title: Defining optic nerve tortuosity.
abstract: OBJECTIVE
  Optic nerve tortuosity is one of several nonmalignant abnormalities documented on MR imaging in patients with neurofibromatosis type 1 and may be related to the development of optic pathway gliomas. This study seeks an operational definition for optic nerve tortuosity.
  
  
  METHODS
  A focus group of 3 pediatric neuroradiologists reviewed 20 MR images of the brain and orbits of patients suspected to have optic nerve tortuosity in the absence of optic pathway glioma and found 6 radiographic factors that occurred frequently. Subsequently, 28 MR images were assessed for the presence of optic nerve tortuosity, using a global assessment question that reflects a neuroradiologist's confidence in the presence of optic nerve tortuosity, and for the presence of the 6 radiographic factors, to identify a combination of these factors that best predicted a diagnosis of optic nerve tortuosity.
  
  
  RESULTS
  We found perfect inter-rater agreement between 3 readers on the presence/absence of tortuosity in 75% of cases. Lack of congruity of the optic nerves, in more than 1 coronal section and dilation of the subarachnoid space surrounding the optic nerves, when found together are sensitive (89%) and specific (93%) for a diagnosis of tortuosity on the global scale. The absence of these 2 factors, along with absence of deviation of the optic nerve within the axial plane, provides a reliable test to exclude tortuosity.
  
  
  CONCLUSIONS
  Lack of congruity of the optic nerves in more than 1 coronal section and dilation of the subarachnoid space surrounding the optic nerves together provide an operational radiographic definition of optic nerve tortuosity.
authors.affiliation: Division of Oncology, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine Philadelphia, PA, USA. greg.armstrong@stjude.org
authors.forename: G T
authors.initials: GT
authors.lastname: Armstrong
authors.forename: A R
authors.initials: AR
authors.lastname: Localio
authors.forename: T
authors.initials: T
authors.lastname: Feygin
authors.forename: L
authors.initials: L
authors.lastname: Bilaniuk
authors.forename: P C
authors.initials: PC
authors.lastname: Phillips
authors.forename: M J
authors.initials: MJ
authors.lastname: Fisher
authors.forename: B L
authors.initials: BL
authors.lastname: Strom
authors.forename: R
authors.initials: R
authors.lastname: Zimmerman
mesh_terms: D001921:Brain; D006801:Humans; D008279:Magnetic Resonance Imaging; D015233:Models, Statistical; D009456:Neurofibromatosis 1 / Q000150:complications / Q000473:pathology; D015588:Observer Variation; D009900:Optic Nerve / Q000002:abnormalities*; D020339:Optic Nerve Glioma / Q000150:complications / Q000473:pathology; D009915:Orbit / Q000473:pathology