title: Dependence of the optic nerve sheath diameter on acutely applied subarachnoidal pressure - an experimental ultrasound study.
abstract: OBJECTIVE
  To determine the distensibility and elastic characteristics of the optic nerve sheath for development of a basic understanding of ultrasound studies aimed to measure optic nerve sheath diameter (ONSD) for detection of acutely elevated intracranial pressure (ICP).
  
  
  METHODS
  Isolated human optic nerves preparations obtained from autopsies were submitted to predefined pressure alterations, and consecutive changes in ONSD were measured by B-scan ultrasound under defined conditions.
  
  
  RESULTS
  Following submission to pressure, the diameter of the nerve sheath increased up to 140% of its baseline value. The increase (mean 1.97 mm, SD 0.52 mm) corresponded to the magnitude of pressure steps measured in the perineural subarachnoidal space (SAS). Similarly, the ONSD declined in each of the preparations within a few minutes after the optic nerve was decompressed. However, it did not reach its baseline value again when pressure loads of 45-55 mmHg or more had been applied.
  
  
  CONCLUSIONS
  The elasticity of the anterior sheath of the optic nerve is sufficient for the detection of pressure changes in the SAS especially for upward pressure steps. This is basically important for the application of clinical monitoring of the sheath diameter to facilitate the identification of patients with elevated ICP non-invasively (screening). However, further implementation of this procedure in neurointensive care and emergency medicine has to consider that the sheath diameter reversibility may be impaired after episodes of prolonged intracranial hypertension and a model for hysteresis is proposed.
authors.affiliation: Department of Neurology & Psychiatry, Friedrich-Ebert-Hospital Neumuenster/University of Hamburg, Hamburg, Germany. hc.hansen@fek.de
authors.forename: Hans-Christian
authors.initials: HC
authors.lastname: Hansen
authors.forename: Wolf
authors.initials: W
authors.lastname: Lagrèze
authors.forename: Oswald
authors.initials: O
authors.lastname: Krueger
authors.forename: Knut
authors.initials: K
authors.lastname: Helmke
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001930:Brain Injuries / Q000000981:diagnostic imaging; D004548:Elasticity; D006801:Humans; D019586:Intracranial Hypertension / Q000000981:diagnostic imaging*; D007427:Intracranial Pressure; D008875:Middle Aged; D009186:Myelin Sheath / Q000000981:diagnostic imaging*; D009900:Optic Nerve / Q000000981:diagnostic imaging*; D013346:Subarachnoid Space; D014463:Ultrasonography