title: Identification of ossification of the posterior longitudinal ligament extending through the dura on preoperative computed tomographic examinations of the cervical spine.
abstract: METHODS
  To establish the diagnosis of dural penetration on preoperative computed tomographic studies of the cervical spine in patients with ossification of the posterior longitudinal ligament (OPLL).
  
  
  OBJECTIVE
  To define before surgery the pathognomonic computed tomographic findings of OPLL extending to and through the dura.
  
  
  BACKGROUND
  On preoperative computed tomographic studies, Hida et al have described the single-layer sign characterized by a solid mass of hyperdense OPLL and the double-layer sign defined by two (anterior and posterior) ossified rims surrounding a central nonossified but hypertrophied posterior longitudinal ligament. Only 1 of the 9 patients exhibiting the single-layer sign but 10 of 12 patients showing the double-layer sign had no separate dural plane identified at surgery.
  
  
  METHODS
  Only 2 of 54 patients undergoing multilevel cervical circumferential OPLL procedures had absent dura at surgery. Computed tomographic examinations for all patients were retrospectively reviewed to determine unique signs of dural penetration.
  
  
  RESULTS
  Dura was absent in 1 of 12 patients who had the single-layer CT sign that was additionally characterized by an irregular C angular configuration. Only 1 of 4 patients exhibiting the double-layer computed tomographic sign had absent dura at surgery. The remaining 38 patients had the smooth-layer sign, characterized by more regular margins of classic (22 patients) or early OPLL (16 patients).
  
  
  CONCLUSIONS
  The double-layer computed tomographic sign is more pathognomonic for dural penetration than the single-layer sign. The smooth-layer sign, indicating a clean dural plane, is more typical in North American patients.
authors.affiliation: New York University Medical Center, New York, New York, USA. Don@psych.columbia.edu
authors.forename: N E
authors.initials: NE
authors.lastname: Epstein
mesh_terms: D015984:Causality; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000601:surgery; D003710:Demography; D004388:Dura Mater / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000601:surgery; D005260:Female; D006801:Humans; D017846:Longitudinal Ligaments / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D017887:Ossification of Posterior Longitudinal Ligament / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000601:surgery; D011183:Postoperative Complications; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000379:methods; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome