea / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D005006:Ethnicity; D005260:Female; D006801:Humans; D007194:India; D008296:Malaysia; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D013701:Temporal Bone / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*