title: Use of T2-weighted magnetic resonance imaging of the optic nerve sheath to detect raised intracranial pressure.
abstract: BACKGROUND
  The dural sheath surrounding the optic nerve communicates with the subarachnoid space, and distends when intracranial pressure is elevated. Magnetic resonance imaging (MRI) is often performed in patients at risk for raised intracranial pressure (ICP) and can be used to measure precisely the diameter of optic nerve and its sheath. The objective of this study was to assess the relationship between optic nerve sheath diameter (ONSD), as measured using MRI, and ICP.
  
  
  METHODS
  We conducted a retrospective blinded analysis of brain MRI images in a prospective cohort of 38 patients requiring ICP monitoring after severe traumatic brain injury (TBI), and in 36 healthy volunteers. ONSD was measured on T2-weighted turbo spin-echo fat-suppressed sequence obtained at 3 Tesla MRI. ICP was measured invasively during the MRI scan via a parenchymal sensor in the TBI patients.
  
  
  RESULTS
  Measurement of ONSD was possible in 95% of cases. The ONSD was significantly greater in TBI patients with raised ICP (>20 mmHg; 6.31 +/- 0.50 mm, 19 measures) than in those with ICP of 20 mmHg or less (5.29 +/- 0.48 mm, 26 measures; P < 0.0001) or in healthy volunteers (5.08 +/- 0.52 mm; P < 0.0001). There was a significant relationship between ONSD and ICP (r = 0.71, P < 0.0001). Enlarged ONSD was a robust predictor of raised ICP (area under the receiver operating characteristic curve = 0.94), with a best cut-off of 5.82 mm, corresponding to a negative predictive value of 92%, and to a value of 100% when ONSD was less than 5.30 mm.
  
  
  CONCLUSIONS
  When brain MRI is indicated, ONSD measurement on images obtained using routine sequences can provide a quantitative estimate of the likelihood of significant intracranial hypertension.
authors.affiliation: University Division of Anaesthesia and Wolfson Brain Imaging Center, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 2QQ, UK. thgeeraerts@hotmail.com
authors.forename: Thomas
authors.initials: T
authors.lastname: Geeraerts
authors.forename: Virginia F J
authors.initials: VF
authors.lastname: Newcombe
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Coles
authors.forename: Maria Giulia
authors.initials: MG
authors.lastname: Abate
authors.forename: Iain E
authors.initials: IE
authors.lastname: Perkes
authors.forename: Peter J A
authors.initials: PJ
authors.lastname: Hutchinson
authors.forename: Jo G
authors.initials: JG
authors.lastname: Outtrim
authors.forename: Dot A
authors.initials: DA
authors.lastname: Chatfield
authors.forename: David K
authors.initials: DK
authors.lastname: Menon
mesh_terms: D000328:Adult; D001930:Brain Injuries / Q000175:diagnosis / Q000503:physiopathology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D019586:Intracranial Hypertension / Q000175:diagnosis* / Q000503:physiopathology; D007427:Intracranial Pressure / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D009186:Myelin Sheath / Q000473:pathology*; D009900:Optic Nerve / Q000473:pathology*; D011446:Prospective Studies; D012189:Retrospective Studies; D055815:Young Adult
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