title: Optic nerve ultrasound for the detection of raised intracranial pressure.
abstract: BACKGROUND
  Optic nerve ultrasonography (ONUS) may help identify raised intracranial pressure (ICP). The optimal optic nerve sheath diameter (ONSD) cut-off for the identification of intracranial hypertension has not been established, with some clinical studies suggesting a higher cut-off than may be expected on the basis of prior laboratory investigation.
  
  
  OBJECTIVE
  To validate ONUS performed by neurointensivists as a technique for the detection of intracranial hypertension and identify the optimal ONSD criterion for the detection of ICP > 20 mmHg.
  
  
  METHODS
  Prospective blinded observational study. Patients in the ICU with either external ventricular drains or intraparenchymal ICP monitors at risk for intracranial hypertension were enrolled. The ONSD was measured by neurointensivists at the bedside with simultaneous invasive ICP measurement. An ROC curve was constructed to determine the optimal ONSD for the detection of ICP >  20 mmHg.
  
  
  RESULTS
  A total of 536 ONSD measurements were performed on 65 patients. Diagnoses included subarachnoid hemorrhage, traumatic brain injury, intracerebral hemorrhage, ischemic stroke and brain tumor. ROC curve analysis revealed area under the curve (AUC) = 0.98 (95% CI 0.96-0.99; P < 0.0001 for AUC = 0.5). Optimal ONSD for detection of ICP > 20 mmHg was ≥0.48 cm sensitivity 96% (95% CI 91-99%); specificity 94% (92-96%). Sensitivity of the higher cutoff of ≥0.52 cm proposed by some authors was only 67% (58-75%), with specificity 98% (97-99%).
  
  
  CONCLUSIONS
  Bedside ONSD measurement, performed by neurointensivists, is an accurate, non-invasive method to identify ICP > 20 mmHg in a heterogeneous group of patients with acute brain injury. ONSD ≥0.48 cm has the greatest accuracy, however, internal validation of ONSD criteria may be required.
authors.affiliation: Department of Neurosurgery, University of Michigan Health System, 3552 Taubman Health Care Center, 1500 E. Medical Center Dr, SPC 5338, Ann Arbor, MI 48109-5338, USA. vrajajee@yahoo.com
authors.forename: Venkatakrishna
authors.initials: V
authors.lastname: Rajajee
authors.forename: Monique
authors.initials: M
authors.lastname: Vanaman
authors.forename: Jeffrey James
authors.initials: JJ
authors.lastname: Fletcher
authors.forename: Teresa Lee
authors.initials: TL
authors.lastname: Jacobs
mesh_terms: D000328:Adult; D000368:Aged; D004453:Echoencephalography / Q000295:instrumentation*; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D019586:Intracranial Hypertension / Q000000981:diagnostic imaging* / Q000209:etiology / Q000628:therapy; D007427:Intracranial Pressure / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009900:Optic Nerve / Q000000981:diagnostic imaging*; D010211:Papilledema / Q000000981:diagnostic imaging* / Q000209:etiology; D019095:Point-of-Care Systems; D011446:Prospective Studies; D012372:ROC Curve; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D014159:Transducers; D014696:Ventriculostomy