title: Usefulness of the endoscope in microvascular decompression for trigeminal neuralgia and MRI-based prediction of the need for endoscopy.
abstract: BACKGROUND
  Microvascular decompression (MVD) is a documented effective treatment of trigeminal neuralgia (TN). Lately, reports on endoscopy-assisted microvascular decompression (eaMVD) with better outcome and less risk have emerged. This study was undertaken to verify under which circumstances the endoscope proved essential in identifying the neurovascular conflict (NVC) during eaMVD for TN, and to assess the possibility to predict the need for the endoscope on preoperative magnetic resonance imaging (MRI).
  
  
  METHODS
  Retrospective analysis of 97 patients with TN undergoing eaMVD at the Oslo University Hospital - Rikshospitalet, 1999-2009. To assess the NVC and anatomical variations, surgical reports were evaluated. MRI was available in 66 patients. The MRIs were evaluated by a blinded neuroradiologist.
  
  
  RESULTS
  In 27 of the 97 patients (27.8 %), the endoscope was a significant aid in identifying the NVC, due to a bony ridge obscuring the view of the fifth nerve, a very distal vascular compression, or a combination of both. The preoperative MRI over-diagnosed the presence of a bony ridge. However, the MRI-based fraction of microscopically visible trigeminal nerve (FVN) in the cerebellopontine angle cistern proved diagnostic (ROC curve, AUC 0.89, p = <0.001) with an optimal cut-off value of 0.35. Hence, if less than 35 % of the trigeminal nerve is visible on preoperative MRI, the endoscope will be needed to identify the NVC.
  
  
  CONCLUSIONS
  The endoscope is a valuable tool during MVD for TN, especially under anatomical circumstances such as a bony ridge hiding the direct microscopic view of the NVC. These anatomical circumstances can be predicted with good accuracy on preoperative MRI.
authors.affiliation: Department of Neurosurgery, Oslo University Hospital Rikshospitalet, Pb 4950, Nydalen, N-0424, Oslo, Norway, tiril.sandell@hotmail.com.
authors.forename: Tiril
authors.initials: T
authors.lastname: Sandell
authors.forename: Geir Andre
authors.initials: GA
authors.lastname: Ringstad
authors.forename: Per Kristian
authors.initials: PK
authors.lastname: Eide
mesh_terms: D000328:Adult; D000368:Aged; D005154:Facial Nerve / Q000601:surgery*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D061145:Microvascular Decompression Surgery / Q000295:instrumentation* / Q000379:methods*; D008875:Middle Aged; D044582:Neuroendoscopes; D044583:Neuroendoscopy; D012189:Retrospective Studies; D016896:Treatment Outcome; D014277:Trigeminal Neuralgia / Q000601:surgery*; D020535:Video-Assisted Surgery / Q000379:methods*