title: Comparison of two radiologic methods for measuring the size and growth rate of extracanalicular vestibular schwannomas.
abstract: OBJECTIVE
  To compare two methods for measuring the size and growth rate of extracanalicular vestibular schwannomas: the method recommended in 1995 by the American Academy of Otolaryngology--Head Neck Surgery (AAO-HNS) and the maximum cerebellopontine angle (CPA) tumor diameter, i.e., the method often used in radiologic reports.
  
  
  METHODS
  Retrospective clinical study.
  
  
  METHODS
  Tertiary referral center.
  
  
  METHODS
  Fifty-four patients with a radiologic diagnosis of unilateral extracanalicular vestibular schwannoma whose tumors were managed conservatively for a mean duration of 39.8 months (range 12-194 months).
  
  
  METHODS
  The extracanalicular component was measured by use of high-resolution magnetic resonance imaging (2- to 3-mm axial slices) at 6- to 12-month intervals.
  
  
  METHODS
  Tumor diameter was calculated by two methods. In the AAO-HNS method, the axial image with the largest extracanalicular tumor diameter was selected, and the maximum anteroposterior (A-P) and medial-lateral (M-L) tumor diameters were calculated. The A-P diameter was calculated parallel to the posterior surface of the petrous temporal bone, and the M-L diameter was calculated perpendicular to it. The size of the tumor was calculated as the square root of the product of these two diameters. In the maximum CPA method, the maximum CPA tumor diameter in any direction was also measured.
  
  
  RESULTS
  There was no significant difference between the two methods for measuring the extracanalicular tumor size and growth rate, although the maximum CPA diameter method was consistently greater than the AAO-HNS method. There was a strong positive correlation between the two methods for assessing tumor size and growth. The A-P and M-L extracanalicular tumor diameters also showed a strong positive correlation, suggesting that the extracanalicular portion of vestibular schwannomas tends to enlarge equally in both these directions.
  
  
  CONCLUSIONS
  There is a strong positive correlation between these two methods for assessing both the tumor size and the growth rate of extracanalicular vestibular schwannomas. However, because vestibular schwannomas tend to grow in both the A-P and the M-L directions, this suggests that the AAO-HNS method is preferable.
authors.affiliation: Department of Otolaryngology, University Health Network, Toronto General Hospital, University of Toronto, Ontario, Canada.
authors.forename: R M
authors.initials: RM
authors.lastname: Walsh
authors.forename: A P
authors.initials: AP
authors.lastname: Bath
authors.forename: M L
authors.initials: ML
authors.lastname: Bance
authors.forename: A
authors.initials: A
authors.lastname: Keller
authors.forename: J A
authors.initials: JA
authors.lastname: Rutka
mesh_terms: D000328:Adult; D000368:Aged; D004431:Ear, External / Q000473:pathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009464:Neuroma, Acoustic / Q000175:diagnosis*; D012189:Retrospective Studies