title: The natural history of asymptomatic thoracic disc herniations.
abstract: METHODS
  Magnetic resonance imaging was used to determine the natural history of asymptomatic thoracic disc herniations.
  
  
  OBJECTIVE
  To determine whether thoracic disc herniations change in size over time.
  
  
  BACKGROUND
  Based on previous work by the authors of the present study, the incidence of asymptomatic thoracic disc herniations is approximately 37%. The natural history of thoracic disc herniations is unknown. The natural history of lumbar and cervical disc herniations in symptomatic individuals who become asymptomatic has been shown in multiple studies frequently to result in a decrease in size of the herniation.
  
  
  METHODS
  Twenty patients with 48 asymptomatic thoracic herniations previously diagnosed with magnetic resonance imaging underwent repeat magnetic resonance imaging using sagittal T1-weighted spine echo and axial multiplanar gradient refocused images at each thoracic disc level from T1 to T12 for a mean follow-up period of 26 months. Midsagittal canal diameter was recorded, and disc herniation square area was measured using a computer-assisted digitizing program. Disc herniations were categorized according to percentage of canal compromise. The change in size of the disc herniations over time was analyzed.
  
  
  RESULTS
  All patients remained asymptomatic during the follow-up period. A total of 48 disc herniations were identified from the original magnetic resonance images. There were 21 small (0-10% canal compromise) disc herniations, 20 medium (> 10-20%) disc herniations, and seven large (> 20%) disc herniations. Of the 21 small disc herniations, 18 showed no significant change in size, whereas three showed a measurable increase in size. Of the 20 medium-sized disc herniations, 16 showed either a small or no change in size, one showed a significant increase in size, and three showed a significant decrease in size. Of the seven large disc herniations, three demonstrated no change in size, and four demonstrated a significant decrease in size. In addition, five new disc herniations were detected in four patients; one was small, and four were moderate in size.
  
  
  CONCLUSIONS
  Based on the results of this study, the authors believe that asymptomatic disc herniations may well exist in a state of relative flux, yet exhibit little change in size and remain asymptomatic. There was a trend, however, for small disc herniations either to remain unchanged or increase in size and for large disc herniations often to decrease in size.
authors.affiliation: Orthopedic Center, Ltd., Scottsdale, Arizona, USA.
authors.forename: K B
authors.initials: KB
authors.lastname: Wood
authors.forename: J M
authors.initials: JM
authors.lastname: Blair
authors.forename: D M
authors.initials: DM
authors.lastname: Aepple
authors.forename: M J
authors.initials: MJ
authors.lastname: Schendel
authors.forename: T A
authors.initials: TA
authors.lastname: Garvey
authors.forename: C R
authors.initials: CR
authors.lastname: Gundry
authors.forename: K B
authors.initials: KB
authors.lastname: Heithoff
mesh_terms: D000328:Adult; D018450:Disease Progression; D005260:Female; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000175:diagnosis / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D013904:Thoracic Vertebrae