title: Skull base CT: normative values for size and symmetry of the facial nerve canal, foramen ovale, pterygoid canal, and foramen rotundum.
abstract: OBJECTIVE
  Contrast-enhanced MRI is the mainstay for detecting pathology in the skull base foramina and nerve canals, through demonstration of abnormal enhancement. When MRI is contraindicated, or unable to differentiate tumor from non-neoplastic pathology, high-resolution skull base CT is indicated to assess for nerve canal or foramen widening, which is currently determined subjectively. The purpose of this study is to provide objective CT criteria that may help distinguish between normal asymmetry and pathologic nerve canal or foramen widening.
  
  
  METHODS
  Temporal bone CTs of 50 consecutive adults without facial or trigeminal nerve pathology were retrospectively reviewed. Short axis measurements were obtained in the axial plane for three segments of the facial nerve canal (labyrinthine, tympanic, and mastoid), foramen ovale, pterygoid canal and foramen rotundum on both sides in each subject. Descriptive statistics were obtained, and left-right asymmetry was calculated.
  
  
  RESULTS
  Nerve canal/foramen size was normally distributed across subjects, with a minimal amount of left-right asymmetry. The upper limits of the 95 % confidence interval for absolute left-right asymmetry were: 0.25, 0.21, and 0.15 mm for the labyrinthine, tympanic, and mastoid segments of the facial nerve canal, respectively; 0.62 mm for foramen ovale; 0.36 mm for pterygoid canal; 0.38 mm for foramen rotundum.
  
  
  CONCLUSIONS
  Relative asymmetry is more important than absolute size for determining nerve canal/foramen abnormality. These normative data may be useful adjuncts to subjective assessments of nerve canal/foramen size when using skull base CT to identify tumor.
authors: Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, 757 Westwood Plaza, Suite 1621D, Los Angeles, CA, 90095, USA. ali.sepahdari@gmail.com
authors: Ali R
authors: AR
authors: Sepahdari
authors: Sandy
authors: S
authors: Mong
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D016001:Confidence Intervals; D003287:Contrast Media; D005154:Facial Nerve / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008416:Mastoid / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D008875:Middle Aged; D015588:Observer Variation; D011856:Radiographic Image Enhancement; D012016:Reference Values; D012189:Retrospective Studies; D019291:Skull Base / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D013100:Sphenoid Bone / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult
chemical_list: D003287:Contrast Media