title: The quantitative evaluation of intracranial pressure by optic nerve sheath diameter/eye diameter CT measurement.
abstract: BACKGROUND
  The changes of the optic nerve sheath diameter (ONSD) have been used to assess changes of the intracranial pressure for 20 years. The aim of this research was to further quantify the technique of measuring the ONSD for this purpose.
  
  
  METHODS
  Retrospective study of computed tomographic (CT) data of 1766 adult patients with intracranial hypotension (n=134) or hypertension (n=1632) were analyzed. The eyeball transverse diameter (ETD) and ONSD were obtained bilaterally, and the ONSD/ETD ratio was calculated. The ratio was used to calculate the normal ONSD for patients and to estimate the intracranial pressure of the patients before and after the onset of the pathology. Correlation analysis was performed with invasively measured intracranial pressure, the presence or absence of papilledema, sex, and age.
  
  
  RESULTS
  In hypotension cases, the ONSD by CT was 3.4±0.7 mm (P=.03 against normative 4.4±0.8 mm). In cases with hypertension, the diameter was 6.9±1.3 (P=.02, with a cutoff value ˃5.5 mm). The ONSD/ETD ratio was 0.29±0.04 against 0.19±0.02 in healthy adults (P=.01).
  
  
  CONCLUSIONS
  The ONSD and the ONSD/ETD ratio can indicate low intracranial pressure, but quantification is impossible at intracranial pressure less than 13 mm Hg. In elevated intracranial pressure, the ONSD and the ratio provide readings that correspond to readings in millimeters of mercury. The ONSD method, reinforced with additional calculations, may help to indicate a raised intracranial pressure, evaluate its severity quantitatively, and establish quantitative goals for treatment of intracranial hypertension, but the limitations of the method are to be taken into account.
authors.affiliation: Department of Radiology, Assaf Harofe Medical Center, Affiliated to Sackler Faculty of Medicine, Tel Aviv University, Israel.
authors.forename: Inessa
authors.initials: I
authors.lastname: Bekerman
authors.affiliation: Department of Radiology, Assaf Harofe Medical Center, Affiliated to Sackler Faculty of Medicine, Tel Aviv University, Israel.
authors.forename: Tal
authors.initials: T
authors.lastname: Sigal
authors.affiliation: Stroke Unit, Assaf Harofe Medical Center, Affiliated to Sackler Faculty of Medicine, Tel Aviv University, Israel.
authors.forename: Itzhak
authors.initials: I
authors.lastname: Kimiagar
authors.affiliation: Department of Radiology, Assaf Harofe Medical Center, Affiliated to Sackler Faculty of Medicine, Tel Aviv University, Israel.
authors.forename: Anna
authors.initials: A
authors.lastname: Ben Ely
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Assaf Harofe Medical Center, Affiliated to Sackler Faculty of Medicine, Tel Aviv University, Israel. Electronic address: vaimed@yahoo.com.
authors.forename: Michael
authors.initials: M
authors.lastname: Vaiman
mesh_terms: D000328:Adult; D000367:Age Factors; D005123:Eye / Q000000981:diagnostic imaging* / Q000473:pathology*; D005260:Female; D006801:Humans; D019586:Intracranial Hypertension / Q000000981:diagnostic imaging / Q000503:physiopathology*; D019585:Intracranial Hypotension / Q000000981:diagnostic imaging / Q000503:physiopathology*; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D009186:Myelin Sheath / Q000473:pathology*; D009900:Optic Nerve / Q000000981:diagnostic imaging* / Q000473:pathology; D009929:Organ Size; D010211:Papilledema / Q000503:physiopathology; D012189:Retrospective Studies; D012737:Sex Factors; D014057:Tomography, X-Ray Computed; D055815:Young Adult